The method of calibrating includes selecting discrete levels of cuff pressure and placing the artery or vein under study under discrete levels of induced pressure with a closed pneumatic system contained by the pressure cuff, substantially continually sensing cuff pressures at each discrete level and thereby sensing blood volume change through the artery, electronically determining when a certain number of representative time- based blood volume change signals are substantially equivalent, changing the volume in the closed pneumatic system at each discrete cuff pressure by a pre-determined volumetric amount after determining substantial equivalency, electronically generating a calibration signal at each discrete cuff pressure based upon the calibrated volume change and, correcting the blood volume representative signal based upon the calibration signal at each discrete level of pressure. The calibration device includes, in one embodiment, a controllable pneumatic pump, a pressure sensor, a computerized device for determining when a representative number of blood volume change signals (based on the pressure sensor signals) are substantially similar and thereafter generating a calibration signal. The calibration system also includes a device which changes the volume in the closed pneumatic system by a predetermined calibrated amount in the presence of the calibration trigger signal. This volume changing device may be a series of valves coupled by a chamber having a known volumetric size or a positive displacement pump driven by a stepper motor. The calibration system also includes a computerized device for correcting representative blood volume change signals based on the pressure signals at each discrete level of cuff pressure as corrected by the calibration signals represented by detected pressure signals obtained substantially simultaneously with the change of the volume at each discrete level of cuff pressure.
展开▼
