Medicament dosing system

Details Medicament dosing system Medicament dosing system

1999-06-06

2000-10-10

Kennedy, Sharon

Surgery

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

Treating material introduced into or removed from body...

604250, 604 34, A61M 3100

Patent

active

06129702&

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a medicament dosing system and, in particular, to a medicament dosing system operating according to the overpressure principle.
2. Description of Prior Art
Lately, medicament dosage is carried out predominantly by dosing systems operating according to the overpressure principle. A schematic representation illustrating the over-pressure principle is shown in FIG. 8. Such systems consist of a fluid reservoir 10 and of a flow resistor 12 arranged e.g. on or in a fluid line 14 connected to the fluid reservoir 10. A pressure transmitter means 16 serves to apply pressure to the liquid medicament contained in the fluid reservoir 10. The pressure transmitter means produces a pressure p, whereby the fluid reservoir 10 is acted upon by a specific overpressure P.sub.1 relative to the pressure p.sub.0 at the outlet of the flow resistor 12. The pressure p.sub.1 substantially corresponds to the pressure p produced by the pressure transmitter means 16. When the system is in operation, a flow Q is caused by the differential pressure applied to the flow resistor 12.
For a circular cross-section of the flow resistor, the magnitude of the flow Q can be calculated according to the known Hagen-Poiseuille law: ##EQU1## The flow rate Q is determined by the following influencing quantities: the viscosity of the medium, flow resistor, flow resistor, and temperature-dependent viscosity of the fluid.
For other flow cross-sections, analogous rules can be determined which differ from the rule mentioned in the above equation substantially with regard to the taking into account of the effective flow cross-section of the flow resistor. Such analogous rules e.g. for micromechanically produced flow resistors are described in "Micro Channels for Applications in Liquid Dosing and Flow Rate Measurement" M. Richter, P. Woias, D. Wei.beta., Proceedings of Euro Sensors X, Sep. 8 to 11, 1996, Leuven, Belgium, Vol. 4, pp. 1297 to 1300.
The technical embodiments of existing dosing systems vary greatly and use in a great variety of combinations mechanisms like mechanical systems, e.g. spring-pressure systems, electrochemical systems, e.g. electrolytic cells, thermopneumatic systems, e.g. the evaporation pressure of a highly volatile substance, and the gravitational force. The elements used as flow resistor are normally plastic capillaries, glass capillaries and metal capillaries.
According to the above equation, the radius R influences the flow rate Q through the term R.sup.4 to the fourth power, when the flow resistor is circular in cross-section. This means that, for achieving exact dosage, flow resistors having a high geometrical accuracy must be realized. Such an accuracy is only possible on the basis of a comparatively high technical expenditure. Simple systems including plastic capillaries are additionally disadvantageous insofar as the capillary stretches depending on the pressure applied, whereby the dosing accuracy will decrease.
In addition, comparable micromechanical embodiments used for glucose measurements by means of a microdialysis are known. In such a micromechanical embodiment, a microcapillary for flow adjustment is realized on a silicon chip together with glucose sensors. This known set-up is, however, not used for medicament dosage, but it uses the above-described over-pressure principle only for adjusting the flow rate of the carrier medium for the microdialysis.
A further known implementable micromechanical dosing system uses a solvent reservoir as a constant pressure transmitter and an array of micromechanically realized flow resistors for flow rate adjustment. The geometry of the whole flow path is varied by coupling and decoupling individual microflow resistors via respective microvalves associated therewith, whereby a dosing rate variation switched in steps is achieved. For measuring the flow, pressure sensors located at various points of the array are used. Such a system with an array of microflow restrictions does not permit a continuo

REFERENCES:
patent: 5377524 (1995-01-01), Wise et al.
patent: 5515735 (1996-05-01), Sarihan
R. Werthschutzky, "Application of Silicon Sensors in Process Measuring Dees for Pressure Measurements--Current Status and Coming Opportunities", Sep. 1992, No. 9, Munchen, DE.
Oosterbroek et al., "Designing, Realization and Characterization of a Novel Capacitive Pressure/Flow Sensor", Jun. 16-19, 1997, 1997 International conference of Solid-State Sensors and Actuators.
Boillat, et al., "A Differential Pressure Liquid Flow Sensor for Flow Regulation and Dosing Systems", 1995, IEEE.

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