Elasmobranch pericardial function. 1. Pericardial pressures are not always negative

Area of Science:

• Cardiovascular Physiology
• Comparative Anatomy
• Marine Biology

Background:

• Previous acute studies suggested negative pericardial pressure is crucial for elasmobranch cardiac function.
• The role of pericardial fluid dynamics and the pericardioperitoneal canal (PPC) in vivo was not well understood.

Purpose of the Study:

• To test the hypothesis that pericardial fluid ejection through the PPC during handling affects measured pericardial pressures in horn sharks.
• To investigate chronic pericardial pressure regulation in elasmobranchs.

Main Methods:

• Chronic instrumentation of horn sharks with pericardial catheters.
• Measurement of pericardial pressures and fluid volumes before, during, and after handling.
• Infusion of saline into the pericardium to determine PPC opening pressure.

Main Results:

• Handling horn sharks led to significant pericardial fluid ejection via the PPC, reducing negative pressure.
• Chronic pressures were less negative and less pulsatile than acute pressures; positive pressures were observed.
• The PPC opens at a low infusion volume and pressure, indicating a functional regulatory mechanism.

Conclusions:

• The pericardioperitoneal canal and substantial pericardial fluid volume allow horn sharks to regulate pericardial pressure.
• Elasmobranch cardiac function may tolerate or utilize non-negative pericardial pressures, challenging previous generalizations.
• Pulsatility of pericardial pressure is more critical than a consistently negative mean for venous return in elasmobranchs.