THE STATIC PRESSURE-VOLUME RELATIONSHIP OF THE RESPIRATORY SYSTEM DETERMINED WITH A COMPUTER-CONTROLLED VENTILATOR

The pressure-volume relationship of the respiratory system offers a gu ideline for setting of ventilators. The occlusion method for determina tion of the static elastic pressure-volume (Pel(st)/V) relationship is used as a reference and the aim of the study was to improve it with r espect to time consumption and precision of recording and analysis, Th e inspiratory Pel(st)/V curve was determined with a computer-controlle d ventilator using its pressure and flow sensors. During an automated procedure, an operator-defined volume history preceded each of a numbe r of study breaths. These were interrupted at different volumes evenly distributed over a predefined volume interval. Total positive end-exp iratory pressure (PEEP) was measured and could be separated into its c omponents, external PEEP and auto-PEEP. The volume relationship betwee n the curve and the current tidal volume was defined. An analytical me thod for definition of a linear segment of the Pel(st)/V curve and det ermination of its compliance is presented. In eight healthy human anae sthetized subjects duplicate Pel(st)/V curves were studied with respec t to compliance and the position along the volume axis of the linear s egment. The difference in compliance between measurements was 1.6+/-1. 3 ml cmH(2)O(-1) or 1.2+/-0.9%. The position of the curve differed bet ween measurements by 15+/-10 ml or by 1.1+/-0.9%. In a patient with ac ute lung injury the feasibility of applying a numerical method for a m ore detailed description of the Pel(st)/V curve was illustrated.