GB2348715A

GB2348715A - Heart rate calculating apparatus

Info

Publication number: GB2348715A
Application number: GB9907788A
Authority: GB
Inventors: Ronald David Lessels Mackie
Original assignee: Healthcare Technology Ltd
Current assignee: Healthcare Technology Ltd
Priority date: 1999-04-07
Filing date: 1999-04-07
Publication date: 2000-10-11
Anticipated expiration: 2019-04-07
Also published as: GB2348715B; GB9907788D0

Abstract

Heart rate measuring apparatus incorporates a user operable key (18), for example for use by a health-care practitioner, a display (52, ls), and processing means (50) such as a microcontroller. Each time a pulse beat is felt, the user operates the key (18). The processing means (50) is operational to generate on the display (52) an indication of the frequency, in operations per minute, at which the user is operating the key. Thus, after a few beats have been sensed in this way the resulting display indicates a subject's heart rate.

Description

RATE CALCULATING APPARATUS The present invention relates to rate calculating apparatus, particularly, but not exclusively, to heart rate calculating apparatus.

The rate at which a person's heart is beating can provide important information as to the person's physiological condition. For this reason, measurement of a person's heart rate is a quite common procedure, carried out, for example, by a health-care practitioner on a patient.

The most common technique used to measure heart-rate is for a practitioner to feel for a subject's pulse, typically in an artery in the subject's wrist, and count the number of beats which are felt in a 20 or 30 second period. The number of beats counted is then multiplied by 3 or 2, as the case may be, to arrive at a figure for the number of beats per minute.

This technique is not without disadvantages. A rounding error in the number of beats counted can occur. This error can be one beat for each count, which, when multiplied, gives an error of up to two or three beats per minute.

Furthermore, the technique depends upon the practitioner's ability to time the counting period accurately, normally by observing the seconds hand of a watch. This can lead to a timing error of about one second. The combined effect of there two sources of error can give rise to a significant error in the calculated heart rate.

Moreover, because a practitioner must concentrate both on counting beats and on monitoring the passage of time, conversation with the subject is generally impossible.

Minor distractions can also cause the practitioner to loose count, whereupon the entire counting procedure may have to be restarted. This is inconvenient for the subject and wastes the practitioner's time.

Electronic heart-rate monitors are known which detect electrical signals that occur in a subject's body in time with the beating of the subject's heart. Such monitors contain sensitive electronic detection circuits and are, as a result, expensive. Furthermore, the need to make a reliable electrical connection with the patient's body renders such monitors inconvenient to use for taking oneoff (as opposed to continuous) measurements.

An aim of the invention is to provide apparatus which can be used to measure a subject's heart rate more conveniently and accurately than is possible with conventional techniques.

According to the present invention there is provided heart rate measuring apparatus having a user operable key, a display, and processing means, the processing means being operational to generate on the display an indication of the frequency, in operations per minute, at which a user is operating the key.

To use the device to measure a subject's heart rate, the user (for example, a health-care practitioner) feels for a subject's pulse in the usual way. Each time a pulse beat is felt, the user operates the key. After a few beats have been sensed in this way the resulting display indicates the subject's heart rate. This has been found to provide a more rapid, reliable and accurate measurement of the subject's heart rate than is possible with conventional techniques.

The processing means most typically comprises suitably configured electronic circuitry. The circuitry can conveniently be controlled by a programmed microcontroller, or it may be incorporated into an application-specific integrated circuit. The user-operable key most typically operates an electrical switch, operation of which can be detected by the circuitry.

Conveniently, the apparatus processing means is also operative to generate on the display an indication of the time of day. The apparatus can then substitute for a conventional watch. Additional information may also be presented on the display.

Most conveniently, embodiments of the apparatus have working components contained within a small portable case.

Such a case may particularly conveniently have the general appearance of a fob watch. There may be provided means by which the case can be secured to an article of clothing.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 depicts an embodiment of the present invention in the form of a nurse's fob watch, shown with all segments of a liquid crystal display enabled; Figure 2 shows watch of Figure 1 with a typical display of heart rate and the time of day; Figure 3 shows the watch of Figure 1 in a typical configuration attached to a garment of its user; Figure 4 shows the watch of Figure 1 being operated by the left hand of a user; and Figure 5 is a block diagram of electronic circuitry contained within the watch of Figure 1.

In Figure 1 there is shown a watch which constitutes apparatus embodying the invention.

The watch includes a case 10 which has a shape similar to that of a fob watch of the type typically used by hospital nurses. The case 10 has an approximately circular profile.

A flexible suspension strap 11 is secured to the case 10, and extends radially from it. A fixing pin 12 is provided on the suspension strap 11. In use, the fixing pin 12 is secured to a user's article of clothing, most typically on the user's upper body, with the case 10 hanging from the suspension strap 11 below the fixing pin 12, as shown in Figure 3.

Within the case 10 there is contained electronic circuitry which operates the device and a liquid crystal display.

A suitably-positioned viewing window 13 is provided in a front surface of the case 10 through which the liquid crystal display can be seen. The liquid crystal display has an electroluminescent backlit panel which can be activated to assist viewing the display in conditions of poor light.

In Figure 1, the liquid crystal display is shown with all of its display segments visible. A first region of the liquid crystal display, indicated at 14, can show the time of day in hours, minutes and seconds. A second region of the liquid crystal display, shown at 15, can show a three digit numerical value and is used to indicate a calculated heart rate in beats per minute. Additionally, the liquid crystal display has a pulse indicator 16, in the shape of a heart, to confirm registration of a pulse beat, and a sound indicator 17 to indicate whether the watch is operating in an audible or a silent mode.

Figure 2 shows the watch of Figure 1 with a typical indication on the liquid crystal display 13 showing a measured heart rate and the time of day, respectively in the second and first regions of the display 15,14.

Four external user-operable keys are provided on the case 10. These will be referred to as the pulse key 18, the set key 19, the adjust key 20, and the light key 21. The pulse key 18, the set key 19, and the adjust key 20 project radially from a side wall of the case 10, the pulse key 18 being approximately diametrically opposite the suspension strap 11. The light key 21 is disposed on the front surface of the case 10 next to the viewing window. The purpose and function of each of these keys will be explained below. Each key can be depressed by a user to make an electrical contact which is detected by the electronic circuitry of the watch.

The watch further comprises a sounder which can issue a short audible sound.

Figure 4 shows the watch 10 clasped in the left hand 40 of a user whose thumb 41 is pressing the pulse key 18. The position of the pulse key 18 opposite the suspension strap 11 is chosen as to be convenient for both left-handed and right-handed operation.

With reference now to Figure 5, the electronic circuitry of the device will now be described.

Operation of the circuitry is controlled by a microcontroller 50. A quartz crystal oscillator 51 provides timing signals for the microcontroller 50. An output of the microcontroller 50 provides signals which drive the liquid crystal display 52.

The electroluminescent backlit panel for the liquid crystal display is shown at 53. A signal generator 54 is provided to supply power to the backlit panel 53. An output signal line 56 of the microcontroller is connected to the signal generator 54 to enable the microcontroller 50 to switch on or off the backlit panel 53.

Each of the pulse key 18, the set key 19, the adjust key 20, and the light key 21 are connected to a respective input line of the microcontroller 50. Depression of each of the keys connects the corresponding input line to a local earth potential.

The sounder, shown at 55, is connected to an output of the microcontroller 50.

Software contained within the microcontroller detects key presses and performs all of the timing and time keeping functions requested by the user, as will now be described.

The microcontroller is programmed to respond to a user pressing the set key 19 and the adjust key 20 in a predetermined sequence to control aspects of the operation of the watch. For example, these keys 19,20 may be used to set the correct time of day. They can also be used to select whether the watch should operate in a silent mode or a audible mode. Other aspects of the operation of the watch can be controlled, but for the most part, these are not directly relevant to the invention, and will not be described further.

If the microcontroller 50 detects the sequence of key presses indicative that the audible mode is to be selected, it sends a signal to the liquid crystal display to activate the sound indicator 17. Thereafter, each time any key is depressed, the microcontroller 50 sends a signal to the sounder 55 to produce a short audible tone, so as to provide feedback to a user to confirm that the key press has been recognised. If the microcontroller 50 detects a sequence of key presses indicative that the silent mode is to be selected, it sends a signal to the liquid crystal display to deactivate the sound indicator 17. Thereafter, the sounder is not activated until the audible mode is reenabled.

The default state of the watch is to display only the time of day in the first region 14 of the liquid crystal display. In the default state, the second region 15 of the liquid crystal display is blank.

When a user wishes to calculate the heart rate of a subject, he or she finds a pulse on the subject, and then presses the pulse key 18 repeatedly in synchronism with the subject's heart beat.

At the first press of the pulse key 18, the microcontroller 50 sends a signal to the liquid crystal display to activate the pulse indicator 16, and to display on the second region 15 of the liquid crystal display is set to display a value of"O". After several (typically 5) regular presses of the pulse key 18, the microcontroller 50 calculates an average heat rate, and sends signals to the liquid crystal display to display the calculated heart rate on the second region 15 of liquid crystal display.

Each further press of the pulse key 18 is timed by the microcontroller 50, and the time value is processed by the microcontroller 50 to re-calculate the average heart rate.

Periodically, for example every two seconds, the microcontroller 50 sends signals to the liquid crystal display to display the re-calculated heart rate value.

As the sequence of key presses continues the displayed heart rate value becomes more accurate. The applicant has found that, provided the key presses are carefully made to be in synchronism with the subject's heart beats, accuracy does not significantly increase after about 10 key presses.

Following the user's final key press, the liquid crystal display continues to display the last calculated heart rate value for approximately 10 seconds. After that period, the microcontroller sends signals to the liquid crystal display to de-activate the pulse indicator 16, and to blank the second region 15 of the liquid crystal display.

In the event that the microcontroller 50 detects the pulse key 18 being held down for more than a predetermined period, for example two seconds, the microcontroller suspends the calculation of the heart rate. Calculation is recommenced from a zero value on subsequent presses of the pulse key 18. This enables a user to restart quickly the counting sequence for any reason, for example, if a heart beat is missed.

In the audible mode, the microcontroller 50 sends a signal to the sounder 55 to issue a tone each time the pulse key 18 is pressed. This can provide useful feedback to a user.

In circumstances in which the noise could cause disturbance, the silent mode can be selected to prevent operation of the sounder 55.

The time of day display is similar to that of a standard digital watch, showing hours, minutes and seconds. The user may choose to display time in either of a 12-hour or a 24-hour mode by a suitable sequence of operations of the set key 19 and the adjust key 20.

In the event that the microcontroller 50 detects that the light key 21 has been pressed, it generates a signal on its output line 56 to activate the signal generator 54 for a period, for example three seconds, thereby illuminating the electroluminescent panel 53 to allow the display to be read in poor illumination.

The watch described here provides a low-cost, very easy and quick to use, calculator of the rates of regular processes which are measured in events per minute. In particular, its use in the measurement of heart rates in medical centres may greatly improve the throughput and accuracy of results.

It is clear that the present invention can be embodied in many different structures. In particular, the case may be any of a wide variety of shapes which suit the particular application for which the embodiment is intended, and also to meet the requirements of aesthetics.

Claims

CLAIMS 1. Heart rate measuring apparatus having a user operable key, a display, and processing means, the processing means being operational to generate on the display an indication of the frequency, in operations per minute, at which a user is operating the key.
2. Heart rate measuring apparatus as claimed in claim 1, wherein the processing means comprises suitably configured electronic circuitry.
3. Heart rate measuring apparatus as claimed in claim 2, wherein the circuitry is controlled by a programmed microcontroller.
4. Heart rate measuring apparatus as claimed in claim 2, wherein the circuitry is incorporated into an application-specific integrated circuit.
5. Heart rate measuring apparatus as claimed in any one of claims 2 to 4, wherein the user-operable key operates an electrical switch, operation of which can be detected by the circuitry.
6. Heart rate measuring apparatus as claimed in any preceding claim, wherein the processing means is also operative to generate on the display an indication of the time of day.
7. Heart rate measuring apparatus as claimed in any preceding claim, wherein working components of the apparatus are contained within a small portable case.
8. Heart rate measuring apparatus as claimed in claim 7, wherein the case has the general appearance of a fob watch.
9. Heart rate measuring apparatus as claimed in claim 7 or 8, wherein the apparatus includes means by which the case can be secured to an article of clothing.
10. Heart rate measuring apparatus substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.