Diagnosing ventilation inhomogeneity after COVID-19 by multiple-breath nitrogen washout test

Abstract

The aim was to evaluate the ventilation inhomogeneity (VIH) by the multiple-breath nitrogen washout test (MBNW) after COVID-19 and to identify the relationship of the lung clearance index (LCI) with other functional parameters of the respiratory system. Methods. The cross-sectional study included 35 patients (97% men); the median age was 44 years. Spirometry, body plethysmography, diffusing capacity of the lung for carbon monoxide (DLCO), MBNW test, and impulse oscillometry were performed. Dyspnea was evaluated by mMRC scale. MBNW test was performed using the Easy-One Pro, MBW Module (ndd Medizintechnik AG, Switzerland). Results. The patients were divided into 2 groups. Group 1 included 21 (60%) patients who were not diagnosed with VIH. Group 2 included 14 (40%) patients with VIH. The median testing period was 72 (47 – 109) days from the onset of COVID-19. The median of the maximum volume of lung damage determined by high-resolution computed tomography (CTmax) was 50% in the acute period of the disease and 12% during the study. The medians of all analyzed parameters remained normal in the study cohort as well as in groups 1 and 2, except the resonance frequency (fres) in group 2. Statistically significant differences were found between groups 1 and 2 in the absolute frequency dependence of resistance (R5 – R20), reactance area (AX), fres. Significant differences were also found in pathological changes of vital capacity, forced expiratory volume in the first second (FEV1), (R5 – R20). The abnormalities were more common in group 2. A significant correlation was shown between LCI with the ratio of residual lung volume to total lung capacity, (R5 – R20), AX, fres, relative frequency dependence of resistance, CTmax, FEV1 and trasfer-factor (DLCO). Conclusion. Seventy-two days after the onset of COVID-19, the ventilation inhomogeneity was detected in 40% of the patients, decreased DLCO – in 23%, airway obstruction – in 11.4%, and restrictive ventilatory defect – in 8.6%. Correlations were found between LCI and DLCO, spirometry parameters, body plethysmography, impulse oscillometry, and CTmax.