Abstract
Polyethylene cannulae were implanted in pre- and post-branchial blood vessels allowing nonstressful blood sampling over a variety of activity ranges in an active tropical elasmobranch, the lemon shark (Negaprion brevirostris). TheP50 was found to be 11.8 Torr at 24°C and pH of 7.7. A Bohr shift of −0.36 was also found. BloodPo2 and oxygen content were measured during rest, routine swimming, and exercise in unanesthetized, free swimming juveniles. Under all conditions venous oxygen levels were low with venousPo2 of 7.1±2.7 Torr, and venous oxygen content (\(C\bar v_{O_2 } \)) of 0.56±0.4 vol%. However, a large variability was found in arterial blood measurements. ArterialPo2 ranged from 7 to 80 Torr, while arterial oxygen content (Cao2) varied from 1.6 vol% to 6.8 vol% among ten experimental animals. A significant increase in arterialPo2, oxygen content, and hematocrit was noted during increased activity. Since the venous system provides little or no oxygen reserve, increased oxygen extraction from the blood (\(Ca_{O_{_2 } } - C\bar v_{O_2 } \)) appears to be met by an increase inCao2 rather than a decrease in\(C\bar v_{O_2 } \). Mechanisms to accomplish this may include increasing hematocrit and vacular gill shunts.
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