Abstract
In response to hypoxia, a net vasodilation occurs in the limb vasculature in young healthy humans and this is referred to as “hypoxia‐induced vasodilation”. We performed two separate experiments to determine (1) if hypoxia‐induced forearm vasodilation is impaired in older men (n = 8) compared to young men (n = 7) and (2) if acute systemic infusion of ascorbic acid would enhance hypoxia‐induced vasodilation in older men (n = 8). Heart rate, mean arterial pressure, oxygen saturation, minute ventilation, forearm vascular conductance (FVC, Doppler ultrasound), and cutaneous vascular conductance (CVC, laser Doppler flowmetry) were recorded continuously while subjects breathed 10% oxygen for 5 min. Changes from baseline were compared between groups and between treatments. The older adults had a significantly attenuated increase in FBF (13 ± 4 vs. 30 ± 7%) and FVC (16 ± 4 vs. 30 ± 7%) in response to 5 min of hypoxia. However, skin blood flow responses were comparable between groups (young: 35 ± 9, older: 30 ± 6%). In Experiment 2, FVC responses to 5 min of breathing 10% oxygen were not significantly different following saline (3 ± 10%) and ascorbic acid (8 ± 10%) in the older men. Ascorbic acid also had no physiological effects in the young men. These findings advance our basic understanding of how aging influences vascular responses to hypoxia and suggest that, in healthy humans, hypoxia‐induced vasodilation is not restrained by reactive oxygen species.
Highlights
Hypoxemia is a hallmark of several disease states including obstructive sleep apnea (OSA), chronic obstructive pulmonary disease (COPD), and acute mountain sickness and is experienced during recreational activities
The purpose of this study was to determine the effect of aging on FVC and cutaneous vascular conductance (CVC) responses to hypoxia and whether acute systemic infusion of ascorbic acid could modify these responses in older men
The data from Experiment 2 do not support our original hypothesis that ascorbic acid would enhance hypoxia-induced vasodilation in older men. These findings advance our basic understanding of how aging influences vascular responses to reduced blood oxygen levels and suggest that in healthy humans hypoxia-induced vasodilation is not restrained by reactive oxygen species
Summary
Hypoxemia is a hallmark of several disease states including obstructive sleep apnea (OSA), chronic obstructive pulmonary disease (COPD), and acute mountain sickness and is experienced during recreational activities (e.g., diving, hiking). In these conditions, maintaining (or restoring) oxygen delivery to skeletal muscle, cardiac muscle, and the brain is fundamentally important or impaired performance and eventual tissue necrosis may ensue. An increase in muscle sympathetic nerve activity helps to redistribute blood flow to vital organs Despite this acute rise in vasoconstrictor nerve traffic to the resting limb, a net vasodilation occurs in both skeletal muscle and the skin in young healthy subjects (Heistad and Wheeler 1970; Kravec et al 1972; Leuenberger et al 1991; Moradkhan et al 2007; Simmons et al 2007).
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