Abstract:
Methods and systems for controlling and monitoring pressurization data. The methods and systems advance beyond the prior art in their ability to convey pressurization data unambiguously. The methods and systems include a novel combination of visual cues and control features to insure that pressurization data may be analyzed accurately. For example, the visual cues and control features include changing the background color of the display area and providing a pressurization arrow to indicate pressurization or depressurization; a time showing the elapsed time of pressurization or depressurization; a pressurization number indicating the number of pressurization cycles that have occurred; software keys for making configuration choices; and text and graphic display modes. A touch interface may be provide for user interaction. To insure accurate pressure measurements, at least one pressure reference standard may also be utilized.

Description:
BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present invention relates to methods and systems for controlling and monitoring pressurization data. More specifically, the methods and systems may be used to control and monitor the pressurization of a control syringe during certain medical procedures. 
     2. The Prior State of the Art 
     One of the most common medical procedures that requires precise measurement of pressurization data is balloon coronary angioplasty, more technically known as percutaneous transluminal coronary angioplasty (“PTCA”). PTCA was developed about twenty years ago as an alternative to existing techniques for treating coronary artery disease. Bypass surgery and drug therapy had been the principal treatment options of the day. However, bypass surgery is extremely traumatic on the patient and drug therapy attempts only to compensate for the effects of coronary artery disease as opposed to treating the disease itself. PTCA, in contrast, is a comparatively minor procedure directed at eliminating (rather than merely compensating for) the dangers posed by coronary artery disease. Notwithstanding the comparatively minor nature of PTCA procedures, strict control and monitoring of pressurization data is essential to the patient&#39;s safety. 
     A leading cause of death for many years, coronary artery disease is a narrowing or blockage (“stenosis”) of the arteries that supply oxygen-rich blood to the heart. In coronary artery disease, the narrowing or blockage is caused by artherosclerosis, a buildup of waxy material (cholesterol and other fats) called plaque inside the artery walls. The waxy buildup reduces the amount of oxygenated blood that can flow to the heart through the coronary arteries. For many, this reduced blood supply results in a symptom of coronary artery disease called angina pectoris (“angina”). 
     Angina is characterized by chest pain or pressure that may radiate to the arm or jaw, and is caused by insufficient oxygen being delivered to the heart muscle. At rest, the reduced flow of oxygenated blood caused by coronary artery disease may remain undetected, particularly in the early stages of the disease. However, under exertion or stress, the heart demands increasing amounts of oxygen to continue functioning properly. When the narrowed or obstructed coronary arteries prevent the heart from receiving the extra supply of oxygen-rich blood that is required to sustain a given heart rate, the resulting oxygen deficiency causes angina. 
     As noted earlier, up until the early seventies there were two basic ways to treat coronary artery blockages: drug therapy or coronary artery bypass surgery. Drug therapy involved administering various medications to decrease the work of the heart by slowing the heart rate, dilating the blood vessels, or lowering blood pressure. However, drug-based treatment did not restore normal supply of blood to the heart, the medicine simply alleviated the discomfort that may be associated with coronary artery disease. The underlying problem of reduced blood flow remained and continued to present a risk that at some point the blockage would become serious enough to require surgical intervention. 
     In coronary artery bypass surgery, a blood vessel from the chest or leg is grafted beyond the point of blockage so that blood flow detours around the blockage in order to reach the heart muscle. In some severe cases, multiple bypasses must be performed. As is well known, coronary artery bypass surgery is an expensive, high-risk procedure and often requires prolonged hospitalization and recovery periods. 
     PTCA, in contrast, is a much less traumatic procedure than coronary artery bypass surgery. PTCA procedures typically last about two hours and are performed under local anesthesia. Often, a patient can be walking and active in a matter of hours. Because PTCA is much less expensive and less traumatic than bypass surgery and yet in many cases effectively removes blockage, PTCA has experienced a dramatic increase in the number of procedures performed each year. For example, according to some reports, by 1987 some 200,000 patients suffering from coronary artery disease had been treated using PTCA. Significantly, as of 1987, approximately six million cases of coronary artery disease were reported in the United States alone. Therefore, PTCA may be expected to continue playing an important role in the treatment of coronary artery disease. 
     In performing PTCA, an introducer sheath is inserted through an incision made in the groin or in the artery of an arm. Through a catheter that is introduced through the sheath, an x-ray sensitive dye is injected into the coronary artery. The dye enables the doctor, through the use of real time x-ray techniques, to clearly view the arteries on a television monitor and to thereby locate the artery blockage. With the help of images from the x-ray monitor, a balloon-tipped catheter is fed over a guide wire and advanced through the artery to the point of the blockage. 
     The balloon catheter is advanced to the middle of the blockage site. This catheter, which is also filled with a radio-opaque fluid, is coupled at its other end to a control syringe being manipulated by a cardiologist. Once the balloon catheter is in place, the cardiologist uses the control syringe to inflate the balloon for time periods ranging from about 20 to 60 seconds. At the end of each time period, the cardiologist operates the control syringe to deflate the balloon. Typically, the inflation/deflation cycle is repeated several times to compress the plaque on the arterial wall. After the results are checked, the balloon catheter and guide wire are removed. 
     Even though PTCA is a much less traumatic procedure than coronary artery bypass surgery, exacting control with respect to inflation pressure and duration of the inflation periods is essential to the safety of the patient. When the balloon catheter is inflated so as to begin compressing the plaque, blood flow to that area of the heart is temporarily shut off. Depriving the heart muscle of its blood supply, even temporarily, creates the potential for initiating cardiac arrest. Accordingly, the attending cardiologist and other personnel must carefully control both the pressure exerted on the artery walls and the duration of the temporary blockage. The inflation pressure and duration for each inflation are based on the cardiologist&#39;s assessment of the patient&#39;s overall health and ability to withstand a temporary stoppage of blood flow to the heart. 
     In the past, PTCA syringe systems have used standard pressure gauges to sense and read the pressure of an inflated balloon catheter, with human observation of stop clocks and the like controlling the duration of each inflation. While these prior art techniques have been widely used with success, they introduce a serious risk of human error. The gauges used on such syringe systems are often awkward and difficult to read accurately, and are subject to malfunction. Thus, improper recording of inflation pressure and/or duration may occur. 
     To enhance the monitoring, display, and recording of pressurization data, U.S. Pat. No. 5,300,027 issued to Foote, et al. on Apr. 5, 1994 and entitled “SYSTEM AND METHOD FOR MONITORING AND DISPLAYING BALLOON CATHETER INFLATION AND DEFLATION DATA” (hereinafter “Foote”), which is incorporated herein by reference, introduces an electronic control system. The control system includes a monochromatic LED display showing the pressurization data (number, time, and pressure) for the current pressurization cycle. 
     At the time, Foote represented a vast improvement over the prior art. Nevertheless, continuously improving medical care requires constant innovation. In the case of monitoring and controlling pressurization data, there is an ongoing need to enhance the information that may be conveyed to a cardiologist and/or clinician. The systems and methods of the present invention offer novel solutions to providing medical professions with immediate access to information, helping insure the best possible healthcare for their patients. 
     SUMMARY OF THE INVENTION 
     The present invention is directed toward methods and systems for electronically tracking pressurization data. For example, the present invention includes an electronic controller for receiving, displaying, and storing pressurization data. The present invention combines novel control features and display elements for conveying pressurization data in ways that were previously unknown. A preferred embodiment of the present invention is designed for use in displaying, monitoring, and storing pressurization data during a balloon coronary angioplasty procedure for treating coronary artery disease. Throughout these balloon catheter procedures, it is imperative for the medical professional performing the surgery to have immediate access to clear and accurate pressurization data. 
     In this environment, the electronic controller receives pressurization data from a control syringe equipped with a transducer for converting pressure information to electrical signals that can be interpreted by the controller. Optionally, the electronic controller may be attached to a printer and may also act as host for a remote electronic controller. When connected to a remote electronic controller, the host functions and displays are duplicated in both controllers. However, a control syringe may be connected only to the host. 
     As described above, balloon catheter procedures for treating coronary artery disease involve the insertion of an inflatable balloon catheter into a narrowed or blocked area of the arteries supplying oxygenated blood to the heart muscle. Using a control syringe, a clinician treating coronary artery disease inflates the balloon to compress plaque that has been deposited within the artery walls and is restricting the flow of blood. Because the inflated balloon temporarily stops blood from flowing through the artery, it is vital for the physician to know how much pressure the balloon is exerting on the artery wall and how long the balloon has been inflated. 
     The principal danger of the procedure is that interrupting the flow of blood to the heart will cause the patient to experience a cardiac arrest. Therefore, the precise pressure and duration of each inflation must be based on an assessment of the patient&#39;s health and the patient&#39;s ability to withstand temporarily halting the flow of blood to an area of the heart. Because the consequences of over inflating or stopping blood flow for too long are grave, the capability to clearly and accurately track pressurization data is critical to appropriate patient care. 
     The present invention is an advancement over the prior art in its ability to convey pressurization data unambiguously. Specifically, the present invention provides a unique combination of visual cues and control features to insure accurate analysis of pressurization data. For example, the background color of the display area changes when pressurization data transitions from one pressurization state to another (e.g., from a state of depressurization to a state of pressurization). Each transition between pressurization states also starts a timer showing the elapsed time since the transition occurred. To insure a clear understanding of pressurization data, units of measure are included with the display of pressurization values. 
     Together with changes in background color, a pressurization arrow in the display area visually communicates whether pressurization values indicate a state of pressurization or a state of depressurization. Within the pressurization arrow, the electronic controller displays a count of the pressurization cycles (i.e., the number of times pressurization values have transitioned between a predefined sequence of pressurization states). The bottom of the display area includes software buttons that allow for altering the operation of the electronic controller, such as how the display is organized. Specifically, one of the software buttons toggles between a text display mode and a graphical display mode. 
     The display also includes a touch interface for all interaction with the electronic controller. Pressing the display area showing the units of measure toggles between the various options for pressure units. Likewise, the software buttons along the bottom of the display are also activated through the touch interface. 
     To insure accurate pressure measurements, the present invention may include at least one reference standard. The reference standard may be read at various times during operation of the electronic controller to verify that the controller measures the same pressure at a consistent value. Minor variations in reference standard measurements are accounted for by defining an appropriate tolerance value or range. 
     Notwithstanding that the foregoing summary and later detailed description refer to balloon catheter treatment of coronary artery disease, the present invention is in no way limited to use in those procedures or even limited to medical applications in general. The present invention integrates various display cues, setup parameters, and control features to provide novel methods and systems for tracking pressurization data. These methods and systems may improve healthcare or offer the benefits of clarity, accuracy, and convenience to any other field or application. 
     These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by practicing the invention as set forth below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more extensive description of the present invention, including the above-recited features, advantages, and objects, will be rendered with reference to the specific embodiments that are illustrated in the appended drawings. Because these drawings depict only exemplary embodiments, the drawings should not be construed as imposing any limitation on the present invention&#39;s scope. As such, the present invention will be described and explained with additional specificity and detail through use of the accompanying drawings in which: 
     FIGS. 1A and 1B show a preferred embodiment of an electronic controller according to the present invention; 
     FIGS. 2A,  2 B,  2 C, and  2 D depict various display options for pressurization data and software menu keys; 
     FIG. 3A shows the setup options available from the electronic controller&#39;s main menu; 
     FIG. 3B illustrates the entry of setup parameters; 
     FIG. 4 depicts a block diagram of a system for acquiring, displaying, storing, and monitoring pressurization data according to the present invention; and 
     FIG. 5 shows a flow chart of the electronic controller&#39;s operating states. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention is described below with reference to drawings. These drawings illustrate certain details of specific embodiments that implement the systems and methods of the present invention. However, describing the invention with drawings should not be construed as imposing, on the invention, any limitations that may be present in the drawings. The present invention relates to both methods and systems for electronically tracking pressurization data. As used in this application, “pressurization data” is a broad term intended to encompass virtually any data that may be relevant in pressure related display, control, setup, or monitoring. In contrast, the term pressurization value generally indicates a measured quantity of pressure. 
     The terms “pressurization state” and “pressurization cycle,” as used in this application, are also broad terms. Pressurization state refers to a category of pressurization data that may be of interest. In a preferred embodiment that is described below, there are two possible pressurization states, depressurization and pressurization. However, nothing in this application should be construed as limiting the present invention to distinguishing between only two pressurization states. For example, practicing the present invention may entail distinguishing between high, medium, and low states of pressurization values. Alternatively, pressurization states could be defined in terms of time intervals. Pressurization states generally are defined in terms of the conditions that are necessary for moving from one state to another, such as reaching a threshold or boundary pressurization value. 
     Pressurization cycle refers to moving between an arbitrary sequence of pressurization states. A preferred embodiment, described in more detail below, defines a pressurization cycle as a state of depressurization, followed by a state of pressurization, followed by returning to a state of depressurization. However, nothing in this application should be construed as limiting the present invention to any particular sequence of pressurization states. 
     A preferred embodiment of the present invention is useful for receiving, displaying, monitoring, and storing pressurization data during balloon coronary angioplasty, more technically known as PTCA. PTCA is a surgical procedure used in treating the narrowing of arteries that occurs in coronary artery disease. During the procedure, a balloon catheter is inserted into an artery of the groin or arm and then advanced through the artery using a guide catheter. An x-ray sensitive dye in the artery and catheters, used in conjunction with real-time x-ray techniques, aids in navigating the catheters through the body&#39;s arteries. 
     The balloon catheter is advanced to the site of narrowing or blockage. Once the site is reached, the balloon catheter is inflated to a pressure of approximately 7 to 10 atmospheres for a duration of about 20 to 60 seconds and then deflated. The inflation/deflation cycle is repeated several times, with pressure increasing slightly each inflation, to compress the buildup of plaque along the artery wall and thereby increase the amount of blood flow to the heart muscle. After the artery is cleared, the balloon catheter may be removed or directed to another site of narrowing or blockage. 
     Although the present invention is described in terms of a preferred embodiment for use in PTCA procedures as a treatment for coronary artery disease, the systems and methods of the invention are not limited to use in PTCA. It is anticipated that the present invention will be useful in a wide variety of applications where tracking pressurization data is of value. Some of these applications may include other medical uses whereas others may involve completely unrelated fields. 
     The present invention integrates various display cues, setup parameters, and control features to provide novel methods and systems for tracking pressurization data. FIGS. 1A and 1B show a preferred embodiment of an electronic controller for use in PTCA procedures, designated generally as  100 . FIGS. 1A and 1B show the front and back of the controller, respectively. As shown in FIG. 1A, the controller includes Display  200 , Outer Case  110 , and Syringe Input Connector  130 . Display  200  is a color LCD graphics display with a touch screen interface. The operational details of Display  200  are described with reference to FIGS. 2A-2D. Further information about Syringe Input Connector  130  is provided with reference to FIGS. 4 and 5. FIG. 1B shows Power Area  150  (with Power Connector  152 , Fuse Holder  154 , and Power Switch  156 ), Grounding Lug  158 , Cooling Fans  160 , Decal Area  170  (for serial and model numbers, manufacturer information, instructions, etc.), and Fiber Optic Connector  140 . Fiber Optic Connector  140  is described in more detail with reference to FIG.  4 . 
     Turning now to FIGS. 2A,  2 B,  2 C, and  2 D, the various display options for pressurization data and software menu keys (“soft keys”) are shown. FIG. 2A shows Display  200  after a control syringe is connected to the electronic controller through Syringe Input Connector  130  (FIG.  1 A). Pressure Unit Label  210  shows the units of measure as atmospheres, abbreviated “ATM.” Pressure Reading  260  displays the pressurization value received from the control syringe. It is worth noting that although Pressure Reading  260  may be negative, zero, or positive, all pressurization values fall within two pressurization states, either depressurization or pressurization. (The details of how these two pressurization states are defined is presented below while describing Low Trigger  355  in connection with FIG. 3A.) To account for variations in pressurization values that are of minor clinical significance, Pressure Reading  260  displays zero for a range or band of pressurization values around zero. For example, in the embodiment currently being described, the band or range of values is zero ±2 psi. The present invention does not impose any particular limit on the size of the zero band. Some uses of the present invention may require a relatively narrow zero band while others may benefit from a relatively large zero band. 
     By pointing down, Pressurization Arrow  220  indicates depressurization as the current pressurization state. The Pressurization Number  230  within Pressurization Arrow  220  shows the number of pressurization cycles that have occurred. (For the embodiment currently being described, a pressurization cycle begins with a state of depressurization, followed by a state of pressurization, and ends with another state of depressurization. As previously indicated, the transitions between depressurization and pressurization will be  11 described below along with Low Trigger  355  of FIG. 3A.) Duration  250  displays the elapsed time for the current state of depressurization,  22  seconds. Soft Keys  240  appear along the bottom of Display  200 . 
     FIG. 2B also shows Soft Keys  240 , including Menu Key  242 , Graph Key  244 , and Mark Key  246 . Menu Key  242  is available under two circumstances. First, as shown in FIGS. 2A and 2B, Menu Key  242  may be selected when a control syringe is connected, but pressurization data indicates a state of no pressurization. Menu Key  242  is also displayed when no syringe is connected to Electronic Controller  100 . However, as shown in FIG. 3A, Menu Key  242  provides different options based on whether or not a control syringe has been connected. 
     Turning briefly then to FIG. 3A, the options of Main Menu  300  are shown. If a control syringe is connected, but is not pressurized ( 304 ), History  310  and Set Units  320  are the only selections that are displayed. These selections also are available when no syringe is connected ( 302 ). History  310  is a record of pressurization data that has been stored for a particular syringe connection. The historical pressurization data does not include all pressurization data received by Electronic Controller  100 . Rather, discrete events such as the peak pressure, starting time, and duration of an inflation are stored. By dividing pressurization data into discrete events, the stored information provides clinically significant data, with minimal redundancy (e.g., storing one entry describing a 30 second pressurization rather than 30 entries storing the pressurization value each second of the pressurization). Mark Key  246  (FIGS. 2B,  2 C, and  2 D) allows the user to identify the current readings as an event to be stored. By selecting History  310 , the user may scroll through a list of the syringe histories that are stored. Once identified, the syringe history of interest may be selected in order to review the stored pressurization data for the desired syringe history. 
     Set Units  320  sets the default units of measure for pressurization values. Choices include atmospheres, bars, psi, mmHg, and kPa. As will be described later, a user may change the displayed units of measure, at any time. The default simply determines what units will be used in the absence of an alternate user selection. 
     If no syringe is connected ( 302 ), the Main Menu  300  includes two additional options, Clear  330  and Setup  350 . Clear  330  erases the historical pressurization data stored in Electronic Controller  100 . To avoid accidental clearings, the controller requires confirmation that all historical data should be deleted from memory when Clear  330  is selected. Setup  350  leads to a submenu of options that includes, Language  351 , Time  352 , Date  353 , High Trigger  354 , Low Trigger  355 , Printer  356 , and Remote  357 . 
     FIG. 3B shows the submenu displayed when Setup  350  is selected. A column of Entry Soft Keys  360  displays along the right side of the display. Depending on the type of setup information being entered, different Entry Soft Keys  360  may be displayed. The Entry Soft Keys  360  for the Setup  350  menu include Up Arrow  362 , OK  364 , and Down Arrow  366 . At the Setup 350 menu, it is only necessary to indicate which of the setup parameters is being changed. Language  351  is highlighted. As the screen text indicates, pressing OK  364  will lead to the language selection menu. Pressing Up Arrow  362  or Down Arrow  366  navigates the highlighting to other setup parameters. When the desired setup parameter is highlighted, selecting OK  364  allows the highlighted setup parameter to be modified. For example, Language  351  offers English, German (Deutsch), French (Francais), and Spanish (Espafiol) as options. Once a particular language is selected, all text (prompts, menus, date formats, etc.) is displayed in the newly chosen language. 
     Time  352  and Date  353  set the current system date and time for Electronic Controller  100 . Although not shown, Time  352  and Date  353  provide examples of Entry Soft Keys  360  that are specific to the type of setup information being entered. Both Time  352  and Date  353  include up and down arrows for altering a numerical representation of the date or time, right and left arrows for moving between digits, and an OK key for saving the changes. A flashing numeral indicates the current digit being modified. Generally, all numerical setup data is modified in this manner. Soft Keys  340  of the date/time entry include Exit  348  (similar to the Exit  348  as is shown on the Setup  350  submenu display) for canceling any changes made to the system date or time. 
     High Trigger  354  allows for setting a maximum pressurization value that should be received from the control syringe. When the pressurization value received from the control syringe meets or exceeds High Trigger  354  the display provides a visual alert. The present invention does not limit the visual alert to any particular form, but in Electronic Controller  100  the visual alert includes flashing the display of Pressure Reading  260  (FIGS.  2 A- 2 D). Once pressurization values drop below High Trigger  354 , the controller returns to normal continuous display. 
     Before describing Low Trigger  355 , it may be helpful to explain the boundaries or transitions that divide a state of depressurization from a state of pressurization in the embodiment currently being described. Two threshold pressurization values are used in defining the transition between pressurization states. One value, Low Trigger  355 , specifies the threshold pressurization value that divides depressurization from pressurization, starting from a current pressurization state of depressurization. In other words, if the current pressurization state is depressurization, pressurization values must reach Low Trigger  355  before the pressurization state will transition to a state of pressurization. The second value specifies the threshold pressurization value that divides pressurization from depressurization, starting from a current pressurization state of pressurization. Analogous to Low Trigger  355 , this second threshold value must be crossed before the pressurization state will transition to a state of depressurization. The second threshold value is set to zero and may not be configured in this embodiment. However, nothing in this description should be interpreted to preclude the second threshold value from also being configurable or from adding additional threshold values. 
     Note also that the transition from depressurization to pressurization occurs when Low Trigger  355  is reached, whereas the transition from pressurization to depressurization occurs when the second threshold value is crossed (i.e., pressurization values are negative). Remember, however, that the zero band may result in a negative pressure being displayed as zero. Therefore, to a user it may appear that the transition from pressurization to depressurization occurred at zero pressure. 
     Selecting Printer  356  leads to the printer setup screen. Assuming a printer is attached to the controller, printer setup allows for selection between three printout modes (graph, text, and none) and a test option. “Graph mode” provides a detailed graphics printout, “text mode” produces a summarized tabular printout, and “none” disables printing. Selecting “test” sends a diagnostic printout to the printer and then returns to the printout mode that was previously selected (i.e., graph, text or none). Electronic Controller  100  also displays printer status messages such as “Printing,” “Paper Out,” “Busy,” “Unavailable,” or “Ready” to aid in troubleshooting printer operation. 
     Remote  357  allows for enabling or disabling remote operation of a controller. The operation of a remote electronic controller will be described in conjunction with FIGS. 4 and 5. At this time, it is sufficient to recognize that a controller may operate in either host or remote mode and that Remote  357  enables or disables this feature. 
     Returning again to FIG. 2B, the operation of Display  200  will be described in more detail. As indicated above, Display  200  includes a touch interface. One of the touch entries supported is the ability to change the units of measure for Pressure Reading  260 . Electronic Controller  100  is capable of displaying Pressure Reading  260  in atmospheres, bars, psi, mmHg, and kPa. With each touch of Pressure Unit Label  210 , the controller cycles through the units of measure options one at a time. A change to Pressure Unit Label  210  includes converting the value displayed by Pressure Reading  260  to the newly selected units of measure. 
     In FIG. 2B, Pressurization Number  230  has been increased to a value of “1.” This means that the first pressurization cycle is in process. Prior Pressurization  270  shows the Prior Peak Pressure  272  and Prior Duration  274 . The maximum pressure reached during the prior pressurization cycle of 3 seconds was 12.8 atmospheres. When Prior Pressurization  270  is displayed, changing Pressure Unit Label  210  converts both the value displayed by Pressure Reading  260  and the value displayed by Prior Peak Pressure  272  to the newly selected units of measure. Note that Pressure Reading  260  and Pressurization Arrow  220  indicates that Electronic Controller  100  is receiving pressurization data indicating a state of depressurization. According to Duration  250 , the current state of depressurization has a total elapsed time of 27 seconds. 
     Duration  250  is limited to 99 minutes and 59 seconds for display purposes. After that limit is exceeded, Display  200  will provide a visual alert to indicate that the elapsed time is no longer accurate. The present invention does not necessary impose any particular limit on Duration  250  or on the type of visual alert provided if an established time limit is exceeded. Nevertheless, in the PTCA embodiment of Electronic Controller  100 , Duration  250  is limited to 99 minutes and 59 seconds and Duration  250  will flash when that limit is exceeded. 
     Moving next to FIG. 2C, as Electronic Controller  100  receives pressurization data indicating a state of pressurization, the background color of Display  200  changes from a bluish-red to green. The bluish-red color indicates a state of depressurization and green indicates a state of pressurization. In FIG. 2C, Pressure Reading  260  indicates a pressurization value of 16.1 atmospheres. Because the received pressurization data indicates a state of pressurization, Pressurization Arrow  220  points up. As indicated by Pressurization Number  230 , pressurization values have exceeded Low Trigger  355  on two occasions, once during Prior Pressurization  270  and once for the current Pressure Reading  260  of 16.1 atmospheres. 
     Making the transition between a state of depressurization, as shown in FIGS. 2A and 2B, to a state of pressurization, as shown in FIGS. 2C and 2D, also restarts the elapsed time display. Duration  250  indicates that Electronic Controller  100  has been receiving pressurization values in excess of the Low Trigger  355  (FIGS. 3A and 3B) for 12 seconds. In PTCA procedures, this means that a control syringe has been applying pressure to a balloon catheter for that elapsed time. 
     Selecting Graph  244  from Soft Keys  240  changes the display of Electronic Controller  100  to the graph mode illustrated in FIG.  2 D. Essentially the same information is presented in graph mode as in text mode. Display  200  shows a current Pressurization Reading  260  of 16.1 atmospheres during the current state of pressurization&#39;s elapsed time of  12  seconds (Duration  250 ). Pressurization Arrow  220  is pointing up due to the pressurization indicated by Pressure Reading  260 . Prior Pressurization  270  shows a Prior Peak Pressure  272  of 12.8 atmospheres and a Prior Duration  274  of 3 seconds. Pressurization Number  230  remains unchanged from FIG.  2 C. 
     The primary difference between FIGS. 2C and 2D is the presence of Pen  280  and Scales  290 , including Pressure Scale  292  and Time Scale  294 . Pressure Scale  292  and Time Scale  294  form a grid for graphing pressurization data. Initially, Pressure Scale  292  shows the full range of possible pressurization values. (When Pressure Unit Label  210  indicates mmHg as the units of measure, Electronic Controller  100  limits pressurization values to 9999 mmHg for display purposes. Electronic Controller  100  is capable of operating with pressurization values up to approximately 25 atmospheres. However, the present invention does not necessarily impose any requirement for establishing a maximum pressurization value, for display purposes or otherwise.) Pen  280  draws the current pressurization value at the right side of the display in a continuous manner. Placing the current pressurization at the right, with prior pressurization values moving to the left, mimics the operation of most medical instrumentation, making Electronic Controller  100  more intuitive to use. 
     Just as described with reference to FIGS. 2B and 2C, Display  200  includes a touch interface. However, several differences between text mode and graph mode operation will become readily apparent. First, changes to the units of measure will require adjusting Pressure Scale  292  in addition to converting Pressure Reading  260  and Prior Peak Pressure  272 . Furthermore, an additional feature available in graph mode is the ability to zoom. Zooming reduces the size of Pressure Scale  292  to show finer detail in pressurization value changes. The zoom function is activated and deactivated by touching Pressurization Arrow  220 . 
     In zoom mode, Pressure Scale  292  is divided by four divisions. The size of the divisions depends on the units of measure indicated by Pressure Unit Label  210 . When Pressure Unit Label  210  is atmospheres or bars, the divisions are 1 unit apart; for psi and kPa, the divisions are 10 units apart; and, the divisions are 100 units apart for mmHg. Depending on the units of measure, Pressure Scale  292  uses integer values (atm, bar), integer values divisible by 10 (psi, kPa) or integer values division by 100 (mmHg). These four divisions produce three regions of pressurization values. For example, if Pressure Scale  292  ranges from 3-6 atmospheres (with divisions at 3, 4, 5, and 6 atmospheres), the corresponding three ranges would include 3-4 atmospheres, 4-5 atmospheres, and 5-6 atmospheres. 
     The initial range of Pressure Scale  292  is calculated to show the current pressurization value in roughly the middle of the scale. With the three-region arrangement described above, the approach for roughly centering the current pressurization value is relatively straightforward. The process simply entails providing one full region below and one full region above the current pressurization value. For example, the three regions described above would result from a current pressurization value of 4.3 atmospheres. Division sizes of 10 or 100 are processed in an analogous manner. In other words, Pressure Scale  292  would range from 30-60 psi or 300-600 mmHg for current pressurization values of 43 psi or 430 mmHg, respectively. 
     Once activated, the zoom feature uses auto-ranging to update Pressure Scale  292 . Auto-ranging is a feature that dynamically adjusts the pressurization values included within Pressure Scale  292 . To keep the currently displayed pressurization value roughly in the middle of Pressure Scale  292 , auto-ranging recalculates Pressure Scale  292  when pressurization values near the scale&#39;s endpoints. Auto-ranging defines borders at the edges of Pressure Scale  292  that are 60% of a division wide. Whenever pressurization values fall within the 60% border, auto-ranging recalculates Pressure Scale  292 . For example, if Pressure Scale  292  included pressurization values from 3 to 6 atmospheres with divisions every 1 atmosphere, auto-ranging would recalculate Pressure Scale  292  when pressurization values reach either 3.6 atmospheres or 5.4 atmospheres. Auto-ranging adjusts Pressure Scale  292  by 1 division. Thus, in the example provided above, if pressurization values reached 3.6 atmospheres, Pressure Scale  292  would be adjusted to range from 2 to 5 atmospheres. Naturally, the range of pressurization values covered by Pressure Scale  292  is also recalculated when the units of measure are changed. 
     The foregoing description of zoom mode and auto-ranging is intended as exemplary only and not as necessarily imposing any particular limitation on the scope of the present invention. A wide variety of similar criteria could be used to produce equivalent results. For example, the size of the divisions may be dynamically calculated based on how quickly pressurization values are changing, the current pressurization value could be placed exactly in the center of Pressure Scale  292 , Pressure Scale  292  could range from any arbitrary pressurization value to another, or the size of the borders used in auto-ranging could be adjusted. Alternatively, zoom mode could be implemented as showing any one of several predefined regions of pressurization values. 
     Graph mode also includes the ability to set a target or goal pressurization value. Selecting Goal Key  243  places a reference pressurization goal line across Display  200 . Touch selectable up and down arrows along the right side (like Entry Soft Keys  360  of FIG. 3B) allow the goal line to be moved to a desired pressurization value. Once in place, selecting an OK key places the pressurization goal line on the display. (In FIG. 2D, the pressurization goal line would appear as a horizontal blue line at the chosen pressurization value.) Pressing Goal Key  243  twice removes (disables) the pressurization goal line. 
     Another feature of graph mode is a visual indication for marked events. When Mark Key  246  is selected in graph mode, a yellow dashed vertical line is displayed to indicate the pressurization data at that time has been marked as an event. As described above, marked events are noted in the syringe history for later review. Pressing Text Key  241  returns Display  200  to text mode. 
     FIG. 4 presents a block diagram of a system for acquiring, displaying, storing, and monitoring pressurization data according to the present invention. Included within the system are Electronic Controller  100 , Peripheral Devices  470 , and Communication Links  460 . Peripheral Devices  470  include Control Syringe  480 . Control Syringe  480  has two basic components, Syringe  482  and Transducer  484 . 
     One example of Syringe  482  and Transducer  484  is described in U.S. Pat. No. 5,300,027, previously incorporated herein by reference. Syringe  482  is capable of generating either a positive or negative pressure. During PTCA procedures, the generated pressure is used to inflate and deflate a balloon catheter. Transducer  484  converts the generated pressure into electrical signals for processing. The electrical signals produced by Transducer  484  are transferred to Electronic Controller  100  through Communication Link  464  and Data Acquisition Interface  410 . (Data Acquisition Interface  410  includes Syringe Input Connector  130  as shown in FIG. 1A.) 
     The present invention does not impose any particular limitations on Communication Link  464  and Data Acquisition Interface  410 . In the PTCA embodiment described herein, Communication Link  464  is a cable that carries electrical signals and Data Acquisition Interface  410  is a keyed electrical connection with some filtering hardware to condition the received signal. Alternative implementations may include a wireless, optical, sonic, or some other link capable of transferring pressurization data from Syringe  482  to Electronic Controller  100 . 
     After the pressurization data is received through Data Acquisition Interface  410 , A/D Converter  430  converts the analog signals generated by Transducer  484  to digital quantities suitable for processing by Processing Hardware  450 . Processing Hardware  450  includes CPU  454 , Timer  452 , ROM  456 , and RAM  458 . Here again, the present invention does not impose any particular requirements on Processing Hardware  450  other than those described in the appended claims. Processing Hardware  450  (executing relevant program code instructions) is one example of a processor means for performing the various steps required by the present invention. A processor means as used in the present invention may include generic digital processors as well as specialized signal and/or display processors. In a preferred embodiment, CPU  454  is a generic digital processing unit. 
     Processing Hardware  450  integrates Timer  452  to facilitate the various time measurements that occur in practicing the present invention, such as tracking the elapsed time of pressurization/depressurization and other internal events that are regularly monitored. ROM  456  is primarily used to store program instructions that govern the operation of Electronic Controller  100 . (The operation of Electronic Controller  100  is described in more detail below, with respect to FIG. 5.) RAM  458  includes volatile and non-volatile portions. The volatile portion of RAM  458  is used as a memory space for CPU  454 . The non-volatile portion of RAM  458  stores the syringe histories described in conjunction with FIG.  3 A and setup/configuration settings, such as the default units of measure, etc. When power to Electronic Controller  100  is shut off, a backup battery retains the information stored in the non-volatile portion of RAM  458 . 
     Electronic Controller  100  also includes Electronic Reference Standards  420 . Electronic Reference Standards  420  are an electronic representation of two pressurization values, a high value and a low value. Reading the Electronic Reference Standards  420  allows Electronic Controller  100  to verify that it is operating correctly over the device&#39;s useful lifetime. The details of how Electronic Controller  100  interacts with Electronic Reference Standards  420  are described below, with reference to FIG.  5 . 
     Display  200  of Electronic Controller  100  is a color LCD graphics display. As described above, Display  200  includes a touch interface so that interaction with Electronic Controller  100  may be accomplished without the need for an external input device, such as a mouse or a keyboard. However, the present invention does not necessarily require that input only occur through the touch interface of Display  200 . 
     I/O Interface  440  and Communication Link  462  allow Electronic Controller  100  to communicate with Peripheral Devices  470 , including Printer  472  and Remote Electronic Controller  474 . Communication Link  462  and I/O Interface  440  are implemented as an optical fiber communication channel. (I/O Interface  440  includes Fiber Optic Connector  140  as shown in FIG. 1B.) However, like Communication Link  464  and Data Acquisition Interface  410 , the present invention does not necessarily impose any particular limitation on the technology used to implement I/O Interface  440  and Communication Link  462 . Alternative implementations may include a wireless, electrical, sonic, or some other link capable of transferring data from Electronic Controller  100  to Peripheral Devices  470 . 
     As described above with reference to the Printer  356  setup option of Main Menu  300  (FIG.  3 A), Printer  472  may operate in several modes. Graph mode provides a detailed graphics printout and text mode produces a summarized tabular printout. Selecting test sends a diagnostic printout to Printer  472 . As part of the interaction that occurs through Communication Link  462 , Electronic Controller  100  displays various printer status messages, including “Printing,” “Paper Out,” “Busy,” “Unavailable,” or “Ready.” As shown in FIG. 4, multiple Peripheral Devices  470  may be daisy-chained together using Communication Link  462 . That is, both Printer  472  and Remote Electronic Controller  474  may be connected to Electronic Controller  100  at the same time through Communication Link  462 . 
     Remote Electronic Controller  474  allows all of the functions of Electronic Controller  100  (termed a primary or host controller) to be controlled through a remote device. For example, the units of measure and display modes, text or graph, of both devices may be controlled through either device. While the functionality of the host, Electronic Controller  100 , is duplicated at Remote Electronic Controller  474 , historical data is stored only at the host device. Furthermore, Remote Electronic Controller  474  ignores any control syringe that is connected while operating as a remote device. The Remote Electronic Controller  474  is substantially identical to Electronic Controller  100 . To be considered substantially identical, Remote Electronic Controller  474  and Electronic Controller  100  must share a compatible I/ 0  Interface  440  so that the devices may communicate with each other and support similar or complementary display and/or control features. Although a preferred embodiment for use in PTCA procedures includes a Remote Electronic Controller  474  and “host” Electronic Controller  100  that support identical display and control features, the present invention does not require the devices to be identical in that way. 
     FIG. 5 shows a flow chart for use in describing the operation of Electronic Controller  100 . Electronic Controller  100  is capable of functioning in either remote or host mode. Features on the “Host Only” side of Dashed Line  522  relate to Electronic Controller  100  operating in host or primary mode, features on the “Remote Only” side of Dashed Line  562  relate to Electronic Controller  100  operating in remote mode, and features between Dashed Lines  522  and  562  are for changing the configuration of Electronic Controller  100  between remote and host modes. 
     When Electronic Controller  100  is Powered On  504 , the device initializes itself by performing a Boot Operation  508 . Following the Boot Operation  508 , Electronic Controller makes a Reference Check  512  of Electronic Reference Standards  420  (FIG.  4 ). The first time Electronic Controller  100  is Powered On  504 , the values represented by Electronic Reference Standards  420  are stored in a non-volatile area of RAM  458  (FIG.  4 ). When Electronic Controller  100  is Powered On  504  subsequent to the first time, the Reference Check  512  compares the previously stored values of Electronic Reference Standards  420  with newly read values of Electronic Reference Standards  420 . If the stored values and newly read values vary by more than an allowable tolerance, Electronic Controller  100  displays an error message and will not operate. 
     Reference Check  512  has two components, reading the high pressure reference and the low pressure reference of Electronic Reference Standards  420 . The tolerance for these readings is defined by establishing a range or window of values that are acceptable for each reference standard. For example, the high pressure reference standard has a maximum acceptable high value and a minimum acceptable high value. Any reading of the high pressure reference standard must fall within the high window to pass the tolerance requirement. Likewise, the low pressure reference standard has a minimum acceptable low value and a maximum acceptable low value. Any reading of the low pressure reference standard must fall within the low window to pass the tolerance requirement. 
     If operating in host mode, Electronic Controller  100  then displays a message indicating that no syringe has been connected ( 520 ). Once a syringe is connected ( 524 ), Electronic Controller  100  acknowledges that a syringe has been detected ( 528 ). Electronic Controller  100  then performs several checks to insure that both Control Syringe  480  (FIG. 4) and Electronic Controller  100  are operating correctly. A Zero Check  532  of Control Syringe  480  is performed to insure that the control syringe is not pressurized when connected. The zero check allows for minor variations, but requires essentially no pressurization (i.e., pressurization values equivalent to ambient air pressure) of the control syringe when the control syringe is connected. After the Zero Check  532 , a Reference Check  536 , like Reference Check  512 , is performed. Stabilizing  540  requires that the pressurization data received from the control syringe remain essentially constant during the stabilization period. If any of the checks fail, Electronic Controller  100  displays an appropriate error message. 
     The checks require only a few seconds to complete. When the checks succeed, Electronic Controller  100  displays a message indicating that the control syringe has been accepted ( 544 ). Once accepted, Electronic Controller  100  zeros the control syringe ( 548 ). In other words, Electronic Controller  100  interprets the pressurization data it receives from the control syringe as indicating zero or no pressurization. After zeroing, Electronic Controller  100  is ready to Display Pressurization Data  552 . 
     When operating in remote mode, Electronic Controller  100  displays a message indicating that no host is detected ( 560 ) after performing Reference Check  512 . Once a host connection ( 564 ) is made, Electronic Controller  100  acknowledges detecting the host ( 568 ). After detecting a host, Electronic Controller  100  displays that no syringe is connected ( 572 ), indicating that the host (not the remote) does not have a control syringe connected. From this point on, the Electronic Controller  100  operating as a remote device mirrors the display of the host device ( 578 ). 
     Regardless of operating mode, Electronic Controller  100  may be configured to operate in host mode or remote mode prior to the connection of a control syringe or the connection of a host. At the no syringe message ( 520 ) or host not detected message ( 560 ), a host/remote mode configuration key may be selected ( 582 ). In a preferred embodiment for performing PTCA procedures, the host/remote mode configuration key is a question mark displayed on Display  200 . Once the host/remote mode configuration key is selected ( 582 ), Electronic Controller  100  displays a host/remote mode indicator ( 586 ). Again, in a preferred embodiment for performing PTCA procedures, the host mode indicator is an “H” and the remote mode indicator is an “R,” each displayed in the upper right-hand comer of Display  200 . The touch screen interface allows for pressing either the “H” or “R” to select the operating mode ( 590 ). By pressing the “H” or “R,” Electronic Controller  100  toggles operation from host to remote (pressing “H”) or from remote to host (pressing “R”), based on the mode of operation at the time either “H” or “R” is pressed. If remote mode is selected, Electronic Controller  100  returns ( 594 ) to the host not detected message ( 560 ). If host mode is selected, Electronic Controller  100  returns ( 594 ) to the no syringe message ( 520 ). 
     The present invention may be embodied in other forms without departing from its spirit or essential characteristics. As properly understood, the preceding description of specific embodiments is illustrative only and in no way restrictive. The scope of the invention is, therefore, indicated solely by the appended claims as follows.