Augmented venoarteriolar response with ageing is associated with morning blood pressure surge.

The venoarteriolar response (VAR) is a non-adrenergic, non-baroreflex-mediated mechanism of vasoconstriction, which has been proposed to contribute ∼45% of the increase in total peripheral resistance during orthostasis. Despite its importance in human cardiovascular control during orthostatic stress, there is no information available regarding the impact of age and sex on the VAR or its role in diurnal blood pressure (BP) variation. We studied 33 (15 women) young (mean ± SD; 28 ± 4 years old) and 26 (12 women) older (71 ± 3 years old) healthy individuals. Brachial and femoral blood flow were measured using Doppler ultrasound. The percentage reduction in vascular conductance (blood flow/mean BP) during 4 min of limb dependency (35-40 cm below the heart level) was used to assess the VAR. The morning surge in BP was assessed using 24 h ambulatory BP monitoring. Peak VAR in the lower limb, but not in the upper limb, was significantly higher in the older than the younger adults (33 ± 4 versus 26 ± 6%, older versus young; P < 0.05). There was no sex difference in the VAR in either the young or the older group. A greater leg VAR was related to a greater morning surge in BP in older adults (r = -0.4, P = 0.02) but not in the young adults (r = -0.26, P = 0.1). Thus, advancing age enhances the VAR in the lower limb and is associated with the morning blood pressure surge in older adults. Sex does not affect this local axonal reflex in healthy humans.