Dizziness is associated with decreased vasoreactivity in right cerebral hemisphere for head-down manoeuvre--near-infrared spectroscopy study.

To investigate the vasoreactivity of cerebral hemisphere in patients with dizziness and syncope, we compared changes in total haemoglobin (THbl) and regional oxygen saturation (rSO2) of the right and left frontal lobes in response to head-down manoeuvre. Ninety-six right-handed subjects (aged 59 +/- 19 years) were asked to perform a head-down or a standing manoeuvre. Head-down manoeuvre produced a greater increase in right side THbl in subjects under 70 years of age (8.5 +/- 3.1) when compared with subjects older than 70 years (0.40 +/- 0.08). In contrast, the head-down manoeuvre had no effects on left side THbl, irrespective of patient age. Similarly, the head-down manoeuvre resulted in a greater decrease of right side rSO2 in subjects under 70 years of age (-5.2 +/- 2.1%) when compared with subjects older than 70 years (0.31 +/- 0.9%). In contrast, the head-down manoeuvre had no effects on left side rSO2, irrespective of patient age. The head-down manoeuvre produced a smaller increase in right side THbl in subjects with dizziness (0.38 +/- 0.19) than in those without dizziness (9.4 +/- 3.5). A standing manoeuvre produced a smaller increase in right side THbl in subjects with syncope (-0.057 +/- 0.047) than in those without syncope (0.063 +/- 0.028). The head-down manoeuvre produced a decrease in right side rSO2 in subjects without dizziness (-6.4 +/- 2.4%) and a slight increase in right side rSO2 in subjects with dizziness (1.1 +/- 0.4%). Subjects with dizziness (67 +/- 2.1 years) were significantly older than those without dizziness (53 +/- 2.7 years) or those with syncope (44 +/- 4.2 years). These data indicate that reduced vasoreactivity to right hemispheric pressure changes is associated with dizziness in older subjects. Further, decreases in right hemispheric THbl during a standing manoeuvre are associated with syncope in relatively younger subjects.