An ultrasonic physical and care monitoring system has been developed for monitoring the physiological parameters of body movement, heart contraction, and respiration of patients on low-repulsion, anti-decubitus (anti-bedsore) hospital beds. These beds, of several designs, are intended to reduce pressure on the body surface of immobilized patients, in order to prevent decubitus ulcers, which are often fatal. Since low-repulsion mattresses lack conventional springs, padding and air space, this system employs a polyvinyl chloride tube under the mattress, which has a 40 kHz ultrasonic transmitter and receiver at its ends. The shape of the tube is altered by body, heart and respiratory movements, which modulate the complex diffusion of the ultrasonic energy in the tube. As a result, the amplitude of the received ultrasonic signal is movement-modulated. This received signal is then demodulated and low, high and band pass filtered, to yield the three separate patient movement parameters. These are recorded and can be real-time computer analyzed, to activate alarms if the patient has not moved, or not been moved by the staff, within programmable time limits. These data may also be employed to indicate relative patient medical condition. A major system advantage is that it does not require any body-attached sensors.
Keywords: Ultrasound, cardiac pulse, respiration, body movement, low-repulsion mattress, decubitus ulcer.