Investigation of the potential for vascular bubble formation in a repetitively diving dolphin

Abstract

SUMMARYThe production of venous gas emboli (VGE) resulting from altered dive behavior is postulated as contributing to the stranding of beaked whales exposed to mid-frequency active sonar. To test whether nitrogen gas uptake during repetitive breath-hold diving is sufficient for asymptomatic VGE formation in odontocetes, a bottlenose dolphin (Tursiops truncatus Montagu) was trained to perform 10-12 serial dives with 60s surface intervals to depths of 30, 50, 70 or 100m. The dolphin remained at the bottom depth for 90s on each dive. Doppler and/or two-dimensional imaging ultrasound did not detect VGE in the portal and brachiocephalic veins following a dive series. Van Slyke analyses of serial, post-dive blood samples drawn from the fluke yielded blood nitrogen partial pressure (P N2 ) values that were negligibly different from control samples. Mean heart rate (HR; ±1s.d.) recorded during diving was 50±3beatsmin -1 and was not significantly different between the 50, 70 and 100m dive sessions. The absence of VGE and elevated blood P N2 during post-dive periods do not support the hypothesis that N 2 supersaturation during repetitive dives contributes to VGE formation in the dolphin. The diving HR pattern and the presumed rapid N 2 washout during the surface-interval tachycardia probably minimized N 2 accumulation in the blood during dive sessions.

Evaluating cardiac physiology through echocardiography in bottlenose dolphins: using stroke volume and cardiac output to estimate systolic left ventricular function during rest and following exercise

“…Our resting f H was significantly lower (41±8 beats min −1 ) than values from previous studies in the awake, unrestrained (60-105 beats min −1 ; Houser et al, 2010;Noren et al, 2004;Williams et al, 1993) or anesthetized bottlenose dolphin (84-140 beats min −1 ; Sommer et al, 1968). The most likely explanation is our conservative approach in estimating f H and SV exclusively after cardiac frequency had stabilized in between breaths.…”

“…In cetaceans, no published data exist on cardiac contractile responses during forced or voluntary dives, with most studies being largely focused on cardiac frequency (Houser et al, 2010;Noren et al, 2004). One study measured CO in anesthetized bottlenose dolphins (Sommer et al, 1968), but the experimental artifacts of mechanical ventilation under general anesthesia and restraint out of water may have altered normal physiological function, so these data may have to be viewed with caution when compared with awake individuals.…”

Evidence of injury caused by gas bubbles in a live marine mammal: barotrauma in a California sea lion Zalophus californianus

“…Houser and colleagues have recently re-visited the question of nitrogen saturation in the bottlenose dolphin Tursiops truncatus and concluded that nitrogen supersaturation is likely. However, they were unable to demonstrate vascular bubble formation in a repetitively diving trained animal (Houser et al 2010).…”

Solubility of nitrogen in marine mammal blubber depends on its lipid composition

“…These instruments yield very reliable solubility measurements and are still in use today (e.g. Houser et al, 2010); however, their use is somewhat limited as so few remain in existence. The empirical studies that have been carried out on lipids (for reviews, see Langø et al, 1996;Weathersby and Homer, 1980) indicate that manufactured oils of different biochemical composition have different N 2 solubility coefficients (e.g.…”