Abstract:
An inverted sensor module for sensing physical and chemical fluid characteristics in a vessel in a living body. The inverted sensor module includes an inverted sensor bonded to a hollow carrier so that sensing occurs in the lumen of the inverted sensor module. An inverted sensor module comprising one or more inverted sensors is implantable and allows fluid to flow through, thereby allowing for measurements of acute and chronic conditions. The inverted sensor module may be used in series with other inverted sensor modules to assess trends such as pressure gradients along a bloodstream.

Description:
RELATED APPLICATION 
     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. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     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. 
     2. Related Art 
     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, O 2 , CO 2 , 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. 
     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. 
     SUMMARY OF THE INVENTION 
     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. 
     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. 
     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. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein. 
         FIG. 1A  is a top view of an inverted sensor module according to one embodiment of the present invention. 
         FIG. 1B  is an end view of an inverted sensor module according to one embodiment of the present invention. 
         FIG. 1C  is a bottom view of an inverted sensor module according to one embodiment of the present invention. 
         FIG. 2  is a side view of one embodiment of an inverted sensor module bonded to rigid tubing, according to one embodiment of the present invention. 
         FIG. 3  is an isometric view of an inverted sensor module with multiple sensors, bonded to rigid tubing, according to another embodiment of the present invention. 
         FIGS. 4A and 4B  are cross-sectional and isometric views, respectively, of an inverted sensor module with a protective housing, according to one embodiment of the present invention. 
         FIG. 5  is a flowchart of steps used to implant an inverted sensor module. 
         FIG. 6  is a drawing of one embodiment of an inverted sensor module implanted in a human body. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
     Now referring to the figures,  FIGS. 1A ,  1 B, and  1 C 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 . 
     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. 
     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, O 2 , CO 2 , 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. 
     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 . 
     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. 
     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. 
       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 . 
     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 . 
     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. 
       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. 
     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. 
     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. 
     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 . 
     In step  540 , the communication medium  120  is connected to a monitoring device and measurements of the fluid characteristics may be taken. 
     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. 
       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,  6 A and  6 B, 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. 
     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.