An Electrooptical Sensor for Cardiac Sound and Vibrations

An electrooptical sensor for long-term recording of the apex cardiogram in a clinical environment is reported here. The active elements of the sensor include three red light-emitting diodes (LED's) and eight phototransistors. These function by detecting the change in light reflection from the chest wall caused by the mechanical vibrations and motions of the heart. The advantages of this sensor over the existing microphone include wide bandwidth (3.1 Hz-9.0 kHz), small physical size, and ease of attachment to patients in all positions.