Expiratory flow limitation during exercise in prepubescent boys and girls: prevalence and implications

The purpose of this study was to compare the prevalence and implications of expiratory flow limitation (EFL) during exercise in boys and girls. Forty healthy, prepubescent boys (B; n=20) and girls (G; n=20) were tested. Subjects completed pulmonary function tests and an incremental cycle maximal oxygen uptake (VO2max) test. EFL was recorded at the end of each exercise stage using the % tidal volume overlap method. Ventilatory and metabolic data were recorded throughout exercise. Arterial oxygen saturation (SpO2) was determined via pulse oximetry. Body composition was determined using dual-energy X-ray absorptiometry. There were no differences (P>0.05) in height, weight, or body composition between boys and girls. At rest, boys had significantly higher lung volumes (total lung capacity, B=2.6+/-0.5 liters, G=2.1+/-0.5 liters) and peak expiratory flow rates (B=3.6+/-0.6 l/s; G=1.6+/-0.3 l/s). Boys also had significantly higher VO2max (B=46.9+/-5.9 ml.kg lean body mass(-1).min(-1), G=41.7+/-6.6 ml.kg lean body mass(-1).min(-1)) and maximal ventilation (B=49.8+/-8.8 l/min, G=41.2+/-8.3 l/min) compared with girls. There were no sex differences (P>0.05) at VO2max in VE /VCO2, end-tidal PCO2, heart rate, respiratory exchange ratio, or SpO2. The prevalence (B=19/20 vs. G=18/20) and severity (B=58+/-7% vs. G=43+/-8% tidal volume) of EFL was not significantly different in boys compared with girls at VO2max. A significant relationship existed between % EFL at VO2max and the change in end-expiratory lung volume from rest to maximal exercise in boys (r=0.77) and girls (r=0.75). In summary, our data suggests that EFL is highly and equally prevalent in prepubescent boys and girls during heavy exercise, which led to an increased end-expiratory lung volume but not to decreases in arterial oxygen saturation.