Method of Assessing Blood Volume Using Photoelectric Plethysmography

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.

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.

A method for facilitating detection of physiological changes of a subject, the method comprising:

• analyzing a cardiovascular waveform representing physiological characteristics of a subject using a processor, wherein the analyzing of the cardiovascular waveform includes:
• identifying a first component of the cardiovascular waveform reflective of a cardiovascular impact of respiration;
• analyzing a characteristic of the first component reflective of amplitude variations of the first component, wherein the amplitude variations are indicative of changes in blood volume of the subject, wherein the analyzing the characteristic of the first component of the cardiovascular waveform includes calculating an index responsive to the amplitude variations of the first component, wherein the first component is normalized and wherein index variations are indicative of changes in blood volume of the subject;
• wherein the cardiovascular waveform is a photoplethysmograph waveform generated using a photoplethysmographic device.