Patent Application
20150343140
This disclosure relates to apparatus or equipment for regulating the flow rate of liquids that are administered at very low rates.
Clogging is a known problem for tubes used in liquid delivery systems, particularly for systems in which the flow rate is very low or in which there are temperature fluctuations that may affect the stability of the liquid being measured. In addition to clogging, the mere measurement of very low flow rates requires meticulous attention to the manufacturing process as pressure differentials are low and clearances and tolerances are especially small.
The uses for the flow restricting devices for very low flow rates are many; including in the medical field in the administration of drugs, the process chemical field for the injection of particular additives to mixtures, in food processing, and many others. In the medical field in particular, low flow dispensation is useful for constant administration of drugs for treatment of chronic conditions, e.g. pain.
It would be of great benefit to have a flow regulating device that is accurate, relatively independent of temperature and that did not easily clog. It would be of added benefit if the device were easy to assemble and compact so that it was inconspicuous when worn by a patient for medical use, for example.
The present disclosure addresses the problems described above by providing a compact, low flow regulating device. The device has a housing and tubing, the housing holding the tubing within it, the tubing reducing liquid pressure from a higher pressure at a first tubing end to a second pressure at a second tubing end, the housing adapted to be worn by a patient and the liquid delivered to said patient at the second end at the second pressure.
Other objects, advantages and applications of the present disclosure will be made clear by the following detailed description.
These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings in which:
Reference will now be made in detail to one or more embodiments, examples of which are illustrated in the drawings. It should be understood that features illustrated or described as part of one embodiment may be used with another embodiment to yield still a further embodiment. It is intended that the claims include these and other modifications and variations as coming within the scope and spirit of the disclosure.
The present disclosure addresses the problems described above by providing a compact, flow regulating device.
According to Poiseuille's law, the velocity of the steady flow of a fluid through a narrow tube (as a blood vessel or a catheter) varies directly as the pressure and the fourth power of the radius of the tube and inversely as the length of the tube and the coefficient of viscosity. The Poiseuille equation may be expressed as:
Q=ΔPπr
4/8 μL
where:
ΔP is the pressure loss
L is the length of pipe
P is the dynamic viscosity
Q is the volumetric flow rate desired
r is the radius
π is the mathematical constant Pi (3.14159)
If one assumes a constant input pressure to the tube, using, for example, a controlled (fixed) pump discharge pressure and a tube discharge pressure of approximately zero gage (atmospheric pressure or less than 0.5 psig, more particularly less than 0.25 psig and still more particularly less than 0.1 psig), the equation can be solved for L. In the table below, the first four columns provide the input variables for the equation in English units and the last column the computed L needed. Conversion of units may be necessary and may be done by one skilled in the art.
As can be seen from the table, low flow rates require a lengthy tube or, of course a tube of a smaller diameter with its associated higher pressure drop. As noted above, however, a smaller diameter tube poses much greater problems with clogging, especially with a higher viscosity fluid. For this reason, a larger diameter tube is desired. A larger diameter tube must be much greater in length, however, to achieve the same pressure drop. Tethering a patient to a long tube for long term administration of a drug presents problems in patient mobility. Administration of a drug for pain management, for example, is often done on a continuous basis. Immobilizing an otherwise ambulatory patient for long periods of time is not desirable and may not be tolerable by the patient. Another solution is necessary.
One way of overcoming the problem of using a long length of tubing is to provide a compact device that may be worn by the user against his body. This provides the added benefit of maintaining the drug to be dispensed at a relatively constant (body) temperature and therefore a constant viscosity and dispensing rate. The compact device provided herein allows the patient to be ambulatory yet to receive the prescribed medication on a continuous basis.
Turning to the table above, if a flow rate of 0.5 ml/hour of a fluid with a viscosity of 0.0000205 lb.sec/ft2 is desired from a pump with a discharge pressure of 6 psig, tubing of 0.00265 inches ID and about 6 inches in length should produce the requisite flow rate.
Turning to the table above, if a flow rate of 5 ml/hour of a fluid with a viscosity of 0.0000205 lb.sec/ft2 is desired from a pump with a discharge pressure of 6 psig, tubing of 0.00265 inches ID and about 0.6 inches in length should produce the requisite flow rate.
Stated more generally from the principles of the Poiseuille equation and the table; there is disclosed herein a compact flow restriction device that delivers a liquid flow rate of between 0.5 ml/hour and 10 ml/hr of a fluid from a pump with a discharge pressure of between 3 and 15 psig, the liquid flowing through tubing of between 0.001 to 0.01 inches ID and of between about 0.3 and 6 inches in length. The device has a io housing adapted to be worn by a patient and the liquid is delivered to the patient at approximately atmospheric pressure.
The device may be of varying sizes provided it accommodates the desired length of tubing and may be successfully worn by a patient. In one embodiment the device is about 2 inches (5 cm) in length, 0.75 inches (1.9 cm) wide and 0.3 inches (0.75 cm) thick. In various embodiments the inner diameter of the tubing can be from 0.001 inches to 0.01 inches, more particularly between 0.002 inches and 0.005 inches. While it is true that a smooth or rough tube interior will affect flow somewhat, the velocities of flow are generally so low as to be laminar and so are relatively unaffected by the roughness of the tube interior.
It should also be noted that although tubing wound around a spool is illustrated, the tubing may be assembled in other configurations without a spool. This could include the tubing being laid back and forth into the housing like a ribbon, placing it in a circular configuration without a spool, or laying it in the housing in a figure eight configuration. The device may also have a spool with a slotted hub so that the middle of the tube can be inserted into the spool and the spool spun so that it winds the tubing onto the hub in either direction.
Materials of construction for the tubing and the device generally (e.g. housing, spool, tubing) can be metals or plastics. Stamped metal may be used for the housing, for example, for better heat transfer from the body than plastic. Plastic includes PVC, polypropylene, polyethylene, Nylon®, Teflon®, polycarbonate and other common plastics. Moreover, all parts of the device need not be made from the same material. As noted above, the housing may be made of metal or other heat conducting material for improved heat transfer and the spool and tubing may be plastic, since this compact device may be worn by the user against his body. In this manner, this device provides the added benefit of maintaining the drug to be dispensed at a relatively constant temperature and therefore a constant viscosity and dispensing rate. The housing may have a volume that allows for an insulating effect from the ambient air temperature by simply using still air. The housing may alternatively be filled with foam (e.g. closed celled foam) to surround the spool and tubing and provide insulation from ambient temperature variations as well.
While the present invention has been described in connection with certain preferred embodiments it is to be understood that the subject matter encompassed by way of the present disclosure is not to be limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternatives, modifications and equivalents as can be included within the spirit and scope of the claims.
