The impact of aging and habitual physical activity on static respiratory work at rest and during exercise.

We investigated the effects of aging on the elastic properties of lung tissue and the chest wall, simultaneously quantifying the contribution of each component to static inspiratory muscle work in resting and exercising adults. We further evaluated the interaction of aging and habitual physical activity on respiratory mechanics. Static lung volumes and elastic properties of the lung and chest wall (pressure-volume relaxation maneuvers) in 29 chronically sedentary and 29 habitually active subjects, grouped by age, were investigated: young (Y, 20-30 years), middle-aged (M, 40-50 years), and older (O, >60 years). Using static pressure-volume data, we computed the elastic work of breathing (joules per liter, J.l(-1)), including inspiratory muscle work, over resting and exercising tidal volume excursions. Elastic work of the lung (Y = 0.79 +/- 0.05; M = 0.47 +/- 0.05; O = 0.43 +/- 0.05 J.l(-1)) and chest wall (Y = -0.49 +/- 0.06; M = -0.12 +/- 0.07; O = 0.04 +/- 0.05 J.l(-1) ) changed significantly with age (P < 0.05). With aging, a parallel displacement of the chest wall pressure-volume curve resulted in a shift from energy being stored primarily during expiration to energy storage during inspiration, and driving expiration, both at rest and during exercise. Although deviating significantly from young adults, this did not significantly elevate static inspiratory muscle work but resulted in a redistribution of the tissues on which this work was performed and the phase of the respiratory cycle in which it occurred. Nevertheless, static inspiratory muscle work remained similar across age groups, at rest and during exercise, and habitual physical activity failed to influence these changes.