The new sensor is designed for easy placement in epidural space and acts as a pneumatic flow switch. Air enters plenum at 40 cc/mm. Outside pressure against membrane will close off exhaust. The pressure which builds up within the plenum to overcome pressure against the membrane and re-establish air flow represents the ICP. The sensor is injection molded and disposable.
Computer modeling of physiological systems typically requires some knowledge of computer programming. The ultimate goal is to provide computer programs which allow the users to simply insert the necessary equations so they can devote their full attention to the models they are simulating. By using a language such as BASIC, which is easily learned, even the non expert can solve complex mathematical problems with relative ease. While some authors have stressed the uses of modeling for teaching purposes, this paper will emphasize the research aspect.
An intracranial pressure (ICP) monitoring system has been developed, consisting of an epidural sensor acting as a pneumatic flow switch connected by tubing to a pneumatic system and microprocessor-based monitoring unit. The frequency response to the system is 8 Hz at 10 mmHg measured peak to peak. ICP and arterial pressure data are collected and maintained in memory. The ICP in memory can be scrolled across a 2-hour or 24-mm graphic and digital video display. When memory is not being recalled, the previous 2 hours or 24 mm of data are displayed on the screen in graphic form. High and low ICP, low cerebral perfusion pressure, and abnormal pressure waves trigger alarms. Calibration of the system is maintained automatically by periodic rezeroing of all transducers to air. Changes in volume within the pneumatic system indicate a leak, and airflow ceases. The software management and alarm systems, as well as available memory, represent the latest in computerized technology.
During the typical 30s microgravity flight maneuvers of the NASA KC-135 aircraft, it is essential that pitch and power requirements are strictly adhered to in order to provide a laboratory space within an aircraft that is free of inertial accelerations. Thrust must precisely offset drag, which at first diminishes, then increases with passage through the apex of the parabola. During the maneuver, the pitch angle of the aircraft changes from approximately +45 deg to a -45 deg, causing a torque at every station except at the aircraft’s center of mass.
Auscultatory blood pressure measurement uses the presence and absence of acoustic pulses generated by an artery (i.e., Korotkoff sound), detected with a stethoscope or a sensitive microphone, to noninvasively estimate systolic and diastolic pressures. Unfortunately, in high noise situations, such as ambulatory environments or when the patient moves moderately, the current auscultatory blood pressure method is unreliable, if at all possible. Empirical evidence suggests that the pulse beneath an artery occlusion travels relatively slow compared with the speed of sound. By placing two microphones along the bicep muscle near the brachial artery under the occlusion cuff, a similar blood pressure pulse appears in the two microphones with a relative time delay. The acoustic noise, on the other hand, appears in both microphones simultaneously. The contribution of this paper is to utilize this phenomenon by filtering the microphone waveforms to create spatially narrowband information signals. With a narrowband signal, the microphone signal phasing information is adequate for distinguishing between acoustic noise and the blood pressure pulse. By choosing the microphone spacing correctly, subtraction of the two signals will enhance the information signal and cancel the noise signal. The general spacing problem is also presented.
A skin conductance monitoring system was developed and shown to reliably acquire and record hot flash events in both supervised laboratory and unsupervised ambulatory conditions. The 7.2 × 3.8 × 1.2 cm3 monitor consists of a disposable adhesive patch supporting two hydrogel electrodes and a reusable, miniaturized, enclosed electronic circuit board that snaps onto the electrodes. The monitor measures and records the skin conductance for seven days without external wires or telemetry and has an event marker that the subject can press whenever a hot flash is experienced. The accuracy of the system was demonstrated by comparing the number of hot flashes detected by algorithms developed during this research with the number identified by experts in hot flash studies. Three methods of detecting hot flash events were evaluated, but only two were fully developed. The two that were developed were an artificial neural network and a matched filter technique with multiple kernels implemented as a sliding form of the Pearson product-moment correlation coefficient. Both algorithms were trained on a ‘development’ cohort of 17 women and then validated using a second similar ‘validation’ cohort of 20. All subjects were between the ages of 40 and 60 and self-reported ten or more hot flashes per day over a three day period. The matched filter was the most accurate with a mean sensitivity of 0.92 and a mean specificity of 0.90 using the data from the development cohort and a mean sensitivity of 0.92 and a mean specificity of 0.87 using the data from the validation cohort. The matched filter was the method implemented in our processing software.
The photoplethysmographic signals acquired during pulse oximetry can be compromised in many ways. Intrapartum fetal pulse oximetry in particular presents challenges to signal processing. Period domain analysis can overcome the low pulsatile amplitudes, noise, and maternal modulation found in these signals. The efficiency of an incremental algorithm reduces the processing requirements for period domain analysis, facilitating use in low-power and portable devices.
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