WO2007053892A1

WO2007053892A1 - A device and method for indicating a relationship between heart rate and external stimuli

Info

Publication number: WO2007053892A1
Application number: PCT/AU2006/001668
Authority: WO
Inventors: Michael O'rourke
Original assignee: Atcor Medical Pty Ltd
Priority date: 2005-11-10
Filing date: 2006-11-08
Publication date: 2007-05-18

Abstract

A device (10) for indicating the relationship between heart rate and external stimuli, said device measuring at least a waveform related to activity of the heart, characterised in that an indication is provided when one or more pre-defined relationships exist between the phase or rate of the stimuli and the phase or rate of the heart beat.

Description

A device and method for indicating a relationship between heart rate and external stimuli

Field of the invention

The present invention relates to a device and method for indicating a relationship between heart rate and external stimuli. The invention has been primarily developed for use in indicating the effects of stimuli through the body of a regular nature, such as running or industrial vibrations of a similar rate to running, and will be described hereinafter with reference to these uses. However, the invention is not limited to these particular uses and is also suitable for use in identifying cardiovascular related complications during running.

The present invention also relates to a training device and also a computer program product, including a computer readable medium having recorded thereon a computer program, for indicating a relationship between heart rate and external stimuli.

Background of the invention

It has been generally been considered that the arterial pulse in humans, whilst clearly varying under different stresses, does not have characteristics greatly influenced by external vibrations.

The present invention seeks to provide an arrangement whereby undesirable relationships between the arterial pulse waveform and external stimuli can be minimised or avoided, and/or whereby favourable effects can be enhanced.

Summary of the invention

Accordingly, in a first aspect, the present invention provides a device for indicating a relationship between heart rate and external stimuli, characterised in that an indication is provided when one or more pre-defined relationships exist between the phase or rate of the stimuli and the phase or rate of the heart beat. It has been determined by the inventor that, contrary to generally held belief in the field, stimuli such as running do induce pressure surges within the circulatory system, and in particular, if the maximum pressure during the operation of the heart and maximum pressure due to the external stimuli coincide, then an undesirable, additive effect results. This may be damaging to the heart and circulatory system, and may be the cause of some of the incidents of exercise related cardiac ischaemia.

On the other hand, if the pressure surge induced by the activity, for example running, is precisely out of phase with the heart beat, then the pressure surge associated with the heart beat is in fact reduced, and a second pressure peak will occur immediately (180°) out of phase with the pulse. This results in overall lower pressure within the circulatory system while the heart is actively expelling blood, and a higher pressure for perfusion of the coronary arteries when the heart is relaxing between beats; this provides an improved performance by the athlete because the pressure is maintained at an optimal level.

The present invention may also be applicable to industrial situations where vibrations may be present which are at a similar rate to running (for example, about or above 120 beats per minute or ≥2 Hz), producing a beating effect.

The pre-defined relationship preferably relates to a regular coincidence of peaks of the heart waveform and the stimuli waveform at a selected vessel, being one of the ascending aorta, another systemic artery, or a vascular bed.

The device preferably includes a display device adapted to issue a display indicative of BAD when the heart waveform and the stimuli waveform are substantially in phase.

The device preferably includes a display device adapted to issue a display indicative of GOOD when the heart waveform and the stimuli waveform at the selected vessel being substantially out of phase (e.g. 180 degrees out of phase).

In one form, the display device is a visual indicator. In another form, the display device is an aural indicator. The waveform is preferably measured at the upper body or an upper limb (e.g. pressure, flow or volume waveforms). More preferably, the waveform is measured by a finger photo plethysmograph.

In a second aspect, the present invention provides a method for determining the relationship between external stimuli and heart rate, including at least the steps of: obtaining a waveform relating to heart activity when external vibrational stimuli are present; analysing said waveform to determine whether one or more predefined relationships exists between the external stimuli and heart rate within said waveform; and if any of said predefined relationships exist, provide an indication that such a relationship exists.

The step of providing an indication indicative of a BAD condition is preferably when the predefined relationship is the heart waveform being substantially in phase with the stimuli waveform. The step of providing an indication indicative of GOOD is preferably when the predefined relationship is the heart waveform being substantially out of phase with the stimuli waveform (e.g. 180 degrees out of phase).

The method preferably, further includes the steps of: a. determining heart rate by counting wave peaks over a set period of time; b. seeking "beating" by identifying a situation where the amplitude of the pulse varies between a high maximum and a low minimum at a frequency less than 10 beats/min; c. if beating occurs as per step b., providing an indication of the beating frequency; d. if a consistent signal results without beating as per step b., subjecting the signal results to Fourier analysis to calculate a first and second harmonic; e. if Fourier analysis indicates that the second harmonic is less than 20% of the first harmonic, providing an indication that an undesirable situation is occuring; and f. if the Fourier analysis indicates that the second harmonic is greater than the first harmonic, providing an indication that a desirable situation is occurring. In a third aspect, the present invention provides a computer program product having a computer readable medium having a computer program recorded therein for indicating the relationship between heart rate and external stimuli, said computer program product comprising: computer program code means for receiving a waveform relating to heart activity when external vibrational stimuli are present; and computer program code means for analysing said waveform to determine whether one or more predefined relationships exists between the external stimuli and heart rate within said waveform; and if any of said predefined relationships exist, provide an indication that such a relationship exists.

hi a fourth aspect, the present invention provides a computer program for indicating the relationship between heart rate and external stimuli, said program comprising: code for receiving a waveform relating to heart activity when external vibrational stimuli are present; and code for analysing said waveform to determine whether one or more predefined relationships exists between the external stimuli and heart rate within said waveform; and if any of said predefined relationships exist, provide an indication that such a relationship exists.

hi a fifth aspect, the present invention provides a training device for indicating the relationship between heart rate and external stimuli, said training device comprising: means for measuring at least a waveform related to activity of the heart; and an indicator for indicating to a user when one or more pre-defined relationships exist between the phase or rate of the stimuli and the phase or rate of the heart beat.

hi one form, the indicator is adapted to issue a signal indicative of BAD when the predefined relationship is the heart waveform and the stimuli waveform being substantially in phase. In another from the indicator is adapted to issue a signal indicative of GOOD when the pre-defined relationship is the heart waveform and the stimuli waveform being substantially out of phase (e.g. 180 degrees out of phase). In an embodiment, the indicator includes a light source adapted to provide at least two colours respectively indicative of at least two said pre-defined relationships.

In another embodiment, the indicator includes a speaker adapted to provide at least two tones respectively indicative of at least two said pre-defined relationships.

Brief description of the drawings

Preferred embodiments of the invention will now be described, by way of examples only, with reference to the accompanying drawings, in which:

Figures l(a), (b) and (c) are illustrations of three aortic pressure pulses showing normal, bad and good phase relationships respectively;

Figure 2 is a block diagram of an embodiment of a device from indicating a relationship between heart rate and external stimuli;

Figure 3 is a block diagram showing an exemplary arrangement of the beating detector of

Figure 2;

Figure 4 is a flow diagram showing a method performed in accordance with the embodiment shown in Figs. 2 and 3;

Figures 5 (a) and (b) are illustrations respectively of an exemplary waveform and a beating waveform detected in accordance above device and method embodiments; and

Figure 6 is a schematic block diagram of a general purpose computer upon which the above device and method embodiments can be practiced.

Detailed description of the preferred embodiments

Figure 1 shows three typical curves A to C of a pressure pulse in an artery, with pressure on the Y-axis and time on the X-axis.

Curve A illustrates what could be expected when the heart is operating without any vertical movement or vibrations or other stimuli being transmitted, for example, during cycling or when at rest. This is considered to be a "normal" situation,

Curve B illustrates what occurs if the pressure pulse is in phase with a runner's step, so that the change in pressure within the ascending aorta related to stimulis from overall gross bodily movement is in phase with cardiac ejection. Both these pressure effects are added together, so that a potentially dangerously high peak results during cardiac ejection and a low nadir during cardiac relaxation. This is considered to be a "bad" situation.

Curve C illustrates what occurs if the pressure pulse generated by the heart beat and the surge created by body movement stimulis are 180° out of phase. In this case, the peak is reduced, and a second peak results, optimising cardiac ejection and coronary flow. This is considered to be a "good" situation.

The invention seeks to identify the second and/or third situations, so as to avoid dangerous situations and encourage optimal performance by, for example, an athlete. It has been determined by the inventor that, in effect, the result of the "good" situation shown in curve C is that the second harmonic of the pressure pulse becomes dominant over the first (and other) harmonics of the measured wave.

The invention contemplates detecting a suitable waveform, which may be flow, pressure, or volume variation, in the upper body or an upper limb, for identifying these situations. Waveform detection can be made with a finger photo plethysmograph or, in a static training application, a more tethered type device could be utilised. Any suitable measurement device can be used.

The invention has a variety of possible applications. One application relates to providing a static, training type device which could be used, for example, on a treadmill for athletes. A second application relates to a portable device which could be carried by an athlete during training runs, or competition. A third application relates to industrial safety type situations, where a regular, large scale vibration occurs affecting the operator of equipment. Embodiments of the invention will be described with reference to the first two applications, although it will be appreciated that the invention is not limited to these.

Once a waveform is detected by any suitable means, it is subjected to Fourier analysis in order to determine the harmonics thereof. If the first harmonic falls within a pre-defined range, for example, between 2 and 3.1 Hz, corresponding to between 120 and 190 beats per minute, then a possibility of the above described type of undesirable and desirable event occurring to a reasonable extent arises. Once the waveform has been Fourier analysed, the ratio of the first harmonic to the second harmonic can be determined. This determination can then be used so as to cause indicator lights to show, for example, green when the "good" relationship is present, i.e., when the second harmonic of the wave is dominant over the first harmonic, such that they can be said to be "in rhythm", or red when the "bad" relationship is present, i.e., when the first harmonic of the wave is markedly dominant over the second and other harmonics, such that they can be said to be "out of rhythm". Alternatively, different tones or tone rates could be generated and emitted by a speaker to indicate these relationships. It will be appreciated that an envelope of relationships close to the situations described would be utilised in a real situation.

An example of a method of determining and indicating these relationships can be summarised to include at least the following:

Determine heart rate by counting wave peaks over a set period of time (say 15 seconds);

Seek "beating" by identifying a situation where the amplitude of the pulse varies between a high maximum and a low minimum at a frequency less than 10 beats/min (see Figure 5(b));

If beating occurs, provide an indication of the beating frequency;

If a consistent signal results without beating, then subject it to Fourier analysis.

If the second harmonic is less than 20% of the first harmonic, then provide an indication that an undesirable situation occurs; and

If the second harmonic is greater than the first harmonic, indicate that a good situation occurs.

Figure 2 illustrates a embodiment of a device 10 for indicating a relationship between heart rate and external stimuli. The device 10 includes a waveform detector, in the form of a finger photo plethysmograph 20, which receives a waveform for processing. Other devices that can non invasively measure pressure or flow waveforms in the upper limb can alternatively be used. The received waveform is provided to a "beating" detector 30 for detecting whether the waveform is undergoing a beating effect. The presence of beating in the waveform does not allow for accurate harmonic analysis, hi response to a signal from the beating detector 30 indicating that beating is not present, the waveform detector 20 provides the waveform to waveshape and frequency identification means 40. The frequency is identified by considering the peaks of the waveform over time to give the heart rate. If this is not between about 120 and 200 beats per minute then an indication of this is sent to the detector 20.

After identifying the amplitude and frequency of the waveform, the waveform is averaged from at least 10 seconds of waveforms by averaging means 50 and analysis means 60 applies Fourier analysis on this averaged waveform to determine the harmonics. Amplitude measurement means 70 is provided to measure the amplitude of the first and second harmonics determined by the analysis means 60, and these amplitudes are compared by a comparator 80 to provide the ratio thereof. Based on the comparison result an indication of the first to second harmonic ratio is given by indicator, in the form LED indicator lights 90 which provide an indication in accordance with the above- described possible indications. Alternatively, the indictor 90 can be a speaker, as also discussed above. Notification that the comparison has been performed is provided to the detector 20 by the comparator 80. hi a static (i.e. treadmill) application, the items 30, 40, 50, 60, 70 and 80 are incorporated into software running on a computer 100, as is described in more detail below with reference to Figure 6. hi a portable application, the items 30, 40, 50, 60, 70 and 80 are incorporated into software running on a dedicated chip, such as an application specific integrated circuit (ASIC) or signal processing microchip.

Figure 3 illustrates the component parts of the beating detector 30 in more detail. A processor 33 is provided for receiving the waveform from the detector 20. Amplitude measurement means 34 is provided responsive to the processor 33 for measuring the amplitude of the waveform pulse used to identify the occurrence of beating based on the change in amplitude over time. This can be accomplished by using an envelope detection algorithm (as is used in digital signal processing for communication) or by using a Hubert Transform of a finite impulse response filter. The measured amplitude is provided to the processor 33 via connection 32 and the processor determines whether beating occurs over time using a clock 100. A beating indicator 35 is provided for indicating that beating is present when this is determined by the processor 33.

The processor 33 notifies the detector 20 as to whether or not beating has been detected via connection 31. It will be understood by those skilled in the art that the components described in relation to Figures 2 and 3 are merely exemplary and additional or other components are within the scope of the invention. Further, the connections 31 and 32, and the other connections not specifically described, can be either wired or wireless.

The above-described method, performed by the device 10 described in relation to Figures 2 and 3, is illustrated in more detail in the flow diagram of Figure 4.

Referring to Figure 4, in step (1) the peak and amplitude of each pulse in the waveform, as illustrated in the Figure 5 (a) by arrows A and B, are identified. In step (2) whether beating is present is identified by determining the phasic alternation of the wave amplitude between the maximum and minimum amplitudes of the waveform. This beating is shown in Figure 5(b). If some level of beating is detected, "YES" at step (3), then at step (3 a) the beating frequency is determined.

If the beating frequency is less than 10 per minute, the detected beating and frequency thereof is indicated and the process returns to step (1) (step 3(c)). If the beating frequency is more than 10 per minute, no indication is given and the process proceeds directly to step 3(c). On the other hand, if beating is not detected, "NO" at step (3), then the process proceeds to step (4).

hi step (4) the waveshapes and frequency are identified by considering the peaks and amplitudes measured in step (1), where the frequency must be between about 120 to about 200 beats per minute in order to proceed since this gives rise to the undesirable/desirable situations to be detected. If the frequency identified is not within this range, "NO" at step (4), then the process returns to step (1) (step (4a)). Otherwise, "YES" at step (4), the process proceeds to step (5) in which the waveform is averaged and Fourier analysis is applied to this averaged waveform. From this Fourier analysis, the first and second harmonics are determined. The amplitudes of these first and second harmonics are then measured at step (6). In step (7) these amplitudes are compared to provide the ratio of the first to second harmonic. The following actions at step (8) are then performed based on this determined ratio. If the second harmonic is greater than the first, "YES" at step (8), then an indication is given that the relationship between the harmonics is "good" (step (9a)) and the process returns to step (1) (step (9c)). If the second harmonic is about 20% or less than the first (step (8a)), then an indication is given that the relationship between the harmonics is "bad" (step (9b)) and the process returns to step (1) (step (9c)). Otherwise, the process returns directly to step (1) (step (8b)). A process cycle can be set to take about one minute, so that it is repeated in one minute intervals. Accordingly, these indications can be performed for a predetermined amount of time within this cycle length or until the next process cycle has been completed.

Finally, at step (8), if the second harmonic is in the range of greater than about 20% but less than about 100% of the first harmonic, then the process moves directly to step (9) and no indication is given.

Accordingly, the device 10 and associated method detect and indicate pressure surges within the circulatory system induced by external stimuli, so as to provide a way of reducing the occurrence of damage being done to the heart and circulatory system, especially exercise-related damage.

Figure 5 (a) shows the peak and amplitude (arrows A and B respectively) of each pulse which are needed for beating detection. Figure 5(b) shows an example of beating when the amplitude and peak of each pμlse vary.

Figure 6 shows an example of the computer 100 and a system 110 that can be used to implement the method described with reference to Figure 4, and detect beating as illustrated in Figure 5, for example in association with a treadmill 131 upon which runs an athlete 132. The steps shown in Figure 4 can be implemented as software, such as one or more application programs executable within the computer 100. hi particular, the steps of the method are effected by instructions in the software that are carried out within the computer 100. The instructions may be formed as one or more code modules, each for performing one or more particular tasks. The software may also be divided into two separate parts, in which a first part and the corresponding code modules performs the method and a second part and the corresponding code modules manage a user interface between the first part and the user. The software may be stored in a computer readable medium, including the storage devices described below, for example. The software is loaded into the computer 100 from the computer readable medium, and then executed by the computer 100. A computer readable medium having such software or computer program recorded on it is a computer program product. The use of the computer program product in the computer system 110 preferably effects an advantageous apparatus for the device 10.

As seen in Figure 6, the computer 100 is formed by a computer module 111, input devices such as a keyboard 112 and a mouse pointer device 113, and output devices including a display device 114, a printer 115 and loudspeakers 116. An external Modulator- Demodulator (Modem) transceiver device 117 may be used by the computer module 111 for communicating to and from a communications network 120 via a connection 121. The network 120 may be a wide-area network (WAN), such as the Internet or a private WAN. Where the connection 121 is a telephone line, the modem 117 may be a traditional "dial-up" modem. Alternatively, where the connection 121 is a high capacity (eg: cable) connection, the modem 117 may be a broadband modem. A wireless modem may also be used for wireless connection to the network 120.

The computer module 111 typically includes at least one processor unit 125, and a memory unit 126 for example formed from semiconductor random access memory (RAM) and read only memory (ROM). The module 111 also includes a number of input/output (I/O) interfaces including an audio-video interface 127 that couples to the video display 114 and loudspeakers 116, an I/O interface 128b for the keyboard 112 and mouse 113 and optionally a joystick (not illustrated), and an interface 128a for the external modem 117 and printer 115. In some implementations, the modem 117 may be incorporated within the computer module 111, for example within the interface 128a. The computer module 111 also has a further sensor interface 129 which, via a connection 130, permits coupling of the computer 100 to the athlete 132 exercising upon the treadmill 131. The connection 130 desirably includes sensors configurable upon the athlete 132 to detect the waveforms. The interface 129 and associated connection 130 may be formed using an Ethernet™ circuit card, a wireless Bluetooth™, an IEEE 802.21 wireless arrangement, or a USB connection, as appropriate.

The interfaces 128a and 128b may afford both serial and parallel connectivity, the former typically being implemented according to the Universal Serial Bus (USB) standards and having corresponding USB connectors (not illustrated). Storage devices 133 are provided and typically include a hard disk drive (HDD) 134. Other devices such as a floppy disk drive and a magnetic tape drive (not illustrated) may also be used. An optical disk drive 136 is typically provided to act as a non- volatile source of data. Portable memory devices, such optical disks (eg: CD-ROM, DVD), USB-RAM, and floppy disks for example may then be used as appropriate sources of data to the computer 100.

The components of the computer module 111 typically communicate via an interconnected bus 135 and in a manner which results in a conventional mode of operation of the computer 100 known to those in the relevant art. Examples of computers on which the described arrangements can be practised include IBM-PC's and compatibles, Sun Sparcstations, Apple Mac™ or alike computer systems evolved therefrom.

Typically, the application programs discussed above are resident on the hard disk drive 134 and read and controlled in execution by the processor 125. Intermediate storage of such programs and any data fetched from the network 120 and via the sensor interface 129 may be accomplished using the semiconductor memory 126, possibly in concert with the hard disk drive 134. In some instances, the application programs may be supplied to the user encoded on one or more CD-ROM and read via the corresponding drive 136, or alternatively may be read by the user from the network 120. Still further, the software can also be loaded into the computer 100 from other computer readable media. Computer readable media refers to any storage medium that participates in providing instructions and/or data to the computer system 100 for execution and/or processing. Examples of such media include floppy disks, magnetic tape, CD-ROM, a hard disk drive, a ROM or integrated circuit, a magneto-optical disk, or a computer readable card such as a PCMCIA card and the like, whether or not such devices are internal or external of the computer module 111. Examples of computer readable transmission media that may also participate in the provision of instructions and/or data include radio or infra-red transmission channels as well as a network connection to another computer or networked device, and the Internet or Intranets including e-mail transmissions and information recorded on Websites and the like.

The second part of the application programs and the corresponding code modules mentioned above may be executed to implement one or more graphical user interfaces (GUIs) to be rendered or otherwise represented upon the display 114. Through manipulation of the keyboard 112 and the mouse 113, a user of the computer system 100 and the application may manipulate the interface to provide controlling commands and/or input to the applications associated with the GUI(s).

For example, the beating data, as shown in Figure 5(b), can be graphically presented on the display 114 in substantially real-time, and can be supplemented by an audio indication via the loudspeakers 116. A print out of beat information obtained during an exercise session upon the treadmill 132 may be reproduced by the printer 115. Further, data from the exercise session may be uploaded via the network 120 for analysis by a third party (eg: a sports physician).

The method shown in Figure 4 may alternatively be implemented in dedicated hardware such as one or more integrated circuits performing the functions or sub functions of waveforms sensing, processing and indication. Such dedicated hardware may include graphic processors, digital signal processors, or one or more microprocessors and associated memories.

It will be appreciated that variations and additions are possible within the spirit and scope of the invention.

Claims

Claims:

1. A device for indicating the relationship between heart rate and external stimuli, said device measuring at least a waveform related to activity of the heart, characterised in that an indication is provided when one or more pre-defined relationships exist between the phase or rate of the stimuli and the phase or rate of the heart beat.

2. The device according to claim 1, wherein the relationship relates to a regular coincidence of peaks of the heart waveform and the stimuli waveform at a selected vessel, being one of the ascending aorta, another systemic artery, or a vascular bed.

3. The device according to claim 2, wherein the device includes a display device to adapted to issue a display indicative of BAD when the heart waveform and the stimuli waveform are substantially in phase.

4. The device according to claim 2, wherein the device includes a display device adapted to issue a display indicative of GOOD when the heart waveform and the stimuli waveform at the selected vessel being substantially out of phase.

5. The device as claimed in claim 4 or 5, wherein the display device is a visual indicator.

6. The device as claimed in claim 4 or 5, wherein the display device is an aural indicator.

7. The device according to any one of claims 1 to 6, wherein the waveform is measured at the upper body or an upper limb.

8. The device according to claim 7, wherein the measured waveform is a pressure waveform.

9. The device according to claim 7, wherein the measured waveform is a flow waveform.

10. The device according to claim 7, wherein the measured waveform is a volume waveform.

11. A device as claimed in anyone of claims 7 to 11, wherein the waveform is measured by a finger photo plethysmograph.

12. A method for determining the relationship between external stimuli and heart rate, including at least the steps of: obtaining a waveform relating to heart activity when external vibrational stimuli are present; analysing said waveform to determine whether one or more predefined relationships exists between the external stimuli and heart rate within said waveform; and if any of said predefined relationships exist, provide an indication that such a relationship exists.

13. The method as claimed in claim 12, indicating the step of providing an indication indicative of a BAD condition when the relationship is the heart waveform being substantially in phase with the stimuli waveform.

14. The method as claimed in claim 12, including the step of providing an indication indicative of GOOD when the relationship is the heart waveform being substantially out of phase with the stimuli waveform.

15. The method as claimed in claim 12, further including the steps of: a. determining heart rate by counting wave peaks over a set period of time; b. seeking "beating" by identifying a situation where the amplitude of the pulse varies between a high maximum and a low minimum at a frequency less than lO beats/min; c. if beating occurs as per step b., providing an indication of the beating frequency; d. if a consistent signal results without beating as per step b., subjecting the signal results to Fourier analysis to calculate a first and second harmonic; e. if Fourier analysis indicates that the second harmonic is less than 20% of the first harmonic, providing an indication that an undesirable situation is occurring; and f. if the Fourier analysis indicates that the second harmonic is greater than the first harmonic, providing an indication that a desirable situation is occurring.

16. A computer program product having a computer readable medium having a computer program recorded therein for indicating the relationship between heart rate and external stimuli, said computer program product comprising: computer program code means for receiving a waveform relating to heart activity when external vibrational stimuli are present; and computer program code means for analysing said waveform to determine whether one or more predefined relationships exists between the external stimuli and heart rate within said waveform; and if any of said predefined relationships exist, provide an indication that such a relationship exists.

17. A computer program for indicating the relationship between heart rate and external stimuli, said program comprising: code for receiving a waveform relating to heart activity when external vibrational stimuli are present; and code for analysing said waveform to determine whether one or more predefined relationships exists between the external stimuli and heart rate within said waveform; and if any of said predefined relationships exist, provide an indication that such a relationship exists.

18. A training device for indicating the relationship between heart rate and external stimuli, said device comprising: means for measuring at least a waveform related to activity of the heart; and an indicator for indicating to the user when one or more pre-defined relationships exist between the phase or rate of the stimuli and the phase or rate of the heart beat.

19. The device according to claim 18, wherein the indicator is adapted to issue a signal indicative of BAD when the pre-defined relationship is the heart waveform and the stimuli waveform being substantially in phase.

20. The device according to claim 18, wherein the indicator is adapted to issue a signal indicative of GOOD when the pre-defined relationship is the heart waveform and the stimuli waveform being substantially out of phase.

21. The device as claimed in claim 19 or 20, wherein the indicator includes a light source adapted to provide at least two colours respectively indicative of at least two said pre-defined relationships.

22. The device as claimed in claim 19 or 20, wherein the indicator includes a speaker adapted to provide at least two tones respectively indicative of at least two said predefined relationships.