Hokkanen J E
Department of Pure and Applied Biology, University of Leeds, U.K.
J Theor Biol. 1990 Aug 23;145(4):465-85. doi: 10.1016/s0022-5193(05)80482-5.
A mathematical model of heat loss from an aquatic animal to the surrounding water is presented. Heat is generated in metabolically active tissues and distributed by circulating blood and by conduction. The time dependent radial temperature profile of the animal is numerically solved from heat transfer equations by a computer. The model is applied to large whales, porpoises, and seals. For the whales, blood circulation to the dermal layer below appendage and body skin surfaces proved to be essential for sufficient heat dissipation. When decreasing the blood flow below a certain value (dependent on sea temperature and whale activity) the large whales would overheat. Blubber thickness was found to be of minor importance in whale thermoregulation, because the blubber coat can be bypassed by blood circulation. On the other hand, it is in general not possible for small porpoises and seals to stay warm in the coldest waters using normal mammalian resting metabolic rates, even if the peripheral circulation is shut off (or artery-vein heat exchangers used). Heat loss can be reduced if the outermost tissue layers are allowed to cool. This is achieved by minimizing convective radial heat flow via the circulation. (For large whales even minute radial blood flow raises the muscle temperatures to the core temperature level.) Seasonal acclimatization of harbour seals is explained by changes in their effective insulation thickness. Differences in whale activity induce changes in the temperature profile mainly within the first few centimeters from the skin surface. These superficial temperatures, if known, could be used to estimate whale metabolic rates. Since they drop close to the sea water temperature within minutes after whale death, the measurements should be done of live whales.
本文提出了一个水生动物向周围水体散热的数学模型。热量在代谢活跃的组织中产生，并通过血液循环和传导进行分布。通过计算机从热传递方程中数值求解动物随时间变化的径向温度分布。该模型应用于大型鲸鱼、鼠海豚和海豹。对于鲸鱼来说，事实证明，向附肢和身体皮肤表面下方的真皮层的血液循环对于充分散热至关重要。当血液流量降至某个值以下（取决于海水温度和鲸鱼活动）时，大型鲸鱼会过热。研究发现，鲸脂厚度在鲸鱼体温调节中不太重要，因为血液循环可以绕过鲸脂层。另一方面，对于小型鼠海豚和海豹来说，即使关闭外周循环（或使用动静脉热交换器），通常也不可能以正常哺乳动物的静息代谢率在最冷的水域中保持温暖。如果允许最外层组织冷却，则可以减少热量损失。这是通过使通过循环的径向对流热流最小化来实现的。（对于大型鲸鱼，即使是微小的径向血流也会将肌肉温度提高到核心温度水平。）港海豹的季节性适应是由其有效隔热厚度的变化来解释的。鲸鱼活动的差异主要在距皮肤表面最初几厘米内引起温度分布的变化。如果已知这些表面温度，则可用于估计鲸鱼的代谢率。由于鲸鱼死后几分钟内这些温度就会降至接近海水温度，因此测量应在活鲸身上进行。
