AGING EFFECT ON OXYGEN-CONSUMPTION OF RESPIRATORY MUSCLES IN HUMANS

The first purpose of the present study was to develop a new method to examine oxygen consumption of respiratory muscles (V̇O2(resp)) in human subjects. The apparatus consists of an expandable dead space and a respirometer. When the dead space was increased at a constant rate (~100 ml/min), minute ventilation (V̇E) and V̇O2(resp) increased gradually. Because the logarithm of V̇O2 was found to be approximately linearly related to V̇E, we characterized this relationship by the slope (logV̇O2/V̇E) and the intercept at V̇E = 0 (V̇O2(met)) of the semilog regression line. The second purpose of this study was to examine the relationship between V̇O2(resp) and aging. Six anthropometric and spirometric factors (age, height, weight, vital capacity, forced expiratory volume in 1 s, and body surface area) were analyzed in 37 normal subjects by simple and stepwise multiple regression analyses. We found a significant increase in logV̇O2/V̇E and a significant decrease in V̇O2(met) with age. In conclusion, 1) the present method is convenient to use, and we are able to study V̇O2(resp) over a wide range of ventilation without voluntary effort, and 2) age per se is one of the factors accounting for the observed increase in V̇O2(resp) with age.