Recovery of brain energy metabolism following a period of combined hypoxia and hypotension.

Rats were "stressed" by a 30-min period of hypoxia (FIO2 = 7.5%) and hypotension (x arterial pressure = 30 mm Hg), and then "resusciated" by restoring FIO2 = 30% and reinfusing shed blood to restore arterial pressure toward baseline values. Concentrations of brain phosphocreatine, ATP and lactate were measured after "stress" and 20, 60, and 120 min after "resuscitation". A biphasic response was noted in which ATP was initially restored to baseline values by "resuscitation", and then progressively decreased. Physiologic mechanisms to explain the observed data are presented.