Meeting Abstract
The American lobster (like other decapod crustaceans) employs a single pumping chamber, the ventricle, to push hemolymph into an arterial tube network. The ventricle (V) is suspended in a space, the pericardial sinus (PS), by an array of suspensory ligaments. Hemolymph returning from the tissues passes through the gill circulation, is collected in the PS, and moves from the PS into the V during ventricular relaxation through three pairs of openings (called ostia) located in its dorsal, lateral, and ventral walls. However, the exact mechanism of ventricular filling is not well understood. In this study we investigated hydrostatic pressure distribution in the PS in relation to ventricular lumen pressure over the cardiac cycle. Hemolymph pressure was measured continuously in the ventricular lumen and in different locations in the PS in quiescent animals. The digitized pressures were overlaid electronically and the integrated difference between V and PS pressures was expressed as the cardiac filling index (Pa·sec). We also investigated how the cardiac filling index (CFI) changes during periods of higher metabolic demand (while the animals walked on a submerged treadmill) when heart rate (HR) is elevated. We found a significant difference between CFI when comparing rest and exercise conditions (34.3 Pa·sec and 21.5 Pa·sec respectively; n=5). CFI decreased with increased HR during exercise. We found that hemolymph pressure is not homogeneous throughout the PS, and therefore CFI varies within these different regions of the PS. These observed differences likely owe to the complex geometry of the PS. We suggest that some ostia may be more important in the ventricular filling process because PS pressure is not homogeneous in this space.
