| Author/s | Coulson J, Murphy K, Harris A, Fjodorova M, Cockcrof J, Wise R |
| Year | 2011 |
| Type of publication | Conference proceeding |
| Link | https://doi.org/10.1097/00004872-201106001-00349 |
| Abstract | Objective: The aetiology of hypertension, in the majority of cases, remains unclear. Increased sympathetic nervous system (SNS) activity has been observed in young adults with hypertension. The neuro-anatomical location of this apparent increase in SNS activity is unknown. We used blood oxygenation level dependent functional magnetic resonance imaging (BOLD fMRI) to identify areas of the brainstem and higher brain structures whose activity correlate with the SNS-mediated, pressor response to voluntary isometric forearm contraction (IFC) in young adults.
Methods: 6 adults (2 female) without a history of hypertension, aged 24 - 37 years, preformed 3 experimental runs in which voluntary IFC was performed at ˜40% of their maximum grip strength for periods of time ranging from 11 to 180 seconds whilst acquiring fMRI images. A 3 T scanner with an 8-channel receive coil (General Electric, US) was used, 170 image volumes (scan time = 12m 39s) were collected for each of the 3 repetitions. Each volume covered the entire brain and brainstem (57 slices, 2.3 mm slice thickness, field of view = 19.2 cm2, 128×128 TR = 4385 ms, TE = 25 ms, flip = 90°). Structural images were collected using a T1-weighted sequence in order to facilitate visualisation. Analysis was performed using FEAT (Fmrib). Blood pressure changes were modelled with a waveform derived from continuous, non-invasive, blood pressure data (Finapres Medical Systems, The Netherlands) obtained during an out-of-scanner recording.
Results: IFC was associated with an increase in mean arterial blood pressure of 22% ± 7 % SD from the baseline. Group analyses showed increased activation in the right subgenual anterior cingulate cortex in response to linear increases in blood pressure at a rate of 0.3 mmHg.s−1. The contralateral motor cortex, right anterior insular cortex, left insular cortex, thalamus, cerebellum and medulla also showed activation during IFC.
Conclusion: We have identified areas of regional brain activity that correlate with the pressor response to IFC. These areas have also been association with the initiation of a pressor response in studies that used electrode stimulation studies or other imaging modalities. We now intend to use this technique to investigate potential differences between young hypertensives and healthy controls
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