Accuracy of tidal volume, lung volume, and flow measurements by inductance vest in COPD patients

We analyzed the accuracy of the inductance vest in measuring several ventilatory parameters in five patients with chronic obstructive pulmonary disease (COPD). We assessed tidal volume (VT) accuracy at different respiratory frequencies in different lying body positions with different thoracic and abdominal contributions to breathing and the accuracy over a 4-h time span. Mean percent error was calculated without regard to direction of error. The mean error of vest VT estimation was 7.6% for all body positions studied and 5.6% for right and left lateral positions combined. Vest VT accuracy was unchanged after 4 h and with changes in thoracic and abdominal contributions to VT. The mean errors for inspiratory and expiratory times were 3.3 and 2.0%, respectively. Volume was differentiated to flow. For respiratory rates ranging from 12 to 30 breaths/min, the mean error of the vest and our differentiation circuit in duplicating peak flows measured at the mouth was 3.5%. The ability of the vest to estimate changes in end-expiratory position or functional residual capacity was not as good as with VT; the mean error was 30.7%. For estimation of VT, ventilatory timing, and airflow in COPD patients, the inductance vest performs well. For measurement of changes in lung volume, improvements in vest design need to be made.