Reduced leg blood flow during dynamic exercise in older endurance-trained men

Abstract

It is currently unclear whether aging alters the perfusion of active muscles during large-muscle dynamic exercise in humans. To study this issue, direct measurements of leg blood flow (femoral vein thermodilution) and systemic arterial pressure during submaximal cycle ergometry (70, 140, and 210 W) were compared between six younger (Y; 22-30 yr) and six older (O; 55-68 yr) chronically endurance-trained men. Whole body O2 uptake, ventilation, and arterial and femoral venous samples for blood-gas, catecholamine, and lactate determinations were also obtained. Training duration (min/day), estimated leg muscle mass (dual-energy X-ray absorptiometry; Y, 21.5 +/- 1.2 vs. O, 19.9 +/- 0.9 kg), and blood hemoglobin concentration (Y, 14.9 +/- 0.4 vs. O, 14.7 +/- 0.2 g/dl) did not significantly differ (P > 0.05) between groups. Leg blood flow, leg vascular conductance, and femoral venous O2 saturation were approximately 20-30% lower in the older men at each work rate (all P < 0.05), despite similar levels of whole body O2 uptake. At 210 W, leg norepinephrine spillover rates and femoral venous lactate concentrations were more than twofold higher in the older men. Pulmonary ventilation was also higher in the older men at 140 (+24%) and 210 (+39%) W. These results indicate that leg blood flow and vascular conductance during cycle ergometer exercise are significantly lower in older endurance-trained men in comparison to their younger counterparts. The mechanisms responsible for this phenomenon and the extent to which they operate in other groups of older subjects deserve further attention.

Angiotensin II in the Elderly

“…Clinically, further characterization of age-related changes in AT 1 receptor function are particularly important, given that the combination of sympathetic and renin-angiotensin system activation adversely affects prognosis in renal and cardiovascular diseases. 11 The age-related elevation in vascular tone and subsequent decline in resting limb blood flow subsists during exercise, with evidence from our group 12,13 and others, 14,15 for a reduction in exercise hyperemia in the leg of elderly subjects. The mechanisms responsible for this apparent reduction in vasodilatory capacity remain unknown, although studies in the forearm suggest that the augmented sympathetic vasoconstriction seen at rest may carry over during handgrip exercise in older individuals, resulting in a lesser "magnitude of sympatholysis" in older individuals.…”

“…These data are suggestive of a powerful mechanism within the active muscle tissue, likely multiple byproducts of aerobic and/or anaerobic metabolism, that is capable of overcoming the potent vasoconstrictor effects of Ang II and, again, indicates that age-related elevations in resting AT 1 receptor sensitivity do not contribute significantly to the blunted exercise hyperemia widely observed in the elderly. [12][13][14][15] Indeed, it seems that the profound "lysing" of both nonadrenergic ( Figure 1) and adrenergic 16 vasoconstriction may be nondiscriminate yet essential events in the overall series of reactions that collectively produce a sufficient increase in skeletal muscle blood flow, raising the degree of exercise hyperemia in the elderly cohort toward that of the young.…”

Limb Blood Flow and Vascular Conductance Are Reduced With Age in Healthy Humans

“…With respect to function, evidence is accumulating that older adults are limited in their ability to augment limb blood flow and vascular conductance in response to acute increases in functional demand imposed by large-muscle dynamic exercise, 8 energy intake, 38 and ambient heat stress. 25,26 The present findings indicate that an elevated limb vasoconstrictor state is present even in healthy older adults.…”

“…Because limb blood flow is closely linked to oxygen demand, 1,8 any reduction in flow with age may be related to a reduced oxygen consumption. If so, the latter might be, in turn, due to a smaller limb tissue mass.…”

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

“…In addition, aging affects the myogenic control of vascular conductance Behnke et al, 2006), reduces the bioavailability of nitric oxide (NO), and attenuates endothelium-dependent vasodilation (Muller-Delp et al, 2002b;Muller-Delp, 2006) resulting in a reduced ability to regulate vascular tone. These alterations are likely to contribute to the age-induced decrease in blood flow observed during dynamic leg exercise (Proctor et al, 1998) and electrically-induced muscle contractions (Hammer & Boegehold, 2005), which may be accompanied by a redistribution of flow among different fiber types . Impaired active peripheral circulatory control results in temporal reduction of muscle O 2 delivery relative to the O 2 demands of exercise (Behnke et al, 2005).…”