COMPARISON OF DIAPHRAGM STRENGTH BETWEEN HEALTHY ADULT ELDERLY AND YOUNG MEN

To test the hypothesis that aging is associated with a reduction in the diaphragm's force-generating capacity, we compared the maximum transdiaphragmatic pressure (Pdi(max)) obtained during voluntary maximal inspiratory efforts in nine young (19-28 yr) and ten elderly (65-75 yr) subjects. The relationship between Pdi and lung volume was compared in the two groups by having subjects make maximal inspiratory maneuvers at specified lung volumes (i.e., 20, 40, and 80% vital capacity). Subjects underwent symptom-limited exercise tests to characterize their aerobic capacities and evaluate the relationship between aerobic capacity and Pdi(max). The average Pdi(max) of the elderly subjects (128 +/- 9 cm H2O) was significantly lower (p < 0.003) than the average Pdi(max) of the younger subjects (171 +/- 8 cm H2O). In the elderly, Pdi was lower across the range of lung volumes tested (p < 0.001), and Pdi(max) occurred at similar relative lung volumes (elderly, at 47% total lung capacity [TLC]; young, at 50% TLC) in both groups. The elderly subjects were quite fit based on their VO(2)max, and there was no significant relationship between Pdi(max) and VO(2)max. This study suggests that diaphragm strength is reduced in elderly individuals. This age-related decrease in diaphragm strength may predispose elderly patients to diaphragm fatigue in the presence of conditions that impair inspiratory muscle function or increase ventilatory load.