Elastic properties of the lung and the chest wall in young and adult healthy pigs.

Understanding of the elastic pressure/volume (Pel/V) curve is still limited in health and disease. The aim of the present study was to elucidate the Pel/V curve and elastance of the respiratory system (ERS) lung (EL) and chest wall (ECW) in healthy pigs. Six young (20.8 kg) and seven adult (58.9 kg), anaesthetized, paralysed and ventilated pigs were studied. Pel/V curves were recorded at zero end-expiratory pressure (ZEEP) and at positive end-expiratory pressure (PEEP) up to 40 cmH2O with a computer controlled ventilator during an insufflation at a low, constant flow. Pel/V curves of the respiratory system showed a complex pattern in both young and adult pigs. During the insufflation, ERS decreased, increased, fell, and increased again. A second Pel/V curve recorded immediately after the first one showed lower elastance and only one early fall in ERS. ECW fell over the initial segment and was then nearly stable. Difference between 1st and 2nd curves reflected changes in EL caused by recruitment during the 1st insufflation. At PEEP, such signs of collapse and recruitment were reduced. A strong tendency to lung collapse contributes to a complex pattern of elastic pressure/volume curves. At low volumes and distending pressures the chest wall contributes significantly to changes in respiratory system elastance.