AIRWAY DIMENSIONS OF DOG LUNGS BY AEROSOLS - COMPARISON OF BOLUS AND SINGLE-BREATH TECHNIQUES

Monodisperse aerosols were used to determine airway dimensions as a fu nction of volumetric lung depth in vivo. Two different techniques were compared in anesthetized mechanically ventilated dogs (mean body wt. +/- SD, 13.6 +/- 0.9 kg). Monodisperse di-(2-ethyl-hexyl) sebacate par ticles (mean aerodynamic diameter +/- SD, 0.89 +/- 0.097 mum) were inh aled as bolus (half-width 8 ml) at 10-85% of the normalized (50% funct ional residual capacity, FRC) inspired volume (Bolus Technique). Alter natively, the total inspired volume contained the test aerosol, formal ly representing inspiration of a train of aerosol boluses of infinites imal small volume (Single-Breath Technique). The particle concentratio n was continuously recorded ai the airway opening by a miniaturized in -line aerosol photometer incorporating a 2 mW laser diode (lambda = 82 0 nm) and a photodiode. The airway diameters determined at a given vol umetric lung depth were related to the animal's total lung capacity (T LC) to account for lung volume differences between dogs. The in-vivo a erosol-derived airway diameters of dog lungs revealed close correspond ence with morphometric estimates from excised lungs. No systematic dif ferences were found between the two aerosol techniques. The coefficien t of variation for repeated measurements was < 3% for the single-breat h technique and about 10% for the bolus technique. The estimation of a erosol-derived airway diameters by the single-breath method displays s everal advantages over the bolus technique: i) less time-consuming, ii ) better spatial resolution, and iii) higher reproducibility.