Age‐associated impairments in contraction‐induced rapid‐onset vasodilatation within the forearm are independent of mechanical factors

Abstract

Contraction-induced rapid-onset vasodilatation (ROV) is modulated by perfusion and transmural pressure in young adults; however, this effect remains unknown in older adults. The present study examined the mechanical contribution to ROV in young versus older adults, the influence of perfusion pressure and whether these responses are associated with arterial stiffness. Forearm vascular conductance (in millilitres per minute per 100 mmHg) was measured in 12 healthy young (24 ± 4 years old) and 12 older (67 ± 3 years old) adults during: (i) single dynamic contractions at 20% of maximal voluntary contraction; and (ii) single external mechanical compression of the forearm (200 mmHg) positioned above, at and below heart level. Carotid-radial pulse-wave velocity characterized upper limb arterial stiffness. Total ROV responses to single muscle contractions and single external mechanical compressions were attenuated in older adults at heart level (P < 0.05); however, the relative mechanical contribution to contraction-induced peak (46 ± 14 versus 40 ± 18%; P = 0.21) and total (37 ± 21 versus 32 ± 18%; P = 0.27) responses were not different between young and older adults. Reducing or enhancing perfusion pressure altered ROV responses to a similar extent between young and older adults (P < 0.05). Upper limb arterial stiffness was not associated with peak (r = 0.02; P = 0.93) or total vascular conductance (r = -0.01; P = 0.96) in the group as a whole. Our data suggest that: (i) age-associated attenuations in ROV are not attributable to a mechanical component; (ii) enhancing perfusion pressure augments ROV to a similar extent between young and older adults; and (iii) basal upper limb arterial stiffness is not associated with the vasodilator responses after a single skeletal muscle contraction in young and older adults.

The role of vascular function on exercise capacity in health and disease

“…2013; Hughes et al . 2016, 2018; Sinkler et al . 2016; Sinkler & Segal, 2017) are then supplemented by a spectrum of vasodilators providing a fine‐tuning of ‐to‐ matching.…”

“…This is important as old age slows the dilatation of conduit arteries (Hughes et al . 2016, 2018), feed arteries (Park et al . 2016) and resistance arterioles (Behnke & Delp, 2010), as well as disrupts the coordination of up‐ and down‐stream resistance vessel vasomotor responses by attenuating ascending vasodilatation via blunted hyperpolarization conduction (Sinkler et al .…”

“…Collectively, these investigations emphasized the importance of the muscle pumping action on perfusion and also raised awareness that rapid vasodilatory mechanisms including hyperpolarization and the effects of mechanical compression (Naik et al 1999;Clifford & Hellsten, 2004;Clifford et al 2006;Clifford & Tschakovsky, 2008) may provide an effective increase ofQ O 2 in parallel with muscle contraction(s). These almost instantaneous (typically less than 1 s) dilatory mechanisms (Clifford & Hellsten, 2004;Wray et al 2005;Clifford et al 2006;Clifford & Tschakovsky, 2008;Behnke & Delp, 2010;McDaniel et al 2010;Casey & Joyner, 2011;Casey et al 2013;Hughes et al 2016Hughes et al , 2018Sinkler et al 2016;Sinkler & Segal, 2017) are then supplemented by a spectrum of vasodilators providing a fine-tuning ofQ O 2 -to-V O 2 matching. That such fine-tuning occurs is supported by fractional O 2 extractions as high as 80-90% across healthy muscles during maximal exercise (Knight et al 1992;Richardson et al 1993).…”

“…More recently, work from Casey and colleagues has found that, in older individuals, exercise training abolished age-related differences in rapid onset vasodilatation (ROV) in conduit arteries (both brachial and femoral), arguably through a speeding of dilatory kinetics (Casey et al 2013). This is important as old age slows the dilatation of conduit arteries (Hughes et al 2016(Hughes et al , 2018, feed arteries (Park et al 2016) and resistance arterioles (Behnke & Delp, 2010), as well as disrupts the coordination of up-and down-stream resistance vessel vasomotor responses by attenuating ascending vasodilatation via blunted hyperpolarization conduction (Sinkler et al 2016). The latter is intricately involved in ROV (Crecelius et al 2013) and, with old age, greater H 2 O 2 availability increases Ca 2+ -activated K + channel function that impairs endothelium electrical conduction (Socha et al 2015).…”

Dynamics of skeletal muscle blood flow and vasodilation with age

“…Collectively, these data indicate that exercise hyperemia and vasodilation are severely attenuated with age; however the mechanisms and magnitude for age-related reductions appear to differ between limbs. Chapter 2 of this dissertation addresses the gap in literature pertaining to mechanisms for the age-related reduction in contraction-induced rapid vasodilation within the forearm, and a version of this chapter has recently been published in Experimental Physiology (116). Chapter 3 of this dissertation addresses whether there are limb differences with age in respect to contractioninduced rapid vasodilation and a version of this Chapter has been previously published in Physiological Reports (120).…”