Method for analysis of single pulse pressure waves
This invention relates to a method for analysing pressure-signals derivable from pressure measurements on or in a body of a human being or animal, comprising the steps of identifying during given time sequences in a series of time sequences the single pressure waves, including related parameters [pressure amplitude ΔP, latency (ΔT), rise time coefficient (ΔP/ΔT)], determining numbers of single pressure waves with pre-selected combinations of two or more of said single pressure wave parameters during said time sequence. For the time sequences is further determined the balanced positions of single wave parameters. Two-dimensional values of balanced position may be presented as a one dimensional value after weighting of the matrix cells. The signal processing method may be used for more optimal detection of single pressure waves by means of non-invasive sensor devices.
This application is a Divisional of coppending application Ser. No. 10/613,122 filed on Jul. 7, 2003, and for which priority is claimed under 35 U.S.C. § 120; and this application claims priority of Application No. 60/422,111 filed in United States on Oct. 30, 2002 and Application No. PCT/NO03/00229 under 35 U.S.C. § 119; the entire contents of all are hereby incorporated by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
Monitoring of pressures within human body cavities has an important role in diagnosis and management of a large number of diseases and clinical conditions. The present invention relates to a method for analyzing pressure signals derivable from pressure measurements on or in a body of a human being or animal, comprising the steps of sampling said signals at specific intervals, and converting the pressure signals into pressure-related digital data with a time reference.
Further, the present invention relates to a system for analyzing pressure-signals derivable from pressure measurements on or in a body of a human being or animal.
More specifically, the invention relates to a method and a system as defined in the preamble of attached independent claims 1 and 49.
2. Related Art
Continuous monitoring of pressures in humans and animals has a widespread place. During continuous pressure monitoring, today's existing technology, not the inventive technology (hereafter referred to as conventional or current technology) calculates a mean or area under curve of several seconds of pressure recordings. For example, for a given time sequence of 6 seconds, mean pressure may be computed as the sum of all pressure sample levels divided by the numbers of samples. Most modern monitors update the calculated pressure value each 5-10 seconds. Thereby information within the single waves is lost. Whether or not the mean pressure corresponds to single pressure waves during said time sequence is not known. Therefore, absolute numbers of systolic, mean and diastolic pressures shown on the scope of vital signs monitors do not reveal single wave distribution. The basis for this praxis is the assumption of a linear relationship between mean pressure and amplitude of the single waves.
There are several problems with the current strategies of assessing continuous pressure recordings. Current technology uses calibration of pressures against a zero pressure level, usually the atmospheric pressure. This situation raises various problems, such as drift of zero pressure level during a period of recording. Differences in absolute zero pressure levels may cause false or inaccurate differences in pressures between different pressure recordings, making it difficult to compare pressure curves. Other causes of erroneous continuous pressure recordings are sensor failure, misplacement of pressure sensor, low quality of sensor signals related to movement of patient, and low signal-noise ratio of other reasons. Whether the quality of pressure signals is good or bad may be difficult to decide according to current strategies of assessing continuous pressure signals. The present invention aims at solving these problems, introducing a new strategy of analysis of pressure related digital data, including assessment of the single pressure waves.
A continuous pressure signal fluctuates over time related to the cardiac beats. In the human or animal body cavities, single pressure waves are built up from the waves created by each of the cardiac pulsation's. For example, the intracranial and arterial blood pressure waves are intimately related as the intracranial pressure waves arise from the contractions of the left cardiac ventricle. Each heart beat results in a pulse pressure wave, termed single pressure wave. Related to the cardiac beats, these waves have a diastolic minimum pressure and a subsequent systolic maximum pressure. When it has not previously been possible to take the knowledge of single wave parameters into daily clinical practice, this situation is related to the facts that heart rate is variable, single waves fluctuate a lot over time, and the inter-individual variation is large. So-called spectrum analysis or Fourier analysis assesses fluctuations in pressure, but not by analyzing the single pressure waves.
Non-invasive pressure monitoring is partially established for blood pressure and ocular pressure monitoring, though no methods or devices allows for continuous single wave monitoring with identification of single wave distribution. In particular, applanation tonometry is a non-invasive method for intraocular pressure measurement, blood pressure measurement, and measurements of intracranial pressure in infants.
SUMMARY OF THE INVENTIONThere are a number of human or animal body cavities in which pressures may be recorded for diagnostic and therapeutic reasons. For example, pressures in a human or animal body cavity relate to arterial blood pressure, intracranial pressure, cerebrospinal fluid pressure, ocular pressure, urinary tract pressure, gastrointestinal tract pressure. The present invention primarily was designed for analysis of pressure signals derivable from monitoring of single waves in blood vessels, the intracranial compartment, the cerebrospinal fluid (CSF) system, the ocular bulb and the urinary tract and bladder. These cavities represent, however, no limitation in the context of the invention. Other cavities may be the esophageal tract, the anal canal, and others not specified. Thus, this invention is not limited to analysis of pressures from only some particular human or animal body cavities, as the invention relates to a generic method for analysis of pressure derivable signals.
This invention relates to analysis of continuous pressure related signals. Such pressure related data may be derived from a variety of pressure sensors and pressure transducers. Independent of the type of sensor, a continuous pressure signal is measured, providing the opportunity for sampling of single waves. Examples of such sensors are solid or fiber-optic mechanical sensors for invasive monitoring, and sensors for invasive monitoring of pressure within a fluid system such as arterial or venous blood vessels, cerebrospinal fluid, or urinary bladder/tract. There are various other types of sensors providing signals indicative of pressures. Examples are sensors for non-invasive measurement of blood pressure, using principles of Doppler technology, or measurement of oxygen saturation, and non-invasive measurements of intracranial pressure using Doppler technology or acoustic signals. The most well-known principle of non-invasive pressure monitoring uses the principles of applanation tonometry. For example, applanation tonometry is used for monitoring of fontanel pressure in infants, and ocular pressure and arterial blood pressure. The unique with the present invention is the opportunity for determining single wave distribution by more optimal detection of single pressure waves using the inventive method of analyzing single pressure waves.
More specifically, the method according to the invention is inventive, wherein for selectable time sequences the method further comprises the steps of
a) identifying from said digital data single pressure waves, related to cardiac beat-induced pressure waves,
b) computing time sequence parameters of said single pressure waves during individual of said time sequences,
c) establishing an analysis output selected from one or more of said time sequence parameters of said single pressure waves during the individual of said time sequences:
c1)—absolute mean pressure for each identified single pressure wave (wavelength Pmin−Pmin) within said time sequence,
c2)—mean of mean pressure for all identified single pressure waves (wavelength Pmin−Pmin) within said time sequence,
c3)—standard deviation of absolute mean pressure for all identified single pressure waves (wavelength Pmin−Pmin) within said time sequence,
c4)—numbers of single pressure waves during said time sequence,
c5)—single pressure wave derived heart rate during said time sequence,
c6)—relative pressure amplitude (ΔP) value for each identified single pressure wave (wavelength Pmin−Pmin)within said time sequence,
c7)—standard deviation of relative pressure amplitude (ΔP) values for all identified single pressure waves (wavelength Pmin−Pmin) within said time sequence,
c8)—relative latency (ΔT) value for each identified single pressure wave (wavelength Pmin−Pmin) within said time sequence,
c9)—standard deviation of relative latency (ΔT) values for all identified single pressure waves (wavelength Pmin−Pmin) within said time sequence,
c10)—rise time (ΔP/ΔT) coefficient for each identified single pressure wave (wavelength Pmin−Pmin) within said time sequence,
c11)—standard deviation of rise time (ΔP/ΔT) coefficients for all identified single pressure waves (wavelength Pmin−Pmin) within said time sequence,
c12)—balanced position within a first matrix for combinations of single pressure wave amplitude (ΔP) and latency (ΔT) values within said time sequence,
c13)—balanced position within a second matrix for combinations of single pressure wave rise-time (ΔP/ΔT) coefficient values within said time sequence,
d) establishing a deliverable first control signal related to an analysis output in step
c) for a selectable number of said time sequence windows, said first control signal being determined according to one or more selectable criteria for said analysis output, and
e) modifying said deliverable first control signal into a regulator deliverable second control signal said second control signal corresponding to said first deliverable control signal, and
f) to provide a performance modifying signal.
Further embodiments of the method of the invention are defined in sub-claims 2-48.
The system comprises, according to the invention:
-
- a) control means which on basis of said pressure signals receivable from a pressure sensor via pressure transducer means is configured to control performance of a pressure sensor regulating device to optimize single pressure wave detection,
- b) a processing unit having means for analyzing said pressure signals said processing unit including sampling means for sampling said pressure signals at specific intervals,
- c) converter means for converting the sampled pressure signals into pressure related digital data with a time reference,
- d) identifying means operative during selectable time sequences to identify from said digital data single pressure waves related to one of: cardiac beat-induced pressure waves, artifacts, and a combination of cardiac beat-induced waves and artifacts,
- e) analyzing means for analysis of said digital data single pressure waves during said selectable time sequences,
- f) output means configured to output to a regulator device one or more first control signals derivable from one or more time sequences parameters related to a selectable number of time sequences elected from the group of:
- f27) absolute mean pressure for each identified single pressure wave (wavelength Pmin−Pmin) within said time sequence,
- f28) mean of mean pressure for all identified single pressure waves (wavelength Pmin−Pmin) within said time sequence,
- f29) satandard deviation of absolute mean pressure for all identified single pressure waves (wavelength Pmin−Pmin) within said time sequence,
- f30) numbers of single pressure waves during said time sequence,
- f31) single pressure wave derived heart rate during said time dequence,
- f32) relative pressure amplitude (ΔP) value for each identified single pressure wave (wavelength Pmin−Pmin) within said time sequence,
- f33) standard deviation of relative pressure amplitude (ΔP) values for al identified single pressure waves (wavelength Pmin−Pmin) within said time sequence,
- f34) relative latency (ΔT) value for each identified single pressure wave (wavelength Pmin−Pmin) within said time sequence,
- f35) standard deviation of relative latency (ΔT) values for all identified single pressure waves (wavelength Pmin−Pmin) within said time sequence,
- f36) rise time (ΔP/ΔT) coefficient for each identified single pressure wave (wavelength Pmin−Pmin) within said time sequence,
- f37) standard deviation of rise time (ΔP/ΔT) coefficients for all identified single pressure waves (wavelength Pmin−Pmin) within said time sequence,
- f38) balanced position within a first matrix for combinations of single pressure wave amplitude (ΔP) and latency (ΔT) values within said time sequences, and
- f39) balanced position within a second matrix for combination of single pressure wave rise-time (ΔP/ΔT) coefficient values within said time sequence, and
g) regulator means connectable to said processing unit for receiving at least one of said first control signals, said regulator means being capable of establishing a device performance modifying second control signal by means of at least one of said first control signals or establishing a combination effect obtained from using at least two of said first control signals, wherein said performance modifying second control signal deliverable from said regulator means being capable of controlling said sensor regulating device.
Further embodiments of the system of the invention are defined in sub-claims 50-74.
Thus, this invention is not limited to specific types of pressure signals, however, the signal has to be continuous for a given time sequence. During continuous pressure monitoring, single pressure waves are sampled along with a time reference. Analog pressure signals are converted into digital pressure-related data. Since each wave represents a heart beat, the heart rate is known when the sampling rate is known. Determination of single wave distribution may be used in the real-time and online monitoring of pressures. Processing of single waves may be performed after sampling of pressure signals. Though data processing is performed with some delay, monitoring is real-time since the delay has no significance for the observed phenomenon. During identification of the single pressure waves, the continuous pressure signals undergo filtering and concatenation procedures wherein noise signals are removed. Each single pressure wave is identified according to the diastolic minimum (Pmin) and systolic maximum (Pmax) values. False Pmin and Pmax values are removed. Identification of correct Pmin/Pmax values are made by means of pre-determined thresholds for the single wave amplitude (ΔP), latency (ΔT) and rise time coefficient (ΔP/ΔT) values. For the correctly identified single pressure waves, the single wave parameters [amplitude (ΔP), latency (ΔP), and rise time coefficient (ΔP/ΔT)] are determined for short time sequences (e.g. each 5 seconds). Such short time sequences with identified single pressure waves are accepted or rejected according to selected criteria. The latencies represent the time sequence when pressures increases from diastolic minimum to systolic maximum, and the pressure change occurring during this time sequence is the amplitude. The maximum (Pmax) and minimum (Pmin) values for the single waves are identified, and the matrix computed containing the amplitudes (ΔP) on the vertical column and latencies (ΔT) on the horizontal row. Accordingly, the amplitudes are related to the naming of the columns and the latencies to the naming of the rows. The number or percentages of the single waves with the various combinations of amplitude and latency are computed within a first matrix. The balanced position of occurrences of amplitude (ΔP) and latency (ΔT) are determined. In a one-dimensional second matrix is plotted the number of occurrences of single pressure waves with a given rise time coefficient (ΔP/ΔT) plotted, and the balanced position determined. Furthermore, the absolute pressure values during said time sequence is determined, either as mean pressure for the whole time sequence or as mean pressure for the single pressure waves solely during said time sequence. All of these single pressure wave parameters related to a recording sequence may be stored in a database.
Single waves are recorded repeatedly during a fixed time sequence (e.g. each 5 seconds). Such selected time sequences may have various durations, preferentially between 5 to 15 seconds. The actual heart rate should not influence the results in this particular situation). Various types of on-line presentation are possible. When balanced position of amplitude (ΔP) and latency (ΔT) are plotted in a two-dimensional weighted matrix, the balanced position may be represented as one weighted value, e.g. in a trend plot (weighted value on the Y axis and time on the X axis), or in a histogram (weighted value on the X axis and proportion or absolute number of occurrences on the Y axis). For the given time sequence, the numbers or percentages of single wave combinations are presented within the histogram. On the Y-axis is indicated percentage occurrence of the various single wave combinations of latency and amplitude, and the various latency/amplitude combinations are indicated on the X-axis. For example, the bar within the histogram with label on the X-axis of 0.2|3.5 indicates the percentage occurrence of the single wave with a latency of 0.2 seconds and amplitude of 3.5 mmHg in percentage of the total numbers of single waves during the actual recording time of 5 seconds. The matrix and/or histogram may be subject to a number of statistical analyses. In one embodiment it is useful to determine the balanced position within the histogram or matrix. This balanced position may be termed the centroid or the centre of distribution, though these terms represent no limitation of the scope of the invention. In this invention the term balanced position is preferred. Balanced position may refer to the balanced position of occurrences of amplitude (ΔP) and latency (ΔT) combinations in the first matrix (see Table I), or to balanced position of rise-time coefficients (ΔP/ΔT) in the second matrix. In this situation, balanced position is the mean frequency distribution of the single pressure wave parameter combinations.
According to the invention the matrixes and histograms of single wave distribution may be computed repeatedly online including alarm functions for the single wave distributions that may be considered as abnormal. Thereby, continuous update of single waves is an alternative way of presenting pressures. In such an implementation single wave distribution may be updated each 5 or 10 seconds.
According to the invention, a method is described for more optimum analysis of pressure signals from detection of single pressure waves by means of non-invasive pressure sensors. During short time sequences of pressure recordings (e.g. each 3 seconds) the single pressure wave parameters are computed. Between each of said time sequences a sensor-regulating device is modified by a regulator providing a control signal to the sensor-regulating device. Results of said analysis within the processing unit provide a control signal to the regulator that in turn provide another control signal to the sensor-regulating device. Thereby, the inventive method of single wave analysis may modify the function of the sensor device to give the most optimal single pressure wave detection. An example is described with regard to applanation tonomtery, though this represents no limitation of the scope of the invention. A pneumatic pump and bellow press the transducer array against the skin and tissue above the cavity wherein pressure is measured (e.g. artery), usually referred to as the hold down pressure. In some devices the monitor searches through a range of pressure values until it measures an optimal signal in order to determine optimal hold-down pressure. Determining single wave distribution is however not possible by these methods. The present invention enables optimum single pressure wave detection. Furthermore, according to the present invention, there is no need for calibration by an independent technique. With regard to monitoring of fontanel pressure in infants basically the same principles are used. In these cases, tonometry enables pressures to be measured non-invasively on neonates. None of the techniques of tonometry provides the opportunity for sampling of single pressure waves.
The particular features of the invention are described in the attached independent method claims, whereas the related dependent claims describe advantageous, exemplifying embodiments and alternatives thereof, respectively.
BRIEF DESCRIPTION OF THE DRAWINGS
With regard to sampling, analysis and presentation of single pulse pressure waves 1, relative differences in pressures are computed, not related to a zero pressure level such as the atmospheric pressure. The invention provides measurement and analysis of the following parameters included in the time sequences (
a) Minimum (Pmin) 2 is defined as the diastolic minimum pressure of the single wave, or as the valley of the wave. An individual single pressure wave starts and ends with a diastolic minimum (Pmin) value.
b) Maximum (Pmax) 3 is defined as the systolic maximum pressure of the single wave, or defined as the peak of the wave.
c) Amplitude (ΔP) 4 is defined as the pressure difference when pressures increase from diastolic minimum pressure (Pmin) to systolic maximum pressure (Pmax).
d) Latency (ΔT) 5 is defined as the time interval of the single wave when the pressures change from diastolic minimum pressure (Pmin) to systolic maximum pressure (Pmax).
e) Rise time coefficient (ΔP/ΔT) 6 is defined as the relationship between amplitude divided by latency.
f) Wavelength 7 is defined as the duration of the single pulse pressure wave between the diastolic minimum pressure (Pmin) 2 representing the start of the wave and the diastolic minimum pressure (Pmin) 2 representing the end of the wave. Wavelength is referred to as Pmin−Pmin duration wherein first Pmin is inclusive and ending Pmin is not inclusive.
Whether the waveform is reproduced properly or not depends as well on a sufficient resolution order and a sufficient sampling rate. In
In another embodiment reference may be to the second (P2) 9 and third (P3) 10 peaks. The maximum and minimum values may be specified for the different peaks (P1-P3), wherein also the single pressure wave parameters amplitude 4, latency 5, and rise time 6 coefficients are with reference to each of the specific pressure peaks (P1-P3) 8-10. In this situation, the identification of the first peak (P1) 8 is relative to maximum 3 and minimum 2. The identification of the second peak (P2) 9 also is relative to the first peak (P1) 8, and the third peak (P3) 10 is relative to the second peak (P2) 9. This embodiment requires that each peak (P1-P3) is determined within the single pressure wave 1. Thereby, latency 4, amplitude 5, and rise time coefficient 6 may be with reference to each of said single pressure waves.
An important inventive step is the identification of single pressure wave parameters within given time sequences 11. A time sequence 11 refers to a specified time period of pressure recording during a continuous pressure monitoring. With reference to current technology absolute mean pressure of continuous pressure signals usually is computed within short time sequences 11 of 5-10 seconds. This is done because it is useful to update regularly the pressure values during a time of continuous pressure recording. In order to be comparable against current technology, the inventor select time sequences of between 5 and 15 seconds duration. Thus, it is suggested that the lengths of the time sequences should be in the range of 5-15 seconds. The inventor found it useful to use time sequences of 5 or 6 seconds. In the latter situation, a continuous recording period is considered as built up of a series of numerous continuous short time sequences of 6 seconds. The number of 6 seconds time sequences 11 are 10 during one minute, 300 during 30 minutes, 600 during 1 hours, 6 000 during 10 hours and 12 000 during 20 hours of continuous pressure recording. The inventor considered these 6 second time sequences 11 as the building blocks of the recording period. However, these suggestions of durations (e.g. 5 or 6 or 8 second durations) of time sequences 11 (or building blocks) should not be regarded as a limitation of the scope of the invention, as the time sequences might be of any duration selected by the user.
With reference to
The method of analysis of continuous pressure signals described in this invention is applied to continuous pressure signals during such selected time sequences. The method is applied to all continuous pressure signals for each of said time sequences in a continuous series of said time sequences during a continuous measurement period. Accordingly, a continuous pressure recording period is considered as built up of a continuous series of said time sequences wherein said time sequences are accepted or rejected for further analysis according to selected criteria.
Based on measurement of a continuous pressure signal, various strategies may be used to identify the single waves. Each pressure signal may be identified on the time scale 12 because pressures are recorded along with a time reference. In one implementation, single waves are identified according to the maximum (Pmax) 3 and minimum (Pmin) 2 values. The following is an example of the procedure of identifying maximum (Pmax) 3 and minimum (Pmin) 2 values, though the example is not intended to limit the scope of the invention.
The procedure of sampling signals indicative of pressure and converting said signals into digital data are described. The specific steps described here represent no limitation as several strategies may be used. The first part of the signal conditioning is the software filter. This filter removes a great deal of the high frequency noise. The source of the high frequency noise is not always possible to point out, but it will always be present in many different shapes and magnitudes. Various filters may be used. The inventor found it useful to apply a 25th order Bessel low pass filter, with a 25 Hz cut-off frequency. Other filters are available. The filter is programmed in a manner that removes both the transient part and phase lag. This is done by taking a copy of the first 100 samples in the signal, and then reversing the order. Then the copy of the first 100 samples is concatenated to the original signal. This process is also repeated for the 100 last samples in the signal. Then this signal is processed in the digital filter, the transient part will appear in the “new concatenated” part in the signal. It will not destroy the original signal. In order to remove phase lag, the filtered signal is restored by taking a subset of data from the signal processed by the filter algorithm. The subset is taken from sample index 109, with a length equal to the original signal. The specific values referred to in this paragraph depend on sampling frequency and other variables, and should not be regarded as limitations of the scope of the invention.
Reference is now given to
With reference to
Thus, during a given recording period all single pulse pressure waves are identified. However, due to artifacts some waves are missed. The software allows the computation of numbers of artifacts and missed single waves, as well as relates this to total counts of single waves. Hence, the artifact ratio may be computed. Given that the numbers of artifacts are considered as too high a recording period may be omitted from analysis. Such artifacts relate to pressure recording sequences without accepted single pressure waves (i.e. accepted Pmin/Pmax pairs). There are several reasons for not identifying single pressure waves: Failure of pressure sensor may cause erroneous pressure recordings. Noise in pressure signals is another reason. The identification of the correct single pressure waves provides the opportunity for only including those parts of the pressure recordings that include single pressure waves.
Measurement of single waves requires a continuous pressure signal, though the pressure signals may be sampled at a variable rate. The sampling frequency preferably should be above 10 Hz. The inventor initially found it sufficient to use a sampling rate of at least 100 Hz to identify maximum (Pmax) 3 and minimum (Pmin) 2 values. A higher sampling rate (at least 200 Hz) may be required to find the maximum Pmax 3 and minimum Pmin 2 values for the individual peaks (P1-P3) 8-10. When valleys (Pmin) and peaks (Pmax) are determined with reference to the specific peaks P1-3, said valleys and peaks are relative to maximum values (Pmax) related to systolic maximum pressure and minimum values (Pmax) related to diastolic minimum pressure for said single pressure waves.
The invention is not limited to a particular range of sampling frequencies. Rather the sampling rate should be sufficient to detect the various single pressure wave parameters (i.e. Pmin, Pmax, ΔP, ΔT, and ΔP/ΔT).
In summary, the procedure of identifying correct Pmin/Pmax pairs includes different steps: (1) Filter and concatenation of digital pressure signals. (2) All minimum (Pmin) and maximum (Pmax) values are identified and represented with an amplitude value and a location value (or time stamp). (3) All Pmin/Pmax pairs are identified, where the subsequent minimum (Pmin) value is found for every maximum (Pmax) value. (4) Only those Pmin/Pmax pairs meeting certain pre-selected criteria concerning thresholds for ΔP, ΔT and ΔP/ΔT are accepted. (5) The single pressure wave parameters for given time sequences are determined. (6) The time sequences are subsequently accepted or rejected, according to criteria for the time sequences.
With reference to the time sequences 11, a question is which single pressure waves that should be included. A time sequence may contain parts of single waves both in the first and final part of the time sequences. It is not useful to discard waves of this reason. During a continuous recording period, single pressure waves 1 occurring between two time sequences are included in the first or second time sequence according to selected criteria. The invention is not limited to which criteria that are used. The inventor used the following procedure: First, with regard to the final part of a time sequence 11, the inventor found it useful to include in the time sequence 11 the single wave 1 that is terminating within the time sequence 11, which is the single wave terminating with its last Pmin within said time sequence. Thus, the last single pressure wave 11 included within a time sequence 11 will have its whole wavelength (Pmin−Pmax−Pmin) within that particular time sequence, including its last Pmin. As indicated in
In
The absolute pressure levels of the single pressure waves 1 may as well be determined. The pressure scales 13 of
This invention introduces a new inventive step concerning computation of absolute mean pressure, related to time sequence. This method is hereafter referred to as Method 2, as opposed to Method 1, representing conventional or current technology. The differences between conventional technology (Method 1) and the method according to this invention (Method 2) are illustrated in
The time sequence indicated in
In
Despite a very high correlation between absolute mean pressures computed by either of the methods, a major advantage with the inventive method (Method 2) is that absolute mean pressure is computed only when single pressure waves are identified. If no single pressure waves are accepted or identified, no absolute mean pressure is computed. Method 1, on the other hand, computes mean pressure whether single pressure waves are present or not. Reference is now given to
Reference now is given to
Another strategy (HR-method 2) is defining heart rate as numbers of waves divided by the total wavelength of said single pressure waves. In one single pressure wave, the entire wavelength is defined as the duration from Pmin to Pmin. The heart rate is the number of single pressure waves during a time sequence divided by the duration of the time sequence wherein these waves occurs. Heart rate method 2 is somewhat more accurate than Heart rate method 1, since the first method only includes the duration of the time sequence wherein single waves occurred. With reference to
The invention includes through its methods of analysis at least two levels of verifying whether a time sequence 11 includes correct single pressure waves: (1) Criteria for accepting or rejecting single pressure waves entering into the time sequences. (2) Criteria for accepting or rejecting the individual time sequence. If the time sequence 11 is not accepted according to the criteria, the time sequence 11 is rejected for further analysis.
First, the main strategy for identification of single waves 1 are related to criteria applied to accepted Pmin/Pmax pairs concerning ranges for amplitude (ΔP) 4, latency (ΔT) 5, and rise-time coefficients (ΔP/ΔT) 6. Single pressure waves not meeting the pre-selected requirements are rejected. A new time sequence 11 is started including the first accepted Pmin/Pmax pair, which is the first accepted Pmin/Pmax pair that has its final Pmin 2 within that particular time sequence 11. This has been commented on for
Second, criteria may be applied to the individual time sequences 11, determining whether the entire time sequence is accepted or not. The strategy is related to the numbers of single pressure waves (or the heart rate) during the time sequence. During a time sequence the heart rate 16 should be within physiological limits. Ranges for numbers of single waves within a time sequence may be defined. The inventor found it useful to define that the heart rate should be 40-180 (i.e. 4 to 18 single waves within a time sequence of 6 seconds). Thus, time sequences of 6 seconds duration containing a number of single pressure waves outside 4-18 are not accepted for further analysis. Other criteria may as well be used. In addition, thresholds may be defined for accepted variation of numbers of single waves within a time sequence. For several time sequences, standard deviation of numbers of single waves within the time sequence may be computed, wherein time sequences with numbers of single waves deviating too much from standard deviations are rejected.
When several pressures are monitored simultaneously with identical time reference, numbers of single pressure waves within identical time sequences may be compared, as illustrated in
Comparisons between numbers of waves for one pressure type within a time sequence also may be compared against heart rate measurement from another source, for example pulse oxymetri (spO2), or electrocardiography (ECG). Heart rate 16 during a given recording period derived from either arterial blood pressure or intracranial pressure waves should be equal to heart rate derived from oxygen saturation measurements or by electrocardiography (ECG) [HRP-O2−HRICP<2; HRECG−HRICP<2]. The inventor found it useful to use criteria for differences in single waves <2, though other criteria may as well be applied.
For each time sequence 11, all the single waves and single wave parameters are known. Accordingly, standard deviations for all the single pressure wave parameters may be computed. Standard deviations for relative pressures include the parameters amplitude (ΔP) 4, latency (ΔT) 5, and rise time coefficient (ΔP/ΔT) 6 for all single pressure waves 1 within the time sequences 11. Standard deviations for absolute pressures include absolute pressure values such as mean pressure for all individual single pressure waves (i.e. mean pressure from Pmin to Pmin for each individual of all single waves within the time intervals), standard deviations for diastolic minimum (Pmin) 2 for all individual single pressure waves during said time sequence, standard deviations for systolic maximum pressure (Pmax) 3 for all individual single waves 1 during the time sequence 11. Other criteria for acceptance or rejection of a time sequence may be related to limits for the standard deviations referred to here.
Repeated up-dates are made concerning numbers/proportion of accepted and rejected time sequences (and single waves). A log is made for numbers of rejected time sequences and numbers of rejected single pressure waves. A log also is made for reasons of rejection, such as abnormal ΔP 4, ΔT 5, ΔP/ΔT 6, or abnormal changes in HR 16. Rejected portions of trend plot may be indicated by color of graph or background. Examples of such statistics were made for
After identification of the single pulse pressure waves 1 during a recording period, the single pressure waves are subject to analysis. Fundamental to the invention is the computation of a matrix 36 of numbers or percentages of single pulse pressure waves with pre-selected wave characteristics. Examples of such characteristics are latencies (ΔT) 5 and amplitudes (ΔP) 4. The matrix 36 of amplitude (ΔP) 4 and latency (ΔT) 5 combinations are referred to as the first matrix in this document. Again, the latencies and amplitudes in the matrix presented in Tables I, V and VI refer to single waves identified by diastolic minimum (Pmin) 2 and systolic maximum (Pmax) 3 values. As indicated, the group of amplitudes are shown on the horizontal row, and the grouping of the latencies on the vertical column. Each number 37 within the cells of said matrix 36 represents the total numbers of single waves with the given combination of amplitude 4 and latency 5. In another situation the numbers 37 may refer to percentages. When percentages are used, it is against total numbers of waves. The amplitudes 4 are usually expressed in mmHg and the latencies 5 in seconds. The numbers of cells in such a matrix 36 may differ depending on the number of columns and rows. An example is given based on experience of the inventor. For intracranial pressure, the inventor found it useful to use the range of amplitudes (ΔP) 4 equal to 0 to 30.0 mmHg, with intervals of 0.5 mmHg, giving a total of 60 columns. The range of latencies (ΔT) 5 is 0.10 seconds to 0.40 seconds with intervals 0.01 seconds, giving a total of 30 rows. In this matrix the total cell number is 1800. The example represents no limitation of the scope of the invention. For arterial blood pressure, on the other hand, the inventor used the range of amplitudes (ΔP) from 30 to 120 mmHg, with intervals of 2.0 mmHg, giving a total of 45 columns. The range of latencies (ΔT) is 0.10 seconds to 0.40 seconds with intervals 0.01 seconds, giving a total of 30 rows. In this matrix the total cell number is 1350. However, these are only examples, and are not intended to limit the scope of the invention.
An example of a small part of a matrix applied to intracranial pressure is shown in Table I. The matrix 36 (referred to as first matrix) illustrate only a small fraction of a large matrix of 1800 cells.
The amplitude (ΔP) 4 values are presented in the columns and the latency (ΔT) 5 values in the rows. For example the first column corresponds to the first amplitude (ΔP) group, named 0.5 (corresponding to 0.5 mmHg); this group includes amplitude (ΔP) 4 values greater or equal to 0.5 mmHg, but less than 1.0 mmHg (indicated by the group range 0.5≦ΔP<1). The midpoint (or mean) of the group is 0.75 [(0.5+1.0)/2]. Similarly, the first latency group is termed 0.1, corresponding to a latency of 0.1 seconds. This latency group includes latencies with a duration greater or equal to 0.10 seconds, but less than 0.11 seconds (indicated by the group range 0.10≦ΔT<0.11). The group midpoint is 0.105 [(0.10+0.11)/2]. The amplitude/latency (ΔP/ΔT) matrix can be seen as a two dimensional collection of bins, where the rows are labelled ΔT and the columns are labelled ΔP. A cell equals a bin. Each bin denotes how often ΔP/ΔT combinations have appeared. When the observation is categorized or grouped, the midpoint of the group is used. The data are categorized when the data are in a “range”. As an example the first bin in the matrix presented in Table I contains all ΔP values which fall in the range greater or equal to 0.5 mmHg and less than 1 mmHg, with a ΔT value greater or equal to 0.10 seconds and less than 0.11 seconds. The matrix cells found at intersections between columns and rows indicate numbers or proportions of single pressure waves with specific combinations of amplitude (ΔP) and latency (ΔT). The numbers presented in Table I refers to an intracranial pressure recording lasting one minute including 10 time sequences 11, each lasting 6 seconds. During these 6 time sequences a total of 67 single pressure waves occurred. The distribution of the various single pressure waves during this recording period is shown in Table I. For example, single pressure waves 1 with an amplitude (ΔP) 4 greater or equal to 1.5 mmHg but less than 2.0 mmHg and a latency (ΔT) greater or equal to 0.14 seconds, but less than 0.15 seconds occurred 5 times during the time sequence represented in this matrix.
During real time monitoring, the matrix may be computed each 5 seconds. The centre of mass of distribution (balanced position) of single waves with combinations of latency and amplitude may be computed, without taking into account the heart rate. Another implementation may be continuous update of single wave distribution each 5 or 10 seconds. On the monitor display a histogram is presented each 5 seconds in many monitors, though there may be differences between the monitors. The invention does not give any limitations concerning the frequency of updates of matrix.
The preferable approach suggested by the inventor, is repeated computation of the matrix during a continuous pressure monitoring. For each of said time sequences 11 the matrix 36 is computed. For example, with reference to
The matrix 36 presentations may be subject to various types of analyses. The balanced position within the matrix may be presented as numerical value combinations 38 such as centroid or centre of distribution. According to the present invention, the single waves 1 with pre-selected characteristics of latency 5 and amplitude 4 are computed, and the matrix 36 of single wave combinations computed, with presentation of the distribution of single wave combinations. For the 5 second period the balanced position of single wave combinations may be computed, for example as centroid or centre of distribution. For example, a combination 38 of 0.17|2.0 refers to the single wave combination of latency of 0.17 seconds and amplitude of 2.0 mmHg. During real-time monitoring these numerical value combinations may be updated each time sequence 11 of 5 seconds. In one embodiment, the numerical value combinations 38 may be presented on the display of the apparatus, though this is no limitation of the scope of the invention. For example, presentation on the display of monitoring systems is possible.
The balanced position of single wave combinations, for example determined as centroid or centre of distribution, may also be presented on the y axis in a xy chart with time on the x axis (see
Balanced position within a matrix may have different names, such as centroid, centre of distribution, or centre of mass. In this document it is preferred to use the term balanced position. In the context described here, balanced position refers to mean frequency distribution of occurrences of single pressure wave parameters. In this document the terms balanced position of amplitude (ΔP), balanced position of latency (ΔT) and balanced position of rise time coefficient (ΔP/ΔT) are used as terms with respect to the first and seconds matrixes, respectively. However, the term balanced position per se is a method for determining the mean occurrence either within a one- or two-dimensional matrix in general.
With reference to the matrix presented in Table I, the procedure of computing balanced position of the distribution of different amplitude (ΔP) and latency (ΔT) combinations is described. The numbers referred to in Table I relates to a recording period of 1 minute. The method is however, similar whether the recording period is 5, 6 or 10 seconds, or 1 minute or 10 hours. The balanced position relates to the frequency distribution of the different occurrences of amplitude (ΔP) 4 and latency (ΔT) 5 during the selected time period. The method is similar independent on factors such as type of pressure, group ranges, or numbers of cells. Depending on the range of amplitude and latency values, the matrixes may contain a variable number of columns and rows. However, the balanced position result is dependent on the matrix resolution.
With reference to the matrix presented in Table I, the columns refer to amplitude (ΔP) 4 groups and the rows to the latency (ΔT) 5 groups. The system will have i rows, and j columns. When computing balanced position/centroid/mean frequency of such a two-dimensional distribution (referred to as first matrix), both dimensions have to be considered. Since there are two variables the mean (or balanced position) must be given by two numbers, like the ΔT|ΔP values. With reference to Table I, if the values from the row and column mean are considered, the results may be interpreted as the mean value for the distribution. The mean distribution (or balanced position) for the numbers presented in Table I, is located in the crossing point between the two lines ΔP=1.64 and ΔT=0.135. This is the most accurate way to describe the balanced position (or mean value) for this two dimensional distribution. The balanced position in the matrix shown in Table I is ΔP=1.64 and ΔT=0.135, corresponding to the cell with count 12. In the following, some details are given concerning computation of mean row and mean column values. First, the latency (ΔT) mean value (or row mean), with respect to the amplitude (ΔP) values (columns) is determined. The mi for each latency (ΔT) row is determined, by using the equation 2.
where Aj is the jth column midpoint, referring to an amplitude (ΔP) group value;
wij is the frequency (count) of the ith ΔT row and jth ΔP column cells. Then,
where Bi is the ith row ΔT midpoint value (r=row). The term “ith ΔT row and jth ΔP column cell” may also need an explanation. If a horizontal line is drawn through the midpoint in row i, and a vertical line through the midpoint in column j, the two lines will cross each other in a cell. This cell has the coordinates “ith row and jth column cell”. As an example, the data of Table I are used to calculate the mean row value. Application of the equations (2) and (3) gives a row mean with respect to columns equal to 0.135 seconds (14.9/110.25). The calculations are shown in more detail in Table II.
Row mean: 14.9/110.25 = 0.135 seconds
Second, the ΔP mean value (columns), with respect to the ΔT value (rows), is determined. The column ΔP mean value are found using the same approach as used for finding the mean row ΔT value. First, the mj for each ΔP column is found, as given in equation (4).
where Bi is the ith row ΔT midpoint, and referring to a ΔT group value and wij is the frequency for the ith row and jth column. Then,
where Aj is the jth column ΔP value midpoint (c=column). The calculations are shown in Table III, using the equations (4) and (5), the column mean with respect to rows will be equal to 1.64 mmHg (14.9/9.055).
Column mean: 14.9/9.055 = 1.64 mmHg
Finally, it should be mentioned that balanced position may as well be determined within a one-dimensional matrix (termed second matrix). Such a matrix is used for determining balanced position of occurrences of rise-time coefficients during a given time sequence. It may be used for other one-dimensional matrix variables/relations as well. In this situation the rise time coefficients are plotted in a one-dimensional matrix of pre-defined rise time coefficients. In such a one-dimensional frequency distribution we have two variables xi, and wi (xi equal to the value of each observation, wi equal to the frequency or count). xi is comparable to ΔP/ΔT and wi is comparable to the number of occurrences of the various ΔP/ΔT combinations. The mean of this distribution may be computed according to equation 6:
It has been discussed computation of a two-dimensional matrix of combinations of amplitude (ΔP) and latency (ΔT) combinations (referred to as the first matrix), and also computation of a one-dimensional matrix of combinations of rise-time coefficients (ΔP/ΔT) (referred to as the second matrix). It should be noted that these are examples, and not intended to limit the scope of the invention. A matrix may contain any of the single pressure wave parameters discussed in this document, and any combinations are possible. Matrixes may be computed for any type of pressure. The numbers of groups may be selected.
Reference is now given to
With regard to time sequences, absolute mean pressure and balanced position of either amplitude (ΔP) or latency (ΔP) are only few of many different single pressure wave parameters. The various parameters related to single pressure waves 1 are discussed in the following. An inventive step of this invention is to store in a database the single pressure wave related parameters computed according to the invention. The single wave 1 related parameters relate to said time sequences 11. Before creating a database, the duration of said time sequences may be selected. The inventor suggest that the duration preferably should be of 5-15 seconds duration. Specific durations of said time sequences are not a limitation. The inventor computed a database wherein time sequences of 6 seconds duration were selected. Within each time sequence the single wave related parameters may either be related to each of the individual single pressure waves within said time sequence, or to the group of individual single waves within said time sequence.
For each of the individual single pressure waves 1 within said time sequence 11, the following parameters are stored (referred to as Single wave parameters 1-6):
-
- 1. Absolute pressure value for diastolic minimum (Pmin) 2 value for each individual single pressure wave 1 (i.e. accepted Pmin/Pmax pair) during said time sequence 11.
- 2. Absolute pressure value for systolic maximum (Pmax) 3 value for each individual single pressure wave 1 (i.e. accepted Pmin/Pmax pair) during said time sequence 11.
- 3. Absolute mean pressure for each accepted single wave 1 (i.e. accepted Pmin/Pmax pair) (related to each accepted Pmin/Pmax pair), that is mean pressure from Pmin to Pmin (wavelength) 7 for each individual single pressure wave 1 during said time sequence 11.
- 4. Relative amplitude (ΔP) 4 pressure value for each individual single pressure wave 1 (i.e. accepted Pmin/Pmax pair) during said time sequence 11.
- 5. Relative latency (ΔT) 5 value for each individual single pressure wave 1 (i.e. accepted Pmin/Pmax pair) during said time sequence 11.
- 6. Relative rise time coefficient (ΔP/ΔT) 6 value for each individual single pressure wave 1 (i.e. accepted Pmin/Pmax pair) during said time sequence 11.
For the group of single pressure waves within said time sequence 11, the following parameters are stored (referred to as time sequence parameters 1-12):
-
- 1. Numbers of single waves (NSW) during said time sequence.
- 2. Single pressure wave derived heart rate 16, computed as numbers of single pressure waves 1 divided with the total duration of wavelengths (Pmin to Pmin) 7 of single pressure waves within said time sequence 11.
- 3. Single pressure wave derived heart rate 16, computed as numbers of single pressure waves 1 divided with the duration of said time sequence 11 wherein said single pressure waves occur.
- 4. Absolute mean pressure for said time sequence 11, computed as the sum of absolute mean pressure (entire wavelength 7 from Pmin to Pmin) for all individual single waves 1 during said time sequence 11, divided by numbers of single waves within said time sequence 11 (referred to as Method 2).
- 5. Standard deviation for mean pressure of mean pressure for the individual single waves 1 occurring during said time sequence 11.
- 6. Standard deviation for diastolic minimum (Pmin) 2 during said time sequence, which is computed as standard deviation for diastolic minimum (Pmin) 2 of all individual single waves 1 during said time sequence 11.
- 7. Standard deviation for systolic maximum (Pmax) 3 during said time sequence 11, which is computed as standard deviation for systolic maximum (Pmax) 3 of all individual single waves 1 occurring during said time sequence 11.
- 8. Standard deviation for amplitude (ΔP) 4 of all individual single pressure waves 1 occurring during said time sequence 11.
- 9. Standard deviation for latency (ΔT) 5 of all individual single pressure waves 1 occurring during said time sequence 11.
- 10. Standard deviation for rise time coefficient (ΔP/ΔT) 6 of all individual single pressure waves 1 occurring during said time sequence 11.
- 11. Balanced position of amplitude (ΔP)/latency (ΔT) combinations in said amplitude/latency matrix (referred to as first matrix).
- 12. Balanced position of rise time coefficients (ΔP/ΔT) in rise time coefficient matrix (referred to as second matrix).
All the single pressure wave related parameters are computed for each time sequence. Given that the duration of each time sequence is set to 6 seconds, an individual recording of 10 hours consists of 6000 time sequences. For example, the sole parameter Balanced position of amplitude (ΔP) and latency (ΔT) consists of two values (e.g. 0.12 seconds|6.25 mmHg), that gives 12000 values during a 10 hours recording period (20 values/minute×60 minutes/hr×10 hrs). These 12000 values include 6000 values of balanced position amplitude (ΔP) 4 and 6000 values of balanced position latency (ΔT) 5. Thus, for every time sequence the single wave related parameters are stored. The inventor first created a database based on time sequences of 6 seconds. At an early stage the database consisted of several millions of said time sequences. Since the data are continuous, it is easy to change the duration of the time sequence (e.g. to 5 seconds duration), though the computer requires time to process the digital data.
The database serves several purposes; an important purpose is to determine relationships between the different single wave parameters. Since relationships between several parameters within identical time sequences may be determined, it is also possible to determine one parameter as a function of two or more other parameters. For example, for one individual pressure recording, the single pressure wave parameters within each time sequence may be related. This procedure may be computed in a scatter plot with one parameter on the y axis and the other on the x axis. An example is given. A continuous pressure recording of 10 hours contains a total of 6000 time sequences, each lasting 6 seconds. Provided that 5400 of 6000 time sequences are accepted from said pressure recording, this pressure recording contains a total of 5400 values of balanced position of amplitude (ΔP) 4 and 5400 values of latency (ΔT) 5. In a scatter plot each value refers to a combination of balanced position of amplitude (ΔP) 4 and balanced position of latency (ΔT) 5. The relationships between the 5400 plots may further be determined by computing the best fitted curve. Goodness of fit may be determined by various strategies. For a given relationship, it is the experience of the inventor that the goodness of fit as well as the spread of the plot may differ among different pressure recordings.
The relationships between parameters may as well be determined for a group of individual pressure recordings. For example, for a group of 100 individual pressure recordings the relationships between balanced positions of amplitude (ΔP) 4 and latency (ΔT) 5 may be determined. Given that each individual pressure recording contains an average of 5400 values of balanced position of amplitude (ΔP) 4 and 5400 values of balanced position of latency (ΔT) 5, an averaged total of 540 000 values of each variable is available. Various mathematical procedures are possible to determine the relationships between these variables in such a large sample. A scatter of 540 000 plots may be made. A relationship may as well be made by a random selection of the total material. The invention does not limit to a particular strategy for determining relationships within a large material, as various mathematical strategies are possible.
In
Predicted mean pressure=3.214+1.3×ΔP+63.609×ΔT3 (7)
It should be noted that this equation is relevant for the data presented in
An important aspect of determining relationships between single pressure wave related parameters is an inventive procedure of giving weights to cells within a matrix. Reference has been made to said first matrix of amplitude (ΔP) and latency (ΔT) combinations (see Table I). The cells within the matrix described in Table I may be represented as weight values. Instead of the word weight, the word score might be used. In this description the word weight is preferred. A weighted cell value means that each cell in said matrix (see Table I) is represented by one value instead of two values corresponding to the respective column and row numbers. According to the invention, weight values are made on the basis of observations. In this context, observations refer to the relationships established by means of the database.
Reference is now given to Table IV that is a weight matrix. The group names, ranges and midpoints correspond to the amplitude/latency matrix shown in Table I. For example, the amplitude (ΔP) group named 1.5 mmHg includes amplitude values equal to or larger than 1.5 mmHg, but less than 2.0 mmHg, with group midpoint value equal to 1.75 mmHg. The latency (ΔT) group termed 0.11 seconds includes latency values equal to or larger than 0.11 seconds, but less than 0.12 seconds, with group midpoint value of 0.115 seconds. With reference to Table IV, the equation of the relationships presented in
It should be noted that the numbers and equations presented are used as illustrative examples and are not intended to limit the scope of the invention. The weight values computed depend on the relationships determined according to the observational data. Which absolute pressure levels that correspond to which balanced position ΔP and ΔT levels depend on the fitted curve equations computed for the particular data set. The invention sets no limitations concerning which types of observations the relationships are based on. Preferentially the plots should be based on a group of patients. However, separate plots may be made for different patient groups, patient ages, and disease states. These curves may to some extent differ depending on the types of pressures measured, compartments where pressures are measured, method by which pressures are measured, age of patient in whom pressures are measured, as well as disease state of the patient. In these situations certain weight matrixes may be used only for particular patient groups or disease states.
In
During on-line monitoring it may be difficult for the physician or nurse to relate to new numerical values presented each 5 seconds. Therefore, various examples of presentations are given in
Reference is now given to
Reference is now given to
Reference is now given to
Reference is now given to
Though the sensor device itself is not a part of the invention, nor a method by which such a sensor device is used on an animal or human body cavity, some examples are given to illustrate the concept, though this represents no limitation of the scope of the invention. First, applanation tonometry are widely used for non-invasive pressure measurement. Pressure gradients exist across the walls of a pressurised elastic sphere. When a pressure sensor is applied to the surface of the flattened area, no pressure gradient exists over the flattened portion. Pressure measurements can be made when a constant pressure is applied to the flattened area. Applanation tonometry may for example be used in non-invasive blood pressure monitoring, monitoring of ocular pressure (i.e. pressure within the ocular bulb), and even monitoring fontanel pressure in infants with an open fontanel. The pressure sensor 46 consists of the pressure element that is in contact with the skin or eye bulb. Signals from the sensor 46 are converted within the pressure transducer 47. When pressures are measured using the principles of applanation tonometry, it is well known that the pressure pulsation's detected by the tonometer depend on the pressure by which the tonometer is applied to the measurement surface. With increasing pressure from the tonometer, pressure waves increase until the waves with highest amplitudes are recorded. The pressure by which the applanation tonometry is applied to the surface determines quality of signal detection. Therefore, devices for applanation tonometry may include a sensor-regulating device 48, which controls the pressure by which the tonometer is applied to the surface. Such a sensor-regulating device 48 may be an inflatable balloon housed in a solid frame, under control of a pneumatic system. Such a sensor-regulating device 48 provides the opportunity for controlled inflation of air into an air chamber of the sensor. The pneumatic system is automatic and controlled by a processing unit 49, in the way that the air chamber pressure is automatically regulated to show the best single pressure waves. Other sensors 46 apply Doppler signals to detect pressure related signals. The signal detected by the Doppler may be modified within the transducer 47. In such a system the sensor-regulating device 48 incorporates a system wherein Doppler signals are applied to/receive from the object, including acquisitions of direction of signal emission as well as the signal quantity and quality. The emission and detection of Doppler signals heavily depend on the angulations of the signal emitting source. In this situation the sensor-regulating device 48 determines how Doppler signal are applied to the object, including acquisitions of signal direction and strength. When the sensor 46 and transducer 47 use acoustic signals the sensor-regulating device 48 may as well control signal direction and signal quantity and quality. Since the sensor device itself is not a particular feature of the invention, a more detailed description is not given.
The procedure for controlling and changing the sampling mode of signals derivable from a pressure sensor device is further illustrated in
- (1) absolute mean pressure for each identified single pressure wave 1 [wavelength 7 (Pmin−Pmin)] within said time sequence 11;
- (2) mean of mean pressure for all identified single pressure waves 1 [wavelength 7 (Pmin−Pmin)] within said time sequence 11;
- (3) standard deviation of absolute mean pressure for all identified single pressure waves 1 [wavelength 7 (Pmin−Pmin)] within said time sequence 11;
- (4) numbers of single pressure waves 1 during said time sequence 11;
- (5) single pressure wave derived heart rate 16 during said time sequence 11;
- (6) relative pressure amplitude (ΔP) 4 value for each identified single pressure wave 1 [wavelength 7 (Pmin−Pmin)] within said time sequence 11;
- (7) standard deviation of relative pressure amplitude (ΔP) 4 values for all identified single pressure waves 1 [wavelength 7 (Pmin−Pmin)] within said time sequence 11;
- (8) relative latency (ΔT) 5 value for each identified single pressure wave 1 [wavelength 7 (Pmin−Pmin)] within said time sequence 11;
- (9) standard deviation of relative latency (ΔT) 5 values for all identified single pressure waves 1 [wavelength 7 (Pmin−Pmin)] within said time sequence 11;
- (10) rise time (ΔP/ΔT) coefficient 6 for each identified single pressure wave 1 [wavelength 7 (Pmin−Pmin)] within said time sequence 11;
- (11) standard deviation of rise time (ΔP/ΔT) coefficient 6 for all identified single pressure waves 1 [wavelength 7 (Pmin−Pmin)] within said time sequence 11;
- (12) relative latency (ΔT) 5 value for each identified single pressure wave 1 [wavelength 7 (Pmin−Pmin)] within said time sequence 11;
- (13) balanced position within said first matrix 36 for combinations of single pressure wave amplitude (ΔP) 4 and latency (ΔT) 5 values within said time sequence 11; and
- (14) balanced position within said second matrix 36 for combinations of single pressure wave rise-time (ΔP/ΔT) 6 coefficients within said time sequence 11.
The output of said analysis within the processing unit 49 establishes or amends a first control signal 50 that is applied to a regulator 52. The mode of the first control signal 50 is determined by the output of said single pressure wave related analysis. Between each new time sequence, a first control signal 50 may be determined, depending on criteria applied to the analysis results. The first control signal 50 is converted within a regulator 52. The regulator 52 may be considered as a transducer converting the first control signal 50 into another second control signal 51. The regulator 52 deliverable second control signal 51 may depend on the type of sensor-regulating device 48 incorporated in the sensor device. Therefore, the deliverable second control signal 51 may modify a sensor-regulating device 48 in a wide sense. An example is given with reference to applanation tonometry wherein a pneumatic system controls the pressure by which the sensor 46 is applied to the surface. The second control signal 51 delivered from the regulator 52 may determine the pressure level within the pneumatic system, which determines the pressure by which the tonometer is applied to the surface. This example is further illustrated in
The results of said single pressure wave 1 analysis are compared for different time sequences 11. Changes in a first control signal 50 and subsequent in another second control signal 51 both produce modifications of the sensor-regulating device 48. The deliverable control signals corresponding to analysis output wherein single pressure wave parameters meet one or more selectable criteria would be used during subsequent pressure monitoring. The selectable criteria correspond to the control signal wherein the most optimum single pressure wave detection is obtained.
It is not within the scope of the invention to limit the strategy by which the process is performed. The system provides feedback interaction between the processing unit 49 performing said analysis, the deliverable first control signal 50 to the regulator 52 controlling and changing the deliverable second control signal 51 applied to the sensor-regulating device 48. It is described one example of the interactive operation of the regulator 52 and processing unit 49 related to the description shown in
Claims
1. A method for analyzing pressure signals derivable from pressure measurements on or in a body of a human being or animal, comprising the steps of sampling said signals at specific intervals, and converting thus sampled pressure signals into pressure-related digital data with a time reference,
- wherein for selectable time sequences the method comprises the further steps of:
- a) identifying from said digital data single pressure waves related to cardiac beat-induced pressure waves,
- b) computing time sequence parameters of said single pressure waves during individual of said time sequences, and
- c) establishing an analysis output selected from one or more of said time sequence parameters of said single pressure waves during individual of said time sequences:
- c1) balanced position of amplitude (ΔP)/latency (ΔT) combinations,
- c2) balanced position of rise time coefficients (ΔP/ΔT),
- c3) absolute mean pressure for said single pressure waves of said time sequence.
2. A method according to claim 1, wherein each of said selectable time sequences is a selected time duration of said pressure-related digital data with a time reference.
3. A method according to claim 2, wherein said selected time duration lies in the range 5-15 seconds.
4. A method according to claim 1, wherein the method is applied to each of said selectable time sequences in a continuous series of said time sequences during a recording.
5. A method according to claim 1, wherein said identifying step a) includes identification of peaks and valleys in said sampled signal.
6. A method according to claim 5, wherein all minimum and maximum values are identified and represented with an amplitude value and a location value or time stamp.
7. A method according to claim 1, wherein said identifying step a) includes identification of included pair combinations of peaks and valleys in said signal.
8. A method according to claim 1, wherein said identifying step a) includes identification of included pair combinations of valleys and peaks in said signal, corresponding to included pair combinations of diastolic minimum pressure (Pmin) and systolic maximum pressure (Pmax), characterizing single pressure waves created by the cardiac beat-induced pressure waves.
9. A method according to claim 1, wherein said identifying step a) excludes for further analysis pressure waves during said time sequences with single pressure wave parameters outside selected criteria for thresholds and ranges of said parameters, said parameters selected from the group of:
- starting diastolic minimum pressure defining the start of the single pressure wave (Pmin),
- ending diastolic minimum pressure defining the end of the single pressure wave (Pmin),
- systolic maximum pressure of the single pressure wave (Pmax,),
- amplitude (ΔP) of the single pressure wave,
- latency (ΔT) of the single pressure wave,
- rise time coefficient (ΔP/ΔT) of the single pressure wave,
- wave duration of the single pressure wave, and
- absolute mean pressure of said single pressure wave.
10. A method according to claim 1, wherein said identifying step a) includes for further analysis single pressure waves having single pressure wave parameters within selected criteria for thresholds and ranges of said single pressure wave parameters.
11. A method according to claim 1, wherein said identifying step a) excludes for further analysis time sequences with time sequence parameters outside selected criteria for thresholds and ranges of said parameters, said parameters selected from the group of:
- number of single waves (NSW),
- single pressure wave derived heart rate,
- absolute mean pressure,
- standard deviation for mean pressure of mean pressure for the individual single waves,
- standard deviation for diastolic minimum (Pmin),
- standard deviation for systolic maximum (Pmax),
- standard deviation for amplitude (ΔP) of all individual single pressure waves,
- standard deviation for latency (ΔT) of all individual single pressure waves,
- standard deviation for rise time coefficient (ΔP/ΔT) of all individual single pressure waves,
- balanced position of amplitude (ΔP)/latency (ΔT) combinations,
- balanced position of rise time coefficients (ΔP/ΔT).
12. A method according to claim 1, wherein said identifying step a) includes for further analysis time sequences having time sequence parameters within selected criteria for thresholds and ranges of said time sequence parameters.
13. A method according to claim 1, wherein said identifying step a) is applied to each consecutive time sequence in a continuous series of time sequences of a signal.
14. A method according to claim 1, wherein said identifying step a) further includes selecting single pressure waves which occur between two consecutive of said time sequences and placing such waves in one or the other of said two consecutive individual time sequences according to selected criteria.
15. A method according to claim 14, wherein said selected criteria define that a first of said single pressure waves within said individual time sequence must have its ending diastolic minimum pressure value (Pmin) within said individual time sequence.
16. A method according to claim 14, wherein said selected criteria define that a last of said single pressure waves within said individual time sequence must have both its starting (Pmin) and ending (Pmin) diastolic minimum pressure values within said individual time.
17. A method according to claim 1, wherein said computing step b) for accepted time sequences further includes determining said time sequence parameters, said parameters selected from the group of:
- c1) balanced position of amplitude (ΔP)/latency (ΔT) combinations,
- c2) balanced position of rise time coefficients (ΔP/ΔT),
- c3) absolute mean pressure for said single pressure waves of said time sequence.
18. A method according to claim 1, wherein said establishing step c) includes determining balanced position of amplitude (ΔP)/latency (ΔT) combinations, said determining comprising the steps of creating a first matrix based on determining number of single pressure waves with pre-selected values related to amplitude (ΔP) and latency (ΔT), one axis of said first matrix being related to an array of pre-selected values of pressure amplitude (ΔP) and the other axis of said first matrix being related to an array of pre-selected values of latencies (ΔT), and indicating for each matrix cell at respective intersections in said first matrix a number of occurrences of matches between a specific pressure amplitude (ΔP) and a specific latency (ΔT) related to successive measurements of single pressure waves over said individual time sequences.
19. A method according to claim 18, wherein the single pressure wave parameters of amplitude (ΔP) and latency (ΔT) are categorized into groups, said groups reflecting ranges of said single wave parameter values.
20. A method according to claim 18, wherein the occurrence of matches in said first matrix is indicated through actual number of matches during individual of said time sequence windows.
21. A method according to claim 18, comprising the further step of computing balanced position for a number of occurrences of said single pressure wave parameters of amplitude (ΔP) and latency (ΔT) values during individual of said time sequences in said first matrix.
22. A method according to claim 21, wherein said balanced position of said first matrix of numbers of amplitude (ΔP) and latency (ΔT) combinations corresponds to mean frequency distribution of the different occurrences of amplitude (ΔP) and latency (ΔT) during said individual time sequences.
23. A method according to claim 1, wherein said establishing step c) includes determining balanced position of rise time coefficients (ΔP/ΔT), said determining comprising the steps of creating a second matrix based on determining number of single pressure waves with pre-selected values related to rise time coefficient (ΔP/ΔT), the axis in said second matrix being related to an array of pre-selected values of rise time coefficient (ΔP/ΔT), and wherein for each matrix cell in said second matrix indicating a number of occurrences of pre-selected rise time coefficients (ΔP/ΔT) related to successive measurements of single pressure waves during said individual time sequences.
24. A method according to claim 23, wherein the single pressure wave parameter rise time coefficient (ΔP/ΔT) is categorized into groups, said groups reflecting ranges of said single wave (ΔP/ΔT) parameter values.
25. A method according to claim 23, comprising the further step of computing balanced position for a number of occurrences of said single pressure wave parameter rise time coefficient (ΔP/ΔT) in said second matrix, to yield an analysis output.
26. A method according to claim 25, wherein said balanced position of said second matrix of numbers of rise time coefficient (ΔP/ΔT) combinations corresponds to the mean frequency distribution of rise time coefficient (ΔP/ΔT) of said time sequence.
27. A method according to claim 1, wherein said establishing step c) yields analysis output related to the absolute mean pressure for said single pressure waves of said time sequence, corresponding to the sum of mean pressure values for all individual single pressure waves during said time sequence divided by number of said individual single pressure waves during said individual time sequence.
28. A method according to claim 27, wherein absolute mean pressure for an individual of said single pressure waves is the sum of sample values during the time of a wave duration, i.e. from starting diastolic minimum pressure (Pmin) to ending diastolic minimum pressure (Pmin) divided by number of samples.
29. A method according to claim 1, wherein said establishing step c) yields output of analysis of parameters c1)-c3) during each individual of said time sequence windows in a continuous series of said time sequence windows of said pressure-related signal.
30. A method according to claim 1, wherein the duration of each selectable time sequence window lies in a time range of 3-15 seconds.
31. A method according to claim 1, wherein establishing step c) yields output of analysis of one or more of said parameters c1)-c3), said analysis output being presented as numerical values on a display for each of said time sequences during ongoing sampling of said pressure-related signals.
32. A method according to claim 1, wherein establishing step c) yields output of analysis of one or more of parameters c1)-c3), said analysis output being presented as histogram distribution of values of said parameters c1)-c3) for a selectable number of time sequence windows of said pressure-related signal.
33. A method according to claim 1, wherein establishing step c) yields output of analysis of one or more of parameters c1)-c3), said analysis output being presented as a quantitative matrix for a selectable number of time sequences of said pressure-related signal.
34. A method according to claim 33, wherein said quantitative matrix is created based on determining numbers of one of said parameters c1)-c3) with selected parameter values, wherein one axis of the quantitative matrix is related to an array of selected parameter values, wherein the other axis is related to an array of selected numbers of consecutive included time sequences, and wherein indicating for each matrix cell at respective intersections in said quantitative matrix a number of occurrence of matches between a specific parameter value and a specific number of time sequences.
35. A method according to claim 34, wherein said parameter values are categorized into groups, said groups reflecting ranges of said parameter values.
Type: Application
Filed: Aug 8, 2007
Publication Date: Nov 29, 2007
Inventor: Per Eide (Oslo)
Application Number: 11/882,994
International Classification: A61B 5/02 (20060101);