Linear and nonlinear analyses of respiratory patterns in preoperative evaluation

Introduction: The adaptive capacity of the respiratory system is of vital importance to cope with its functional decline after major abdominal and thoracic surgery and to prevent postoperative pulmonary complications. In this feasibility study we investigated the discriminatory properties of linear (variability) and nonlinear (entropy) analyses of the respiratory pattern in the assessment of the adaptive capacity of the respiratory system for use in the preoperative stratification and by use of a short-term sample time (3–5 minutes). Methods: Six young healthy volunteers (controls: 2 female/4 male; age 24±4 years) and 10 persons indicated as high-risk for postoperative pulmonary complications (patients: 4 female/6 male; 71±13 years) were included. All subjects performed a respiratory test covering 70 eupneic breathing cycles. Variability of the pressure curve was quantified by the coefficient of variation (CV) of the inter-breath intervals and the amplitudes. Complexity was determined as sample entropy (SE). Differences between the groups were analyzed by the Mann Whitney U test. Results: The median CV of the inter-breath intervals was 0.11 (IR 0.09–0.15) for controls and 0.10 (IR 0.07–0.13) for patients (p=0.45). The median CV of the amplitudes of the inspiratory curves was 0.19 (IQR 0.13–0.22) and 0.13 (IR 0.09–0.20) for controls and patients, respectively (p=0.19). For the expiratory curves the median was 0.22 (IR 0.13–0.31) for controls and 0.12 (IR 0.07–0.22) for patients (p=0.16). The median SE was 0.29 (IQR 0.22–0.43) for controls and 0.19 (IR 0.14–0.24) for patients (p=0.03). Conclusion: We demonstrated the feasibility of linear and nonlinear measures in the preoperative assessment of the adaptive capacity of the respiratory system. Sample entropy significantly distinguished young/healthy persons from persons at high risk for postoperative pulmonary complications after major abdominal and thoracic surgery. (N oninear anlyses of resiratory paterns in preerative evuation 53