Experimentally Manipulating Mechanical Ventilatory Constraint During Exercise Does Not Influence Dyspnea in Older Men and Women

Abstract

During exercise at a standardized metabolic work load, the perception of dyspnea is higher in older women than older men, which is thought to be related to sex-differences in mechanical ventilatory constraint; however, this hypothesis has yet to be experimentally tested. PURPOSE: To determine the effect of manipulating the magnitude of mechanical ventilatory constraint during submaximal exercise on dyspnea in older men and women. METHODS: Thirteen healthy subjects (60-80 y; n=7 women) completed two days of testing. On Day 1, subjects performed pulmonary function testing and a maximal incremental cycle exercise test. On Day 2, esophageal pressure (Pes) and diaphragm electromyography (EMGdi) were recorded during three constant load cycle exercise tests (6 min each) at ventilatory threshold (VTh). Constant load exercise tests were performed under three conditions in a single blind, randomized, counterbalanced fashion: i) breathing normoxic helium-oxygen gas (HeO2) to reduce the work of breathing (W b ) and alleviate expiratory flow limitation (EFL); ii) inspiratory resistance (RES) of 5 cmH2O·l-1·s-1 to increase W b ; and iii) control (CON) breathing room air. During exercise on Day 2, Pes-derived measures of Wb, EMGdi, and EFL were assessed. RESULTS: During the HeO2 condition, there was a significant decrease in Wb (men=-20±4%, women= -16±5%) and EMGdi (men= -11±7%, women= -9±7%) relative to CON (both p<0.01). Moreover, if EFL was present during the CON condition (n=3 men, n=5 women), it was alleviated during HeO2. Conversely, during the RES condition, there was a significant increase in Wb (men= 34±11%, women= 50±12%) and EMGdi (men=32±15%, women= 23±12%) relative to CON (both p<0.01). The effect of condition on Wb and EMGdi was not significantly different between the sexes (both p>0.05). Across conditions, women reported significantly higher levels of dyspnea than men (3.3±0.4 vs. 1.9±0.4 Borg units, p<0.05). However, despite significant differences in the degree of mechanical ventilatory constraint between conditions, there was no effect of condition on the perception of dyspnea intensity, regardless of sex (p=0.46). CONCLUSION: Our results suggest that during short bouts of exercise at VTh, sex-differences in dyspnea in older adults are not related to sex-differences in mechanical ventilatory constraint.