188
L. Geregele et al.
It is interesting that pressure-volume curve plotted during increase in ICP has
different shape than plotted using the subsequent decrease [42].
Finally, the Eq. (8.7) can be helpful in the theoretical evaluation of the relationship between the pulse wave amplitude of ICP and the mean CSF pressure. If we
presume that the rise in the blood volume after a heart contraction is equivalent to
a rapid bolus addition of CSF fluid at the baseline pressure P b , the pulse amplitude
(AMP) can be expressed as
AMP = p p − p b = (p b − p o ) ·
e
EEV
− 1
(8.10)
In almost all the cases, when CSF pressure is being increased by an external
volume addition, the pulse amplitude rises [2, 40] (see Fig. 8.3b, d). The gradient
of the regression line between AMP and p is proportional to the elasticity. The
intercept, theoretically, marks the reference pressure P o .
In all pressure-volume testing techniques, parameters of model (8.5) are estimated using various algorithms and various volume-adding techniques. However,
the presented model has a limited scope: it cannot interpret dynamic interactions
between the rising CSF pressure, expanding ventricles, and cerebral blood volume.
More sophisticated models have been formulated, but none of them has yet become
established in clinical practice.
8.4 Infusion Test
The computerised infusion test [43, 44] is a modification of the traditional constant
rate infusion as described by Katzman and Hussey [39]. The method requires fluid
infusion to be made into any accessible CSF compartment. Lumbar infusion, even
if it has understandable limitations, is less invasive than intraventricular.
The alternative is an infusion into a subcutaneously positioned reservoir, connected to an intraventricular catheter or shunt antechamber. In such cases, two
hypodermic needles (gauge 25) are used: one for the pressure measurement and
the second for the infusion.
During the infusion, the computer calculates and graphically presents mean
pressure and pulse amplitude over time (Fig. 8.3a, b). The resistance to CSF outflow
can be calculated using simple arithmetic as the difference between the value of the
plateau pressure during infusion and the baseline pressure, divided by the infusion
rate. However, the precise measurement of the final plateau pressure is not possible
when strong vasogenic waves arise or an excessive elevation of the pressure above
the safe limit of 40 mmHg is recorded. Computerised analysis produces results even
in difficult cases when the infusion is terminated prematurely. The pressure-volume
curve is additionally investigated (Fig. 8.3c). It represents relative rise in CSF
pressure as a function of effective change of CSF volume (i.e. volume infused and
produced minus volume absorbed). The algorithm utilises time series analysis for
L. Geregele et al.
It is interesting that pressure-volume curve plotted during increase in ICP has
different shape than plotted using the subsequent decrease [42].
Finally, the Eq. (8.7) can be helpful in the theoretical evaluation of the relationship between the pulse wave amplitude of ICP and the mean CSF pressure. If we
presume that the rise in the blood volume after a heart contraction is equivalent to
a rapid bolus addition of CSF fluid at the baseline pressure P b , the pulse amplitude
(AMP) can be expressed as
AMP = p p − p b = (p b − p o ) ·
e
EEV
− 1
(8.10)
In almost all the cases, when CSF pressure is being increased by an external
volume addition, the pulse amplitude rises [2, 40] (see Fig. 8.3b, d). The gradient
of the regression line between AMP and p is proportional to the elasticity. The
intercept, theoretically, marks the reference pressure P o .
In all pressure-volume testing techniques, parameters of model (8.5) are estimated using various algorithms and various volume-adding techniques. However,
the presented model has a limited scope: it cannot interpret dynamic interactions
between the rising CSF pressure, expanding ventricles, and cerebral blood volume.
More sophisticated models have been formulated, but none of them has yet become
established in clinical practice.
8.4 Infusion Test
The computerised infusion test [43, 44] is a modification of the traditional constant
rate infusion as described by Katzman and Hussey [39]. The method requires fluid
infusion to be made into any accessible CSF compartment. Lumbar infusion, even
if it has understandable limitations, is less invasive than intraventricular.
The alternative is an infusion into a subcutaneously positioned reservoir, connected to an intraventricular catheter or shunt antechamber. In such cases, two
hypodermic needles (gauge 25) are used: one for the pressure measurement and
the second for the infusion.
During the infusion, the computer calculates and graphically presents mean
pressure and pulse amplitude over time (Fig. 8.3a, b). The resistance to CSF outflow
can be calculated using simple arithmetic as the difference between the value of the
plateau pressure during infusion and the baseline pressure, divided by the infusion
rate. However, the precise measurement of the final plateau pressure is not possible
when strong vasogenic waves arise or an excessive elevation of the pressure above
the safe limit of 40 mmHg is recorded. Computerised analysis produces results even
in difficult cases when the infusion is terminated prematurely. The pressure-volume
curve is additionally investigated (Fig. 8.3c). It represents relative rise in CSF
pressure as a function of effective change of CSF volume (i.e. volume infused and
produced minus volume absorbed). The algorithm utilises time series analysis for