Sodium Nitroprusside Induced Vasodilatation Encompasses Cerebral Blood Flow in Young Men

Abstract

PurposeSodium nitroprusside (SNP) reduces blood pressure by vasodilatation, but is reported to lower cerebral blood flow (CBF). We evaluated the influence of SNP on CBF when mean arterial pressure (MAP) was reduced by 20% and by 40%, while keeping MAP ≥ 50 mmHg.MethodsIn 19 healthy men (age 24 ± 4 years; mean ± SD) right internal carotid (ICA) and vertebral artery (VA) blood flow was evaluated by duplex ultrasound. Cerebral CO2 reactivity was determined during hyperventilation and CBF ((ICA + VA flow) × 2) also ‘corrected’ according to reduction in arterial CO2 tension. Evaluation of MAP was by brachial artery catheterisation and total peripheral resistance was derived by pulse contour analysis (Modelflow). Analysis was by a repeated measure mixed model and comparison of the relative change in ICA vs. VA flow was by paired t‐test. Values are presented as mean ± SD or median (IQR) and changes as mean (95% CI). The study was registered at clinicaltrials.gov (NCT03317652) prior to subject enrolment.ResultsThree subjects developed presyncopal symptoms during the large reduction in MAP and data obtained at that time was not included in the analysis. Infusion of SNP at 2.0 μg kg–1 min–1 (1.5–2.5) reduced MAP by 17 ± 5% and at 8.6 μg kg–1 min–1 (6.0–9.4) by 31 ± 6% (both P < 0.0001) as total peripheral resistance decreased from 17 ± 4 to 10 ± 2 and 7 ± 1 l min−1 mmHg−1 (both P < 0.001). The PaCO2 decreased from 5.5 ± 0.3 to 5.2 ± 0.4 and 4.9 ± 0.6 kPa (both P < 0.001) at the low and high SNP rate. With no ‘correction’ for change in PaCO2, ICA flow increased at the low infusion rate (from 336 ± 66 to 365 ± 69 ml min−1; P = 0.013) with no change in VA flow and CBF while ICA and VA vascular conductance increased with increasing SNP rate. With ‘correction’ for the reduction in PaCO2, ICA flow increased similarly at the two levels of MAP with maintained VA flow with a larger increase in ICA than VA flow (16 ± 14% vs. 5 ± 21%; P = 0.023) during moderate reduction in MAP. Thus, CBF increased by 50 (95% CI: 27–72) and 50 ml min−1 (95% CI: 26–73; both P < 0.001) at the two rates of SNP infusion.ConclusionInfusion of SNP reduces MAP by vasodilatation and by determination of ICA and VA flow in young men vasodilatation encompasses the brain and more so ICA than VA. The results indicate that CBF is controlled not only by its perfusion pressure when blood pressure is reduced.Support or Funding InformationThis study was supported by the University of Copenhagen.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.