Effect of acute changes in aortic pressure on the coronary reserve.

STUDY OBJECTIVE: The aim was to evaluate the effect of acute changes in aortic pressure on the coronary reserve and hyperaemic response. DESIGN: Aortic pressure changes were induced either by intra-aortic balloon pumping or by the production of acute aortic regurgitation. A transient 20 s occlusion of the left anterior descending coronary artery was used as the hyperaemic stimulus. EXPERIMENTAL SUBJECTS: The experiments were performed on 19 open chest anaesthetised dogs, weight 13-32 kg. MEASUREMENTS AND MAIN RESULTS: During intra-aortic balloon pumping the mean diastolic aortic pressure increased by 24.7(SEM 2.9) mm Hg (p less than 0.001), while in aortic regurgitation it decreased by 47.7(11.1) mm Hg (p less than 0.01). At the peak hyperaemic response the driving coronary pressure was 121.4(2.8) mm Hg during intra-aortic balloon pumping and 59.8(11.5) mm Hg during aortic regurgitation. The peak hyperaemic flow increased by 12.0(3.8) ml.min-1 (p less than 0.01) during intra-aortic balloon pumping, compared to the values before pumping and decreased by 14.9(4.2) ml.min-1 (p less than 0.01) during aortic regurgitation, compared to the values before aortic regurgitation. The coronary reserve, expressed as the ratio of the hyperaemic to the resting flow, increased by 0.7(0.1) (p less than 0.001) during intra-aortic balloon pumping and decreased by 0.4(0.2) (p less than 0.05) during aortic regurgitation. A positive significant correlation coefficient was found at the peak hyperaemic response between the mean aortic pressure and the total forward effective coronary flow, and between the mean diastolic aortic pressure and the diastolic component of the coronary flow, during both intra-aortic balloon pumping and aortic regurgitation. CONCLUSIONS: The results suggest that coronary reserve increases during intra-aortic balloon pumping and decreases during aortic regurgitation; these changes could be attributed to the effect of the pressure changes on the hyperaemic flow.