Ageing attenuates regional vasoconstriction during acute lowering of upper and lower limbs.

The venoarteriolar and myogenic response (VMR) is a non-adrenergic, non-baroreflex-mediated mechanism that increases local vascular resistance and contributes to blood pressure (BP) regulation during orthostasis. Despite the importance of the VMR in human cardiovascular control, no information exists elucidating possible differences in the VMR with ageing and sex. We studied 26 healthy young adults [9 male; mean (SD) 28 (4) years old] and 18 healthy older adults [7 male; 71 (3) years old] during acute arm and leg dependency (i.e., limb lowering below heart level) to evoke the VMR. Brachial and femoral artery blood flows were assessed with duplex ultrasound. The VMR was estimated as the percentage reduction in vascular conductance (blood flow/mean arterial BP; in millilitres per minute per millimetre of mercury) from baseline during 5 min of limb dependency. Arm VMR was attenuated in the older versus young adults [-8.7 (1.9)% vs. -26.6 (2.4)%, p < 0.001]. Likewise, leg VMR was also attenuated in the older versus young adults [-14.4 (0.8)% vs. -29.1 (2.2)%, p < 0.001]. Despite these age-related differences, there were no sex differences for leg (p = 0.096) or arm VMR (p = 0.825). These data suggest that ageing attenuates the VMR in both the upper and lower limbs, but sex does not impact these responses. This phenomenon might contribute to altered BP regulation in older adults, either protecting against excessive orthostatic BP elevations or contributing to orthostatic hypotension. Future research is needed to determine the mechanisms of an attenuated VMR with ageing and whether these findings extend to populations with hypertension and cardiovascular/metabolic disease.