Influence of pericardial fluid on cardiogenic gas mixing in the lung

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Abstract
In 8 open-chested dogs, the end-inspiratory N2 concentration was measured within 12 airways, 2.5-8.3 mm in diameter during constant flow inflations with 0.5 l of O2 before and after the introduction of saline into the pericardial sac. The critical flow rate necessary to achieve a given end-inspiratory F[flow]N2, as well as the maximal amplitude of cardiogenic N2 fluctuations, became smaller in the presence of pericardial fluid (PF). In the presence of only 25-50 ml of saline in the pericardium, the effective diffusion coefficient, incorporating cardiogenic gas mixing, decreased by as much as 50-66%, respectively. Studies in 2 dogs with the chest intact showed that PF caused a qualitatively similar impairment of gas mixing during breath holding. Multiple-breath N2 washouts did not reflect the decreases in gas mixing produced by PF. PF decreases cardiogenic gas mixing mainly by protecting the lung from the rotational thrust of the heart during myocardial contraction.

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