• Non ci sono risultati.

2.5 – The Smart Shunt concept

On the other hand, the external subsystem should include a personal computer or a hand-held smartphone, with a screen and an user-friendly interface, a data storage to collect and save data detected by the sensors and a bidirectional communication system that works through radio frequency. This unit should be able to interface and to communicate wireless with the outside and to download data from the implantable subsystem; in addition the external subsystem could be managed by the clinician or by the patient at home, during his daily routine (in a limited way):

the clinician, through the external subsystem, could change the valve set- ting or the valve opening pressure; he also could verify the patient clinical parameters (ICP value or CSF flow) and the correct shunt functioning. While the patient could use the smartphone at home to provide feedbacks about his symptoms, his physical conditions and his daily activities and he could save these informations in a digital medical chart.

Figure 2.21: The Smart Shunt concept: the implantable system and the external system communicate and interact each other and the medical centre to improve the life quality of a shunted patient[22].

Additionally, the presence of intelligent and technologically advanced compo-nents and of specific algorithms in the smart shunt concept would allow the device

to self-regulate through different inputs, like the patient feedbacks and the oper-ations realized by the clinician. In this way it would be possible to reduce the hospitalization of the patient and the shunt revisions.

The smart shunt, as it has been previously described in this subsection, still re-mains a planning idea as the researchers have to confront several challenges (techno-logical, financial and about legislation) about the device itself and its components.

Analysis of the different smart shunt parts reveals some considerations about both the limitations to overcome and the necessary requirements for these compo-nents: the pressure sensors, the CSF flow sensors and the sensors of the patient ori-entation should supply accurate, reliable, real-time and continuous measurements about the physical quantities of interest; they would require a periodic calibration after the smart shunt implantation, without subjecting the patient to further surg-eries and they should avoid producing a significant drift during their employment.

The sensors also should be electrically isolated from both the body fluids and the moisture, they have to be hermetic and they can absorb power.

In addition, the sensors dimensions should be small as they condition the device positioning in the body and, in this specific case, in the brain; the materials used for the sensors construction should be biocompatible, compatible with the current and modern imaging techniques like magnetic resonance, computed tomography, ultrasound investigation and they should comply with the FDA guidelines.

The last three requirements should be in general respected by the smart shunt itself, but they are in particular required by the flow control mechanism, the device housing and the actuator.

The power source and the communication system prove to be the biggest chal-lenges for the researchers.

A smart shunt should be powered through a battery to operate: a battery usually requires a periodic recharge or it is replaced when it exhausts; after the device implantation in the patient body, to avoid further surgeries, a solution to recharge

2.5 – The Smart Shunt concept

Thus in addition the battery size that condition the general device dimensions and its positioning, an other important aspects concern the battery energy consumption that could generate heat damaging the tissues around the implant.

Regarding the communication system, it should be a bidirectional system as it should permit both the transmission of data detected by the sensors to the external subsystem, and the device handling from the outside by the clinician to change the smart shunt settings.

Radio frequency is the most used wireless communication method: the principal challenge concerns the choice of the frequency range that depends on the device location, the necessary power for the smart shunt functioning, the quantity of down-loading data. There are different frequency ranges to use in a wireless device, but for a device that has to implant in the human body, RF with a frequency in the low range is the best solution: in this way the researchers reaches a compromise between the bandwidth, the heat absorption and the tissue energy.

The most important smart shunt limitations can be summarized as follows:

• inaccuracy or breakage of the pressure (ICP), CSF flow, patient orientation sensors;

• technical issues;

• power limitation (battery’s charge and dimensions) ;

• product size limitation;

• potential faults;

• patient and clinicians mentality;

Currently there are no public evidences that a smart shunt has been completely developed and realized; on the other hand the single components, that could com-pose the smart shunt, are commercially available and they have different applica-tions, also in medicine.

This technological device is still a concept, an idea of project, despite from 1980 until today several studies, scientific researches and patents, regarding the smart shunt development, have been published. These references discuss the ad-justments and the improvements of the different components of a commercially available shunting device.

Recently, some monitoring systems have been developed as optional compo-nents of the shunting devices to detect ICP; for example Telesensor (Radionics), SensorReservoir (Miethke), flow probes and sensors (Transonic).

Chapter 3

Intracranial Pressure Sensors

Documenti correlati