GUADAGNOLI, J. A.*; TOBITA, K.; REIBER, C.L.; Touro University – Nevada, Henderson; University of Pittsburgh, PA; University of Nevada, Las Vegas: Assessing changes in the pressure-area relationship in the open circulatory system of a decapod crustacean, Palaemonetes pugio in response to hypoxia.

Cardiovascular changes during hypoxic exposure have been studied extensively in both vertebrate and invertebrate systems. Pressure-volume loops have been used extensively in vertebrate systems to study the cardiac contraction cycle and ventricular function, however this tool has not previously been used to assess ventricular function in the open circulatory system of invertebrates. Invertebrate systems are often regarded as less efficient than closed circulatory systems yet there are remarkable similarities in the pressure wave-forms of the open system of decapod crustaceans to pressure wave forms of animals with a closed system. Given these similarities and the ability of animals to alter cardiac function in response to hypoxia, we used the pressure-area (P-A) relationship as a measure of changing ventricular function in grass shrimp exposed to hypoxia. Grass shrimp were exposed to normoxia (150Torr) and hypoxia (50 and 15Torr) while simultaneously measuring intra-ventricular pressure and ventricular area (via digital imaging). A computer program synchronized the pressure-area signals to generate P-A loops. The P-A relationship of the single ventricle of this open circulatory system possesses many features similar to the P-A relationship of the mammalian ventricle. The area encompassed by the P-A loop provides an estimate of stroke work, which fell during hypoxic exposure. There was a significant drop in peak pressure and an increase in minimal pressure that resulted in an overall fall in pressure during hypoxic exposure. Cardiac output was maintained at 50Torr but fell significantly at 15Torr. These alterations in cardiac parameters contributed to alterations in the P-A relationship and overall cardiac work.