Detection of Peripheral Ventilation Inhomogeneity in Smokers

Abstract

BACKGROUND: In smokers, ‘small airways’ narrowing alters the conventional, vital capacity single breath washout (SBW_VC). Although, in some studies, the test predicts smokers at risk of developing chronic airflow limitation, its wide variability partly explains its poor positive predictive value. An alternative explanation for the test’s poor predictive value is that it may not accurately reflect small airway narrowing in the lung periphery.OBJECTIVE: To determine whether smoke-induced increases in ventilation inhomogeneity differ between SBW_VC manoeuvres, which augment topographical (apex-to-base) ventilation inhomogeneity, and submaximal manoeuvres (SBW_SM), which enhance peripheral ventilation inhomogeneity.STUDY GROUP AND DESIGN: Cross-sectional study of 21 current smokers and 21 nonsmokers with similar age and forced expiratory volumes in 1 s (FEV₁).METHODS: Smokers and nonsmokers performed SBW with either slow vital capacity inhalation and exhalation of test gas without breath holding (SBW_VC); or slow inhalation of test gas from functional residual capacity to one-half inspiratory capacity and, after 0 s or 10 s of breath holding, slow exhalation to residual volume (SBW_SM). For all SBW the normalized phase III helium slope (S_n), closing capacity (CC) as a percentage of total lung capacity (TLC) and mixing efficiency (E_mix) were measured.RESULTS: For SBW_VC, smoking had no effect on S_n or E_mix. However, CC/TLC was increased in smokers (P<0.05), but did not correlate with pack years or age. For SBW_SM, smoking had no effect on E_mix or CC/TLC, but resulted in a steeper S_n (P <0.05), which decreased more with breath holding (P<0.01) and correlated with pack years (P<0.05) at 0 s but not 10 s of breath holding.CONCLUSIONS: In smokers with normal FEV₁, SBWSM manoeuvres reveal increases in breath hold time-dependent ventilation inhomogeneity in the lung periphery, not detected by conventional SBW_VC.