Abstract
The aim of this study was to examine whether electrical impedance tomography (EIT) could determine the presence of ventilation inhomogeneity in patients with chronic obstructive lung disease (COPD) from measurements carried out not only during conventional forced full expiration maneuvers but also from forced inspiration maneuvers and quiet tidal breathing and whether the inhomogeneity levels were comparable among the phases and higher than in healthy subjects. EIT data were acquired in 52 patients with exacerbated COPD (11 women, 41 men, 68 ± 11 years) and 14 healthy subjects (6 women, 8 men, 38 ± 8 years). Regional lung function parameters of forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), forced inspiratory vital capacity (FIVC), forced inspiratory volume in 1 s (FIV1), and tidal volume (VT) were determined in 912 image pixels. The spatial inhomogeneity of the pixel parameters was characterized by the coefficients of variation (CV) and the global inhomogeneity (GI) index. CV and GI values of pixel FVC, FEV1, FIVC, FIV1, and VT were significantly higher in patients than in healthy subjects (p ≤ 0.0001). The ventilation distribution was affected by the analyzed lung function parameter in patients (CV: p = 0.0024, GI: p = 0.006) but not in healthy subjects. Receiver operating characteristic curves showed that CV and GI discriminated patients from healthy subjects with an area under the curve (AUC) of 0.835 and 0.852 (FVC), 0.845 and 0.867 (FEV1), 0.903 and 0.903 (FIVC), 0.891 and 0.882 (FIV1), and 0.821 and 0.843 (VT), respectively. These findings confirm the ability of EIT to identify increased ventilation inhomogeneity in patients with COPD.
Highlights
Chronic obstructive pulmonary disease (COPD) is a highly prevalent lung disease associated with high mortality (GBD 2019 Diseases and Injuries Collaborators, 2020)
The respiratory rates during spontaneous tidal breathing directly preceding these examinations are given in Table 1, and they showed no significant differences between patients and healthy subjects
The global inhomogeneity (GI) indices of pixel values of forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), forced inspiratory vital capacity (FIVC), forced inspiratory volume in 1 s (FIV1), and VT were higher in patients than in healthy subjects (Figure 3)
Summary
Chronic obstructive pulmonary disease (COPD) is a highly prevalent lung disease associated with high mortality (GBD 2019 Diseases and Injuries Collaborators, 2020). The forced full expiration is an established ventilatory maneuver that the subjects are asked to perform during the spirometric examination This maneuver carried out after preceding deep inspiration to total lung capacity, renders the well-known lung function parameters of forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), and their ratio FEV1/FVC. These parameters are used to stage the disease severity, to follow the disease progression and the effects of therapy in patients with COPD. Reference values based on worldwide examinations of tens of thousands of healthy subjects of different genders, ages, and ethnicities are available (Quanjer et al, 2012a,b)
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