Healthy Aging Alters Ventilatory Responses to Venous Distension during Submaximal Constant‐Load Exercise
Authors: Van Iterson Erik H. , Gramm Courtney , Randall Nicholas R. , Keller‐Ross Manda L , Olson Thomas P. 
Published: November 2023

Background

Neurophysiological coupling between ventilation and locomotor muscle group III/IV muscle afferent fibers during exercise is an important relationship that favorably influences ventilation in young healthy adults. In contrast, we have shown that group III/IV locomotor muscle afferents provoke aberrant ventilation in aging heart failure patients, which is suggested to be a primary effect of heart failure. However, there remains a limited understanding of the effect of aging in the absence of cardiovascular disease on the group III/IV muscle afferent pathway. Subsystolic circulatory occlusion to elicit venous distension has been suggested to stimulate locomotor muscle afferent neurologic feedback. The purpose of this study was to compare ventilatory responses in young vs aging healthy adults during submaximal constant‐load exercise with intermittent bilateral subsystolic occlusion of locomotor muscles.

Methods

Healthy 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 ergometry 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) and intermittent subsystolic bilateral thigh cuff inflations to 20, 40, 60, 80, or 100 mm Hg for 2 min (randomized), with 2 min deflation between occlusions thereafter. Minute ventilation (VE), respiratory rate (RR), tidal volume (VT), oxygen uptake (VO2) indexed to weight, carbon dioxide output (VCO2), respiratory exchange ratio (RER), VE/VCO2, and end tidal partial pressure CO2 (PETCO2) were measured continuously via breath by breath system.

Results

At rest, VE, RR, VT, or RER did not differ in YNG vs OLD (P>0.05); whereas VO2 (6.3±0.3 vs 3.9±0.2 mL/kg/min) and VCO2 (0.3±0.0 vs 0.2± 0.0 L/min) were higher in YNG vs OLD (respectively, P<0.05). During all exercise occlusions, VE was higher in YNG vs OLD, with the largest difference at 100 mm Hg (36.7±1.7 vs 30.2±1.6 L/min, respectively, P<0.05). However, the % change from rest to 0 mm Hg or each cuff occlusion resulted in no differences in YNG vs OLD for VE (P>0.05). In contrast, in YNG vs OLD, the largest % change from 0 mm Hg to the cuff occlusion resulting in between group differences included VE (3.3±3.0 vs 17.3±3.6 at 80 mm Hg, P<0.05), VCO2 (2.3±2.3 vs 20.8±3.4 at 100 mm Hg, P<0.05) and VE/VCO2 (7.0±2.6 vs 0.5±1.8 at 100 mm Hg, P<0.05). In addition, there was a trend for significant differences between YNG and OLD for VT (−1.2±4.4 vs 5.9±4.1 % at 80 mm Hg, P=0.15), VO2 (−2.1±1.5 vs 3.3±1.8 %, at 100 mm Hg, P=0.09) and PETCO2 (−6.4±1.9 vs −2.3±1.4 % at 100 mm Hg, P=0.11).

Conclusions

These data suggest that aging is associated with altered ventilatory responses to venous occlusion of locomotor muscles during constant load submaximal exercise. These changes may be a result of an increased contribution of locomotor muscle afferents on ventilatory control with aging.

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