Determinants of intrapericardial pressure in dogs

This study investigates factors that influence the pressure measured in the intrapericardial (IP) space. Seven dogs were studied after they were anesthetized with pentobarbital sodium. With the chest closed, intravascular volume expansion by dextran infusion from a mean left atrial (LA) transmural pressure of 8.4 +/- 1.2 (SD) to 15.5 +/- 1.6 Torr caused an increase in mean IP of from 2.6 +/- 1.2 to 3.9 +/- 1.7 Torr (P less than 0.01). This reflected a predominant increase in the influence of the cardiac fossa (CF), which accounted for 56% of the IP pressure after volume expansion. In the open-chest state an increase in mean LA transmural pressure from 9.5 +/- 2.5 to 16.4 +/- 0.6 Torr caused IP pressure to increase from 1.1 +/- 0.9 to 3.0 +/- 1.6 (P less than 0.005), representing the influence of the elastic pericardium alone. The use of positive end-expiratory pressure (PEEP) significantly increased the influence of the CF. Of note, the relation of LA to right atrial (RA) pressure was significantly different with and without the influence of the CF; the RA-to-LA ratio was higher with the chest open under each set of volume conditions with and without PEEP. In four dogs, acute transection of the pericardiodiaphragmatic ligaments led to a small (1-2 Torr) but distinct drop in IP pressure. Thus, IP pressure is affected by the intracardiac volume, the elastic pericardium, the CF, and the pericardiodiaphragmatic attachments, all of which must be considered in an analysis of diastolic properties of the heart in situ.