Meeting Abstract
105.6 Thursday, Jan. 7 “Bending” the Rules: The role of cardiovascular exercise responses in protecting the brain of diving marine mammals WILLIAMS, T.M.**; NOREN, S.R.; BERRY, P.S.; Univ. of California, Santa Cruz; Univ. of California, Santa Cruz; Disney Animal Programs-The Seas, Orlando, FL williams@biology.ucsc.edu
Cardiovascular adjustments associated with the dive response have long been considered major factors for protecting the brain from hypoxic damage and decompression illness (the “bends”) in marine mammals. A hallmark of this control is bradycardia, a marked lowering of heart rate during submergence. Seemingly in conflict with the dive response is the cardiovascular response to exercise which typically includes elevated heart rate and a redistribution of blood to active tissues. To determine how these competing responses may compromise neuroprotection in diving mammals, we examined variability in heart rate and diving-induced bradycardia in adult bottlenose dolphins, and used these data to model susceptibility to the bends. EKG signals were monitored continuously with an animal-borne microprocessor during rest and exercise when the dolphins were at the water surface or diving to 10 m. Regardless of position in the water column, swimming exercise resulted in a significant increase in mean heart rate over resting values (t = -2.331, df = 13, P = 0.037 for surface swimming; t = -2.362, df = 20, P = 0.028 for submerged). Exercise responses were superimposed on dive responses when submerged. Thus, mean heart rate during routine swimming was 113 ± 6 beats.min-1 near the water surface, 47 ± 4 beats.min-1 when submerged, and approx. 21% higher than the respective resting level for each position. This variability in bradycardia coincident with exercise provides an avenue for increased mobilization of gases associated with decompression illness. Furthermore, it may explain in part the differences in neuroprotecting brain globins observed for mammals specialized for fast swimming or slow diving. (Supported by ONR)
