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Dynamic cerebral autoregulation is preserved during acute head-down tilt
William H Cooke1, Guy L Pellegrini, Olga A Kovalenko
1Dept. of Biomedical Engineering, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, USA. william.cooke@amedd.army.mil
Journal of Applied Physiology (Bethesda, Md. : 1985)
|July 2, 2003
Summary
Acute head-down tilt, a maneuver reducing sympathetic activity, did not impair dynamic cerebral autoregulation in healthy individuals. This suggests the cerebral vasculature maintains flow velocity regulation despite mild autonomic changes.
Area of Science:
- Physiology
- Autonomic Nervous System
- Cerebrovascular Regulation
Background:
- Complete ganglion blockade disrupts dynamic cerebral autoregulation.
- Autonomic nervous system activity influences cerebral blood flow velocity regulation.
- Head-down tilt is a physiological maneuver that decreases systemic sympathetic activity.
Purpose of the Study:
- To test the hypothesis that acute head-down tilt disrupts dynamic cerebral autoregulation.
- To investigate the effect of reduced sympathetic activity on cerebral blood flow velocity regulation.
Main Methods:
- 10 healthy young subjects (5 male, 5 female) participated.
- Measurements included ECG, beat-by-beat arterial pressure, respiratory rate, end-tidal CO2, and middle cerebral blood flow velocity.
- Data were collected during controlled breathing and Valsalva maneuvers in supine and -10 degrees head-down tilt positions, analyzed using frequency domain and cross-spectral techniques.
Main Results:
- Head-down tilt significantly reduced Valsalva phase IV systolic pressure overshoot (36 to 25 mmHg).
- Low-frequency spectral power of systolic and mean arterial pressure decreased during head-down tilt.
- Cerebral blood flow velocity and transfer function dynamics between arterial pressure and cerebral blood flow velocity remained unaffected.
Conclusions:
- Mild physiological manipulation of autonomic activity via acute head-down tilt does not affect dynamic cerebral autoregulation in healthy humans.
- The cerebral vasculature effectively regulates flow velocity despite changes in systemic sympathetic activity.