STUDY OBJECTIVE: The aim was to characterise reactive hyperaemia and endothelium dependent (ADP) and independent (adenosine) vasodilatation after ischaemic periods of increasing duration, and in the stunned myocardium. DESIGN: The left anterior descending coronary artery was occluded 5-7 cm distal from its origin for consecutive periods of 2, 2, 5, 10, and 2 min separated by 30 min of reperfusion. Coronary flow was continuously measured by Doppler flowmetry proximal to the occlusion site. ADP and adenosine were infused into the left coronary artery proximal to the flowprobe. EXPERIMENTAL MATERIAL: 11 domestic pigs, weight 25-36 kg, were used. MEASUREMENTS AND MAIN RESULTS: In the stunned myocardium maximal reactive hyperaemia after 2 min of ischaemia was preserved, whereas all other variables describing reactive hyperaemia were diminished: time to maximal hyperaemia by 40% (p less than 0.01), duration of hyperaemia by 44% (p less than 0.001), volume of hyperaemia by 53% (p less than 0.001), and repayment of flow debt by 43% (p less than 0.001). The vasodilating effects of ADP and adenosine (dose-response curves) were not altered after development of stunning. CONCLUSIONS: Preserved maximal hyperaemia and vasodilation during ADP and adenosine infusion, but reduced volume of hyperaemia, indicate normal coronary reactivity but diminished release in the stunned myocardium of the vasodilator(s) responsible for the prolonged postischaemic flow increase.
STUDY OBJECTIVE: The aim was to characterise reactive hyperaemia and endothelium dependent (ADP) and independent (adenosine) vasodilatation after ischaemic periods of increasing duration, and in the stunned myocardium. DESIGN: The left anterior descending coronary artery was occluded 5-7 cm distal from its origin for consecutive periods of 2, 2, 5, 10, and 2 min separated by 30 min of reperfusion. Coronary flow was continuously measured by Doppler flowmetry proximal to the occlusion site. ADP and adenosine were infused into the left coronary artery proximal to the flowprobe. EXPERIMENTAL MATERIAL: 11 domestic pigs, weight 25-36 kg, were used. MEASUREMENTS AND MAIN RESULTS: In the stunned myocardium maximal reactive hyperaemia after 2 min of ischaemia was preserved, whereas all other variables describing reactive hyperaemia were diminished: time to maximal hyperaemia by 40% (p less than 0.01), duration of hyperaemia by 44% (p less than 0.001), volume of hyperaemia by 53% (p less than 0.001), and repayment of flow debt by 43% (p less than 0.001). The vasodilating effects of ADP and adenosine (dose-response curves) were not altered after development of stunning. CONCLUSIONS: Preserved maximal hyperaemia and vasodilation during ADP and adenosine infusion, but reduced volume of hyperaemia, indicate normal coronary reactivity but diminished release in the stunned myocardium of the vasodilator(s) responsible for the prolonged postischaemic flow increase.