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’