LAUSR

This study examined the impact of aging on the elastic and resistive components of the work of breathing (Wb) during locomotor exercise at a given 1) ventilatory rate, 2) metabolic rate, and 3) operating lung volume. Eight healthy younger (25±4yr) and 8 older (72±6yr) participants performed incremental bicycle exercise, from which retrospective analyses identified similar ventilatory rates (approximately 40, 70, and 100L·min-1), similar metabolic rates (VO2: approximately 1.2, 1.6, and 1.9L·min-1), and similar operating lung volumes (end-inspiratory and end-expiratory lung volumes (EILV/EELV: approximately 75/34%, 84/32%, and 87/34% of vital capacity). Wb at each level was quantified by integrating the averaged esophageal pressure-volume loop, which was then partitioned into elastic and resistive components of inspiratory and expiratory work using the modified Campbell diagram. EILV was higher in the older participants during exercise at ventilations of 70 and 100 L·min-1 and during exercise at the 3 metabolic rates (P<0.05). Mainly due to a greater inspiratory elastic and resistive Wb in the older group (P<0.05), total Wb was augmented by 40-50% during exercise at matched ventilatory and matched metabolic rates. When examined during exercise evoking similar operating lung volumes, total Wb was not different between the groups (P=0.86). Taken together, while aging exaggerates total Wb during locomotor exercise at a given ventilatory or a given metabolic rate, this difference is abolished during exercise at a given operating lung volume. These findings highlight the significance of operating lung volume in determining the age-related difference in Wb during locomotor exercise.