Diurnal variation of vascular diameter and reactivity in healthy young men

Abstract

The higher incidence of cardiovascular events in the morning is accompanied by an increased vascular tone. However, there are few published studies designed to evaluate the diurnal variation of vascular and endothelial parameters in healthy subjects. In the present investigation, we evaluated the diurnal variation in brachial artery diameter (BAD), flow-mediated dilation (FMD) and endothelium-independent dilation (NFMD) in a homogeneous sample of healthy non-smoker young men. Fifty subjects aged 20.8 ± 0.3 years (range: 18 to 25 years) were investigated by brachial artery ultrasound. Exclusion criteria were female gender and evidence of clinically significant health problems, including obesity. Volunteers were asked to rest and avoid fat meals as well as alcoholic beverages 48 h before and until completion of the evaluations. BAD, FMD and NFMD were measured at 7 am, 5 pm, and 10 pm and tested by repeated measures ANOVA. BAD was smaller at 7 am (mean ± SEM, 3.8 ± 0.1 mm) in comparison with 5 pm (3.9 ± 0.1) and 10 pm (4.0 ± 0.1 mm; P < 0.001). FMD values did not change significantly during the day, while NFMD increased more at 7 am (18.5 ± 1.1%), when compared to 15.5 ± 0.9% at 10 pm and 15.5 ± 0.9% at 5 pm (P = 0.04). The physiological state of vasoconstriction after awakening, with preserved capability to dilate in the morning, should be considered to be part of the healthy cardiovascular adaptation before considering later life risk factors and endothelial dysfunction.

The impact of early compared to late morning hours on brachial endothelial function and long-term cardiovascular events in healthy subjects with no apparent coronary heart disease

“…Our findings, which demonstrate that early morning postwaking hours blunted FMD, are in accord with previous reports [4][5][6][7], but discordant with Bau et al [9]. Furthermore, like Etsuda et al [6] we found no significant change in NTG in early compared with late morning hours.…”

“…However, Kawano et al [8] reported no differences in the conduit vessels of healthy subjects in the morning, compared with late afternoon hours. Bau et al [9], found no significant change in FMD during the day in 50 healthy young men, but reported that NTG was significantly higher in early morning compared with late evening hours.…”

“…Furthermore, like Etsuda et al [6] we found no significant change in NTG in early compared with late morning hours. Compared with previous reports, which evaluated only young males [4][5][6][7]9], our current study includes the largest number of relatively older healthy subjects, with a 36% female participation. In addition, although previous researchers found FMD to be lower in the morning compared with other times of the day, unlike our and some other appraisals [7,9], these studies [4][5][6] did not include measurements of NTG in parallel with those of FMD.…”

“…However, controversy still exists as to whether endothelial function decreases during early morning hours [4][5][6][7][8][9].…”

Effect of black tea consumption on brachial artery flow-mediated dilation and ischaemia–reperfusion in humans

“…Premenopausal women were scheduled in the first week of their cycle for both measurements. We performed all tests between 0800 h and 1600 h to control for variation in FMD between subjects (Bau et al 2008;Jones et al 2010Jones et al , 2012ter Avest et al 2005), and for each volunteer tests were performed at the same time of day to prevent interference of diurnal variation of FMD.…”