Otolithic and tonic neck receptors control of limb blood flow in humans

The aim of this study was to evaluate the role of otolithic receptors and neck mechanoreceptors on the control of the cardiovascular system. We measured calf (CBF) and forearm blood flow (FBF) by strain-gauge plethysmography, mean arterial pressure (MAP), and heart rate (HR) in 12 healthy subjects in two body positions (lying prone and on the left side) and three head positions (reference, flexion, and extension). When the subjects were lying prone, CBF and FBF were lower in head flexion (5.2 +/- 0.6 and 3.2 +/- 0.4 ml.min-1.100 ml-1, respectively) than in reference position (5.8 +/- 0.4 and 3.8 +/- 0.3 ml.min-1.100 ml-1; P < 0.05), with no significant difference in MAP and HR. When the subjects were lying on the side, changing the head position from reference to flexion significantly increased FBF (from 3.7 +/- 0.2 to 4.2 +/- 0.4 ml.min-1. 100 ml-1), MAP (from 97.2 +/- 3.3 to 102.4 +/- 5.8 mmHg), and HR (from 63.7 +/- 1.4 to 65.9 +/- 2.5 beats/min; P < 0.05). Because otolithic receptors and neck mechanoreceptors are involved when the subjects are lying prone, and otolithic receptors are not involved when the subjects are lying on the side, the results suggest that otolithic and neck mechanoreceptors exert significant influences over the cardiovascular system.