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Giai đoạn cuối của căn bệnh này (khoảng 2 tuần sau khi bắt đầu) được đi kèm bởi sự vắng mặt của LIP và tuân thủ của một nhỏ hơn, có thể là do sự phát triển của xơ kẽ [4, 9]. LIP thấy trong giai đoạn đầu của ARDS được cho là đại diện cho mở lại sụp đổ đường hô hấp và các đơn vị phế nang trong nguồn cảm hứng, trong khi vắng mặt của nó trong giai đoạn cuối có thể phản ánh một phổi cứng. . | 34 V.R. Cagido W.A. Zin Factors altering the P-V curve Duration of disease The modifications of the P-V curve during the course of ARDS were described by Matamis et al. who used the super-syringe method 9 . They showed that in the early stage of ARDS although the LIP could be detected the compliance calculated using the linear segment was normal. The late stage of the disease approximately 2 weeks after its onset was accompanied by the absence of LIP and a smaller compliance probably due to the development of interstitial fibrosis 4 9 . The LIP seen in the early stage of ARDS was believed to represent the reopening of collapsed airways and alveolar units during inspiration while its absence in the late stage could reflect a stiffer lung. Use of PEEP During inspiration two phenomena may occur recruitment and distension of the distal air spaces. When the alveoli open up compliance increases and it persists throughout alveolar recruitment. However after a certain point compliance falls. The benefits of the use of PEEP come in part from the resulting increase in FRC. The shape of the P-V curve and the value of LIP may vary according to the end-expiratory lung volume that marks the beginning of inspiration 14 . Increasing PEEP values can eliminate the LIP and decrease the compliance at the linear portion of the curve. These phenomena may theoretically reflect recruitment of some parts of the lung and distension or overdistension of other regions. The effect of PEEP on LIP may indicate good lung recruitment 14 31 32 . Effect of the chest wall The effects of the chest wall on the slope of the P-V curve have been investigated by many researchers 33-35 . In patients in whom ARDS was consequent on major abdominal surgery a rightward shift of the thoracic and abdominal V-P curves was observed. The flattening of the P-V curve of the respiratory system and lung was attributed in part to the higher abdominal pressure which increases chest wall stiffness and decreases its .
