© 2007 American Thoracic Society
A Pressure Increase Due to Hydrostatic Pressure of Perfluorocarbon Is Not Obvious as Sensed by Pulmonary Stretch ReceptorsTo the Editor:Although a large number of animal studies have been published on the beneficial effects of partial liquid ventilation (PLV), clinical studies such as the recent article by Kacmarek and coworkers (1) have not yet presented results that encourage future clinical applications of this ventilatory strategy. Still, there seem to be remaining questions regarding the effects of perfluorocarbons on the mechanical properties of the lungs, especially the hydrostatic pressure this liquid exerts on different parts of the lung and also the circulation. Roemer and coworkers (2) have suggested means by which the combined hydrostatic pressure in combination with the measured airway pressure could be calculated, and Kacmarek and coworkers (1) suggested that the higher complication rate during PLV than during gas ventilation (GV) might be explained by a higher peak alveolar pressure. These conclusions might be contradicted by our recently published studies performed on mammals with normal lungs during GV and PLV (3, 4). As it is very difficult to assess the pressure changes within the small airways, we explored the activity of slowly adapting pulmonary stretch receptors (PSRs). As these receptors are highly sensitive to changes in pressure and volume, and located in close relation to the alveoli, they provide information about pressure changes from the small airways. To our surprise, the phasic character of PSR activity was maintained in a similar way during GV as during PLV (3). In addition, PSR activity was not higher during PLV than during GV in animals with healthy lungs, indicating no extensive stretching of the lungs during PLV, even at peak pressures of 27 cm H2O (PEEP = 5 cm H2O) (3). This suggests that mechanisms other than hydrostatic pressures might be involved in the possibly detrimental effects of PLV. Also, calculations of hydrostatic pressure need to take into account the position of the subject, the horizontal and vertical branching of the airways, the viscosity of the fluids used, and differences in regional pulmonary ventilation and perfusion.
Uppsala University, Uppsala, Sweden FOOTNOTES Conflict of Interest Statement: None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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