Hipertension

Hypertension. Author manuscript; available in PMC 2011 November 1.
Published in final edited form as:
Hypertension. 2010 November; 56(5): 859–864.
Published online 2010 September 27. doi:  10.1161/HYPERTENSIONAHA.110.160002
PMCID: PMC3040032
NIHMSID: NIHMS252929
Hypertension and Cerebral Vasoreactivity: A Continuous Arterial Spin Labeling MRI study
Ihab Hajjar, MD, MS, Peng Zhao,PhD, David Alsop, PhD, and Vera Novak, MD, PhD
Author information ► Copyright and License information ►
The publisher's final edited version of this article is available free at Hypertension
See other articles in PMC that cite the published article.
Go to:
-------------------------------------------------
Abstract
Hypertension is associated with microvascular and macrovascular brain injury but itsdirect influence on the cerebral circulation is not fully clear. Our objective was to investigate the association of hypertension with global and regional cerebral vasoreactvity to CO2 using continuous arterial spin labeling magnetic resonance imaging, independent of stroke and white matter hyperintensities. Participants (n=62; mean age 66.7±1.0 years, 55% women, 84% white, 65% hypertension, 47%stroke) underwent arterial spin labeling perfusion MRI during normal breathing, 5% CO2 rebreathing, and hyperventilation as well as 24-hour ambulatory blood pressure monitoring. Vasoreactivity was the slope of the regression between cerebral perfusion and end-tidal CO2. White matter hyperintensity volumes were quantified. Nighttime dipping was calculated as the percent decline in nighttime/daytimeblood pressure. After accounting for stroke and white matter hyperintensity volume, hypertensive participants had lower global vasoreactivity (1.11±0.13 vs. 0.43±0.1 ml/100gm/min/mmHg, p= 0.0012). Regionally, this was significant in the frontal, temporal and parietal lobes. Higher mean systolic blood pressure was associated with lower vasoreactivity (decreased by 0.11 units/10 mm Hg increase insystolic blood pressure, p=0.04), but nighttime dipping was not (p=0.2). The magnitude of decrease in vasoreactivity in hypertension without stroke was comparable to the magnitude of decrease in vasoreactivity in stroke without hypertension. Hypertension has a direct negative effect on the cerebrovascular circulation independent of white matter hyperintensities and stroke that is comparable to thatseen with stroke. Since lower vasoreactivity is associated with poor outcomes, studies of the impact of antihypertensive on vasoreactivity are important.
Keywords: Hypertension, cerebrovascular circulation, vasoconstriction, vasodilation
Go to:
-------------------------------------------------
Introduction
Decline in cerebrovascular reactivity is associated with cognitive decline,1–4 slowergait speed and possibly falls. 5 Prior studies suggest that hypertension may have an influence on cerebrovascular reactivity.6 Most of these studies have assessed cerebrovascular reactivity in hypertension by measuring changes in cerebral blood flow at the middle cerebral artery in response to changes to end-tidal carbon dioxide (CO2) using Transcranial Doppler (TCD).7 Although these studies haveshown that hypertensives may have lower cerebral vasoreactivity to CO2, gaps in our knowledge remain unanswered. Hypertension is a major risk factor for stroke and white matter hyperintensities (WMH), both associated with impaired cerebral vasoreactivity.8–9 TCD cannot assess if the lower vasoreactivity noted in hypertension is related or independent of stroke or WMH. TCD, moreover, does not providesimultaneous assessment of vasoreactivity in multiple brain regions. Identifying specific regions that may have lower vasoreactivity in the brain offers an insight to the potential processes by which the brain is affected by hypertension.
Continuous arterial spin labeling (CASL) perfusion magnetic resonance imaging (MRI) can detect cerebral perfusion changes, provide detailed cerebral blood...