Abstract:
A system for monitoring and regulating pressure and concentration in a moving fluid stream inside of a conduit is provided. The fluid stream includes a first fluid. The system comprises an infusion assembly that includes a catheter having a series of holes distributed around an exterior surface and a pumping system for introducing a second fluid into said catheter to create a solution mixture. A data collection system is provided for collecting data indicative of pressure and conductivity values. Data from the data collection system is forwarded to a data processing and control apparatus. The data processing and control apparatus comprises conversion means for converting the measured conductivity into a concentration value and control means for controlling operation of the infusion assembly based on a comparison of selected values with data received from the data collection system. A user control and analysis system allows user interaction. The system allows complete automatic control over the fluid distribution within a fluid conduit in response to measured values.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a system for monitoring and regulating fluid concentration and fluid pressure within a fluid conduit. Specifically, the system monitors and controls a concentration and a pressure value in an arterial or a venous line during continuous fluid flow.  
         BACKGROUND OF THE INVENTION  
         [0002]    Traditionally, it has been difficult to obtain accurate data about fluid concentrations within a fluid stream without using an invasive technique. U.S. Pat. No. 5,477,468, hereby incorporated by reference, discloses a concentration analyzer that achieves instantaneous measurement of fluid concentration in a moving fluid stream. However, the system disclosed in the prior patent did not provide any mechanism for measuring or controlling pressure within a fluid conduit.  
           [0003]    There is also a need for a system for measuring and controlling the delivery and dispersion of an anticoagulant agent, a radio-opaque contrast agent, and various other chemical agents entering an artery or a vein.  
           [0004]    There is also a need for a system to effectively monitor and regulate pressure variations within a fluid conduit.  
         SUMMARY OF THE INVENTION  
         [0005]    It is therefore an object of the invention to provide a system that allows complete control over the distribution of a fluid entering an artery or a vein.  
           [0006]    It is an additional object of the present invention to provide a pressure measurement system that effectively monitors and regulates pressure variations within a fluid conduit.  
           [0007]    It is an additional object of the invention to provide a system that effectively monitors pressure variations and concentration variations within a fluid conduit and that automatically controls fluid flow in response to a variation.  
           [0008]    Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.  
           [0009]    To achieve the objects and in accordance with the purposes of the invention as embodied and broadly described herein, a system is provided for monitoring and regulating pressure in a moving fluid stream inside of a conduit. The system comprises an infusion assembly including a catheter having a series of holes distributed around an exterior surface. The infusion assembly further includes injection means for introducing a fluid into the catheter and a pump for delivering fluid to the injection means. The invention further comprises a data collection system including a first pressure transducer attached to a pressure chamber of the pump and a second pressure transducer attached to the end of the catheter for measuring the pressure in a pressure chamber line of the catheter. A data processing and control system is provided for processing data collected from the second pressure transducer attached to the end of the catheter and for controlling operations of the infusion assembly based on a comparison of a plurality of selected values and the data received from the data collection system. A user control and analysis system allows user interaction.  
           [0010]    In an additional aspect of the invention, a system is provided for monitoring and regulating pressure and concentration in a moving fluid stream inside of a conduit, wherein the fluid stream includes a first fluid. The system comprises an infusion assembly including a catheter having a series of holes distributed around an exterior surface and injection means for introducing a second fluid into the catheter to create a solution mixture, and a pump for delivering the second fluid to the injection means. A data collection system is provided that includes a first pressure transducer attached at a first end of the catheter for measuring the pressure in a pressure chamber line of the catheter, a second pressure transducer attached at a second end of the catheter, and a sensor means within the conduit for measuring a conductivity of the first and second solution mixture. A data processing and control apparatus is provided that includes conversion means for converting the measured conductivity into a concentration value, and control means for controlling operation of the infusion assembly based on a comparison of a plurality of selected values with data received from the data collection system. A user control and analysis system allows user interaction.  
           [0011]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a block diagram illustrating the main components of the system of the invention;  
         [0013]    [0013]FIG. 2 a  is a block diagram showing the components of the infusion assembly;  
         [0014]    [0014]FIG. 2 b  is a side view showing an embodiment of the catheter of the infusion assembly;  
         [0015]    [0015]FIG. 2 c  is a diagram showing the pumping components and injection means of the infusion assembly;  
         [0016]    [0016]FIG. 2 d  is a circuit diagram showing connections within the infusion assembly;  
         [0017]    [0017]FIG. 3 a  is a block diagram showing the components of the data processing and control system;  
         [0018]    [0018]FIG. 3 b  illustrates the details of the pressure monitoring system;  
         [0019]    [0019]FIG. 3 c  illustrates additional components of the conductivity monitoring system;  
         [0020]    [0020]FIG. 4 illustrates the pressure data collection apparatus for the data collection system;  
         [0021]    [0021]FIG. 5 a  illustrates the conductivity data collection apparatus for the data collection system;  
         [0022]    [0022]FIGS. 5 b - 5   c  illustrate additional details of a preferred embodiment of the conductivity data collection system;  
         [0023]    [0023]FIG. 6 is a block diagram showing a preferred embodiment of the components of the fluid monitoring and control system;  
         [0024]    [0024]FIG. 7 a - 7   d  are sample tables generated by the control and analysis system; and  
         [0025]    [0025]FIGS. 8 a  and  8   b  illustrate insertion of the catheter. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings in which like reference numerals refer to corresponding elements.  
         [0027]    [0027]FIG. 1 is a block diagram illustrating the major components of an embodiment of a system for monitoring and regulating pressure in a moving fluid stream inside of a conduit in accordance with the invention, fluid monitoring and control system  1 . An infusion assembly  100  provides fluid flow through a conduit  10 . The system  1  of the invention is particularly suited for use in a conduit  10  such as a human vein or an artery. A data collection system  200  collects data related to the fluid flow through the conduit  10 . From the data collection system  200 , one or more data signals are transmitted to a data processing and control system  300 , which processes data for display on a display mechanism  400  and further controls the infusion assembly  1   00  with the processed data. A user control and analysis system  500  allows user input and communicates with the data processing and control system  300  to receive processed data and convey selected values. Each of the aforementioned subsystems is explained in further detail below.  
         [0028]    A. Infusion Assembly  100   
         [0029]    [0029]FIG. 2 a  illustrates the components of the infusion assembly  1   00 . The infusion assembly  100  includes a pumping assembly  120 , an injection means  160 , and a catheter  180 . These portions of the infusion assembly  100  will be described in greater detail below.  
         [0030]    1. Catheter  180   
         [0031]    [0031]FIG. 2 b  illustrates catheter  180 , which preferably is inserted into the conduit  10 , which may be a vein or an artery of a human patient, in a conventional fashion using a guide wire  185  as shown in FIGS. 8 a  and  8   b . The guide wire  185  is subsequently removed after insertion of the catheter  180 . The catheter  180  is adapted for mounting one or more data collection components to be described in more detail below.  
         [0032]    [0032]FIGS. 8 a  and  8   b  further illustrate the components of the catheter  180  and a technique for its insertion. A commercially available guide wire  185  made from a thin, highly flexible alloy is used to guide insertion of the catheter  180  into the conduit  10 . The guide wire  185  comes in a plurality of diameters to accommodate catheters of varying sizes.  
         [0033]    Current practice is to introduce an angiographic needle for injection at a point of introduction  187  to an artery as shown in FIG. 8 b . The angiographic needle has a steel rod, called a stylette (not shown), through its center. The angiographic needle is introduced through the skin at the point of introduction  187  into the artery with the stylette in place. The stylette is then pulled out and the guide wire  185  is introduced through the angiographic needle. The angiographic needle is then removed by passing it over the guide wire  185 . The catheter  180  is then passed over the guide wire  185  via a pressure space  182  of the catheter  180  and the guide wire  185  is then pulled out. A piezo-resistive transducer  214  (described in detail below) is then connected to the pressure space  182  and pumping can begin through a pumping space  184  of the catheter  180 .  
         [0034]    The guide wire  185  is necessary for insertion because, without it, the catheter  180  may become off-center and cause damage to the arterial wall. The guide wire  185  is very flexible and will not cause damage to the arterial wall.  
         [0035]    Measuring devices such as transducers cannot be placed on the side of the catheter  180 , because they also may cause damage to the arterial wall.  
         [0036]    [0036]FIG. 8 b  illustrates a need for two different types of guide wires  185 . Artery  187  is a curved brachial artery which requires a guide wire  185  with an angled tip. Artery  189  is a straight femoral artery which requires a guide wire  185  with straight tip. In either case, the guide wire  185  has a proximal end that is more flexible than a distal end.  
         [0037]    The catheter  180  should include a plurality of holes  186 . Preferably, a total surface area of all of the holes  186  is roughly equivalent to a total cross-sectional area of the conduit  10  in order to obtain an effective flow. The holes  186  should point in all directions in order to ensure an equal distribution of fluid throughout the conduit  10 . Optimally, the catheter  180  is disposed in operation centrally within the conduit  10 . In a preferred embodiment, the catheter  180  should include about seventy holes  186 . Because conduit  10  sizes will vary, catheters  180  providing different aperture sizes should be provided. A diaphragm (not shown) including a puncturable latex or rubber inserted in a brass fitting is provided in an embodiment of the invention to facilitate insertion of the catheter  180  into the conduit  10 .  
         [0038]    2. Injection Means  160   
         [0039]    [0039]FIG. 2 c  illustrates a plurality of components of the injection means  160 . A syringe  163  is provided for injecting fluid into the catheter  180 . A reservoir  162 , filled with the fluid to be pumped, is operatively connected with the syringe  163 . Reservoir  162  enables refilling of syringe  163  when prompted by the data processing and control system  300 .  
         [0040]    3. Pumping Components  
         [0041]    Also as shown in FIG. 2 c , a pump  125  is provided for pumping fluid from the above-described reservoir  162  to syringe  163  for injection into catheter  180 . Pump  125  is preferably a pulsatile pump with a capability of pumping  25 , 000  pulses per second and is provided with varying pulse rates and a fixed pulse volume. The catheter  180  is inserted into a circulatory system emulates a human circulatory system by providing multiple fluid pathways, adjustable compliance and adjustable resistance for purposes of experimentation.  
         [0042]    Pump  125  is powered by a stepper motor  128 . A plurality of drive components  122  for pump  125  preferably include a linear drive shaft and a belt to deliver the stepper motor  128  output to a syringe pumping chamber  135 . The syringe pumping chamber  135  preferably handles pumping pressures of up to  500  pounds per square inch (PSI). The pumping chamber  135  is preferably constructed of a thick heavy duty transparent plastic. A pressure switch  132  is provided for setting the desired pumping pressure in order to enable pumping at a constant pressure.  
         [0043]    A wire  145  delivers a plurality of electronic signals to a stepper motor pulse counter  129 . The electronic signals delivered are those which originated by tapping into the line from the pressure monitor  320  (further described below) to the stepper motor controller  148 . The stepper motor pulse counter  129  counts and displays a cumulative number of pulses of the stepper motor  128 .  
         [0044]    Stepper motor  128  maintains a constant pressure in the syringe  163  as set by the pressure switch  132 . A pumping electronic switch  143  provides an electronic signal to indicate when the syringe  163  is full. A refill electronic switch  146  provides an electronic signal indicating that the syringe  163  is empty. In a preferred embodiment of the invention, both the pumping electronic switch  143  and the refill electronic switch  146  remain open until the syringe  163  is either empty or full, in which case, the appropriate switch closes. A suitable switch for use for the pumping electronic switch  143  and the refill electronic switch  146  includes a Cherry E61 subminiature switch rated at 5 amps, 125/250 volts AC.  
         [0045]    A crack valve  136  is provided that permits fluid to flow only in one direction from the reservoir  162  to the syringe  163  when the syringe  163  is refilling. A bleeder valve  138  facilitates removal of all of the air and bubbles from the syringe  163  before pumping is commenced.  
         [0046]    A solenoid valve  133 , which preferably has less than a  4  millisecond delay, controls pumping from the syringe  163  into the catheter  180 . Solenoid valve  133  is connected with a solenoid valve circuit board  134  via a wire  140 . In operation, fluid moves directly from the pump  125  to the solenoid valve  133 , into the catheter  180 .  
         [0047]    A low compliance connecting tube  144  is provided to deliver flow through the pump  125 , the solenoid valve  133 , and subsequently into the catheter  180 .  
         [0048]    If the solenoid valve  133  is continuously open, then the pump  125  operates continuously. The pump  125  is controlled directly from a pressure monitoring system  320  that is described below.  
         [0049]    [0049]FIG. 2 d  is a circuit diagram showing the preferred connections between solenoid valve  133  and stepper motor  128 . A plurality of pulses  301  are sent from the data processing and control system  300  to control the solenoid valve  133 . Solenoid valve  133  is selectively operates by a power supply  147 , which transmits signals to a stepper motor controller  148 , which is preferably a 5-phase driver, to operate the stepper motor  128 .  
         [0050]    B. Data Collection System  200   
         [0051]    1. Pressure Data Collection Subsystem  210   
         [0052]    As shown in FIG. 4, the data collection system  200  preferably includes a pressure data collection subsystem  210 , that includes two transducers in an experimental mode for measuring pressure. Each of the two pressure transducers is attached to an end of the catheter  180 . A first signal is received from a Harvard pressure transducer  212  at a first distal end of the catheter  180  and a second signal is received from a piezo-resistive transducer  214  at an opposite proximal end of the catheter  180 . The piezo-resistive transducer  214  preferably includes a steel diaphragm and has a resonant frequency of approximately 50 khz. Harvard pressure transducer  212  is a non piezo-resistive transducer placed into the wall of the plastic tubing adjacent to the tip of the catheter  180 . The Harvard pressure transducer  212  is used during experimentation for gathering data. Once the necessary experimental data is gathered, the Harvard pressure transducer  212  is removed for actual use of the catheter  180  during treatment.  
         [0053]    Piezo-resistive transducer  214  measures the pressure in a pressure chamber line  181  of the catheter  180 . The pressure chamber line  181  of catheter  180  delivers the pressure wave from the tip of the catheter  180  to the piezo-resistive transducer  214 . Accordingly, pressure measurements are taken at both ends of the catheter  180  and the delay between the generated signals is taken into account. A wire  182  delivers the electronic signal from the piezo-resistive transducer  214  to a pressure monitoring subsystem  320  of the data processing and control system  300 .  
         [0054]    2. Conductivity Data Collection Subsystem  230   
         [0055]    Also provided within the conduit  10  is a conductivity data collection subsystem  230  as shown in FIGS. 5 a - 5   c  including a conductivity probe  230   a . The conductivity probe  230   a  comprises multiple regions of electrodes  233  to give a representation of the fluid being infused in each region of the conduit  10 .  
         [0056]    In a preferred embodiment, the conductivity probe  230   a  includes a sensor  231  having nineteen real electrodes  233   a , mapped to forty-two regions  232 . As shown in FIG. 5 b , the conductivity probe  230   a  further includes forty-two primary virtual electrodes  233   b , each of which are located at a midpoint between any two real electrodes  233   a . Regions  232  are joined to provide sixty-two points. The sixty-two points connect to form ninety-six equilateral triangles, as shown in FIG. 5 c . The addition of the virtual electrodes  233   b  increases the number of regions  232  thereby allowing finer measurements of concentration values. The data from the electrodes  233  is transmitted into a code processor (further described below) that in a preferred embodiment processes 800,000 triangles per second and 50 to 60 frames per second.  
         [0057]    In the preferred embodiment, the conductivity probe  230   a  includes 19 Teflon insulated surgical stainless steel wires with uninsulated tips as real electrodes  233   a . Other suitable metals may also be used for the wires forming the real electrode  233   a  cluster of sensor  231 . The wires are preferably 0.19 mm in diameter, tapering slightly at the ends, and 25 mm in length. The Teflon coating is preferably 0.005 mm thick. Stainless steel fittings are used for the side of the real electrode  233   a  cluster of sensor  231 . The stainless steel fittings are pressed in place, and the body of the conductivity probe  230   a  is counter-bored, so that there is no change in the inside diameter. A shielded cable connects the head of the conductivity probe  230   a  to additional data collection components.  
         [0058]    C. Data Processing and Control System  300   
         [0059]    The data collection system  200  sends all of the collected data to the data processing and control system  300  as shown in FIG. 3 a . The data processing and control system  300  comprises two main subsystems. A first of these subsystems is a pressure monitoring subsystem  320  and a second subsystem is a conductivity monitoring subsystem  360 .  
         [0060]    1. Pressure Monitoring Subsystem  320   
         [0061]    The operation of the infusion assembly  100  is controlled by the data processing and control system  300  as shown in FIG. 3. The data processing and control system  300  includes the pressure monitoring subsystem  320 . The pressure monitoring subsystem  320  includes a pressure meter  321  powered by a power supply  322 . A first output  324  of the pressure meter  321  sends a plurality of pressure signals to the user control and analysis system  500 . A second output  326  of the pressure meter  321  sends a plurality of pressure signals to the infusion assembly  100 , and a third output  328  of the pressure meter  321  sends a plurality of pressure signals to the display mechanism  400 .  
         [0062]    More specifically, the second output  326  delivers a plurality of electronic pressure signals to the infusion assembly  100  via a cable  329  to the stepper motor controller  148 . A cable  318 , which is preferably a rainbow ribbon cable, delivers a plurality of electronic pressure signals from the pressure monitoring subsystem  320  to a Commport  502  of the user control and analysis system  500 .  
         [0063]    As illustrated in FIG. 3 b , the pressure meter  321  includes an amplifier  330 , an A/D converter  340 , and a CPU  350 . Pressure signals from the pressure data collection subsystem  210  are forwarded to the amplifier  330  which outputs a plurality of signals to the A/D converter  340  and subsequently to the CPU  350  for output to other components of the system  1 . FIG. 3 b  illustrates a preferred embodiment of the circuitry used for connecting the components of pressure meter  321 , although specific resistance and capacitance values may be varied as appropriate.  
         [0064]    It is through the above-described signal transmission that data provided from the pressure data collection subsystem  210  activates the pump  125 . When the pressure of transducer  214  drops below a pre-selected level, the pump  125  starts. A constant pressure can thereby be created. The above-described solenoid valve  133  is programmed to open and close in accordance with the pulses received from the data processing and control system  300 .  
         [0065]    Pressure monitoring subsystem  320  uses several parameters to control pumping, including pulse width and dead time. In a preferred embodiment, pressure monitoring subsystem  320  is comprised of a microprocessor and an EPROM chip programmed to control the pressure using an assembly code programming language. The pressure monitoring subsystem  320  is thereby programmed to completely control pulse generation, operate the pump  125  at a constant pressure, and control the opening and closing of the solenoid valve  133 . The pressure monitoring subsystem  320  is also programmed to limit the pulse width of the pulses generated to the solenoid valve  133  based on the pulses generated to the stepper motor  128 . The pressure monitoring subsystem  320  is also programmed to monitor dead time, which determines the amount of time the solenoid valve  133  must stay off before another pulse. If the pressure exceeds a preselected threshold level, pumping will stop. Additionally, the pressure monitoring subsystem  320  may also be programmed to limit the total number of pulses that can be generated in one pumping session.  
         [0066]    2. Conductivity Monitoring Subsystem  360   
         [0067]    Also included in data processing and control system  300  is a conductivity monitoring subsystem  360  including a conductivity meter  361 , powered by a power supply  362 . An output  378  of the conductivity meter  361  is directed to the user control and data analysis system  500 . An input  368  of the conductivity meter  361  is connected from the data collection system  200  to the conductivity meter  361  through a probe circuit board  376  and a potentiometer circuit board  374 . The conductivity probe  230   a  within the data collection system  200  is mechanically mounted to the probe circuit board  376 . Adjustment of a plurality of potentiometers on the potentiometer circuit board  374  provides a way of equalizing the total circuit resistance in each probe circuit.  
         [0068]    Conductivity data processing and control begins with an input signal from the conductivity probe  230   a  to the probe circuit board  376 . Through the input  368 , a plurality of selector switches are provided and are used to activate a pair of the electrodes  233   a  in the electrode cluster of sensor  231  at any given point in time. The probe circuit board  376  repeatedly measures the conductivity difference between the electrodes  233   a  in the electrode cluster of sensor  231  by isolating one pair of electrodes  233   a  at a time. The conductivity between each activated, selected electrode pair  233   a  is measured by passing a small electrically-isolated constant voltage pulse from a voltage pulse source through the two activated, selected electrodes  233   a . A voltage drop between the two activated, selected electrodes  233   a  is measured and is used to indicate a conductivity of the fluid in the conduit  10 .  
         [0069]    In a preferred embodiment, the probe circuit board  376  includes a pair of input multiplexer selector switches that are each sent a six bit sensor code which identifies the particular pair of electrodes  233   a  which is to be connected to a voltage pulse source. Each input multiplexer channel is normally an “open circuit,” but any two input multiplexer channels can be activated simultaneously by sending the six bit sensor code to the channel to be connected to the voltage pulse source thus closing the channel and connecting an electrode  233   a  from the selected electrode  233   a  pair to the voltage pulse source causing to the other electrode  233   a  in the electrode pair to be connected to ground. The two electrode  233   a  sensor heads to be accessed are also connected to an instrumentation amplifier that measures the potential difference between the two accessed electrodes  233   a . Independent multiplexers are also connected to the instrumentation amplifier so that an error is not introduced by a voltage drop in the current source/sink circuit. The time between accessing or activating any electrode  233   a  pair is less than one microsecond.  
         [0070]    In the preferred embodiment, the input multiplexer is comprised of a  16  channel, dual 8-channel CMOS analog multiplexer, such as a DG 406 /DG 407  multiplexer manufactured by Maxim Integrated Products. A conductivity meter  361  is comprised of a low voltage, low current pulse circuit—about 10 millivolts at 10 microamps—which provides the pulse to make the conductivity measurement. A voltage pulse is applied across a balanced circuit consisting of two resistors of equal resistivity value and a pair of electrodes  233   a  for which the conductivity measurement is to be made. The voltage between the pair of electrodes  233   a  will be dependent upon the conductivity of the fluid between them. The original voltage pulse is compared to the voltage pulse between the pair of electrodes  233   a  and the resulting difference is differentially amplified. This difference is captured by a peak detector and is then digitized by an A/D converter for processing by the user control and analysis system  500 . Because the duration of the voltage pulse applied is extremely short, it effectively allows conductivity to be measured without probe capacitance or double layering.  
         [0071]    Signals from the probe circuit board  376  are forwarded along the input  368  to the potentiometer circuit board  374  that includes a plurality of resistors to equalize electronic difference in the circuits of the different regions produced by the electrode  233  array.  
         [0072]    From the potentiometer circuit board  374 , signals are forwarded along the input  368  to the conductivity meter  361 . The components of the conductivity meter  361  are shown in FIG. 3 c . Signals are forwarded through an amplifier  364  and an A/D converter  365 .  
         [0073]    The amplifier  364  has three functions. First, it measures the voltage difference between an electrode  233  pair. Second, it amplifies the input voltage reading from an electrode  233  pair since the input voltage is lower than the dynamic range of the A/D converter  365  to which the amplifier  364  is connected. Finally, it buffers an output signal of the electrode  233  pair since the A/D converter  365  input draws several milliamps of current. In the preferred embodiment, the amplifier  364  is a 3-op amp design, such as the INA114 amplifier manufactured by Burr-Brown Corporation.  
         [0074]    The A/D converter  365  receives the output from the amplifier  364  and converts the input analog voltage signal to a digital output signal to send to a control CPU  366 . In the preferred embodiment, the A/D converter  365  is an A/D converter chip, such as one manufactured by Maxim Integrated Products. The A/D converter  365  preferably reads the input voltage every four microseconds giving a 250,000 sample second throughput.  
         [0075]    The signal data are forwarded from A/D converter  365  to CPU  366 . CPU  366  stores a region electrode  233  pair file that contains a list of six bit sensor codes for activating specific electrode  233  pairs. The CPU  366  outputs a six bit multiplexer control signal to the input multiplexer for selection of a specific electrode  233  pair. Additionally, CPU  366  receives a plurality of commands from the user control and analysis system  500 .  
         [0076]    A known problem in achieving accurate conductivity measurements relates to the passing of electric current through a saline solution. A phenomenon referred to as “double layering” occurs as the concentration goes up and the resistance goes down, thereby causing the solution to break down into ions.  
         [0077]    Through testing, it was found that at 14 microseconds, before double layering occurs, pure current flows through the fluid without capacitance. Accordingly, accurate measurements can be taken during the initial time period of fluid flow, which in the system of the preferred embodiment, is approximately the first 14 microseconds.  
         [0078]    An additional problem found in the original conductivity measurement scheme relates to the programming of A/D conversion. When the computer sees a “null,” it begins taking readings of each of the  42  electrode regions  232 . When the computer sees another “null” it begins taking readings again. However, sometimes, a natural zero occurs that the computer would interpret as a “null.” This problem is solved by using the spare bits in a 16-bit memory word. The A/D value returned by the A/D converter  365  utilizes only 14 bits of the 16-bit word. One of the spare bits is always set to a valid A/D value while a “null” is sent as all “0” bits. The A/D converter  365  is preferably one manufactured by Maxim Integrated Products which utilizes a “2&#39;s” complement numbering system. The conductivity meter  361  converts the “2&#39;s” complement number to an unsigned positive binary value prior to sending information to the user control and analysis system  500 .  
         [0079]    D. Display Mechanism  400   
         [0080]    The display mechanism  400  may include an oscilloscope  402  which is provided to show measured pressures. The oscilloscope  402  is preferably a 4-channel Hitachi oscilloscope. An additional oscilloscope  402  may be provided and is preferably a two-channel Hitachi oscilloscope. A motor pulse display  48  taps into the line from the pressure box to the stepper motor controller  148  for hookup to the oscilloscope  402 . A ground terminal is provided for the stepper motor  148  pulse display on the oscilloscope  402 .  
         [0081]    E. User Control and Analysis System  500   
         [0082]    As shown in FIG. 6, the user control and analysis system  500  comprises a computer that is preferably a Gateway 2000 computer using a Windows®-based operating system. A main program running on a CPU  510  of the user control and analysis system  500  comprises multiple subprograms. The main program is interactive so that a user of system  1  can selectively view previously recorded analyses or portions thereof. The user can also select particular maps and graphs and change the format of these displays as desired. In operation, a user interface program is executed to allow a user to select items to be viewed. If the user selects a new electrode  233  pair, the program commands the user control and analysis system  500  to read in the region electrode  233  pair file. The six bit sensor codes control the input multiplexer selector switches to select a particular pair of electrodes  233 .  
         [0083]    As stated above, the main program running on the user control and analysis system  500  consists of several subprograms. After initialization, the main program will display several subprogram options for selection by the user. The various subprogram options are briefly described below.  
         [0084]    An “about” subprogram is provided to create an “about box” for disclosing basic information about the main program.  
         [0085]    A “calibrate” subprogram is provided to calibrate the probe  231 . When selecting the “calibrate” subprogram, the user will be required to enter the concentration value of the known, second solution which is to be injected into the conduit  10  at the infusion sight. The probe  231  then takes a plurality of conductivity readings for each electrode  233  pair and these conductivity readings are recorded in a calibration table as calibration data points. If the probe  231  is replaced, a new calibration table must be created. A user can interact with the calibrate subprogram in order to delete or add calibration data points in the calibration table.  
         [0086]    A “calpressure” subprogram allows for calculation of a plurality of pressure related values including an average pressure value, a maximum pressure value, a minimum pressure value, a diastolic pressure value, a systolic pressure value, and a pulse rate. The user can select one or more desired values and the calpressure subprogram will calculate the other values.  
         [0087]    A “config” subprogram configures the display of electrode tables on the screen display of the user&#39;s computer including a real electrode  233   a  table, a virtual electrode  233   b  table, a triangle table and a hexagon table. The config subprogram ensures that proper distances between electrodes  233  will be displayed. The config subprogram allows the user to set various aspects of the configuration including the electrode delay time.  
         [0088]    A “comm” subprogram facilitates the transfer of data from the data processing and control system  300  through a Commport 1 and a Commport 2 to the user control and analysis system  500 . Specifically, the comm subprogram includes a read routine for reading bytes of data from the Commports 1 and 2 and sorts the data read into appropriate locations.  
         [0089]    An “extensions” subprogram provides a definition for each of a plurality of macros that provide convenience to the user, such as a toolbar message macros, a progress bar extension macro, a track bar extension macro, and an up/down extension macro.  
         [0090]    A “genmap” subprogram generates a plurality of maps that allow the real electrodes  233   a  and the virtual electrodes  233   b  to be plotted on the screen display of the user&#39;s computer. A graphical display subprogram also includes a region map image display function which identifies the parts of the screen which are reserved for each region  232  of the cross-section of the conduit  10 . When displayed on the screen, each region  232  corresponds to a particular pair of sensor  231  electrodes  233  and will be displayed in a color that indicates a solution concentration of the particular pair of electrodes  233  currently under observation.  
         [0091]    An “initialization” subprogram performs an initialization routine for each of the other subprograms in the main program. A plurality of windows and icons are created through this subprogram.  
         [0092]    A “log” subprogram is provided to save data to a hard disk. The saved data may be transferred to a CD-ROM using a commercially available CD-ROM transfer program. The log subprogram further includes a sub-routine entitled “load observation.” In this load observation sub-routine, a plurality of actual observations of solution concentration are stored to a disk for later display on the screen display of the user&#39;s computer. The log subprogram is interactive and allows the user to add comments to a log file.  
         [0093]    A “mainframe” subprogram processes a plurality of messages for a main window and allows the user to select a plurality of appropriate context menus.  
         [0094]    A “palette” subprogram creates a color palette to be used for display.  
         [0095]    A “playback” subprogram allows the user to retrieve a stored client file and playback the recorded history of measured concentration and pressure values. This playback subprogram is capable of generating the display of a single frame for prolonged study or multiple frames in order to view an entire procedure or specified portion of a procedure. The playback subprogram can be implemented through the use of standard VCR components.  
         [0096]    A “run” subprogram includes a routine for establishing a run time for the main program and for continuously displaying an elapsed time. The elapsed time is displayed in a run window that can be reconfigured at the request of the user.  
         [0097]    A “screen” subprogram fills each triangular region  232  with specified colors corresponding to the concentration value of that region  232 . The display image is updated constantly as the fluid flows through the conduit  10  and offers a real-time display of the solution concentration in the conduit  10 .  
         [0098]    A “setup” subprogram includes a plurality of routines that process a plurality of messages for the main window, setting a plurality of windows within the view of the user, canceling the windows, and determining an appropriate context to display.  
         [0099]    A “triangle” subprogram defines a triangle class for an electrode configuration and a complete table structure to be displayed. The triangle subprogram includes a plurality of routines to construct and clear a hexagon table and a triangle table and to test for a new triangle. The triangle subprogram further includes a routine to generate a contour map implementing a plurality of colors of a palette.  
         [0100]    The user control and analysis system  500  functions as an analysis system for both concentration and pressure data. The user control and analysis system  500  is able to give an accurate representation of the chemical agent which is being infused in each region  232 .  
         [0101]    The user control and analysis system  500  allows the user to control, on a pulse-by-pulse basis, the distribution of fluid, the number of pulses, and all of the pressure parameters. A sample output of the user control and analysis system  500  is shown in FIGS. 7 a - 7   d . FIG. 7 a  illustrates a real electrode  233   a  table and a virtual electrode  233   b  table. FIGS. 7 b - 7   d  illustrate sample triangle tables.  
         [0102]    It will be apparent to those skilled in the art that various modifications and variations can be made in the system and method of the present invention without departing from the scope or spirit of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided as long as they come within the scope of the appended claims and their equivalents.