Method Of Apparatus For Generating An R-interval Histogram

Abstract

A method and apparatus for automatically and directly generating a graphical data display, particularly an R-interval histogram, over a monitoring time period in which data is continuously received. The apparatus is portable and may be worn by a patient for relatively long time periods without impairing freedom of motion. As R-intervals are sensed, they are separated into ranges, or time-bins, and the signals in the time-bins are applied to arrayed electrochemical signal accumulating and displaying devices to directly generate a readable R-interval histogram. The electrochemical displays incorporate an overflow prevention scheme to prevent distortion of the histogram due to signal overflow.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the automatic and continuous production of a graphical display of data in real time and, more particularly, to a relatively small, portable apparatus which directly generates a readable R-interval histogram during a monitoring time period.

2. Description of the Prior Art

In the field of cardiology, it has been generally recognized that arrythemia, or irregular heartbeats, may be an important warning sign of serious heart problems. A tool for evaluating such arrythemias is a bar chart, or histogram, of the relative frequency of occurrence of heartbeats falling within several different ranges of heatbeat rate taken over a monitoring time period. Typically, since heartbeat rate can be reliably determined by measuring the time interval between the "R" portions of an electrocardiogram waveform, the bar chart is generally known as an R-interval histogram.

Unfortunately, useful R-interval histograms can only be made after the patient has been monitored for a considerable period of time, normally measured in terms of hours, and the enormous task of measuring and categorizing the time interval between each pair of heartbeats of a patient for such long periods of time has led to various methods of automatic analysis.

For example, systems have been used in which a tape recorder records the electrocardiogram waveform for the requisite number of hours and the tape is played back at high speed into analysis equipment which subsequently generates an R-interval histogram from the recorded data on the tape. Unfortunately, the patient must either remain relatively motionless throughout the entire monitoring period or else utilize miniaturized, but extremely expensive, portable recording equipment. Therefore, in some cases, the monitoring period may not include various types of activity for the patient, leading to possible erroneous conclusions. Other attempts to free the patient from the monitoring equipment has resulted in the use of some telemetry equipment but, again, there is a limited range to such equipment and it is also extremely expensive.

Thus, while the usefulness of an R-interval histogram has been recognized, the expensive equipment needed and the inconvenience in its use has practically limited the use of the histogram to those situations where such expense and inconvenience has been warranted, such as in the case of patients with known or suspected cardiac problems. Hence, the use of the R-interval histogram has not been practical as a general examining tool for practicing physicians.

It will be apparent from the foregoing that there has long been a need for a simple and inexpensive apparatus which would quickly, inexpensively, reliably and conveniently generate an R-interval histogram for use in an ordinary physical examination procedure. The method and apparatus of the present invention satisfies that need.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for automatically and directly generating a graphical display of continuously received data. The illustrated presently preferred embodiment of the invention generates an R-interval histogram which requires no intermediate processing or analysis.

Further, the apparatus of the invention can be made extremely small and portable, permitting a patient to conveniently and comfortably wear the apparatus throughout the entire monitoring period with few restrictions on his freedom of movement. Therefore, use of the apparatus of the invention enables a resultant R-interval histogram which can reflect the patient's engaging in a number of different activities throughout the monitoring period, thereby providing more useful and meaningful results.

The system of the invention incorporates an apparatus with detachable and reusable display units so that a physician need only have a basic monitoring unit and a few display units on hand in order to fully utilize the equipment. In its use, the physician would supply the unit to a patient to wear for a monitoring period, typically from four to eight hours. The patient would then return to the physician with the unit and the R-interval histogram could be directly examined at that time. Another histogram display unit could then be placed on the monitoring unit for another patient. As the apparatus can be made relatively inexpensively, and its use requires no special analyzing equipment, the physician may routinely utilize the apparatus to check even supposedly well patients at little expense.

In its operation, the apparatus of the invention monitors the R-interval between each pair of successive heartbeats and that interval is assigned to one of a plurality of ranges of intervals, or "time-bins". Each interval signal supplied to a time-bin increments a physical display so that the displayed value indicates the total number of intervals falling within that time-bin. Gradually, the monitoring period generates an R-interval histogram which may be read directly without further processing.

The presently preferred embodiment of the invention utilizes relatively small digital, solid-state electronic components and an incrementing electrochemical display device which is completely reusable. In addition, a further feature of the presently preferred embodiment is that the unit is automatically turned off after a preset monitoring time or if any of the time-bin display devices should overflow. The overflow protection prevents distortion of the resultant histogram.

Thus, the present invention provides a small, portable apparatus whereby a graphical display of continuously received data is directly generated. While the method and apparatus of the presently preferred embodiment is for the generation of an R-interval histogram, it will be appreciated that the technique of the invention may be used for numerous other applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a normal electrocardiogram waveform illustrating the R portion used to time the interval between heartbeats;

FIG. 2 is a graphical representation of the desired R interval histogram display for the apparatus of the presently preferred apparatus;

FIG. 3 is a block diagram of the basic operational system of the invention;

FIG. 4 is a logic diagram of a presently preferred embodiment of the system;

FIG. 5 is a pictorial perspective view of one overflow sensing arrangement;

FIG. 6 is an exploded pictorial perspective view of portions of a second overflow sensing arrangement;

FIG. 7 is a bottom plan view taken in the direction of the arrow 7 in FIG. 6; and

FIG. 8 is a diagrammatic view of the operating configuration of the second overflow sensing arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to the drawings, particularly FIG. 2 thereof, the object of the presently preferred embodiment of the invention is to produce an R-interval histogram based on the monitoring of the heartbeat of a patient over a relatively long period of time, typically four to eight hours. The R-interval histogram is basically a bar graph with the length of any particular bar indicative of the relative number of heartbeats during a monitoring period which fell within a range of heartbeat rates.

The heartbeat rate is typically measured by means of the R-interval, which is the time between the R portions of time adjacent heartbeats. As shown in FIG. 1, for a normal electrocardiogram waveform, the R portion 10 has a relatively high amplitude which can be sensed relatively easily by conventional electronic circuitry. The abscissa 12 of the R-interval histogram shown in FIG. 2 represents a plurality of ranges of R intervals with the ranges, or time-bins as they will be hereinafter called, arranged as an array of vertical bars.

The total permissible span of R-interval is empirically chosen, based on average heartbeat rates. In the presently preferred embodiment of the invention, the span was chosen as 300 milliseconds to 1,500 milliseconds with each time-bin comprising a range of 40 milliseconds for a total of 32 time-bins.

It should be appreciated that choosing a uniform millisecond time-bin range across the entire histogram results in a non-linear heartbeat per minute scale. In particular, the 40 millisecond time-bin between 1,460 and 1,500 milliseconds permits a heartbeat range of only about 0.1 beats per minute while the 40 millisecond time-bin between 300 and 340 millisecond permits a heartbeat range of about 27 heartbeats per minute. Thus, if the R-interval is used as a controlling argument on the abscissa, the histogram may be considered linear but if heartbeats per minute is to be the controlling factor, the non-linearity of the histogram would have to be taken into account. At the present time, the interpretation of R-interval histograms is not completely understood and the significance, or lack of significance, of the non-linearity in analyzing the histogram has not been determined.

In the presently preferred embodiment of the invention, a time scale 14 is provided to limit the monitoring time to a predetermined number of hours. In the illustrated histogram of FIG. 2, a total of 8 hours is provided. However, it should be appreciated that, not only can the time scale be changed, but the operation of the unit can be manually stopped at any time and the total number of monitoring hours will be registered on the time scale 14.

It will be appreciated that the apparatus of the invention does not actually generate bars of a particular height but small indicators, for example indicator 15, within each time-bin display device is moved incrementally upward for each R-interval signal which falls within that time-bin. Thus, the height of the indicator in the time-bin display device corresponds to the length of the bar on a conventional bar graph. The operation of the time-bin display devices used in the presently preferred embodiment of the invention will be more fully described below.

The basic operation of the method and apparatus of the invention is illustrated by the block diagram of FIG. 3. An electrocardiogram signal is obtained in the conventional manner from electrocardiograph electrodes and applied to a terminal 30 which serves as the input to a signal processor 32. The signal required by the apparatus of the invention is any usable signal which tracks the R portion 10 of the cardiac signal. Thus, the signal processor 32 may be constructed in numerous ways well known to those skilled in the art and which form no part of the present invention.

The signal processor 32 produces an "R signal" on the line 34 which serves as the input to the time-bin sorting logic 36. The time-bin sorting logic determines the interval between R signals on the line 34, hereinafter called the "R-interval", selects a time-bin corresponding to that R-interval and generates a suitable time-bin signal. It should be noted that each R-interval should fall within one of the provided time-bins between 300 milliseconds and 1,500 milliseconds.

The output on line 38 from the time-bin sorting logic 36 serves as the input to a time-bin display 40 and, for each time-bin signal, an associated time-bin display device is incremented, as will be described below.

FIG. 4 is a logic diagram illustrating the operation of the presently preferred embodiment of the invention. Again, the basic input on line 30, is from the electrodes to the signal processor 32. Generally, such a signal processor 32 will include a preamplifier 42 to greatly increase the relatively low level cardiac signal. Thereafter, the output of the preamplifier on line 44 would be typically applied to the input of some threshold device, such as a Schmitt trigger 46, which would respond only to the relatively peaked R portion 10 of the cardiac signal. The Schmitt trigger 46 also serves to process the signal to a regular pulse waveform, as is well known in the art. The output of the Schmitt trigger 46 on line 34 serves as the reset input to an R-S flip-flop 48 within the time-bin sorting logic 36.

From the configuration of FIG. 2, it can be seen that the useful range of R-intervals is from 300 to 1,500 milliseconds. Therefore, the sorting of the R-interval signals into the 40 millisecond time-bins does not occur until after 300 milliseconds have passed. The time delay is provided by a 300 millisecond start clock 50 and the normal time-bin sorting is controlled by a 40 millisecond sort clock 52. Both the start and sort clocks 50 and 52, respectively, have inhibit inputs which stop and reset the clocks in any conventional manner known to those skilled in the art.

The operation of the time-bin sorting logic 36 can best be explained by first assuming that an R signal is received on line 34 to the reset input of the R-S flip-flop 48. A Q output 54 of the flip-flop 48 is then conventionally a binary 1 and the Q output 54 is applied into a first input to an AND gate 56. A second input 58 to AND gate 56 is derived from the output of a NAND gate 60, the output of which is normally a binary 1 enabling AND gate 56. As both the first and second inputs 54, 58, respectively, to AND gate 56 are binary 1's, the output 62 is also a binary 1 and the output 62 is applied to an inhibit input to the sort clock 52 to turn it off.

When the Q output of the R-S flip-flop 48 was set to binary 1, the Q output was set to binary zero. The Q output 64 is connected to the inhibit input of the start clock 50 so that, when the Q output goes to the binary zero state, the start clock begins operating. The start clock 50 produces a pulse at its output 66 at the end of 300 milliseconds, the output pulse serving to reset a 5-bit binary counter 68 and also sets the R-S flip-flop 48 at its set input 70. The Q output 64 of flip-flop 48 is then set to binary 1 and inhibits the start clock 50 from further operation. The Q output 64 of flip-flop 48 is also connected to an inhibit input of a 1 out of 32 decoder 72 turning off its output.

Since the Q output of the R-S flip-flop 48 is now at binary zero, the output of AND gate 56 is also binary zero, removing the inhibit signal from the sort clock 52 permitting it to begin operation. Thereafter, after every 40 milliseconds, the sort clock 52 generates a pulse at its output 74 which is connected to a count input of the 5-bit binary counter 68. Thus, after every 40 milliseconds, counter 68 is incremented.

The sort clock 52 continues to deliver a count pulse every 40 milliseconds until a following R signal is delivered on line 34 to the reset input of the R-S flip-flop 48. Upon that occurrence, the Q output of the flip-flop 48 is a binary 1 which is connected through AND gate 56 to the inhibit input of the sort clock 52, stopping its operation. Simultaneously, the Q output 64 of flip-flop 48 goes to a binary zero which removes the inhibit signal from the start clock 50 beginning a complete new cycle. The Q output 64 also removes the inhibit signal from the decoder 72. The 5-bit binary number then in the counter 68 is converted to a single output on one of the 32 output lines 76 of the decoder 72 to supply a time-bin signal to the display unit 40.

The time-bin signal on one of the lines 76 is connected to the appropriate driver 78 to operate its associated electrochemical display device 80. It will be appreciated that the configuration of the drivers 78 is dependent upon the type of display device utilized. As such, the configuration of the drivers 78 forms no part of the present invention and is conventionally designed for the display device 80 used. While a presently preferred embodiment of the electronic circuitry utilized with the present invention has been described in detail, it should be appreciated that numerous other circuit configurations are possible.

One arrangement of the electrochemical display devices utilized in the presently preferred embodiment of the invention is shown in FIG. 5. Generally, the display device is commonly used as an elapsed time indicator and consists of an elongated capillary tube 82 generally shown in FIG. 5. The capillary tube is completely filled with mercury except for a small gap 84 which is filled with an electrolytic gel. The application of a direct current voltage between electrodes 86 and 88 at either end of the capillary tube 82 causes an electrochemical reaction within the electrolytic gel in the gap 84 resulting in an electroplating process which causes the gap 84 to move within the capillary tube 82. The rate of movement of the gap 84 is known and can be calibrated to indicate elapsed time for a particular direct current voltage.

In the present application, however, the tubes 82 are arranged in an array to represent the R-interval histogram and each tube represents one R-interval time-bin. As each time-bin signal is generated, the drivers 78 of FIG. 4 generate an appropriate signal to be applied to the terminals 86, 88 of the appropriate capillary tube 82 to slightly move, or "increment", the gap 84.

The capillary tubes 82 themselves or their operation form no part of the present invention and are commercially available in numerous configurations from Curtis Instruments, Inc., Mt. Kisco, New York. In the presently preferred embodiment of the invention, the plurality of capillary tubes 82 are arranged in an array by any suitable means to represent the graphical display shown in FIG. 2 with one of the tubes being actuated continuously to serve as the time scale 14.

As briefly mentioned above, the time-bin display 40 of the present invention includes an overflow protection device and one form of overflow protection is illustrated in FIG. 5. In the illustrated embodiment, a transmitting fiber optic rod 90 is arranged perpendicularly to the array of capillary tubes 82. The fiber optic rod 90 is completely covered with opaque material except where it is adjacent a capillary tube 82. At those points, there is a small aperture 92 in the opaque material permitting light from a light source 94 to exit from the fiber optic rod 90. Immediately above the fiber optic rod 90 is another receiving fiber optic rod 94 also completely covered with an opaque material except at the intersections with the capillary tubes 82 where there are similar apertures 96. At one end of the receiving fiber optic rod 94 is a photocell 98.

Because the capillary tubes 82 are filled with mercury, light from the light source 94 in the transmitting fiber optic rod 90 normally cannot pass through the apertures 94 to an adjacent aperture 96 in the receiving fiber optic rod 94. Only when one of the gaps 84 is in position between the aperture 92 and 96 (as at reference numeral 99, for example) can light from the transmitting fiber optic rod 90 pass through to the receiving fiber optic rod 94 to the photocell 98. Thus, when one of the gaps 84 reaches an overflow position near its maximum travel, the photocell 98 will detect light and stop the operation of the system by means of well known conventional electronic circuitry (not shown).

FIGS. 6 through 8 illustrate an alternate version for the time-bin display 40. In this form, a glass plate 100 is provided with a plurality of aligned grooves 102 which are filled with mercury and an electrolytic gel gap. A conventional printed circuit board 104 has appropriately placed electrodes positioned on the board 104 so that when the board and plate 100 are bonded together, the electrodes will be at the ends of the grooves 102. The printed circuit board 104 includes a conventional connector terminal strip 106 which allows quick and easy connection to a standard printed circuit connector. The time-bin display 40 of this configuration may also be interchanged on the basic unit.

In this form of display device, the overflow detection arrangement is provided by spaced terminals 108, 110 at one end of the printed circuit board 104, as is best shown in FIG. 7. Alternate terminals 108, 110 are connected together so that when the grooves 102 are filled with mercury, a series connection of all the terminals is made.

In the conventional operation of the capillary tubes, one end of each of the tubes can be connected to a common voltage level, preferably ground. As illustrated in FIG. 8, when gaps 112 in the grooves 102 are in the normal position, the grooves 102 are filled with mercury interconnecting all of the terminals 108, 110 to ground. When a gap 112 reaches the overflow position between the terminals 108, 110 the connection of all of the grooves 102 to ground is broken, or the resistance to ground changes markedly, and a ground sensing circuit 114 senses that condition and stops the operation of the system.

In summary, the method and apparatus of the present invention provides an efficient portable system for directly generating a readable graphical display of continuously received data. In the preferred embodiment, sensed R-intervals are separated into R-interval ranges, or time-bins, and the time-bin signals are applied to an electrochemical signal accumulating device to directly generate the visual display. A signal overflow prevention arrangement is provided to prevent distortion of the resultant R-interval histogram.

While a presently preferred embodiment of the method and apparatus of the invention has been described in detail, it will be apparent that various modifications of the invention may be made without departing from the spirit and scope of the invention. Therefore, the invention is not to be limited except as by the following claims.

Claims

I claim

1. Apparatus for displaying the frequency of occurrence of time intervals between events, said apparatus comprising:

means for measuring the time interval between events;

means for determining the number of predetermined time periods which elapse during each time interval and generating time-bin signals in accordance therewith;

means for directly displaying in the form of a histogram the frequency of occurrence of said time-bin signals as a function of said time-bin signals, said means for displaying including a plurality of electrochemical capillary timing tubes arranged in a side-by-side ordered array in the form of a histogram with one tube associated with each time-bin;

and incrementing means connected to said determining means and said tubes for causing the capillary gap within a tube to move an incremental distance for each associated time-bin signal.

2. The displaying apparatus as defined in claim 1 wherein:

said displaying means is detachable from said determining means, said displaying means being resettable for reuse.

3. Apparatus for displaying the frequency of occurance of time intervals between events, said apparatus comprising:

means for measuring the time interval between events;

means for determining the number of predetermined time periods which elapse during each time interval and generating time-bin signals corresponding to said number in accordance therewith, said determining means including,

clock means for generating sort signals at the rate of said predetermined time period, said clock means being started at a point in time between time intervals and stopped at the end of a time interval,

counter means for counting said sort signals in binary form, and

decoder means for converting the binary count in said counter means to a single time-bin signal at the end of a time interval; and

means for displaying the frequency of occurance of said time-bin signals as a function of said time bin signals.

4. The displaying apparatus as defined in claim 3 wherein said displaying means includes:

a plurality of electrochemical capillary timing tubes arranged in an array with one tube associated with each time-bin; and

incrementing means connected to said determining means and said tubes for causing the capillary gap within a tube to move an incremental distance for each associated time-bin signal.

5. The displaying apparatus as defined in claim 4 wherein:

said displaying means is detachable from said determining means, said displaying means being resettable for reuse.

6. Apparatus for generating an R-interval histogram comprising:

means for measuring the time interval between the R portions of an electrocardiogram waveform;

means for determining the number of predetermined time periods which elapse during each time interval and generating time-bin signals in accordance therewith, said predetermined time period being substantially shorter than said time interval; and

means for continuously and directly displaying in the form of a histogram the frequency of occurrence of said time-bin signals as a function of said time-bin signals over a monitoring time period, said displaying means being connected to said determining means, said displaying means including a plurality of electrochemical capillary timing tubes arranged in a side-by-side ordered array in the form of a histogram with one tube for each time-bin and;

incrementing means connected between said determining means and said tubes for causing the capillary gap within each tube to move an incremental distance for each associated time-bin signal.

7. Apparatus for generating an R-interval histogram comprising:

means for measuring the time interval between the R portions of an electrocardiogram waveform;

means for determining the number of predetermined time periods which elapse during each time interval and generating time-bin signals corresponding to said number in accordance therewith, said predetermined time period being substantially shorter than said time interval, said determining means including,

start clock means for generating a start signal and start time period after the beginning of a time interval, said start time period being slightly less than the shortest anticipated time interval,

sort clock means for generating sort signals at a rate equal to said predetermined time period, said sort clock means being started by said start signal and stopped at the end of a time interval, said predetermined time period being substantially shorter than the difference between the shortest anticipated time interval and the longest anticipated time interval,

counter means connected to said sort clock means for counting said sort signals in binary form,

decoder means connected to said counter means for converting the binary count in said counter means to a single time-bin signal, and

means for continuously displacing the frequency of occurance of said time-bin signals as a function of said time-bin signals over a monitoring time period, said displaying means being connected to said determining means.

8. The apparatus defined in claim 7 wherein said displaying means includes:

a plurality of electrochemical capillary timing tubes arranged in an array with one tube for each time-bin; and

incrementing means connected between said determining means and said tubes for causing the capillary gap within each tube to move an incremental distance for each associated time-bin signal.

9. The apparatus defined in claim 8 wherein:

said displaying means is detachable from said determining means, said displaying means being resettable for reuse.

10. The apparatus defined in claim 10 including:

a transmitting fiber optic rod perpendicularly disposed across said array of capillary timing tubes near the point of furthest movement of said capillary gaps, said fiber optic rod being encased in an opaque material except at the points of contact with said tubes;

a light source disposed at one end of said transmitting fiber optic rod and supplying light thereto;

a receiving fiber optic rod disposed across said array of capillary tubes on the opposite side thereof from said transmitting fiber optic rod, said receiving fiber optic rod being encased in an opaque material except at the points of contact with said tubes; and

photosensitive means disposed at one end of said receiving fiber optic rod, said photosensitive means being activated when a capillary gap is positioned substantially between said transmitting and said receiving fiber optic rods.

11. The apparatus defined in claim 7 wherein said displaying device includes:

a transparent plate having an array of elongated grooves in one side thereof;

a backing plate of substantially non-conductive material overlying said grooved side of said transparent plate, said grooves forming the capillary tubes of electrochemical timing devices;

electrical circuitry bonded to said non-conductive backing plate on the side contacting said transparent plate, said circuitry providing an electrical terminal in each end of each of said grooves, said circuitry further providing electrical connections to said terminals from an in-lying terminal strip along an edge of said backing plate.

12. The apparatus defined in claim 11, including:

terminal means at one end of each of said grooves, said terminal means having an immediate end terminal and a terminal displaced a short distance along said groove, the end terminal of one groove being connected to the displaced terminal of an adjacent groove.

13. A method of displaying the frequency of occurrence of time intervals between events, said method comprising the steps of:

measuring the time interval between events;

determining the number of predetermined time periods which elapse during each time interval and generating time-bin signals in accordance therewtih; and

displaying as a directly generated histogram the frequency of occurrence of said time-bin signals as a function of said time-bin signals, said displaying step including providing an electrochemical capillary timing tube for each of said time-bin signals, arranging said timing tubes in a side-by-side ordered array in the form of a histogram; and

applying said time-bin signals to their associated timing tubes to cause the capillary gap within each tube to move an incremental distance for each applied time-bin signal.

14. The method defined in claim 13 including:

resetting said capillary timing tubes following a use thereof.

15. The method defined in claim 14 including:

removing said array of tubes prior to resetting them.