Graviceptive control of blood pressure in man

The purpose of the study was to demonstrate a rapid 'graviceptive' influence on blood pressure in man. Subjects, sitting in an electrically powered car, made discrete head tilts, some of which were unpredictably accompanied by transient linear accelerations of the car i) with head tilting to align with the direction of the resulting inertial force vector (gravity + car acceleration) so that the graviceptors were not stimulated; ii) with head tilting in the opposite direction 'misaligning' which stimulated the graviceptors but otherwise maintained similarity of other sensory inputs. Stimuli were dispensed in a balanced, cross over, repeated measures design on 8 normal males. Recordings were made of arterial blood pressure in the left radial artery, the electrocardiogram and plethysmographic responses in the right hand first digit. Comparisons of 10s pre-stimulus baseline with 10s post stimulus responses. Misaligned head tilts provoked highly significant peak increases in systolic (7.6-9.4 mm Hg) and diastolic (5-6 mm Hg) BP and average BP over 10s was significantly raised. Head tilts maintaining alignment with the inertial force vector provoked raised systolic BP by 4-6 mm Hg for only one or two heartbeats. Head movements alone caused a slight lowering of BP. Effects were evident within 1-2 heartbeats of the acceleration onset. The results demonstrate that the graviceptors have a direct influence on BP in normal man. They also help to explain the profound vaso-vagal symptoms of patients with vertigo and why patients with autoregulatory impairment may be further compromised by uncontrolled accelerating and braking when they are transported in an ambulance.