Search

American lobsters Homarus americanus were exercised on an underwater treadmill at speeds from 1.7 to 8 m min−1 to determine the effects of exercise on heart rate, ventilation rate and acid–base status. Heart and ventilation rates showed almost instantaneous increases at the start of exercise, but the magnitude of the increase was not related to speed. Maximum heart rate was approximately 80–90 beats min−1 and maximum ventilation rate was 175–180 beats min−1 at all speeds tested. Exercise at all speeds caused a decrease in haemolymph pH, with the acidosis after exercise at 8 m min−1 being significantly greater than at the other three speeds. Concomitant with this acidosis was a large increase in partial pressure of carbon dioxide, with the largest increase occurring after exercise at 8 m min−1. The concentration of lactate in the haemolymph increased to similar levels at all speeds of walking. Davenport analysis indicates that the acidosis was predominantly respiratory in nature. Although it was anticipated that heart and ventilation rates would show increases proportional to the speed of exercise, this was not the case. Rather, the responses were fixed regardless of walking speed. The reason for this phenomenon remains unexplained.

Decapod crustaceans with normal heart function respond to the increased oxygen delivery requirements during walking with a step increase in heart and ventilation rate. In American lobsters, ventilation rate increased by the same amount during exercise at two walking speeds (2.4 and 8 m min(-1)); however, ventilation volume was significantly greater at the fastest walking speed (280 mL min(-1)) compared to animals at rest or walking at the slower speed (180 mL min(-1)). The heart responded in a similar manner to locomotion. Heart rate was elevated to the same level at the two different walking speeds, but cardiac stroke volume was greater, implying increased cardiac output, at the faster walking speed. The communication and compensation between the cardiac and ventilatory systems was revealed when the function of one was impaired. Ventilatory rate was significantly elevated when cardiac output was impaired by sectioning two of the alary ligaments and/or the regulatory nerves to the heart. When cardiac output was more severely impaired, ventilation rate was greater. Despite ventilatory compensation, anaerobic metabolism made a greater contribution to energy production with impaired heart function. Hemolymph lactate concentration was three to five times greater in impaired animals than controls. It is known that the ventilatory and cardiac systems of lobsters are coregulated. These data demonstrate that the performance of one system can respond to compensate for impaired function in the other.