Determinants of Expiratory Flow Limitation in Healthy Women during Exercise PAOLO B. DOMINELLI, JORDAN A. GUENETTE, SABRINA S. WILKIE, GLEN E. FOSTER, and A. WILLIAM SHEEL School of Human Kinetics, The University of British Columbia, Vancouver, British Columbia, CANADA ABSTRACT DOMINELLI, P. B., J. A. GUENETTE, S. S. WILKIE, G. E. FOSTER, and A. W. SHEEL. Determinants of Expiratory Flow Limitation in Healthy Women during Exercise. Med. Sci. Sports Exerc., Vol. 43, No. 9, pp. 1666–1674, 2011. Purpose: Expiratory flow limitation (EFL) can occur in healthy young women during exercise. We questioned whether the occurrence and severity of EFL were related to aerobic fitness or anatomical factors. Methods: Twenty-two healthy young (G40 yr) women performed a progressive cycle test to exhaustion. The subjects’ maximum expiratory flow–volume curve was compiled from several effort-graded vital capacity maneuvers before and after exercise. The maximum expiratory flow–volume curve, along with inspiratory capacity maneuvers, was used to de- termine lung volumes and expiratory flows and to quantify EFL. To determine relative airway size, we used a ratio sensitive to both airway size and lung volume, called the dysanapsis ratio. The subjects were partitioned into two groups based upon the appearance of 95% EFL. Results: Ten subjects showed EFL during exercise. Forced vital capacities (4.4 T 0.4 vs 3.7 T 0.4 L, P G 0.001) and forced expiratory flows for any given lung volume were significantly larger in the non–expiratory flow–limited (NEFL) group. The NEFL group’s dysanapsis ratio was significantly larger than that of the EFL group (0.27 T 0.06 vs 0.21 T 0.04, respectively, P G 0.05), indicating larger airways in the NEFL group. There was no difference between the NEFL and EFL groups with respect to maximal aerobic capacity (50.8 T 10.0 vs 46.7 T 5.9 mLIkg j1 Imin j1 , respectively, P = 0.264). At peak exercise, the NEFL group had a significantly higher end-expiratory lung volume than the EFL group (40.1% T 4.8% vs 33.7% T 5.7% FVC, respectively, P G 0.05). Conclusions: We conclude that EFL in women can largely be explained by anatomical factors that influence the capacity to generate flow and volume during exercise rather than fitness per se. Key Words: DYSANAPSIS, EXPIRATORY FLOW LIMITATION, GENDER, LUNG MECHANICS I ndividuals with similar lung volumes do not necessarily have similar airway diameters. This loose coupling be- tween airway size and lung volume has been termed ‘‘dysanapsis’’ (10). Differences in individual airway size are believed to explain, in part, the variability of expiratory flows between people of similar-sized lungs (10). It has also been shown that there are considerable sex differences with respect to dysanapsis, with women having smaller air- ways for a given lung volume than men (27). Recently, it has been shown using high-resolution computed tomography that when older men and women are matched for lung size, the larger conducting airways in females are significantly smaller (36). In addition, women in general have smaller lung volumes, lower maximal expiratory flows, and a re- duced diffusion capacity relative to men, and these differ- ences persist even when corrected for age and standing height (25,27). Expiratory flow limitation (EFL) occurs when transpul- monary pressure increases and there is no further increase in expiratory flow (18). The presence of EFL during exercise may lead to an increase in operating lung volumes (22,31) resulting in an increased mechanical work and oxygen cost of breathing (12,21,30). The increased operating lung vol- umes and tachypneic breathing pattern associated with EFL may result in diaphragm fatigue (2), exercise-induced arte- rial hypoxemia (38), and ultimately diminished exercise performance (19) in otherwise healthy individuals. It is reasonable to hypothesize that women may be more likely to develop EFL during exercise owing to their reduced airway diameters, lung volumes, and greater levels of dys- anapsis and, thus, their reduced ventilatory capacity (27). Indeed, there is some evidence to suggest that EFL is com- mon in young healthy women during dynamic exercise (12,25), but the mechanisms of EFL in this group are un- known. Moreover, there is one report that suggests women with higher levels of aerobic fitness develop more severe EFL than their less fit counterparts (25). Accordingly, the purpose of this study was to examine differences in pulmo- nary function, dysanapsis, breathing pattern, and operating lung volumes in flow-limited and non–flow-limited young women of varying fitness levels during cycle exercise. We Address for correspondence: A. William Sheel, Ph.D., 6108 Thunderbird Blvd., Vancouver, British Columbia, Canada V6T 1Z3; E-mail: Bill.sheel@ubc.ca. Submitted for publication November 2010. Accepted for publication February 2011. 0195-9131/11/4309-1666/0 MEDICINE & SCIENCE IN SPORTS & EXERCISE Ò Copyright Ó 2011 by the American College of Sports Medicine DOI: 10.1249/MSS.0b013e318214679d 1666 BASIC SCIENCES Copyright © 2011 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.