Increased cerebral oxygen delivery during sodium nitroprusside administration despite reduced blood flow velocity in the middle cerebral artery

Abstract

We investigated whether the nitric oxide donor sodium nitroprusside (SNP) dilates and phenylephrine constricts the MCA in 10 supine young healthy volunteers. We combined transcranial Doppler (TCD) measurements of the MCA with near infrared spectroscopy (NIRS) over the frontal cortex. Cerebral oxyhemoglobin and total hemoglobin increased by 14±1 and 15±1 μM/L with 100μg SNP despite hypotension, and were reduced by 6±1 and 7±1 μM/L with 150μg phenylephrine despite hypertension. SNP increased NIRS derived cerebral blood flow estimates by approximately 40±8% from baseline, while TCD derived CBFv decreased by 15±3%. Phenylephrine decreased NIRS derived cerebral blood flow estimates by approximately 11±5% from baseline, while TCD derived CBFv increased by 5±3%. Studies using upright tilt and lower body negative pressure were consistent with the literature and demonstrated similar relative changes in cerebral blood flow and CBFv as orthostatic stress progressed. We concluded that the MCA dilates to SNP and constricts to phenylephrine, but does not dilate during orthostatic stress in healthy volunteers. Supported by NIH (HL‐074873) and (HL‐087803).