A frequency to voltage converter including input terminals for receiving a stream of pulses with either fixed or variable time intervals between pulses, means for producing a voltage that varies as an inverse function of the time interval between the pulses applied thereto, first means responsive to the pulses of the stream of pulses for sampling the voltage output of the voltage producing means, and second means responsive to the pulses of the stream of pulses for applying input pulses to the voltage producing means subsequent to the sampling of the voltage output thereof by the first means whereby each sample voltage output of the sampling means is proportional to a frequency corresponding to a time interval between sequentially applied pulses.

A portable pulse meter comprising a rigid body, a detector plate provided with a light source and a photoelectric element for detecting the light from said source as reflected by a blood stream in a blood vessel, and means for resiliently mounting said detector plate on said rigid body so that said detector plate is movable relative to said rigid body.

A cardiac monitor generates infrared light which is directed at the skin of an individual to be monitored. The light reflected from the skin is detected and automatically controlled. The pulsatile flow of blood in the underlying vascular network modulates the reflected light which is detected by a photo sensitive sensor which generates a signal indicative of the modulations. The modulated signal is coupled to a pulse detector which filters our spurious signals and generates one pulse for each systole in a cardiac cycle. The systolic pulse is coupled to a pulse interval to heartbeat rate converter which converts the interval between each succeeding systolic pulse into a signal which is preferably continuously and visually displayed to provide a continuous monitor of the heartbeat rate of the monitored individual.

The invention relates to a method and apparatus for continuously monitoring systolic blood pressure of a subject. The instrument includes a light transducer for detecting variations in light intensity corresponding to variations in blood volume of tissue of the subject under the transducer and for converting the changes in light intensity to changes in voltage. In one embodiment, a heater is provided to dilate the tissue under the transducer. The voltage signals are differentiated with respect to time, and the differentiated signal is sampled once every heart beat of the subject at the beginning of diastole, or at the maximum value of the differentiated signal sampled during diastole, to produce a sampled voltage signal. To this sampled voltage signal is added a voltage representative of a steady pressure, and the sum is a voltage representative of systolic pressure. The amplitude of the steady pressure is a function of blood pressure in the aorta and large arteries of the subject, stiffness of the aorta and large arteries, and the total peripheral resistance of the subject.

In a blood pressure measuring system in which a pressure signal comprised of both applied pressure and pulsatile pressure is detected and subsequently filtered to separate the pulsatile pressure component, circuitry is provided to minimize start-up transients in the separated signal. Such start-up transients, which normally persist for some time after start-up as a result of the AC time constants of the filters, are otherwise capable of generating erroneous measurements. The circuitry initializes the filters by clamping their outputs to predetermined voltage levels during a start-up interval and thereby avoids the generation of the transients.