Liquid purification or separation – With alarm – indicator – register – recorder – signal or... – Fluid pressure responsive
Reexamination Certificate
2001-12-07
2003-11-18
Kim, John (Department: 1723)
Liquid purification or separation
With alarm, indicator, register, recorder, signal or...
Fluid pressure responsive
C210S097000, C073S715000, C073S716000, C073S717000, C073S723000
Reexamination Certificate
active
06649046
ABSTRACT:
FILED OF THE INVENTION
The present invention relates to a device for measuring blood pressure.
More particularly, the present invention relates to a device for measuring the pressure of blood which is used in an extracorporeal blood treatment device in which the blood is taken from a patient in order to be treated then reintroduced into the body of the patient (especially for the purpose of carrying out dialysis) by means of an extracorporeal blood circuit comprising pipes and including at least one section for measuring the pressure of blood circulating in a pipe.
BACKGROUND OF THE INVENTION
A known type of pressure measurement section forms a compartment which is delimited especially by a main wall and by a secondary wall facing it, the two walls being substantially rigid and parallel; the main wall comprises a hole which is sealed by a main closure element, the internal face of which is in contact with the blood and the external face of which is in contact with the ambient air, it being possible to elastically deform or displace the entire main closure element along a deformation or displacement axis which is substantially orthogonal to its general plane, under the effect of the blood pressure; a portion of the external face of the main closure element, in its rest state, is in direct or indirect contact with a load sensor which is able to measure the force applied axially to the internal face of the main closure element by the pressure of the blood, in order to calculate therefrom the value of this pressure.
Generally, this type of extracorporeal blood treatment device comprises a circuit part which is formed from a casing, or cassette, of the “disposable” type, integrating pipes which are connected to the extracorporeal blood circuit.
The pressure measurement section may be an attached module which is mounted in a housing associated with the casing.
The casing is mounted on a support apparatus which comprises, for example, sensors, display means, pumping means, a control interface, an electronic control unit, etc.
In this type of extracorporeal blood treatment device, the blood pressure must be measured without contact between the measuring member and the blood.
Several systems for carrying out this pressure measurement are known.
In a first pressure measurement system, which is shown in
FIG. 1
, a pressure measurement section
10
in a pipe
12
comprises a measurement chamber
14
in which a membrane
16
, or diaphragm, separates the blood flowing in the pipe
12
from the air contained in a compartment
18
.
The membrane
16
can be deformed along a deformation axis A—A orthogonal to its general plane, such that it is axially displaced according to the blood pressure in the pipe
12
.
The extreme deformation positions of the membrane
16
are shown in dotted lines.
The air compartment
18
is sealed shut when the pressure measurement section
10
is mounted on a support apparatus
20
.
The support apparatus
20
comprises a sensor
22
which directly measures the pressure in the air compartment
18
.
When the blood pressure changes, the membrane
16
is axially displaced to an equilibrium position in which the pressure is equal on each side of the membrane
16
.
The pressure measured by the sensor
22
in the air compartment
18
is therefore equal to the blood pressure in the pipe
12
.
By virtue of a suitable geometry, in particular by virtue of a suitable volume of the compartment
18
and a suitable surface for the membrane
16
, this first pressure measurement system makes it possible to measure, on the one hand, so-called “positive” blood pressures, that is blood pressures which are greater than a reference pressure, in this case atmospheric pressure, and, on the other hand, so-called “negative” blood pressures, that is blood pressures which are less than the reference pressure.
This measurement system operates correctly provided there are no leaks in the air compartment
18
, otherwise the membrane
16
is then displaced to its end stop and it no longer carries out the function of transmitting pressure.
The sealing of the air compartment
18
during mounting of the pressure measurement section
10
on the support apparatus
20
is a weak point of the measurement system.
In particular, the seal may be impaired while the measurement system is in use.
In a second pressure measurement system, which is shown in
FIG. 2
, the pressure measurement section
10
forms a compartment
24
containing the blood and a wall
26
of which includes a hole
28
which is sealed by a flexible membrane
30
.
When the pressure measurement section
10
is mounted on the support apparatus
20
, the external face of the central part of the flexible membrane
30
is in contact with a load transmitter
32
which is inserted between the membrane
30
and a load sensor
34
.
The load sensor
34
makes it possible to measure the forces applied to the internal face of the membrane
30
due to the effect of the blood pressure in the compartment
24
, when the blood pressure is greater than the ambient air pressure.
The blood pressure is calculated from the equation:
P
=
F
-
F
0
S
a
(
1
)
In this equation, F is the force measured by the load sensor
34
, F
0
is the force measured in the rest state, that is in the absence of a pressure gradient between the two sides (external and internal faces) of the membrane
30
, and S
a
is the area of the active surface of the membrane
30
.
The area of the active surface S
a
of the membrane
30
has a value between the total area of the internal face of the membrane
30
in contact with the blood and the area of contact between the membrane
30
and the load transmitter
32
.
For very flexible membranes
30
, the active surface S
a
is substantially equivalent to the area of contact between the membrane
30
and the load transmitter
32
.
This measurement system makes it possible to measure a positive pressure but it does not allow a negative pressure to be measured.
This is because, for negative pressures, the membrane
30
tends to come away from the load transmitter
32
. The load sensor
34
can therefore no longer measure the forces which are applied to the membrane
30
.
This system has therefore been adapted to measure negative pressures.
In order that the load sensor
34
can continue to measure the forces which are applied to the membrane
30
, when the blood pressure is negative, the membrane
30
is secured in axial displacement to the load transmitter
32
.
Thus, according to an improved embodiment of the second pressure measurement system, which is shown in
FIG. 3
, the membrane includes a metal disc
36
on its external face and the load transmitter
32
includes a magnet
38
at its axial end facing the membrane
30
.
The magnetic attraction exerted by the magnet
38
on the metal disc
36
makes it possible to secure the membrane
30
in axial displacement to the load transmitter
32
.
When the pressure is positive, the membrane
30
exerts an axial force which pushes against the load transmitter
32
.
When the pressure is negative, the membrane
30
exerts an axial force which pulls on the load transmitter
32
.
This device for securing the membrane
30
to the load transmitter
32
is expensive since it requires a special membrane
30
fitted with a metal disc
36
and a special load transmitter
32
fitted with a magnet
38
.
The metal disc
36
must have a large area in order to allow effective magnetic coupling.
Furthermore, the membrane
30
experiences a significant jolt when the metal disc
36
“sticks” to the magnet
38
of the load transmitter
32
, which could impair its mechanical characteristics.
The invention aims to remedy these drawbacks.
SUMMARY OF THE INVENTION
For this purpose, the invention proposes a device for measuring the pressure of blood in a pipe of an extracorporeal blood circuit, comprising a pressure measurement section having a compartment which is delimited especially by a main wall and by a secondary wall facing it, the two walls being substantially rigid and parallel, the main wall having a hole whic
Hospal International Marketing Management
Kim John
LandOfFree
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