Elastic and Resistive Work of Breathing in Older and Younger Adults

Abstract

Aging results in significant alterations in the structure and function of the pulmonary system. For example, aging is associated with the loss of elastic recoil, stiffening of the chest wall as well as decreased airway caliber, and expiratory flow rates. During exercise, older adults exhibit greater expiratory flow limitation (EFL) and increased operating lung volumes than younger adults; however, it is not known if these translate to a higher total work of breathing (WOB) owing to elevated elastic and resistive WOB. PURPOSE: To compare the total WOB and its components (inspiratory and expiratory elastic and resistive WOB) in older and younger adults at matched ventilations (VE). We hypothesized that older compared to younger adults would exhibit a greater total WOB as a result of greater inspiratory and expiratory elastic and resistive WOB. METHODS: Older (OA: n=9; 60±8 yrs) and younger (YA: n=9; 38±7 yrs) adults were recruited for this study. Participants performed an incremental cycling test to volitional fatigue. Esophageal pressure, lung volumes, EFL, and ventilatory variables were measured at matched VE (i.e. 25, 50, and 75 L/min) during exercise. Modified Campbell diagrams were used to determine the inspiratory and expiratory elastic and resistive WOB. RESULTS: At VE of 75 L/min, older adults had greater % EFL and tidal volume to forced vital capacity ratio (p 0.19). Older compared to younger adults had greater total WOB at VE of 50 (OA: 47±20 vs. YA: 31±7 J/min) and 75 L/min (OA: 97±41 vs. YA: 64±18 J/min) (p≤0.05 for both). At VE of 50 L/min, older adults had a greater inspiratory resistive WOB (OA: 13±8 vs. YA: 6±2 J/min, p<0.03). At VE of 75 L/min, older adults had a greater inspiratory elastic and resistive WOB (OA: 44±27 vs. YA: 24±22 and OA: 23±15 vs. YA: 11±3 J/min, respectively) (p<0.02 for both) and expiratory resistive WOB (OA: 23±19 vs. YA: 14±9 J/min, p=0.04) than younger adults. CONCLUSIONS: These data demonstrate that aging-induced pulmonary alterations result in a greater WOB during exercise owing to greater inspiratory (elastic and resistive) and expiratory resistive WOB. These findings suggest that the respiratory muscles necessitate an increased blood flow demand in older than younger adults for a given VE during exercise.