Circadian variation in coronary flow velocity reserve and its relation to α1-sympathetic activity in humans

The circadian change in coronary microvascular function has not been directly assessed in human beings. Recent advances in transthoracic Doppler echocardiography (TTDE) provide noninvasive, physiological assessment of coronary flow velocity reserve (CFVR).

This study consisted of 20 young healthy subjects (24 ± 2 years, 20 men) who underwent CFVR examinations at 3 different times; early morning (6AM), late morning (11AM) and late evening (10PM). The flow velocity in the distal portion of the left anterior descending coronary artery was measured with TTDE at baseline and during adenosine infusion to calculate CFVR. These examinations were repeated with the intake of α1-blocker (prazosin 1mg) on the other day.

CFVR showed a circadian variation with an increase from the early morning to the late morning, following a decrease to the late evening thereafter (4.4 ± 0.9 at 6AM; 5.2 ± 1.3 at 11AM; 4.2 ± 1.1 at 10PM, p<0.001). In the study with α1-blocker, CFVR was comparable between the early morning and the late morning, whereas CFVR in the late evening was lower than those in other 2 time points (5.0 ± 1.1 at 6AM; 4.9 ± 0.9 at 11AM; 4.3 ± 0.9 at 10PM, p<0.001).

This study demonstrates that CFVR has a circadian variation in humans, with an increase from the late evening to the late morning. Adding α1-blocker ameliorated CFVR only in the early morning, indicating that α1-sympathetic activity plays a heterogeneous and important role in the circadian change of CFVR in humans.