Calibrated measurement of blood vessels and endothelium after reactive hyperemia and method therefor

Abstract

Calibrated method characterizing blood flow in a patient's limb during reactive hyperemia episode utilizes a blood pressure cuff, establishes a predetermined, near diastolic, pressure in the cuff during the episode, continually senses the pressure cuff and periodically changes the internal volume of the cuff by a predetermined volumetric amount to calibrate the system with a calibration pressure pulse. The method may determine the condition of blood vessels and endothelium by determining, for each calibration cycle, a blood volume peak and comparing the peak with peak volume values for healthy blood vessels and endothelium (potentially waveform analysis). The method, implemented as a system, inflates, during pre-test, the cuff to a suprasystolic pressure, and establishes the near diastolic pressure in the cuff during the episode. A sensor generates a pressure signal and a subsystem periodically changes the volume during calibration such that a corrected and calibrated blood volume signal is calculated.

What is claimed is:  
     
         1 . A calibrated method for characterizing blood flow in a limb of a patient during reactive hyperemia with a blood pressure cuff bound about said limb comprising the steps of: 
 establishing a predetermined, near diastolic, pressure in said blood pressure cuff during the reactive hyperemic episode;    substantially continually sensing the pressure in said blood pressure cuff during the reactive hyperemic episode;    during the reactive hyperemic episode, periodically changing a volume of said blood pressure cuff by a predetermined volumetric amount and substantially concurrently sensing a resultant change in the pressure as a calibration pressure pulse;    calculating pulsatile blood volume by correcting the sensed pressure with the ratio of the predetermined volumetric amount and calibration pressure pulse.    
     
     
         2 . A calibrated method for characterizing blood flow as claimed in  claim 1  wherein the step of sensing the pressure includes sensing a pressure pulse due to blood flow through the patient's arteries and the step of periodically changing said volume of said blood pressure cuff by a predetermined volumetric amount includes the step of changing said volume based upon a periodic presence of a predetermined plurality of sensed pressure pulses.  
     
     
         3 . A calibrated method for characterizing blood flow as claimed in  claim 2  wherein the periodic presence of a predetermined plurality of sensed pressure pulses defines a cyclic calibration routine for calculating a plurality of pulsatile blood volumes during the reactive hyperemic episode.  
     
     
         4 . A calibrated method for characterizing blood flow as claimed in  claim 3  including the step of selecting at least one of said sensed pressure pulses during each cyclic calibration and calculating said pulsatile blood volume based thereon, said step of calculating a plurality of pulsatile blood volumes during the reactive hyperemic episode including the step of utilizing said at least one of said sensed pressure pulses for each said cyclic calibration.  
     
     
         5 . A calibrated method for characterizing blood flow as claimed in  claim 4  including the step of reducing motion artifacts by averaging one from the group of a predetermined number of sensed pressure pulses in each cyclic calibration and a predetermined number of pulsatile blood volumes in each cyclic calibration.  
     
     
         6 . A calibrated method for characterizing blood flow as claimed in  claim 4  including the step of correlating an episodic time with each cyclic calibration.  
     
     
         7 . A calibrated method for characterizing blood flow as claimed in  claim 6  wherein said pulsatile blood volume is a wave and the method includes the step of calculating a plurality of peak values for the pulsatile blood volume during the reactive hyperemic episode.  
     
     
         8 . A calibrated method for characterizing blood flow as claimed in  claim 7  including the step of graphically presenting said plurality of peak values for the pulsatile blood volume with respect to the correlated episodic time for substantially the entire reactive hyperemic episode.  
     
     
         9 . A calibrated method for characterizing blood flow as claimed in  claim 3  wherein the step of changing said volume based upon a periodic presence of a predetermined plurality of sensed pressure pulses includes the step of counting sensed pressure pulses.  
     
     
         10 . A calibrated method for characterizing blood flow as claimed in  claim 9  wherein the step of changing said volume based upon counting a periodic presence of a predetermined plurality of sensed pressure pulses includes the step of counting at least three substantially similar pressure pulses and subsequently changing said volume with said predetermined volumetric amount.  
     
     
         11 . A calibrated method for characterizing blood flow as claimed in  claim 10  including the step of ignoring a second predetermined plurality of sensed pressure pulses subsequent to changing said volume with said predetermined volumetric amount.  
     
     
         12 . A calibrated method for characterizing blood flow as claimed in  claim 11  wherein said steps of counting at least three substantially similar pressure pulses, subsequently changing said volume with said predetermined volumetric amount, and ignoring a second predetermined plurality of sensed pressure pulses subsequent to changing said volume defines a cyclic calibration period.  
     
     
         13 . A calibrated method for characterizing blood flow as claimed in  claim 8  wherein the step of changing said volume based upon a periodic presence of a predetermined plurality of sensed pressure pulses includes the step of counting sensed pressure pulses.  
     
     
         14 . A calibrated method for characterizing blood flow as claimed in  claim 13  changing said volume based upon counting a periodic presence of a predetermined plurality of sensed pressure pulses includes the step of counting at least three substantially similar pressure pulses and subsequently changing said volume with said predetermined volumetric amount.  
     
     
         15 . A calibrated method for characterizing blood flow as claimed in  claim 14  including the step of ignoring a second predetermined plurality of sensed pressure pulses subsequent to changing said volume with said predetermined volumetric amount.  
     
     
         16 . A calibrated method for characterizing blood flow as claimed in  claim 15  wherein said steps of counting at least three substantially similar pressure pulses, subsequently changing said volume with said predetermined volumetric amount, and ignoring a second predetermined plurality of sensed pressure pulses subsequent to changing said volume defines a cyclic calibration period.  
     
     
         17 . A calibrated method for characterizing blood flow as claimed in  claim 16  including the step of obtaining said patient's diastolic blood pressure prior to said reactive hyperemic episode and utilizing one of said patient's diastolic pressure and a predetermined, step-down diastolic pressure in the step of establishing said predetermined pressure in said blood pressure cuff during the reactive hyperemic episode.  
     
     
         18 . A calibrated method for characterizing blood flow as claimed in  claim 17  including the step of occluding blood flow through the limb of said patient for a predetermined time period prior to the step of establishing said predetermined pressure in said blood pressure cuff thereby creating said reactive hyperemic episode in the limb of said patient.  
     
     
         19 . A calibrated system for characterizing blood flow in a limb of a patient during reactive hyperemia with a blood pressure cuff bound about said limb comprising: 
 means, coupled to said blood pressure cuff, for inflating, for a predetermined pre-test time, said blood pressure cuff to a suprasystolic pressure and thereafter establishing a predetermined, near diastolic, pressure in said blood pressure cuff during the ensuing reactive hyperemic episode;    a sensor, pneumatically coupled to said blood pressure cuff, substantially continually sensing the pressure in said cuff and generating a pressure signal during the reactive hyperemic episode;    means, coupled to said blood pressure cuff, for periodically changing a volume of said blood pressure cuff by a predetermined volumetric amount during the reactive hyperemic episode;    means, coupled to said sensor, for generating a calibration pressure pulse signal based upon a resultant change in the pressure signal during the periodic change of volume;    means for calculating a blood volume signal by correcting the sensed pressure signal with a ratio of the predetermined volumetric amount and said calibration pressure pulse signal.    
     
     
         20 . A calibrated system for characterizing blood flow during reactive hyperemia as claimed in  claim 19  including means for quickly releasing said suprasystolic pressure in said blood pressure cuff prior to establishing said predetermined, near diastolic, pressure in said cuff.