SMALLER LUNGS IN WOMEN AFFECT EXERCISE HYPERPNEA

We subjected 29 healthy young women (age: 27 +/- 1 yr) with a wide ran ge of fitness levels [maximal oxygen uptake ((V) over dot O-2 max): 57 +/- 6 ml.kg(-1).min(-1); 35-70 ml.kg(-1).min(-1)] to a progressive tr eadmill running test. Our subjects had significantly smaller lung volu mes and lower maximal expiratory flow rates, irrespective of fitness l evel, compared with predicted values for age-and height-matched men. T he higher maximal workload in highly fit ((V) over dot O-2 max > 57 ml .kg(-1).min(-1), n = 14) vs. less-fit ((V) over dot O-2 max < 57 ml.kg (-1).min(-1), n = 15) women caused a higher maximal ventilation ((V) o ver dot E) with increased tidal volume (VT) and breathing frequency (f (b)) at comparable maximal VT/vital capacity (VC). More expiratory flo w limitation (EFL; 22 +/- 4% of VT) was also observed during heavy exe rcise in highly fit vs. less-fit women, causing higher end-expiratory and end-inspiratory lung volumes and greater usage of their maximum av ailable ventilatory reserves. HeO2 (79% He-21% O-2) vs. room air exerc ise trials were compared (with screens added to equalize external appa ratus resistance). HeO2 increased maximal expiratory flow rates (20-38 %) throughout the range of VC, which significantly reduced EFL during heavy exercise. When EFL was reduced with HeO2, VT, f(b), and (V) over dot E (+16 +/- 2 l/min) were significantly increased during maximal e xercise. However, in the absence of EFL (during room air exercise), He O2 had no effect on (V) over dot E. We conclude that smaller lung volu mes and maximal flow rates for women in general, and especially highly fit women, caused increased prevalence of EFL during heavy exercise, a relative hyperinflation, an increased reliance on fb, and a greater encroachment on the ventilatory ''reserve.'' Consequently, VT and (V) over dot E are mechanically constrained during maximal exercise in man y fit women because the demand for high expiratory flow rates encroach es on the airways' maximum flow-volume envelope.