Noninvasive method for measuring respiratory system compliance during pressure support ventilation

Purpose: To date, few methods have been accepted for assessing the respiratory system compliance (C_rs) in patients under assisted ventilation at the bedside. The aim of this study was to evaluate our adaptive time slice method (ATSM) to continuously calculate the C_rs. Methods: One breath is divided into several time periods (slices). For each slice, a compliance value C_i is calculated. The slice width is adapted according to the confidence interval of C_i. After all C_i values are obtained and the outliers are eliminated, the C_rs of this breath is calculated as the mean value of the remainder of C_i´s. Seven patients with Chronic Obstructive Pulmonary Disease were evaluated during pressure support ventilation. The results are compared with the values calculated with the transdiaphragmatic pressure (P_di). Results: 95±4% of the recorded data could be analyzed with ATSM. In 6 patients out of 7, the results delivered with ATSM and with P_di had similar variation (standard deviation) and accuracy (difference<;20%). They were strongly correlated (weighted correlation coefficient = 0.86, p<;10^-5) with a mean difference of 3.22 ml/mbar. Conclusions: The ATSM is a robust method and able to provide accurate C_rs in spontaneously breathing patients during pressure support ventilation noninvasively without extra instrumentation or complicated maneuvers.