The Lung-thorax Compliance Function Of The Volume Dependence In Mechanical Ventilation

Objective:The objective of this paper is to obtain the volume dependent function of lung-thorax compliance by means of describing the lung-thorax compliance curve of patients with normal pulmonary function in mechanical ventilation, and analyzing the trend of lung-thorax compliance changes in breathing cycle.Methods:Select normal lung function patients undergoing elective surgery, enforce total intravenous anesthesia and mechanical ventilation, and adopt low-flow method and breathing damping terms to describe compliance curve of the lung-thorax. Use a graphical analysis software named Find Graph to obtain the series values of tidal volume and airway pressure, and calculate the corresponding value of lung-thorax compliance so as to observe the changeable trends of compliance in respiratory cycle. Analyze the relationship between the tidal volume and the compliance, then obtain a function with tidal volume (V) as the independent variables, and the lung-thorax compliance(C) as the dependent variable. Then analyze the compliance functional parameter changes between different groups.Results:The accurate and integrated lung-thorax compliance curve has been obtained. Lung-thorax compliance in the respiratory process is constantly changing. In the inspiration phase, the compliance is in slowly increasing trend, with a function of tidal volume relationship:C= a In VT-b, in which a, b are parameters. If compliance is better, a, b values are relatively larger; with the reduction of compliance, a, b values decrease gradually. The compliance is also the ever-changing in the expiration process. In the beginning of expiration the value of lung-thorax compliance is still a gradual increase, while compliance value is a downward trend in end expiratory. The function between compliance and the volume shows CE=cVE2+dVE+e, in which c, d, e are parameters.Conclusion:In the case of the mechanical ventilation in patients with normal lung function, in the context of 1000ml tidal volume, respiratory phase chest compliance increases along with the gradual increase in tidal volume, and seems a logarithmic function of tidal volume.In the beginning stages of breathing, compliance is increasing gradually and slowly while compliance is in a downward trend in end-expiratory.