Effect of elevations of coronary artery partial pressure of carbon dioxide (Pco₂) on coronary blood flow

This study was designed to examine the effect of increases in the partial pressure of carbon dioxide (Pco₂) in coronary artery blood on coronary blood flow, coronary reactive hyperemia and the coronary response to intra-coronary adenosine administration. The left anterior descending coronary artery was cannulated and perfused over a wide range of perfusion pressure (P) and flow (F) with blood equilibrated with 0 to 40% carbon dioxide in 16 open chest dogs. Increases in coronary artery Pco₂ from 20 ± 2 to 93 ± 8 to 211 ± 22 mm Hg (mean ± SEM) increased the coronary flow from 28 ± 3 to 68 ± 16 to 87 ± 22 ml/min, respectively, at a perfusion pressure of 60 mm Hg and from 49 ± 6 to 139 ± 30 to 206 ± 48 ml/min, respectively, at a perfusion pressure of 100 mm Hg. Coronary reactive hyperemia following a 30 second coronary perfusion line occlusion and the response to an intracoronary bolus of adenosine (60 μg) were prominent at a low Pco₂ but absent at a high Pco₂. Beta-adrenergic blockade did not abolish the increase in coronary flow that occurred at increased Pco₂. Thus, progressive elevations of regional coronary Pco₂ produced substantial increases in coronary blood flow and maximal or near maximal coronary vasodilation.