THE EFFECT OF THE PERICARDIUM ON CARDIAC DISTENTION AS DETERMINED BY THE X-RAY

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Abstract
Using planimeter measurements of cardiac size and keeping a constant relationship between the distance of film to the dog and to the Coolidge tube, the authors compared cardiac silhouette areas in 41 dogs at various venous pressures, both before and after operative opening of the pericardium. Their principal conclusions are as follows: The attachments of the pericardium to the diaphragm in the dog prevent complete filling of the heart. Hence the heart dilates even at low normal venous pressures, after removal of the pericardium. With these attachments severed, the uncomplicated restraint exerted by the pericardium on diastolic heart size is first noticed at a venous pressure of 0 cm. of water, and reaches an appreciable magnitude at 2 cm. of water. This restraint increases gradually until the heart fills the pericardium and then becomes more and more apparent as the venous pressure is elevated farther. At a venous pressure of about 8 cm. of water, or at an effective venous pressure of 15 or 16 cm. of water, the dog''s heart completely fills the pericardium.

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