Influence of pericardial fluid on cardiogenic gas mixing in the lung

Respirat. Environ. Exercise Physiol. 42(1): 5-12, 1977. -In eight open-chested dogs we measured the end-inspiratory N2 concentration within 12 airways, 2.5-8.3 mm in diameter during constant flow inflations with 0.5 liter of O2 before and after the introduction of saline into the pericardial sac. The critical flow rate necessary to achieve a given end-inspiratory FN2, 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 two 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. We believe that PF decreases cardiogenic gas mixing mainly by protecting the lung from the rotational thrust of the heart during myocardial contraction.