Method and device for controlling the cuff pressure in measuring the blood pressure in a finger by means of photo-electric plethysmograph

An improved method for controlling cuff pressure in an indirect, non-invasive, continuous measurement of blood pressure in a finger by using a photo-electric plethysmograph providing a pulsatile plethysmographic signal and used with a fluid-filled pressure cuff, an electronic control circuit having an open and closed-control loop operation, an electric pressure valve connected to said cuff and a cuff pressure transducer providing a cuff pressure signal, the cuff pressure being controlled by the plethysmographic signal in closed-loop operation by means of a servo-reference level, so that the arterial volume is maintained at a preadjusted value, wherein the improvement includes the steps of:

• continuously changing, within a control range, for initial open loop adjustment, the cuff pressure or the servo-reference level by means of a control wave form provided to the electronic control circuit;
• periodically detecting each peak-trough differential amplitude of the pulsatile plethysmographic signal or cuff pressure signal;
• comparing each said peak-trough differential amplitude with the preceding peak-trough differential amplitude;
• and
• storing the associated value of peak-trough differential amplitude in the control range and the associated value of the cuff pressure or servo-reference level, and using said associated value of cuff pressure or servo-reference level at the end of the initial adjustment as the for set value measurement of the blood pressure after initial open-loop adjustment.