[The effect of hypocapnia and hypercapnia on myocardial oxygen tension in hemorrhaged dogs].

To investigate the effect of carbon dioxide on the myocardial oxygenation during hemorrhagic shock, myocardial oxygen tension and coronary flow were measured during normocapnia, hypocapnia and hypercapnia. Eight adult mongrel dogs were anesthetized with pentobarbital, intubated and ventilated mechanically with 100% oxygen to maintain normocapnia. Then their chest was opened. An electromagnetic blood flow probe was applied on the left anterior descending artery. Two pairs of combined polarographic needle electrodes were carefully inserted, one pair in the epicardial layer, and the other in the endocardial layer of the heart. The animals were progressively bled in increments of 35-40ml.kg-1 (body weight). Hypocapnia was produced by increasing respiratory rate, and then normocapnia and hypercapnia were induced by adding the exogenous carbon dioxide. Hypocapnia decreased the coronary flow, and myocardial oxygen tension in outer and inner layer. On the contrary, hypercapnia increased them. It is possible that hypocapnia may compromise the oxygenation of the myocardium during hemorrhagic shock.