Using the Electronic Nose to Identify Airway Infection during COPD Exacerbations

Abstract

Background: The electronic nose (e-nose) detects volatile organic compounds (VOCs) in exhaled air. We hypothesized that the exhaled VOCs print is different in stable vs. exacerbated patients with chronic obstructive pulmonary disease (COPD), particularly if the latter is associated with airway bacterial infection, and that the e-nose can distinguish them.

Methods: Smell-prints of the bacteria most commonly involved in exacerbations of COPD (ECOPD) were identified in vitro. Subsequently, we tested our hypothesis in 93 patients with ECOPD, 19 of them with pneumonia, 50 with stable COPD and 30 healthy controls in a cross-sectional case-controlled study. Secondly, ECOPD patients were re-studied after 2 months if clinically stable. Exhaled air was collected within a Tedlar bag and processed by a Cynarose 320 e-nose. Breath-prints were analyzed by Linear Discriminant Analysis (LDA) with "One Out" technique and Sensor logic Relations (SLR). Sputum samples were collected for culture.

Results: ECOPD with evidence of infection were significantly distinguishable from non-infected ECOPD (p = 0.018), with better accuracy when ECOPD was associated to pneumonia. The same patients with ECOPD were significantly distinguishable from stable COPD during follow-up (p = 0.018), unless the patient was colonized. Additionally, breath-prints from COPD patients were significantly distinguished from healthy controls. Various bacteria species were identified in culture but the e-nose was unable to identify accurately the bacteria smell-print in infected patients.

Conclusion: E-nose can identify ECOPD, especially if associated with airway bacterial infection or pneumonia.

Fig 1. Flow chart of the studied population at every visit.

Fig 2. Identification of bacteria in vitro. Experimental setting.

Fig 3. Two-dimensional principal component (PC) analysis plots: showing breath-prints discrimination between ECOPD versus ECOPD with pneumonia in case of infection (A) and absence of infection (B); ECOPD with infection versus ECOPD without infection (C); ECOPD versus ECOPD with pneumonia without infection (D).

Fig 4. Comparison between e-nose smell-prints among different species of bacteria.

The graphs shows two-dimensional principal component (PC) analysis plots showing smell-prints discrimination between 2 species of bacteria.