REPORT DOCUMENTATION PAGE Form Approved OMB NO. 0704-0188 Public Reporting burden for this collection of infotmation is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comment regarding this burden estimates or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for infomiation Operations and Reports, 1215 Jeflfersrai Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget. Paperwork Reduction Project (0704-0188,) Washington, DC 20503. 1. AGENCY USE ONLY {Leave Blank) 2. REPORT DATE 1 Dec 03 4. TITLE AND SUBTITLE Fluctuations in cerebral hemodynamics 6. AUTHOR(S) Miroslaw Latka and Dariusz Latka 3. REPORT TYPE AND DATES COVERED 5. FUNDING NUMBERS g: DAAD19-03-1-0349 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland. 8. PERFORMING ORGANIZATION REPORT NUMBER DOD-ICP 02 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) U. S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 10. SPONSORING/MONITORING AGENCY REPORT NUMBER vs^o^. 1^ mf}- II. SUPPLEMENTARY NOTES The views, opinions and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other documentation. 12 a DISTRIBUTION / AVAILABILITY STATEMENT Approved for public release; distribution unlimited. 12 b DISTRIBUTION CODE 13. ABSTRACT (Maximum 200 words) We demonstrate that the scaling properties of intracranial pressure (ICP) fluctuations and fluctuations of blood flow velocity in middle cerebral arteries are characterized by two scaling exponents. The short-time scaling exponent (STSE) determines the statistical properties of fluctuations in short-time intervals while the Hurst exponent describes the long-term fractal properties. Thus, the scaling properties of cerebral hemodynamics are reminiscent of those of arterial blood pressure (ABP). Specifically, in physiological conditions the mean value of arterial and cerebral short-time scaling exponents coincide. However, in patients with severe brain injuries the Integrity of cerebral autoregulation may be compromised which leads to statistically significant discrepancy between the mean values of ABP and ICP scaling exponents. To shed new light on cerebral hemodynamics we employ a complex continuous wavelet transfomi to determine the instantaneous phase difference between ABP and ICP waveforms. For moderately elevated intracranial pressure the phase difference slowly evolves in time. However, high intracranial pressure may lead to synchronization of arterial and intracranial pressure signals. Such pathological synchronization may persist even for several hundreds cardiac beats. We use Shannon entropy to quantify the stability of ABP-ICP phase difference and discuss the applicability of such measure for assessment of cerebral autoregulation integrity. 14. SUBJECT TERMS cerebrovascular circulation, cerebral autoregulation, fractal time series, ABP, ICP, TCD IS. NUMBER OF PAGES 0 \^ 16. PRICE CODE 17. SECURITY CLASSIFICATION OR REPORT UNCLASSIFIED 18. SECURITY CLASSIFICATION ON THIS PAGE UNCLASSIFIED 19. SECURITY CLASSIFICATION OF ABSTRACT UNCLASSIFIED 20. LIMITATION OF ABSTRACT UL NSN 7540-01-280-5500 239-18 Standard Form 298 (Rev.2-89) Prescribed by ANSI Std. 298-102