THE PULMONARY VASCULAR RESPONSES TO SHORT-TERM HYPOXIA IN HUMAN SUBJECTS.
Joint research rept.,
EMORY UNIV ATLANTA GA
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The acute circulatory reactions to short periods of hypoxia were studied in 8 normal individuals and in 12 individuals with cardiopulmonary dysfunction. In the normal group, a rapid reduction in the arterial oxygen saturation to about 75 per cent caused a considerable increase in the pulmonary vascular resistance and in the cardiac output. The pulmonary capillary pressure was not altered. In the abnormal group, a similar reduction in the arterial oxygen saturation caused a much smaller increase in the pulmonary vascular resistance and little or no increase in the cardiac output. The pulmonary capillary pressure was not altered. A few exceptions to this were noted. In contrast with the normal group, the inhalation of the low oxygen mixture caused severe dyspnea. The most probable cause of the increase in the pulmonary arterial pressure during hypoxia is a direct effect of the low oxygen tension of the returning venous blood on the walls of the pulmonary arterioles. The increase in the cardiac output is a compensatory reaction, initiated by a fall in the peripheral vascular resistance, whereby oxygen transport to the tissues is maintained. In pulmonary disease these reactions may serve a useful purpose. In the presence of severe cardiopulmonary disease these reactions are impaired. Definite evidence of alterations of the pulmonary blood volume during hypoxia could be demonstrated in neither the normal nor the abnormal group. Author