DIFFERENT MECHANICAL-PROPERTIES OF THE LUNG IN BOYS AND GIRLS

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Abstract
Partial (PEFV) and maximal (MEFV) expiratory flow-volume curves were obtained from 47 healthy children, 3-13 yr of age, while they breathed air or a He-O2 gas mixture. Girls had significantly higher (P < 0.02) flows at FRC [functional residual capacity] (.ovrhdot.Vmax [maximum ventilation] FRC) on the air-MEFV curves than on the air-PEFV curves; boys had similar flows on both curves. There was a significant (P < 0.04) relationship between the inspiratory volume (before initiating a PEFV curve) and .ovrhdot.Vmax FRC (on PEFV curves) for girls but not boys. No differences in .ovrhdot.Vmax FRC (PEFV) and .ovrhdot.Vmax FRC (MEFV) were observed for either sex when He-O2 was breathed. Apparently girls, with a deep inspiration, can increase their maximal flows, possibly by altering the tone of their airways. Comparison of the air and He-O2 data suggested that girls may tend to dilate preferentially their larger airways with a maximal inspiration. Boys may generally be unable to do this. Such possible sex differences in the mechanical properties of the lung may relate to the different prevalence rates for severe lower respiratory tract illnesses and asthma in the 2 sexes.