Meeting Abstract
P3.8 Saturday, Jan. 5 Diastolic filling time limits cardiac output in thermally stressed grass shrimp (Palaemonetes pugio): Physiological limits to temperature extremes REIBER, C.L.; MIKA, T.L.*; University of Nevada Las Vegas; University of Nevada Las Vegas carl.reiber@unlv.edu
Metabolic rate increases with increasing temperature in poikilothermic animals, to maintain aerobic metabolism, internal oxygen delivery rates must also increase. Total hemolymph perfusion rates are dependent on cardiac output, which in turn is a function of both heart rate and cardiac stroke volume. Critical thermal maximum temperatures, LT50�s and metabolic rates were determined for Grass shrimp (Palaemonetes pugio) acclimated to 20° C (temp range 5° � 40° C). Cardiac parameters (heart rate, stroke volume, cardiac output, ejection fraction and pressure-volume loops) were determined over the temperature range to determine when and how the system failed. Cardiac energetics were determined using the volume enclosed by the P-V loop as a measure of stroke work and when multiplied by heart rate allowed for the calculation of cardiac work and an estimate of myocardial oxygen consumption. In grass shrimp we have found that cardiac stroke volume appears to be temperature insensitive thus cardiac output or whole body perfusion rates are dependent on heart rate. Thus, the determining parameter for cardiac output is diastolic filling time and as heart rate increases filling time decreases to a point where stroke volume can no longer be maintained and cardiac output declines. Our calculated theoretical minimal cardiac filling time corresponds to the heart rate, and temperature at which these animals fail (CTmax). Given the sensitivity of the crustacean heart to both oxygen and temperature, these data support the hypothesis that the heart may be a primary factor in determining this animal�s maximal critical temperature.
