Mortola J P
Department of Physiology, McGill University, Montreal, Quebec, Canada.
Respir Physiol. 1999 Aug 3;116(2-3):95-103. doi: 10.1016/s0034-5687(99)00038-9.
The most immediate response to acute hypoxia in newborn mammals is hyperventilation, like in the adult. However. hyperventilation is often achieved by a reduction in metabolic rate (hypometabolism), rather than by an increase in ventilation (hyperpnea). This response is a regulated phenomenon largely based on inhibition of thermogenesis in all its forms, shivering, non-shivering and behavioural, with a resetting of the thermocontrol at a lower value of body temperature (Tb). Forcing Tb to the normoxic value in an hypoxic newborn can therefore provoke responses that are disadvantageous to the general strategy against hypoxia. The small or absent hyperpnea in the hypoxic newborn is the expected response to the decrease in metabolic rate; therefore, it should not be necessarily regarded as an expression of inadequate ventilatory control. However, during hypoxia the low metabolic rate can enhance the relative efficacy of inputs inhibitory on breathing, and this could be a mechanism contributing to ventilatory irregularities and apneas. The advantages of the hypometabolic strategy are numerous, and are at the basis of the extraordinary ability of newborn mammals to survive periods of severe hypoxia. The disadvantages become apparent with chronic hypoxia, because the reduced growth of tissues and organs may be incompatible with survival, or could lead to long-lasting structural and functional alterations.
新生哺乳动物对急性缺氧的最直接反应是过度通气，这与成年动物一样。然而，过度通气通常是通过代谢率降低（低代谢）来实现的，而不是通过通气增加（呼吸急促）。这种反应是一种受调节的现象，很大程度上基于对各种形式的产热（颤抖、非颤抖和行为性产热）的抑制，体温调节设定在较低的体温（Tb）值。因此，在缺氧的新生动物中将Tb强制恢复到常氧值可能会引发不利于应对缺氧总体策略的反应。缺氧新生动物中轻微或无呼吸急促是对代谢率降低的预期反应；因此，不一定应将其视为通气控制不足的表现。然而，在缺氧期间，低代谢率可增强对呼吸有抑制作用的输入的相对效力，这可能是导致通气不规则和呼吸暂停的一种机制。低代谢策略的优点很多，是新生哺乳动物在严重缺氧时期生存的非凡能力的基础。慢性缺氧时缺点就会显现出来，因为组织和器官生长减缓可能与生存不相容，或者可能导致长期的结构和功能改变。
