### Abstract

The effects of orthostatic stress, induced by lower body negative pressure (LBNP), on cerebral hemodynamics were examined in a nonlinear context. Spontaneous fluctuations of beat-to-beat mean arterial blood pressure (MABP) in the finger, mean cerebral blood flow velocity (MCBFV) in the middle cerebral artery, as well as breath-by-breath endtidal CO_{2} concentration (P_{ETCO2}) were measured continuously in ten healthy subjects under resting conditions and during graded LBNP to presyncope. A two-input nonlinear Laguerre-Volterra network model was employed to study the dynamic effects of MABP and P_{ETCO2} changes, as well as their nonlinear interactions, on MCBFV variations in the very low (VLF; below 0.04 Hz), low (LF; 0.04-0.15 Hz) and high frequency (HF; 0.15-0.30 Hz) ranges. Dynamic cerebral autoregulation was described by the model terms corresponding to MABP, while cerebral vasomotor reactivity was described by the model P_{ETCO2} terms. The magnitude of the linear and nonlinear MABP-MCBFV Volterra kernels increased substantially above -30 mm Hg LBNP in the VLF range, implying impaired dynamic autoregulation. In contrast, the magnitude of the P_{ETCO2}-MCBFV kernels reduced during LBNP at all frequencies, suggesting attenuated cerebral vasomotor reactivity. These changes may reflect a progressively more unstable circulation that could ultimately lead to cerebral hypoperfusion and syncope.

Original language | English (US) |
---|---|

Title of host publication | Proceedings of the 7th International Workshop on Mathematical Methods in Scattering Theory and Biomedical Engineering |

Publisher | World Scientific Publishing Co. Pte Ltd |

Pages | 362-369 |

Number of pages | 8 |

ISBN (Print) | 9812568603, 9789812568601 |

Publication status | Published - 2006 |

Event | 2005 7th International Workshop on Mathematical Methods on Scattering Theory and Biomedical Engineering - Nymphaio, Greece Duration: Sep 8 2005 → Sep 11 2005 |

### Other

Other | 2005 7th International Workshop on Mathematical Methods on Scattering Theory and Biomedical Engineering |
---|---|

Country | Greece |

City | Nymphaio |

Period | 9/8/05 → 9/11/05 |

### Fingerprint

### ASJC Scopus subject areas

- Biomedical Engineering
- Applied Mathematics

### Cite this

*Proceedings of the 7th International Workshop on Mathematical Methods in Scattering Theory and Biomedical Engineering*(pp. 362-369). World Scientific Publishing Co. Pte Ltd.