Davis R W, Kanatous S B
Department of Marine Biology, Texas A&M University at Galveston, Galveston, TX 77553, USA.
J Exp Biol. 1999 May;202(Pt 9):1091-113. doi: 10.1242/jeb.202.9.1091.
Unlike their terrestrial counterparts, marine mammals stop breathing and reduce their convective oxygen transport while performing activities (e.g. foraging, courtship, aggressive interactions, predator avoidance and migration) that require sustained power output during submergence. Since most voluntary dives are believed to remain aerobic, the goal of this study was to examine the potential importance of the dive response in optimizing the use of blood and muscle oxygen stores during dives involving different levels of muscular exertion. To accomplish this, we designed a numerical model based on Fick's principle that integrated cardiac output (Vb), regional blood flow, convective oxygen transport (Q(O2)), muscle oxymyoglobin desaturation and regional rates of oxygen consumption (VO2). The model quantified how the optimal matching or mismatching of QO2 to VO2 affected the aerobic dive limit (ADL). We chose an adult Weddell seal Leptonycotes weddellii on which to base our model because of available data on the diving physiology and metabolism of this species. The results show that the use of blood and muscle oxygen stores must be completed at the same time to maximize the ADL for each level of VO2. This is achieved by adjusting Vb (range 19-94 % of resting levels) and muscle QO2 according to the rate of muscle oxygen consumption (VMO2). At higher values of VMO2, Vb and muscle perfusion must increase to maintain an appropriate QO2/VO2 ratio so that available blood and muscle oxygen stores are depleted at the same time. Although the dive response does not sequester blood oxygen exclusively for brain and heart metabolism during aerobic dives, as it does during forced submersion, a reduction in Vb and muscle perfusion below resting levels is necessary to maximize the ADL over the range of diving VO2 (approximately 2-9 ml O2 min-1 kg-1). Despite the reduction in Vb, convective oxygen transport is adequate to maintain aerobic metabolism and normal function in the splanchnic organs, kidneys and other peripheral tissues. As a result, physiological homeostasis is maintained throughout the dive. The model shows that the cardiovascular adjustments known as the dive response enable the diving seal to balance the conflicting metabolic demands of (1) optimizing the distribution and use of blood and muscle oxygen stores to maximize the ADL over the normal range of diving VO2 and (2) ensuring that active muscle receives adequate oxygen as VMO2 increases.
与它们的陆地同类不同，海洋哺乳动物在进行需要在潜水期间持续输出功率的活动（例如觅食、求偶、攻击性互动、躲避捕食者和迁徙）时会停止呼吸并减少对流氧输送。由于大多数自主潜水被认为是有氧的，本研究的目的是研究潜水反应在涉及不同程度肌肉运动的潜水中优化血液和肌肉氧储备利用方面的潜在重要性。为了实现这一目标，我们基于菲克原理设计了一个数值模型，该模型整合了心输出量（Vb）、局部血流、对流氧输送（Q(O2)）、肌肉氧合肌红蛋白去饱和以及局部氧消耗率（VO2）。该模型量化了QO2与VO2的最佳匹配或不匹配如何影响有氧潜水极限（ADL）。我们选择了一只成年威德尔海豹（Leptonycotes weddellii）作为模型基础，因为有关于该物种潜水生理学和代谢的可用数据。结果表明，必须同时完成血液和肌肉氧储备的利用，以在每个VO2水平上最大化ADL。这是通过根据肌肉氧消耗率（VMO2）调整Vb（范围为静息水平的19 - 94%）和肌肉QO2来实现的。在较高的VMO2值时，Vb和肌肉灌注必须增加，以维持适当的QO2/VO2比值，以便同时耗尽可用的血液和肌肉氧储备。尽管在有氧潜水中，潜水反应不像在强制潜水时那样仅为大脑和心脏代谢保留血氧，但在潜水VO2范围（约2 - 9毫升O2·分钟-1·千克-1）内，将Vb和肌肉灌注降低到静息水平以下对于最大化ADL是必要的。尽管Vb降低，但对流氧输送足以维持内脏器官、肾脏和其他外周组织的有氧代谢和正常功能。因此，在整个潜水中生理稳态得以维持。该模型表明，被称为潜水反应的心血管调节使潜水海豹能够平衡相互冲突的代谢需求：（1）在正常潜水VO2范围内优化血液和肌肉氧储备的分布和利用，以最大化ADL；（2）随着VMO2增加，确保活跃肌肉获得足够的氧气。
