Masters Theses

Date of Award

12-1981

Degree Type

Thesis

Degree Name

Master of Science

Major Professor

Edward T. Howley

Committee Members

Michael H. Sims, Hugh G. Welch, B. Don Franks

Abstract

The purpose of this study was to investigate the relationship between hypoxia and plasma catecholamine concentrations during rest and very light exercise. Five males and one female served as subjects for the experimental testing protocol.

All subjects were exposed to five different gas mixtures while sitting at rest and while exercising at approximately 40% of their maximal oxygen uptake on a bicycle ergometer. The five inspired gas mixtures contained 21%, 19%, 17%, 15% and 13% oxygen. The duration of exposure to each mixture was 10 continuous minutes at rest, followed by 10 continuous minutes at exercise. In hopes of preventing an ordering effect the order of the experimental treatments was randomized. Measurements of oxygen uptake, heart rate, ventilation and withdrawal of blood samples were taken during the last two minutes of exposure to each inspired oxygen fraction, during rest and exercise.

There was no significant change in plasma epinephrine at rest (p > 0.2) or exercise (p > 0.2) . Plasma norepinephrine concentrations were not affected by variable inspired oxygen during either the resting test (p > 0.2) or the exercise test (p > 0.1) . During the exercise test, heart rate was significantly elevated with exposure to 13% and 15% oxygen (p < 0.001) and ventilation was greater at 13% oxygen than at the higher oxygen percents (p < 0.001) .

Although increases in heart rate have been associated with increased levels of circulating catecholamines, it was not possible to demonstrate such a relationship in this study. It is possible that norepinephrine, released from the sympathetic nerve endings at the SA node, stimulated an increased heart rate response. The failure to demonstrate elevated levels of catecholamines in the blood is perhaps indicative of the efficiency of the reuptake of norepinephrine back into the neuron that released it via an active transport mechanism.

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