GB2567678A

GB2567678A - Device and method for guiding breathing of a user

Info

Publication number: GB2567678A
Application number: GB1717276.8A
Authority: GB
Inventors: Christopher Wegerif Simon; Kay Mcconnell Alison; Miguel Fernandes Vargas Pedro
Original assignee: Bournemouth Univ Higher Education Corp
Current assignee: Bournemouth Univ Higher Education Corp
Priority date: 2017-10-20
Filing date: 2017-10-20
Publication date: 2019-04-24
Also published as: WO2019077304A1; GB201717276D0

Abstract

A device for guiding breathing of a user comprising outputting a breathing signal for guiding the user to breathe in and breathe out during a breathing cycle defined over a time period. A heartbeat interval of a user is measured, for example using photoplethysmography (PPG). In an embodiment, the respiratory sinus arrhythmia (RSA) can be measured from a heartbeat interval, for example the heart rate variability. The breathing frequency of a user is guided breath-by-breath to increase or decrease in such a way that RSA amplitude increases. The guide can be a visual, auditory or haptic signal provided to the user. The device may reduce blood pressure or provide stress-reduction.

Description

DEVICE AND METHOD FOR GUIDING BREATHING OF A USER

BACKGROUND

Field of the Disclosure

The present technique relates to a device and method for guiding breathing of a user.

Description of the Related Art

The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in the background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present technique.

It has been shown that controlling oneself to undertake a slow breathing exercise comprising breathing more slowly than normal (for example, 6 breaths per minute instead of breathing spontaneously at around 12-15 breaths per minute) for a set time (for example, 10 to 20 minutes) on a regular basis (for example, once a day) may have beneficial effects to a person’s physical and/or mental health. For example, such exercises may reduce blood pressure [1] and may have neurophysiological effects such as stress-reduction [2],

Because of the complex cardiorespiratory interactions involved, different people may have different optimal slow breathing rates for optimising the potential beneficial effects of slow breathing exercises. However, it is difficult for a user to know what their personal optimal slow breathing rate is. There is therefore a need for a user to be able to know how to adjust their breathing rate during a slow breathing exercise in an automatic, easy and intuitive manner so as to approach their optimal slow breathing rate, thus improving the potential beneficial effects.

SUMMARY

The present technique provides a device for guiding breathing of a user, the device comprising circuitry configured: to output a breathing signal for guiding the user to breathe in and breathe out during a breathing cycle defined over a time period; to receive a first input signal indicative of a first physiological property of the user, wherein a heartbeat of the user is recognisable based on the first input signal; based on the first input signal, to determine, at the end of a first breathing cycle, if there is a negative rate of change in the heartbeat interval of the user and, if there is a negative rate of change in the heartbeat interval of the user, to control the breathing signal to increase the time period of the breathing cycle during which the user is guided to breathe in and breathe out; to receive a second input signal indicative of a second physiological property of the user, wherein a physiological response of the user to a perturbation of the cardiovascular system of the user during the breathing cycle is recognisable based on the second input signal; based on the second input signal, to determine, at the end of a second breathing cycle, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than a predetermined threshold and, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than the predetermined threshold, to control the breathing signal to reduce the time period of the breathing cycle during which the user is guided to breathe in and breathe out.

In an embodiment, the first input signal comprises plethysmographic data of the user.

In an embodiment, the circuitry is configured to receive the first input signal from a fingermountable photoplethysmography device.

In an embodiment, the second input signal comprises plethysmographic data of the user.

In an embodiment, the circuitry is configured to receive the second input signal from a fingermountable photoplethysmography device.

In an embodiment, the circuitry is configured to determine if there is a negative rate of change in the heartbeat interval of the user at the end of the first breathing cycle by determining whether the heartbeat interval at the end of the first breathing cycle is shorter than the previous heartbeat interval.

In an embodiment, based on the second input signal, the circuitry is configured to determine the amplitude of the respiratory sinus arrhythmia (RSA) at the end of the breathing cycle as an indicator of the physiological response of the user to the perturbation of the cardiovascular system of the user during the breathing cycle.

In an embodiment, the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is determined to be less than the predetermined threshold when the RSA at the end of the second breathing cycle is less than a value proportional to an average of the RSA of one or more other breathing cycles previous to the second breathing cycle.

In an embodiment, the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is determined to be less than the predetermined threshold when the RSA at the end of the second breathing cycle is less than A * weighted exponential average of the RSA of one or more other breathing cycles previous to the second breathing cycle, wherein A is a predetermined numerical factor.

In an embodiment, A is defined within the range 0.7 to 0.9.

In an embodiment, A = 0.9.

In an embodiment, the predetermined time period over which the breathing cycle is defined is initially defined so as to guide the user to complete between 6 and 16 breathing cycles per minute.

In an embodiment, the predetermined time period over which the breathing cycle is defined is initially defined so as to guide the user to complete 7.5 breathing cycles per minute.

In an embodiment, if there is a negative rate of change in the heartbeat interval at the end of the first breathing cycle, the breathing signal is controlled to increase the time period of the breathing cycle during which the user is guided to breathe in and breathe out by between 0.2 to 1.0 seconds.

In an embodiment, if there is a negative rate of change in the heartbeat interval at the end of the first breathing cycle, the breathing signal is controlled to increase the time period of the breathing cycle during which the user is guided to breathe in and breathe out by 0.2 seconds..

In an embodiment, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than the predetermined threshold, the breathing signal is controlled to reduce the time period of the breathing cycle during which the user is guided to breathe in and breathe out by between 0.2 to 1.0 seconds.

In an embodiment, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than the predetermined threshold, the breathing signal is controlled to reduce the time period of the breathing cycle during which the user is guided to breathe in and breathe out by 0.2 seconds.

In an embodiment, the breathing signal is configured to drive a display to guide the user to breathe in and breath out using a visual prompt.

In an embodiment, the visual prompt comprises an image of an object which gradually expands in size to guide the user to breathe in and which gradually reduces in size to guide the user to breathe out.

In an embodiment, the visual prompt comprises an image of a line which gradually moves in a first direction to guide the user to breathe in and which gradually moves in a second direction to guide the user to breathe out.

In an embodiment, the breathing signal is configured to drive a loudspeaker to guide the user to breathe in and breathe out using an audio prompt.

In an embodiment, the breathing signal is configured to drive a haptic feedback device to guide the user to breathe in and breathe out using a haptic prompt.

In an embodiment, wherein the circuitry is configured to transmit data determined based on one of the first and second input signals to an external device.

The present technique provides a method of guiding breathing of a user, the method comprising: outputting a breathing signal for guiding the user to breathe in and breathe out during a breathing cycle defined over a time period; receiving a first input signal indicative of a first physiological property of the user, wherein a heartbeat of the user is recognisable based on the first input signal; based on the first input signal, determining, at the end of a first breathing cycle, if there is a negative rate of change in the heartbeat interval of the user and, if there is a negative rate of change in the heartbeat interval of the user, controlling the breathing signal to increase the time period of the breathing cycle during which the user is guided to breathe in and breathe out; receiving a second input signal indicative of a second physiological property of the user, wherein a physiological response of the user to a perturbation of the cardiovascular system of the user during the breathing cycle is recognisable based on the second input signal; based on the second input signal, determining, at the end of a second breathing cycle, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than a predetermined threshold and, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than the predetermined threshold, controlling the breathing signal to reduce the time period of the breathing cycle during which the user is guided to breathe in and breathe out.

The present technique provides a program for controlling a computer to perform the abovementioned method.

The present technique provides a storage medium storing the above-mentioned program.

The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Figure 1 describes a known phenomenon of increased heart rate (decreased beat to beat intervals) during inhalation and decreased heart rate (increased beat to beat intervals) during exhalation of a user, known as respiratory sinus arrhythmia (RSA);

Figure 2 describes how the amplitude of the difference in heart rate during inhalation and exhalation (that is, the amplitude of the RSA) generally becomes more pronounced for slower breathing, but that breathing too slowly (in this example, 3 breaths per minute) attenuates the amplitude of RSA;

Figure 3 describes a device according to an embodiment of the present technique;

Figures 4A and 4B describe, respectively, an example of a visual prompt used for guiding a user to breathe in and breathe out and a change in lung volume as the user is guided to breathe in and breathe out; and

Figure 5 shows a flow chart showing a method according to the present technique.

DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.

The present technique generates a biofeedback signal (such as a visual, auditory or haptic signal provided by a suitable electronic device) to automatically guide a user to adopt a personalised, slower than normal breathing frequency during a slow breathing exercise (for example, approximately 6 breaths per minute rather than normal frequency at approximately 12 breaths per minute). This allows the above-mentioned potential beneficial effects of slow breathing to be realised more effectively for an individual user.

It is thought that breathing causes swings in intra-thoracic pressure that induce changes in venous return and cardiac stroke volume, changing cardiac haemodynamics, thereby inducing a highly individual perturbing influence that contributes to an acute physiological response. One example of such a physiological response is respiratory sinus arrhythmia (RSA) [3],

It is understood that the benefits of slow breathing are related to the way in which the abovementioned perturbation of the cardiovascular system is increased during slow breathing. Accordingly, it is desirable to drive breathing frequency dynamically in accordance with optimising a suitable measure of the extent to which breathing has perturbed the cardiovascular system. For example, when the amplitude of RSA is used as such a measure, breathing frequency may be adjusted automatically and dynamically during a slow breathing exercise of a user so as to maximise RSA. Thus, in one embodiment of the present technique, the breathing frequency of a user is driven up or down, breath-by-breath, in such a way that RSA amplitude increases. It is noted that, in this description, when a “value”, “measurement” or the like of RSA is mentioned, what is being referred to is the amplitude of RSA.

Although RSA is used as an example of a measured physiological response in the described embodiments, it will be appreciated that there are other physiological responses (which may be derivable from the same signal as RSA, for example, a photoplethysmographic (PPG) signal transmitted from a finger-mountable PPG device, including the morphological characteristics of the PPG signal itself), that change in accordance with the cardiovascular changes caused by breathing and which are thought to be driving the beneficial effects of slow breathing. That is, as an alternative to RSA, any other physiological response which is measurable based on one or more physiological properties of the body and which is responsive to perturbation of the cardiovascular system caused by breathing (for example, variations in cardiac stroke volume, pulse wave velocity and/or blood pressure perturbations) may be used with the present technique.

In one embodiment, the present technique works by synchronising the breathing of the user with beat to beat fluctuations in haemodynamic responses to said breathing. It differs from other systems that try to achieve this by operating in the phase domain. That is, a breathing stimulus is provided at a precise moment to add energy to the physiological control loop in the body comprising the baroreceptors, autonomic nervous system and the heart pacemaker. It does this by sensing continually the direction of change of the duration of adjacent beat to beat intervals (a beat to beat interval being represented by, for example, an R-R or P-P interval on an electrocardiogram (ECG)). When a person inhales, autonomic reflexes and intrinsic properties of the cardiovascular system cause the beat to beat intervals to shorten, and when they exhale, the same factors cause the beat to beat intervals to lengthen. This phenomenon of increased heart rate (decreased beat to beat intervals) during inhalation and decreased heart rate (increased beat to beat intervals) during exhalation is known as respiratory sinus arrhythmia (RSA), and is schematically illustrated in Figure 1 (in which HR is the heart rate and LV is the lung volume, which increases when a user inhales and decreases when a user exhales). RSA may be measured using any suitable method. For example, in one method, RSA may be measured as a difference between the minimum beat to beat interval during inhalation and the maximum beat to beat interval during exhalation. It can be seen from Figure 2 (taken from [4]) that the variability in heart rate during inhalation and exhalation generally becomes more pronounced for slower breathing, thus resulting in a general increase in measured RSA for slower breathing rates. It is also noteworthy in Figure 2, however, that when breathing frequency becomes too low (in this example, 3 breaths I minute), the heart rate variability (and therefore the RSA) diminishes. The present invention recognises this, and provides a dynamic breathing control system that is able to identify the correct breathing frequency for RSA maximisation, rather than one that simply drives breathing frequency lower (which may result in a diminishing of the RSA amplitude when the breathing frequency becomes too low).

In an embodiment, at the start of the slow breathing exercise, breathing is set to a rate that is comfortable for the target user group. This may be, for example, 7.5 breaths I minute, or possibly higher (for example, in the case of user groups with pathology such as lung or cardiovascular disease). More generally, the initial breathing rate may be set from within a range of 6 to 15 breaths per minute, depending on the target user group. More particularly, the initial breathing rate may be set from within a range of 6 to 14, 6 to 13, 6 to 12, 6 to 11, 6 to 10, 6 to 9, 6 to 8 or 6 to 7 breaths per minute. Alternatively, the initial breathing rate may be set from within a range of 7 to 14, 7 to 13, 7 to 12, 7 to 11, 7 to 10, 7 to 9, or 7 to 8 breaths per minute. The user is then guided to lower their breathing rate gradually during the session to maximise the potential beneficial effects. As mentioned above, this may involve monitoring and maximising the amplitude of, say, RSA, although other measures may also be used. Conversely, for the reasons mentioned in the previous paragraph, the breathing rate should not become too low for the user, as this is counterproductive.

In an embodiment, the user is provided with a guiding signal (such as a visual, auditory or haptic signal provided by a suitable electronic device, as mentioned above) for guiding the user’s breathing during each breath cycle. Each breath cycle has a certain duration and consists of an inhalation period in which the user is instructed to inhale and an exhalation period in which the user is instructed to exhale. The guiding signal thus changes automatically from instructing inhalation to instructing exhalation after a predetermined fraction of the total cycle duration, which may be 50%, or some other fraction. At the start of the breath cycle, a timer is started and the guiding signal provides a stimulus in response to which the user breathes in. This stimulus may be visual (such as a screen animation), an audio signal and/or a haptic signal. When the breath cycle duration is complete, the direction of the two most recent heartbeat intervals is sensed. If the most recent interval is shorter than the previous one, this is taken as a sign that the RSA amplitude could be increased if the breath duration is extended, and the subsequent breath cycle duration is increased slightly. The duration of the subsequent breath cycle may be increased by a value within a range of 0.2 to 1.0, 0.2 to 0.9, 0.2 to 0.8, 0.2 to 0.7, 0.2 to 0.6, 0.2 to 0.5, 0.2 to 0.4 or 0.2 to 0.3 seconds. More particularly, the duration of the subsequent breath cycle may be increased by 0.2 seconds.. On the other hand, if the most recent interval is not shorter, then the breath duration is kept constant. However, the breath duration may be extended if a subsequent breath cycle does meet the criterion mentioned above (that is, if the most recent heartbeat interval of that subsequent cycle is shorter than the previous heartbeat interval of that subsequent cycle).

During the guided breathing session, an overall measure of its effect upon a suitable physiological response (for example, RSA) is calculated. If extending the breath cycle duration does not produce a favourable change in the measured physiological response (for example, increase of RSA), then the breath duration will be reduced. The duration of the subsequent breath cycle may be reduced by a value within a range of 0.2 to 1.0, 0.2 to 0.9, 0.2 to 0.8, 0.2 to 0.7, 0.2 to 0.6, 0.2 to 0.5, 0.2 to 0.4 or 0.2 to 0.3 seconds. More particularly, the duration of the subsequent breath cycle may be increased by 0.2 seconds. The duration of the subsequent breath cycle may be reduced by the same amount by which it was increased previously. This helps to optimise the value of the measured physiological response. When RSA is measured as the physiological response, RSA is optimised by maximising the value of RSA. However, it will be appreciated that, if an alternative physiological response to RSA is measure, it may be that the value of a parameter indicative of this alternative physiological response is optimised by, for example, minimising the value, allowing the value to exceed or fall below a predetermined threshold value or allowing the value to approach a predetermined reference value.

An example of a device 300 for implementing the present technique is shown in Figure 3. The device comprises output circuitry 301, input circuitry 302, communication circuitry 307 and a processor 303. The output circuitry 301 and input circuitry 302 are controlled by the processor 303.

The output circuitry 301 outputs a breathing signal S₃ for guiding the user to breathe in and breathe out during a breathing cycle defined over a time period. In this case, the breathing signal is output to a display 306 for displaying a visual prompt to guide the user to breathe in and out. However, it will be appreciated that the breathing signal may instead or in addition be output to another device such as a loudspeaker 308 and/or suitable haptic feedback device 309 (in this example, a vibrating device 309 (vibrator)) in order to provide an audio and/or haptic prompt to guide the user to breath in and breathe out. It will be appreciated that the breathing signal S₃ need only be output to one of the display 306, loudspeaker 308 and haptic feedback device 309 (and thus only one of the display 306, loudspeaker 308 and haptic feedback device 309 need be present in embodiments).

The input circuitry 302 receives a first input signal Si indicative of a first physiological property of the user, wherein a heartbeat of the user is recognisable based on the first input signal. The first input signal Si is received from a first sensor 304 configured to measure the first physiological property of the user. In an embodiment, the first sensor 304 is a plethysmography device such as a finger-mountable photoplethysmography device. In this case, the first input signal Si comprises plethysmographic data of the user (and the first physiological property is the volume of a part of user’s body such as blood vessels in the user’s finger). However, it will be appreciated that a different type of sensor may be used as the first sensor 304, as long as the user’s heartbeat is recognisable based on the first input signal Si generated by that sensor. For example, an electrocardiogram (ECG) sensor may be used, thus providing a first input signal Si comprising ECG data (in this case, the first physiological property is electrical activity of the user’s heart). The first sensor 304 could also be a sensor for generating a ballistocardiogram, impedance cardiogram or sonic cardiogram sensor, for example. The first sensor 304 could also be, for example, a sensor which implements contactless optical methods that employ cameras to detect ‘microblushes’ in the skin (particularly the face) (for example, as implemented in the VitalSigns Camera from Philips ®, see http://www.ip.philips.com/licensing/program/115).

Based on the first input signal Si, the processor 303 determines, at the end of a first breathing cycle, if there is a negative rate of change in the heartbeat interval of the user. If there is negative a rate of change in the heartbeat interval of the user, the processor 303 controls the output breathing signal to increase the time period of the breathing cycle during which the user is guided to breathe in and breathe out. That is, the user is prompted to breathe in and breathe out at a slower rate. The determination of a negative rate of change in the heartbeat interval may be made using any suitable technique. For example, it may be determined that there is a negative rate of change at the end of the first breathing cycle when the heartbeat interval at the end of the first breathing cycle is shorter than the previous heartbeat interval (in particular, the temporally adjacent previous heartbeat interval). The heartbeat interval at the end of the first breathing cycle is the final measured heartbeat interval prior to the end of the first breathing cycle, for example.

The input circuitry 302 receives a second input signal S₂ indicative of a second physiological property of the user, wherein a physiological response of the user to a perturbation of the cardiovascular system of the user during the breathing cycle (for example, to a perturbation of cardiac stroke volume, pulse wave velocity and/or blood pressure) is recognisable based on the second input signal. The second input signal S₂ is received from a second sensor 305 configured to measure the second physiological property of the user. In an embodiment, the second sensor 305 is a plethysmography device such as a finger-mountable photoplethysmography device. In this case, the second input signal S₂ comprises plethysmographic data of the user (and the second physiological property is the volume of a part of user’s body such as blood vessels in the user’s finger). However, it will be appreciated that a different type of sensor may be used as the second sensor 305, as long as a physiological response of the user (as indicated by RSA, for example) to a perturbation of the cardiovascular system of the user during the breathing cycle is recognisable based on the second input signal S₂ generated by that sensor. For example, an electrocardiogram (ECG) sensor may be used, thus providing a second input signal S₂ comprising ECG data (in this case, the second physiological property is electrical activity of the user’s heart). The second sensor 305 could also be a sensor for generating a ballistocardiogram, impedance cardiogram or sonic cardiogram sensor, for example. The second sensor 304 could also be, for example, a sensor which implements contactless optical methods that employ cameras to detect ‘microblushes’ in the skin (particularly the face) (for example, as implemented in the VitalSigns Camera from Philips ®, see http://www.ip.philips.com/licensing/’program/115). It will be appreciated that there may be a single sensor (for example, a single plethysmography or ECG device) which carries out the function of both the first and second sensors 304 and 305. In this case, the first and second input signals Si and S₂ are the same input signal. Alternatively, the first and second sensors 304 and 305 may be physically separate sensors and, furthermore, may be different types of sensor. For example, the first sensor 304 may be a plethysmography sensor and the second sensor 305 may be an ECG sensor, or vice versa.

In the case that one of the first and second sensors is a plethysmography device such as a finger-mountable PPG sensor and the other of the first and second sensors is an ECG device (such as, for example, an AliveCor Kardia Band ® ECG device), supplementary information to that determined on the basis of the first and second signals Si and S₂ may be derived. For example, upon the start of each heartbeat, there is a delay in the recognition of the start of the heartbeat by the plethysmography device compared to the recognition of the start of the heartbeat by the ECG device. This is because the ECG device detects the start of the heartbeat based on an electrical signal whereas the plethysmography device detects the start of the heartbeat based on a pressure change in blood vessels at the part of the user’s body at which the plethysmography device is used (e.g. the finger), and the electrical signal travels faster than the pressure pulse from the heartbeat which results in the blood vessel pressure change. It is known that this delay is proportional to the stiffness of the blood vessels of the user, thus allowing supplementary information relating to the stiffness of the blood vessels of the user to be determined. This stiffness can be related to the magnitude of the effect exerted by breathing upon the cardiovascular system. It will thus be appreciated that using a different type of sensor for each of the first and second sensors 304 and 305 may allow further physiological information relating to the user to be determined whilst the user undertakes a breathing exercise in accordance with the present technique. Said information could also be used to determine the breathing rate.

Based on the second input signal, the processor 303 determines, at the end of a second breathing cycle subsequent to the first breathing cycle (in particular, a temporally adjacent subsequent breathing cycle to the first breathing cycle), if the physiological response of the user to a perturbation of the cardiovascular system of the user (such as a perturbation of cardiac stroke volume, pulse wave velocity and/or blood pressure) during the second breathing cycle is less than a predetermined threshold. If the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than the predetermined threshold, the processor 303 controls the breathing signal to reduce the time period of the breathing cycle during which the user is guided to breathe in and breathe out. That is, the user is prompted to breathe in and breathe out at a faster rate.

As previously mentioned, the respiratory sinus arrhythmia (RSA) at the end of the breathing cycle may be used as an indicator of the physiological response of the user to a perturbation of the cardiovascular system of the user (such as a perturbation of the cardiac stroke volume, pulse wave velocity and/or blood pressure of the user) during the breathing cycle. The physiological response of the user to the perturbation of the cardiovascular system during the second breathing cycle is then determined to be less than the predetermined threshold when the RSA at the end of the second breathing cycle is less than a value proportional to an average of the RSA of the first breathing cycle and one or more other breathing cycles previous to the second breathing cycle. In one example, this value may be A * weighted exponential average of the RSA of the first breathing cycle and one or more other breathing cycles previous to the second breathing cycle, where A is a predetermined factor. In one example, A is set to be within the range 0.7-0.95. More particularly, A may be set to be within the range 0.7 to 0.9. More particularly, A may be set to be within the range 0.8 to 0.9. More particularly, A may be set to be 0.9. Such values (and, in particular, A = 0.9) allows larger reductions in RSA (for example, reductions of more than 0.1 * weighted exponential average of previous RSA values when A = 0.9) to cause a decrease in the length of the breathing cycle whilst not reducing the length of the breathing cycle in the case of smaller reductions in RSA (for example, reductions of less than 0.1 * weighted exponential average of previous RSA values when A = 0.9). This helps to reduce the effect of small changes in RSA which occur due to natural fluctuations, measurement errors or the like which do not represent a sufficiently large reduction in RSA to warrant reducing the length of the breathing cycle. In one example, the average (such as the weighted exponential average) of the RSA for each breathing cycle previous to the second breathing cycle may be used. As previously mentioned, the RSA for each breathing cycle may be calculated by the processor 303 as the difference between the minimum beat to beat interval during inhalation and the maximum beat to beat interval during exhalation forthat breathing cycle. It is noted that a user’s heartbeat (and therefore heartbeat intervals and RSA) are detectable from photoplethysmography and/or ECG signals using techniques known in the art. For the sake of brevity, such techniques are not discussed in detail here.

It will be appreciated that the processor 303 may comprise various sub-units for providing functionality in accordance with embodiments of the present disclosure as explained further herein. These sub-units may be implemented as discrete hardware elements or as appropriately configured functions of the processor 303. Thus the processor 303 may be suitably configured I programmed to provide the desired functionality described herein using conventional programming I configuration techniques for equipment in wireless telecommunications systems. The output circuitry 301, input circuitry 302 and processor 303 are schematically shown in Figure 3 as separate elements for ease of representation. However, it will be appreciated that the functionality of these units can be provided in various different ways, for example using a single suitably programmed general purpose computer, or suitably configured applicationspecific integrated circuit(s) I circuitry. It will be appreciated the device 300 will in general comprise various other elements associated with its operating functionality, for example a power source, user interface, and so forth, but these are not shown in Figure 3 in the interests of simplicity. It will also be appreciated that the display 306 (for example, a liquid crystal display) and sensors 304 and 305 may be comprised as part of the device 300 or may be separate devices connected to the device 300 such that wired and/or wireless signals may be transmitted between the device 300 and each of the display 306 and sensors 304 and 305. In the embodiment described below, the device 300 is a smartphone (such as an iOS ® or Android ® device) comprising a display 306 and in which the present technique is implemented as a software application (or “app”). The functionality of the sensors 304 and 305 is provided by a single finger-mountable photoplethysmography sensor which connects to the smartphone via, for example, a 3.5mm headphone jack (not shown). Examples of such sensors include the ithlete Finger Sensor (available from www.myithlete.com) or other devices available from manufacturers such as Philips ®, Massimo ® and Nelcor®. Wired sensors (such as those which connect to the device 300 via a 3.5mm headphone jack) with a low and predictable latency are particularly suitable for use with the present technique. Alternatively, the smartphone may comprise equipment (such as a camera) which may be used as a photoplethysmography sensor when a user places a part of their body (such as a finger) on it. It will be appreciated, however, that the device 300 may be any other suitable device such as personal computer, laptop, wearable device (such as a smartwatch or the like) or tablet computer.

Figures 4A and 4B schematically show an example of a visual prompt used for guiding a user to breathe in and breathe out in response to the output breathing signal S₃. In this case, the device 300 is a smartphone and the display 306 is a display of the smartphone (which may be comprised as part of a touchscreen, for example).

The visual prompt comprises an image of an object which gradually expands in size to guide the user to breathe in and which gradually reduces in size to guide the user to breathe out. In this case, the object is a shaded area 401 underneath a Gaussian-style curve 402. As the object expands in size (indicating to the user to breathe in), the peak of the curve becomes greater, resulting in a greater shaded area 401. The position of the curve 401 when it is at its maximum peak is represented on the screen by dashed curve 400. Various positions of the curve which occur during a single breathing cycle are shown in Figure 4A. The breathing cycle itself is illustrated in Figure 4B, which schematically shows how the lung volume of the user changes during the breathing cycle. Each breathing cycle comprises a first time period T| in which the user breathes in (inhales) and a second time period T_E in which the user breathes out (exhales). The total time period of the breathing cycle is denoted T| + T_E = T_s. It will be appreciated that Figure 4B represents a highly simplified diagram of the change in lung volume over the breathing cycle for the sake of clarity. In reality, the lung volume may change differently due to a number of physiological factors which vary between individual users.

The breathing of the user is guided by the movement of the curve 402 and the corresponding expansion and contraction of the shaded area 401. That is, the user controls their breathing (in particular, when to inhale and for how long, and when to exhale and for how long) in response to the movement of the curve 402 so as to breathe at a rate as indicated by the breathing signal

S₃. At time fl, it is close to the beginning of the breathing cycle and the user is breathing in. The curve 402 is positioned such that its peak is relatively low and such that the shaded area 401 is relatively small. At this point, the user’s lungs have reached a comfortable, relaxed exhalation volume. At a later time t₂, the curve is positioned such that its peak is higher and such that the shaded area 401 has increased in size. At this point, the user’s lungs are approximately half full of air. At a later time t₃, the curve 402 is positioned such that it is aligned with the position of maximum peak denoted by dashed curve 400 and such that the shaded area 401 is at its maximum size. At this point, the user’s lungs have reached a comfortable fullness, the volume of which is determined by the user’s breathing control system (brainstem, chemoreceptors and lung volume receptors), which adjusts breathing volume automatically to take account of changes in breathing frequency. This marks the end of the inhale period T|. At a later time t4, the curve 402 returns to being positioned such that its peak is lower than at the maximum peak curve positioned marked by dashed line 400 and such that the shaded area 401 is no longer at its maximum size. At this point, the user’s lungs have a reduced amount of air compared to the maximum amount of air allowed by the breathing cycle. This is because the exhale period T_Ehas started and therefore the user is now breathing out. At a later time t₅, the curve 402 is positioned such that its peak is lower and such that the shaded area 401 is further reduced in size. At this point, the user’s lungs have a further reduced amount of air. Finally, at a later time te, the end of the exhale period T_E and the end of the breathing cycle is reached. At this point, the curve 402 becomes a flat line and the size of the shaded area 401 is reduced to zero. At this point, the user’s lungs are empty of air. It is noted that, although not shown, the curve 402 will have been a flat line and the size of the shaded area 401 will have been zero previously at time 0 at the start of the breathing cycle shown in Figure 4B.

Thus, throughout the breathing cycle, the user is instructed to inhale or exhale at an appropriate time based on the moving curve 402 and expanding and contracting shaded area 401. Because of the dashed line 400, the user is also able to predict when the inhale period becomes the exhale period. Such an arrangement allows the user to easily and conveniently follow the breathing rate determined by the processor 303 according to the above-mentioned embodiments and signalled by the breathing signal S₃. In one embodiment, although not shown, the user may, in addition to the moving curve 402 shown in Figures 4A and 4B, be prompted with suitable visual or audio messages at the points in time at which to start inhaling or exhaling. For example, at time t₀, the user may be presented with the message “Breath in” on the display 306 and/or an audio cue, and/or a haptic cue. At time t₃, the user may be presented with the message “Breath Out” on the display 306 and/or an audio cue, and/or a haptic cue.

In the example of Figures 4A and 4B, the breathing signal S₃ is, for example, a signal for driving the display 306 to display the moving curve 402 and expanding and contracting shaded area 401. The moving curve 402 and expanding and contracting shaded area 401 may be rendered as a moving computer graphic by the processor 303 with an expansion and contraction rate which is equal to the desired breathing rate determined by the processor 303. Techniques for generating such graphics are known in the art and are therefore not described in detail here. It will be appreciated that, although Figure 4A only shows the curve 402 and shaded area 401 at discrete points in time during the breathing cycle, the curve 402 is actually re-positioned at a rate (equivalent to 15, 30, 50 or 60 frames per second, for example) such that its motion appears to be continuous (fluid) on the display 306. This makes it easier for the user to follow the determined breathing rate.

It will be appreciated that, although the shaded area 401 is shown as being shaded (crosshatched) in the drawings, in reality, when displayed on a colour display (for example), it will be shown in a distinctive colour which distinguishes it from the background colour of the display). It will also be appreciated that, rather than having both the curve 402 and shaded area 401, only one of the curve 402 (or, more generally, a line which moves in one direction to indicate inhale and the opposite direction to indicate exhale) and shaded area 401 may be used to prompt the user to inhale and exhale. It will furthermore be appreciated that any other suitable visual prompt may be used instead of the curve 402 and/or shaded area 401. For example, a coloured circle which expands and contracts in a radial direction (akin to a ball alternately inflating and deflating or the like) may be used to guide the user’s breathing.

It will be appreciated that, in other embodiments in which the user is prompted to breathe in and out and the determined breathing rate via an audio and/or haptic signal, the breathing signal S₃will take an appropriate alternative form. For example, in the case of an audio signal, the breathing signal S₃ may be an electronic audio signal which is transmitted to loudspeaker 308. The loudspeaker 308 may be a loudspeaker comprised within the device 300 when the device is a smartphone, for example, or may be a separate device connected to the device 300 via any suitable wired or wireless connection (for example, via a Universal Serial Bus (USB) ® or Lightening ® wired connection or Bluetooth ® wireless connection when the device 300 is a smartphone or tablet computer). The electronic audio signal is generated by the processor 303 and comprises, for example, a voice which says “breathe in, two, three, four” followed by “breath out, two, three four”, or an audio tone with distinct, dynamically changing characteristics during inhale and exhale, or similar in order to guide the user to breathe at the determined breathing rate. In another example, in the case of a haptic signal, the breathing signal S₃ may be an electric pulse signal which controls vibrator 309 to vibrate each time the user is to begin inhaling and begin exhaling (that is, a first pulse indicates to begin inhaling, a second pulse indicates to begin exhaling, a third pulse indicates to begin inhaling again, a fourth pulse indicates to begin exhaling again, and so on), or to vibrate with a vibration that changes vibrational frequency such that the vibrational frequency, for example, increases during inhale and decreases during exhale. This guides the user to breathe at the determined breathing rate. The vibrator 309 may be integral to the device (such as the vibrator comprised within devices such as smart phones for alerting the user to calls, messages and the like), or may be a separated device connected to the device 300 via any suitable wired or wireless connection (for example, via a Universal Serial Bus (USB) ® or Lightening ©wired connection or Bluetooth ® wireless connection when the device 300 is a smartphone or tablet computer). It will be appreciated that the breathing signal S₃ may be generated by the processor 303 based on the above-mentioned embodiments in any suitable way depending on the way in which a user is to be notified (prompted) to breathe in and breathe out and the determined breathing rate. In an embodiment, the type of signal output to the user (be it visual, audio and/or haptic) is selectable by the user in advance using, for example, an interactive menu system (not shown) displayed on the display 306.

Figure 5 shows a flow chart showing a method according to the present technique. The method of Figure 5 may be implemented by the processor 303, for example. The method starts at step 500. At step 501, a breathing signal is output for guiding the user to breathe in and breathe out during a breathing cycle defined over a time period. At step 502, a first input signal indicative of a first physiological property of the user is received, wherein a heartbeat of the user is recognisable based on the first input signal. At step 503, it is determined, based on the first input signal and at the end of a first breathing cycle, if there is a negative rate of change in the heartbeat interval of the user. If there is a negative rate of change in the heartbeat interval of the user, then, at step 504, the breathing signal is controlled to increase the time period of the breathing cycle during which the user is guided to breathe in and breathe out. The method then proceeds to step 505. On the other hand, if there is not a negative rate of change in the heartbeat interval of the user, then the process proceeds straight to step 505 (without step 504 being implemented). At step 505, a second input signal indicative of a second physiological property of the user is received, wherein a physiological response of the user to a perturbation of the cardiovascular system of the user during the breathing cycle is recognisable based on the second input signal. At step 506, it is determined, based on the second input signal and at the end of a second breathing cycle subsequent to the first breathing cycle, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than a predetermined threshold. If the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than the predetermined threshold, then the method proceeds to step 507. At step 507, the breathing signal is controlled to reduce the time period of the breathing cycle during which the user is guided to breathe in and breathe out. The method then ends at step 508. On the other hand, at step 506, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is not less than the predetermined threshold, then the process ends at step 508 (without step 507 being implemented).

In an embodiment, at a given breathing frequency (which defines an associated breathing cycle time period), the breathing cycle time period may only be increased if it is the second or subsequent breathing cycle at that breathing frequency. That is, although not shown, there may be an extra step between steps 501 and 502 which determines whether the current breathing cycle is a second or subsequent breathing cycle at the current breathing frequency. In the case that the current breathing cycle is a second or subsequent breathing cycle at the current breathing frequency, the process then proceeds to step 502. On the other hand, in the case that the current breathing cycle is not a second or subsequent breathing cycle at the current breathing frequency (that is, it is the first breathing cycle at the current breathing frequency), then the process proceeds direction to step 505 (skipping steps 502, 503 and 504, thus alleviating the processing burden of the processor 303 in carrying out these steps).

It will be appreciated that variations in the above-mentioned method are possible. For example, in the even of a “No” decision at step 503 (indicating that there is not a negative rate of change in the heartbeat interval of the user at the end of the first cycle), the method may simply end at step 508 (thus skipping the steps 504, 505, 506 and 507).

In the above-mentioned embodiments, it is determined as to whether there is a negative rate of change in the heartbeat interval (and therefore that the time period of the breathing cycle should be increased) at the end of a first breathing cycle and it is determined as to whether a physiological response of the user to a perturbation of the cardiovascular system during the breathing cycle is less than a predetermined threshold (and therefore the time period of the breathing cycle should be reduced) at the end of a second breathing cycle, the second breathing cycle being subsequent to the first breathing cycle. It may be the case, however, that the first and second breathing cycles are the same breathing cycle. In this case, a negative rate of change in the heartbeat interval at the end of the breathing cycle will result in the time period of the breathing cycle being increased whilst, at the same time, a physiological response of the user to a perturbation of the cardiovascular system during the breathing cycle being less than a predetermined threshold will result in the time period of the breathing cycle being reduced. If the amount by which the breathing cycle is increased and decreased is the same, the net result will be that the time period of the breathing cycle remains unchanged.

Such an arrangement recognises that many users will not follow every breathing cycle perfectly throughout the session. This may result in, for example, there being a false determination of a negative rate of change in the heartbeat interval at the end of a breathing cycle (if the user does not follow the breathing prompt exactly, then a negative rate of change in the heartbeat interval at another point during the breathing cycle may be incorrectly determined to have occurred at the end of the breathing cycle). Thus, by determining both whether there has been a negative rate of change in the heartbeat interval and whether a physiological response of the user to a perturbation of the cardiovascular system during the breathing cycle is less than a predetermined threshold at the end of the same breathing cycle, the breathing cycle time period will only be increased if the physiological response of the user to a perturbation of the cardiovascular system during the breathing cycle (as measured by RSA, for example) is not below the predetermined threshold. This helps to ensure that a user’s breathing rate only continues to be reduced if there are likely to be continued benefits to doing so.

In an embodiment, data generated by the device 300 may be transmitted to an external device (such as a server - not shown) for storage and/or analysis. The processor circuitry 303 controls the communication circuitry 307 to transmit such data. The communication circuitry 307 may be configured to transmit data using any suitable wired or wireless method. Such methods include Ethernet ®, Wi-Fi ®, Bluetooth ® or cellular communication methods such as Long Term Evolution (LTE), for example. The data may be transmitted from the device 300 to the external device over a network such as the internet. Data that may be transmitted may include, for example, how often the user conducts a slow breathing exercise using the device 300 and their optimal slow breathing rate during each slow breathing exercise conducted. Other information such as heart rate, RSA amplitude or any other data determinable by the device 300 may be transmitted to the external device. By transmitting such data to the external device, the user is able to, for example, retrieve this data using another device (not shown) which is connectable to the external device. For example, if the device 300 is the user’s smartphone (such as an iPhone ®) and the user also owns a tablet computer (such as an iPad ®) or laptop computer, then, once the data has been transmitted to the external device, the user is also able to retrieve that data from the external device using their tablet or laptop computer. The data is therefore easily and conveniently retrievable using more than one device accessible by the user. It is also envisaged that the user’s data may also be accessed by an authorised third party, such as a healthcare professional. This would allow the healthcare professional to monitor the user’s data (such as how often they are conducting slow breathing exercises and their optimal slow breathing rate) so as to determine the extent of the beneficial effects of the present technique. The data stored at the external device may be secure such that it is only accessible by authorised parties. Such parties include the user themselves and any other party (e.g. a healthcare professional) who the user has authorised to access their data. An authentication process involving the need for a username and password (for example) for each authorised user may be implemented at the external device in order to help ensure the security of the user’s data. Such authentication processes are known in the art, and are therefore not discussed here.

Thus, with the present technique, a user’s breathing is dynamically guided during a slow breathing exercise in an automatic, easy and intuitive way so as to maximise the potential benefits of conducting such slow breathing exercises.

Numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced otherwise than as specifically described herein.

In so far as embodiments of the disclosure have been described as being implemented, at least in part, by software-controlled data processing apparatus, it will be appreciated that a nontransitory machine-readable medium carrying such software, such as an optical disk, a magnetic disk, semiconductor memory or the like, is also considered to represent an embodiment of the present disclosure.

It will be appreciated that the above description for clarity has described embodiments with reference to different functional units, circuitry and/or processors. However, it will be apparent that any suitable distribution of functionality between different functional units, circuitry and/or processors may be used without detracting from the embodiments.

Described embodiments may be implemented in any suitable form including hardware, software, firmware or any combination of these. Described embodiments may optionally be implemented at least partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of any embodiment may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the disclosed embodiments may be implemented in a single unit or may be physically and functionally distributed between different units, circuitry and/or processors.

Although the present disclosure has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in any manner suitable to implement the technique.

REFERENCES

Γ1Ί____Zou, Y., Zhao, X., Hou, Y. Y., Liu, T., Wu, Q., Huang, Y. H., etal. (2017). Meta-Analysis of Effects of Voluntary Slow Breathing Exercises for Control of Heart Rate and Blood Pressure in Patients With Cardiovascular Diseases. Am J Cardiol, 120(1), 148-153.

[2] Perciavalle, V., Blandini, M., Fecarotta, P., Buscemi, A., Di Corrado, D., Bertolo, L., et al. (2017). The role of deep breathing on stress. [Randomized Controlled Trial], Neurol Sci, 38(3), 451-458.

[3] Elstad, M. (2012). Respiratory variations in pulmonary and systemic blood flow in healthy humans. [Research Support, Non-U.S. Gov't], Acta Physiol (Oxf), 205(3), 341-348.

[4] Song, H and Lehrer, P. (2003). The Effects of Specific Respirator Rates on Heart Rate and Heart Rate Variability. Applied Psychophysiology and Biofeedback 28(1), 13-23.

Claims

1. A device for guiding breathing of a user, the device comprising circuitry configured:

to output a breathing signal for guiding the user to breathe in and breathe out during a breathing cycle defined over a time period;

to receive a first input signal indicative of a first physiological property of the user, wherein a heartbeat of the user is recognisable based on the first input signal;

based on the first input signal, to determine, at the end of a first breathing cycle, if there is a negative rate of change in the heartbeat interval of the user and, if there is a negative rate of change in the heartbeat interval of the user, to control the breathing signal to increase the time period of the breathing cycle during which the user is guided to breathe in and breathe out;

to receive a second input signal indicative of a second physiological property of the user, wherein a physiological response of the user to a perturbation of the cardiovascular system of the user during the breathing cycle is recognisable based on the second input signal;

based on the second input signal, to determine, at the end of a second breathing cycle, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than a predetermined threshold and, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than the predetermined threshold, to control the breathing signal to reduce the time period of the breathing cycle during which the user is guided to breathe in and breathe out.

2. A device according to claim 1, wherein the first input signal comprises plethysmographic data of the user.

3. A device according to claim 2, wherein the circuitry is configured to receive the first input signal from a finger-mountable photoplethysmography device.

4. A device according to any preceding claim, wherein the second input signal comprises plethysmographic data of the user.

5. A device according to claim 4, wherein the circuitry is configured to receive the second input signal from a finger-mountable photoplethysmography device.

6. A device according to any preceding claim, wherein the circuitry is configured to determine if there is a negative rate of change in the heartbeat interval of the user at the end of the first breathing cycle by determining whether the heartbeat interval at the end of the first breathing cycle is shorter than the previous heartbeat interval.

7. A device according to any preceding claim, wherein, based on the second input signal, the circuitry is configured to determine the amplitude of the respiratory sinus arrhythmia (RSA) at the end of the breathing cycle as an indicator of the physiological response of the user to the perturbation of the cardiovascular system of the user during the breathing cycle.

8. A device according to claim 7, wherein the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is determined to be less than the predetermined threshold when the RSA at the end of the second breathing cycle is less than a value proportional to an average of the RSA of one or more other breathing cycles previous to the second breathing cycle.

9. A device according to claim 8, wherein the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is determined to be less than the predetermined threshold when the RSA at the end of the second breathing cycle is less than A * weighted exponential average of the RSA of one or more other breathing cycles previous to the second breathing cycle, wherein A is a predetermined numerical factor.

10. A device according to claim 8, wherein A is defined within the range 0.7 to 0.9.

11. A device according to claim 10, wherein A = 0.9.

12. A device according to any preceding claim, wherein the predetermined time period over which the breathing cycle is defined is initially defined so as to guide the user to complete between 6 and 16 breathing cycles per minute.

13. A device according to claim 12, wherein the predetermined time period over which the breathing cycle is defined is initially defined so as to guide the user to complete 7.5 breathing cycles per minute.

14. A device according to any preceding claim, wherein, if there is a negative rate of change in the heartbeat interval at the end of the first breathing cycle, the breathing signal is controlled to increase the time period of the breathing cycle during which the user is guided to breathe in and breathe out by between 0.2 to 1.0 seconds.

15. A device according to claim 14, wherein, if there is a negative rate of change in the heartbeat interval at the end of the first breathing cycle, the breathing signal is controlled to increase the time period of the breathing cycle during which the user is guided to breathe in and breathe out by 0.2 seconds..

16. A device according to any preceding claim, wherein, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than the predetermined threshold, the breathing signal is controlled to reduce the time period of the breathing cycle during which the user is guided to breathe in and breathe out by between 0.2 to 1.0 seconds.

17. A device according to any preceding claim, wherein, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than the predetermined threshold, the breathing signal is controlled to reduce the time period of the breathing cycle during which the user is guided to breathe in and breathe out by 0.2 seconds.

18. A device according to any preceding claim, wherein the breathing signal is configured to drive a display to guide the user to breathe in and breath out using a visual prompt.

19. A device according to claim 18, wherein the visual prompt comprises an image of an object which gradually expands in size to guide the user to breathe in and which gradually reduces in size to guide the user to breathe out.

20. A device according to claim 18 or 19, wherein the visual prompt comprises an image of a line which gradually moves in a first direction to guide the user to breathe in and which gradually moves in a second direction to guide the user to breathe out.

21. A device according to any preceding claim, wherein the breathing signal is configured to drive a loudspeaker to guide the user to breathe in and breathe out using an audio prompt.

22. A device according to any preceding claim, wherein the breathing signal is configured to drive a haptic feedback device to guide the user to breathe in and breathe out using a haptic prompt.

23. A device according to any preceding claim, wherein the circuitry is configured to transmit data determined based on one of the first and second input signals to an external device.

24. A method of guiding breathing of a user, the method comprising:

outputting a breathing signal for guiding the user to breathe in and breathe out during a breathing cycle defined over a time period;

receiving a first input signal indicative of a first physiological property of the user, wherein a heartbeat of the user is recognisable based on the first input signal;

based on the first input signal, determining, at the end of a first breathing cycle, if there is a negative rate of change in the heartbeat interval of the user and, if there is a negative rate of change in the heartbeat interval of the user, controlling the breathing signal to increase the time period of the breathing cycle during which the user is guided to breathe in and breathe out;

receiving a second input signal indicative of a second physiological property of the user, wherein a physiological response of the user to a perturbation of the cardiovascular system of the user during the breathing cycle is recognisable based on the second input signal;

based on the second input signal, determining, at the end of a second breathing cycle, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than a predetermined threshold and, if the physiological response of the user to the perturbation of the cardiovascular system of the user during the second breathing cycle is less than the predetermined threshold, controlling the breathing signal to reduce the time period of the breathing cycle during which the user is guided to breathe in and breathe out.

25. A program for controlling a computer to perform a method according to claim 24.

26. A storage medium storing a program according to claim 25.