Noninvasive hypovolemia monitor

• US 20060058691A1
• Filed: 09/06/2005
• Published: 03/16/2006
• Est. Priority Date: 09/07/2004
• Status: Active Grant

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Kiani, Massi E.
• Granted Patent: US 7,976,472 B2
• Time in Patent Office: Days
• US Class Current: 600/507
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/02042 Determining blood loss or bleeding, e.g. during a surgical procedure
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters

Abstract

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.

Claims

1. A hypovolemia monitoring method comprising the steps of:

inputting a plethysmograph responsive to light intensity after absorption by fleshy tissue;

measuring a respiration-induced variation in said input;

normalizing said measurement; and

converting said normalized measurement into a hypovolemia parameter.

2. The hypovolemia monitoring method according to claim 1 comprising the further step of providing at least one of an audible indication and a visual indication of hypovolemia.

3. The hypovolemia monitoring method according to claim 2 wherein said inputting step comprises the substep of generating a pulse oximeter plethysmograph.

4. The hypovolemia monitoring method according to claim 3 wherein said measuring step comprises the substeps of:

detecting an envelope of said plethysmograph; and

determining a magnitude of said envelope.

5. The hypovolemia monitoring method according to claim 3 wherein said measuring step comprises the substeps of:

fitting a curve to a locus of points on said plethysmograph;

determining a magnitude of said variation from a characteristic of said curve.

6. The hypovolemia monitoring method according to claim 3 wherein said measuring step comprises the substeps of:

determining a frequency spectrum of said plethysmograph;

identifying a frequency component of said frequency spectrum proximate a respiration rate; and

calculating a magnitude of said frequency component.

7. The hypovolemia monitoring method according to claim 4 wherein said normalizing step comprises the substeps of:

calculating an average value of said plethysmograph; and

dividing said magnitude by said average value.

8. The hypovolemia monitoring method according to claim 7 wherein said converting step comprises the substep of:

constructing a calibration curve of said hypovolemia parameter versus variation magnitude;

utilizing said calibration curve to determine said hypovolemia parameter from said normalized measurement.

9. The hypovolemia monitoring method according to claim 8 wherein said providing step comprises the substep of displaying at least one of a percentage of normal total blood volume and a percentage of total blood volume loss based upon said hypovolemia parameter.

10. The hypovolemia monitoring method according to claim 8 wherein said providing step comprises the substep of generating at least one of an audible alarm and a visual alarm indicating a hypovolemia condition.

11. A hypovolemia monitor comprising:

a variation function having a sensor input and generating a variation parameter, said sensor input responsive to light intensity after absorption by fleshy tissue, said variation parameter providing a measure of respiration-induced cyclical variation in said sensor input;

a normalization function applied to said variation parameter so as to generate a normalized variation parameter responsive to an average value of said sensor input; and

a conversion function applied to said normalized variation parameter so as to generate a hypovolemia parameter responsive to blood volume of a living subject.

12. The hypovolemia monitor according to claim 11 wherein said variation function comprises:

an envelope detector adapted to determine an envelope of said sensor input; and

a magnitude processor configured to calculate a magnitude of said envelope.

13. The hypovolemia monitor according to claim 11 wherein said variation function comprises:

a curve-fit processor adapted to determine a locus of said sensor input representative of said cyclical variation; and

a magnitude processor configured to calculate a magnitude of said cyclical variation from said locus.

14. The hypovolemia monitor according to claim 11 wherein said variation function comprises:

a frequency transform processor configured to generate a frequency spectrum of said sensor input; and

a frequency component processor configured to determine the magnitude of a frequency component of said spectrum corresponding to a respiration rate of said living subject.

15. The hypovolemia monitor according to claim 12 wherein said normalization function calculates said magnitude divided by said average value so as to generate a normalized magnitude.

16. The hypovolemia monitor according to claim 15 wherein said conversion function comprises a look-up table containing a curve representing a hypovolemia parameter versus said normalized magnitude.

17. The hypovolemia monitor according to claim 16 wherein said hypovolemia parameter corresponds to a percentage blood volume loss of said living subject.

18. A hypovolemia monitor comprising:

a variation means for measuring a magnitude of respiration-induced cyclical variations in an input plethysmograph;

a normalization means for normalizing said magnitude relative to a DC value of said plethysmograph; and

a conversion means for translating said normalized magnitude to a hypovolemia parameter responsive to blood volume loss in a living subject.