Effects of inhaled nitrous oxide 50% on estimated cerebral perfusion pressure and zero flow pressure in healthy volunteers

The role of vascular tone in determining cerebral perfusion pressure is increasingly being appreciated. It has been suggested that zero flow pressure, the arterial pressure at which blood flow ceases, represents the effective downstream pressure of the cerebral circulation. Nitrous oxide is a cerebral vasodilator and may therefore decrease zero flow pressure and increase cerebral perfusion pressure. However, these effects may be opposed by the increase in intracranial blood volume produced by cerebral vasodilation. We studied eight healthy volunteers at normocapnia and studied the effects of the inhalation of nitrous oxide 50% on estimated cerebral perfusion pressure and zero flow pressure using transcranial Doppler ultrasonography. We found that nitrous oxide 50% significantly increased estimated cerebral perfusion pressure (p = 0.03), whilst decreasing zero flow pressure (p = 0.01). These results suggest that the vasomotor effects of nitrous oxide predominate in determining the effective downstream pressure of the cerebral circulation in healthy individuals.