PubMed Health⌕ Search

Biomedical subjects

J W Frazier

Publications and source records attributed to J W Frazier.

5 recordsLinked to original sources
PubMed1985

An application of optimization methods to evaluate conditioning intervals.

A decision rule is obtained to determine when exercise is beneficial. The term beneficial used in this context refers to the extension of lifetime based on studies of cardiovascular conditioning. Models are used to characterize changes in heart rate with intense exercise. In addition, it is necessary to consider a model involving a heartbeat bank to help determine the conditioning interval. Optimization procedures are used to develop the decision rule, to examine the assumptions in the problem, and to point out when a unique solution exists. This procedure is applied to empirical data for one individual (inter-subject study) and a unique conditioning interval is obtained.

Animals↗
PubMed1985

Hemodynamic effects of anti-G suit inflation in a 1-G environment.

This study evaluated effects of various anti-G inflation pressures on cardiac volumes and the relationship of these volume changes to mean arterial pressure changes. Ventricular volumes were calculated using two-dimensional echocardiography. An anti-G suit was inflated to 2, 4, and 6 psi in the standing and supine positions for 10 male subjects. In the supine position, mean arterial pressure increased from base line for all three inflation pressures (P = 0.05). The end-diastolic volume increased after 2-psi inflation (P = 0.03). Cardiac output or stroke volume did not change. After standing, mean arterial pressure (P = 0.002), end-diastolic volume (P = 0.002), and stroke volume (P = 0.05) fell after suit deflation. Peripheral vascular resistance fell in the 2- and 4-psi inflation profiles. In the standing protocol, mean arterial pressure, end-diastolic volume, stroke volume, and cardiac output rose with all three inflation pressures (P less than 0.05). After reclining, heart rate increased (P = 0.02) and mean arterial pressure fell (P less than 0.05) in the 4- and 6-psi inflation profiles after suit deflation. Increases in mean arterial pressure are caused by increases in cardiac preload and cardiac output after inflation of the anti-G suit while subjects were standing. Increased cardiac preload was not consistently seen after inflation while subjects were supine. Changes in end-diastolic volume and mean arterial pressure were dependent on the pressure used to inflate the anti-G suit.

Adult↗
PubMed1982

Human tracking performance changes during combined +Gz and +/- Gy stress.

An experiment has been conducted on the centrifuge to examine roll-axis tracking performance in both static and stress environments. The stress environments were +5 Gz from 95 s and combined +5 Gz/+/- 1 or +/- 2 Gy for 95 s. Compared to the static condition, performance decrements of 19% were measured at +5 Gz, 45% at combined +5 Gz/+/- 1 Gy, and 70% at combined +5 Gz/+/-2 Gy. Heart rate increases were noted during the stress environments but no significant heart rate differences were noted between the +5 Gz and the combined +5 Gz/+/-2 Gy conditions. The conventional lap belt and shoulder harness restraint system, while not optimum, was adequate for these G environments.

Acceleration↗