Adaptive method for assessment of cerebrospinal fluid outflow conductance

Queckenstedt's test repurposed for the quantitative assessment of the cerebrospinal fluid pulsatility curve

PURPOSE

Before the era of spinal imaging, presence of a spinal canal block was tested through gross changes in cerebrospinal fluid pressure (CSFP) provoked by manual compression of the jugular veins (referred to as Queckenstedt's test; QT). Beyond these provoked gross changes, cardiac-driven CSFP peak-to-valley amplitudes (CSFPp) can be recorded during CSFP registration. This is the first study to assess whether the QT can be repurposed to derive descriptors of the CSF pulsatility curve, focusing on feasibility and repeatability.

METHOD

Lumbar puncture was performed in lateral recumbent position in fourteen elderly patients (59.7±9.3 years, 6F) (NCT02170155) without stenosis of the spinal canal. CSFP was recorded during resting state and QT. A surrogate for the relative pulse pressure coefficient was computed from repeated QTs (i.e., RPPC-Q).

RESULTS

Resting state mean CSFP was 12.3 mmHg (IQR 3.2) and CSFPp was 1.0 mmHg (0.5). Mean CSFP rise during QT was 12.5 mmHg (7.3). CSFPp showed an average 3-fold increase at peak QT compared to the resting state. Median RPPC-Q was 0.18 (0.04). There was no systematic error in the computed metrics between the first and second QT.

CONCLUSION

This technical note describes a method to reliably derive, beyond gross CSFP increments, metrics related to cardiac-driven amplitudes during QT (i.e., RPPC-Q). A study comparing these metrics as obtained by established procedures (i.e., infusion testing) and by QT is warranted.

A mechatronic valve in the management of hydrocephalus: methods and performance

The problem of excess cerebrospinal fluid in the brain (hydrocephalus) is generally managed using a passive pressure or flow regulated mechanical shunt. Despite the success of such devices, they have been plagued with a number of problems. It is desirable to have a shunt valve that responds dynamically to the changing needs of the patient, opening and closing according to a dynamic physiological pattern, rather than simply to the hydrostatic pressure across the valve. Such a valve would by necessity be mechatronic, electronically controlled by software. In this article, different methods for controlling such a mechatronic valve are explored, and the effect of current hydrocephalus management techniques on the intracranial hydrodynamics of acute hydrocephalus patient compared with those based on a mechatronic valve was investigated using numerical simulation. Furthermore, the performance of these techniques was evaluated based on a proposed multi-dimensional figure of merit. In addition, an empirical valve schedule was proposed based on different criterions. An intelligent shunting system is seen as the future in hydrocephalus management and treatment, and towards this end, suitably programmed mechatronic valves would attempt to mimic normal physiology and potentially overcome many of the problems associated with current mechanical valves.

Real-time estimation of cerebrospinal fluid system parameters via oscillating pressure infusion

Hydrocephalus is related to a disturbed cerebrospinal fluid (CSF) system. For diagnosis, lumbar infusion test are performed to estimate outflow conductance, C (out), and pressure volume index, PVI, of the CSF system. Infusion patterns and analysis methods used in current clinical practice are not optimized. Minimizing the investigation time with sufficient accuracy is of major clinical relevance. The aim of this study was to propose and experimentally evaluate a new method, the oscillating pressure infusion (OPI). The non-linear model of the CSF system was transformed into a linear time invariant system. Using an oscillating pressure pattern and linear system identification methods, C (out) and PVI with confidence intervals, were estimated in real-time. Forty-two OPI and constant pressure infusion (CPI) investigations were performed on an experimental CSF system, designed with PVI = 25.5 ml and variable C (out). The ARX model robustly estimated C (out) (mean C (out,OPI) - C (out,CPI) = 0.08 μl/(s kPa), n = 42, P = 0.68). The Box-Jenkins model proved most reliable for PVI (23.7 ± 2.0 ml, n = 42). The OPI method, with its oscillating pressure pattern and new parameter estimation methods, efficiently estimated C (out) and PVI as well as their confidence intervals in real-time. The results from this experimental study show potential for the OPI method and supports further evaluation in a clinical setting.