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

Abstract

.-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, Ͼ60 years). Using static pressure-volume data, we computed the elastic work of breathing (joules per liter, J ⅐ l Ϫ1 ), including inspiratory muscle work, over resting and exercising tidal volume excursions. Elastic work of the lung (Y ϭ 0.79 Ϯ 0.05; M ϭ 0.47 Ϯ 0.05; O ϭ 0.43 Ϯ 0.05 J ⅐ l Ϫ1 ) and chest wall (Y ϭ Ϫ0.49 Ϯ 0.06; M ϭ Ϫ0.12 Ϯ 0.07; O ϭ 0.04 Ϯ 0.05 J ⅐ l Ϫ1 ) changed significantly with age (P Ͻ 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. chest wall; compliance; respiratory mechanics; work of breathing QUANTITATIVE STUDIES of the respiratory system indicate that aging lungs contain fewer, but larger, alveoli (1, 40), respiratory muscle strength is reduced (5, 10), there is an increased calcification of the intrathoracic joints (9, 11), and the diaphragmatic contribution to ventilation is elevated, particularly during exercise (35). These changes are likely to affect the mechanics of the respiratory system and, in turn, modify the static work of breathing. Accordingly, the literature contains several reports that aging humans experience a reduction in lung tissue elastic work (14,15,38).We have had particular interest in the possible effect that a greater calcification of the aging rib cage joints may have on chest wall stiffness, since a more rigid chest wall would increase the static work of breathing, similar to that seen in restrictive pulmonary disorders or chest strapping (8). Such changes may possibly result in a ventilatory limit to exercise. However, there has been very little research focusing on changes in chest wall mechanics in aging humans (27,29,35), with only one study specifically concerned with changes in chest wall elastic work during senescence (21); this project demonstrated that aging was accompanied by an increase in chest wall elastic work. Indeed, ...

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