title: Aging alters muscle reflex control of autonomic cardiovascular responses to rhythmic contractions in humans.
abstract: We investigated the influence of aging on the group III/IV muscle afferents in the exercise pressor reflex-mediated cardiovascular response to rhythmic exercise. Nine old (OLD; 68 ± 2 yr) and nine young (YNG; 24 ± 2 yr) males performed single-leg knee extensor exercise (15 W, 30 W, 80% max) under control conditions and with lumbar intrathecal fentanyl impairing feedback from group III/IV leg muscle afferents. Mean arterial pressure (MAP), cardiac output, leg blood flow (QL), systemic (SVC) and leg vascular conductance (LVC) were continuously determined. With no hemodynamic effect at rest, fentanyl blockade during exercise attenuated both cardiac output and QL ∼17% in YNG, while the decrease in cardiac output in OLD (∼5%) was significantly smaller with no impact on QL (P = 0.8). Therefore, in the face of similar significant ∼7% reduction in MAP during exercise with fentanyl blockade in both groups, LVC significantly increased ∼11% in OLD, but decreased ∼8% in YNG. The opposing direction of change was reflected in SVC with a significant ∼5% increase in OLD and a ∼12% decrease in YNG. Thus while cardiac output seems to account for the majority of group III/IV-mediated MAP responses in YNG, the impact of neural feedback on the heart may decrease with age and alterations in SVC become more prominent in mediating the similar exercise pressor reflex in OLD. Interestingly, in terms of peripheral hemodynamics, while group III/IV-mediated feedback plays a clear role in increasing LVC during exercise in the YNG, these afferents seem to actually reduce LVC in OLD. These peripheral findings may help explain the limited exercise-induced peripheral vasodilation often associated with aging.
authors.affiliation: Departments of Internal Medicine and Discipline of Physiology, School of Medicine, The University of Adelaide, Australia; and simran.sidhu@adelaide.edu.au.
authors.forename: Simranjit K
authors.initials: SK
authors.lastname: Sidhu
authors.affiliation: Exercise and Sport Science, University of Utah.
authors.forename: Joshua C
authors.initials: JC
authors.lastname: Weavil
authors.affiliation: Departments of Internal Medicine and Department of Biomedical Sciences for Health, University of Milan, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Venturelli
authors.affiliation: Exercise and Sport Science, University of Utah.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Rossman
authors.affiliation: Department of Anesthesiology, University of Utah, Salt Lake City, Utah;
authors.forename: Benjamin S
authors.initials: BS
authors.lastname: Gmelch
authors.affiliation: Department of Anesthesiology, University of Utah, Salt Lake City, Utah;
authors.forename: Amber D
authors.initials: AD
authors.lastname: Bledsoe
authors.affiliation: Departments of Internal Medicine and Exercise and Sport Science, University of Utah, Geriatric Research Education and Clinical Centers, Veterans Affairs Medical Center, and.
authors.forename: Russell S
authors.initials: RS
authors.lastname: Richardson
authors.affiliation: Departments of Internal Medicine and Exercise and Sport Science, University of Utah, Geriatric Research Education and Clinical Centers, Veterans Affairs Medical Center, and Department of Anesthesiology, University of Utah, Salt Lake City, Utah;
authors.forename: Markus
authors.initials: M
authors.lastname: Amann
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000701:Analgesics, Opioid / Q000494:pharmacology; D062186:Arterial Pressure / Q000187:drug effects / Q000502:physiology; D001341:Autonomic Nervous System / Q000187:drug effects / Q000502:physiology*; D002302:Cardiac Output / Q000187:drug effects / Q000502:physiology; D002320:Cardiovascular Physiological Phenomena / Q000187:drug effects; D002319:Cardiovascular System / Q000187:drug effects / Q000294:innervation*; D005263:Femoral Artery / Q000187:drug effects / Q000502:physiology; D005283:Fentanyl / Q000494:pharmacology; D006801:Humans; D007866:Leg / Q000098:blood supply; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D052097:Quadriceps Muscle / Q000187:drug effects / Q000502:physiology*; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology; D055815:Young Adult
chemical_list: D000701:Analgesics, Opioid; D005283:Fentanyl
keywords: afferent feedback; dynamic exercise; exercise pressor reflex