Correlation between baseline blood pressure and the brainstem FMRI response to isometric forearm contraction in human volunteers: A pilot study

It has been shown previously that changes in brainstem neural activity correlate with changes in both mean arterial pressure (MAP) and muscle sympathetic nerve activity (MSNA) during static handgrip (SHG). However, the relationship between baseline MAP and brainstem neural activity is unclear. We investigated changes in blood oxygen level-dependent (BOLD) signal induced by SHG in 12 young adults using BOLD functional magnetic resonance imaging (FMRI). An estimation of the blood pressure response to SHG was obtained in seven subjects during a session outside the MRI scanner and was used to model the blood pressure response to SHG inside the scanner. SHG at 40% of maximum grip increased MAP (mean±s.d.) at the end of the 180-s squeeze from 85±6 mm Hg to 108 ±15 mm Hg, P=0.0001. The brainstem BOLD signal change associated with SHG was localised to the ventrolateral medulla. This regional BOLD signal change negatively correlated with baseline MAP, r=-0.61, P=0.01. This relationship between baseline MAP and brainstem FMRI responses to forearm contraction is suggestive of a possible role for brainstem activity in the control of MAP and may provide mechanistic insights into neurogenic hypertension.