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Viscoelasticity is a mechanical characteristic of most biological tissues, and the lungs are no exception. It implies that stress is not constant during a sustained constant strain; for example, when the lungs are maintained inflated at a constant volume, the transpulmonary pressure decreases with time. This article briefly discusses some of the implications of pulmonary viscoelasticity, the frequency dependence of lung compliance, the prolonged expiratory time required for exhalation, and the consequence on forced expiratory maneuvers, such as the forced expiratory volume at 1 second (FEV1). With respect to the latter, the article concludes by presenting new experimental data on 57 male and 43 female individuals. These normal subjects performed FEV1 immediately after reaching total lung capacity (TLC) or after a breath-hold at TLC of 5 or 10 seconds. After the breath-hold at TLC, FEV1 decreased in all, but significantly more in female than in male individuals. The sex difference in the viscoelastic properties of the lungs could have implications on differences in pulmonary pathophysiology between sexes.