Method for noninvasive continuous determination of physiologic characteristics

Abstract

The invention comprises methods for noninvasively monitoring physiological characteristics of a patient's blood. Determinations of blood constituent concentrations may be made by comparing absorbance of radiation at varying parameters, such as path length and blood pressure. Preferably, changes in pressure are effected by changing the height of the probes relative to the patient's heart. Determinations of blood pH may be made by comparing absorbance of the blood at different wavelengths. The temperature of the blood, and thus of the patient's core, may also be accurately determined. Further, cardiac output characteristics and blood pressures may be noninvasively determined using the methods of the invention.

1 - 6 . (canceled) 
     
     
         7 . A method for noninvasively determining physiologic parameters of a patient, comprising the steps of:
 providing a first tissue probe, said first tissue probe including a first radiation emitter adapted to emit first radiation having a first wavelength and a first radiation detector adapted to receive said first radiation after absorbance through a first radiation path length of the patient's blood;   measuring absorbance of the patient's blood by transmitting said first radiation at said first wavelength through the patient's blood and detecting said first radiation after passage through the patient's blood; providing a second tissue probe, said second tissue probe including a second radiation emitter adapted to emit second radiation having a second wavelength and a second radiation detector adapted to receive said second radiation after absorbance through a second radiation path length; measuring second absorbance of the patient's blood at a second patient site by transmitting said second radiation at said second wavelength through the patient's blood and detecting said second radiation after passage through the patient's blood;   determining first hemoglobin absorbance at said first patient site and second hemoglobin absorbance at said second patient site; timing the arrival of pulse and flow waves at the first and second patient sites by comparing said first and second hemoglobin absorbances; and   determining a cardiac characteristic based on said arrival times of said pulse and flow waves.   
     
     
         8 - 16 . (canceled) 
     
     
         17 . A method for noninvasively determining physiologic parameters of a patient, comprising the steps of:
 providing a first tissue probe, said first tissue probe including a first radiation emitter adapted to emit first radiation having a first wavelength and a first radiation detector adapted to receive said first radiation after absorbance through a first radiation path length of the patient's blood;   providing a second tissue probe, said second tissue probe including a second radiation emitter adapted to emit second radiation having a second wavelength and a second radiation detector adapted to receive said second radiation after absorbance through a second radiation path length;   varying the volume and pressure of the patient's blood at first and second patient sites, said first patient site being proximate said first tissue probe, said second patient site being proximate second tissue probe; measuring first absorbance of the patient's blood at said first patient site as said blood volume and pressure are varied by transmitting said first radiation at said first wavelength through the patient's blood and detecting said first radiation after passage through the patient's blood;   measuring second absorbance of the patient's blood at said second patient site as said blood volume and pressure are varied by transmitting said second radiation at said second wavelength through the patient's blood and detecting said second radiation after passage through the patient's blood;   timing the arrival of pulse and flow waves at said first and second patient sites by comparing said first and second absorbances measured said first and second patient sites probe; and   determining a cardiac characteristic based on said arrival times of said pulse and flow waves.   
     
     
         18 . The method of  claim 17 , further comprising the step of using an electrocardiogram to correlate timing of said first and second hemoglobin absorbance measurements. 
     
     
         19 - 29 . (canceled) 
     
     
         30 . A method for non-invasively determining a cardiac characteristic of a patient, comprising the steps of:
 measuring pulse wave velocity in a first extremity;   determining flow wave velocity; and   computing the cardiac output characteristic using the flow wave velocity.   
     
     
         31 . The method of  claim 30 , wherein said step of computing the cardiac characteristic comprises determining a characteristic selected from the group comprising cardiac output, cardiac index, cardiac stroke volume, cardiac ejection fraction, and blood volume. 
     
     
         32 . The method of  claim 30 , further comprising the step of measuring pulse wave velocity in a second, opposite extremity and wherein the step of determining flow wave velocity comprises computing the flow wave velocity using the ratios of the pulse wave velocities in said first and second extremities. 
     
     
         33 . The method of  claim 32 , wherein the first and second extremities comprise the patient's left and right hands. 
     
     
         34 . The method of  claim 32 , wherein the steps of measuring pulse wave velocity comprise measuring the time intervals for arrival of pulses in said first and second extremities. 
     
     
         35 . The method of  claim 30 , further comprises the step of measuring blood pressure and wherein the step of determining flow wave velocity comprises computing the flow wave velocity using said blood pressure and said pulse wave velocity. 
     
     
         36 . The method of  claim 32 , wherein the steps of measuring pulse wave velocity comprises the steps of placing first and second tissue probes on different locations of the patient's body, continuously monitoring oxygen saturation in the patient's blood through said first and second tissue probes, inducing a change in oxygen saturation, and comparing the arrival time of the saturation change at said first and second tissue probes. 
     
     
         37 . The method of  claim 36 , wherein the step of inducing a change in oxygen saturation comprises having the patient breath-hold. 
     
     
         38 . The method of  claim 30 , further comprising the step of inducing a change in oxygen saturation. 
     
     
         39 . The method of  claim 38 , wherein the cardiac characteristic is selected from the group comprising cardiac index, cardiac stroke volume and cardiac output, and the cardiac characteristic is computed by determining the time interval between said inducement of change in oxygen saturation and a first measured change in oxygen saturation. 
     
     
         40 . The method of  claim 38 , wherein the cardiac characteristic comprises cardiac ejection fraction and the cardiac characteristic is computed by determining the time interval between a first measured change in oxygen saturation and maximal change in oxygen saturation. 
     
     
         41 . The method of  claim 38 , wherein the cardiac characteristic comprises blood volume and the cardiac characteristic is computed by determining the time interval between said inducement of change in oxygen saturation and return to a baseline measured oxygen saturation. 
     
     
         42 . The method of  claim 36 , wherein the step of inducing a change in oxygen saturation comprises providing an enriched oxygen atmosphere. 
     
     
         43 . A method for noninvasively determining the blood pressure of a patient comprising the steps of:
 measuring the pulse wave velocity in a first extremity of the patient at a first pressure; inducing pressure change in the first extremity;   measuring the pulse wave velocity in the first extremity at a second pressure; and computing the blood pressure using ratios of said pulse wave velocities and the hydrostatic pressure difference of said first and second pressures.   
     
     
         44 . The method of  claim 43 , wherein the step of inducing a pressure change in said first extremity comprises varying the height of said first extremity relative to the patient's heart. 
     
     
         45 . The method of  claim 43 , further comprising the step of measuring pulse wave velocity in a second extremity. 
     
     
         46 . The method of  claim 45 , further comprising the step of inducing pressure change in said second extremity. 
     
     
         47 . A method for noninvasively determining the blood pressure of a patient comprising the steps of:
 measuring a first time interval for a pulse to reach a first location in a first extremity at a first pressure;   inducing a pressure change in said first extremity by varying the height of the first extremity relative to the patient's heart;   measuring a second time interval for a pulse to reach said first location in said first extremity at a second pressure; and computing the blood pressure using the ratios of said first and second time intervals and the hydrostatic pressure difference of said first and second pressures.   
     
     
         48 - 49 . (canceled) 
     
     
         50 . A method for noninvasively determining a patient's blood pressure, comprising the steps of:
 measuring pulse wave velocities in two opposite patient extremities; and   computing the blood pressure using the ratios of said pulse wave velocities.   
     
     
         51 . A method for noninvasively determining the blood pressure, comprising the steps of:
 measuring the time intervals for arrival of a pulse in two opposite extremities; and   computing the blood pressure using the ratios of said two time intervals.   
     
     
         52 - 55 . (canceled)