Analysis of Total Lung Compliance in Spontaneously Breathing Patients with the Adaptive Time Slice Method

Purpose: To date, few methods have been accepted for clinical use to evaluate the respiratory system compliance (C_rs) in spontaneously breathing patients at the bedside. The aim of this study was to introduce our adaptive time slice method (ATSM) to continuously calculate the C_rs. Methods: One breathing cycle is divided into several slices along the time axis. For each slice, a least-square-fit based on the first order equation of motion is applied to calculate a slice-specific compliance value C_i and an intercept. The slice width is determined according to the confidence interval of C_i. At the end, after all C_i values are obtained and the outliers are eliminated, the C_rs of this breathing cycle is calculated as the mean value of the C_i. Two spontaneously breathing patients with Chronic Obstructive Pulmonary Disease were included for this preliminary evaluation. The results are compared with the values calculated with the esophageal pressure (P_es). The compliance measured during controlled mechanical ventilation (CMV) with interrupt technique was used as reference. Results: The intercept calculated with the ATSM can be used to depict the pressure generated by respiratory muscles to some extent. No significant differences in the results were observed between the ATSM method (38.07±3.60 ml/mbar, first patient; 27.71±5.11 ml/mbar, second patient) and the method with P_es (38.20±2.81 ml/mbar, first patient; 27.22±4.71 ml/mbar, second patient), while the compliance values during CMV are 22 ml/mbar (first patient) and 30 ml/mbar (second patient). Conclusions: The ATSM is a robust method and may be able to provide accurate C_rs in spontaneously breathing patients without applying invasive and complicated maneuvers.