Detector of bubbles in blood

A device for detecting the presence of a gaseous fluid in relation to a predetermined level of liquid in an elastically deformable vessel comprises a U-shaped body capable of accommodating within it a portion of the vessel at a predetermined liquid level. A pair of piezoelectric transducers in the body, used as transmitter and receiver, is fixed face-to-face on opposite arms of the U-shaped body. The device moreover comprises a cover capable of confining the portion of the vessel inside the U-shaped body, and an elastic device disposed between the cover and the U-shaped body and capable of producing an elastic deformation of the vessel and causing the contact surfaces of transducers to contact intimately the said portion of the vessel without entrapment of air.

FIELD OF THE INVENTION 
The present invention concerns a device detecting the presence of a gaseous 
fluid in relation to a predetermined level of a liquid in a vessel. More 
particularly, this invention concerns a device using, as a means for 
detecting the presence of a gaseous fluid, transducers capable of 
transmitting and of receiving a signal which is sensitive to the presence 
of a gaseous fluid. For this purpose, it is preferable to use 
piezoelectric transducers capable of transmitting and of receiving 
ultrasonic frequency signals whose propagation is strongly affected by the 
presence of a gaseous fluid even in very small quantities. 
PRIOR ART 
To prevent air from being trapped between the transducers and the 
corresponding facing surfaces of the vessel in which the measurement is to 
be effected, it is known to use elastic means which push the transducers 
against the respective facing surfaces of the vessel. These means are 
generally helical springs accommodated within a body supporting the vessel 
and elastically pushing the support elements of the transducers along 
slides arranged in the body of the apparatus. In one variant of such an 
embodiment, one of the transducers is fixed to the body of the apparatus, 
while the other is detachable and is connected to the body of the 
apparatus by a helical spring. 
Whilst the known devices mentioned above effectively make it possible to 
detect the presence of a gaseous fluid with reasonable accuracy and 
reliability, they are particularly expensive, essentially because of the 
cost of manufacturing very accurate guides for the supporting elements for 
the transducers. 
Moreover, the use of a detector device wherein it is only one of the 
transducers that is detachable, renders the preparatory operation for the 
measurement more complex because it is necessary to maintain the spring 
stretched with one hand and to position the vessel correctly between the 
two transducers with the other hand. 
OBJECT OF THE INVENTION 
It is an object of the present invention to provide a detector device which 
would allow the drawbacks of the known devices mentioned above to be 
overcome, and in particular to provide a device which does not require the 
execution of accurate guides for the support of the transducers and which 
should, moreover, be easy to use. 
SUMMARY OF THE INVENTION 
This object is attained by the present invention which provides a device 
for detecting the presence of a gaseous fluid in relation to a 
predetermined level of liquid in a deformable and elastic vessel, such 
device comprising: 
a hollow body having a compartment capable of accommodating a portion of 
the said vessel disposed in relation to said predetermined level; 
a pair of transducers, respectively transmitting and receiving a 
predetermined signal, said transducers being fixed to said hollow body in 
diametrically opposite positions and facing each other and said 
compartment, the receiver transducer being capable of cooperating with the 
said transmitter transducer and of emitting a signal responsive to the 
quantity of gaseous fluid interposed between said transducers; and 
a movable element connected to said hollow body by elastic means and 
capable of transmitting a radial thrust which can create a deformation of 
said portion of the vessel and its intimate contact with the transducers 
in opposite zones without air entrapment therebetween.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2 in particular, there can be seen a device 1 for 
detecting the presence of a gaseous fluid in relation to a predetermined 
level of liquid in a vessel 2. Vessel 2 is essentially of a tubular type 
with walls which are partially elastically deformable. The tubular vessel 
2 has an upper opening 3 enlarged for the entry of a liquid and a 
convergent lower opening 4 for the emergence of the same liquid. 
Advantageously, the vessel 2 could be incorporated along an extracorporeal 
blood circuit in which case blood would be the liquid within which one 
would wish to detect the presence of gaseous fluid. The device 1 is 
capable of accommodating a portion 5 of the vessel 2 between the upper 
opening 3 and the lower opening 4 of the vessel 2 itself. 
Referring more particularly to FIG. 3, the device 1 essentially comprises: 
a hollow body 7 having a compartment 8 capable of accommodating the 
intermediate portion 5 of vessel 2; 
a pair of transducers 9, 10 (FIGS. 3 and 4) of the piezoelectric type, used 
respectively as transmitter and receiver of an ultrasonic frequency 
signal, the transducers being fixed to the body 7 in diametrically 
opposite positions and facing each other relative to the intermediate 
portion 5 of the vessel, and facing the compartment 8; and 
a cover 11 connected to the body 7 by a helical compression spring 12 (FIG. 
3) as will be described in greater detail below, the essential function 
being to transmit a radial thrust to the portion 5 of vessel 2 with the 
purpose of entailing a deformation, and as a result, the intimate contact 
of the opposite sides 13, 14 of intermediate portion 5 with the 
transducers 9 and 10 without trapping any air between the contacting 
surfaces. 
Examining the device 1 in greater detail, it will be observed that the 
hollow body 7 is essentially U-shaped and that it supports transducers 9 
and 10 by means of respective limbs 17 and 18. In particular, the 
transducer 9 is supported directly by limb 17, whilst the other transducer 
10 is supported by an element 19 force-fitted within a transverse hole 20 
in the other limb 18. 
The compartment 8 is constructed in such a way as to be slightly 
elliptical, the major axis of the ellipse being identical with the common 
axis of symmetry of the two transducers 9 and 10. On their faces turned 
towards the compartment 8, these transducers are covered by a layer 23, 24 
of a plastic material, such as an epoxy resin. Referring to FIGS. 3 and 4, 
it will be observed that the free surface of each layer 23, 24 has the 
shape of a saddle so as to create a slight restriction of the portion of 
the compartment 8 in contact with the intermediate vessel portion 5 in 
which the presence of the gaseous fluid is to be detected. 
On the side of each transducer remote from the compartment 8 are two 
chambers 25, 26 which allow the piezoelectric transmitter transducer 9 and 
the receiver transducer 10 to vibrate. The facing sides of each transducer 
9, 10 are connected by fine conducting wires to electric conductors 27, 
28; in particular, the connection between the fine conducting wires and 
the conductors 27 and 28 is effected inside the respective chambers 29 and 
30 in the intermediate bight portion 31 of the U-shaped body 7 and they 
are advantageously filled with a setting resin 32, 33 of a suitable 
plastic material. 
Referring to FIGS. 2, 3 and 4, it will be observed that the cover 11 has an 
essentially rectangular shape and that it can pivot around a pin 36 (FIGS. 
2 and 3) supported by the ends 37 of a pair of rods 38 each of which can 
slide inside a longitudinal housing within the limb 17. Each rod 38 has, 
on its end remote from the pin 36, a threaded portion 39 (see FIG. 3) on 
which a nut 40 is screwed. The housing for each rod 38 is essentially 
enlarged in the vicinity of the threaded portion 39 to constitute a 
cylindrical chamber 41 which contains the above-mentioned helical spring 
12, which is coaxial with the rod 38 and can be pre-strained by the 
tightening of the nut 40. 
On the opposite side of the cover 11 to that which turns around the pin 36, 
is a catch 44 capable of cooperating with a corresponding catch 45 
disposed at the end of an arm 46 capable of pivoting around a pin 47 fixed 
transversely to the limb 18 of the body 7. Referring to FIG. 2, it will be 
seen that the catch 45 of the pivoting arm 46 is essentially trapezoidal 
in shape and narrows towards the end, whilst the catch 44 is situated 
below a recess 48, also of a trapezoidal shape and complementary to that 
of the catch 45 so as to facilitate the locking of the catch 45 on catch 
44. 
On the end remote from that comprising the catch 45 the pivoting arm 46 has 
an end 49 which delimits a part of the housing for a helical compression 
spring 50. Such a spring is comprised between the said end 49 of the 
pivoting arm 46 and the adjacent outwardly facing surface of the limb 18 
of the body 7 and transmits to the pivoting arm 46 a resilient thrust 
capable of causing the arm 46 to turn in a clockwise direction (see FIG. 
3) so as to facilitate the fastening of the catch 44 of the cover 11 with 
the catch 45 of the pivoting arm 46. 
On its opposite side facing away from the spring 50, the end 49 of the arm 
46 has a bulge 52 essentially forming a pyramid frustum on whose surface 
is a circular hollow concave area 53. 
Finally it will be observed, by referring to FIGS. 1 and 3, that the cover 
11 has, on its side facing the compartment 8 of the hollow body 7, a 
plurality of longitudinal parallel ribs 54 which each extend essentially 
from the pivot end near pin 36 as far as the opposite end provided with 
the catch 44. In the portion facing the compartment 8 each rib 54 has a 
profile which essentially constitutes the arc of an ellipse to complete 
and close the compartment 8. 
The device 1 is used as follows: 
First of all, the vessel 2 is inserted in the compartment 8, as shown in 
FIG. 1. Then the cover 11 is closed by swinging it across and pushing it 
until the catch 45 is locked on the catch 44 (see FIG. 2). In these 
conditions, the cover 11 is maintained against the hollow body 7 on the 
one side by the catch 44 and on the opposite side by the pin 36 and rods 
38. 
Since the rods 38 are subjected to axial elastic traction under the effect 
of the coil springs 12, it follows that the cover 11 transmits to the 
intermediate part 5 of the vessel 2, a radial compressive force through 
the intermediary of the elliptical profiles 55 of the longitudinal ribs 
54. Such radial forces result in the deformation of the vessel portion 5 
comprising the opposite zones 13, 14 so as to cause them to press 
intimately, without trapping any air, against the opposite surfaces 23, 24 
of the transducers 9 and 10. The deformation of the intermediate portion 5 
of the vessel 2 in the direction of the transducers 9 and 10 is promoted 
by the fact that the compartment 8 is partially elliptical and, as already 
mentioned, has its major axis aligned in the direction of vibration of the 
transducers. 
In these conditions, the device 1 is ready to be used as a detector for the 
presence of a gaseous fluid at the level of the intermediate portion 5 of 
the vessel 2. For this purpose, it suffices to provide the transmitter 
transducer 9 with a predetermined frequency signal, an ultrasonic one for 
example, and to pick up the corresponding electric signal from the 
receiver transducer 10. Since, as is known, the amplitude of the electric 
signal delivered by the receiver transducer 10 depends on the presence of 
a gaseous fluid, for instance, very fine air bubbles, between the 
transducers 9 and 10, it will be sufficient to compare the effective value 
of such an amplitude with a reference value in order to detect the 
possible presence of a gaseous fluid at the level of the intermediate zone 
5. 
It is obvious that the device 1 can equally well be used for detecting the 
presence of a gaseous fluid in the liquid of the vessel 2, as for 
detecting the lowering of the level of such a liquid below the zone 
between, and under the control of, the transducers 9 and 10. 
When it is desired to withdraw vessel 2, it suffices to press with one 
finger on the hollow circular area 53 at the end 49 of the pivoting arm 46 
(FIG. 3) to effect rotation of the pivoting arm 46 in an anticlockwise 
direction around pin 47 and to compress the spring 50 until the catch 45 
releases the catch 44 of the cover 11. The cover then swings open by 
partially rotating around pin 36 under the effect of the elastic reaction 
exerted by the intermediate portion 5 of vessel 2, and it can then be 
opened completely by the operator to the position indicated in dashed 
lines in FIG. 3. 
An examination of the characteristics of the detector device in accordance 
with the present invention makes it possible to reveal the advantages 
obtained. In particular, the making of accurate guides for the supporting 
elements of the piezoelectric transducers is unnecessary, since the 
transducers are fixed on the hollow body 7. The body 7 can be injection 
moulded which contributes to a reduction in the cost of device 1. 
Moreover, the operations needed for arranging the vessel 2 in the 
compartment 8 and then for closing cover 11 are elementary and can be 
easily performed with one hand. 
Finally, it is clear that various modifications and variants of the 
embodiment can be applied by the expert to device 1 described above 
without thereby departing from the scope of the present invention.