Persistent myocardial ischemia following chronic hyperoxia in conscious dogs.

Following acute occlusion of the proximal left anterior descending (LAD) coronary artery, dogs were exposed continuously for 4 days in an environmental chamber to either 21% or 40% oxygen. Regional transmural myocardial blood flow was then determined by means of radioactive microspheres (8 to 10 microD) while each animal breathed room air (approximately equal to 21% oxygen). Blood flows in the anterolateral and apical regions of the left ventricle in normoxic animals (n = 5) averaged 0.95 +/- 0.03 and 0.69 +/- 0.13 ml/min X gm-1, respectively. In hyperoxic dogs (n = 5), blood flows in these regions were significantly lower, averaging 0.71 +/- 0.07 and 0.28 +/- 0.08 ml/min X gm-1, respectively in the anterolateral free wall, the greatest disparity in perfusion between experimental groups occurred in the subendocardial layers, and macroscopic evidence of necrosis was more widespread after hyperoxia.