Note: Descriptions are shown in the official language in which they were submitted.
1049811
LIQUID FLOW-RATE MEASURING DEVICE
This invention relates to a liquid flow-rate measuring
device. More particularly, the invention is concerned with a
liquid flow-rate measuring device adapted for measuring the flow
rate of blood in an extracorporeal blood handling system.
Methods employed for measuring the flow of liquids,
particularly blood, involve the use of an electronic flow meter
or measurement of the time taken for a gas bubble injection into
a blood line to traverse a predetermined distance. Other means
for measuring flow rate of liquid comprise measurement by physical
means, such as by means of a pendulum located in the liquid flow
line. For expense reasons, most liquid flow-rate measuring devi-
ces ane not disposable, and it is an object of this invention to
; provide a device of sufficiently low cost to enable disposal after
a single use, e.g. in measuring the flow-rate of blood in an
extracorporeal blood handling system.
In accordance with the invention, there is provided a
liquid flow-rate measuring device comprising a cylindrical liquid
` receiver chamber having an inlet at its head for connection to a
liquid supply line and having a liquid outlet opening defined by
a thin wall at its base, and a cylindrical liquid delivery chamber
having an outlet at its base for connection to a liquid take-off
line, said liquid delivery chamber enclosing said liquid receiver
chamber and being arranged to receive liquid from the liquid
receiver chamber, a pressure equalising aperture being provided
in the liquid receiver chamber at or towards its head to equalise
pressures developed above volumes of liquid in the liquid receiver
chamber and liquid delivery chamber.
The liquid receiver chamber and liquid delivery chamber ~-
are most preferably of transparent material enabling visual
observation of the level of liquid in the liquid receiver chamber.
Otherwi~e, some other means for determiming the level of liquid
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in the liquid receiver chamber would be necessary, such as an
electronic blood level monitoring device.
The liquid receiver chamber may be provided with cali-
brated liquid level markings which indicate the flow-rate of
liquid through the device as a function of the height of liquid
in the liquid receiver chamber.
A filter for filtering liquid passing through the device
may be provided at the base of the liquid delivery chamber. For
use in measuring the flow rate of blood, the filter material and
indeed ~11 other parts which come into contact with the blood,
must be of a sterile material which is compatible with the blood.
As already indicated, the liquid flow-rate measuring
device of the invention may be adapted for measuring blood flow-
rate in a blood line of an extracorporeal blood handling system.
Thus the apertures and size of the cylindrical liquid receiver
chamber and cylindrical liquid delivery chamber, inlets and out-
` lets may be dimen~ioned to measure the flow rate of blood.
At least one access conduit leading into the side of theliquid delivery chamber may be provided, which access conduit may
be employed for taking samples of blood by conventional means,
such as with the aid of a syringe. Similarly, the access conduit
may be employed for measuring the pressure of gas above liquid
(blood) in the liquid delivery chamber.
A control valve for controlling liquid flow-rate and
hence back-pressure in the device may be provided at the outlet
of the liquid delivery chamber. The control valve may be of con- -
ventional type.
The invention will now be described with reference to
the accompanying drawing showing, by way of example, a liquid
flow rate measuring device in accordance with invention.
- The drawing shows a cross section of the liquid flow
~ rate measuring device referréd to generally by reference numeral
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1049811
c;l l o .
The liquid flow-rate measuring device comprises a cyl-
. indrical liquid receiver chamber 12 having an inlet 14 at its
,c~ head for connection to a liquid supply line 16. A liquid outlet
opening 18 is defined by a thin wall 20 at the base of the liquid
receiver chamber 12, said thin wall being formed by the edges
defined by moulding or otherwise producing a frustro-conical cut-
out 22 in the base wall of the liquid receiver chamber.
A cylindrical liquid delivery chamber 24 having an out- :
let 26 at its base for connection to a liquid take-off line 28
encloses the liquid receiver chamber 12 and is arranged to receive ~
liquid f~om the liquid receiver chamber flowing th~ough its liquid
outlet opening 18.
Pressure equalizing apertures 30 are provided in the
liquid receiver chamber 12 towards its head to equalize pressures
developed above volumes of liquid in the liquid receiver chamber
12 and liquid delivery chamber 24.
, . The liquid receiver chamber 12 and liquid delivery
chamber 24 are of transparent material, such as of a suitable
plastics material enabling visual observation of the level of
liquid in the liquid receiver chamber 12. The liquid receiver
chamber is provided with calibrated markings 32 which indicate
the flow-rate of liquid through the device as a function of the ~.
height of l~quid in the rece~ver chamber 12. ~-
A filter 34 for filtering liquid passing through the
device 10 is provided at the base of the liquid delivery chamber
24. The filter 34 is seated over a converging opening 36 in the
base wall of the liquid delivery chamber.
Access conduits 38 and 40 leading at an acute angle into
. 30 the side of the liquid delivery chamber are provided. The access ~.
conduits may be sealed closed with latex rubber caps, and samples ..
of liquid (blood) may be taken from the liquid delivery chamber
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1~49811
with the aid of a syringe. The access conduits 38 and 40 may
find other applications, such as for monitoring the pressure of
gas above liquid (blood~ in the liquid delivery chamber, or for
adding saline, heparine and the like to blood in the liquid
delivery chamber 24.
A control valve 38 for controlling liquid flow-rate and
hence back-pressure in the device 10 is provided at the outlet 26
of the liquid delivery chamber 24, in the liquid take-off line 28.
The liquid flow-rate measuring device of the invention,
in use in an extracorporeal blood handling system such as a hemo-
dialysis system, may conveniently be situated downstream from a
blood pump referred to by reference numeral 42 and downstream
from an artificial kidney or blood dialyser referred to by refer-
ence numeral 44.
In:.operation, liquid (blood) flows through the liquid
supply line 16 and into the liquid receiver chamber 12 through
the inlet 14. The level to which liquid builds up in the liquid
receiver chamber is dependent on the rate of flow of liquid into
the liquid receiver chamber, and the dimension of liquid outlet
opening 18. Liquid continuously flows through the liquid outlet
opening 18 and partially fills the liquid delivery chamber 24.
The liquid then passes out from the liquid delivery chamber 24
through the outlet 26 after having been filtered through the
filter 34.
A stable condition, if flow rate of liquid is substant-
ially constant, sets in fairly rapidly, and the flow-rate of liq-
uid through the device 10 can be read off directly from the
calibrated markings 32 as a function of the height of liquid in
the liquid receiver chamber 12.
