Author: Katie Hefele
Approved: Spring 2019
The American lobster and the Caribbean spiny lobster (like other decapod crustaceans) employ a single pumping chamber, the ventricle (V), to push hemolymph into an arterial tube network. However, the exact mechanism of ventricular filling is not well understood. In previous studies I have investigated hydrostatic pressure distribution in the pericardial sinus (PS) in relation to ventricular lumen pressure over the cardiac cycle in the American lobster. To achieve this, 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 will be expressed as the cardiac filling index (kPa·sec). The cardiac filling index (CFI) was investigated during periods of higher metabolic demand (while the animals walked on a submerged treadmill) when heart rate (HR) is elevated. In the American lobster, I found a significant difference between CFI when comparing rest and exercise conditions. CFI decreased with increased HR during exercise. I 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. I suggest that some ostia may be more important in the ventricular filling process because PS pressure is not homogeneous in this space. Ventricular contractility, measured as the first derivative of ventricular pressure, max dP/dt, for both the American lobster and the Caribbean spiny lobster was measured and compared. Caribbean spiny lobsters had a greater max dP/dt than American lobsters held at 19ºC or 13ºC.