Background: The effects of hypercapnia on coronary arteries in human beings are not known. We used transthoracic Doppler echocardiography to evaluate coronary blood flow velocity (CFV) changes in response to hypercapnia in healthy adults.
Methods: Twenty adults underwent transthoracic Doppler echocardiography of the left anterior descending coronary artery while breathing room air, 40% fraction of inspired oxygen, and 40% fraction of inspired oxygen with carbon dioxide supplemented to end-tidal tensions of +5, +7.5, and +10 mm Hg above baseline.
Results: Mean (SD) diastolic peak CFV values for these conditions were 23.1 (9.1), 23.0 (9.0), 25.5 (9.3), 27.9 (11.5), and 31.5 (13.0) cm/s, respectively. Significant overall differences between conditions (P < .001) and progressive levels of hypercapnia (P < or = .01) were observed. CFV increases remained significant after adjusting for increases in cardiac output (P = .038).
Conclusions: CFV increases with hypercapnia. This is the first report of human coronary artery flow responses to hypercapnia. Transthoracic Doppler echocardiography methodology is feasible for measuring CFV and the effects of hypercapnia on the coronary circulation.