26. Integration of CSF and Cerebral Blood Flow

or From Clinical Practice to Mathematical

Modelling and back again

Thanks to Dr.F.Kashif

Clinical practice: Arterial pressure, ICP and blood flow (velocity)

waveforms

FV

ABP

ICP

mmHg

mmHg

cm/s

Vasogenic waves related to spontaneous vasodilatation.

ICP (Marmarou model) interacts with ABP and CBF (Ursino)

FV

ABP

ICP

mmHg

mmHg

cm/s

LDF

Global Model of Cerebral Blood Flow and

Circulation of Cerebrospinal Fluid

Czosnyka M, Piechnik S, Richards HK, Kirkpatrick P, Smielewski P, Pickard JD. Contribution of mathematical modelling to the

bedside tests of cerebrovascular autoregulation. Journal of Neurology, Neurosurgery, and Psychiatry 1997; 63:721-731

V

Electrical model of cerebrospinal dynamics

… and its state equations

Nonlinear cerebrovascular resistance

Compliance of CSF space

depends on CSF pressure

Arterial compliance

Non-linear resistance of

bridging veins

•Mean Intracranial Pressure: Is it really determined only by CSF circulation?

•Meaning of pulse amplitude of ICP

•Hemodynamic effects of intracranial hypertension and arterial hypotension

•Testing of autoregualtion of cerebral blood flow

Vasogenic component of ICP: it disappears after experimental cardiac arrest

FV

ABP

ICP

mmHg

mmHg

cm/s

Vasogenic component of ICP : Is it associated with pulsation of arterial walls?

ICP= ICPcsf circulation + ICP vasogenic=

=RCSF*Iformation +Pss + ICP vasogenic

Vasogenic component disappears during asystole?

ABP

ICP

mmHg

mmHg

Change in the shape

of ICP waveform

during

intracranial

hypertension

Pulse amplitude of

ICP :

AMP ~ ABPamp*

* Ca/(Ci+Ca)

Modelling explanation of transmission of arterial pulse wave to ICP

Intracranial Hypertension

Intracranial hypertension

CEREBRAL AUTOREGULATION

IMPAIRED (Mx positive):

CEREBRAL AUTOREGULATION INTACT

(Mx<=0):

Mx: an index of autoregulation

Czosnyka M, Smielewski P, Piechnik S, Schmidt EA, Seeley H, al-Rawi P, Matta BF, Kirkpatrick PJ,

Pickard JD. Continuous assessment of cerebral autoregulation--clinical verification of the method in head

injured patients. Acta Neurochir Suppl. 2000;76:483-4

Arterial hypotension: Response of CBFv and ICP

Arterial hypotension: modelling interpretation

Pressure-reactivity index (PRx)

Short term (6 mins window)

moving correlation coefficient

between slow waves of ICP and

ABP

PRx positive- pressure-reactivity

absent

PRx negative: pressure-reactivity

functional

ABP

ICP

ABP

ICP

ICP reacts to changes in Arterial Pressure. This reaction

depends on strength of autoregulation

a.)

Cerebral Perfusion Pressure (mm Hg)

100

- 1

05

95 -

100

90 -

95

85 -

90

80 -

85

75 -

80

70 -

75

65 -

70

60 -

65

55 -

60

50 -

55

PR

x

.5

.4

.3

.2

.1

0.0

-.1

-.2

Both PRx and Mx show the U-shape relationship with mean CPP.

This indicate that for low CPP and CPP above 90 mm Hg both autoregulation

and pressure reactivity are defective. There is an ‘optimal’ CPP from 70 to 90

mm Hg which helps to restore vascular functions after head injury

Steiner LA, Czosnyka M, Piechnik SK, Smielewski P, Chatfield D, Menon DK, Pickard JD. Continuous

monitoring of cerebrovascular pressure reactivity allows determination of optimal cerebral perfusion pressure in

patients with traumatic brain injury. Crit Care Med. 2002 Apr;30(4):733-8.

Optimal CPP

Local FV to CPP correlation coefficients

indicate area of “optimal”perfusion

Piechnik S, Czosnyka M, Pickard JD.: Indices for decreased cerebral blood flow control - A modelling study. ICPX A.Marmarou, R. Bullock, et al. (eds) Acta

Neurochirurgica Supplementum 71:269-271 1998 by Springer-Verlag.

Transient Hyperaemic Response Test:

Good autoregulation Disturbed autoregulation

Smielewski P, Czosnyka M, Kirkpatrick P, Pickard JD. Evaluation of transient

hyperaemic response test in head injured patients. J. Neurosurg 1997; 86:773-778

FV

ABP

FV

ABP

THRT: Modelling interpretation

What happens in different parts of the brain ?

Asymmetry in autoregulation

Schmidt EA, Czosnyka M, Steiner LA, Balestreri M, Smielewski P, Piechnik SK,

Matta BF, Pickard JD. Asymmetry of pressure autoregulation after traumatic brain

injury. J Neurosurg. 2003 Dec;99(6):991-8.

Asymmetry in autoregulation correlates

with increased mortality rate

CO2 Reactivity Asymmetry in case of unilateral stenosis

Reactivity = Slope of regr.

Normal values :

24 + 4.1 %/kPa

Reactivity = 25.1 %/kPa Reactivity = 7.6 %/kPa

-

Gooskens I, Schmidt EA, Czosnyka M, Piechnik SK, Smielewski P, Kirkpatrick PJ, Pickard JD. Pressure-autoregulation, CO(2)

reactivity and asymmetry of haemodynamic parameters in patients with carotid artery stenotic disease. A clinical appraisal. .Acta

Neurochir (Wien). 2003 Aug;145(7):527-32.

R

Bi-lateral model of CSF and cerebral circulation (SK Piechnik 1998)

Piechnik SK, Czosnyka M, Harris NG, Minhas PS, Pickard JD. A model of the cerebral and cerebrospinal fluid circulations to

examine asymmetry in cerebrovascular reactivity. J Cereb Blood Flow Metab. 2001 Feb;21(2):182-92.

Messages to take home

Modelling approach: useful in introducing new concepts into clinical practice

Modelling cannot be purely formal. Models should be varified

Models can explain tests of autoregulation

Bi-lateral model- description of ‘cerebral steal’