Engineering topics

Fitzjerrell, D. G.

Publications and source records attributed to Fitzjerrell, D. G..

8 records

NASA NTRS1986

Oil-Free Compressor

Compressor pistons moved by eccentric shaft need no lubricants. Compressor has shaft, middle section is eccentric in relation to end sections. Driven by brushless dc motor, shaft turns inner races of set of four cam bearings. Outer cam-bearing races in turn actuate four pistons spaced equally apart, around and along shaft. Each outer bearing race held in position by pressure exerted on it by piston. Because no frictional motion between piston and outer bearing race, lubricant between them unnecessary. Cam bearings themselves contain potted internal lubricant. Originally proposed for use in space, new compressor for refrigerators or freezers does not depend on pool of oil for lubricating its pistons. Operated in any orientation.

Fitzjerrell, D. G.↗

NASA NTRS1978

Development of an hypothesis for simulating anti-orthostatic bed rest

The Guyton model, modified by the addition of leg compartments and the effect of the gravity vector, was used to evaluate hypotheses describing leg dehydration and fluid shifts. While the study is not complete, the basic approach was shown to be useful by identifying important mechanisms, identifying systems which need further experimental description and by assisting in the development of a general hypothesis.

Leonard, J. I.↗

NASA NTRS1975

User's instructions for the whole-body algorithms

The design of an algorithm that provides for the simulation of long and short term biological stresses is reported. The physiological responses of models representing circulatory, respiratory, cardiovascular, and thermoregulatory systems during space flight simulation are described.

Grounds, D. J.↗

NASA NTRS1975

Study report on interfacing major physiological subsystem models: An approach for developing a whole-body algorithm

Using a whole body algorithm simulation model, a wide variety and large number of stresses as well as different stress levels were simulated including environmental disturbances, metabolic changes, and special experimental situations. Simulation of short term stresses resulted in simultaneous and integrated responses from the cardiovascular, respiratory, and thermoregulatory subsystems and the accuracy of a large number of responding variables was verified. The capability of simulating significantly longer responses was demonstrated by validating a four week bed rest study. In this case, the long term subsystem model was found to reproduce many experimentally observed changes in circulatory dynamics, body fluid-electrolyte regulation, and renal function. The value of systems analysis and the selected design approach for developing a whole body algorithm was demonstrated.

Fitzjerrell, D. G.↗

NASA NTRS1974

Study report on guidelines and test procedures for investigating stability of nonlinear cardiovascular control system models

A general study of the stability of nonlinear as compared to linear control systems is presented. The analysis is general and, therefore, applies to other types of nonlinear biological control systems as well as the cardiovascular control system models. Both inherent and numerical stability are discussed for corresponding analytical and graphic methods and numerical methods.

Fitzjerrell, D. G.↗

NASA NTRS1974

Design specification for the whole-body algorithm

The necessary requirements and guidelines for the construction of a computer program of the whole-body algorithm are presented. The minimum subsystem models required to effectively simulate the total body response to stresses of interest are (1) cardiovascular (exercise/LBNP/tilt); (2) respiratory (Grodin's model); (3) thermoregulatory (Stolwijk's model); and (4) long-term circulatory fluid and electrolyte (Guyton's model). The whole-body algorithm must be capable of simulating response to stresses from CO2 inhalation, hypoxia, thermal environmental exercise (sitting and supine), LBNP, and tilt (changing body angles in gravity).

Fitzjerrell, D. G.↗

NASA NTRS1974

Cardiovascular model for the simulation of exercise, lower body negative pressure, and tilt experiments

A mathematical model and digital computer simulation of the human cardiovascular system and its controls have been developed to simulate pulsatile dynamic responses to the cardiovascular experiments of the Skylab missions and to selected physiological stresses of manned space flight. Specific model simulations of the bicycle ergometry, lower body negative pressure, and tilt experiments have been developed and verified for 1-g response by comparison with available experimental data. The zero-g simulations of two Skylab experiments are discussed.

Croston, R. C.↗

NASA NTRS1973

Fluid and Electrolyte Balance model (FEB)

The effects of various oral input water loads on solute and water distribution throughout the body are presented in the form of a model. The model was a three compartment model; the three compartments being plasma, interstitial fluid and cellular fluid. Sodium, potassium, chloride and urea were the only major solutes considered explicitly. The control of body water and electrolyte distribution was affected via drinking and hormone levels.

Fitzjerrell, D. G.↗