Evidence for impaired skeletal muscle contraction-induced rapid vasodilation in aging humans

Abstract

We tested the hypothesis that aging is associated with an impaired contraction-induced rapid vasodilation in healthy adults. We reasoned that employing single contractions of a small muscle mass would allow us to isolate the local rapid vasodilatory responses independent of systemic hemodynamic and sympathetic neural influences on forearm hemodynamics. We measured forearm blood flow (Doppler ultrasound) and arterial blood pressure (Finapres) on a beat-by-beat basis and calculated the changes in forearm vascular conductance (DeltaFVC) in response to forearm contractions in 18 young (24 +/- 1 yr) and 13 older (62 +/- 2 yr) healthy subjects. Single, 1-s dynamic forearm contractions were performed with the experimental arm slightly above heart level at 5, 10, 20, and 40% of the subjects' maximal voluntary contraction (MVC) in random order. In general, muscle contractions evoked a rapid increase in FVC that reached a peak within approximately four to five cardiac cycles postcontraction in both age groups. At 5% MVC, there were no significant age-related differences in contraction-induced forearm vasodilation. However, the peak vasodilatory responses were impaired approximately 40-45% in older adults at 10, 20, and 40% MVC, as were the total vasodilatory responses (area under curve approximately 40-50%; all P < 0.05). Additionally, the immediate vasodilation (first cardiac cycle postcontraction) for the 20% and 40% MVC trials was also impaired approximately 50% with age (P < 0.05). There were no significant age-group differences in MVC or forearm fat-free mass, and these variables were not correlated with local vasodilation within a given exercise intensity. Under the experimental conditions employed, the blunted responses with age reflect impaired local contraction-induced rapid vasodilation.

Evidence that the contraction-induced rapid hyperemia in rabbit masseter muscle is based on a mechanosensitive mechanism, not shared by cutaneous vascular beds

“…These rapid hyperemic events, observed in the rabbit masseter muscle, are strikingly similar to those reported in response to artery occlusion, muscle compression, electrically evoked, and spontaneous contractions in different muscle groups and animal species (6,8,10,18,24,33,38,47). This indicates that such rapid dilatation is a characteristic of the musculovascular network that is highly preserved across different species and that the masseteric artery of the rabbit may be a good model for its investigation.…”

“…However, a recent study indicates that K ϩ , released by con-tracting muscle fibers, could also mediate an early dilatory effect (2), which leaves the issue unsettled. Based on the similarity in the rapid hyperemic responses that have been reported in different preparations in response to short-lasting muscle contractions and mechanical stimuli (6,8,10,18,24,33,38,47), we hypothesized that a single mechanosensitive mechanism, activated by changes in transmural pressure, could underlie the different responses. Moreover, since it has been proposed that this rapid hyperemia is functionally meant to provide a prompt increase in muscle perfusion at the onset of exercise (9), we aimed to investigate whether this reactivity to the mechanical stimulus was differently exhibited by muscular and cutaneous vascular beds.…”

Nitric oxide, but not vasodilating prostaglandins, contributes to the improvement of exercise hyperemia via ascorbic acid in healthy older adults

“…Subjects were further evaluated for clinical evidence of cardiopulmonary disease with a physical examination and resting and graded exercise electrocardiograms. Studies were performed after a 4-h fast and 24-h abstention from caffeine and exercise, with subjects in the supine position and the experimental arm abducted to 90°and slightly elevated above heart level on a tilt-adjustable table (2). All studies were performed according to the Declaration of Helsinki.…”

“…Forearm exercise during the trials was performed with weight corresponding to 10% MVC attached to a pulley system and lifted 4 -5 cm over the pulley at a duty cycle of 1 s of contraction-2 s of relaxation (20 contractions/min) with the use of both visual and auditory feedback to ensure the correct timing as described previously (6). We chose this mild-intensity rhythmic handgrip exercise to limit the contribution of systemic hemodynamics to forearm hyperemic responses and eliminate reflex activation of the sympathetic nervous system (2,31). Additionally, this workload and mode of exercise have been shown to be tolerated well by older subjects over a prolonged time course and do not evoke progressive increases in heart rate and arterial pressure (17).…”

The Effects of Aging on Capillary Hemodynamics in Contracting Rat Spinotrapezius Muscle

“…For example, aging is associated with reductions in functional sympatholysis (Dinenno et al, 2005;Parker et al, 2007), myogenic control (Muller-Delp et al, 2002a), and contraction-induced rapid vessel relaxation (Carlson et al, 2008). Moreover, endothelium-dependent vasodilation is impaired (Muller-Delp et al, 2002b), with the dysfunction likely occurring preferentially in arterioles supplying oxidative but not glycolytic muscles (Woodman et al, 2002).…”