Patent Application
20080257412
This invention relates to fluid delivery systems, and more particularly to systems and methods for delivering a fluid to a target location at a substantially uniform delivery rate.
Escalating costs of health care and advances in laparoscopic and other surgical techniques have encouraged minimally invasive surgical procedures with short associated recovery times. To facilitate early patient discharge while providing adequate post-operative pain management, portable drug delivery systems for in-home use are commonly prescribed following surgery.
A portable drug delivery system may continuously infuse pain-relieving drugs into the patient at a predetermined basal rate, usually ranging between about three and about ten milliliters per hour, to provide regional pain management. In some applications, the patient may press a bolus button on a controller to temporarily increase the rate for a preset period of time. Drug delivery may thus be customized according to the patient's perception of pain, while simultaneously preventing the patient from exceeding a safe, prescribed drug dosage.
Various electromechanical pumps have been developed for use in connection with portable drug delivery systems. One type of delivery system, for example, uses a driving force to pump fluid through a length of small diameter tubing where the diameter of the tubing controls the flow rate of the fluid. This type of delivery system, while inexpensive to manufacture and implement, is inherently inaccurate. Particularly, it is subject to delivery rate fluctuations caused by variations in liquid viscosity due to temperature, variations in head backpressure due to height differences between a drug reservoir and the drug infusion site, and variations in fill level of the elastomeric pump.
Peristaltic pumps, on the other hand, rely on controlled rotor motion to provide precisely adjustable delivery rates. Such pumps, however, tend to be less portable and more expensive than other types of pumps. Moreover, because delivery rate is calculated indirectly according to the revolution rate of the rotor, inaccuracies may occur.
Conventional diaphragm-type pumps, piezo pumps, or elastomeric balloon-type pumps, may provide a low-cost alternative for providing effective drug delivery, however, delivery rates effectuated by such pumps are subject to fluctuations caused by variations in liquid viscosity due to temperature, as well as variations in head backpressure. Reliable methods for measuring delivery rates are thus critical to enabling adjustments in diaphragm stroke amplitude and frequency as needed to achieve and maintain a desired rate of delivery.
In view of the foregoing, what is needed is a device and method for delivering fluids to a target site at a substantially uniform delivery rate. Ideally, such a device and method would enable use of non-continuous, diaphragm-type and piezo pumps, facilitate accurate delivery rate measurements, and minimize power supply requirements. Such a device and method is disclosed and claimed herein.
The invention has been developed in response to the present state of the art and, in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available fluid delivery systems. Accordingly, the invention has been developed to provide novel devices and methods for delivering fluids to a target location at an adjustable, uniform delivery rate. The features and advantages of the invention will become more fully apparent from the following description and appended claims and their equivalents, and also any subsequent claims or amendments presented, or may be learned by practice of the invention as set forth hereinafter.
Consistent with the foregoing, a device for delivering a fluid to a target site may include a pump, a flow modulator, a flow meter, and a controller. The pump may generate a fluid stream characterized by a flow rate. The flow rate may depend on a speed at which the pump is operated. In some embodiments, the pump may operate intermittently such that the flow rate is substantially pulsatile. The pump may include, for example, a piezo pump, a diaphragm-type pump, a centrifugal pump, a peristaltic pump, or a piston-type pump.
The flow modulator may smooth out irregularities in the flow rate, thereby generating a second fluid stream having a second flow rate that is substantially more uniform than the first flow rate. In certain embodiments, the flow modulator may include a volume expansion zone to expand upon receiving the first fluid stream. The volume expansion zone may then contract to generate the second fluid stream.
The flow meter may measure the flow rate of the second fluid stream. The controller may receive the flow rate measurement from the flow meter and compare the flow rate of the second fluid stream to a target flow rate. The controller may then adjust the pump speed to substantially align the second flow rate with the target flow rate.
In some embodiments, the device may further include a fluid reservoir to retain the fluid prior to delivery. The device may also include a power source for supplying power to the controller, a check valve to prevent fluid backflow from the flow modulator to the pump, and/or a flow restrictor to regulate the first or second fluid stream. In one embodiment, the device further includes a bypass valve to enable the first or second fluid stream to bypass a flow restrictor.
A method to deliver a fluid to a target site at a substantially uniform delivery rate is also presented herein. The method may include generating a fluid stream characterized by a flow rate. In some embodiments, the flow rate may be substantially pulsatile. As used herein, pulsatile may include any flow rate that rises and falls regularly or irregularly, including those generated by a piston pump, piezo pump, diaphragm pump, other types of pumps, pump duty cycles, and the like. Irregularities or variations in the flow rate may be smoothed to generate a second fluid stream having a second, substantially more uniform flow rate. This may be accomplished by introducing the first fluid into a flow modulator, permitting a second fluid stream having a second flow rate that is substantially more uniform than the first flow rate to exit the flow modulator. Introducing the first fluid stream into a flow modulator may comprise receiving the first fluid stream into a volume expansion zone and may further comprise expanding a volume in the volume expansion zone to accumulate fluid within the flow modulator when the first flow rate is greater than the second flow rate. The method may also comprise contracting a volume in the volume expansion zone to expel fluid from the flow modulator when the first flow rate is less than the second flow rate.
The second flow rate may be measured and compared to a target flow rate. The first flow rate may then be adjusted to substantially align the second flow rate with the target flow rate.
In one embodiment, the first fluid stream may be received into a volume expansion zone to facilitate smoothing irregularities in the first fluid rate. The volume expansion zone may be contracted to generate the second fluid stream. In one embodiment, a flow modulator comprises a volume expansion zone that receives a first fluid stream having a first fluid rate. A second fluid stream having a second fluid rate may exit the volume expansion zone of the flow modulator. When the first fluid rate is greater than the second fluid rate, a volume of the volume expansion zone expands allowing the flow modulator to accumulate fluid. When the first flow rate is less than the second flow rate, the volume of the volume expansion zone contracts expelling the fluid from the volume expansion zone and flow modulator. Thus, the second fluid stream that exits the volume expansion zone of the flow modulator has a generally more uniform flow rate. In other words, the irregularities or variations in the flow rate, whether or not regular or purposeful, are “smoothed out” as the first fluid stream transitions into the second fluid stream in the flow modulator.
In some embodiments, the method may further include preventing the first fluid stream from substantially reversing a direction of flow. In other embodiments, a flow restrictor may be provided to regulate a flow of the first or second fluid stream. A bypass valve may be provided to enable the first or second fluid stream to bypass a flow restrictor.
In accordance with another embodiment of the present invention, a device to deliver fluid to a target site at a substantially uniform delivery rate may include means for generating a first fluid stream having a first flow rate. The device may further include means for smoothing out irregularities in the first flow rate to thereby generate a second fluid stream. The second fluid stream may have a second flow rate that is substantially more uniform than the first flow rate.
The device may further include means for measuring the second flow rate, means for comparing the second flow rate to a target flow rate, and means for substantially aligning the second flow rate with the target flow rate. In certain embodiments, the device may also include means for restricting a flow of the first or second fluid stream, and enabling the first or second fluid stream to bypass a means for restricting the flow.
The present invention provides improved devices and methods for delivering a fluid to a target site at a substantially uniform delivery rate. The features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by practice of the invention as set forth hereinafter.
In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through use of the accompanying drawings in which:
It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of certain examples of presently contemplated embodiments in accordance with the invention.
Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment.
Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.
Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The presently described embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.
Referring to
Where surgery is performed on a shoulder, knee, or foot, for example, the pain medication may be injected at or near the area of the surgery or upstream from the area of the surgery. The amount of pain medication required for each surgery may vary based on the type of surgery or the area where the medication is delivered. As an example, a first delivery site may require a basal delivery rate of three milliliters per hour whereas a second delivery site may require a basal delivery rate of five milliliters per hour. Thus, the delivery rate of the fluid delivery device 100 may be adjustable to provide a desired level of pain management.
The fluid delivery device 100 may be capable of generating a substantially consistent delivery rate in spite of environmental factors, such as varying head pressure or temperature, which may otherwise affect the delivery rate. For example, the head pressure at or near a shoulder area 102 may differ significantly from the head pressure at or near a knee area 104, particularly where the fluid delivery device 100 is located at or near the patent's beltline. As will be explained in more detail hereafter, because the fluid delivery device 100 includes a flow meter, the fluid delivery device 100 may achieve a substantially consistent delivery rate regardless of the height or location of the target delivery area.
Referring to
In selected embodiments, a flow modulator 204 may be provided to smooth out irregularities in the flow rate of the first fluid stream 214, thereby generating a second fluid stream 216 with a substantially more uniform flow rate. In selected embodiments, a check valve 203 and flow restrictor 206 may control the flow of liquid into and out of the flow modulator 204. In particular, the check valve 203 may prevent liquid from flowing back toward the pump and the flow restrictor 206 may restrict the flow of liquids out of the flow modulator 204. The flow restrictor 206 may be as simple as an orifice having a selected diameter, tubing with a selected inside diameter, or the like. The importance and role of these components 203, 206 will be explained in more detail hereafter.
After liquid passes through the flow restrictor 206, a flow meter 208 may measure the flow rate of the liquid. This measurement may be received by a controller 210, where it may be compared to a target delivery rate. If the flow rate differs from the target delivery rate, the controller 210 may attempt to align the flow rate with the target delivery rate by adjusting the pump speed. For the purposes of this description, “pump speed” may include parameters such as pump RPM, duty cycle, stroke amplitude, stroke frequency, or the like, depending on the type of pump that is used. A power source 212, such as a battery 212, may provide power to the controller 210, the pump 202, the flow meter 208, and/or other components, if required.
The flow modulator 204 may allow various types of pumps to be run in a non-continuous mode to enable a large turn down ratio (ratio between the highest and lowest flow rate). This enables utilization of larger more efficient pumps of various kinds, including piezo, diaphragm, centrifugal, peristaltic, and piston-type pumps capable of flow rates higher than those typically required. These pumps can be run at their most efficient rate for a period of time, then be shut down for a period of time such that the average pump rate meets a target delivery rate. Using a more efficient, higher capacity pump and running with a duty cycle provides two benefits: first, it provides extra capacity for a bolus above a basal rate; and second, it allows the pump to be run in a more efficient manner such that it makes better use of batteries.
Although operating with a duty cycle may provide various advantages, operating in this manner generates an irregular (e.g., pulsatile) flow rate which may be unsuitable for medication delivery. An irregular flow rate is also difficult to accurately measure with various types of flow meters 208. The flow modulator 204 may smooth out these irregularities to provide a more uniform flow rate. This, in turn, provides a more uniform delivery rate and enables more accurate measurements by the flow meter 208.
One benefit of the flow modulator 204 is that it enables use of lower cost piezo pumps. In general, flow rates generated by a piezo pump are a function of diaphragm stroke amplitude and frequency, two parameters which may be adjusted by the controller 210. The flow rate may also depend on factors such as liquid viscosity, which is highly temperature dependent, and head pressure, which depends on the height differential between the reservoir 200 and the infusion site. By using a flow meter 208, the flow rate may be accurately measured and provide assurance that a particular delivery rate has been achieved and maintained.
In general, a flow modulator 204 in accordance with the invention may include four features to provide the benefits discussed herein. These features may include (1) a volume expansion zone within the fluid path that can undergo volume changes, (2) means to prevent backflow (e.g., a one-way check valve 203) at the entrance of the volume expansion zone or to the pump, (3) means to create backpressure (e.g., the flow restrictor 206) downstream from the volume expansion zone, and (4) means to act on the boundaries of the volume expansion zone to compress the liquid therein. Several of these features will be discussed in more detail in association with
In one embodiment, the means to prevent backflow may include the structures discussed herein, and may include without limitation, check valves, passive valves, active valves, other types of valves, flow restrictors, gates, traps, weirs, other ways known to those of skill in the art, and combinations thereof. The means to create backpressure to facilitate accumulation of fluid in the volume expansion zone with the flow modulator 204 may include without limitation the structures discussed herein and may include without limitation, flow restrictors, tube or passage diameters or restrictions, tortuous paths, orifices, control or other types of valves, venturis, or other ways known in the art, and combinations thereof. The means to act on the boundaries of the volume expansion zone, or in other words to contract a volume of the volume expansion zone to expel fluid from the volume expansion zone and consequently from the flow modulator 204, may include the structures discussed herein and may also include without limitation, bellows, biasing members, diaphragms, pistons, valves, balloons and other elastomeric devices, and other ways known in the art to expand and contract a volume, and combinations thereof.
In certain embodiments, the controller 210 may include an interface to allow a user or medical professional to select a basal delivery rate. Such a basal delivery rate, for example, may be selected based on the size of the patient, the amount of pain experienced by the patient, the area of the body treated, or the like. In certain embodiments, the controller interface may also enable a user to select a bolus delivery rate when breakthrough pain or other situations occur which may require a temporary increase in the delivery rate. In certain embodiments, the controller 210 may limit the amount of time the device 100 operates at the bolus delivery rate to prevent harm, abuse, or the like. In certain embodiments, the controller 210 may also limit the frequency for selecting a bolus. For example, once the bolus has been selected and delivered, the controller 210 may require that a user wait several hours before a bolus can be selected again. In other embodiments, the controller 210 may limit the number of times a bolus infusion may be selected in a particular period (e.g., a twenty-four hour period).
The fluid delivery device 100 illustrated in
Referring to
Similarly, when the bolus has terminated, the liquid pressure may be decreased (e.g., by decreasing the pump speed) until the bypass valve 300 closes. This will terminate the flow of additional liquid around the flow restrictor 206, thereby returning to the basal delivery rate. In selected embodiments, the bypass valve 300 is a passive valve, meaning that only an increase or decrease in pressure is required to open or close the valve 300. In other embodiments, the bypass valve 300 is an active device controlled by the controller 210. For example, the controller 210 may increase the pump speed and simultaneously open the bypass valve 300 to deliver a bolus.
Like the previous example, the fluid delivery device 100 illustrated in
Referring to
Referring to
The flow modulators 204 described in
It will be appreciated by reference to the
The device may further include means for smoothing out irregularities in the first flow rate to thereby generate a second fluid stream. The second fluid stream may have a second flow rate that is substantially more uniform than the first flow rate. These means may include the volume expansion zone and flow modulator 204 and its components as discussed herein.
The device may further include means for measuring the second flow rate. These means may include without limitation thermal differentials, pressure differentials across an orifice, pressure differentials across a petot tube, pressure differentials across a venturi, other ways known to those of skill in the art, and combinations thereof. The device may also include means for comparing the second flow rate to a target flow rate, and means for substantially aligning the second flow rate with the target flow rate. These means may include a controller, software, firmware, hardware, adjusting the pump speed, including the pump amplitude, pump duty cycle, pump frequencies, and the like, alone or in combination. In certain embodiments, the device may also include means for restricting a flow of the first or second fluid stream. These means may include those discussed in combination with the flow restrictor 206. In certain embodiments, the device may enable the first or second fluid stream to bypass a means for restricting the flow by means including spring-loaded check valves, solenoid valves, manual valves, pluming configurations, other bypass ways known in the art, and combinations thereof.
In some embodiments, as discussed above, it is understood that the flow meter 208, may serve as a means of creating backpressure downstream of the flow modulator 204 that serves to cause the volume in the flow modulator 204 to expand when the flow rate of the second stream is lower than the first stream. This volume may be the volume of volume expansion zone.
A device according to the present invention may have more than one flow restrictor 206. For example a flow restrictor 206 may reside downstream of the flow modulator 204 for the purpose as described herein, and a second flow restrictor 206 may reside upstream of the flow modulator 204 to serve the purpose described herein, as depicted in
Referring again to
Variations of the piping scheme described above may be used to achieve similar results.
An exemplarily device may consist of the following: a variable volume liquid reservoir containing the drugs ropivacaine or bupivacaine or the like, a piezo electric pump with passive check-valves, a line that flows to flow restrictor consisting of a length of small diameter tubing sized such that the flow of the drug with 2 feet head pressure is 3 cc per hour and a spring loaded bypass check valve that opens when the pressure in the line exceeds 4.6 feet of head pressure (2 psi). The bypass check valve and the flow restrictor flow to an elastomeric balloon with an inlet and an outlet. This balloon serves as the flow modulator. Following the balloon, the flow runs to a differential temperature type flow meter. There is sufficient resistance to flow from the flow meter to create a backpressure when the piezo pump strokes resulting in a partial filling of the balloon during the stroke. Between pump strokes, the balloon walls compress on the liquid contents resulting in flow through the flow meter since the check valve on the piezo pump prevents back flow to the reservoir. Following the flow meter the flow is to an entry point of the body to a catheter that has been placed near nerves which when bathed in the drug will prevent pain from a surgery. The flow meter provides flow rate data to a controller that will increase the piezo pump duty cycle to achieve a desired basal flow rate that typically is between 3-10 cc/hour. If the patient begins to feel considerable pain because the basal rate is too low, the patient may activate a bolus where the pump rate increases to 50 cc/h for 15 minutes. During the bolus, the bypass valve may open. After 15 minutes, the controller will reduce the pump rate to resume the basal rate. The controller may have been programmed to prevent another bolus from occurring for a set period of time, say 8 hours.
Referring to
Referring to
Referring to
A temperature differential may then be calculated between the temperature sensors 806. As the flow rate increases, the temperature differential measured at the sensors 806 may decrease. Similarly, as the flow rate decreases the temperature differential measured at the sensors 806 may increase. A flow meter 800 like that illustrated in
The present invention may be embodied in other specific forms without departing from its basic principles or essential characteristics. The described embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
This application claims the benefit of U.S. Provisional Patent Application No. 60/912,463 filed Apr. 18, 2007, which application is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60912463 | Apr 2007 | US |
