Abstract: A fat depth measuring apparatus and method for use in measuring in an animal the depth of a fat layer between hide and muscle. An ultrasonic generator generates ultrasonic pulses and an ultrasonic echo detector generates echo signals indicative of ultrasonic pulses received by the detector after reflection from boundaries or discontinuities within the tissues of the animal. Variable gain amplifier amplifies the echo signals and produces detector signals. Gain control means varies the gain of the amplifier to increase the probability of having exactly two detector signals identifiable as arising from echoes from a hide/fat boundary and a fat/muscle boundary. A fat depth determining means receives the detector signals and if they exceed primary threshold levels identifies the two required detector signals so as to thereby enable determination of the depth of the fat layer. If more than three detector signals have levels exceeding 60% of the threshold level, the depth determination is considered invalid.

Abstract: A heart pacer in which the magnitude of the end-of-life test current source is programmable. This effectively allows the physician to program the condition which will control a switch-over to end-of-life operation. It also allows the physician to override end-of-life operation after it initially takes place following a failing of the end-of-life test. The pacer also includes an additional end-of-life test involving the continuous monitoring of the supply potential and a switch-over to end-of-life operation should the pacer powering potential momentarily fall below a threshold level.

Abstract: A dual-chamber heart pacer whose ventricular pacing rate is closely matched to the physiological requirements of the patient. A "true" atrial rate is determined by counting over a 3-second interval the number of sensed atrial beats, including those which occur during atrial refractory periods. When the atrial rate rises to a threshold level, the ventricular pacing rate decreases gradually from the Wenckebach rate to a fall-back rate independent of atrial sensing. During this decline, atrial pacing pulses may be generated simultaneously with ventricular pacing pulses in an effort to terminate tachycardia. The controlled decline in ventricular pacing rate begins after a 3:2 block has resulted, but before a 2:1 block would otherwise result. The fall-back rate is higher than the standby rate to compensate for the lack of atrial pacing when the system operates at the fall-back rate.