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The Effects of Hypoxemia on Cardiac Output: A Dose-Response Curve
Section snippets
Subjects
We studied 20 normal young men (aged 20 to 34 years). All subjects gave written, informed consent to the experimental protocol, which was approved by the Human Investigations Committee of the University of Kentucky College of Medicine. All subjects were nonsmokers.
Induction and Measurement of Hypoxemia
After a baseline period of at least ten minutes, during which the subjects breathed room air through a face mask, hypoxemia was induced by a modification of the partial rebreathing method of Severinghaus et al.16 We have developed a
Cardiac Output
The dose-response curve for the effect of hypoxemia on cardiac output measured with continuous wave Doppler echocardiography is shown in Figure 3 and Table 1. Cardiac output increases as SaO2 falls from 99 to 80 percent. Compared with room air, the mean increases in CO at 85 percent and 80 percent SaO2 were 13 percent and 20 percent, respectively. As expected, comparable increases also occurred in cardiac index (cardiac output/body surface area), with increasing hypoxemia (Table 1). Means of
DISCUSSION
The findings of this work are that cardiac output rises in a dose-dependent fashion with increasing hypoxemia in healthy men and that there is a significant increase in cardiac output compared to baseline with SaO2 of 85 percent and 80 percent. Further, this increase is due primarily to increased heart rate. There is minimal change in blood pressure, suggesting that systemic vascular resistance decreases. The time course of cardiovascular response to hypoxemia is brisk, with all but one subject
ACKNOWLEDGMENT
Claudine Moffet provided technical assistance. We are grateful to N. K. Burki, M.D., for his ideas and critical review and to John Reeves, M.D., for his encouragement.
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Supported by a grant from the American Lung Association of Kentucky.
Manuscript received Au~t 7; revision accepted September 29.