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- Flipper stroke rate and venous oxygen levels in free-ranging California sea lions
- The depletion rate of the blood oxygen store, development of hypoxemia, and dive capacity are dependent on the distribution and rate of blood oxygen delivery to tissues while diving. Although blood oxygen extraction by working muscle would increase the blood oxygen depletion rate in a swimming animal, there is little information on the relationship between muscle workload and blood oxygen depletion during dives. Therefore, we examined flipper stroke rate, a proxy of muscle workload, and posterior vena cava oxygen profiles in four adult female California sea lions (Zalophus californianus) during foraging trips at sea. Flipper stroke rate analysis revealed that sea lions minimized muscle metabolism with a stroke-glide strategy when diving, and exhibited prolonged glides during the descent of deeper dives (> 100 m). During the descent phase of these deep dives, 55±21% of descent was spent gliding with the longest glides lasting over 160 s and covering a vertical distance of 340 m. Animals also consistently glided to the surface from 15-25 m depth during these deeper dives. Venous hemoglobin saturation (SvO2) profiles were highly variable throughout dives, with values occasionally increasing during shallow dives. The relationship between SvO2 and flipper stroke rate was weak during deeper dives, while this relationship was stronger during shallow dives. We conclude that 1) the depletion of oxygen in the posterior vena cava in deep diving sea lions is not dependent on stroke effort, and 2) stroke-glide patterns during dives contribute to a reduction of muscle metabolic rate.
- Tift, Hückstädt, McDonald, Thorson, Ponganis
- Effects of inhalational anesthesia on blood gases and pH in California sea lions
- Despite the widespread use of inhalational anesthesia with spontaneous ventilation in many studies of otariid pinnipeds, the effects and risks of anesthetic-induced respiratory depression on blood gas and pH regulation are unknown in these animals. During such anesthesia in California sea lions (Zalophus californianus), blood gas and pH analyses of opportunistic blood samples revealed routine hypercarbia (highest PCO2 = 128 mm Hg [17.1 kPa]), but adequate arterial oxygenation (PO2 > 100 mm Hg [13.3 kPa] on 100% inspiratory oxygen). Respiratory acidosis (lowest pH = 7.05) was limited by the increased buffering capacity of sea lion blood. A markedly widened alveolar-to-arterial PO2 difference was indicative of atelectasis and ventilation-perfusion mismatch in the lung secondary to hypoventilation during anesthesia. Despite the generally safe track record of this anesthetic regimen in the past, these findings demonstrate the value of high inspiratory O2 concentrations and the necessity of constant vigilance and caution. In order to avoid hypoxemia, we emphasize the importance of late extubation or at least maintenance of mask ventilation on O2 until anesthetic-induced respiratory depression is resolved. In this regard, whether for planned or emergency application, we also describe a simple, easily employed intubation technique with the Casper “zalophoscope” for sea lions.
- Ponganis, McDonald, Tift, Gonzalez, DaValle, Gliniecki, Stehman, Hauff, Ruddick, Howard