Inspiratory Muscle Performance of Former Smokers and Nonsmokers Using the Test of Incremental Respiratory Endurance

Background: Smoking has potential deleterious effects on respiratory muscle function. Smokers may present with reduced inspiratory muscle strength and endurance. We compared inspiratory muscle performance of nonsmokers with that of former smokers without overt respiratory problems via the Test of Incremental Respiratory Endurance.

Methods: This study was performed on 42 healthy subjects between the ages of 30 and 79 y (mean ± SD of 56.5 ± 14.4 y). Fourteen male and 7 female former smokers were matched to nonsmokers based on sex, age, height, and weight. Subjects completed a questionnaire about their health and current smoking status. Testing included the best of 3 or more consistent trials. The Test of Incremental Respiratory Endurance measurements included maximal inspiratory pressure measured from residual volume as well as sustained maximal inspiratory pressure and inspiratory duration measured from residual volume to total lung capacity during a maximal sustained inhalation.

Results: No significant difference in inspiratory performance of the entire group of former smokers compared with nonsmokers was found. However, separate sex analyses found a significant difference in sustained maximal inspiratory pressure between male former smokers and nonsmokers (518.7 ± 205.0 pressure time units vs 676.5 ± 255.2 pressure time units, P = .041).

Conclusions: We found similar maximal inspiratory pressure between former smokers and nonsmokers via the Test of Incremental Respiratory Endurance, but the significant difference in sustained maximal inspiratory pressure between male former smokers and nonsmokers suggests that the sustained maximal inspiratory pressure may have greater discriminatory ability in assessing the effects of smoking on inspiratory muscle performance. Further investigation of the effects of smoking on inspiratory performance via the Test of Incremental Respiratory Endurance is warranted.