Pumping and pressure detection using flexible tubes

Details Pumping and pressure detection using flexible tubes Pumping and pressure detection using flexible tubes

1996-09-12

1998-09-15

Buiz, Michael

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

A61M 3100

Patent

active

058073221

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to peristaltic pumps, and in particular although not exclusively to peristaltic pumps for portable drug infusion devices. In certain aspects, the invention further relates to pressure detecting within flexible tubes generally.
A peristaltic pump comprises a length of flexible tubing along which a fluid is to be moved. There are various types of peristaltic pump, but in one type the pumping pressure is provided by an external pusher or piston which partially compresses the tube, the liquid being constrained to move in one direction only by some sort of non-return valve arrangement such as movable fingers which act to compress and seal the tube. This is known as a three-finger pump. In another type of pump--the linear peristaltic pump--a plurality of fingers move up and down, each finger compressing the tube at a different point. A camshaft mechanism ensures that the fingers move in a wave-motion-like sequence that forces fluid through the tube. In yet another type--the rotary peristaltic pump--the tube is carried in a circular track, and fluid is pushed along using one or more rollers.
Peristaltic pumps have been used for some time in devices for continuous drug infusion, and they are particularly convenient, because of their simplicity and small size, for use in portable devices for delivering continuous relatively large doses of drugs (for example anti-cancer drugs) to ambulatory patients.
Problems with such devices in the past have included the difficulty of providing, conveniently and cheaply, a reliable pump monitoring mechanism which can rapidly warn the patient if anything goes wrong with the infusion. The three-finger pump (which is otherwise very suitable for use in drug infusion devices) is rather non-linear, in that the fluid displacement is a non-linear function of the amount by which the tube is compressed. FIG. 1 shows, schematically, the plunger finger 12 of a conventional prior art three-finger peristaltic pump, in which a tube 10 is compressed between a pusher or plunger, which moves downwardly in the direction of the arrow 14, and a stationary pressure plate 16. It will be appreciated that the plunger 12 may also move upwardly against the direction of the arrow 14 to reduce compression of the tube. It will be seen that as both the plunger and the pressure plate are flat and parallel, with both being much wider than the tube, the tube as it is compressed bulges out sideways into the oval shape shown.
If the distance d is taken to be the minimum distance between the plunger 12 and the pressure plate 16, it is found in practice that the fluid displacement of the pump is a non-linear function of d. The force that is needed to move the plunger downwardly is also a non-linear function of d. In a conventional infusion pump, used for the infusion of drugs, either or both of the tube 10 and the pressure plate 16 are likely to be replaceable. Accordingly, if accurately repeatable infusion rates are to be achieved, it is essential that the replaceable tube and/or back plate can be positioned very accurately with respect to the plunger 12. If the size or thickness of the replaceable tube differs, or if the pressure plate 16 is not mounted in exactly the same position as it was previously, the infusion rate is likely to differ.
It is an object of the present invention to provide a peristaltic pump in which at least some of the above difficulties are at least ameliorated.
It is a further more general object to provide a peristaltic pump which incorporates an improved mechanism for pump monitoring.
According to a first aspect of the present invention there is provided a peristaltic pump comprising a flexible line carrying fluid to be pumped, cyclical line compression means arranged repeatedly to compress the line, pressure sensing means arranged during part of the cycle to provide a signal representative of a downstream pressure, and during another part of the cycle to provide a signal representative of an upstream pressure, the said signals being supplied to pump monitoring

REFERENCES:
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patent: 4255088 (1981-03-01), Newton et al.
patent: 4277226 (1981-07-01), Archibald
patent: 4617014 (1986-10-01), Cannon et al.
patent: 4650469 (1987-03-01), Berg et al.
patent: 4690673 (1987-09-01), Bloomquist
patent: 5103211 (1992-04-01), Daoud et al.
patent: 5292306 (1994-03-01), Wynkoop et al.

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