Robertshaw David
Weill Cornell Medical College in Qatar, PO Box 24144, Doha, Qatar.
J Appl Physiol (1985). 2006 Aug;101(2):664-8. doi: 10.1152/japplphysiol.01380.2005. Epub 2006 May 4.
Panting is a controlled increase in respiratory frequency accompanied by a decrease in tidal volume, the purpose of which is to increase ventilation of the upper respiratory tract, preserve alveolar ventilation, and thereby elevate evaporative heat loss. The increased energy cost of panting is offset by reducing the metabolism of nonrespiratory muscles. The panting mechanism tends to be important in smaller mammalian species and in larger species is supplemented by sweating. At elevated respiratory frequencies and body temperatures alveolar hyperventilation begins to develop but is accompanied by a decline in the control of carbon dioxide partial pressure in arterial blood, probably through central chemoreceptors. Most heat exchange takes place at the nasal epithelial lining, and venous drainage can be directed to a special network of arteries at the base of the brain whereby countercurrent heat transfer can occur, which results in selective brain cooling. Such a phenomenon has also been suggested in nonpanting species, including humans, and although originally thought to be a mechanism for protecting the thermally vulnerable brain is now considered to be one of the thermoregulatory reflexes whereby respiratory evaporation can be closely controlled in the interests of thermal homeostasis.
喘气是呼吸频率的可控增加，同时伴有潮气量减少，其目的是增加上呼吸道的通气量，维持肺泡通气，从而提高蒸发散热。喘气增加的能量消耗通过减少非呼吸肌的代谢来抵消。喘气机制在较小的哺乳动物物种中往往很重要，而在较大的物种中则通过出汗来补充。在呼吸频率和体温升高时，肺泡过度通气开始出现，但可能通过中枢化学感受器，同时伴随着动脉血二氧化碳分压控制的下降。大多数热交换发生在鼻上皮衬里，静脉引流可导向脑底部的一个特殊动脉网络，从而发生逆流热传递，导致选择性脑冷却。在包括人类在内的非喘气物种中也有人提出过这种现象，尽管最初认为这是一种保护易热的大脑的机制，但现在被认为是一种体温调节反射，通过这种反射可以为了热稳态而密切控制呼吸蒸发。
