Aging alters muscle reflex control of autonomic cardiovascular responses to rhythmic contractions in humans (1165.8)

Abstract

We investigated the influence of aging on the role of group III/IV muscle afferents in determining circulatory responses to physical activity. Six old (OLD; 70 ± 2 years) and 8 young (YNG; 24 ± 2 years) males performed single‐leg knee extensor exercise (14 W / 30 W / 80% max) under control conditions and with lumbar intrathecal fentanyl impairing feedback from µ‐opioid receptor‐sensitive lower limb muscle afferents. Cardiac output (Q), leg perfusion pressure (PP), leg vascular conductance (LVC), and femoral blood flow (QL) were collected continuously. There were no hemodynamic differences between conditions at rest. Fentanyl blockade during exercise did not affect Q in OLD (P=0.2); however, secondary to significant decreases in heart rate and stroke volume, Q was attenuated by ~20% in YNG (P<0.05). Furthermore, in the face of a similar 5‐7% reduction in PP (P<0.05) during exercise with fentanyl blockade in both groups, LVC increased ~13% in OLD, but decreased ~10% in YNG (both P<0.05). The net effect of these blockade‐induced changes was an unaltered QL response to exercise in OLD, contrasting the significant 15‐17% decrease in YNG. In conclusion, healthy aging alters muscle reflex control of autonomic circulatory responses to exercise. While muscle afferent feedback remains critical in regulating PP, their contribution to central (Q) and peripheral (QL) hemodynamic responses might diminish with age.Grant Funding Source: HL_103786; HL‐116579