COLLECTION AND ANALYSIS OF A VOLUME OF EXHALED GAS WITH COMPENSATION FOR THE FREQUENCY OF A BREATHING PARAMETER
Apparatuses are described to accurately determine a gas concentration of a sample of a patient's breath. The apparatuses may include a sample compartment, a breath speed analyzer, a gas analyzer, and a processor. The sample compartment includes an inlet that receives the breath. The breath speed analyzer determines the speed of a portion of the breath. The gas analyzer determines a gas concentration. The processor includes an algorithm that determines a degree of non-homogeneity of the sample based on the speed, and a corrected gas concentration based on the degree of non-homogeneity. In some variations, the gas correction is determined independently of patient cooperation. Apparatuses may be tuned based on the intended population's expected breathing pattern ranges such that the sample compartment is filled with a homogenous end-tidal gas sample regardless of an individual's breathing pattern. These apparatuses are useful, for example, for end-tidal CO analysis. Methods are also described.
This application claims the benefit of U.S. Provisional Application No. 61/578,811, filed Dec. 21, 2011, the disclosure of which is incorporated herein in its entirety.
FIELD OF THE INVENTIONDescribed here are devices and methods for the analysis of breath exhalant for diagnostic purposes. More specifically, devices and methods for sampling and analysis of gas from a person's breath for correlation to and diagnosis of an underlying physiologic condition are described.
BACKGROUNDThere are two general techniques employed for obtaining a person's breath for gas analysis. In a first technique a person can cooperatively breathe into an instrument, which receives the gas for analysis. In a second technique an instrument can obtain a gas sample from the person's airway independent of the person's cooperation. In either technique, achieving a precise collection and precise analysis of a gas from a specific portion of the breathing cycle can be challenging, given the often random and erratic nature of a breathing pattern. For example, reliably measuring breath CO at exactly the end-tidal portion of exhalation, with high levels of accuracy and precision (for example <0.5 ppm accuracy), has proven difficult. Typically, a measurement of breath CO2 is used to determine the end-tidal portion of the breath, and gas from that portion of the breath can be sampled and analyzed accordingly. Using an end-tidal CO2 signal is a convenient approach in that the technology is well known, and provides an instantaneous measurement of the breath waveform. However, in order to obtain accuracy and precision in the remainder of the overall system, the instrumentation considers only some of the possible external factors that may be useful.
Typically, a constant flow rate is employed for withdrawing the gas from the person, for a fixed collection time, and placing the drawn sample in a fixed volume sample compartment. When using this approach, there may be breath pattern related inaccuracies. For example, some of the sample compartment may have non-end-tidal gas in it, or only a fraction of the end-tidal portion of the breath might get sampled and stored in the sample compartment for analysis. While the repeatability at a certain breath rate is very good, the accuracy may vary as the breath rate varies, because of the pneumatics and timing of the system.
Therefore, it may be beneficial to improve on the accuracy of known systems in a way that is equally accurate across a range of breath patterns and breath rates. To this end, various approaches and algorithms have been conceived and described herein.
BRIEF SUMMARYDescribed herein are breath gas analyzers that achieve an accurate compositional analysis of a breath-borne gas from a specific portion of a breath. The system can accommodate a wide range of breathing patterns and rates without losing accuracy. The system can assure that enough volume of gas is obtained for the analysis to be sufficiently accurate, and that the gas obtained is from the desired portion of the breath, and is representative of the entire desired portion of the breath. In some variations, these advantages are achieved by modulating the gas sampling flow rate depending on the breath pattern, and/or by obtaining gas samples from the desired portion of the breath for multiple breaths until a threshold volume of gas is obtained for analysis, and/or by applying a correction factor to the computed result to compensate for heterogeneity of the sampled gas. In addition to these methods for obtaining target volumes of gas, some variations may identify the desired portion of the breath in order to accurately sample the correct portion of the breath and/or tune the system to always collect for analysis a substantially homogenously end-tidal sample regardless of breathing pattern.
To achieve the above features, variations of a breath analyzer or method for analyzing breath may include one or more of the following benefits: identification of different sub-portions of an expiratory phase; accurate sample collection from a desired sub-portion of the expiratory phase; assured collection of a predetermined quantity of gas for analysis by a gas composition analyzer; reliability and repeatable for a wide variety of breathing patterns that are expected to be encountered.
In one variation, a method for breath analysis comprises measuring a time-related parameter of a person's breathing pattern, collecting gas from a target portion of at least one of the person's breaths into a sample compartment having a target volume, adjusting the gas collection based on the time-based-parameter, and analyzing the collected gas to determine a compositional parameter of the gas. In further variations, adjusting the gas collection can include at least one selected from the group consisting of: (1) adjusting the gas collection speed, (2) adjusting the number of breaths the gas is collected from, and (3) adjusting for the homogeneity of the collected gas with a correction factor. In yet further variations, the time-based-parameter comprises at least one parameter selected from the group consisting of: (1) breath rate, (2) end-tidal time period, (3) expiratory time period, (4) inspiratory time period, (5) breath period. In further variations, the target portion of the breath comprises the end-tidal portion and the compositional parameter comprises carbon monoxide. In further variations, the target portion of the breath comprises at least one phase selected from the group consisting of: (1) an expiratory phase; (2) an end-tidal phase; (3) a beginning portion of exhalation; (4) a middle portion of exhalation; (5) a last portion of exhalation; (6) a post-expiratory period; and (7) an inspiratory pause. In further variations, measuring a time-based parameter comprises at least one technique selected from the group consisting of: (1) capnometry, (2) monitoring airway pressure, (3) monitoring airway temperature, (4) monitoring airway flow, (5) plethysmography, (6) monitoring sound, and (7) monitoring exhaled oxygen. In yet further variations, the time-based-parameter is differentiated to determine a time period of a target breath portion. Further variations may include defining a start time and an end time for collecting the gas, wherein defining a start time and an end time comprises comparing the measured breath parameter against at least one selected from the group consisting of: (1) a threshold amplitude of the measured breath parameter; (2) a threshold time period of the measured breath parameter, (3) a peak value of the measured breath parameter, (4) a substantially zero value of the measured breath parameter, (5) a negative value of the measured breath parameter, (6) a change in slope of the measured breath parameter, and (7) a change in sign of the measured breath parameter. Other variations may include defining a start time and an end time for collecting the gas wherein defining a start time and an end time comprises calculating a rate of change of the measured breath parameter and comparing it to at least one selected from the group consisting of: (1) a threshold value of the rate of change; (2) a zero value of the rate of change; (3) a first rate of change against a second rate of change; (4) a negative slope approaching zero; (5) a positive slope approaching zero; (6) a peak positive value of the rate of change; (7) a peak negative value of the rate of change; (8) an increasing rate of change; (9) a decreasing rate of change; and (10) a sign change of the rate of change. In further variations, collecting the gas further comprises applying a sampling cannula in communication with the sample compartment to the person's airway, and applying a vacuum to the sampling cannula. Further variations may include isolating the sample compartment with an inlet valve, and opening the inlet valve to begin collecting the gas from the target breath portion and closing the inlet valve to finish collecting the gas from the target breath portion. In further variations, the gas collected in the sample compartment comprises at least a portion of a breath from which the time-based breath parameter is measured. In further variations, the gas collected in the sample compartment comprises at least a portion of a breath that is not a breath from which the time-based breath parameter is measured.
In another variation, a method for breath analysis comprises identifying a time period of a portion of a breath, collecting a gas sample from the portion in a sample compartment having a target volume, wherein the gas sample is drawn into the compartment using a flow mechanism, and wherein a flow rate of the mechanism is based on the identified time period, and analyzing the collected gas sample for compositional analysis.
In another variation, a method for breath analysis comprises measuring an end-tidal time period of a person's breathing pattern with a breath sensor, collecting gas from the end-tidal period of at least one of the person's breaths into a sample compartment having a target volume with a flow mechanism, wherein the collection flow rate of the flow mechanism is adjusted based on the measured end-tidal time period and selected to substantially fill the target volume with gas from the end-tidal period, and analyzing the collected gas to determine a compositional parameter of the gas.
In another variation, a method for breath analysis comprises the steps (a) identifying a time period of a portion of a breath, (b) collecting a gas sample from the portion in a sample compartment having a target volume, wherein the gas sample is drawn into the compartment using a flow mechanism, (c) wherein (a) and (b) are repeated for a number of times, wherein the number of times is determined at least in part by the identified time period, and (d) analyzing the collected gas sample for compositional analysis.
In another variation, a method for breath analysis comprises (a) measuring an end-tidal time period of a person's breathing pattern with a breath sensor, (b) collecting gas from the end-tidal period of the person's breath into a sample compartment having a target volume using a flow mechanism, (c) wherein (a) and (b) are repeated until the compartment is substantially filled with gas from end-tidal periods, and (d) analyzing the collected gas to determine a compositional parameter of the gas. In another variation, the method includes tuning the breath collection system to always collect a substantially homogenously end-tidal sample, regardless of breathing pattern
Also described herein are various breath gas analyzers. In one variation, an apparatus for analyzing gas in a target portion of a person's breath cycle comprises a sample compartment of a target volume, a pneumatic system operable to collect gas from a person's breath and deliver the gas to the sample compartment, a breath sensor operable to measure a time-based-parameter of the target portion of the person's breath, a control system operable to adjust the pneumatic system based on the time-based-breath parameter, and an analyzer for analyzing the gas composition. In further variations, a gas flow system adjustment is provided that comprises at least one adjustment selected from the group consisting of: (1) an adjustable speed flow generator; (2) a processor configured to execute an algorithm that varies the number of breaths gas is collected from, and (3) a processor configured to execute an algorithm to adjust for the homogeneity of the collected gas with a correction factor. In further variations, the time-based-component comprises at least one component selected from the group consisting of: (1) a breath rate, (2) an end-tidal time period, (3) an expiratory time period, (4) an inspiratory time period, and (5) a breath period. In further variations, the target portion of the breath comprises the end-tidal portion and the gas analyzer comprises a carbon monoxide analyzer. In further variations, the target portion of the breath comprises at least one portion selected from the group consisting of: (1) an expiratory phase; (2) an end-tidal phase; (3) a beginning portion of exhalation; (4) a middle portion of exhalation; (5) a last portion of exhalation; (6) a post expiratory phase; and (7) an inspiratory pause. In further variations, the breath sensor comprises at least one selected from the group consisting of: (1) a capnometer, (2) an airway pressure transducer, (3) an airway temperature sensor, (4) an airway flow sensor, (5) a plethysmograph, (6) a microphone, (7) an oxygen sensor, and (8) an ultrasonic sensor. In further variations, the apparatus further comprises (1) a differentiator adapted to differentiate the signal from the breath sensor and (2) a processor, wherein the processor executes an algorithm to correlate the differentiated signal to the target portion of the breath cycle. In further variations, the apparatus further comprises a processor, wherein the processor executes an algorithm to determine the start time and end time for collecting the gas, wherein the algorithm comprises a comparison of the measured breath parameter against at least one selected from the group consisting of: (1) a threshold value, (2) a threshold time period, (3) a peak value, (4) a substantially zero value, (5) a negative value, (6) a change in slope, and (7) a change in sign. In further variations, the apparatus comprises a differentiator to determine a rate-of-change of the measured breath parameter, and a processor to execute an algorithm, wherein the algorithm comprises a comparison of the rate of change with at least one selected from the group consisting of: (1) a threshold value; (2) a zero value; (3) a first rate of change against a second rate of change; (4) a negative slope approaching zero; (5) a positive slope approaching zero; (6) a peak positive value; (7) a peak negative value; (8) an increasing rate of change; (9) a decreasing rate of change; and (10) a sign change of the rate of change. In further variations, the apparatus further comprises a sampling cannula attachable at a first end to the gas analysis apparatus and engageable at a second end to the person's airway; and a flow generator adapted to draw gas from the person's airway through the sampling cannula to the sample compartment. In further variations, the apparatus comprises a valve system arranged to isolate the sample compartment, wherein the control system controls the valve system to permit gas from the target breath portion to enter the sample compartment. In further variations, the control system is further adapted to deliver gas to the sample compartment from the measured breath. In further variations, the control system is further adapted to deliver gas to the sample compartment from a breath after the measured breath.
In another variation, a breath gas analyzer for analyzing gas in a target portion of a person's breath comprises a breath sensor for identifying the target portion of the breath cycle, a processor for determining the time period of the target portion, wherein the time period is determined at least in part from the identified portion, a gas collection compartment of a target volume, a pneumatic system for delivering a gas sample from the target portion of the breath to the gas collection compartment, a control system for adjusting the gas delivery rate of the pneumatic system based on the determined time period, and a gas analyzer for analyzing the composition of the gas.
In another variation, a breath gas analyzer for analyzing gas in the end-tidal portion of a person's breath comprises a breath sensor for identifying the end-tidal period of the breath cycle, a processor for determining the time period of the end-tidal period, wherein the time period is determined at least in part from the identified portion, a gas collection compartment of a target volume, a vacuum source for drawing a gas sample from the end-tidal period of the breath to the gas collection compartment, a control system for adjusting the flow rate of the vacuum source based on the determined end-tidal time period to substantially fill the compartment with end-tidal gas, and a gas analyzer for analyzing the composition of the gas.
In another variation, a breath gas analyzer for analyzing gas in a target portion of a person's breath, comprises a breath sensor for identifying the target portion of the breath cycle, a processor for determining the time period of the target portion, wherein the time period is determined at least in part from the identified portion, a gas collection compartment of a target volume, a pneumatic system for delivering a gas sample from the target portion of the breath to the gas collection compartment, a control system and algorithm for controlling the pneumatic system to deliver gas until the compartment is substantially filled with gas from the target breath portion, and a gas analyzer for analyzing the composition of the gas.
In another variation, a breath gas analyzer for analyzing gas in a target portion of a person's breath comprises a breath sensor for identifying the target portion of the breath cycle, a processor for determining the time period of the target portion, wherein the time period is determined at least in part from the identified portion, a gas collection compartment of a target volume, a pneumatic system for capturing a gas sample from the target portion of the breath into the gas collection compartment, a processor for executing an algorithm for applying a correction factor to the captured gas sample, wherein the correction factor is based on the determined time period of the target breath portion to correct for the non-homogeneity of the captured gas, and a gas analyzer for analyzing the composition of the gas.
In another variation, a method for breath analysis comprises (a) identifying a time period of an end-tidal portion of a breath, (b) collecting the end-tidal portion in a sample tube having a sample volume, wherein a time of collection is based on the identified time period, (c) repeating steps (a) and (b) until the sample volume is filled with a plurality of end-tidal portions from a respective plurality of breaths, and (d) analyzing the collected plurality of end-tidal portions to determine the concentration of a gas.
In another variation, a breath gas analyzer comprises a system operable to measure at least one characteristic of a patient's breath, a processor operable to determine a starting and an ending point of an end-tidal portion of the breath, wherein the determination is based upon the at least one characteristic, a sample tube comprising a proximal end, a distal end, a first valve coupled to the proximal end, a second valve coupled to the distal end, and a sample volume, wherein the sample volume is configured to store a plurality of end-tidal breath portions from a respective plurality of breaths, and a sensor for analyzing the concentration of a gas in the stored plurality of end-tidal breaths.
In another variation, a method of collecting an end-tidal portion of a patient's breath comprises identifying a starting point of the end-tidal portion, opening a container configured to collect the end-tidal portion, wherein the container is opened to correlate to the identified starting point of the end-tidal portion, identifying an ending point of the end-tidal portion, and closing the container, wherein the container is closed to correlate to the identified ending point of the end-tidal portion.
In another variation, a gas measurement correction database for determining a gas concentration at an inlet of an apparatus is populated by a method that may include measuring a plurality of gas concentrations in the apparatus for a respective plurality of known gas concentrations at the inlet (wherein the gas concentrations are measured at a plurality of breath rates), deriving a first plurality of polynomial equations (wherein each of the first plurality of polynomial equations fits the measured gas concentrations of a respective one of the plurality of breath rates and wherein each of the first plurality of polynomial equations comprises a coefficient at each order of the equation), deriving a second plurality of polynomial equations (wherein each of the second plurality of polynomial equations fits the coefficients of a respective order of the first plurality of polynomial equations wherein each of the second plurality of polynomial equations comprises a coefficient at each order of the equation), and recording each of the coefficients of the second plurality of polynomial equations in the database. The first plurality of polynomial equations may comprise a plurality of linear equations. The plurality of breath rates may be at least five in number. The plurality of breath rates may include breath rates of 10 breaths per minute, 20 breaths per minute, 30 breaths per minute, 40 breaths per minute, and 50 breaths per minute. The second plurality of polynomial equations may comprise a plurality of quadratic equations. The coefficients of the second plurality of polynomial equations may comprise a first plurality of coefficients and a second plurality of coefficients, wherein the first plurality of coefficients correspond to breath rates at or below a predetermined breath rate and the second plurality of coefficients correspond to breath rates at or above the predetermined breath rate. The predetermined breath rate may be 30 bpm. The second plurality of polynomial equations may comprise a first plurality of quadratic equations and a second plurality of quadratic equations, wherein each of the first plurality of quadratic equations fits the first plurality of coefficients at each order, and wherein each of the second plurality of quadratic equations fits the second plurality of coefficients at each order. The plurality of known gas concentrations at the inlet may comprise three in number. The plurality of known gas concentrations at the inlet may comprise at least one selected from each of the following: a region of relatively low breath rate, a region of relatively high breath rate, and a region of intermediate breath rate.
In another variation, a method for determining a gas concentration of a patient's breath at an inlet of an apparatus may comprises determining a breath rate of the patient, measuring a gas concentration in the apparatus, accessing a database to obtain a first plurality of coefficients corresponding to the patient's breath rate, deriving a first plurality of polynomial equations based on the first plurality of coefficients, deriving a second plurality of coefficients by inputting the breath rate into each of the first plurality of polynomial equations, deriving a compensation equation using the second plurality of coefficients, and determining the gas concentration at the inlet by inputting the measured gas concentration into the compensation equation. Each of the first plurality of polynomial equations may be a quadratic equation and the first plurality of coefficients may be three in number. The compensation equation may be linear and the second plurality of coefficients may be two in number. The database may include a first subset of coefficients and a second subset of coefficients, wherein the first subset of coefficients correspond to breath rates at or below a predetermined breath rate and the second subset of coefficients correspond to breath rates at or above the predetermined breath rate. The predetermined breath rate may be 30 bpm.
In another variation, an apparatus for analyzing a gas concentration of a patient's breath may comprise a gas analyzer that measures a gas concentration in the apparatus, an inlet that receives the patient's breath, a breath speed analyzer that determines a breathing parameter frequency of the patient's breath, a database comprising a plurality of coefficients corresponding to a plurality of breathing parameter frequencies, and a processor containing a non-transitory computer readable medium containing executable instructions that when executed perform a method of determining the gas concentration of the patient's breath at the inlet of the apparatus, wherein the method includes accessing the database to obtain a first plurality of coefficients based on the patient's breathing parameter frequency, deriving a first plurality of polynomial equations based on the first plurality of coefficients, deriving a second plurality of coefficients by inputting the breathing parameter frequency into each of the first plurality of polynomial equations, deriving a compensation equation using the second plurality of coefficients, and determining the inlet gas concentration by inputting the measured gas concentration into the compensation equation. The first plurality of polynomial equations may be a quadratic equation and the first plurality of coefficients may be three in number. The compensation equation may be linear and the second plurality of coefficients may be two in number. The database may comprise a first subset of coefficients and a second subset of coefficients, wherein the first subset of coefficients correspond to breathing parameter frequencies at or below a predetermined breathing parameter frequency and the second subset of coefficients correspond to breathing parameter frequencies at or above the predetermined breathing parameter frequency. The predetermined breathing parameter frequency may be 30 bpm.
In another variation, a method for determining a gas concentration of a patient's breath at an inlet of an apparatus includes determining a breathing parameter frequency of the patient, measuring a gas concentration in the apparatus, accessing a database to obtain a plurality of coefficients based on whether the patient's breathing parameter frequency is at, above, or below a predetermined breathing parameter frequency, wherein the database comprises a first subset of coefficients and a second subset of coefficients, wherein the first subset of coefficients correspond to breathing parameter frequencies at or below the predetermined breathing parameter frequency and the second subset of coefficients correspond to breathing parameter frequencies at or above the predetermined breathing parameter frequency, deriving a compensation equation using the plurality of coefficients, and determining the gas concentration at the inlet by inputting the measured gas concentration into the compensation equation. The predetermined breathing parameter frequency may be 30 bpm.
In another variation, an apparatus for analyzing a gas concentration of a patient's breath may comprise a gas analyzer that measures a gas concentration in the apparatus, an inlet that receives the patient's breath, a breath speed analyzer that determines a breathing parameter frequency of the patient's breath, a database comprising a plurality of coefficients corresponding to a plurality of breathing parameter frequencies, wherein the database comprises a first subset of coefficients and a second subset of coefficients, wherein the first subset of coefficients correspond to breathing parameter frequencies at or below a predetermined breathing parameter frequency and the second subset of coefficients correspond to breathing parameter frequencies at or above the predetermined breathing parameter frequency, and a processor containing a non-transitory computer readable medium containing executable instructions that when executed perform a method of determining the gas concentration of the patient's breath at the inlet of the apparatus, the method including accessing the database to obtain a plurality of coefficients based on whether the patient's breathing parameter frequency is at, above, or below the predetermined breathing parameter frequency, deriving a compensation equation based on the plurality of coefficients, and determining the inlet gas concentration by inputting the measured gas concentration into the compensation equation. The predetermined breathing parameter frequency may be 30 bpm.
In another variation, a method for determining a gas concentration of a patient's breath at an inlet of an apparatus may comprise determining a breathing parameter frequency of the patient, measuring a gas concentration in the apparatus, accessing a database to obtain a plurality of coefficients corresponding to the patient's breathing parameter frequency, deriving a compensation equation using the plurality of coefficients, and determining the gas concentration at the inlet by inputting the measured gas concentration into the compensation equation. The compensation equation may be a polynomial equation. The compensation equation may be linear. The database may comprise a first subset of coefficients and a second subset of coefficients, wherein the first subset of coefficients correspond to breathing parameter frequencies at or below a predetermined breathing parameter frequency and the second subset of coefficients correspond to breathing parameter frequencies at or above the predetermined breathing parameter frequency. The predetermined breathing parameter frequency may be 30 bpm.
In another variation, an apparatus for analyzing a gas concentration of a patient's breath comprises a gas analyzer that measures a gas concentration in the apparatus, an inlet that receives the patient's breath, a breath speed analyzer that determines a breathing parameter frequency of the patient's breath, a database comprising a plurality of coefficients corresponding to a plurality of breathing parameter frequencies, and a processor containing a non-transitory computer readable medium containing executable instructions that when executed perform a method of determining the gas concentration of the patient's breath at the inlet of the apparatus, the method comprising accessing the database to obtain a plurality of coefficients based on the patient's breathing parameter frequency, deriving a compensation equation using the plurality of coefficients, and determining the inlet gas concentration by inputting the measured gas concentration into the compensation equation. The compensation equation may be a polynomial equation. The polynomial equation may be a linear equation. The database may comprise a first subset of coefficients and a second subset of coefficients, wherein the first subset of coefficients correspond to breathing parameter frequencies at or below a predetermined breathing parameter frequency and the second subset of coefficients correspond to breathing parameter frequencies at or above the predetermined breathing parameter frequency. The predetermined breathing parameter frequency may be 30 bpm.
In another variation, an apparatus for collecting gas from a patient's breath comprises a sample volume, a flow generator comprising a sampling flow rate (wherein the flow generator may completely, or nearly completely, fill the sample volume with an end-tidal portion of the patient's breath when the patient's breath has a determined breathing parameter frequency), and a processor configured to discard a gas collected from the patient's if a breathing parameter frequency of the patient exceeds the predetermined breathing parameter frequency. The flow generator may be a pump. The end-tidal period of the patient's breath may be assumed to be a fraction such as one quarter of a breath period of the patient, wherein the breath period comprises one inspiratory and expiratory cycle of the patient's breath.
In another variations, an apparatus for analyzing a gas concentration of a sample of a patient's breath may comprise a sample compartment with an inlet that receives the patient's breath, a breath speed analyzer that determines the speed of a portion of the patient's breath, a gas analyzer that determines a gas concentration of the gas in the sample compartment, and a processor comprising an algorithm that determines a corrected gas concentration based on the speed of a portion of the patient's breath, wherein the corrected gas concentration is determined independently of patient cooperation.
In another variation, an apparatus for analyzing a gas concentration of a sample of a patient's breath may comprise a sample compartment with an inlet that receives the patient's breath, a breath speed analyzer that determines the speed of a portion of the patient's breath, a gas analyzer that determines a gas concentration of the gas in the sample compartment, and a processor comprising an algorithm, wherein the algorithm determines a degree of non-homogeneity of the breath sample in the sample compartment based on the speed of a portion of the patient's breath, wherein the algorithm determines a corrected gas concentration based on the degree of non-homogeneity, and wherein the corrected gas concentration is determined independently of patient cooperation.
In another variation, an apparatus for analyzing a gas concentration of a sample of a patient's breath may comprise a breathing parameter frequency measuring sensor, an algorithm comprising a defined maximum breathing parameter frequency, a sample compartment with a volume and with an inlet that receives the patient's breath, a gas analyzer that determines a gas concentration of the gas in the sample compartment, and a sampling flow rate control unit that delivers the sample from the patient into the sample compartment at a desired rate, wherein the sample compartment volume and the desired rate are determined based on the defined maximum breathing parameter frequency.
Described here are devices and methods for capturing and analyzing an exhaled breath. In some variations, one or more breathing parameters are measured to identify the different constituent portions of a breath and the respective time periods, and a pneumatic system is used for capturing the portion of exhaled breath in a sampling tube using an identified time period. In some variations, one or more valves and/or flow control mechanisms—such as a vacuum pump, for example—are used to regulate the flow rate of gas drawn into the sampling tube. In some variations, the captured portion of breath is analyzed for indications of a patient's physiological state.
A portion of a breath may include an end-tidal portion, a beginning portion, a middle portion, and an end portion of an exhaled breath. Measured breathing parameters may include one or more of carbon dioxide, oxygen, airway pressure, airway temperature, breath flow rate, and breath pressure. Identifying the time period of a portion of a breath may include identifying approximately the start and termination of that time period.
In some variations of a multiple breath end-tidal sample collection algorithm, the number of samples collected varies with the breath rate, in order to fill a fixed sample collection volume with the complete end-tidal portion of the breath(s). In some variations of a variable sampling vacuum rate algorithm, vacuum rate is modulated based on a breath rate, allowing the sample collected to be the entire end-tidal section of the breath.
The composition of exhaled gas may vary corresponding to different stages of the expiratory period. For example, gas sampled near the end of exhalation may be representative of gas that has most recently diffused out of the blood stream into the alveoli. In the example shown in
In some variations, the level of CO2 in an exhaled breath is used to determine the duration of a period of a breath. In further variations, a duration of a period of breath may be characterized by a start and a termination of that period. In some variations, a CO2 level is used to determine a start or a termination of a period of a breath. In other variations, a first time derivative of a CO2 level is used to determine a start or a termination of a period of a breath. In yet other variations, a second time derivative of a CO2 level is used to determine a start or a termination of a period of a breath. In some variations, a combination of CO2 levels and CO2 level time derivatives may be used to determine a start or a termination of a period of a breath. In some variations, a start of an end-tidal period may be determined by a change in the first time derivative of a CO2 level of the exhaled breath, such as a sudden decrease in the first time derivative of the CO2 level. In some variations, a decrease in the first time derivate of the CO2 level is more than a 10% decrease. In some variations, a decrease in the first time derivate of the CO2 level is more than a 25% decrease. In some variations, the derivative will approach or become zero showing very little rate of change or a peak plateau, respectively. In other variations, the start of an end-tidal period may be determined by a large second time derivative of the CO2 level. In some variations, a termination of an end-tidal period may be determined by a maximum CO2 level, which may be detected or confirmed by a change in the sign of the first time derivative of the CO2 level as the derivative becomes negative (associated with a drop of the CO2 level from its peak value). In further variations, a start of a beginning period may be determined by a sudden increase in the first time derivative of the CO2 level. In other variations, the start of a beginning period may be determined by an increase in the CO2 level from zero CO2 level. In some variations, the increase in CO2 level may be non-zero, such as near-zero or from a baseline. In some variations, a termination of a middle period may be determined by a change in the first time derivative of a CO2 level of the exhaled breath, such as a sudden decrease in the first time derivative of the CO2 level. In some variations, a CO2 level, first time derivative thereof, second time derivative thereof, or a combination of the foregoing may be used to determine the start and termination of one or more periods.
In some variations, airway pressure is used to determine a start or a termination of a period of a breath. In other variations, a first time derivative of an airway pressure is used to determine a start or a termination of a period of a breath. In yet other variations, a second time derivative of an airway pressure is used to determine a start or a termination of a period of a breath. In some variations, a combination of airway pressures and airway pressure time derivatives may be used to determine a start or a termination of a period of a breath. In some variations, a start of an end-tidal period is determined by maximum airway pressure, that is, by a zero first time derivative of the airway pressure. In some variations, a termination of an end-tidal period may be determined by zero airway pressure. In some variations, an airway pressure, first time derivative thereof, second time derivative thereof, or a combination of the foregoing may be used to determine the start and termination of one or more periods.
In some variations, the breath sensor monitors the person's breathing over time, and trends the breathing pattern by determining a continually updated value that is characteristic of the breathing pattern. For example, peak positive values of a breathing signal may be measured and updated for each breath. Peak values may be compared with previous peak values. Peak values may be averaged over a previous number of multiple breaths. Similarly, time-related aspects of the breaths may be trended, such as the expiratory time. Various breath-related events that are not normal breaths may be identified and exception algorithms may exist in order to not include these non-normal breath events inadvertently in deterministic steps. For example, the characteristic waveform of a sneeze, cough, stacked breath, or non-full breath may be defined in advance or based on monitoring of a particular patient, and when detected by the breathing sensor, excepted from the appropriate deterministic algorithms.
The threshold techniques described in
For some breath analysis applications, a minimum quantity of gas volume is required by the gas composition analyzer in order for it to provide an accurate analysis. One technique for obtaining the gas sample for analysis is to collect the gas in a temporary storage compartment while it is being drawn from the patient. The storage compartment is sized to a known volume to meet the volume requirement of the gas composition analyzer, and for convenience, the compartment can be a fixed or constant volume. After the compartment is filled with the desired gas, the gas in the compartment can then be sent to the composition analyzer for analysis. The gas stored and analyzed may be purely from the targeted portion of exhalation in order to achieve an accurate analysis. Therefore, the system may be capable of obtaining that volume of gas from the correct part of the breath, under a wide variety of breathing patterns, and yet still collect the requisite quantity of gas for the analyzer to be accurate.
In some variations, the pneumatic system shown in
In the following discussion, reference is made to the device for capturing exhaled breath described above with respect to
In a first variation of a breath-rate-modulated variable, shown in
In the graph 910 of
The resultant CO analysis at 60 bpm shown by the solid line in the graph in
As described above, in order to compensate for any breath rate or breath pattern and still obtain the desired sample volume and gas purity, multiple breaths may be sampled. The number of breaths will depend on the breath pattern and the compartment volume.
After storing each sample, before the next sample is stored, the gas being drawn from the patient is channeled to bypass the storage compartment. These configurations of the system is illustrated in
As described above, in order to compensate for any breath rate or breath pattern variability and still obtain the desired sample volume, the sample flow rate may be adjusted.
In some variations, a measured gas concentration may be adjusted to approximate an actual gas concentration. Such adjustments may account for variations in the fidelity of a breath sampling apparatus over a range of breath rates. The measured concentration may be modified using a correction equation, which may be specific to the apparatus being used, but may also be usable across various apparatuses. In some variations, the correction equation is formulated to cover a range of breath rates. In some variations, a breath rate and a measurement of a gas concentration in the apparatus may be sufficient to approximate the actual concentration of the gas at an inlet of the apparatus using a correction equation.
Table 1420 in
In some variations, the coefficients of a linear or quadratic equation are determined by using a breath simulator. In such variations, the breath simulator provides a known concentration of a gas at the inlet to a breath sampling apparatus at a known breath rate. From the breath rate and the deviation of measured gas concentration at another location of the sampling apparatus from known gas concentration at the inlet, a rate factor equation is derived by fitting the measurements to an equation. For example, the embodiment depicted in
Further variations may provide adjustments for a range of measured gas concentrations to a range of corrected gas concentrations over a range of breath rates. In one variation, a method for deriving a breath rate correction equation may include deriving multiple polynomial equations that span the ranges of measured gas concentrations, actual gas concentrations, and breath rates and utilizing the polynomial equations to populate a look-up table. In other variations, an apparatus may include a processor that references a look-up table to determine a polynomial equation for a given breath rate, where the polynomial equation provides a corrected gas concentration for a measured gas concentration at the given breath rate. In this way, variations of the present disclosure may beneficially provide for determining a gas concentration in a patient's breath independently of patient cooperation. That is, the gas concentration may be determined for patients who are unwilling or unable to regulate their breathing to correlate to a “normal” breathing pattern.
Although ETCO is specifically discussed with respect to
In some embodiments, the look-up table may be populated by drawing a known ETCO through an inlet of an apparatus and then measuring the ETCO at another point in the apparatus. The procedure may be repeated for multiple breath rates.
A specific variation of establishing ETCO accuracy, such as in step 1502, is depicted in graph 1520 of
Returning to
In some variations, non-polynomial equations may be used to describe the relationships, such as logarithmic equations, exponential equations, or other equations. Specific accuracy equations are illustrated in graph 1520 of
Although the variation in
Referring again to
Although
Returning to
Although
Returning again to
ETCO(BR Corrected)=[ETCO(Measured)−b]/M
It should be understood that the above equation may vary if the number of coefficients of the accuracy equation is varied. For example, the variation of
When the apparatus is in use, should the measured breath rate or measured gas concentration be outside of the ranges defined by the above procedure, the apparatus may react in a variety of ways, depending on the details of the clinical application. The apparatus may not compute a corrected ETCO result and notify the user that the measured parameters are outside of the apparatus's range. The apparatus may compute the corrected ETCO despite being out of range, and provide the result to the user while notifying the user that the accuracy of the result may be less accurate because the measured parameters are outside of the operating range. In some variations, the apparatus may simply compute a result by extrapolating with the appropriate equations. In this way, variations of the present disclosure may beneficially provide for determining a gas concentration in a patient's breath independently of patient cooperation. That is, the gas concentration may be determined for patients who are unwilling or unable to regulate their breathing to correlate to a “normal” breathing pattern.
In some variations, the entire set of values within an operating range may be tested in advance, and a look-up database created based on the results. For example, breath rates of 10, 11, 12 and so on to 50 bpm (for example), at gas concentrations of 1.0, 1.1, 1.2 and so on to 25.0 ppm can be pre-tested. When the device is in use, the corrected gas concentration can be obtained by finding the appropriate value in the database for the measured breath rate and measured gas concentration. In some variations, a combined approach is used such as pre-testing all breath rates but only a set of discrete gas concentrations within or near the operating range.
While the above embodiment describes the use of breath rate as the breathing pattern parameter used in the corrections, it is understood that rather than breath rate, the same embodiment may be accomplished with any breathing pattern related parameter. Examples of other parameters include expiratory time, end-tidal time, inspiratory time, inspiratory:expiratory ratio, tidal volume, minute volume, airway pressure amplitude, capnometry signal amplitude, and the duration of the positive slope of the capnometry signal.
In some variations, a method of determining a gas concentration at the inlet of an apparatus may include determining the patient's breath rate and measuring the concentration of the patient's breath somewhere else in the apparatus. As used herein, measured a gas in an apparatus can be understood to mean measuring anywhere within the apparatus, such as at an outlet or an interior point in the apparatus, such as in a tube or compartment. With the measured gas concentration, a database can be accessed to obtain a plurality of coefficients corresponding to the patient's breath rate. In the example of
In some variations, an apparatus may include a processor for carrying out the above method of determining a gas concentration at the inlet of an apparatus. The apparatus may also include a measuring point, a gas analyzer for determining a gas concentration at the measuring point, an inlet, and a breath speed analyzer. The processor may access a database stored on a non-transitory computer readable medium, where the database includes a plurality of coefficients for each breath rate in the operating range.
In some variations, a sampling system may be tuned for an upper limit breath rate. For a given sample volume (sample volume may be determined to meet specifications of a particular application), the flow rate of a flow generator, such as a pump, may be configured to fill the entire sample volume with end-tidal gas for the upper limit breath rate. For breath rates lower than the upper limit breath rate, the sample volume is completely filled with end-tidal gas, albeit not all of the end-tidal gas for that breath. In further variations, the system may include an upper limit cut-off that limits sampling to breaths at or below the upper limit. In this way, these variations may beneficially prevent non-end-tidal gas from entering the sample volume. Thus, variations of the present disclosure may beneficially provide for determining a gas concentration in a patient's breath independently of patient cooperation. That is, the gas concentration may be determined for patients who are unwilling or unable to regulate their breathing to correlate to a “normal” breathing pattern.
In some variations, a gas sampling flow rate may be determined to fit the requirements of a particular application. For example, an upper limit for normal breathing may be described by a breath frequency parameter, such as 60 bpm. However, for certain patients (such as neonates, for example), a normal breath rate may exceed 60 bpm. In such an instance, the upper limit may be higher, such as at 100 bpm. Similarly, the sample volume may be chosen to reflect the needs of a particular application. In some variations, other frequency parameters may be chosen, such as inspiratory time, breath period, expiratory time, end-tidal time, capnometer signal rise duration, or another parameter that describes at least a portion of the patient's breathing. In some variations, an instantaneous carbon monoxide sensor is used.
Method 1600 continues with step 1604, defining a desired sample volume (V(s)). In the variation of method 1600, the sample volume is sized for adequate and reliable analysis. In other variations, the sample volume may be sized to factor in other considerations.
Method 1600 continues with step 1606, determining the gas sampling flow rate (Q(S)). In the variation of method 1600, the flow generator is a pump, but other flow generators could be used, such as the examples described herein. The gas sampling flow rate may be calculated to fill the desired sample volume at the upper limit breath rate.
In some variations, the sampling flow rate is calculated from the following equation Q(S)=TET/V(S), wherein TET is the estimated end-tidal period and is a function of the breath rate. In some variations, TET may be assumed to be half of the expiratory time, which itself may be assumed to be half of the breath period (inspiratory and expiratory periods). The breath period (seconds) is 60/breath rate. For example, if the upper limit breath rate is 60 bpm, then TET may be assumed to be 0.25 seconds. If the sample volume in this example is 0.5 ml, then the sampling flow rate is 2 ml per second.
Some variations include elements and functionality from individual variations described above, that is, some variations may combine different elements of the different variations described above. For example, a user interface of the apparatus may allow the user to enter a certain patient parameter, such as a patient type, for example adult or infant, or for example premature neonate or full term infant. The control system of the apparatus will select a preferred breath rate compensation methodology, selected from the embodiments described above, and use that methodology accordingly. In some variations, the apparatus may, for example, use the embodiment described in
In the foregoing descriptions of variations of the invention, the examples provided are illustrative of the principles of the invention, and that various modifications, alterations, and combinations can be made by those skilled in the art without departing from the scope and spirit of the invention. Any of the variations of the various breath measurement and sampling devices disclosed herein can include features described by any other breath measurement and sampling devices or combination of breath measurement and sampling devices herein. Accordingly, it is not intended that the invention be limited, except as by the appended claims. For all of the variations described above, the steps of the methods need not be performed sequentially.
Claims
1-40. (canceled)
41. A system for the analysis of exhaled gas comprising:
- a breath rate sensor for measuring a breath rate of a breath sample from a patient;
- a sample compartment having a predetermined volume;
- a processor operable to execute an algorithm that measures an end-expiratory time of the breath sample to determine the start time and end time for collecting the breath sample and adjusts a flow rate of the breath sample based on the end-expiratory time;
- a flow generator that draws the breath sample into the sample compartment according to the adjusted flow rate until the predetermined volume of the sample compartment is completely filled with end-tidal portions of the breath sample.
42. The system of claim 41, further comprising a gas analyzer that measures a concentration of a gas within the sample compartment.
43. The system of claim 42, wherein the gas is carbon monoxide, carbon dioxide, or oxygen.
44. The system of claim 41, wherein the algorithm measures the end-expiratory time using a capnometry signal, a differential capnometry signal, or a pressure signal.
45. The system of claim 41, further comprising a user interface configured to allow a user to input a patient parameter.
46. The system of claim 45, wherein the patient parameter is a patient type.
47. The system of claim 46, wherein the patient type is an adult.
48. The system of claim 46, wherein the patient type is a premature neonate.
49. The system of claim 46, wherein the patient type is a full term infant.
50. The system of claim 41, wherein the flow generator comprises a pump.
51. A system comprising:
- a breath rate sensor for measuring a breath rate of a breath sample of a patient;
- a sample compartment that collects end-tidal portions of the breath sample, the sample compartment having a predetermined volume;
- a flow generator having a predetermined flow rate; and
- a processor operable to execute an algorithm that determines the number of end-tidal portions for collection based on the measured breath rate, the predetermined flow rate, and the predetermined sample compartment volume.
52. The system of claim 51, further comprising a gas analyzer that measures a concentration of a gas within the sample compartment.
53. The system of claim 52, wherein the sample compartment contains only the end-tidal portion of the breath sample.
54. The system of claim 51, wherein the gas is carbon monoxide, carbon dioxide, or oxygen.
55. The system of claim 51, further comprising a user interface configured to allow a user to input a patient parameter.
56. The system of claim 55, wherein the patient parameter is a patient type.
57. The system of claim 56, wherein the patient type is an adult.
58. The system of claim 56, wherein the patient type is a premature neonate.
59. The system of claim 56, wherein the patient type is a full term infant.
60. The system of claim 51, wherein the flow generator comprises a pump.
Type: Application
Filed: Jul 9, 2021
Publication Date: Jun 2, 2022
Inventors: Anthony D. WONDKA (San Ramon, CA), Anish BHATNAGAR (Redwood City, CA)
Application Number: 17/372,240