Background: The alveolar volume (VA), 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 VA is smaller than TLC measured by multiple-breath helium dilution (TLCHe). Objectives: The aim of this study was to investigate whether the VA represents the nonemphysematous lung parts. Methods: We measured VA as part of the diffusing capacity for carbon monoxide (DLCO), TLCHe 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 VA (mean 5.2 liters) and nonemphysematous HRCT lung volume (mean 5.2 liters, r2 = 0.9) and between the TLCHe (mean 6.6 liters) and total HRCT lung volume (mean 6.4 liters, r2 = 0.9). Bland-Altman plots showed considerable disagreement between the VA 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 (nonemphysematous/total HRCT lung volume) was observed (r2 = 0.3 and 0.3, respectively). Conclusion: We concluded that the VA correlates with the nonemphysematous HRCT lung volume, although the two measurements are not equivalent, possibly due to technical factors.

Keywords:
High-resolution computed tomography, Emphysema, Chronic obstructive pulmonary disease, Alveolar volume, Density mask
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2006
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