Anoxia tolerance to oxygen necessity: Paradigm shift in the physiology of survival of apneic deep hypothermia in neonatal rodents

Neonatal small rodents stop breathing at body temperatures of 0-6 degreesC, yet they often tolerate such hypothermia for several hours and recover spo ntaneously when rewarmed. The prevailing paradigm of deep-hypothermia toler ance for half a century has been that the heart stops heating; oxygen uptak e and delivery from the environment stop; tissues are tolerant of anoxia; a nd this anoxia tolerance is a key to survival. I here report that the heart does not stop beating in neonates that survive hours of hypothermia, even in species earlier reported to undergo cardiac arrest. Furthermore, as was reported in 1955 but ignored, neonates consume oxygen steadily at low rates while apneic, and this oxygen consumption is essential for survival. Thus, the old paradigm must be succeeded by a new one: Although tissues may beco me hypoxic and benefit From hypoxia tolerance during apneic deep hypothermi a, oxygen is taken up steadily across the lungs; the circulatory system lik ely transports oxygen: and certain vital tissues require oxygen influx if a neonate is to survive.