Abstract Rationale Body plethysmography measures total lung capacity (TLC) by quantifying compressible air volume in the body, regardless of whether it is involved in gas exchange. In contrast, the single-breath diffusing capacity (DLCO) of the lung for carbon monoxide more specifically captures air volume participating in gas exchange. These two methods produce comparable results in healthy subjects but deviate in subjects with compromised gas exchange, e. g. COPD. Because the DLCO test execution is comparably faster, less costly and less complex than a body plethysmographic test, a method to estimate plethysmography TLC (TLCpleth) using DLCO-derived TLC (TLCDLCO) would be valuable for the diagnosis and monitoring of respiratory diseases. Liu et al. 2021 developed one such approach, which they verified on a cohort of Chinese subjects with COPD. We aim to validate their study on a primarily Caucasian population of both healthy and COPD subjects. Methods 23 healthy subjects and 95 subjects with COPD from all four GOLD grades were recruited from the pulmonary department at the Hirslanden Hospital Zurich, Switzerland. Subjects performed three acceptable spirometry and two acceptable single-breath DLCO maneuvers using the EasyOne Pro (ndd Medical Technologies, Switzerland). All tests complied with ATS/ERS recommendations for acceptability and repeatability. Each subject also performed a body plethysmography test using the Master Screen Body (Jaeger, Höchberg, Germany). We used the DLCO rapid gas analyzer technique to calculate TLCDLCO for each maneuver using tracer gas concentration during the entire inspiration and expiration. We then averaged the two TLCDLCO values per subject and applied the method developed by Liu et al. to obtain adjusted TLCDLCO (TLCDLCOAdj). We compared TLCDLCOAdj to the measured TLCpleth of the same subject with a Bland-Altman plot. Results Figure 1 shows a Bland-Altman plot comparing TLC between adjusted TLCDLCOAdj and measured TLCpleth. Each point corresponds to the data from a single subject. The horizontal axis indicates the average of TLCDLCOAdj and TLCpleth measurements while the vertical axis corresponds to the difference TLCDLCOAdj-TLCpleth. The mean difference (-0. 13 L) is plotted with a dashed line, while 95% limits of agreement (LoA) of ± 1. 32 L are plotted as dotted lines. Conversely, TLCDLCO (without adjustment) had mean ± LoA of -1. 12 ± 1. 55 L. Conclusions A lung volume adjustment method developed on Chinese COPD patients is validated on a mainly Caucasian COPD patient and healthy population. The method reliably estimates plethysmographic lung volumes using lung volume derived from a single-breath gas dilution test. This abstract is funded by: ndd Medizintechnik AG
Zhuang et al. (Fri,) studied this question.