Alveolar volume determined by single-breath helium dilution correlates with the high-resolution computed tomography-derived nonemphysematous lung volume.

Background: The alveolar volume (V-A), determined by single-breath helium dilution, is a measure for the total lung capacity (TLC) that is very sensitive to ventilatory disturbances. In chronic obstructive pulmonary disease (COPD), the emphysematous lung parts are less accessible to test gas; therefore, the V-A is smaller than TLC measured by multiple-breath helium dilution (TLCHe). Objectives: The aim of this study was to investigate whether the V-A represents the nonemphysematous lung parts. Methods: We measured V-A as part of the diffusing capacity for carbon monoxide (DLCO), TLC He and spirometry in 50 patients with COPD. High-resolution computed tomography (HRCT) scans of all subjects were analyzed with the density mask method, where parts with an attenuation of less than -950 Hounsfield units were considered as emphysematous. Results: A strong correlation was observed between the V-A (mean 5.2 liters) and nonemphysematous HRCT lung volume (mean 5.2 liters, r(2) = 0.9) and between the TLC He (mean 6.6 liters) and total HRCT lung volume (mean 6.4 liters, r(2) = 0.9). Bland-Altman plots showed considerable disagreement between the V-A and the nonemphysematous HRCT lung volume. A weak correlation between the forced expiratory volume in 1 s (mean 46% predicted) and DLCO (mean 46% predicted) versus the HRCT emphysema ratio (non-emphysematous/ total HRCT lung volume) was observed (R-2 = 0.3 and 0.3, respectively). Conclusion: We concluded that the V-A correlates with the nonemphysematous HRCT lung volume, although the two measurements are not equivalent, possibly due to technical factors. Copyright (C) 2006 S. Karger AG, Basel.