- Email: [email protected]
Is re-breathe diffusing capacity better than single breath in emphysema patients?
Respiratory Physiology & Neurobiology 184 (2012) 113
Contents lists available at SciVerse ScienceDirect
Respiratory Physiology & Neurobiology journal homepage: www.elsevier.com/locate/resphysiol
Letter to the Editor Is re-breathe diffusing capacity better than single breath in emphysema patients? We read the article titled “a comparison of single breath and rebreathe diffusing capacity in emphysema patients and controls” with great interest (Weingarten et al., 2012). In this study the authors found that the DLCO measured by single breath method (DLCO-SB) is less than that measured by re-breathe technique (DLCO-RB) in patients having emphysema. However, we feel that DLCO-RB may be an overestimation of actual transfer of gases. It is known that emphysema causes hypoxia mainly due to ventilationperfusion mismatch and hence, suggests reduced transfer of gases in emphysema patients. The median DLCO in this study is 80% predicted suggesting more than 50% of emphysema patients had normal DLCO. Considering the severity of COPD patients included in the study, we feel that DLCO-RB probably measured falsely high values.
of air available for dilution of the inhaled gas (CO and tracer gas) is substantially higher during re-breathe comparison (very high FRC in COPD) than with DLCO-SB comparison (modestly high TLC in COPD). Hence, the DLCO may get overestimated by re-breathe technique in COPD patients. In addition, we would also like to draw attention to the limitations of the study not discussed by the authors. Inclusion of only 53 out of 382 COPD patients could have lead to significant selection bias. In addition the authors did not adequately discuss the reasons for exclusion of 16 patients from the final analysis. This exclusion might have had bearing on the results in the small sample of subjects in the study. In spite of the limitations, we feel the study has made valuable observations and as suggested by the authors the re-breathe technique may provide better DLCO values than DLCO-SB. However, more studies with consistent observations are required before we choose DLCO-RB over DLCO-SB. We feel presently a more standardized and studied “single breath” method should be used for DLCO measurements even in emphysema patients as advocated by ATS/ERS task force (MacIntyre et al., 2005). References
Fig. 1. Lung volumes in normal subjects and COPD patients. Total lung capacity (TLC) increases marginally while the functional residual capacity (FRC) increases drastically in COPD compared to normal adults.
Higher measurement with DLCO-RB could be because of physiological differences in the lung volumes. The DLCO-SB is measured at total lung capacity (TLC) and DLCO-RB at functional residual capacity (FRC). The TLC either remains unaffected or increases marginally in COPD patients but there is substantial increase in FRC in COPD patients compared to normal healthy adults (O’Donnell et al., 2001), see Fig. 1. This means that compared to normal adults, the amount
1569-9048/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.resp.2012.08.007
MacIntyre, N., Crapo, R.O., Viegi, G., Johnson, D.C., Van der Grinten, Brusasco, V., Burgos, F., Casaburi, R., Coates, A., Enright, P., Gustafsson, P., Hankinson, J., Jensen, R., McKay, R., Miller, M.R., Navajas, D., Pederson, O.F., Pellegrino, R., Wanjer, J., 2005. Standardization of the single-breath determination of carbon monoxide uptake in the lung. European Respiratory Journal 26, 720–735. O’Donnell, D.E., Revill, S.M., Webb, K.A., 2001. Dynamic hyperinflation and exercise intolerance in chronic obstructive pulmonary disease. American Journal of Respiratory and Critical Care Medicine 164, 770–777. Weingarten, J.A., Lederer, D.J., Ozturk, E., Milite, F., Mooney, A.M., Thomashow, B.M., Basner, R.C., 2012. A comparison of single breath and re-breathe diffusing capacity in emphysema patients and controls. Respiratory Physiology and Neurobiology, http://dx.doi.org/10.1016/j.resp.2012.05.009.
N. Vanjare R. Kodgule ∗ B. Brashier S. Salvi Chest Research Foundation, Marigold Premises, Kalyani Nagar, Pune 411 014, India ∗ Corresponding author. E-mail address: drrahul@crfindia.com (R. Kodgule)
Contents lists available at SciVerse ScienceDirect
Respiratory Physiology & Neurobiology journal homepage: www.elsevier.com/locate/resphysiol
Letter to the Editor Is re-breathe diffusing capacity better than single breath in emphysema patients? We read the article titled “a comparison of single breath and rebreathe diffusing capacity in emphysema patients and controls” with great interest (Weingarten et al., 2012). In this study the authors found that the DLCO measured by single breath method (DLCO-SB) is less than that measured by re-breathe technique (DLCO-RB) in patients having emphysema. However, we feel that DLCO-RB may be an overestimation of actual transfer of gases. It is known that emphysema causes hypoxia mainly due to ventilationperfusion mismatch and hence, suggests reduced transfer of gases in emphysema patients. The median DLCO in this study is 80% predicted suggesting more than 50% of emphysema patients had normal DLCO. Considering the severity of COPD patients included in the study, we feel that DLCO-RB probably measured falsely high values.
of air available for dilution of the inhaled gas (CO and tracer gas) is substantially higher during re-breathe comparison (very high FRC in COPD) than with DLCO-SB comparison (modestly high TLC in COPD). Hence, the DLCO may get overestimated by re-breathe technique in COPD patients. In addition, we would also like to draw attention to the limitations of the study not discussed by the authors. Inclusion of only 53 out of 382 COPD patients could have lead to significant selection bias. In addition the authors did not adequately discuss the reasons for exclusion of 16 patients from the final analysis. This exclusion might have had bearing on the results in the small sample of subjects in the study. In spite of the limitations, we feel the study has made valuable observations and as suggested by the authors the re-breathe technique may provide better DLCO values than DLCO-SB. However, more studies with consistent observations are required before we choose DLCO-RB over DLCO-SB. We feel presently a more standardized and studied “single breath” method should be used for DLCO measurements even in emphysema patients as advocated by ATS/ERS task force (MacIntyre et al., 2005). References
Fig. 1. Lung volumes in normal subjects and COPD patients. Total lung capacity (TLC) increases marginally while the functional residual capacity (FRC) increases drastically in COPD compared to normal adults.
Higher measurement with DLCO-RB could be because of physiological differences in the lung volumes. The DLCO-SB is measured at total lung capacity (TLC) and DLCO-RB at functional residual capacity (FRC). The TLC either remains unaffected or increases marginally in COPD patients but there is substantial increase in FRC in COPD patients compared to normal healthy adults (O’Donnell et al., 2001), see Fig. 1. This means that compared to normal adults, the amount
1569-9048/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.resp.2012.08.007
MacIntyre, N., Crapo, R.O., Viegi, G., Johnson, D.C., Van der Grinten, Brusasco, V., Burgos, F., Casaburi, R., Coates, A., Enright, P., Gustafsson, P., Hankinson, J., Jensen, R., McKay, R., Miller, M.R., Navajas, D., Pederson, O.F., Pellegrino, R., Wanjer, J., 2005. Standardization of the single-breath determination of carbon monoxide uptake in the lung. European Respiratory Journal 26, 720–735. O’Donnell, D.E., Revill, S.M., Webb, K.A., 2001. Dynamic hyperinflation and exercise intolerance in chronic obstructive pulmonary disease. American Journal of Respiratory and Critical Care Medicine 164, 770–777. Weingarten, J.A., Lederer, D.J., Ozturk, E., Milite, F., Mooney, A.M., Thomashow, B.M., Basner, R.C., 2012. A comparison of single breath and re-breathe diffusing capacity in emphysema patients and controls. Respiratory Physiology and Neurobiology, http://dx.doi.org/10.1016/j.resp.2012.05.009.
N. Vanjare R. Kodgule ∗ B. Brashier S. Salvi Chest Research Foundation, Marigold Premises, Kalyani Nagar, Pune 411 014, India ∗ Corresponding author. E-mail address: drrahul@crfindia.com (R. Kodgule)