Saline aerosol bolus dispersion. I. The effect of acinar airway alteration.

We explored the possibility of using a saline aerosol for bolus dispersion measurements to detect peripheral airway alterations in smokers. Indexes of ventilation inhomogeneity in conductive (S(cond)) and acinar (S(acin)) lung zones, as derived from the multiple-breath N(2) washout (Verbanck S, Schuermans D, Van Muylem A, Noppen M, Paiva M, and Vincken W, J Appl Physiol 83: 1807-1816, 1997), were also measured. The saline bolus test consisted of inhaling 60-ml saline aerosol boluses to different volumetric lung depths (VLD) in the 1.1 liter volume above functional residual capacity. In the never-smoker group (n = 12), saline boluses showed bolus dispersion values consistent with normal values reported in the literature for 0.5- to 1-microm aerosols. In the smoker group (n = 12; 28 +/- 9 pack years, mean +/- SD), significant increases were seen on dispersion and skew of the most peripherally inhaled saline boluses (VLD = 800 ml; P < 0.05) as well as on S(acin) (P = 0.007) with respect to never-smokers. Shallow inhaled boluses (VLD = 200 ml) and S(cond) did not reveal any significant differences between smokers and never-smokers. This study shows the consistent response of two conceptually independent tests, in which both saline aerosol and gas-derived indexes point to a heterogeneous distribution of smoking-induced structural alterations in the lung periphery.