Effects of arterial hypoxia on the heart and circulation: an integrative study

An integrative series of investigations progressed from simplified systems, where cause-and-effect relations were relatively clear, to the virtually intact animal with separately perfused carotid arteries. Arterial pO2 below 40 mm Hg (about 75% oxygen saturation) caused edema of the heart muscle; however, the contractile strength and performance of isolated hearts were compromised severely only when the arterial pO2 had fallen below 15 mm Hg (about 25% saturation). The ‘acute circulatory crisis" which is known to occur when the arterial oxygen saturation falls below 80% was not caused by weakness of the heart muscle but by reflexes from the carotid artery territory: even when the oxygen saturation of systemic arterial blood had fallen as low as 50% this did not cause heart failure as long as the carotids were perfused with blood of normal pO2. Severe heart failure occurred when the blood in the carotid arteries was moderately hypoxic (pO2 below 50, sat. below 80%) while the rest of the circulation was ful...