Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M15/00—Inhalators
  • A61M15/0065—Inhalators with dosage or measuring devices
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F11/00—Apparatus requiring external operation adapted at each repeated and identical operation to measure and separate a predetermined volume of fluid or fluent solid material from a supply or container, without regard to weight, and to deliver it
  • G01F11/02—Apparatus requiring external operation adapted at each repeated and identical operation to measure and separate a predetermined volume of fluid or fluent solid material from a supply or container, without regard to weight, and to deliver it with measuring chambers which expand or contract during measurement
  • G01F11/021—Apparatus requiring external operation adapted at each repeated and identical operation to measure and separate a predetermined volume of fluid or fluent solid material from a supply or container, without regard to weight, and to deliver it with measuring chambers which expand or contract during measurement of the piston type
  • G01F11/024—Apparatus requiring external operation adapted at each repeated and identical operation to measure and separate a predetermined volume of fluid or fluent solid material from a supply or container, without regard to weight, and to deliver it with measuring chambers which expand or contract during measurement of the piston type the pistons reciprocating in rotatable cylinders

Definitions

• Fluid metering devices are among the oldest and most diverse of man's inventions.
• the main types are positive displacement dispensers, as used in fuel injection systems; fixed or variable restrictors which control the flow rate of pressurised fluids - e.g. needle valves; automatic cisterns which discharge a predetermined quantity of water once a certain level is reached; and, often, metering combined with pumping, as with peristaltic pumps.
• Metering devices are used extensively in the health care industry, and most types are represented in that industry. The examples that follow are taken from the health care field, but are equally applicable to other fields.
• Typical of the applications are syringe pumps for delivering medicaments directly into the patient's bloodstream, wherein a stepper motor drives a lead screw to move the plunger of the syringe to dispense the medicament.
• the metering is accomplished by controlling the motor speed and hence the frequency of plunger travel.
• peristaltic pump Another type of metering pump used extensively in hospitals and for ambulatory drug delivery devices is the peristaltic pump.
• This consists of an elastomeric tube containing a fluid, one end of the tube being connected to a reservoir of the fluid to be pumped, and at least one pair of rollers spaced apart which are pressed onto the tube to trap a bolus of fluid therein, and which traverse along the tube to move the bolus towards an outlet.
• Such pumps employ a number of rollers around a drum or on a linear track, so that there is a slightly intermittent delivery rate of fluid as each bolus is delivered.
• the intake suction is created by the tube springing out after the passage of a roller.
• Peristaltic pumps deliver a reasonably accurate flow when the pump tubes are new, but the tube material quickly loses some of its elasticity and the flow rate drops. Furthermore, it is quite common for tubes to split unless changed frequently. The good features are that they are simple to set up and maintain; no glands or sliding seals are required; the tubes are often contained conveniently within a disposable cartridge, including the rollers; they are relatively inexpensive.
• the basic device consists of a clamp which is adjusted to partially occlude a resilient tube leading from the infusion drug container.
• the flow rate is determined by counting the drops within a viewing chamber; some equipment monitors the drip rate electronically. They are less complicated than pumps, and the fluid is pressurised by fixing the container above the delivery level. They have no moving parts, and few maintenance problems.
• the pressure head as the infusion drug is consumed, the flow rate falls, and such controllers require frequent adjustment.
• various types of tube clamps are in use, inevitably the soft tubing material creeps after the initial setting, necessitating further adjustment. Also they present difficulties when used with viscous solutions. More sophisticated controllers use feedback to control the variable restrictor, but there are few, if any, suitable flow measuring devices that can cover the range of flow rates required with accuracy, at a reasonable cost.
• the pump could build up a pressure on the delivery side if a blockage occurs, and a pressure warning device is essential.
• a blockage downstream would merely cause the flow to cease, but again, an alarm is essential.
• MDI metered dose inhaler
• the device contains a drug mixed with a liquefied gas propellant; a metered volume of the mixture is first isolated from the bulk, and then opened to atmosphere, whereupon the propellant boils almost explosively and dissipates the drug as a fine spray.
• valves which are viscosity sensitive and suffer from particulate contamination which increases flow resistance, and flow interrupts such variable frequency on-off valves,
• the present invention seeks to overcome some of the drawbacks of existing metering devices by providing a fluid metering dispenser for use with pressurized fluids, having a rotor containing a piston free to oscillate within a bore extending transverly to the rotor axis, and which piston is driven by the fluid to be metered.
• the rotor is sealingly retained within a stator having an inlet port connected to a pressurised fluid source, and an outlet port.
• a first end of the bore becomes in fluid connection with the inlet port of the stator, and the piston is urged by the pressurized fluid to move in a first direction towards the outlet port.
• the second end of the bore becomes in fluid connection with the inlet port, whilst the first end of the bore becomes in fluid connection with the outlet port, and the piston, again urged by the fluid, reverses to move in a second direction, i.e. towards the outlet port; thus the fluid which previously had moved the piston in a first direction is discharged through the outlet port.
• the rotor may be turned back and forth to dispense successive metered doses of fluid, or may be rotated in the same direction continuously or intermittently for a similar result.
• a motorised version will deliver accurate metered quantities of fluid as the rotor rotates and the piston oscillates.
• the piston may have a small clearance within the bore, to reduce the friction losses to a very small amount, and the mass may be small to minimise inertial losses.
• the rotor may be operated manually or by a motor, which includes various electric, air, clockwork, hydraulic and gravimetric types. It is intended that for some applications, such as IV infusion, the metering element is to be disposable. The main benefits are that there will be no need to clean and sterilize the device, the duty cycle of the metering element is very short, which enables low-cost manufacture, and the more expensive parts such as the drive unit are retained for use with a fresh metering element.
• Detectors may be fitted to measure the piston frequency and/or position and operate an alarm or flow rate display in dependence thereon.
• the enhancement may be part of the drive unit, so keeping the metering element simple and inexpensive.
• a first preferred embodiment provides a short cylindrical rotor having a cylindrical bore at right angles to, and passing through, the axis of rotation of the rotor.
• a piston is located within the bore and has a running clearance sufficiently small to prevent leakage of the fluid to be metered. (This clearance may vary according to the viscosity and pressure of the fluid).
• Each end of the cross bore is connected to a respective circumference groove. The grooves are not connected together, and serve as distribution channels for the fluid.
• the rotor is sealingly retained within a stator, which has inlet and outlet ports aligned to connect to the distribution grooves.
• the distribution grooves connect alternately with the inlet and outlet ports of the stator, and thus each end of the cross bore in the rotor is alternately presented to the pressure inlet port. This results in the piston oscillating within the cross bore, and discharging the swept volume fluid content of the bore through the outlet port of the stator.
• the rotor is driven by a motor and gearbox, and is releasably attached to the metering dispenser, so that the latter may be replaced easily.
• the rotor and stator are not lubricated, and the materials of construction are chosen to minimise friction and be compatible with the fluid and application.
• the motor is fitted with a speed controller, by which means the output of the metering dispenser may be altered.
• a second preferred embodiment provides a similar device to the first, except that it is adapted to work at high pressures.
• the rotor is of frusto-conical form and mates with a similar form within the stator.
• the rotor is biassed by a spring to ensure sealing contact between the two at pressures of up to 500 bars.
• the piston is sealingly fitted within the cross bore, or has a very small running clearance that will prevent significant leakage between the piston and bore.
• the materials of each are suitable for dry friction without a lubricant, although certain lubricants such as molybdenum disulphide may be used if the inevitable contamination of the fluid by the lubricant is permissible.
• Figures la, lb and lc show different views of a first embodiment, Figure la being a plan view, and Figures lb and lc being sectional views along lines B-B and C-C, respectively, shown in Figure la;
• Figure 2 shows a high pressure version, as provided by a second embodiment
• Figures 3a, 3b and 3c illustrate the operating sequence of the metering dispenser.
• Figures la to lc show a stator 2 defining a cavity therein and having connectors 4 and 5, and a rotor 1 with a transverse bore 4, at right angles to the axis of rotation of the rotor 1 , containing a piston 3.
• the rotor has a drive shaft 9 connected thereto.
• the rotor is circular in cross-section, and in the embodiment of Figures la to lc it is generally cylindrical.
• Each end of the bore 4 is in fluid connection with distribution grooves 7 in the periphery of the rotor 1.
• Stator 2 has an outlet port 12 terminating with the connector 5, and an inlet port 11 terminating with the connector 6. (Note that in the configuration shown, the ports are interchangeable as regards function).
• Piston 3 is a small clearance fit within bore 4, so that the fluid will not leak through the capillary annulus, and the piston 3 may optionally be limited by stop pins 10 inserted in the rotor 1 after assembly of the piston 3. Alternatively, the piston may be stopped by coming to rest against the stator 2. Where pins 10 are fitted, they may be used to trigger timing circuits and alarms etc.
• rotor 1 is retained within stator 2 by a retaining lip 8, and drive shaft 9 is suitably adapted to fit a plug-in drive means, not shown.
• rotor 1 is made from a transparent material such as polymethylmethacrylate or similar hard plastic
• stator 2 is made from a low friction resilient plastic material such as PTFE or polypropylene.
• PTFE polymethylmethacrylate
• stator 2 is made from a low friction resilient plastic material such as PTFE or polypropylene.
• inlet port 6 is connected to a source of pressurized fluid, and rotor 1 is shown in one extreme stroke position: the volume of bore 4 to the left of piston 3 as seen in Figure 3a contains only air, and ports 11 and
• the rotor 1 may be turned continuously, which will result in the delivery of a continuous succession of metered doses of fluid 17 at a rate determined by the rotational speed of rotor 1.
• the fluid that first acted on the piston 3 to displace the piston becomes the fluid acted upon by the piston 3.
• the device will deliver very accurate metered doses.
• the rotor may oscillate back and forth, for example through 180°.
• stator 22 but using a frusto-conical rotor 21 sealingly and rotatably assembled into stator 22.
• Rotor 21 has a shaft 29, fitted with a collar 40.
• a stack of disc springs 41 in compression acts on face 42 of collar 40 and reacts against thrust face 43 of stator 22 to bias the conical surface of rotor 21 sealingly against the corresponding conical surface of stator 22.
• the metering dispenser is operated as previously described.
• a rotor may be made from graphite or modified PTFE, and the stator from stainless steel.
• the piston should have a small clearance in the bore (typically about 0.1 % of the diameter).
• seals for example lip seals or 'O' rings, and/or lubricants may be required.
• the metering device may be integral with, or permanently secured to (e.g. by crimping), a pressurized container of fluid, or a container of fluid which is subsequently pressurized.
• a pressurized container of fluid or a container of fluid which is subsequently pressurized.
• a simple example of the latter is an IV infusion bag containing the liquid to be metered: it does not have a working pressure until it is lifted to a height above the patient onto a support stand, or placed into a holder and compressed with a weight or spring.
• the metering device may be inserted into a pressurized pipeline for a wide range of metering applications.
• One application where the metering device of the present invention may be of particular value is for metering fluid from a so-called "bag-in-can M dispensing system.
• the can contains a substance for pressurising the interior itself, e.g. butane in liquid form, whereby to exert a dispensing pressure on the bag when the outlet from the bag to the exterior is opened.

Landscapes

• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Pulmonology (AREA)
• Biomedical Technology (AREA)
• General Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• Bioinformatics & Cheminformatics (AREA)
• Physics & Mathematics (AREA)
• Anesthesiology (AREA)
• Biophysics (AREA)
• Heart & Thoracic Surgery (AREA)
• Hematology (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Infusion, Injection, And Reservoir Apparatuses (AREA)

Applications Claiming Priority (3)

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• 1997
  • 1997-02-25 GB GBGB9703918.4A patent/GB9703918D0/en active Pending
• 1998
  • 1998-02-17 AU AU62246/98A patent/AU6224698A/en not_active Abandoned
  • 1998-02-17 JP JP53740898A patent/JP2001504234A/ja active Pending
  • 1998-02-17 EP EP98904304A patent/EP0963543A1/de not_active Ceased
  • 1998-02-17 WO PCT/GB1998/000491 patent/WO1998038480A1/en not_active Application Discontinuation
  • 1998-02-23 ZA ZA981480A patent/ZA981480B/xx unknown

Non-Patent Citations (1)

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