Deciphering the neural signature of human blood pressure control

Kurzfassung

The aim of this study was to measure the activity of hypothalamic and brainstem centers regulating blood pressure in humans The human body has several systems to regulate blood pressure, one of which is the baroreflex. It is mediated by a number of nuclei in the brainstem and hypothalamus that via autonomic efferents adjust the mean arterial pressure by altering both the force and speed of the heart's contractions, as well as systemic vascular resistance. While cortical centers influencing the baroreflex have been studied in humans using functional magnetic resonance imaging (fMRI), the brainstem region suffers from strong physiological noise that makes detection more difficult. Here, we combined high-resolution fMRI with lower body negative pressure (LBNP) and concomitant autonomic recordings hypothesizing that such an approach would make it possible to detect hypothalamic and brainstem nuclei controlling the baroreflex in humans. 15 healthy subjects were scanned using a 3T MR scanner. The protocol involved SMS-EPI functional scans (voxel size=2×2×2 mm3) as well as T1-weighted structural scans (voxel size=1*1*1.2 mm3). LBNP stimulation was delivered using a custom-made MR-compatible pressure chamber and a vacuum cleaner that was controlled by a digital pressure gauge. FMRI data were minimally preprocessed using tools from FMRIB Software Library (FSL v5.0) including motion correction, unwarping, temporal high-pass filtering and normalization to a study template. The data were masked to retain only the brainstem and hypothalamus, excluding the adjacent areas with high physiological noise. Statistical analysis was conducted using masked independent component analysis (mICA), spectral analysis, and network modelling. We found activations related to the LBNP paradigm in multiple nuclei known to be involved in baroreflex regulation. These included the nucleus of the solitary tract and the caudal ventrolateral medulla in the lower brainstem as well as the paraventricular hypothalamic nucleus and lateral hypothalamus. We further observed significant activity changes on the lower ventral medullary surface. Frequency analysis revealed that the BOLD signal in the rostroventrolateral medulla showed spectral changes in the Mayer band (0.1 ± 0.035 Hz) during LBNP. Being able to measure baroreflex nuclei in vivo is an important step towards the understanding of this system in humans. Our results show the importance of selected nuclei in the hypothalamus and brainstem.