MEASURING ALVEOLAR DIMENSIONS AT TOTAL LUNG CAPACITY BY AEROSOL-DERIVED AIRWAY MORPHOMETRY

A technique based on particle sedimentation, aerosol-derived airway mo rphometry (ADAM), was modified to investigate the morphometry of human lung airspaces at full inflation in 54 subjects with normal lung func tion, ages 18 to 69 years. The technique compares the recovered concen trations of monodisperse aerosol particles after gravitational settlin g during breath holds to determine effective airspace diameters (EADs) as a function of volumetric lung depth. The method is simple and noni nvasive, requiring only several inhalations of aerosol to total lung c apacity, breath holds at end inhalation and exhalation to residual vol ume (RV). The method is sensitive enough to detect differences in the smallest observed airspaces (EAD(min)) due to normal aging of healthy lungs when older subjects are compared to younger subjects. The averag e EAD(min) was larger (p=0.009) for the oldest adults (293+/-54 um, s. d., 50-70 years, n=13) at the deepest volumetric lung depth (near 40% of TLC into the lung) when compared to the youngest adults (250+/-38 u m, s.d., 18-40 years, n=22). The two groups had similar EADs at a dept h of 5% of TLC. No gender difference in EAD(min) was found when compar ing all males and females. No correlation was found between EADs and T LC implying number of alveolar airspaces rather than airspace size det ermines lung volume. The effects of changing the aerosol inhalation vo lume to TLC ratio was also investigated. Compared to the dichotomous W eibel morphometric model, the average EADs of 22 18-40 year old subjec ts were found to be equivalent near 1% TLC and 40% TLC, but were large r in size than the model between those extremes with a maximum differe nce occurring at approximately 3% TLC. This method appears to be extre mely sensitive to in vivo changes in airspace dimensions and may prove useful in determining changes in these dimensions associated with nor mal lung development and early disease states.