Ventilatory Pattern monitoring by Electrical Impedance Tomography (EIT) in Chronic Obstructive Pulmonary Disease (COPD) patients

Abstract

Introduction. The calibration equations obtained to validate TIE4sys depend on anthropometric parameters which affect the magnitude of the recorded impedance changes, thus the equations for healthy people may not be adequate for COPD patients. Objectives. To validate the procedure and equations developed for health volunteers in a group of COPD patients and to find out a model for the possible differences between the results obtained with the pneumotach and TIE4sys. Materials and Methods. A group of 30 COPD male patients (FEV1/FVC<70%) was used in this research. Anthropometric parameters (age, weight, height, skinfolds) and values of several pulmonary function tests, such as spirometry (FVC, FEV1 and FEV1/FVC), static volumes (RV and TLC) and pulmonary diffusion (DLCO and DL/VA) were recorded. The EIT system (TIE4sys) and a pneumotach were simultaneously connected to monitor the tidal volume. Results. The anthropometric main values of COPD patients were: Age 68±9 years; height 1.65±0.07 m; weight 77±12 kg; BMI 28.3±4.2 kg/m2; Subscapular skinfold 27±9 mm. The mean values of pulmonary function test were Spirometry (M:30) FVC 71±16, FEV1 43±13% of reference value and FVE1/FVC 43±9 %. Static Volume test (M:22) RV 158±44% and TLC 110±19% of reference value. Pulmonary diffusion test (M:19) DLCO 58±17 and DL/VA 76±25 % of reference value. The mean tidal volumes estimated with TIE4sys and the pneumotach were: 0.530±0.22 L and 0.687±0.18 L rho=0.716 (p<0.01). The mean difference was 0.156±0.157 L (p<0.01). The differences show a strong correlation with the subscapular skinfold and the pulmonary diffusion values. Conclusion. The differences of determinations estimated with pneumotach and TIE4sys can be attributed to lung’s internal anatomy (DLCO, DLAdj, DL/VA) and anthropometrical characteristics like subscapular skinfold.KeywordsElectrical Impedance Tomography (EIT)COPDVentilatory Patterncalibration