Elastic pressure-volume curves of the respiratory system reveal a high tendency to lung collapse in young pigs

Abstract

Objective: To study pressure-volume (P/V) curves over a wide pressure and volume range in pigs. Design : Dynamic and static P/V curves (P(dyn),/V and P(st)/V) and compliance of the respiratory system were studied. The effects of recruitment, positive end-expiratory pressure (PEEP) and body position were analysed. Setting: Research animal laboratory. Materials: Seven anaesthetised, paralysed and ventilated healthy pigs of 21 kg. Measurements: P/V curves up to a pressure of about 40 cmH2O were recorded with a computer-controlled ventilator. P(st)/V curves were obtained with the static occlusion method and P(dyn)/V curves during an insufflation at a low constant flow rate. Results: P(dyn)/V recording showed a complex pattern. During the insufflation compliance increased, fell, increased and fell again. A 2nd P(dyn)/V recording immediately following the 1st one was displaced towards higher volumes and showed only one maximum of compliance. The difference between the two curves reflected: (1) lung collapse during a period of 5 min of ventilation at zero end-expiratory pressure (ZEEP) following a recruitment manoeuvre. (2) recruitment during the measurement of the 1st P(dyn)/V curve. These observations were similar in the supine and in the left lateral position. After ventilation at PEEP, 4 cmH2O, the signs of collapse and recruitment were reduced. It was confirmed that PEEP offers a partial protection against collapse. P(st)/V curves showed higher volumes and higher compliance values compared to P(dyn)/V curves. This reflects the influence of viscoelastance on P(dyn)/V curves. Conclusion: The study demonstrates a particularly strong tendency to lung collapse in pigs.