Impact of Aging on Inspiratory and Expiratory Work during Exercise

BACKGROUND In addition to the reduction in lung elastance and diaphragm function, aging is associated with a greater ventilatory response for a given metabolic rate. Together these age‐related pulmonary alterations may result in a higher energetic cost (i.e. work) of breathing for the elderly during exercise. PURPOSE To examine the impact of aging on the inspiratory and expiratory components of exercise‐induced respiratory work in physically active participants. METHODS Physical activity (PA) was monitored in seven healthy young (25 ± 4 yr) and older (72 ± 6 yr) participants for one week. The Tiffeneau‐Pinelli Index (TFPI) of pulmonary function (forced expiratory volume in one second (FEV 1 )/forced vital capacity (FVC)) was quantified prior to exercise. Following a 6 min warmup at 30 W, all participants performed an incremental cycling exercise test (30 W + 30 W/2 min) to exhaustion. The work of breathing (WOB) was acquired during the final minute of each stage by integrating the averaged esophageal pressure‐volume loop (~10 breaths). Furthermore, the WOB was partitioned into inspiratory (elastic + resistive) and expiratory work by 1) drawing a line connecting end‐expiratory lung volume (EELV) and end‐inspiratory lung volume (EILV) and 2) forming a right angle by adding an isovolume line from EILV and an iso‐pressure line from EELV. As there were no differences were found between inspiratory elastic or resistive work, combined inspiratory work is presented. In order to examine age‐related differences in WOB, the following two analyses were performed. First, for each individual, a 3 rd order polynomial fit was calculated for the WOB across all minute ventilations (V E ) obtained during the incremental test. T‐tests were then performed for each coefficient of the regression equation to determine if the slope for V E and WOB were different between groups. Second, to compare the impact of aging on total, inspiratory, and expiratory WOB, a mixed model ANOVA was performed including 3 matched flow rates (40, 70, and 100 L·min −1 ). RESULTS PA (~8700 steps/day) and TFPI (~80%) were similar between groups ( P > 0.28). During exercise, the young attained a greater peak workrate compared to the older participants (291 ± 66 W vs 184 ± 37 W, respectively, P < 0.05). Furthermore, at any given workrate, V E was 18 to 29% greater in the old and this was reflected in a higher V E /VCO 2 compared to the young ( P < 0.05). At each matched V E , the older individuals demonstrated a 17 to 28% greater EELV ( P < 0.05). While the total WOB increased with V E in both groups, the slope coefficient was greater in the old ( P < 0.05). Specifically, both expiratory and total WOB were greater in the old at 100 L·min −1 (representing 58% and 90% of maximal V E in young and old, respectively). Additionally, 5 of the 7 old and 1 of the 7 young participants demonstrated expiratory flow limitation (> 15%) at 100 L·min −1 . CONCLUSION The WOB increases with advancing age due to both a greater ventilatory response to a given workrate and a greater WOB at a given ventilatory rate. The greater WOB at a given V E is primarily accounted for by the elevated expiratory work which is likely attributable to the age‐related reduction in elastic recoil of the lung. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .