Coronary circulatory effects of increased intrathoracic pressure in intact dogs

The effect of increased intrathoracic pressure on coronary hemodynamics and coronary venous oxygen tension was evaluated in surgically instrumented dogs. Following abrupt increase in intrathoracic pressure, as systolic pressure decrease, the tension time index (TTI) fell 83 percent (P less than 0.001) compared to control. The diastolic pressure time index (DPTI) decline proportionately less, effecting an increase in the ratio of DPTI/TTI from 1.19 +/- 0.08 to 1.78 +/- 0.16 (P LESS THAN 0.05). The mean circumflex coronary blood flow declined only minimally toward the end of the test (5.1 +/- 9.0 ml/min; P less than 0.05), and stroke systolic circumflex coronary blood flow increased 116 percent (P less than 0.01) as late diastolic coronary resistance decreased 31 percent (P less than 0.01). The mean coronary venous oxygen pressure increased transiently above control values from 21 +/- 1 to 24 +/- 2 mm Hg (P less than 0.05). These data suggest that in anesthetized dogs, brief periods of high intrathoracic pressure abruptly reduce determinants of myocardial demand for oxygen, while myocardial perfusion decreases to a lesser degree.