Effects of oxygen on acute myocardial infarction: a thermographic study in the dog.

An acute myocardial infarction was created in a series of dogs by ligation of a branch from the left anterior descending coronary artery. The effects on the infarction with 100% oxygen were studied by thermography in 23 animals. The changes in the infarction size were registered on polaroid photographs. In 10 dogs the infarction showed a uniform cool area, permitting accurate measurement by cutting out and weighing the black, infarcted area from the photographs. During oxygen administration 2 dogs showed a considerable increase in the cool area and 6 other dogs a moderate but significant increase. The remaining 2 dogs in this group showed non-significant change in the infarcted area. In the other 13 animals the cool area was not sufficiently uniform to allow accurate measurement. However, all the dogs in this group, except one, presented a visable increase of the cool area of varying degree. High oxygen supply does not seem to have a favourable effect on an experimentally induced acute myocardial infarction. It is known to promote a lowering of the coronary artery perfusion pressure. In addition to this, it may somehow decrease the arterial supply from the vascular bed round the ischaemic area.