Cerebral blood flow regulation : control and physiology

Cerebral blood flow regulation : control and physiology

Martens, E. G. H. J., Gommer, E. D., Reulen, J. P. H., & Vosse, van de, F. N. (2008). Cerebral blood flow regulation : control and physiology. Poster session presented at Mate Poster Award 2008 : 13th Annual Poster Contest.

Document status and date: Published: 01/01/2008 Document Version:

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Cerebral blood flow regulation:

control & physiology

Esther Martens, Erik Gommer, Jos Reulen, Frans van de Vosse

Cardiovascular Biomechanics and fluid dynamics

Department of Biomedical Engineering

Introduction

Neurovascular Coupling (NVC) is the control mechanism which adjusts the cerebral blood flow to the local metabolic need. For example, a visual stimulus results in a higher metabolic need and thus increased blood flow to and in the visual cortex.

Fig 1. Transcranial Doppler Ultrasonography

When blood flow velocity to the visual cortex is measured by Transcranial Doppler Ultrasonography (TCD, fig. 1) of the posterior cerebral artery (PCA), the blood flow respons to a visual step stimulus can have different time courses:

Type 1 Type 2 Type 3

Fig. 2 The three types of responses measured in humans Type 1: generally found in healthy subjects

Type 2 & 3: mainly found in case of endothelial dysfunction Type 3: thought to be related to increased vessel stiffness.

Research Questions

1. Are abnormal time courses due to changes in the passive physiological system or to active control? 2. How can the finding of the abnormal responses,

type II and type III, be explained physiologically?

Method

Control

The measured blood flow response to a visual step can be fitted with the step response of a 2nd order control system, so that control system parameters can be obtained.

Fig 3. The NVC mechanism described as 2nd_{order control system} However, the input-output relation or transfer function does not reveal which part is responsible for the control and what part for the passive system. The transfer function can be split by assuming different controllers with accesory system. The resulting responses will be evaluated.

Fig 4. The transfer function split in control and system part

Physiology

The perfusion of the visual cortex is provided by one supplying vessel, the P2 segment of the PCA, and the microcirculation. These may be modelled by a simple lumped parameter model.

Fig 5. Simple lumped parameter model of the visual cortex vasculature

Coupling

The information from the control system approach can be incorperated in the physiological lumped parameter model. Control system information may be linked to physiology, so that data interpretation by physicians is facilitated.

SOP + - error input output + + Pgain D d/dt L R C Cp Ra Z₀

Supplying vessel

Microcirculation

P

(t)

Supplying vessel

Microcirculation

P

(t)

L R

C Cp Ra

Z₀

Supplying vessel

Microcirculation

L R C Cp Ra Z₀ L R L R C C CCpp Ra Z₀

Supplying vessel

Microcirculation

P

(t)

Input Control_system Output

1 s 2 s ) s * Tv 1 ( K ) s ( H 2 2 + ϖ ξ + ϖ + =