Dynamic Cerebral Autoregulation is Preserved During Acute Head-down Tilt
Abstract
Complete ganglion blockade alters dynamic cerebral autoregulation, suggesting links between systemic autonomic traffic and regulation of cerebral blood flow velocity. We tested the hypothesis that acute head-down tilt, a physiological maneuver that decreases systemic sympathetic activity, would similarly disrupt normal dynamic cerebral autoregulation. We studied 10 healthy young subjects (5 men and 5 women; age 21 + or - 0.88 yr, height 169 + or - 3.1 cm, and weight 76 + or - 6.1 kg). ECG, beat-by-beat arterial pressure, respiratory rate, end- tidal CO 2 concentration, and middle cerebral blood flow velocity were recorded continuously while subjects breathed to a metronome. We recorded data during 5-min periods and averaged responses from three Valsalva maneuvers with subjects in both the supine and 10 head-down tilt positions (randomized). Controlled-breathing data were analyzed in the frequency domain with power spectral analysis. The magnitude of input-output relations were determined with cross-spectral techniques. Head-down tilt significantly reduced Valsalva phase IV systolic pressure overshoot from 36 + or - 4.0 (supine position) to 25 + or - 4.0 mmHg (head down) ( P = 0.03). Systolic arterial pressure spectral power at the low frequency decreased from 5.7 + or - 1.6 (supine) to 4.4 + or - 1.6 mmHg2 (head down) ( P = 0.02), and mean arterial pressure spectral power at the low frequency decreased from 3.3 + or - 0.79 (supine) to 2.0 + or - 0.38 mmHg 2 (head down) (P = 0.05). Head-down tilt did not affect cerebral blood flow velocity or the transfer function magnitude and phase angle between arterial pressure and cerebral blood flow velocity.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 27, 2003
- Accession Number
- ADA630482
Entities
People
- Guy L. Pellegrini
- Olga A. Kovalenko
- William H. Cooke
Organizations
- United States Army Institute of Surgical Research