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Effects of sustained pressure application on compliance and blood gases in healthy porcine lungs
Author(s) -
Markström A.,
Hedlund A.,
Sjöstrand U.,
Nordgren A.,
LichtwarckAschoff M.
Publication year - 2001
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1034/j.1399-6576.2001.451011.x
Subject(s) - medicine , pulmonary compliance , compliance (psychology) , anesthesia , airway , volume (thermodynamics) , inflection point , respiratory physiology , ventilation (architecture) , respiratory system , mathematics , psychology , social psychology , mechanical engineering , physics , geometry , quantum mechanics , engineering
Background: Short periods of sustained increase in airway pressures (Press up ) are believed to re‐open lung areas that collapsed upon induction of anaesthesia. Recruitment of alveolar surface is usually assessed in terms of changes in the pressure–volume (PV) curve. The purpose of this study was to analyse PV‐curves before and after a Press up and to ascertain whether such changes are compatible with the concept of recruitment of lung volume. Methods: During ketamine anaesthesia, 12 healthy piglets were subjected to a Press up with end‐expiratory pressure (PEEP) of 12 cmH 2 O and end‐inspiratory pressure of 40 cmH 2 O. Before and after Press up , PV‐curves were obtained from a slow insufflation of 630 ml at zero PEEP (ZEEP). Results: Compliance was non‐linear both before and after Press up increasing up to 300 ml and sharply decreasing thereafter. After Press up , the entire compliance curve was shifted to a higher absolute level. Up to 100 ml and a pressure level corresponding to the lower inflection point on the PV‐curve (LIP), compliance was higher before Press up . No effects on blood gases could be observed. Conclusion: If the similar shape of the compliance curve corresponds to a similar chain of re‐opening and overdistension events, this would imply that all volume gained by Press up is lost within 10 min, without explaining the higher absolute compliance following Press up . We speculate that a) re‐opening of rapidly collapsing small airways determines the initial compliance increase; b) the lower compliance after Press up until LIP indicates reduced intratidal re‐opening of lung regions; and c) changes in bronchomotor tone induced by Press up raise the absolute compliance, with a similar scenario of alveolar and small airway recruitment now taking place but at different degrees of airway stiffness.