Aerosol measurement of airspace diameter correlates with morphometry in normal and papain-exposed air dried lungs.

Aerosol measures of effective airspace diameter (EAD) were correlated with morphometric parameters in a series of 8 canine lungs, 5 of which had been exposed to papain in order to cause experimental emphysema. In an effort to preserve alveolar dimensions without shrinkage, the lungs were fixed by air drying at total lung capacity. EAD was measured with 400-cm2 boluses, with mean penetration index (Pen), defined as volumetric bolus penetration/total lung capacity, equal to 0.34 (EAD400), and with 800-cm2 aerosol boluses, with mean Pen equal to 0.59 (EADdeep). Morphometric analysis, following measurement of EADs, determined the mean linear intercept and other parameters of the chordlength distribution, including the 90th, 95th, and 99th percentiles (p90, p95, p99), the standard deviation, and the geometric standard deviation (GSD). EAD400 was significantly correlated with Lm (r2 = .68, P < .05), p95, (r2 = .85, P < .01), p99 (r2 = .94, P < .001), and GSD (r2 = .94, P < .001). Similar results were found with EADdeep. In general, correlations were stronger between EAD and p95, p99, or GSD than between EAD and Lm. A comparison with a previous similar study relating EAD to morphometry in a series of lungs fixed by formalin fixation found closer agreement between EAD and morphometry when lungs were fixed by air drying. Overall, the data support the validity of EAD as an in vivo method of determining airspace size at total lung capacity.