NONINVASIVE HYPOVOLEMIA MONITOR
A hypovolemia monitor comprises a plethysmograph input responsive to light intensity after absorption by fleshy tissue. A measurement of respiration-induced variation in the input is made. The measurement is normalized and converted into a hypovolemia parameter. An audible or visual indication of hypovolemia is provided, based upon the hypovolemia parameter.
The present application claims priority benefit under 35 U.S.C. §120 to, and is a continuation of U.S. patent application Ser. No. 11/221,411, filed Sep. 6, 2006 entitled “Noninvasive Hypovolemia Monitor,” now U.S. Pat. No. 7,976,472, which claims priority benefit under 35 U.S.C. §119(e) from U.S. Provisional Application No. 60/607,562, filed Sep. 7, 2004, entitled “Noninvasive Hypovolemia Monitor.” The present application also incorporates the foregoing disclosures herein by reference.
BACKGROUND OF THE INVENTIONPulse oximetry, a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, is responsive to pulsatile blood flowing within a fleshy tissue site.
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One aspect of a hypovolemia monitor comprises a plethysmograph input responsive to light intensity after absorption by fleshy tissue and a measurement of respiration-induced variation in the input. The measurement is normalized and converted into a hypovolemia parameter. The plethysmograph may be generated by a pulse oximeter, and an audible or visual indication of hypovolemia may be provided. In one embodiment, an envelope of the plethysmograph is detected and a magnitude of the envelope is determined in order to measure the respiration-induced variation. In an alternative embodiment, a curve-fit is made to a locus of points on the plethysmograph and the variation magnitude is determined from a characteristic of the resulting curve. In yet another embodiment, a frequency spectrum of the plethysmograph is determined and a frequency component of that spectrum proximate a respiration rate is identified. The variation magnitude is calculated from the magnitude of that frequency component.
In other embodiments of the hypovolemia monitor, the normalized measurement is calculated by dividing the variation magnitude by an average value of the plethysmograph. Conversion is accomplished by constructing a calibration curve of hypovolemia parameter versus variation magnitude and using that calibration curve to determine the hypovolemia parameter from the normalized measurement. A percentage of normal total blood volume or a percentage of total blood volume loss may be displayed based upon the hypovolemia parameter. An audible alarm or a visual alarm indicating a hypovolemia condition may also be generated.
Another aspect of a hypovolemia monitor is a variation function having a sensor input and generating a variation parameter. The sensor input is responsive to light intensity after absorption by fleshy tissue and provides a measure of respiration-induced cyclical variation in the sensor input. A normalization function is applied to the variation parameter so as to generate a normalized variation parameter responsive to an average value of the sensor input. A conversion function is applied to the normalized variation parameter so as to generate a hypovolemia parameter responsive to blood volume of a living subject. In one embodiment, the variation function comprises an envelope detector adapted to determine an envelope of the sensor input and a magnitude processor configured to calculate a magnitude of the envelope. In another embodiment, the variation function comprises a curve-fit processor adapted to determine a locus of the sensor input representative of the cyclical variation. A magnitude processor is configured to calculate a magnitude of the cyclical variation from the locus. In yet another embodiment, the variation function comprises a frequency transform processor configured to generate a frequency spectrum of the sensor input. A frequency component processor is configured to determine the magnitude of a frequency component of the spectrum corresponding to a respiration rate of the living subject.
In other embodiments, the normalization function calculates the magnitude divided by the average value so as to generate a normalized magnitude. The conversion function comprises a look-up table containing a curve representing a hypovolemia parameter versus the normalized magnitude. In a particular embodiment, the hypovolemia parameter corresponds to a percentage blood volume loss of the living subject.
A further aspect of a hypovolemia monitor comprises a variation means, a normalization means and a conversion means. The variation means is for measuring a magnitude of respiration-induced cyclical variations in an input plethysmograph. The normalization means is for normalizing the magnitude relative to a DC value of the plethysmograph. The conversion means is for translating the normalized magnitude to a hypovolemia parameter responsive to blood volume loss in a living subject.
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Although the variation measurement and normalization functions are described above with respect to a time domain analysis, similar results can be achieved by a frequency domain analysis. For example, the variation measurement function 510 can be determined by performing a Fast Fourier Transform (FFT) or similar computation on the plethysmograph. In particular, the magnitude of the resulting spectral component at or near the respiration rate RR is determined. In one embodiment, respiration rate RR 503 is an input to the variation measurement function 510, as provided by a ventilator, a respiration belt transducer or similar device.
A noninvasive hypovolemia monitor has been disclosed in detail in connection with various embodiments. These embodiments are disclosed by way of examples only and are not to limit the scope of the claims that follow. One of ordinary skill in the art will appreciate many variations and modifications.
Claims
1. A method of determining a indication of blood volume in a monitored patient using a noninvasive optical sensor, the method comprising:
- receiving a plethysmograph responsive to light detected by a noninvasive optical sensor, said light being attenuated by tissue of a patient being monitored;
- electronically determining variations in said plethysmograph due to respiration of said patient; and
- electronically calculating a blood volume parameter responsive to said variations, said blood volume parameter indicative of blood volume of said patient at the time of said monitoring.
2. The method of claim 1, wherein the calculating said blood volume parameter comprises normalizing said variations.
3. The method of claim 1, wherein the calculating said blood volume parameter comprises converting said variations to a numeric value.
4. The method of claim 3, wherein said converting comprises accessing clinical data including blood volume information.
5. The method of claim 3, wherein said numeric value comprises a percentage of blood loss.
6. The method of claim 3, wherein said numeric value comprises a total volume of blood.
7. The method of claim 1, wherein the calculating said blood volume parameter comprises accessing input parameters usable in determining said blood volume parameter.
8. The method of claim 7, wherein said input parameters include patient type.
9. The method of claim 8, wherein said patient type includes at least two of adult, pediatric, and neonatal.
10. The method of claim 7, wherein said input parameters include patient characteristics.
11. The method of claim 10, wherein said patient characteristics include at least one of height, weight, and blood pressure.
12. The method of claim 1, wherein the calculating said blood volume parameter comprises calculating using frequency domain information.
13. The method of claim 1, wherein the calculating said blood volume parameter relies on time domain information.
14. The method of claim 1, wherein the calculating said blood volume parameter comprises calculating a magnitude of said variations.
15. The method of claim 14, wherein said magnitude comprises one of a variation in a minimum, a variation in a maximum, and a curve fit.
16. A method of activating a blood volume alarm indicative of a blood volume needing caregiver attention, said volume detected with a noninvasive optical sensor, the method comprising:
- receiving data responsive to light detected by a noninvasive optical sensor, said light being attenuated by tissue of a patient being monitored;
- electronically selecting a subset of said data responsive to respiration of said patient; and
- activating a low blood volume alarm configured to attract a caregiver's attention responsive to said subset of said data.
17. The method of claim 16, wherein said activating said alarm comprises evaluation of additional input parameters, including at least one of patient type and patient characteristic.
18. The method of claim 16, comprising displaying a numeric value to said caregiver responsive to a blood volume of a patient being monitored.
19. The method of claim 18, wherein said numeric value comprises at least one of a percentage of blood loss and a total volume of blood.
20. A blood volume monitor comprising:
- an input configured to receive a plethysmograph responsive to light detected by a noninvasive optical sensor, said light being attenuated by tissue of a patient being monitored; and
- a processor configured to electronically determine variations in said plethysmograph due to respiration of said patient, and to calculate a blood volume parameter responsive to said variations, said blood volume parameter indicative of blood volume of said patient at the time of said monitoring.
Type: Application
Filed: Jul 11, 2011
Publication Date: Nov 3, 2011
Inventor: Massi E. Kianl (Laguna Niguel, CA)
Application Number: 13/180,429
International Classification: A61B 6/00 (20060101);