Noninvasive hypovolemia monitor

1. A method of monitoring a hypovolemia parameter of a patient with electronic oximetry monitoring circuitry configured to noninvasively and electronically monitor the patient, the method comprising the steps of:

inputting a plethysmograph responsive to an output from a noninvasive oximetry sensor applied to said patient, said output responsive to light intensity after absorption by fleshy tissue;

electronically measuring a respiration-induced variation in said input;

electronically normalizing said measurement;

electronically converting said normalized measurement into a numeric value indicating a blood volume level wherein said value indicates hypovolemia; and

providing at least one of an audible indication and a visual indication of said value to a caregiver of said patient.

2. The hypovolemia monitoring method according to claim 1 wherein said inputting step comprises the substep of generating a pulse oximeter plethysmograph.

3. The hypovolemia monitoring method according to claim 2 wherein said measuring step comprises the substeps of:

detecting an envelope of said plethysmograph; and

determining a magnitude of said envelope.

4. The hypovolemia monitoring method according to claim 2 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.

5. The hypovolemia monitoring method according to claim 2 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.

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

calculating an average value of said plethysmograph; and

dividing said magnitude by said average value.

7. The hypovolemia monitoring method according to claim 6 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 numeric value from said normalized measurement.

8. The hypovolemia monitoring method according to claim 7 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 numeric value.

9. The hypovolemia monitoring method according to claim 7 wherein said providing step comprises the substep of generating at least one of an audible alarm and a visual alarm indicating a hypovolemia condition.

10. A hypovolemia monitor comprising one or more processors programmed to include 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; the one or more processor also programmed to include 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 the one or more processor programmed to include a conversion function applied to said normalized variation parameter so as to generate a numeric value indicating a blood volume level wherein said value indicates hypovolemia; and

an output providing at least one of an audible indication and a visual indication to one of a display and additional instrumentation.

11. The hypovolemia monitor according to claim 10 wherein said variation function comprises:

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

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

12. The hypovolemia monitor according to claim 10 wherein said variation function comprises:

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

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

13. The hypovolemia monitor according to claim 10 wherein said variation function comprises:

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

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

14. The hypovolemia monitor according to claim 11 wherein said normalization function calculates said magnitude divided by said average value so as to generate a normalized magnitude.

15. The hypovolemia monitor according to claim 14 wherein said conversion function comprises a look-up table containing a curve representing a numeric value versus said normalized magnitude.

16. The hypovolemia monitor according to claim 15 wherein said numeric value corresponds to a percentage blood volume loss of said living subject.

17. 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 into a numeric value indicating a blood volume level wherein said value indicates hypovolemia.