The effects of progressive hypoxia on the crustacean cardiovascular system: a comparison of the freshwater crayfish, ( Procambarus clarkii  ), and the lobster ( Homarus americanus )

The heart rate of crayfish (Procambarus clarkii) and lobsters (Homarus americanus) decreased (bradycardia) as partial pressure of O sub(2) (Po sub(2)) decreased, yet cardiac output (V sub(b)) was maintained via an increased stroke volume (S sub(v)) to Po sub(2)s of 40 mmHg and 75 mmHg for crayfish and lobsters, respectively. V sub(b) was redistributed in both animals. Flow through the anterior aorta increased while flow dropped through the posterior aorta and sternal artery to a Po sub(2) of 30 mmHg; below this flow was no longer maintained in crayfish. In the lobster, flow increased to the lateral arteries and the ventral thoracic artery while flow through the anterior and posterior aortas, sternal artery and ventral abdominal artery decreased to a Po sub(2) of 75 mmHg. Anterior hemolymph flow was maintained or increased in both animals presumably to supply nervous tissue and cephalic sense organs better. Crayfish showed an increase in intracardiac and mean arterial hemolymph pressures as Po sub(2) declined. The increased pressures combined with the net increase in cardiac filling pressure and diastolic filling time could have accounted for the increased S sub(V). The cardiovascular response exhibited by both the crayfish and lobster was Po sub(2) dependent; below a critical water Po sub(2) active compensation was no longer observed.