Inverted sensor module

[0001] The current application shares some specification and figures with U.S. patent application Ser. No. 10/247,807, entitled “External Fluid-Filled Catheter Pressure Transducer” filed on Sep. 19, 2002, which is commonly owned or assigned and hereby incorporated by reference.

[0002] 1. Field of the Invention

[0003] The present invention relates to a sensor module. More specifically, the present invention relates to an inverted sensor module for use in a fluid vessel in a living body.

[0004] 2. Related Art

[0005] In the medical field, and particularly in the field of medical research, sensors greatly aid in the evaluation of performance and fluid characteristics of vessels in a living body. Sensors are used to determine characteristics such as fluid pressure, temperature, O₂, CO₂, sugar levels, and/or pH in blood vessels, lymph vessels, ureters, intestines, and chambers of the heart. Medical personnel use this information to evaluate the overall health of a person, and medical researchers use this information to aid in the evaluation of new drugs or procedures.

[0006] Typically, sensors are mounted on a catheter for insertion into the vessel. Several patents describe the use of sensors mounted on catheters. However, the use of prior art catheters is not always possible due to the size of the vessel to be monitored in comparison with the catheter. For example, researchers studying cardiac performance in small animals such as mice may encounter blood vessels less than 1 mm in diameter. In these applications, it may not be possible, using prior art sensors, to be able to accurately monitor the cardiac performance directly. In particular, the size of the catheter may be so large that insertion into a blood vessel may block the blood vessel, impair cardiac performance, prevent accurate measurements and cause injury to the subject. It is therefore desirable to provide an improved method and sensor apparatus for detecting and measuring various fluid characteristics in vessels in a living body. It is further desirable to provide a sensor apparatus capable of being used in small vessels.

[0007] The present invention achieves these goals with a unique and advantageous structure for an inverted sensor module that may be used directly inside a living body. The inverted sensor module provides for accurate measurement of fluid characteristics in vessels.

[0008] The present invention also provides unique advantages relating to the modularity of the inverted sensor module. Embodiments of the present invention include an inverted sensor device that may be easily inserted into a vessel or bonded to a catheter. In addition, the inverted sensor module may be readily removed and replaced.

[0009] In one embodiment, the present invention comprises an inverted sensor module having a sensor operable to provide a signal representative of a physical or chemical characteristic of a fluid in a vessel in a living body. A signal transmission media is coupled to the sensor for transmitting the representative signal. A bonding material is provided for mounting the sensor to the carrier.

[0010] In another embodiment, the present invention describes an inverted sensor module with a plurality of inverted sensors mounted thereon. Multiple sensors allow researchers to observe trends in the fluid characteristics along a vessel.

[0020] The present invention overcomes the shortcomings of the prior art with an inverted sensor module operable to detect physical and chemical fluid characteristics in small vessels in a living body.

[0021] Now referring to the figures, FIGS. 1A, 1B, and 1C are top, end, and bottom views of one embodiment of an inverted sensor module 100 of the present invention. The inverted sensor module 100 comprises a carrier 105 having an inner surface and an outer surface. The carrier 105 is preferably constructed of a high strength biocompatible material such as stainless steel, platinum, titanium or ceramic. The inverted sensor module 100 further comprises a sensor 110, which is inverted such that the sensing side faces the inner surface of the carrier 105. The inverted sensor module 100 further comprises wires or other communication media 120.

[0022] The sensor carrier 105 is optimally designed for compatibility with a living body. Although the carrier 105 may have any shape, in a preferred embodiment, the carrier 105 is a convex shape for easier insertion into vessels. The carrier 105 comprises rigid tubing with a known inner cross-sectional area, and maintains the sensor 110 position in close proximity with the fluid being monitored. In some embodiments, the sensor carrier 105 is manufactured from polyimide tubing. An opening 102 such as a window or slot is machined in the carrier 105 such that the sensor 110, which is attached to the carrier 105, detects fluid characteristics on the inside of the carrier 105. Sensor 110 is attached to sensor carrier 105 preferably by bonding material 106. In the preferred embodiment, sensor 110 is bonded to sensor carrier 105 with Room Temperature Vulcanizing (RTV) silicone rubber, although any method of attaching the sensor 110 to the carrier 105 may be used without departing in scope from the present invention. The ends of the carrier 105 can be attached to a vessel in a living body, such as a blood vessel, lymph vessel, ureter, or intestine, for example. Alternatively, the ends of the carrier 105 can be attached to semi-rigid or flexible tubing. Generally, the ends of the carrier 105 are attached to these vessels using any suitable attachment means, such as sutures, clamps, or adhesives.

[0023] The sensor 110 detects physical fluid characteristics such as pressure, conductance, and temperature. The sensor 110 may also detect chemical fluid characteristics such as pH, O₂, CO₂, and blood sugar levels. The type of sensor 110 used may be resistive, capacitive, or semiconductor-based without departing from the scope of the present invention. Sensors 110 may include, but are not limited to, silicon strain gauge sensors, photoelectric, chemical, Doppler, electromagnetic flow profile sensors, and fiber-optic sensors.

[0024] The sensor 110 is held in place on the carrier 105 with an appropriate bonding material 106. A preferred material 106 for bonding a sensor 110 to the carrier 105 is RTV silicone rubber (RTV). RTV is a soft, pliant material that does not distort the sensor 110 and provides some electrical isolation of the sensor 110 from the carrier 105.

[0025] The communication media 120 provide for communication between the sensor 110 and a monitoring device, as well as power to the sensor 110. Wires or fiber optic lines may be used for communication and power. The communication media 120 may also be part of any standard electrical communication system, such as a Wheatstone bridge. In an alternative embodiment (not shown) communication between sensors 110 and external monitoring devices occur through telemetry.

[0026] The inner surface of the inverted sensor module 100 may be coated or lined with an anti-thrombogenic substance 108 to prevent clotting and to provide a clean flow profile (less turbulence) with substantially no bubble traps. Examples of anti-thrombogenic substances include without limitation Parylene® and heparin. The inner surface of the carrier may be alternatively or additionally coated with an anti-infective agent.

[0027] FIG. 2 is an isometric drawing of an inverted sensor module 102 according to one embodiment of the present invention. In this embodiment, the inverted sensor module 100 is bonded to rigid tubing section 101. As a result, inverted sensor module 102 is formed, which generally resembles a tube with a lumen, and inverted sensor module 102 is adapted for monitoring characteristics of fluids flowing through inverted sensor module 102. In a preferred embodiment, the section of tubing 101 and the inverted sensor module carrier 105 are manufactured from the same material, such as polyimide tubing, and are of identical internal diameter to reduce turbulent flow, corrosion, or other effects from using dissimilar materials or varying geometry. Advantageously, the ability to position a sensor to face the concave side or lumen of an inverted sensor module 102 manufactured with tubing of known cross-sectional area and flow-through capabilities allows the sensor 110 to be inserted closer to a source or target, thereby increasing the accuracy of the measurements of the sensor 110.

[0028] Additionally, inverted sensor module 102 may also have surface features 112 located at either end for attaching vessels or tubing. Surface features 112 include lips, grooves, knurls, or any other surface feature that may be used in combination with any attachment technique to prevent a vessel from slipping off inverted sensor module 102. Ideally, surface feature 112 is such that any attached vessel is not damaged by the attachment to the feature 112.

[0029] In FIG. 3, an embodiment of an inverted sensor module 102 having a plurality of pressure sensors 110 is shown. In this embodiment, the sensors 110 are a known distance from each other. Since the cross-sectional area of the inverted sensor module 102 lumen and the distance between the sensors 110 are known, a volumetric flow rate for the vessel may be determined. It will be apparent to those skilled in the art that an accurate assessment of the volumetric flow rate in a vessel may be used to assess or predict performance of the body. It will also be apparent to those skilled in the art that a series of inverted sensor module 102 may used in a vessel at known distances to determine vessel performance.

[0030] FIGS. 4A and 4B show a cross-sectional side view and an isometric view of an embodiment in which an inverted sensor module 104 is assembled with a protective housing 140 covering inverted sensor module 100. Protective housing 140 may be manufactured from rigid tubing similar to the rigid tubing used to manufacture sensor carrier 105, or housing 140 may be manufactured of other materials. Protective housing 140 helps protect the sensor 110 and the connection to the communication media 120 from damage resulting from use inside a living body. The protective housing 140 may be bonded to the carrier 105 using Room Temperature Vulcanizing (RTV) silicone rubber, a biocompatible epoxy, or any other adhesive, mechanical or thermal technique.

[0031] Reference is now made to FIG. 5, which depicts the process flow for using an inverted sensor module 104 as shown in FIGS. 4A and 4B to determine the fluid characteristics within a body vessel. In step 510, an appropriate sized inverted sensor module 104 is selected based on the size of the vessel to be monitored. Inverted sensor module 104 of different lumen diameters, carrier lengths, or overall sizes give medical personnel and researchers the ability to take measurements of more characteristics, closer to a target region, on different size vessels, and with less impact on the surrounding body tissues. Additionally, this minimizes the negative physiological effects of monitoring a vessel, such as the disruption of blood circulation. By minimizing the negative physiological effects, trauma may be reduced, recovery may be quicker, and an inverted sensor module 104 may be left in the body for longer periods of time, allowing monitoring of both acute and chronic conditions.

[0032] In step 520, the vessel is opened for insertion of an inverted sensor module 104. For purposes of this disclosure, opening the vessel generally means the vessel may be cut all the way through or the vessel may be scored. For purposes of this disclosure, scoring a vessel means generally that an opening, such as a slit, is made in the vessel. The choice of whether to cut or score a vessel may be based on the particular application, size of the inverted sensor module 104, size of the vessel, health of the living body being monitored, type of vessel being monitored, fluid characteristic being monitored, or any other parameter, without departing in scope from the present invention.

[0033] In step 530, the inverted sensor module 104 is inserted into the vessel and the vessel is closed or sealed around the inverted sensor module 104. In situations in which the vessel is cut all the way through, the ends of the cut vessel are attached to the ends of the inverted sensor module 104 so that all fluid moving through the vessel must pass through the inverted sensor module 104. The ends may be attached with sutures, adhesives, clamps, or any other technique that ensures all fluid travels through the inverted sensor module 104 and that has little negative physiological effect on the vessel. In situations in which the vessel is scored, the inverted sensor module 104 is inserted into the vessel and the vessel is then sutured or sealed around the inverted sensor module 104 so that all fluid moving through the vessel must pass through the inverted sensor module 104.

[0034] In step 540, the communication medium 120 is connected to a monitoring device and measurements of the fluid characteristics may be taken.

[0035] Once the inverted sensor module 104 is inserted in the vessel and the vessel is attached to the ends of the inverted sensor module 104 or closed around the inverted sensor module 104, the living body may then be closed so that only the communication medium 120 protrudes from the body. In this manner, long-term monitoring may occur.

[0036] FIG. 6 is an illustration of an inverted sensor module 104, according to the preferred embodiment of the invention, implanted in an artery in a living body. As shown, a vessel is cut and the ends, 6A and 6B, are attached to the ends of inverted sensor module 104 such that all fluid flowing through the vessel must pass through inverted sensor module 104. As discussed above, the present invention is not limited for use in an artery, but may be used in intestines, ureters, lymph vessels, veins, chambers of the heart, or any other type of fluid vessel without departing in scope from the present invention.

[0037] Further modifications and alternative embodiments of this invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the manner of carrying out the invention. It is to be understood that the forms of the invention herein shown and described are to be taken as exemplary embodiments. Various changes may be made in the shape, size, and arrangement of parts. For example, equivalent elements or materials may be substitute for those illustrated and described herein, and certain features of the invention may be utilized independently of the use of other features, all as would be apparent to one skilled in the art after having the benefit of this description of the invention.