[Macro- and microcirculatory shifts in the brain of cats during hypoxia and hypercapnia].

The cat hemodynamically isolated brain, when transferred from the air artificial ventilation to the respiration with 10% oxygen or 5-10% carbon dioxide mixtures, developed a decrease in vascular resistance and an increase in the venous outflow. The capillary hydrostatic pressure dropped and the intercellular fluid absorption reduced in both cases. The brain capillary filtration coefficient increased in hypoxia and decreased in hypercapnia. The character of emptying of venous cerebral area was passive in hypoxia and active in hypercapnia. The differences in responses of precapillary sphincters, cerebral capillaries and veins were due to involvement of intracerebral noradrenergic system.