The Navicon: a noninvasive monitor of instantaneous blood pressure using a compressible air-space servocontroller

The operation of the monitor is based on the method of Penaz (1973), in which the cross-section of a finger artery is clamped to a value corresponding to its unloaded size by enclosing the finger in an inflatable cuff which incorporates a photoelectric source/detector pair, and using the signal from the detector to drive a pressure servocontroller which is pneumatically connected to the inflatable cuff. Unlike other embodiments of this method, cuff pressure is controlled by an air-filled miniature bellows driven by a linear motor. Because of the lightweight construction of the voice-coil armature, the frequency response of this servocontroller is flat to above 100 Hz, and the closed-loop response of the entire servomechanism (including finger) far exceeds the 25 Hz bandwidth required for high-fidelity reproduction of the arterial pressure waveform. This, plus a new cuff design, ensures higher accuracy than previously reported.<
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