Head-down manoeuvre in patients with a high symptom score for orthostatic intolerance reveals impaired right brain frontal lobe vasoreactivity.

OBJECTIVE Autonomic nerve dysregulation produces a sense of impaired well-being and interferes with work performance in affected individuals. In this study, we characterized the pathophysiology of this condition. METHODS Six patients with high symptom scores for orthostatic intolerance (OI) along with age- and sex-matched normal volunteers were directed to perform a head-down manoeuvre, and the change in cerebral blood flow (CBF) and cerebral oxygen levels (rSO(2)) in the right and left frontal lobes was measured using near-infrared spectroscopy (NIRS). RESULTS The head-down manoeuvre induced a much greater increase in right-sided total haemoglobin concentration (THbl) in normal volunteers (0.51+/-0.24) when compared to symptomatic patients (0.0+/-0.04) but had no effect on left-sided THbl (P<0.05) in either group. Five of 6 patients showed a gradual decrease in right-sided THbl when assuming a sitting position, and all patients with this pattern complained of symptoms of multiple autonomic dysfunction. Further, this pattern of changes in right-sided THbl was not observed in normal volunteers. CONCLUSIONS The gradual decrease of THbl with the sitting position and the lack of increase during the head-down manoeuvre in symptomatic patients suggest that these patients have impaired vasoreactivity in the right frontal lobes. SIGNIFICANCE This impaired vasoreactivity likely reflects dysfunction of the right hemisphere and the sympathetic nervous system in patients with OI.