Intracorporeal measuring system

A Measurement device for medical applications is disclosed, comprising an intracorporeal sensor element (5), a extracorporeal evaluation unit and electrical connections (2, 6) between the sensor element (5) and the evaluation unit. The device comprises a flexible foil tape cable (1), which is intended for the electrical and mechanical connection of the evaluation unit with the sensor element (5) and a substrate (4), which is mechanically connected with the one end (3) of the foil tape cable (1) around the sensor element (1). The substrate (4) has an higher mechanical strength than the foil tape cable (1). The sensor element (5) is connected to electric cables (2) of the flexible foil tape cable (1) and the substrate (4) is enclosed with the sensor element (5) in a flexible mass (7).

In medical applications, measurement sensors are inserted into the body 
with the aid of a catheter (intracorporeal) and guided to positions where 
biosignals are to be measured. When measuring inside of the skull 
(intracranial), the sensors must have an extremely small cross-section. 
Therefore, semiconductor sensors are given preference, assembled and 
contacted in a carrier capsule. 
For example, the cerebral pressure is measured by intracranial sensor 
measurement in the intensive care ward of the clinic for the diagnosis of 
hydrocephalus. The sensor is then removed and disposable sensors are 
destroyed, i.e. reusable sensors are sterilized and used on the next 
patient. 
If, for example, a hydrocephalus is diagnosed, a so-called shunt system is 
applied. If the cerebral pressure increases above a certain limit, 
cerebral water (cerebrospinal fluid) is redirected to the peritoneal 
cavity, thus avoiding a dangerously high pressure in the brain. 
The measurement of cerebral pressure can be made both epi- and subdural. 
Epidural means that the cerebral pressure can be determined indirectly 
between the hard meninge (dura mater) and the brain pan (calotte) by the 
pressure exerted by the cerebrospinal fluid on the meninge. 
This measuring point has the advantage that the hard meninge is not 
penetrated, thus avoiding any infection of the meninge, the intervention 
is considerably more simple, no brain tissue is damaged during this 
intervention and the sensor can remain in measuring position for a longer 
period of time. 
A subdural measurement means that the sensor is pushed beneath the and 
penetrates the meninge. This allows for the measurement of the pressure in 
the brain tissue (parenchyma). In frequent cases, the brain tissue is 
penetrated in order to allow for a measurement in the ventricle 
(intraventricular). 
Various intracranial measurement systems are commonly familiar. For 
example, the firm B. Braun Melsungen AG offers an epidural measurement 
system under the name `epidyn`. In this version, a semiconductor sensor is 
attached within a metal casing. The sensor is connected to strands of a 
cable, transmitting the electrical signals to an extracorporeal evaluation 
unit. This system has high manufacturing costs. Additionally, the minimum 
bending radius is no more than a few centimeters. If this radius is not 
achieved, then the danger is that these strands will break. However, 
medical applications require lesser bending radii, as the patients move 
around in bed and need to be washed. 
Traditional pressure sensors involve the manufacturing of a metal case, 
into which the cable and the pressure sensor are pushed. In order to 
reduce the strain, the individual wires are wrapped around the pressure 
sensor, bonded with the pressure sensor and sealed with plastic. As a 
result of the small dimensions, this process can only be implemented with 
a lot of effort using tools of precision engineering. 
In the U.S. Pat. No. 4,738,267, an implantable, intracranial pressure 
sensor is depicted, whereby electric cables are formed of cased strands in 
order to connect the sensor element with an extracorporeal evaluation 
unit. During production, these strands must be connected with each other 
in a laborious process. Additionally, there is the risk that the cable 
fibres will tear under strain and, the necessarily small bending radius 
mean that the strands may break. 
In DE 43 15 987 C1, an extracorporeal body electrode is depicted, whereby a 
single sensor is attached to a flexible carrier foil. In order to connect 
an evaluation unit, a cable is attached to the end of the carrier foil 
using a clamp. The extracorporeal body electrode is only suited to 
measuring voltage and must not be given intracorporeal application. It 
would also not be suited to fulfil intracorporeal chemical, biological or 
physical sensory tasks. 
In U.S. Pat. No. 5,263,244, a process for the manufacturing of a flexible 
semiconductor sensor arrangement for the optical pulse measurement is 
described. Integrated sensor elements are attached in a traditional manner 
to a flexible foil, fitted with electrically conductive tapes. The sensor 
elements, e.g. light-emitting diodes and photodetectors are connected with 
the conductive tapes using SMD engineering. The ends of the relatively 
short tapes are formed by contacts onto which the encased strands are 
soldered. This necessitates a fairly laborious soldering process, whereby 
the soldering points constitute a quality risk. Additionally, there is the 
risk that the strands break under tight bending radii. It is also not 
possible to solder integrated pressure sensors to the corresponding 
contacts on the conductive tapes using SMD engineering. 
OBJECT OF THE INVENTION 
The object of the invention was to create a measurement device for medical 
applications with an intracorporeal sensor element, an extracorporeal 
evaluation unit and electric connections between the sensor element and 
the evaluation unit. Furthermore, the system must be reliable, light and 
cost-efficient and must allow the patient to move around in bed. 
The object was solved using the measuring system with the characteristics 
of claim 1. The manufacturing of the measurement system can take place 
simply and cost-effectively using the automatable process according to 
claim 6. 
The invented measuring system can be produced at much less cost and has a 
greater tensile strength with a lower permissible bending radius. Movement 
and shearing of the sensor on the tape are compensated by the 
strengthening of the end of the foil with a plate-shaped substrate.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION 
A cerebral pressure measurement system is to be presented as a preferred 
embodiment. Equally, the structural engineering can also be used for other 
medical applications. 
FIGS. 1 and 2 depict an intracorporeal cerebral pressure measuring device. 
In order to replace the wires for energy supply and measurement signal 
transmission, a cable 3 is provided comprising a flexible tape 1 which 
carries a plurality of electrical tracks 2. At the end of the cable 3 
there is a substrate 4 which strengthens the structural engineering of the 
sensor element. The pressure sensor 5 is attached to the substrate 4 and 
bonded with the connecting wires 6. After this, the bond wires of the 
pressure sensor 5 are fixed using a moulded mass 7. Subsequently, the 
pressure sensor 5 is moulded in a mass 7 made of polyumide or 
polyurethane. A silicon mass is given preference for this, as this is a 
flexible material through which pressure can be transmitted. Additionally, 
it offers sufficient insulation against electric current. This is 
particularly important for medical applications in order to protect the 
patient. The carrier material 8 of the flexible tape 1 is, e.g. a FR4 
foil. The substrate 4 to strengthen the cable end 3 is currently made of a 
FR4 substrate. On the second contact end 9 of the flexible tape 1, there 
is a plug contact 10 or, in a further development, an electronic switch 
onto which the leveling switch is fitted. 
In order to manufacture the tape cable 1, the carrier foil 8 is exposed, 
etched and stamped using traditional methods. 
A plug contact 10 is attached to the second contact end 9. Alternatively, 
the electrical tracks 2 could be fanned out over the board with the 
evaluation switch then manufactured directly onto tape 1. 
In order to carry out an intraventricular measurement of the cerebral 
pressure, the meninge is penetrated and the sensor 5 with the tape cable 
are fed into the ventricle through the brain mass. The ventricle is the 
part of the brain in which the cerebrospinal fluid circulation of the 
brain is closest to the spinal cord. In the even of a hydrocephalus, the 
ventricle is expanded and its discharge is occluded and impossible, thus 
meaning that the pressure there is a very exact and reliable indication 
for a disturbance of the circulation of the cerebrospinal fluid. The main 
advantage of an intraventricular cerebral pressure measurement is the high 
measurement exactness.