Usefulness of the desaturation–distance ratio from the six-minute walk test for patients with COPD

Abstract

Purpose

A straightforward, noninvasive method is needed to assess emphysema and pulmonary hypertension (PH) in COPD patients. The desaturation–distance ratio (DDR) is an index derived from the distance traveled and level of desaturation during a six-minute walk test (6MWT); it has previously been shown to be associated with percentage of forced expiratory volume in the first second of expiration (%FEV_1.0) and percentage of diffusion capacity of the lung for carbon monoxide (%DLCO). The aim of this study was to examine the associations between DDR and emphysema and PH.

Patients and methods

We collected the following data for 74 stable COPD outpatients: lung function tests (%FEV_1.0 and %DLCO), 6MWT distance and desaturation, and area of emphysema on computed tomography (percentage of low attenuation area). Enlargement of the pulmonary artery (PA) was assessed by the ratio of the diameter of the PA to that of the aorta (PA:A ratio) as an index of PH. DDR was calculated by the distance traveled and the degree of desaturation reached during a 6MWT. The relationships between study outcomes were assessed with Spearman’s rank-correlation analysis. Receiver operating characteristic (ROC) curves were used to determine the threshold values with the optimum cutoff points for predicting severe or very severe airway obstruction, pulmonary diffusing capacity disorder, moderate or severe emphysema, and enlargement of the PA.

Results

DDR correlated significantly with %FEV_1.0, %DLCO, %LAA, and PA:A ratio. DDR showed high accuracy (area under the ROC curve >0.7) for predicting severe or very severe airway obstruction, pulmonary diffusing capacity disorder, moderate or severe emphysema, and enlargement of the PA.

Conclusion

The results suggest that DDR is a good index of emphysema and PH in COPD patients. The 6MWT is widely used to assess COPD, and DDR could help with the early diagnosis of COPD.

Keywords:

• six-minute walk test
• COPD
• desaturation–distance ratio
• exercise-induced oxygen desaturation
• emphysema
• pulmonary hypertension

Acknowledgments

The authors would like to thank the members of the Department of Rehabilitation, Kobe City Medical Center West Hospital, including Akihiro Honda, Chisato Nagatani, Takashi Kadooka, Shoko Mitani, Haruko Yamamoto, and Kumi Takamori for cooperation in acquisition of data, and the members of the Department of Community Health Sciences, Kobe University Graduate School of Health Sciences, including Akio Yamamoto, Kazuki Takahashi, Shigefumi Murakami, Kaoru Hanaie, Kentaro Iwata, Yoji Yamada, Yu Watanabe, Takuya Sawada, Kanji Yamada, Yusuke Iwata, Ken Umehara, and Keita Ohashi for constructive comments on this paper. The authors also thank Enago (Tokyo, Japan) for text correction.

Author contributions

Yukari Fujimoto involved in the conception and design of the study, acquisition of data, analysis and interpretation of data, and drafting the article. Yutaro Oki, Masahiro Kaneko, and Akira Ishikawa involved in the conception and design of the study, acquisition of data, analysis and interpretation of data, and revising the article. Hideki Sakai and Shogo Misu involved in the acquisition of data and revising the article. Takumi Yamaguchi, Yuji Mitani, and Hisafumi Yasuda involved in the conception and design of the study, interpretation of data, and revising the article. All authors contributed toward data analysis, drafting and critically revising the paper and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.