The Influence of Subsystolic Occlusion on Cardiac Power during Submaximal Locomotor Exercise in Healthy Aging Adults

Abstract

IntroductionHealthy aging in adults is associated with attenuated cardiac output (Q) for a given exercise workload compared to younger healthy adults. This is important because skeletal muscle perfusion pressure during exercise is dependent on coordinated adjustments between cardiac and vascular hemodynamics. Cardiac power (CP) quantifies the flow and peripheral pressure generating capacity of the heart, and may be the strongest measure of cardiac function during exercise. Group III/IV muscle afferents are suggested to favorably influence Q and arterial pressure during exercise in young healthy adults. However, the influence of group III/IV afferents on cardiac hemodynamic and arterial pressure coupling during exercise remains unclear across the aging spectrum. Venous distension via subsystolic circulatory occlusion of locomotor muscles is suggested to increase group III/IV afferent outflow. The aim of this study was to assess the influence of subsystolic circulatory occlusion of locomotor muscles on CP in young vs aging healthy adults.MethodsHealthy adults completed 2 visits (10 young [YNG] vs 9 OLD; age 22±1 vs 66±3 yrs, BSA 1.8±0.1 vs 1.9±0.1 m2; % predicted peak VO2 99±7 vs 115±7 %; peak workload 188±16 vs 144±9 W, respectively; age and workload P<0.05). Visit 1: peak exercise test. Visit 2: constant load cycle ergometry at 30% peak workload (YNG=56±5 vs OLD=43±3 W, P<0.05) with the first 3 min without cuffing (0 mm Hg), but thereafter included intermittent subsystolic bilateral thigh cuff inflations to 20, 40, 60, 80, or 100 mm Hg for 2 min (randomized), with 2 min deflation between inflations. Non‐invasive Q and mean arterial (MAP) pressure were measured using continuous hemodynamic photoplethysmography. We calculated CP=Q*MAP. Q and CP were indexed to BSA.ResultsAt rest, MAP did not differ in YNG vs OLD, but Q and CP were higher in YNG vs OLD (P<0.05), which persisted throughout each exercise cuff occlusion. In YNG, the greatest increase in CP from 0 mm Hg occurred at 100 mm Hg (754±48 vs 899±48 L/min/m2 · mm Hg, P<0.05) due to increased MAP (19±4%, P<0.05) but not Q (1±2%, P>0.05). In OLD, Q, MAP, and CP did not differ between 0 mm Hg and any occlusion (P>0.05). The % increase in Q from rest to 0, 20, 60, 80, and 100 mm Hg was higher in YNG vs OLD (P<0.05). The % increase in MAP from rest to any occlusion did not differ in YNG vs OLD (P>0.05). The % increase in CP from rest to occlusions of 60 (130±9 vs 98±11%), 80 (142±9 vs 108±20%), and 100 (158±11 vs 114±14%) were higher in YNG vs OLD (all P<0.05). Within YNG, the % increase in CP from rest to 100 mm Hg was higher than the % increase from rest to 0, 20, 40, or 60 mm Hg (P<0.05), driven by increased MAP (P<0.05). Within OLD, these differences for % increase in CP did not occur despite MAP that was similar to YNG (P>0.05).ConclusionsThese data suggest that CP is attenuated in OLD vs YNG healthy adults during subsystolic circulatory occlusion of locomotor muscles during submaximal constant load exercise. The reduced CP generation in older adults is related to a blunted increase in Q mediated by attenuated influence of group III/IV muscle afferents on cardiac function during exercise.