Free Content Head Rotation During Upright Tilt Increases Cardiovagal Baroreflex Sensitivity

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Abstract:

Cooke WH. Head rotation during upright tilt increases cardiovagal baroreflex sensitivity. Aviat Space Environ Med 2007; 78:463–469.



Introduction: Vestibular activation of semicircular canals has been linked to increased activity of parasympathetic neurons and has been proposed as a contributing factor to orthostatic intolerance. However, the functional consequences of head yaw rotation during orthostasis on human autonomic function have not been documented. The purpose of this study was to determine the effects of voluntary head rotation on autonomic function during upright tilt. Methods: ECG, beat-by-beat finger arterial pressure, respiratory rate, PetCO2, and cerebral blood flow velocity were recorded in 10 healthy subjects. Subjects were studied supine and during two separate 5-min periods of upright tilt to 70° with and without continuous head yaw rotation (180° at 0.25 Hz). Breathing frequency was controlled strictly at 0.25 Hz during each trial and data were analyzed in both time and frequency domains. Cross-spectral techniques (transfer functions) were used to assess cardiovagal baroreflex sensitivity and dynamic cerebral autoregulation. Results: Head rotation during upright tilt increased transfer function magnitude between systolic pressure and R-R interval at the low frequency (0.04–0.15 Hz) from 8.1 ± 2.3 to 10.4 ± 1.6 ms · mmHg−1 (p = 0.04), but did not affect estimates of vagal-cardiac efferent activity or cerebral blood flow velocity, hemodynamic oscillations, or dynamic cerebral autoregulation. Conclusions: Increased cardiovagal baroreflex sensitivity in conjunction with preserved cerebral autoregulation suggests that head rotation during upright tilt is unlikely to trigger orthostatic instability in normal, healthy humans.

Keywords: neck afferents; power spectral analysis; semicircular canals; transfer function

Document Type: Research Article

Publication date: May 1, 2007

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