Effect of Sodium Nitroprusside on Cerebral Blood Flow

The subject is instructed to hyperventilate for 6 min to provoke a 0.7-1.2 kPa reduction in PaCO2, and the evaluation is repeated if the reduction in PaCO2 is not within this interval. The order of hyperventilation and 6% CO2 breathing is randomized.

The subject breathes a mixture of 6% CO2 (with 21% O2 and 73% N2) from a bag and a face mask for 6 minutes. The order of hyperventilation and 6% CO2 breathing is randomized.

Using incremental intravenous infusion of sodium nitroprusside MAP is reduced by 20% (15%-25%) and then by 40% (35%-45%, MAP minimally at 50 mmHg).