Meeting Abstract
Lobsters and blue crabs use a single pumping chamber, the heart or ventricle, to push hemolymph into an arterial network in a dynamic way. We are interested in characterizing how the ventricle fills and empties over a cardiac cycle in these animals. Part of this work has entailed estimating contractility of the ventricle employing a commonly-used method: analyzing the time-course of pressure change during ventricular systole. We measured pulsatile intraventricular pressure using both fluid-filled catheters connected to strain gauge pressure transducers and catheter-tip transducers, both in resting and walking (metabolically-challenged) lobsters and crabs. In some animals, we measured hemolymph velocity in the dorsal abdominal artery concurrently in an attempt to define the isovolumetric contraction portion of the ventricular pressure pulse. We analyzed the pressure data to determine the first derivative of pressure with respect to time (dP/dt) over the cardiac cycle, focusing on maximum, positive dP/dt during ventricular systole. We found mean values of 20.5 (+/- 5.6 SE; n=5) kPa/sec in resting lobsters and 32.6 (+/- 5.7) kPa/sec when they were walking steadily on a submerged treadmill (a 50% increase in contractility as measured by our method). Preliminarily, and interestingly, ventricular contractility in resting and exercising blue crabs is substantially higher than that for lobsters. Our data suggest that there is a relationship between heart rate and ventricular contractility in both animal types, although this relationship is not clearly-defined at this time.
