Abstract:
A catheter terminates at a tip that includes an array of pressure sensors. The sensors are responsive to detect and alert the user to variations of pressure that indicate the tip is either encountering an obstruction or constriction of smaller diameter than the catheter, as well as to guide the catheter through the conduit into which it is being inserted.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority to the U.S. Provisional Patent Application filed on Jun. 5, 2006, titled “Catheter with Pressure Sensor and Guidance System” and having Ser. No. 60/803,909, which is incorporated herein by reference. 

   BACKGROUND OF INVENTION 
   The present invention relates to catheters used in invasive medical procedures, and in particular to catheters with a capability to measure pressure. 
   Catheters are extensively used in medical procedures to probe or open restricted vascular structures or other bodily conduits, in for example the delivery of contrast dyes for radiographic procedures, balloon angioplasty to open coronary or other arteries, delivery of stents, insertion of heart monitors and ECD leads as well as numerous other procedures on humans and other living creatures. 
   In such catheterization procedures, it is essential that the physician visualize the location of the catheter in the body with respect to the critical tissues and other biological structures. This is usually accomplished by providing an x-ray source and an an X-ray imaging camera equipment are on opposite sides of the patient&#39;s body. The X-ray source and camera are under motorized control to precess about the patient so that images can be quickly taken from multiple different angles. Usually at least the tip of catheter is radio-opaque, typically comprising a stable barium compound as a filler. During vascular catheterization periodic and repeated injection of X-ray contrast dye from the catheter is required to visualize the blood flow around the catheter, and hence the location of the catheter tip within the arteries or veins. As the contrast agent diffuses into capillaries, it again becomes difficult to visualize the position of the catheter tip. 
   However, difficulties arise as the catheter technology has improved to where it is possible to probe smaller and smaller conduits or channels. However it is also easier to damage thinner tissue. Further, in arterial catheterization, as less contrast is available in thinner arteries, more contrast agent is required. In these procedures, both the physician, who is close to the patient to guide the catheter, and the patient are exposed to X-rays during the entire procedure. Although the patient receives more X-radiation during a single procedure, the skilled clinician can receive significant accumulated dose from multiple procedures. 
   Such catheter devices typically include a pressure sensing means at the tip to determine the local blood pressure to confirm that the device is itself is not blocking the artery being probed. 
   It is therefore an object of the present invention to provide an improved method for guiding catheters without the risk of damage to tissue structures. 
   It is also an object of the invention to provide means for catheterization that use either a lower x-ray dose and/or a smaller quantity of contrast dye. 
   SUMMARY OF INVENTION 
   In the present invention, the first object is achieved by providing a flexible catheter comprising: a smooth elongated tube having a tip, a plurality of pressure sensors distributed about the tip for measuring at least one of pressure fluctuations and variations of pressure associated with the orientation of the catheter within a narrow channel comparable to the width of said smooth elongated tube. 
   A second aspect of the invention is characterized by the process for inserting a catheter within a narrow channel or body conduit, the process comprising the steps of: providing a catheter according to the first embodiment described above, introducing catheter into a bodily conduit of living creature, selecting a pressure threshold at which one or more the pressure sensors or a measured difference in pressure is responsive to transmit an alarm signal to the user that the catheter should not be advanced further within the living creature. 
   The above and other aspects of the invention help the physician avoid damage during vascular and other catheterization procedures as well as provide an alternative and complimentary means for detecting obstructions and blockages to radiography. 
   The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1A  is a schematic illustration of a catheter device according to an embodiment of the invention. 
       FIG. 1B  is a partial view of the tip of the catheter in  FIG. 1A . 
       FIG. 2A  is a longitudinal sectional elevation through the tip of the catheter of  FIG. 1   
       FIG. 2B  is a transverse sectional elevation through the tip of the catheter of  FIG. 1  at reference line B-B in  FIG. 2A . 
       FIG. 3A  is a longitudinal sectional elevation through the tip of a catheter according to another embodiment of the invention. 
       FIG. 3B  is a transverse sectional elevation through the tip of the catheter of at reference line B-B in  FIG. 3A . 
       FIG. 4A  is a longitudinal sectional elevation through the tip of the catheter of another embodiment of the invention. 
       FIG. 4B  is a transverse sectional elevation through the tip of the catheter of at reference line B-B in  FIG. 4A . 
       FIG. 4C  is a transverse sectional elevation through the tip of the catheter of at reference line C-C in  FIG. 4A . 
   

   DETAILED DESCRIPTION 
   Referring to  FIGS. 1 through 4  wherein like reference numerals refer to like components in the various views, there is illustrated therein a new and improved catheter with pressure sensor and guidance system, generally denominated  100  herein. 
     FIG. 1A  illustrates such a catheter device  100  that comprises an elongated tube  105  that is at least partially flexible, and in particular most flexible wherein it terminates at a tip  110 . A plurality of pressure sensors  120 ′ are distributed about the tip  110 , one  120  being preferably at the apex of tip  110  as shown in the enlarged partial view in  FIG. 1B . Additional sensors, preferably pressure sensors such as  120   b,  may be disturbed elsewhere along the elongated tube  105  distal from the tip  110  and closer to the conventional control means  101 . The elongated tube  105  is at least partially flexible and preferably hollow, having an inner tubular cavity  103  (shown in  FIG. 2A ) The inner tubular cavity  103  may be used to deliver special probes, fluids or guide wire  107  (shown in  FIG. 3A ), as well as discrete medical devices or other test instrumentation as is generally known in the art or may be developed at some future time. 
     FIGS. 2A and 2B  show the structure of the sensors in tip  110  in more detail. As seen in the longitudinal sectional elevations in  FIG. 2A , a first pressure sensor  120  is deployed at the apex of tip  110 . A plurality of additional pressure sensors  120 ′ are distributed about the hemispherical portion of the catheter tip  110 . For example, sensors  120 ′, as shown in the transverse sectional elevation of  FIG. 2B  (taken at section reference line B-B in  FIG. 2A ) are preferably arrayed at equal angular spacing at the periphery of the tip region  110 . It should be appreciated that other embodiments include arraying the pressure sensors  120  similarly but on other portions of the catheter distal from tip  110 . 
   Each of the sensors  120  and  120 ′ is connected by wire  122  to a transmitting means. In  FIG. 2A  the transmitting means is a multi-strand cable  108  or signal cable sending multiplexed or digital signal of the output from all sensors  120  to control unit  101  or via link  135  to monitor or data logger  130 , which may include means for signal analysis and processing as will be further described below. The communication link  135  between control means  101  and monitor or data logging means  130  is indicated in  FIG. 1A . 
     FIGS. 3A and 3B  show an alternative embodiment of the invention. As shown in the longitudinal cross sectional elevation of  FIG. 3A , the tip  110  with attached or integrated pressure sensors  120  and  120 ′ may extends from tube  105  via guide wire  107  that is disposed in hollow cavity  103 . Guide wire  107  may include means for signal wire transmission, or as intended to be illustrated in this non-limiting embodiment an alternative embodiment shown in  FIG. 3A  the transmitting means is a wireless transmitter  125 , such as an RF transmitter. Such an embodiment eliminates the need to deploy a signal cable in cavity  103 . Each pressure sensor  120  or  120 ′ is connected to wireless transmitter  125  by signal wire  122 . Alternative, the pressure sensor may include an integrated wireless transmitter on the same chip or circuit board, eliminating the need for discrete wire connections. 
     FIGS. 4A and 4B  show an alternative embodiment of the invention in which a plurality of sensor arrays are disposed about tip region  110 . A first array of pressure sensors  120 ′ is deployed at section C-C located most adjacent to the apex of the tip, which preferably also terminates with a pressure sensor  120 . As in the other embodiments, these sensors  120 ′ are preferably arrayed at equal angular spacing at the periphery of the tip region  110 . A second array of pressure sensors  120 ″ is deployed a section B-B located from the apex of the tip. As in the other embodiments, these sensors  120  are preferably arrayed at equal angular spacing at the periphery of the tip region  110 . 
   The method of using the catheters of  FIG. 1-4  includes determining the difference in force or pressure among the sensors  120  distributed about the tip  110 . It is expected that when the tip  110  is centered within an artery or other body tissue conduit, the difference between the pressures measured at each sensor will be at a minimum. However, as the apex of tip  110  steers toward or into an arterial wall or other dense tissue a difference of pressure is expected. As it is preferable that the tip material be compliant to transmit force, displacement or vibrations to the adjacent and attached pressure sensors  120 , 120 ′ or  120 ″, it is expected that the pressure sensor reading will increase when the tip  110  actually touches the arterial wall. Thus, it is expected that the continuous monitoring of the pressure differences between sensors may be used to steer or guide the catheter down the center of an artery or other tubular tissue structure. 
   It is a further embodiment of the invention that the monitor or data logging means  130  preferably includes provisions for setting a pressure threshold that signals an alarm or alert to the physician indicating the tip  110  of catheter  100  is either misguided from the center of the conduit or is close to a breaching or tearing tissue that it touches. This will permit the physician to withdraw or redirect the catheter tip  110  before such damage occurs. 
   Preferably, sensors  120  are nano-sized or MEMS transducers, such as those disclosed in currently pending patent applications, which are listed in Appendixes 1-4 of the US Provisional Patent Application from which this application depends, being incorporated herein by reference. It should be understood that depending on the compliance and damping characteristics of the preferably compliant material that forms tip  110  and supports or surrounds sensors  120 ,  120 ′ and  120 ″, the term pressure sensor means a mechanical transducer that detects at least one of variations in force, displacement or vibration. 
   While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be within the spirit and scope of the invention as defined by the appended claims.