Abstract:
A balloon catheter has a balloon membrane, a tip connected to the distal end of the balloon membrane and an outer tube connected to the proximal end of the balloon membrane for supplying a medium for inflating and deflating the balloon membrane. A pressure sensor, such as a fiber optic sensor, may be mounted in a pocket in the tip. The pocket may be filled with a flexible substance which both communicates pressure to and protects the pressure sensor. A membrane may overlie the pocket to prevent leakage of the flexible substance therefrom.

Description:
The present application is a continuation of U.S. application Ser. No. 10/308,638, filed Dec. 3, 2002, now U.S. Pat. No. 6,935,999, which is a continuation of U.S. application Ser. No. 09/735,076, filed Dec. 12, 2000, now U.S. Pat. No. 6,616,597. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a catheter having enhanced pressure sensing capabilities. More particularly, the invention relates to a balloon catheter having a micromanometer connected to the catheter and also a fluid-filled transducer system for adjusting micromanometer pressure measurements. 
   2. Description of the Prior Art 
   A key function of many catheters is that of continuously monitoring blood pressure. In many cases, this monitoring must be performed with accurate measurement of high frequency components. For example, reliable detection of the dicrotic notch of the aortic blood pressure waveform typically requires a pressure signal having a bandwidth of 15 Hz or better. Detection of the dicrotic notch is generally used for the inflation/deflation timing of an intra-aortic balloon (“IAB”) catheter. 
   Conventional invasive pressure monitoring is performed with low-cost fluid-filled transducers. A typical disposable monitoring kit, inclusive of all tubing, a continuous flush device, and a pre-calibrated transducer is very affordable. Unfortunately, these systems have several drawbacks. One major drawback is that bubbles or clots in the monitoring lines can reduce the frequency response of the system to a level below 15 Hz, creating an “overdamped” condition. In other cases, the characteristics of the catheter and tubing can result in “ringing”, which is associated with an underdamped condition. Furthermore, fluid-filled catheters can suffer from “catheter whip” (motion artifact), which is manifested as one or more high frequency deflections in the pressure signal. These problems can degrade the usefulness of the signal in applications such as intra-aortic balloon pumping (IABP). In particular, it is difficult, if not impossible, to automatically provide optimal timing of IABP using a pressure signal with a frequency response below 15 Hz, or using signals with ringing or whip artifacts that mimic the physiologic dicrotic notch. 
   Another means for monitoring blood pressure is to use a micromanometer, such as marketed by companies such as Millar, Endosonics, and Radi. See U.S. Pat. Nos. 5,431,628 and 5,902,248, herein incorporated by reference. These devices can have excellent frequency responses, with system bandwidths greater that 200 Hz. They are not subject to the negative effects of bubbles and catheter whip, and retain good performance even in the presence of small blood clots. Unfortunately, they are very expensive, prone to signal drift, and can suffer from electrical interference. A common source of electrical interference in the setting of IABP therapy is the use of electrosurgery. In this situation, it is desirable to maintain a reliable pressure signal with which to trigger the balloon, as the ECG signal which normally triggers IABP operation becomes completely unreliable. Conventional fluid-filled transducer systems are relatively immune from this type of interference. 
   If the above problems were solved, micromanometers could potentially be used in conjunction with IABP systems and other catheters to measure blood pressure. Attempts have been made to use micromanometers for IABP timing, see U.S. Pat. Nos. 3,585,983 and 4,733,652, herein incorporated by reference. These attempts proved to be unreliable, as the device may be damaged during insertion and is also prone to signal drift. To address the drift issue, U.S. Pat. No. 5,158,529, herein incorporated by reference, discloses a method for rezeroing the micromanometer by using the pressure from a partially filled balloon as it rests in the aorta. However, this method requires momentary interruption of IABP, which may be harmful to the critically ill patient. 
   While standard IAB catheters incorporating a fluid-filled transducer pressure measurement system or IAB catheters incorporating micromanometers may be suitable for the particular purpose employed, or for general use, they would not be as suitable for the purposes of the present invention as disclosed hereafter. 
   SUMMARY OF THE INVENTION 
   Accordingly, there is a need for a reliable and affordable pressure monitoring approach that has high bandwidth pressure sensing, low signal drift, and freedom from electrosurgical interference. There is also a need to incorporate this technology into intra-aortic balloon catheters having small cross sectional profiles. 
   The invention is an IAB catheter system having enhanced blood pressure sensing capability. The IAB catheter has a micromanometer, or any high fidelity sensor, built into the tip of the IAB or connected to another part of the catheter, and a fluid-filled transducer kit connected to the y-fitting of the IAB. The IABP console, including a processor, continuously monitors and compares signals from both the micromanometer and the fluid-filled transducer. The signal from the micromanometer may be continuously displayed, and either continuously or intermittently adjusted for baseline drift by comparing it to that of the fluid-filled transducer. The adjustment is preferably made by comparing mean blood pressures as indicated by the two sources. 
   The IABP console could also monitor the micromanometer&#39;s signal for the presence of electrosurgical interference, mechanical damage, or any other possible causes of signal error. If significant errors are detected, the system automatically reverts to the use of the signal from the fluid-filled transducer system. The system also allows the user to manually select the use of the fluid-filled transducer, in the event that electrosurgical interference was anticipated. 
   To the accomplishment of the above and related objects the invention may be embodied in the form illustrated in the accompanying drawings. Attention is called to the fact, however, that the drawings are illustrative only. Variations are contemplated as being part of the invention, limited only by the scope of the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, like elements are depicted by like reference numerals. The drawings are briefly described as follows. 
       FIG. 1  is a perspective view of the system of the present invention. 
       FIG. 2  is a detailed longitudinal cross sectional view of flush device  34  in  FIG. 1 . 
       FIG. 3  is longitudinal cross sectional view of a distal portion of IAB catheter  10  in  FIG. 1 . 
       FIG. 3A  is a perspective view of distal end of inner tube  58 , shown independent of catheter  10 , with pressure sensing line  24  connected to an outer surface of inner tube  58 . 
       FIG. 3B  is a perspective view of a distal end of inner tube  58 , shown independent of catheter  10 , with pressure sensing line sandwiched between an outer surface of inner tube  58  and an outer layer. 
       FIG. 3C  is a perspective view of a distal end of inner tube  58 , shown independent of catheter  10 , with pressure sensing line  24  embedded in the wall of inner tube  58 . 
       FIG. 4  is a longitudinal cross sectional view of a distal portion of a co-lumen IAB catheter having a pressure sensor embedded in the tip. 
       FIG. 4A  is a transverse cross section of the co-lumen IAB, taken along lines  4 A— 4 A in  FIG. 4 . 
       FIG. 5A  is a perspective view of a distal end of the inner tube  58  and the catheter pressure sensor  22 , illustrating a first connection scheme. 
       FIG. 5B  is a perspective view of a distal end of the inner tube  58  and the catheter pressure sensor  22 , illustrating a second connection scheme. 
       FIG. 5C  is a perspective view of a distal end of the inner tube  58  and the catheter pressure sensor  22 , illustrating a third connection scheme. 
       FIG. 6  is a longitudinal cross section of tip  20  and a distal end of inner tube  58  and balloon membrane  30 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates the system of the present invention comprising an intra-aortic balloon (“IAB”) catheter  10 , an intra-aortic balloon pump (“IABP”)  12 , a monitor  14 , a drip bag  16 , and a drip bag holder  18 .  FIG. 1  is a perspective view of the system with the IAB catheter  10  in the foreground and the IABP  12  is the background for clarity. The IAB catheter  10  contains a catheter pressure sensor  22  connected to its tip  20  and a Y-fitting  36  on its proximal end. The catheter pressure sensor  22  is connected to the IAB pump  12  via pressure sensing line  24 , shown as ghost lines in the IAB catheter  10 . Inflate/deflate tube  26 , connecting an outer lumen of the IAB catheter  28  (see  FIGS. 3–4 ) and the IABP  12 , is used for inflation and deflation of a balloon membrane  30  connected between the tip  20  and a distal end of the IAB catheter  10 . Drip tube  32  connects the pressurized drip bag  16  to a flush device  34 . Saline tube  38  connects the flush device  34  with an inner lumen  60  of the IAB catheter (see  FIGS. 3–4 ). Clamp  40  connects the flush device  34  to the drip bag holder  18 . 
   The details of flush device  34  can be seen in  FIG. 2 . The flush device  34  comprises a flush device wall  52 , a microbore passage  42 , a fast flush seal  44  having a handle  46 , flush device lumen  48 , and a fast flush variable lumen  50 . Pressure sensor  40  is located in flush device  34  and communicates with IABP  12  via an independent line (not shown), which may exit through a hole (not shown) in flush device wall  52 , or in any other means known in the art for electrical devices to communicate. Saline, or another appropriate working fluid or gas, flows through the flush device lumen  48  through the microbore passage  42  at a very slow rate, approximately 3 cc/hour. The pressure on the side of the flush device  34  connected to drip bag  16  equals the pressure in the drip bag  16 , generally 300 mmHg. The pressure on the opposite side of the flush device  34  adjacent the pressure sensor  40  equals the blood pressure of the patient being treated with the IAB catheter  10 . The fast flush seal  44  is shown in an open state, however, during therapy fast flush seal  44  is forced against seat  54  by the flush device wall  52 , and therefore, does not allow saline through fast flush variable lumen  50 . In order to fast flush saline tube  38  and bypass microbore passage  42 , handle  46  can be pulled away from the flush device  34  such that fast flush seal  44  is lifted off seat  54 . During normal operation, however, saline drip is forced through microbore passage  42 . Note that the flush device  34  may be replaced with any other known flush device in the art having similar function. 
   The IABP  12  has incorporated therein a processor that controls the inflation/deflation timing of the balloon membrane  30 . Alternatively, the IABP  12  can be connected to a computer or any other type of control mechanism known in the art. The IAB catheter  10  is typically inserted into the femoral artery and moved up the descending thoracic aorta until the distal tip  20  is positioned just below or distal to the left subclavian artery. The proximal end of the catheter remains outside of the patient&#39;s body. The patient&#39;s central aortic pressure is used to time the inflation and deflation of balloon membrane  30  and the patient&#39;s ECG may be used to trigger balloon membrane  30  inflation in synchronous counterpulsation to the patient&#39;s heartbeat. 
   In the preferred embodiment, IABP  12  continuously monitors and compares signals from both saline pressure sensor  40  and catheter pressure sensor  22 . The signal derived from catheter pressure sensor  22  may be continuously displayed on monitor  14  and either, continuously or intermittently adjusted for baseline drift or other errors by comparing it to that of saline pressure sensor  40 . The adjusted signal is displayed on monitor  14  and is used to time the inflation and deflation of the balloon membrane. 
   The balloon membrane is inflated coincident with closure of the aortic valve and is contracted or deflated prior to cardiac ejection. 
   It is preferred that the adjustment be made by comparing mean blood pressures as indicated by the two sources. In operation pressure would be measured over a predetermined period of time via both the catheter pressure sensor  22  and the saline pressure sensor  40 . An indicated mean pressure, based on the catheter pressure sensor  22  measurements, and a true mean pressure, based on the saline pressure sensor  40  measurements, are calculated. If the indicated mean pressure differs from the true mean pressure by less than a predetermined amount, the catheter pressure sensor  22  measurements are displayed without correction; otherwise the catheter pressure sensor measurements are corrected prior to display such that the indicated and true mean pressures are equal. Alternatively, the pressures can be compared on a continuous point-by-point basis and an adjustment made if and when a predetermined pressure differential is reached. 
   IABP  12  may be programmed to provide options as to which sensor is relied on in any given situation and as how to compare the signals from both sensors and use the information contained in these signals to most accurately measure blood pressure. Note also, that in an alternative embodiment of the invention, a pressure cuff or other external or internal independent device known in the art may replace or act as a backup to the saline pressure sensor  40 . The reading from the independent external or internal blood pressure measurement device may be used to correct the drift in the catheter pressure sensor  22  reading in the same manner as used with the saline pressure sensor  40  reading. Use of such an independent external or internal measurement device may be necessary to adjust for drift in tip sensors in intra-aortic catheters without an inner tube and associated saline pressure sensor. 
   The adjustment to the catheter pressure sensor  22  readings, as described above, involves comparing mean blood pressures. Other methods of adjustment may include comparisons of diastolic pressures, systolic pressures, pressures at the end of balloon inflation, and balloon-augmented pressures. The IABP  12  may also monitor the signal from catheter pressure sensor  22  for the presence of electrosurgical interference, mechanical damage, or any other possible cause of signal error. If significant error is detected, the IABP  12  would automatically revert to use of the signal from saline pressure sensor  40 . Similarly, the IABP  12  may monitor the signal from the saline pressure sensor  40  for errors and compensate for these errors by using the signal from the catheter pressure sensor  22 . The IABP  12  may optionally allow a user to manually select the use of the saline pressure sensor  40  or the catheter pressure sensor  22 . Use of the saline pressure sensor  40  may be desirable in the event that electrosurgical interference was anticipated. 
   In an alternate embodiment of the invention, rather than adjusting catheter pressure sensor  22  signal for drift, saline pressure sensor  40  signal may be used solely for numerical display purposes and catheter pressure sensor  22  signal used solely for timing the inflation and deflation of balloon membrane  30 . 
   Catheter pressure sensor  22  may include any type of sensor capable of fitting on the catheter and of measuring blood pressure and producing a signal with a frequency response above approximately 15 Hz. Such sensors include but are not limited to micromanometers such as those produced by companies such as Millar, Endosonics, and Radi. These sensors typically include a small transducer exposed to arterial pressure on one side and often a reference pressure on the opposite side. Blood pressure deforms the transducer resulting in a change in resistance which is translated into a pressure reading. Alternatively, a fiber optic sensor may be used in which case pressure sensing line  24  would comprise a fiber optic line. Co-pending application, entitled Intra-Aortic Balloon Catheter Having a Fiberoptic Sensor, filed on Dec. 11, 2000, herein incorporated by reference in its entirety, discloses specific embodiments of an intra-aortic balloon catheter having an incorporated fiberoptic sensor. 
   The present invention, namely the dual use of both a fluid column pressure sensor and a secondary sensor to measure arterial pressure, is not limited for use with any specific type of catheter. Furthermore, use of different types of intra-aortic balloon catheters is anticipated.  FIG. 3  illustrates a longitudinal cross section of a distal portion of a typical dual lumen intra-aortic balloon (“IAB”) catheter  10  comprising an outer tube  56 , an inner tube  58 , a tip  20 , and a balloon membrane  30  connected on one end to the outer tube  56  and on the opposite end to the tip  20 . Tip  20  defines a tip lumen  21 . The inner tube  58  is disposed within the outer tube  56  and is connected to the tip  20  at its distal end. The inner tube  58  defines an inner lumen  60  and the outer tube  56  defines an outer lumen  28 . Inner lumen  60  communicates with saline tube  38  and is filled with saline or another suitable fluid for pressure sensing (see  FIG. 1 ). Outer lumen  28  is used for shuttling helium or another appropriate working gas or fluid for inflation and deflation of the balloon membrane  30 . The outer tube  56  may be coil or braid reinforced and made from polyurethane or polyimide. Inner tube  58  may be made from polyimide or an alloy with shape memory and superelastic properties commonly referred to as Ni—Ti, NITINOL™, and other industry names. Inner tube  58  may be connected to an inner surface of the outer tube  56  at one or more points or along the entire length of outer tube  56  to enhance pushability, stability, pumping speed, and pressure fidelity. Catheter pressure sensor  22  is embedded in or attached to tip  20 . 
   Pressure sensing line  24  connects catheter pressure sensor  22  to IABP  12  and is sandwiched between the outer surface of inner tube  58  and a secondary layer  64 . Alternatively, the pressure sensing line  24  is embedded in inner tube  58  or attached to the outer surface of inner tube  58  (see discussion of  FIGS. 3A–3C  below). Pressure sensing line  24  will vary dependent on the type of sensor used. If an electrical micromanometer of half-bridge design is used pressure sensing line  24  may consist of three fine wires  62  (see  FIGS. 3A–3C ), each approximately 0.001 inches in diameter. Note that the catheter pressure sensor  22  may be positioned in alternate locations along IAB catheter  10  as well as on a distal tip of an independent catheter that can be disposed within the inner lumen  58 . Dotted box, labeled A, designates another area where the catheter pressure sensor  22  may be located. In this location catheter pressure sensor  22  is exposed to arterial pressure via tip lumen  21  and is less likely to be damaged upon insertion and placement of IAB catheter  10 . 
     FIGS. 3A–3C  illustrate transverse cross sections of inner tube  58  with pressure sensing line  24  connected to inner tube  58  in various configurations. In  FIG. 3A , pressure sensing line  24 , comprising three fine wires  62 , is connected to an outer surface of inner tube  58 . In  FIG. 3B , pressure sensing line  24  is disposed between inner tube  58  and a thin walled tube  64 , which preferably is heat shrinkable. In  FIG. 3C , pressure sensing line  24  is embedded in the wall of inner tube  58 . Note that although pressure sensing line  24  is shown running along a longitudinal axis of inner tube  58  it may also be wound helically. 
     FIG. 4  illustrates a distal portion of another embodiment of the IAB catheter  10 , comprising a balloon membrane  30 , a tip  20 , a co-lumen tube  56 , an inner lumen extension tube  6 , and a catheter pressure sensor  22 . Detailed structure of a co-lumen IAB is disclosed in U.S. Pat. No. 6,024,693 and U.S. patent application Ser. No. 09/412,718, filed on Oct. 5, 1999, both herein incorporated by reference. Tip  20  is connected to a distal end of the balloon membrane  30  and to a distal end of the inner lumen extension tube  66 . Tip  20  defines a tip lumen  21 . A distal end of the co-lumen tube  56  is connected to a proximal end of the balloon membrane  30  and to a proximal end of the inner lumen extension tube  66 . The co-lumen tube  56  may be coil or braid reinforced and made from polyurethane or poly imide. The preferred material for inner lumen extension tube  66  is an alloy with shape memory and superelastic properties commonly referred to as Ni—Ti, NITINOL™, and other industry names. Inner lumen extension tube  66  may also be made from polyimide. The catheter pressure sensor  22  is attached to tip  20  and pressure sensing line  24  which communicates signals generated by the catheter pressure sensor  22  to the IABP  12  (see  FIG. 1 ). 
   Pressure sensing line  24 , as illustrated in  FIG. 4 , is sandwiched between inner lumen extension tube  66  and thin walled tube  64 ; however, pressure sensing line  24  may be connected to the inner lumen extension tube  66  in any of the ways illustrated in  FIGS. 3A–3C . It is preferred that pressure sensing line  24  float freely in outer lumen  28 , as illustrated in  FIG. 4 , however, pressure sensing line  24  may be connected to co-lumen tube  56  in any of the ways illustrated in  FIGS. 3A–3C .  FIG. 4A  illustrates a transverse cross section of outer tube  56 , taken along line  4 A— 4 A illustrated in  FIG. 4 , with pressure sensing line  24  embedded in the wall. Note that pressure sensing line  24  may be embedded at a different location in co-lumen tube  56  or connected to a surface of co-lumen tube  56 . 
   Co-lumen tube  56  defines two distinct lumens, inner lumen  60  and outer lumen  28 . Inner lumen  60  communicates with saline tube  38  (see  FIG. 1 ). Outer lumen  28  communicates with inflate/deflate tube  26  and is used for shuttling helium or another appropriate fluid or gas for inflation and deflation of balloon membrane  30 . Note that the catheter pressure sensor  22  may be positioned in alternate locations along IAB catheter  10  as well as on a distal tip of an independent catheter that can be disposed within the inner lumen  58 . Dotted box, labeled A, designates another area where the catheter pressure sensor  22  may be located. In this location catheter pressure sensor  22  is exposed to arterial pressure via tip lumen  21  and is less likely to be damaged upon insertion and placement of IAB catheter  10 . 
   FIGS  5 A– 5 C illustrate in detail alternate connections between catheter pressure sensor  22  and a distal end of pressure sensing line  24 . In FIG  5 A a distal end of pressure sensing line  24 , extending beyond a distal end of either inner tube  58  ( FIG. 3 ) or inner lumen extension tube  66  ( FIG. 4 ), is stripped of insulation  72  exposing wires  62 . Catheter pressure sensor  22  comprises a transducer  74  connected to a support  68 . Exposed wires  62  are positioned over contacts  70  on support  68  and may be soldered to support  68 . Note that pressure sensing line  24  is connected to inner tube  58  as shown in  FIG. 3B , however, connections shown in  FIGS. 3A and 3C  may also be used. 
     FIG. 5B  illustrates an alternate connection between catheter pressure sensor  22  and pressure sensing line  24 , which is embedded in inner tube  58 . This connection may be used when catheter pressure sensor  22  is located in alternate location A (see  FIGS. 3 and 4 ). Catheter pressure sensor  22  is identical to the embodiment in  FIG. 5A  except contacts  70  are on the underside of the support  68 . Wires  62  are exposed by peeling off insulation  72  and a portion of inner tube  58  directly above pressure sensing line  24 . Catheter pressure sensor  22  fits directly on top of pressure sensing line  24  such that wires  62  fit over contacts  70 . Rather than stripping away an entire section of inner tube  58 , as in FIG  5 B, small holes  78  could be made over the ends of each wire  62 , as illustrated in FIG  5 C. Solder pads  76  project from an under side of catheter pressure sensor  22 . Holes  78  can be aligned perpendicular to the longitudinal axis of the tube or if the wires are wound helically, see dotted lines in FIG  5 C, the holes can be aligned along the longitudinal axis of the inner tube  58 . Note that catheter pressure sensor  22  may shifted proximally such that it does not overhang the distal end of inner tube  58 . In such case, an additional hole through inner tube  58  may be used to allow transducer  74 , which is placed over such hole, to communicate with inner lumen  60 . 
   Alternatively, transducer  74  may face toward an outer surface of catheter tip  20  and sense pressure on the outside of tip  20 . This can be accomplished by using a thicker support  68  or by creating a pocket  90  over transducer  74 , as illustrated in FIG  6 . FIG  6  is a longitudinal cross section of tip  20  and a distal end of inner tube  58  and balloon membrane  30 . Tip  20  has a pocket  90  directly over transducer  74 . Pocket  90  may contain a gel, fluid, gas, elastomer, or any other flexible substance which both communicates pressure and protects transducer  74 . Membrane  92  prevents leakage of gel or other substance from pocket  90 . As an alternative to the use of membrane  92 , balloon membrane  30  can be extended to cover pocket  90 . This catheter pressure sensor  22  arrangement can be used for both the dual lumen (FIG  3 ) and co-lumen catheters (FIG  4 ). 
   Note that for both the typical dual lumen and co-lumen catheter arrangements the portion of the inner tube  5 . 8  disposed within the balloon membrane  30  may be made from a different material from the rest of the inner tube  58 . This can be accomplished by connecting two separate pieces of tubing as disclosed in U.S. Pat. No. 6,024,693, assigned to Datascope Investment Corp., herein incorporated by reference in its entirety. 
   As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.