Smoking is associated with inflammation and fibrosis in small airways and alveoli , and vascular deficiency emphysema . Using conventional vital capacity single breath washout (SBWvc) manoeuvres without breath holding, abnormalities in the phase III slope of nitrogen were found in healthy smokers which correlated with pathological changes in the small airways . However, prospective studies showed that the abnormalities in SBWvc maneouvres did not specifically identify those at risk of developing chronic airflow limitation . Others have proposed the use of more complex physiological techniques that highlight abnormalities in ventilation inhomogeneity in the lung periphery using multibreath washout techniques and gases of differing diffusivities , but these approaches are more demanding to implement as screening tests in large populations.
A refinement of SBWvc manoeuvres with potential application to epidemiological investigation was proposed because it might provide more information about peripheral ventilation inhomogeneity . This refinement (SBWSM) consisted of reducing the inspired volume of the SBW manoeuvre to one-half inspiratory capacity (IC) and initiating the SBW manoeuvre at a preinspiratory lung volume of functional residual capacity (FRC). In smokers with normal forced exhaled flow rates, abnormalities in the normalized phase III slope for helium (Sn) were detected using SBWSM that were not evident using SBWvc manoeuvres .