Biomedical subjects

H A Schwid

Publications and source records attributed to H A Schwid.

12 recordsLinked to original sources

PubMed1992

Educational computer simulation of malignant hyperthermia.

An educational graphic simulator was developed to provide an interactive learning environment to practice the diagnosis and treatment of malignant hyperthermia. The program incorporates a set of dynamically interacting models to present the physiologic changes associated with malignant hyperthermia and the simulated patient's response to management. Cardiovascular, respiratory, and temperature changes are presented through a graphic display of the operating room monitors. Mouse-driven input is used to manage the airway, control ventilation, manage cardiovascular and rhythm disturbances, and control fluids, electrolytes, and temperature. Medications, including dantrolene, antidysrhythmics, diuretics, and sodium bicarbonate, can be administered. Four simulated patients with different presentations of malignant hyperthermia are included to illustrate variations in the syndrome. Two of these patients are described in detail.

Adult↗

PubMed1992

Anesthesiologists' management of simulated critical incidents.

Human error is believed to contribute to the majority of negative anesthesia outcomes. Because retrospective analysis of critical incidents has several shortcomings and prospective studies are limited by the low frequency of critical incidents, an anesthesia simulator was used to evaluate the management of simulated emergency situations by ten anesthesia residents, ten faculty anesthesiologists, and ten anesthesiologists in private practice in order to identify specific patterns of errors in diagnosis and treatment. The simulator is a computer program that presents the patient, monitors, and management choices in a graphical display on an IBM or compatible personal computer. Many errors were observed in the management of these emergency situations, and even anesthesiologists with years of experience made serious errors. Although all experienced anesthesiologists correctly diagnosed simulated esophageal intubation, two residents misinterpreted the lack of end-tidal carbon dioxide. Only 40% of subjects correctly diagnosed simulated anaphylactic reaction; 27% adequately treated simulated myocardial ischemia; and 30% managed a simulated cardiac arrest according to Advanced Cardiac Life Support (ACLS) guidelines. Problems with continuous infusions of vasoactive agents were common. Fixation errors or failure to revise a plan in the presence of inconsistent cues were made by 63% of subjects. The subjects that gathered more information during simulated anaphylaxis made the correct diagnosis more often and made fewer treatment errors. The time since the last ACLS training was found to be an important predictor of correct management of simulated cardiac arrest.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaphylaxis↗

PubMed1991

An objective comparison of intrathecal lidocaine versus fentanyl for the treatment of lower extremity spasticity.

The reduction of spasticity after administration of intrathecal fentanyl, 35 micrograms, and intrathecal lidocaine, 50 mg, was compared with preinjection spasticity levels in ten subjects with central nervous system disease or injury. Spasticity was objectively assessed by an electronic instrument that simultaneously measures degrees of extension and force during passive knee extension. Duration of spasticity relief and adverse effects were recorded. Both drugs equally reduced spasticity and increased the range of motion. There were no supraspinal side effects from the fentanyl, whereas three subjects became hypotensive after receiving lidocaine. The reduction of spasticity with intrathecal fentanyl lasted at least 3 h. The authors postulate that fentanyl reduced spasticity by an effect on spinal pathways. Intrathecal fentanyl should be considered as an alternative to lidocaine for diagnostic blocks in patients with spasticity.

Adult↗

PubMed1991

The dynamic flexometer: an instrument for the objective evaluation of spasticity.

Anesthesiologists may care for patients who have spasticity in the operating room or pain clinic. A number of therapeutic modalities for treatment of spasticity exist, but there are few simple objective methods for evaluating their effect. We describe one instrument, the Dynamic Flexometer, that measures the force required to move the limb passively through its maximum range of motion. The data presented validate the instrument's reliability. Two clinical cases presented here demonstrate the instrument's utility. This device may be of value to anesthesiologists involved in the care of patients with spasticity.

Disability Evaluation↗

PubMed1990

Microcomputer-based data acquisition system for clinical research.

We have described a computerized data acquisition system for clinical investigation that can record over fifty physiologic variables from up to twenty-four electronic monitors. The information is acquired by a personal computer using RS-232C serial communications and analog-to-digital conversion. In its present configuration the system records information from a Spacelabs 500 series physiologic monitor, Hewlett-Packard physiologic monitor with the Careport computer interface, SARA mass spectrometer, Nellcor pulse oximeter, Neurotrac processed EEG, Lawrence cardiac output monitor, Hewlett-Packard capnometer, and Bourns spirometer. The software can be easily modified to accommodate other physiologic monitors. The system records parameter or waveform information and writes the data into a file that can be accessed by commercially available graphical and statistical packages. The data acquisition system is easy to use, transportable, and inexpensive.

Humans↗

PubMed1990

Computer simulation of the hemodynamic determinants of myocardial oxygen supply and demand.

A computer program was developed that uses a mathematical model of the cardiovascular system to predict myocardial oxygen supply and demand as well as cardiac hemodynamics. This model combines the time-varying elastance model of the left ventricle, the modified Windkessel model of the arterial system, and the left ventricular pressure-volume area prediction of myocardial oxygen demand. The computer simulation permits independent control of variables, thus providing the opportunity to design "experiments" and to observe the results. The model predicts that tachycardia leads to reduced myocardial oxygen supply and increased demand. Hypertension caused by increased systemic vascular resistance increases supply more than it increases demand. On the other hand, increased contractility or left ventricular end-diastolic pressure increases demand more than supply, and may cause ischemia in the presence of coronary artery stenosis. The model is an aid in understanding how hemodynamic variables affect the balance between myocardial oxygen supply and demand. It can be used for education and to analyze study protocols prior to animal experimentation.

Animals↗

PubMed1990

The Anesthesia Simulator-Recorder: a device to train and evaluate anesthesiologists' responses to critical incidents.

The Anesthesia Simulator-Recorder is a computer program that trains and evaluates anesthesiologists' management of critical incidents. The program executes on IBM compatible personal computers, combining a graphic display of the operating room with mouse-driven input and using an integrated set of physiological and pharmacological models to predict patient responses. The program records the simulated patient's vital signs and all management decisions, and produces a printed case summary. The Anesthesia Simulator-Recorder was evaluated by 44 resident and attending anesthesiologists at seven different anesthesia training centers. These anesthesiologists found the simulator easy to use with clear presentation of the case and management options. The physiological and pharmacological models produced clinically realistic predictions of patient behavior (mean score = 8.5, where 10 is highly realistic and 1 is unrealistic). The Anesthesia Simulator-Recorder was appraised as an excellent training device (mean score = 8.5, where 10 is outstanding and 1 is poor) because it provides the ability to repeatedly practice the management of critical incidents. The simulator was judged to be a good evaluation device (mean score = 6.6, where 10 is outstanding and 1 is poor). No significant differences were found in evaluations between the institution where the program was developed and other institutions, or between residents and attendings.

Anesthesiology↗

PubMed1988

Frequency response evaluation of radial artery catheter-manometer systems: sinusoidal frequency analysis versus flush method.

It is well recognized that catheter-manometer systems significantly distort direct radial artery pressure measurements. Sinusoidal frequency analysis and the flush method of assessing the degree of distortion caused by the monitoring system were compared to determine whether these two methods agree in the estimation of natural frequency and damping coefficient. The frequency response of 30 radial artery catheter-manometer systems used for intensive-care unit patients was measured by the flush method and sinusoidal frequency analysis. The monitoring system consisted of a 20-gauge cannula, 150-cm pressure tubing, two plastic stopcocks, a continuous infusion device with fast flush valve, an American Edwards dome, a Hewlett-Packard quartz transducer, and a Hewlett-Packard blood pressure amplifier. Sinusoidal frequency analysis demonstrated second-order underdamped response for all 30 catheter-manometer systems. No secondary resonance peaks were observed up to a frequency of 200 Hz. The measured frequency response demonstrated that the average catheter-manometer system in use in our intensive care unit would cause significant distortion of the radial artery pressure, with the mean natural frequency (fn) of 14.7 +/- 3.7 Hz and the mean damping coefficient (zeta) of 0.24 +/- 0.07. Although the 30 monitoring systems had identical configurations and visible bubbles were carefully removed, a wide range of frequency responses was found (fn = 10.2 to 25.3; zeta = 0.15 to 0.44).(ABSTRACT TRUNCATED AT 250 WORDS)

Arm↗

PubMed1988

Electrocardiogram simulation using a personal computer.

A personal computer with a digital-to-analog converter is used as an electrocardiogram simulator. A TurboPascal procedure, given the heart rate, rhythm, and ST segment levels, generates the voltages for Leads II and V5. A simple circuit reduces the voltages to the physiologic range and smoothes the waveforms, removing the staircase effects of digitalization. The procedure can be manually controlled using a software interface or driven by other programs for use in a full-scale operating room simulator.

Computer Simulation↗

PubMed1987

Computer model analysis of the radial artery pressure waveform.

Simultaneous measurements of aortic and radial artery pressures are reviewed, and a model of the cardiovascular system is presented. The model is based on resonant networks for the aorta and axillo-brachial-radial arterial system. The model chosen is a simple one, in order to make interpretation of the observed relationships clear. Despite its simplicity, the model produces realistic aortic and radial artery pressure waveforms. It demonstrates that the resonant properties of the arterial wall significantly alter the pressure waveform as it is propagated from the aorta to the radial artery. Although the mean and end-diastolic radial pressures are usually accurate estimates of the corresponding aortic pressures, the systolic pressure at the radial artery is often much higher than that of the aorta due to overshoot caused by the resonant behavior of the radial artery. The radial artery dicrotic notch is predominantly dependent on the axillo-brachial-radial arterial wall properties, rather than on the aortic valve or peripheral resistance. Hence the use of the radial artery dicrotic notch as an estimate of end systole is unreliable. The rate of systolic upstroke, dP/dt, of the radial artery waveform is a function of many factors, making it difficult to interpret. The radial artery waveform usually provides accurate estimates for mean and diastolic aortic pressures; for all other measurements it is an inadequate substitute for the aortic pressure waveform. In the presence of low forearm peripheral resistance the mean radial artery pressure may significantly underestimate the mean aortic pressure, as explained by a voltage divider model.

Blood Pressure↗

PubMed1987

A flight simulator for general anesthesia training.

A simulator of general anesthesia is described. It consists of an integrated set of physiologic computer models and a graphics display. The model predicts many of the physiologic and pharmacodynamic changes associated with general anesthesia. It is a multiple model consisting of circulatory, respiratory, pharmacokinetic, and pharmacodynamic models and their interactions. The model can account for many pathologic states of the cardiorespiratory system plus poor renal and hepatic function. Both intravenous and inhalation agents are included. Examples of its capabilities are presented, including pharmacokinetic changes associated with thiopental administration to a hypovolemic subject, administration of oxygen in several pulmonary pathologic conditions, and a simulation of an induction using fentanyl or thiopental. The model, combined with the graphics interface, becomes a real-time simulator useful for training students and residents.

Anesthesia, General↗

PubMedDate not supplied

Semiautomatic algorithm to remove resonance artifacts from the direct radial artery pressure.

Resonance artifacts introduced by the catheter-manometer system are removed from the direct radial artery pressure using a three-step algorithm. First, the fast-flush method is used to identify the natural frequency and damping coefficient of the monitoring system by digitizing and analyzing the pressure transient created by the flush. Second, resistor, capacitor, and inductor values are found for an RLC second-order model of the catheter-manometer system in use. Third, the algorithm predicts the undistorted radial artery pressure, removing the resonance artifacts by inverse-filtering the digitized monitored pressure waveform using the RLC circuit derived previously. The algorithm was implemented using a personal computer, but it could also be used without the computer by incorporating an analog-to-digital convertor and a microprocessor in the hemodynamic monitor.

Algorithms↗