Patent ID: 6921367

Claim:
A method for noninvasively determining a physiological characteristic of a patient's blood, comprising the steps of: providing a tissue probe having a first radiation emitter with a first wavelength and a first radiation detector configured to receive the first wavelength after absorbance through the patient's blood; placing said tissue probe proximate an extremity of the patient; placing said extremity at an initial position whereby said tissue probe is positioned at a first probe position relative to a level corresponding to the patient's heart; measuring absorbance of the patient's blood at said first probe position by emitting a first radiation through the patient's blood and detecting the radiation after passage through the patient's blood; computing a blood parameter at said first probe position based on said first probe position absorbance; moving said extremity to at least a second extremity probe position relative to said first probe position; measuring absorbance of the patient's blood at said second extremity position; comparing the rate of change of absorbance at said second extremity position with said first probe position absorbance to determine at least a first rate of change of absorbance value; and determining central venous drainage from said rate of change of absorbance value.