Meeting Abstract
105.5 Thursday, Jan. 7 Bradycardia Redefined: A Variable Cardiovascular Dive Response in Dolphins NOREN, S.R.*; WILLIAMS, T.M.; KENDALL, T.; CUCCURULLO, V.; Univ. of California, Santa Cruz; Univ. of California, Santa Cruz; Univ. of California, Santa Cruz; The Dolphin Experience, Freeport, Bahamas snoren@biology.ucsc.edu
The textbook description of the dive response for marine mammals is marked decrease in heart rate (HR) upon submergence, stable bradycardia at depth, and anticipatory tachycardia on ascent. Based primarily on lab studies, it is difficult to evaluate the effects of routine underwater activities on this pattern for free-ranging diving mammals. We simultaneously recorded electrocardiographic signals and behavior, including stroke frequency (SF) as an index of exercise intensity, in 3 adult bottlenose dolphins (Tursiops truncatus) during rest on the water surface and during rest, low intensity activity, and swimming at 15 m depth in the ocean. Mean HR (±SD) in beats per minute (bpm) during rest at the surface was 105 ± 8 bpm (n = 25), more than double predicted rates based on allometric regressions for mammals. As expected for the dive response, resting HR during submergence (40 ± 6 bpm, n = 15) was significantly lower than recorded on the water surface. Underwater activity modified the level of bradycardia. Low intensity activity such as head bobbing resulted in a mean HR of 56 ± 7 bpm (n = 7) that was 40% higher than submerged rest. Furthermore, in contrast to previous reports for diving mammals, submerged HR was correlated with exercise intensity and was described by HR = 41 + 12 SF (range: 0 – 2.5 strokes sec-1; r = 0.88, P = 0.0001, n = 25) where HR is in bpm and SF is in strokes sec-1. These data demonstrate that the “dive reflex” is not an invariable response in dolphins. Rather, it is graded by activity, similar to the effect of exercise on HR in terrestrial mammals. In addition, based on HR predictions for other mammals, the “normal” resting physiological state of dolphins seems to occur when these mammals are under water. (Supported by ONR)
