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  • Title: Effects of acute prolonged hypoxia on cardiovascular dynamics in dogs.
    Author: Borgia JF, Horvath SM.
    Journal: J Appl Physiol Respir Environ Exerc Physiol; 1977 Nov; 43(5):784-9. PubMed ID: 591470.
    Abstract:
    Intact anesthetized dogs were exposed for 75 min to either 5.75, 9.0, or 12.0% oxygen in nitrogen. Although pulmonary artery pressures were significantly elevated in all hypoxic exposures, systemic hypertension occurred only at the onset of severe hypoxia(5.75% O2). Coronary blood flow increased from an average of 130 during normoxia to a peak of 400 ml/100 g per min during inhalation of 5.75% O2, and coronary sinus oxygen tensions of 8 Torr and oxygen contents of 1.1 ml/100 ml were sustained for 75 min without biochemical, functional, or electrophysiological evidence of myocardial ischemia. Cardiac index (CI) increased significantly only during severe hypoxia (5.75% O2) with the greatest elevation after 30 min. Subsequently, CI decreased concomitantly with a 27% elevation in arterial hemoglobin concentration and oxygen-carrying capacity. It is concluded that the hypoxic threshold for significant elevations of cardiac output is between 6.0 and 9.0% O2.
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