DIFFERENCES IN BOLD MRI SIGNAL INTENSITY BETWEEN HYPERTENSIVE PATIENTS AND HEALTHY VOLUNTEERS

Abstract

Objective: An increased sympathetic tone is associated with the initiation and maintenance of most forms of arterial hypertension. Background activity of a core network of neurons in the brain and brainstem is supposed to be important for long-term blood pressure control. Imaging techniques such as blood oxygen level dependant magnetic resonance imaging (BOLD MRI) are now capable of detecting changes in oxygenation within the brain using blood oxygen levels. So far, the BOLD fMRI signal intensity changes provoked by a cold pressor test (CPT) have not been compared between hypertensive patients (HT) and normotensive subjects (NT). The primary objective was to compare the signal intensity changes in HT and NT participants. Design and method: This was a prospective case-controlled study. A 7 tesla MRI was used for fMRI acquisition. BOLD MRI signal intensity changes during a cold pressure test and during rest were analyzed using statistical parametric mapping (SPM) for whole brain analysis. The connectivity CONN toolbox was used to analyze functional networks. Results: 30 NT subjects (age 34 ± 10 (mean ± SD), BMI 23 ± 2 kg/m2, systolic blood pressure (SBP) 117 ± 10 mm Hg and diastolic blood pressure (DBP) 71 ± 9 mm Hg) and 16 HT patients (age 46.5 ± 13, BMI 27 ± 3 kg/m2, SBP 148 ± 11 mm Hg and DBP 92 ± 6 mm Hg) were enrolled. The CPT increased the SBP by 21 ± 20 (median ± SD) and 25 ± 24 mm Hg in NT and HT, respectively, and the DBP by 20 ± 19 (NT) and 19 ± 17 (HT) mm Hg. BOLD fMRI signal intensity increased significantly in NT but not in HT. The pattern of resting state connectivity was different between NT and HT, with a decreased global connectivity in HT. Conclusions: BOLD fMRI signal intensity responses to CPT test were less pronounced in HTA patients compared to NT. The different response to stress may be secondary to different neuronal activity pattern during the resting state between the two groups as suggested by connectivity analysis.