Background: Arterial stiffness is at least partially controlled by vascular tone. Vascular tone and underlying physiological processes, e.g. sympathetic activity, have been shown to follow diurnal variations.
Methods: This study investigated whether arterial stiffness and perfusion of subendocardial myocardium relative to cardiac workload show diurnal variations under physiological conditions. The aortic augmentation index (AIx) and subendocardial viability ratio (SEVR) were measured noninvasively in 26 healthy young men (27.6 +/- 3.4 years) using applanation tonometry at three different times (8:00, 12:00, 17:00) during one day.
Results: Mean AIx was significantly higher and mean SEVR significantly lower at 8:00 than at the later times. No significant differences were found between mean AIx and mean SEVR at 12:00 and at 17:00.
Conclusions: The observed diurnal variations of AIx and SEVR will be of value when applanation tonometry is used in human research. In order to arrive at comparable data in longitudinal investigations, measurements should be made at similar times during the course of a day. In addition, our observation should assist in studies in which novel pharmacological compounds with activity on the vasculature are investigated.