Effects of high oxygen on coronary flor and heart force

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Abstract
Studies in open-chest dogs were undertaken to assess the effects of abrupt changes in inspired O2 tensions on the relationship between isometric systolic tension (1ST) and coronary flow (CF). Changing the inspired O2 concentration from 25 to 100% resulted in consistent and equivalent reductions in 1ST and CF with alterations in CF preceding those of 1ST. These changes were not abolished by alpha, beta, or complete sympathetic blockade. Although the alterations in CF and BT were similar both in direction and magnitude, they were not related as to cause and effect. Experiments in which CF was maintained constant by pump perfusion showed that, when O2 tension was increased, 1ST decreased to the same degree as before. These data support the view that alterations in CF are not entirely dependent on myocardial O2 demands but that there is some intrinsic component of the coronary vessels sensitive to alterations in O2 tensions. The observed decreases in 1ST at high O2 tensions may be manifestations of early O2 toxicity.

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