Date of Award

January 2012

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

David G. Silverman

Second Advisor

Ki H. Chon

Subject Area(s)

Medicine, Biomedical engineering

Abstract

The identification and delineation of oscillatory patterns of blood flow associated with cerebral autoregulation mechanisms is the focus of three specific aims. 1) Identify a superior spectral analysis method for the identification of activity due to cholinergic oscillatory control of the microvasculature (COCmicvasc) and compare the effectiveness of the Hilbert-Huang transform (HHT), the smoothed pseudo Wigner-Ville (SPWV) distribution, and the variable-frequency complex demodulation (VFCDM) method to detect such activity. 2) Determine if changes in forehead microcirculation as monitored by noninvasive laser Doppler flowmetry may provide a reliable indication of the adequacy of cerebral blood flow during progressive simulated hypovolemia. 3) Identify changes in forehead microvascular activity that is due to parasympathetic activity associated with the onset of mental status changes and show a lack of coherence with potential confounding variables.

The lower body negative pressure (LBNP) protocol is a noninvasive technique that can induce a hypovolemic state through blood pooling in the lower extremities by a portion of the circulating blood volume. Increasing degrees of LBNP is applied to healthy volunteers being monitored with noninvasive laser Doppler (LD) flowmetry to assess levels of forehead perfusion and vascular resistance. MATLAB is utilized as the primary tool for the development of custom mathematical algorithms to analyze this data in the time-frequency-energy domain.

Utilizing the VFCDM technique to analyze forehead laser Doppler data offers greater insight into the identification and understanding of cerebral autoregulatory mechanisms than using other available methods. Techniques to identify COCmicvasc activity in the forehead and distinguish it from respiration, a potential confounder, are discussed. Presented data provides evidence that the observed COCmicvasc activity is due to a locally induced autoregulatory mechanism in the forehead that is unrelated to passive transmission of the mechanical effects of respiration. The close relationship of the forehead vasculature to that of the brain (i.e. part of the forehead is fed by a branch of the internal carotid artery with the remainder from the external carotid artery) suggests that the observed autoregulatory processes in the forehead microvasculature may be the same mechanisms responsible for autoregulation of the brain and other vital organs. This conclusion is also supported by the correlation between changes in mental status (i.e. lightheadedness) and forehead COCmicvasc activity.

Comments

This is an Open Access Thesis.

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