Validation of exhaled volatile organic compounds analysis using electronic nose as index of COPD severity

Abstract

Aim

Six-minute walking test distance (6MWD) and body mass index, obstruction, dyspnea and exercise (BODE) index are measures of functional status in COPD patients, but require space, time and patient’s compliance. Exhaled volatile organic compounds (VOCs) analysis via electronic nose is a quick and easy method that has already been used to discriminate COPD phenotypes. The aim of this study is to evaluate whether VOCs analysis can predict functional status and its variation over time in COPD patients.

Methods

A monocentric prospective study with 1 year of follow-up was carried out. All patients underwent pulmonary function tests, arterial gas analysis, bioimpedance analysis, 6-minute walking test, and VOCs collection. Exhaled breath was collected with Pneumopipe^® and analyzed using BIONOTE electronic nose. Outcomes prediction was performed by k-fold cross-validated partial least square discriminant analysis: accuracy, sensitivity and specificity as well as Cohen’s kappa for agreement were calculated.

Results

We enrolled 63 patients, 60.3% men, with a mean age of 71 (SD: 8) years, median BODE index of 1 (interquartile range: 0–3) and mean 6MWD normalized by squared height (n6MWD) of 133.5 (SD: 42) m/m². The BIONOTE predicted baseline BODE score (dichotomized as BODE score <3 or ≥3) with an accuracy of 86% and quartiles of n6MWD with an accuracy of 79%. n6MWD decline more than the median value after 1 year was predicted with an accuracy of 86% by BIONOTE, 52% by Global Initiative for Chronic Obstructive Lung Disease (GOLD) class and 78% by combined BIONOTE and GOLD class.

Conclusion

Exhaled VOCs analysis identifies classes of BODE and n6MWD quartiles, and outperforms GOLD classification in predicting n6MWD variation.

Keywords:

• volatile organic compounds
• electronic nose
• 6-minute walking test
• COPD
• functional status
• BODE index

Acknowledgments

The authors would like to thank Dr Federica Sabato, Dr Veronica Adiletta and Dr Leonardo Grisafi for their help in data collection. This study was funded by an unrestricted grant from Fondazione Roma, Italy.

Author contributions

PF, CP and RAI participated in planning the study. PF and CP performed data analyses. All authors participated in data collection, revised the final version of the manuscript and gave their consent to publication.

Disclosure

The authors GP, MS and RAI are holders of the Pneumopipe^® patent. The other authors report no conflicts of interests in this work.