[An on-line computer procedure for the analysis of pressure-volume relations in ventilated intensive care patients]

The inspiratory pressure-volume relationship (PV curve) describes elastic and viscous attributes of the respiratory system. The most frequently considered parameter is the quasi-static compliance, which has been used for evaluating optimal positive end-expiratory pressure (PEEP) in the treatment of patients with adult respiratory distress syndrome (ARDS). According to Falke and others, this method has not fulfilled its purpose. Since certain effects of PEEP ventilation such as the recruitment of lung areas on the one hand and the overdilatation of opened areas on the other may be reflected in different courses of parts of the PV curve, the consideration of discrete points on this curve may aid in developing mechanical criteria for the evaluation and control of artificial ventilation. Depending on lung elasticity, resistance, and tidal volume, the PV curve has a characteristic shape: initially it increases progressively until a certain airway pressure is reached, then it turns to a regressive incline. As irregularities of the PV curve due to oscillations of the respiratory gases cannot be avoided in practice, certain points (e.g. the inflection point) cannot be determined directly on the basis of the measured sample pairs. Therefore, we developed an on-line analysis of the PV curve, applying a polynomial function by least-square-fit procedure. The transthoracic pressure gradient was measured at the endotracheal tube by a Statham transducer. Inspiratory flow was measured using a Fleisch pneumotachograph with a differential pressure transducer. The flow-pressure signals were registered with a personal computer including an analog/digital interface board. Sample time was set for 10 ms.(ABSTRACT TRUNCATED AT 250 WORDS)