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

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: PN curves up to a pressure of about 40 cmH(2)O 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 cmH(2)O, 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.