Comparing the Shape of the Maximal Expiratory Flow-Volume Curve Between Healthy Never Smokers and Asymptomatic Ex-Smokers

The maximal expiratory flow-volume (MEFV) curve is a valuable tool for assessing pulmonary function and diagnosing respiratory disease. Quantifying the shape of the MEFV curve may provide additional insight into pulmonary dysfunction compared to spirometry alone. We questioned if the shape of the MEFV curve could detect signs of abnormal lung emptying dynamics in asymptomatic ex-smokers when compared to never smokers free of cardiopulmonary disease. A retrospective analysis of routine spirometry from 22 asymptomatic ex-smokers (50% female) without a formal diagnosis of chronic obstructive pulmonary disease or other chronic respiratory disease was compared against 48 healthy never smokers (65% female). The shape of the MEFV curve was quantified via the slope-ratio method which generates a unitless value corresponding to the ratio between a line of tangency at a specific lung volume and a chord line intersecting the point of interest and residual volume. A SR of 1 would indicate a linear decrease in flow with decreasing lung volume, whereas a SR >1 or <1 would indicate a convex ( i.e., scooped) or concave ( i.e., bump) shape to the MEFV curve; respectively. Slope-ratio was assessed between 80-20% vital capacity in 2% vital capacity increments. A single average slope-ratio was taken as the mean of all slope-ratio values between 80-20% vital capacity per individual. Data are presented as mean ± SD. Patient demographics, including age, height and weight were not different between ex-smokers and never smokers (all p >0.05). No differences in pulmonary function between ex-smokers and never smokers were observed (FEV 1 : 89±22 vs. 95±20%predicted; FVC: 94±21 vs. 98±19%predicted; FEV 1 /FVC: 94±8 vs. 96±9%predicted, all p >0.05). The average slope-ratio was greater in ex-smokers compared to never smokers (1.74±0.29 vs. 1.45±0.41, p <0.0001). This difference was driven by a greater slope-ratio between 70-50% vital capacity (all, p <0.05). These preliminary data suggest slope-ratio analyses reveal a dysfunctional pattern of lung emptying in asymptomatic ex-smokers with no formal diagnosis of pulmonary disease compared to never smokers n that is not observed through spirometry alone. NSERC (PDF-577750-2023; AHR), NIH (HL139854; MJJ) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.