Peristaltic pump provided with a pressure measurement device

Apparatus for circulating a liquid along a tubular conduit comprises a peristaltic pump provided with a rotor which acts through the intermediary of rollers, on an elastically deformable tube disposed in series along the mentioned tubular conduit and a device mounted outside on a section of the deformable tube for emitting an electric signal depending on the deformation induced in operation in the section of tube by the pressure of the said pumped liquid.

FIELD OF THE INVENTION 
The present invention concerns an apparatus for circulating a liquid along 
a tubular line. In particular, such a liquid may be blood which is flowing 
in an extracorporeal circulation, for instance, to be purified by a 
dialysis operation. 
PRIOR ART 
The apparatus to which the present invention relates is of the type 
essentially comprising a peristaltic pump provided with a rotor which is 
acting by means of rollers on the external surface of an elastically 
deformable tube disposed in series with a tubular extracorporeal line for 
the blood and comprising, moreover, a device capable of providing an 
indication of the pressure of the blood which is flowing upstream from the 
peristaltic pump itself. 
In general, this kind of apparatus comprises a tubular reservoir frequently 
called a pulse damper and made of an elastically deformable material which 
is connected in series to the extracorporeal blood line and which, in 
operation, is fitted inside a body constituted by a receptacle closed at 
its upper portion by a lid. The apparatus, moreover, comprises a 
micro-switch mounted on the bottom wall of the receptacle in order to 
detect the deformations induced by the blood pressure, and a screw carried 
by the lid which can be manipulated by the operator in order partially to 
deform the reservoir and thus to make it possible to predetermine an 
intervention threshold for the micro-switch. 
It has been observed that the type of apparatus described above has many 
drawbacks deriving from the use of this reservoir. In fact, the reservoir 
contains, in operation, a quantity of blood representing a significant 
percentage of the extracorporeal line capacity and this entails a high 
inertia level, the response time between the pressure variations and their 
detection often being too long. For practical reasons of manufacture, the 
walls of the reservoir cannot be made of a material having a high degree 
of elasticity and this detracts from the sensitivity of the device. The 
system of regulating the intervention threshold by means of the above 
mentioned screw necessitates an adaptation of the structure of the 
reservoir which affects the sensitivity value and requires the operator's 
intervention for readjusting the intervention threshold each time a new 
line is used since the reservoir can only be removed after the screw 
carried by the lid has been unscrewed. The adoption of the reservoir 
entails very pronounced variations in cross-section of the blood flow 
flowing in the extracorporeal line because the cross-section of the line 
is considerably smaller than that of the reservoir. 
Such variations in cross-section, apart from making it possible for air to 
be drawn in at the junction of the reservoir and of the line, also produce 
a turbulent motion of the blood which can damage it by producing, for 
instance, a haemolysis of the red blood cells. Finally, it is appropriate 
to note that the reservoir is always a component which has to be 
manufactured and assembled, by bonding, in series in the extracorporeal 
blood line and that this entails considerable costs of manufacture and 
labour. 
OBJECT OF THE INVENTION 
It is an object of the present invention to provide apparatus for 
circulating a liquid, for instance blood, along a tubular line and which 
avoids the drawbacks presented by the known types of such apparatus set 
out above. 
SUMMARY OF THE INVENTION 
This object is achieved by the present invention which concerns an 
apparatus for circulating a liquid along a tubular line with a peristaltic 
pump having a rotor which is acting by means of rollers on the external 
surface of an elastically deformable tube placed in series into the said 
tubular line and with a device capable of supplying the pressure values of 
the liquid flowing in the said line ahead of the said pump. It is 
characterised in that it comprises: 
a reference element and a movable element between which it is possible to 
interpose a section of the said tube which is not subjected to the action 
of the said rollers; 
elastic means which transmit to the said movable element a thrust being 
exerted towards the said reference element and in a radial direction to 
the said tube section; and 
measurement means which note the relative position taken by the said 
movable element in relation to the said referene element and which emit a 
corresponding electric signal, depending on the deformation of the said 
tube section, caused in operation by the pressure of the said liquid.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 in particular there will be seen apparatus 1 for 
circulating a liquid along a tubular line 2. Apparatus 1 essentially 
comprises a peristaltic pump 3 provided with a rotor 4 having rollers 5 
which act on the external surface of a first section 7 of a tube 6 formed 
of an elastically deformable material such as, for example, a plasticised 
polyvinyl chloride (PVC) and placed in series along the tubular line 2 
mentioned above. Apparatus 1 comprises, moreover, a device 10 which is 
disposed externally of a second section 8 of tube 6 which extends outside 
the bowl shaped body 9 of the peristaltic pump 3. 
As will be described in greater detail with reference to FIGS. 2 and 3, the 
device 10 is capable of emitting an electric signal depending on the 
deformation induced, in section 8 of the tube 6 in use, by the effect of 
the pressure of the liquid flowing within the portion of the tubular line 
2 disposed ahead of the peristaltic pump 3. 
Apparatus 1 finally comprises an electric circuit generally indicated by 
reference 12 to compare the electric signal emitted by the device 10 with 
an adjustable reference signal with the object of giving an alarm signal 
to a lamp 13 when the divergence between these two signals exceeds 
predetermined safety limits. 
More particularly, the circuit 12 comprises an amplifier 14 which receives 
the electric signal emitted by the device 10 and which delivers such a 
signal, suitably amplified, to the first input of a comparator circuit 15 
whose second input receives the above mentioned adjustable signal supplied 
by the slide contact of a potentiometer 16 whose opposed ends are 
respectively connected to the frame and to a power source of a known type 
connected to a terminal 17. The output of the comparator circuit 15 is 
finally connected, by means of an additional amplifier 18, to the 
signalling lamp 13. 
The structure of device 10 will now be described by referring more 
particularly to FIGS. 1 and 3. Such a device essentially comprises (a) a 
reference element 21 and a movable element 22 between which the section 8 
of the above mentioned tube 6 can be interposed; (b) elastic means 23 
transmitting to the movable element 22 a thrust towards the reference 
element 21 in a radial direction in relation to the section 8 of the tube 
6; and (c) measurement means 24 which detect the relative position of the 
movable element 22 in relation to the reference element 21 and which 
consequently emit the electric signal used in circuit 12. 
More particularly, the device 10 includes a tubular support 26 joined to a 
channel shaped element 28 by means of screws 25 which pass through holes 
(not shown) in a plate 27 which also supports the body 9 of the 
peristaltic pump 3. The channel shaped element 28 forming a receptacle is 
closed at its upper portion by a lid 29 which constitutes said reference 
element 21 and which can rotate around a pivot pin 30. The bowl shaped 
element 28 has, at its base, a hole 32 which axially slidably receives the 
above mentioned movable element 22. 
The movable element is a piston having an upper cylindrical portion 33 with 
a diameter which is slightly smaller than the diameter of the above 
mentioned hole 32 and having a head 34 intended to cooperate, in use, with 
the external surface of tube section 8 of the deformable elastic tube 6. 
The surface of the head 34 opposite the tube section 8 is flat with an 
essentially spherical surface at the periphery. The movable element 22 
has, moreover, a lower cylindrical portion 36 coaxial with the upper 
portion 33 but having a smaller diameter. The lower portion 36 has a 
threaded end 37 engaged in a corresponding tapped hole 38 arranged in the 
upper portion 33. On the end remote from its end 37, the lower cylindrical 
portion 36 carries a head 41 forming a receptacle within which is 
accommodated a permanent magnet 42 capable of acting on the said 
measurement means 24 as will be described below. 
The tubular body 26 of the device 10 defines a cylindrical chamber 44 open 
at its lower portion at a hole (45) which slidably receives the lower 
cylindrical portion 36 of the movable element 22. The internal diameter of 
the chamber 44 is slightly greater than the diameter of the cylindrical 
portion 33; the chamber 44 thus performs a guiding function for the axial 
displacements of this cylindrical element 33, and it receives a coil 
spring 46 coaxial with the smaller diameter cylindrical element 36 in 
order to transmit to the upper cylindrical portion 33 the above mentioned 
thrust towards the reference element 21 and radially in relation to the 
section 8 of the tube 6. This section 8 is thus elastically compressed by 
the spring 46 which, during operation of the pump, deforms the section 8 
indicated in FIG. 3, pressed between, on one side, the flat and circular 
upper surface of head 34 of the upper cylindrical portion 33 of the 
movable element 22 and, on the opposed side, a corresponding flat circular 
surface of a relief 48 on the inwardly facing part of the body of the lid 
29. 
The connection between the lid 29 and the corresponding box shaped part 28 
is effected by not only the pin 30 but also by the catch-engagement of a 
tooth 51 of the lid 29 with a corresponding cavity 52 in the end of an 
elastically deformable element 53 and joined at its base to the 
channel-shaped element 28. More particularly, the connection between the 
deformable element 53 and the channel-shaped part 28 is produced by 
forcing the dovetail-shaped base 54 of the deformable element 53 into a 
cavity at the periphery of the bottom wall of the channel of element 28. 
In conformity with the elastically deformable element 53, the lateral wall 
of the channel-shaped receptacle 28 has an essentially rectangular seat 
designated by reference 56 so as to accommodate practically the whole of 
the deformable element 53, this being arranged so that the element 53 is 
essentially located in the same plane as the corresponding lateral surface 
57 of the lid 29. 
It will finally be observed that near the cavity 52 and the part facing it 
on the outside, the element 53 has a cylindrical relief 59 whose purpose 
is to indicate to the user the most convenient region for exerting 
pressure on the deformable element 53 to disengage the tooth 51 from the 
cavity 52 and hence to open the lid 29. 
The measurement means 24 are supported by a cantilever 61 joined to the 
body 26 of the device 10 by means of a screw 62. Such measurement means 
are thus disposed opposite the permanent magnet 42 and coaxially with it 
and they are capable of emitting an electric signal depending on the 
intensity of the magnetic field in which they are placed, which electric 
signal obviously depends on the distance between magnet 42 and the 
measurement means 24. Preferably these measurement means comprise a "Hall" 
effect transducer. 
The operation of apparatus 1 is as follows. When positioning the 
extracorporeal blood line, the section 8 of the elastically deformable 
tube 6 is situated on the side of the peristaltic pump 3 at the part which 
will be subjected to suction under the effect of rotation of rotor 4. Then 
the section 8 is simply introduced within the channel-shaped part 28 and 
the lid 29 is closed by pressure applied at the part remote from the pivot 
pin 30. In this way, the tooth 51 causes the deformable element 53 to 
buckle elastically inwards until it occupies the corresponding cavity. In 
these conditions the section 8 is disposed between the lid 29 and the flat 
head 34 of the movable element 22 and it is moreover subjected to the 
radial thrust which it receives from spring 46. 
Under normal conditions, the peristaltic pump replaces the flow of the 
liquid along line 2 by drawing it from the portion where the section 8 is 
situated and by driving it on into the opposite portion of tube 6. If 
there is an obstruction of some importance along line 2 ahead of the 
peristaltic pump 3 the pressure of the liquid contained inside line 2 
itself will decrease and in particular also within the section 8. Because 
the section 8 is made of a particularly deformable material, it is 
radially deformed and the action of the spring 46 has the effect of 
keeping the surface of head 34 in contact with the corresponding surface 
of the section 8 consequently increasing the distance between the magnet 
42 and the detector 24. As has already been stated, the electric signal 
emitted by the detector 24 depends on the value of the magnetic field to 
which it is exposed; in this specific case, it is subjected to a reduction 
in amplitude. Such an electric signal, after having been amplified by 
amplifier 14, is compared by the comparator 15 with the reference signal 
transmitted by the sliding contact of the potentiometer 16 and, if the 
divergence between the two signals exceeds predetermined limits, the 
comparator circuit 15 emits an alarm signal which illuminates the lamp 13 
by means of amplifier 18. The adjustment of the intervention threshold in 
the comparator circuit 15 can simply be effected by manipulating the 
sliding contact of the potentiometer 16 and by adjusting the contact until 
the desired threshold value is obtained. 
From an examination of the characteristics of the apparatus 1 described 
above, its advantages will be quite clearly apparent, especially in the 
case where the liquid to be pumped is blood. In fact, the quantity of 
blood used for controlling the pressure is now distinctly less than that 
contained in the reservoirs which have been used previously, because it is 
limited to that contained in the section 8 of the deformable tube 6. This 
entails a lower inertia, which makes it possible to have a rapid response 
with immediate signalling of deformations of the section 8 induced by 
pressure variations in excess of admissible limits. 
A rapid resumption of normal working conditions is also obtained thanks to 
either the considerable elasticity of the walls of section 8 or the 
smaller quantity of blood circulating between the inlet of pump 6 and the 
zone of vascular access of the extracorporeal blood line 2. The 
sensitivity of the device 10 is substantially improved as a result of the 
high elasticity of the walls of section 8 and it is not affected by the 
threshold adjustments which are effected electronically. 
Moreover, the operations of positioning and withdrawing the extracorporeal 
blood line 2 are simplified still further, because it is no longer 
necessary to repeat the calibration every time the tube is changed by 
screwing and unscrewing the screw in the lid as in the known type of 
apparatus. It follows that there are no undesirable changes in 
cross-section of the tubular conduit, apart from those required by the 
connection between line 2 and the tube 6. 
The above mentioned known problems, due to an imperfect seal of the 
junctions between the reservoir and the line in the prior art pump, no 
longer subsist, nor do the difficulties (haemolysis etc. . . . ) due to 
the turbulent blood flow. Finally, it is obvious that since the line no 
longer requires the existence of a reservoir the system is obviously 
simplified and is cheaper as regards costs of manufacture and of labour. 
Finally, it is clear that various variants and modifications may be made to 
the apparatus described above, without thereby departing from the scope of 
the present invention. 
For instance, as shown in FIGS. 4 to 8 the measurement means or detector 24 
could be suitably built by means of a magnetic Reed switch in which case 
it could be mounted on a cross member or cantilever whose position in 
relation to magnet 42 could be axially adjusted in an accurate and precise 
way. The transducer 24 and magnet 42 could also be replaced by a 
differential transformer, or by a potentiometer type of transducer, or yet 
again by an opto electronic type of position transducer which could 
comprise, for example, an optical reflection device in order to obtain 
embodiments equivalent to those described above. 
Another embodiment could employ an analog type indicating instrument 
immediately at the output of the amplifier circuit 14, thereby replacing 
the comparator 15, potentiometer 16, amplifier 18 and the signalling lamp 
13. However, in such a case the indications supplied by such an instrument 
would be monitored at regular intervals.