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Biomedical subjects

T W Moore

Publications and source records attributed to T W Moore.

At least 19 recordsLinked to original sources
PubMed1993

A mathematical model of G time-tolerance.

We propose a model to explain experimentally observed effects of Gz onset rates and levels on the time of occurrence of loss of vision and/or consciousness. The model is based on the existence of two generally accepted parameters: a G limit beyond which cerebral perfusion ceases, and a buffer time between loss of perfusion and loss of function. When applied to ramp onset G profiles, the model predicts a generally hyperbolic locus of endpoints, similar to the well-known Stoll curve, except for the dip. The advantage of the model is its applicability to any G onset profile. Data from the literature support the assumptions of the model and its results, including the absence of the dip in the locus for a ramp onset. The results call into question some concepts used to design G avoidance inflight strategies and the usefulness of some experimental centrifuge methods. The model may enable an increase in the accuracy of predictions of the time of visual or cerebral loss of function under various G profiles.

Adaptation, Physiological↗
PubMed1992

Optimal controller for intraaortic balloon pumping.

An optimal control algorithm was adapted to identify and track the optimal deflation time of the intraaortic balloon pump (IABP). Routines for handling physiologically imposed constraints were added to the algorithm which was implemented in a computer-controlled system. The system was designed to provide real time optimization for the clinical setting. The controller continuously maximizes a performance index while observing the constraints. The index is composed of clinically available hemodynamic variables which indicate changes in myocardial energy balance. Proper values for the algorithm parameters were determined and the system was tested in animal experiments. The results indicate that controlling deflation time relative to the R wave, which precedes the next ejection phase, reduces the time required for optimization when the heart rate varies.

Algorithms↗
PubMed1991

Optimal control system for the intra-aortic balloon pump.

An optimal control system for the intra-aortic balloon pump (IABP) is presented. Control of the IABP is based on a performance index formulated to reflect a tradeoff between maximising cardiac oxygen supply and minimising cardiac oxygen consumption. In the performance index, mean diastolic pressure (MDP) was used to represent oxygen availability and peak systolic pressure (PSP) was used to represent oxygen consumption. An algorithm, implemented using an 8-bit microcomputer, changes the deflation time of the IABP to maximise this performance index by using an optimisation technique that employs both a search and an approximation. The search produces three equally spaced points which define a region that includes the maximum of the performance index. From these points, the optimum deflation time is estimated by a quadratic approximation. The algorithm has been successfully tested using performance index curves generated by computer simulations.

Algorithms↗
PubMed1990

Computer simulation of the mechanically-assisted failing canine circulation.

A model of the cardiovascular system is presented. The model includes representations of the left and right ventricles, a nonlinear multielement model of the aorta and its main branches, and lumped models of the systemic veins and the pulmonary circulation. A simulation of the intra-aortic balloon pump and representations of physiological compensatory mechanisms are also incorporated in the model. Parameters of the left ventricular model were set to simulate either the normal or failing canine circulation. Pressure and flow waveforms throughout the circulation as well as ventricular pressure and volume were calculated for the normal, failing, and assisted failing circulation. Cardiac oxygen supply and consumption were calculated from the model. They were used as direct indices of cardiac energy supply and utilization to assess the effects of cardiac assistance.

Animals↗
PubMed1990

Cardiac energy considerations during intraaortic balloon pumping.

Cardiac oxygen availability and oxygen consumption were used in a theoretical study as indexes of myocardial energy supply and utilization, respectively. A detailed computer simulation of the closed-loop canine cardiovascular system was utilized to study the dependence of these indexes on timing of the intraaortic balloon pump. Oxygen availability exhibited higher sensitivity to balloon timing than oxygen utilization. While maximum augmentation of oxygen availability was 58 percent, oxygen consumption could be reduced by only 13 percent. Animal experiments were initiated to validate the theoretical results. The results of both the animal experiments and the computer simulation suggested that neither balloon timing which maximizes oxygen availability nor timing which minimizes oxygen consumption correlates with timing which minimizes aortic end diastolic pressure. Thus, end diastolic pressure, presently used as a determinant of proper timing in patients undergoing cardiac assistance, was found to be a poor index of ventricular energy consumption. A performance index comprised of clinically available variables, was formulated to reflect myocardial energy balance. In this performance index, mean diastolic pressure was used to represent energy availability and peak systolic pressure was used as an index of oxygen consumption. Their relationship to oxygen balance and their dependence on timing were studied using the computer simulation of the canine cardiovascular system and animal experiments. Theoretical and experimental results suggest that such an index is capable of representing O2 balance and can be used to control phasing of the device.

Animals↗
PubMed1987

An experimental microcomputer controlled system for synchronized pulsating anti-gravity suit.

An experimental system to deliver synchronized external pressure pulsations to the lower body is described in this technical note. The system is designed using a microcomputer with a real time interface and an electro-pneumatic subsystem capable of delivering pressure pulses to a modified anti-G suit at a fast rate. It is versatile, containing many options for synchronizing, phasing and sequencing of the pressure pulsations and controlling the pressure level in the suit bladders. Details of its software and hardware are described along with the results of initial testing in a Dynamic Flight Simulator on human volunteers.

Computers↗
PubMed1985

Control of intraaortic balloon pumping: theory and guidelines for clinical applications.

The effectiveness of intraaortic balloon pumping was investigated by using a lumped parameter model of the cardiovascular/assist device system. The model consists of a time-varying elastance left ventricular simulation, a 2-element windkessel arterial simulation, and an RC venous return and pulmonary simulation. The four major hemodynamic variables, stroke volume (SV), aortic mean diastolic pressure (MDP), tension time index (TTI), and aortic end diastolic pressure (EDP), were divided into two categories related to system energy supply and demand: "external" and "internal" variables. The effects of balloon pumping on these variables can be described by closed-form equations that yield an optimal solution. The model prediction suggests that, in the ideal case, optimization of balloon pumping calls for instantaneous inflation of the balloon to maximum volume at end systole and instantaneous complete deflation at end diastole. For finite inflation/deflation rates, the optimal time for the start of inflation is end systole. Deflation timing, however, involves a tradeoff between maximizing the external variables and minimizing the internal variables. These predictions were tested using a nonlinear digital computer model. The results also suggest that when SV is not being monitored, optimal inflation timing can be controlled from the measurements of TTI or pulmonary venous pressure; optimal deflation timing can be controlled by a weighted combination of MDP and EDP.

Assisted Circulation↗
PubMed1984

Appointment compliance behavior of community mental health patients: a discriminant analysis.

This study evaluated various demographic and psychiatric signs and symptoms of community mental health clients in an attempt to identify those variables which influence appointment compliance behavior. A sample of 172 non-psychotic clients with a primary diagnosis of neurosis, personality disorder, or transient-situational disturbance were studied utilizing discriminant analysis. The results indicate that approximately 85 percent of the clients were properly classified as either compliant or non-compliant in their appointment behavior. The implications for mental health care are discussed.

Adult↗
PubMed1984

A cardiovascular model for studying impairment of cerebral function during +Gz stress.

A digital computer model of the human cardiovascular system has been developed which can be used for studying impairment of cerebral function during +Gz stress. The model includes simulation of the arterial and venous systems, the heart, baroreceptor control of heart rate, control of venous tone, and the effect of gravity. Model predictions suggest that, for unprotected subjects, carotid pressure at eye level decreases to 50 mm Hg (beginning of peripheral light loss) at approximately 2.7 Gz. The pressure decreases to 20 mm Hg (beginning of central light loss) at approximately 3.6 Gz. An anti-G suit provides an extra 1.1 to 1.5 Gz protection. Even though blood pressure supplying retinal vessels drops significantly at the above G levels, cerebral blood flow is maintained due to protective and compensatory mechanisms. These observations compare favorably with results reported in the literature. The results suggest that this model can be used to improve our understanding of the cardiovascular system's response to +Gz stress.

Aerospace Medicine↗
PubMed1983

Systematic error associated with apparatus 2 of the USP dissolution test III: limitations of calibrators and the USP suitability test.

The calibrator tablets now used in the USP suitability test do not reveal common sources of systematic error associated with Apparatus 2. When the apparatus was operated under conditions near or beyond USP tolerances, changes in the results of the USP calibrators were slight, whereas those of several samples of commercial prednisone tablets were significant. Thus, the USP calibrators and requirements do not guarantee suitability of the equipment for general dissolution testing of drug products.

Chemistry, Pharmaceutical↗