Abstract: Calibration apparatus and method for calibrating a movable pressure sensor include the use of a stop device to establish a reference position outside the sensing movement range of a first sensor. While in vitro, a reference pressure is established by applying pressure to the sensor to move it against the stop surface with a controllable pressure source. This reference pressure is stored. During use when the sensor is in an unknown position, such as when in vivo, the controllable pressure source applies pressure to move the sensor against the stop surface and the pressure required to do so is measured. The measured pressure is compared to the reference pressure to determine the unknown pressure and the system is then recalibrated. An optical system may be used as a second sensor to determine the position of the first sensor.

Abstract: A fiber-optic transducer apparatus, and a related method of manufacturing it, for particular use in medical applications such as invasive blood pressure and body temperature measurement. The apparatus includes a catheter comprised of a sheath and an enclosed first set of optical fibers for transmitting a light beam to and from the remote end of the catheter, where a transducer modulates it in accordance with the variable to be measured, e.g., blood pressure. A photosensor located at the near end of the catheter measures the modulated intensity of the returned beam, to produce a corresponding measurement signal. The catheter is further comprised of a second set of optical fibers located within the sheath, for transmitting a reference light beam to and from the remote end of the catheter. A second photosensor measures the intensity of the returned reference light beam, to produce a correction signal indicative of variations in transmittance caused by bending of the catheter.

Abstract: A source fiber receives light from a light source and conducts the light through a catheter to transmit the light to a reflective surface at the catheter end. The reflective surface has a predetermined range of movement and forms a reflected beam from the light transmitted by the source fiber. A reference fiber is located such that it is entirely within the reflected beam throughout the entire range of movement of the reflective surface and its output is substantially constant throughout that range of movement. The output of the reference fiber is used to adjust the light output of the light source. A signal fiber is located such that it is covered by the reflected beam to an extent which is dependent upon the position of the reflective surface in its range of movement. The light output of the signal fiber changes by a relatively large amount through the range of movement of the reflective surface and its output may be used to determine the position of the reflective surface.

Abstract: A method and apparatus for measuring the oxygen saturation level and hematocrit of human blood in real time. A catheter having a notch in its tip is inserted into a blood vessel and guided to a desired location in the body of a patient. Bursts of light at each of three wavelengths are transmitted through the blood in the notch. The intensities of the bursts of light after transmission are utilized along with a set of molecular exinction coefficients and optical scattering coefficients to calculate the oxygen level and hermatocrit. The light is provided by a set of LEDs in a housing connected to the catheter and the intensity of the transmitted light is measured by a photocell in the same housing. Optical fibers transmit the light through the catheter between the housing and the notch. Characterization resistors in the housing are encoded with characteristics such as the wavelengths of the LEDs and the width of the notch.

Abstract: A catheter assembly comprising a catheter having a lumen and characterized by a flexible distal extremity. The assembly further comprises a bolt having a threaded distal extremity for threading into an opening in the skull in sterile relation. The bolt includes an elongated chamber extending between its distal extremity and a threaded proximal extremity of the bolt. The catheter is disposed through the bolt chamber, and includes an opening from the lumen to the exterior of its flexible distal extremity. A clamp is threaded onto the catheter proximal extremity and is operative to forcibly engage the catheter and constrain it against movement relative to the bolt to thereby maintain a predetermined depth of insertion of the catheter into the skull.

Abstract: An output circuit for a digital physiological measuring instrument. The output circuit provides means for a digital signal indicative of a physiological parameter to operate on an excitation signal from a monitor to provide a response signal for driving the monitor to generate a visual display of that parameter. The excitation signal is scaled in a digital-to-analog converter, corrected for a zero offset of the digital signal, and then applied to the monitor. A dummy excitation signal is provided to enable the output circuit to drive a readout device having an analog input but not providing an excitation signal.

Abstract: A heartbeat rate measuring system for monitoring a patient's EKG signal and estimating heartbeat rate. The system includes an artifact detection apparatus for filtering the EKG signal to detect the occurrence of a heartbeat artifact, and for inhibiting the measuring heartbeat intervals whenever an artifact is detected. The system therefore estimates heartbeat rate based solely on measurements of time intervals between actual heartbeats.

Abstract: A continuity detection method and apparatus for use in a system for monitoring a patient's EKG signal and estimating heartbeat rate. The continuity detection apparatus continuously monitors continuity between two EKG electrodes contacting the patient and inhibits the system from its measuring of heartbeat intervals whenever poor continuity is detected. This eliminates the effects on the system of any undetected heartbeats or heartbeat artifacts of the type caused by poor continuity, and thereby improves the accuracy of the system's heartbeat rate estimate.

Abstract: A transducer system that provides accurate measurements of a physical variable such as pressure for any one of a number of different transducers. Each transducer includes special calibration indicators for identifying any inaccuracies in its output signal, and monitoring and correcting circuitry is selectively attachable to any one of the transducers, to read the calibration indicators and apropriately adjust the transducer's output signal, thereby correcting for the identified inaccuracies.

Abstract: A heart rate monitoring apparatus and related method for detecting the successive beats of a heart and providing a reliable estimate of heartbeat rate. The apparatus measures the time intervals between the successive beats and averages a prescribed number of the most recently occurring measurements. The particular measurement that differs most from the computed average is adjusted to be equal to that average, and the adjusted set of measurements is then averaged. These latter steps of adjusting and averaging are repeated a prescribed number of times, and the last-computed average is displayed as an estimate of heartbeat rate. The entire procedure is repeated upon the occurrence of each successive heartbeat.