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A5845 - Postural and Daily Variations in the Single-Breath Diffusion Capacity of the Lungs for Carbon Monoxide
Author Block: M. Gronkvist1, M. LaPelusa2, M. Gennser1, C. A. Machado-Moreira1; 1Environmental Physiology, Royal Institute of Technology, Stockholm, Sweden, 2School of Medicine, University of Texas Rio Grande Valley, Edinburg, TX, United States.
Rationale: The pulmonary diffusion capacity for carbon monoxide (DLCO) test has been regularly used to assess the gas-exchanging capability of the lungs of healthy and diseased individuals. The technical guidelines from the European Respiratory Society (ERS) and the American Thoracic Society (ATS) thoroughly describe various relevant aspects of the DLCO measurement, including the posture of the individual during the test, namely, seated. However, clinical trials show that differences exist when tests take place in the supine position (which is mostly used in hospitalized patients), with less information available in the scientific literature with regard to the standing posture. Furthermore, the 2017-ERS/ATS standards propose an acceptable intra-session variability limit for DLCO (criterion for repeatability): 2 mL•min-1•mmHg-1. Nevertheless, daily (inter-session) variations in DLCO may overcome this limit, and, moreover, these may be different depending on the posture. Herein, we compared DLCO tests performed in sitting (control), standing and supine positions. In addition, we examined daily variations in DLCO at these three postures. Methods: Twelve males and females (40y SD14; 73.7kg SD16.3; 175cm SD9) participated in two trials, separated by at least 24h and conducted at the same time of the day. In each session, a DLCO test was performed in each posture following the ERS/ATS standards. The sequence of the tests was randomized between trials. To adequately address our second aim, it was considered essential that daily variations in the control position situated within the current ERS/ATS limit (N=9). Results: For each posture, data from the two trials were averaged, as intra-postural daily variations were not statistically significant (P>0.05). Higher DLCO was observed when individuals were in the lying position (31.44±2.82 mL•min-1•mmHg-1), followed by the sitting (28.42±1.81 mL•min-1•mmHg-1) and the upright postures (26.66±1.85 mL•min-1•mmHg-1). However, whilst these inter-postural differences were mainly above 2 mL•min-1•mmHg-1, and were consistent with data available in literature, they were not statistically significant (One-way ANOVA; P>0.05). Daily variations in DLCO slightly exceed the accepted limit only in the supine condition (2.04±0.55 mL•min-1•mmHg-1), but inter-postural differences were again not significant [1.09±0.26 (Sitting) and 1.27±0.36 mL•min-1•mmHg-1 (Standing); P>0.05]. Conclusions: Our data confirm that most individuals display greater DLCO values when the test is performed at the supine position, which may be particularly important in clinical scenarios, but these postural variations did not reach statistical significance. Furthermore, it is apparent that daily variations in DLCO are not differently affected by posture.