Meeting Abstract
P3.7 Tuesday, Jan. 6 Physiological limitations to cardiovascular function in thermally stressed grass shrimp (Palaemonetes pugio) MIKA, T.L.*; REIBER, C.L.; University of Nevada, Las Vegas; University of Nevada, Las Vegas mikat@unlv.nevada.edu
Failure of the crustacean cardiovascular system at temperature extremes may be attributed to several different factors including failure at the cardiac ganglion, failure of myocardial contractile mechanisms, or physical limitation to cardiac function. Oxygen delivery rates must keep pace with the increased metabolic rate observed in poikilothermic animals exposed to increased temperature if aerobic metabolism is to be maintained. One possible mechanism for cardiac failure may be a physical failure of the oxygen delivery system to meet this increased demand. Oxygen delivery is a function of cardiac output, which is in turn a function of both heart rate and cardiac stroke volume. Critical thermal maximum temperatures (CTmax), metabolic rates, and cardiac parameters (heart rate, stroke volume, cardiac output, ejection fraction and pressure-volume loops) were determined in grass shrimp (Palaemonetes pugio) acclimated to 20 C over a temperature range (5-40 C) to identify when and how the cardiovascular system failed. Stroke volume appears to be temperature insensitive in normoxic animals, leaving cardiac output dependent on heart rate. As heart rate increases, diastolic filling time decreases to a point where stroke volume can no longer be maintained, leading to a decline in cardiac output and decreased oxygen delivery. To determine if cardiac failure is indeed the result of decreased oxygen delivery, animals were subjected to the same experiments in a hyperoxic environment. CTmax was determined, and cardiac parameters were measured over the temperature range. Animals placed in a hyperoxic environment had a higher CTmax than animals in a normoxic environment, suggesting a physical limitation in oxygen delivery.
