GB2031158A

GB2031158A - Flow measurement

Info

Publication number: GB2031158A
Application number: GB7839422A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-10-05
Filing date: 1978-10-05
Publication date: 1980-04-16

Abstract

A liquid flow meter comprises a closed vessel including upper and lower chambers 11, 13 respectively with liquid inlet and outlet ports, 12, 14, and interconnected by a syphon tube 15 for liquid throughflow and also by a breather tube 16 extending above the syphon tube. Continuous flow applied to the inlet results in discrete, constant volume liquid displacements between the chambers, and the interval therebetween represents applied liquid flow rate. This rate can be measured automatically, suitably by way of a photoelectric detector 18, 19, 20. The meter is suitable for application in a renal dialyser where it serves also as a bubble trap. <IMAGE>

Description

SPECIFICATION Flow measurement devices This invention concerns flow measurement devices and more particularly, but not exclusively, such devices for measuring blood flow rate during renal dialysis.

Blood flow rates during renal dialysis are usually obtained by timing the passage of an air bubble along a known length of blood tubing, the bubble being introduced into the blood flow for this purpose. However this procedure is not fully satisfactory because the necessary introduction of a bubble consumes the time of a nurse or other skilled personnel, and such introduction involves the risk of infection of the blood. An additional disadvantage arises from the fact that the bubble transit time is usually measured with a stop watch, entailing more personnel time and inevitably having unreliable accuracy. Photoelectric timing devices have been proposed with a view to obtaining better accuracy in the measurement of bubble transit time, but the other disadvantages of the bubble procedure remain.

Ultra Doppler flow meters have also been proposed for the relevant measurement, but, while such meters can be more accurate than the above techniques and are non-invasive in use, they are expensive and difficult to correlate accurately with blood flow rate.

A further procedure for blood flow measurement employs the bubble trap commonly found in renal dialysis equipment and involves the provision of a constriction through which the blood is passed in the trap, with the resulting accumulation at the constriction being timed to provide a measure of flow rate.

Although this procedure is inexpensive, noninvasive, and simple to use, it is not very accurate and does not readily lend itself to automation.

Recent advances in dialysis therapy indicate that automatic control of a dialysis monitor by a microprocessor may well be part of the next generation of dialysis equipment and so, bearing in mind that blood flow rate is a critical parameter in any such monitor, there is a requirement for a blood flow rate measurement procedure which is inexpensive, accurate, non-invasive, and capable of automatic monitoring.

An object of the present invention is to facilitate satisfaction of these last requirements and to this end there is provided a liquid flow meter comprising a closed vessel including an upper chamber having a liquid inlet port, a lower chamber having a liquid outlet port, a syphon tube communicating said upper chamber with said lower chamber, and a breather tube communicating said lower chamber with said upper chamber at a level in the latter above the excursion of said syphon A tube therein.

In use of this meter, liquid is supplied to the upper chamber to accumulate until its level reaches the top of the syphon tube bend whereupon the liquid is passed to the lower chamber by syphon action until the liquid level in the upper chamber drops to that of the syphon tube inlet and the syphon action terminates. The liquid then accumulates again in the upper chamber and the procedure repeats in cyclic manner, with the liquid flow rate through the vessel being determined from the liquid volume displaced during each cycle, this being constant and equal to the upper chamber capacity between the syphon inlet and the top of the syphon bend, together with the interval between successive displacements. This last-mentioned interval can of course be timed by a stop watch, but is readily and preferably measured automatically by use of a photoelectric device.

In application to dialysis equipment the proposed meter also provides the normally required bubble trap function.

For a clearer understanding of the present invention, the same will be further described by way of example with reference to the accompanying drawing which schematically illustrates one embodiment of the invention.

The illustrated embodiment comprises a closed vessel denoted generally at 10 including an upper chamber 11 having a liquid inlet 12, and a lower chamber 13 having a liquid outlet 14. The two chambers are interconnected by a transparent syphon tube 15 for transfer of blood therebetween, the top of this tube projecting only to an intermediate level in the upper chamber, and the lower end of this tube extending partway into the lower chamber and being chamfered to provide a smooth delivery to such chamber during blood transfer. The two chambers are additionally interconnected by a breather tube 16 for gas transfer therebetween, this tube having its ends respectively located above the top and bottom of the syphon tube.

A remaining feature of the vessel 10 is the provision of an outlet filter 17 in the lower chamber.

The illustrated embodiment additionally comprises a photoelectric device 18 located around the syphon tube where it passes between the two chambers. This device includes a light source for passing a beam through the syphon tube, and a diametrically opposed photocell 19 or other light responsive means connected to a suitable output device 20.

The operation of the illustrated embodiment is as described above in that application of blood flow to the upper chamber inlet will cause an accumulation of blood to occur in this chamber until the blood level reaches the highest level within the syphon tube, whereupon blood transfer to the lower chamber is initiated and continued by syphon action until the blood level in the upper chamber falls to the syphon tube input. This action repeats in a cyclic manner and the interval between successive liquid transfers between the upper and the lower chambers is indicated by the photocell output which is respectively lower and higher when blood passes through the syphon tube or not. As noted above, the volume of blood which must accumulate between successive transfers is constant, and so the measured interval directly represents the flow rate into the upper chamber.The output device to which the photocell is connected can provide visual representation of the substantially instantaneous flow rate and/or such a representation of flow rate averaged over a suitable period of time. Alternatively, or in addition, the output device can form part of an automatic control system for the associated dialyser to regulate functions such as blood flow rate.

While the invention has been described with.reference to the illustrated embodiment, it is not intended to be limited thereby but is capable of modification. For example, the photoelectric device 18 is suited to measurement of the flow of liquids such as blood which significantly attenuate the passage of light therethrough, but other means for detecting the presence of liquid or not in the syphon tube are possible, such as means operating on the basis of refraction.

CLAIMS (4 Oct 1979) 1. A liquid flow meter comprising a closed vessel including an upper chamber having a liquid inlet port, a lower chamber having a liquid outlet port, a syphon tube communicating said upper chamber with said lower chamber, and a breather tube communicating said lower chamber with said upper chamber at a level in the latter above the excursion of said syphon tube therein.

2. A meter according to Claim 1 comprising detector means for providing automatically a signal representing the interval between successive displacements of liquid from said upper chamber to said lower chamber by way of said syphon tube.

3. A meter according to Claim 2 wherein said detector means is photoelectrically operable to provide said signal in varying form, dependent upon passage of liquid or not through said syphon tube.

4. A liquid flow meter substantially as herein described with reference to the accompanying drawing.

5. A meter according to any preceding claim incorporated in a dialyser, said meter serving additionally as a bubble trap.

6. A meter/dialyser combination according to Claims 2 and 6 comprising an automatic control system for said dialyser which system is at least partially responsive to said signal.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the blood level in the upper chamber falls to the syphon tube input. This action repeats in a cyclic manner and the interval between successive liquid transfers between the upper and the lower chambers is indicated by the photocell output which is respectively lower and higher when blood passes through the syphon tube or not. As noted above, the volume of blood which must accumulate between successive transfers is constant, and so the measured interval directly represents the flow rate into the upper chamber. The output device to which the photocell is connected can provide visual representation of the substantially instantaneous flow rate and/or such a representation of flow rate averaged over a suitable period of time.Alternatively, or in addition, the output device can form part of an automatic control system for the associated dialyser to regulate functions such as blood flow rate. While the invention has been described with.reference to the illustrated embodiment, it is not intended to be limited thereby but is capable of modification. For example, the photoelectric device 18 is suited to measurement of the flow of liquids such as blood which significantly attenuate the passage of light therethrough, but other means for detecting the presence of liquid or not in the syphon tube are possible, such as means operating on the basis of refraction. CLAIMS (4 Oct 1979)

1. A liquid flow meter comprising a closed vessel including an upper chamber having a liquid inlet port, a lower chamber having a liquid outlet port, a syphon tube communicating said upper chamber with said lower chamber, and a breather tube communicating said lower chamber with said upper chamber at a level in the latter above the excursion of said syphon tube therein.