WO2005020808A1

WO2005020808A1 - Blood pressure monitor

Info

Publication number: WO2005020808A1
Application number: PCT/GB2004/003655
Authority: WO
Inventors: Caroline Meyer
Original assignee: University Of Warwick
Priority date: 2003-08-29
Filing date: 2004-08-27
Publication date: 2005-03-10
Also published as: GB0320297D0

Abstract

Blood pressure (BP) does not remain constant over time and may be influenced by a wide range of factors, including stress. Therefore a BP measurement of a stressed person may not reflect their normal BP and may lead to misdiagnosis of high blood pressure. The invention provides a blood pressure monitoring apparatus comprising blood pressure monitoring equipment for determining the blood pressure of a patient; stress measuring equipment for determining the level of stress of the patient; and processing means for comparing the level of stress indicated by the patient with the blood pressure reading for the patient, to produce a corrected blood pressure reading.

Description

Blood Pressure Monitor

The invention relates to a blood pressure monitor, methods of monitoring blood pressure and to methods of monitoring stress therapy.

Blood pressure (BP) measurement is routinely used as an index for cardiac function. As such, BP monitoring provides an important diagnostic tool to evaluate a patient's health. Accurate measurement of BP allows for careful diagnosis of physical conditions such as hypertension (elevated blood pressure), which may result from a person's lifestyle, ageing or disease. The possible consequences of hypertension are numerous, including circulatory disorders, arteriosclerosis, renal failure, stroke and myocardial infarction.

Blood pressure does not remain constant over time. Not only does BP fluctuate during the pumping cycle of the heart, but it is also influenced by a wide range of factors. These factors include activity level, temperature, pain, the presence of drugs, recent eating or drinking, recent smoking and stress. Although many of these transient factors are easily controlled, such as by restriction of food intake prior to measurement, the impact of stress and anxiety is not so readily managed. Due to this influence of stress on BP, there is now a common, well-established condition known as "white coat hypertension" (WCH).

White coat hypertension refers to a transient elevation of blood pressure due to the presence of a physician or nurse, or surgery/clinic environment that is sufficient to promote a significant elevation in BP. This is discussed, for example, in the article by Carel R A, et al, JAMA (1998), Vol. 271, No. 3. The presence of WCH is of utmost concern since it can lead to diagnostic errors and prescription of unnecessary hypertensive medication. Recent evidence suggests that up to one third of patients diagnosed with hypertension, and up to 60% of people with untreated hypertension, suffer from WCH. In addition, WCH has been found to be associated with metabolic risk factors and high mortality rates. There is therefore a need for a blood pressure monitoring system that can provide additional diagnostic information to enable doctors to differentiate between individuals with WCH and those with sustained hypertension. Traditionally, blood pressure has been monitored using a sphygmomanometer. This measures arterial blood-pressure, and involves the inflation of a cuff in order to occlude the blood vessels in a limb, such as the upper arm. The cuff is subsequently deflated. During deflation, a practitioner uses a stethoscope to listen for the Korotcoff sounds (K-sounds). Different identifiable K-sounds in conjunction with their corresponding cuff pressures (usually measured by a mercury sphygmomanometer) provide a single meter reading. There are also several automated blood pressure monitors which generally utilise a pressure sensor to measure cuff pressure, in place of a mercury sphygmomanometer. One example of such a device is shown in US 5,222,020. Such automated devices also have the advantage that measurements can be displayed on a screen, such as a liquid crystal display (LCD). They may also be used to generate data which may be sent to monitoring equipment, such as a computer, or to a remote location via telephone lines.

Other devices may use needles or catheters inserted directly into the aorta or other blood vessels. The needle or catheter is then attached to a pressure transducer in order to measure the blood pressure.

Attempts to overcome the impact of white coat hypertension have been made. These devices tend to use several blood pressure measurements and then provide a mean of these values. In addition, it is well established that the first meter reading in any series of readings is likely to be higher than subsequent values. Accordingly, such devices sometimes ignore the first measurement of the sequence of measurements. One example of such a device is shown in WO 00/76393.

The use of multiple measurements has several drawbacks. In particular, it is a relatively lengthy procedure. Such meter readings should be separated by one or two minutes to allow the release of blood traps in the vessel. If this procedure is not followed, the reading is subject to unreliability. In addition, ambulatory readings are often taken over a 24-hour period, where the patient is allowed to self-monitor at home away from the clinical situation. Such techniques are subject to error or manipulation by the patient and are costly due to need to loan equipment. The inventor has realised that there is a need to provide doctors with additional diagnostic information besides a simple BP reading to enable them to overcome the problems associated with such prior art devices. The inventor has realised that there is a need to be able to take a real-time reading of the impact of white coat hypertension on a patient's blood pressure. This will allow individuals with WCH to be differentiated from those with sustained hypertension, which in turn will reduce the risk of misdiagnosis or unnecessary prescription of drugs. It reduces the amount of health professionals' and patients' time and is cost-effective in reducing drugs and other resources.

The inventor has realised that white coat hypertension is related to the stress or psychological state of the patient. Accordingly, if that level of stress can be measured, and the effect on the patient's blood pressure assessed, then the blood pressure recorded can be corrected to take into account the white coat hypertension.

Initial data obtained by the inventors has shown that a patient's blood pressure is affected by the level of stress that a patient is under at any particular time. By measuring the stress that a patient is under and comparing it to a known blood pressure reading, it is possible to identify the amount of blood pressure associated with that level of stress. This measurement can then be used to provide additional diagnostic information to correct the blood pressure reading for the patient.

Accordingly, a first aspect of the invention provides a blood pressure monitoring apparatus comprising blood pressure monitoring equipment for determining the blood pressure of a patient; stress measuring equipment for determining the level of stress of the patient; and processing means for comparing the level of stress indicated by the patient with the blood pressure reading for the patient, to produce a corrected blood pressure reading.

Preferably, the processing means is a microprocessor or computer. Preferably, the processing means takes the level of stress indicated for the patient, compares it with a predetermined calibration graph of stress level versus blood pressure to produce a correction factor. Preferably the graph is patient-specific. However, the graph may be an averaged graph based on a population of patients. The correction factor is then applied to the blood pressure reading from the blood pressure monitoring equipment to correct the blood pressure reading for the level of stress recorded for the patient.

The corrected blood pressure reading preferably takes into account the stress produced on the patient by being in the clinic or hospital, or by being in the presence of, for example, a doctor.

Preferably, the blood pressure monitoring apparatus comprises a readout to display the corrected blood pressure reading. The blood pressure monitoring apparatus may also comprise a readout to show the actual blood pressure recorded by the blood pressure monitoring equipment. This latter reading enables a comparison between the actual blood pressure and the corrected blood pressure recorded by the monitoring apparatus to be displayed. This can be used by, for example, a doctor to see the effect of the stress being felt by the patient on the patient's blood pressure.

The blood pressure monitoring apparatus may additionally be connected to a suitable computer to enable the actual blood pressure and/or the corrected blood pressure readings to be recorded. One or both readings may also be sent to a remote doctor or other physician by, for example, a telephone line, radio-link or mobile telephone connection.

Preferably, the blood pressure monitoring equipment is a cuff-based system of the type known in the art and used by the NHS. Alternatively, invasive systems such as those using needles or catheters may be used.

Preferably, the blood pressure monitoring equipment is a cuff-based system of the type known in the art. Alternatively, invasive systems such as those using needles or catheters may be used.

The stress measuring equipment may be any suitable biofeedback devices. Such devices include those measuring heart rate, skin conductivity, eye or other muscle movements, brain waves or behavioural patterns. Two or more different stress measurement equipment may be used to improve the identification of the level of stress of the patient. It is known that the heart rate increases with stress. Devices for measuring heart rate are themselves well-known in the art and may be used to produce an indication of stress level.

It is also known that skin conductance can vary according to the emotional state of a person. For example, the palms of the hands or the soles of the feet can be influenced by the sympathetic nervous system. Stress often increases the amount of sweating observed by a patient and therefore alters the conductance of the skin. Devices for measuring skin conductance to obtain an indication of the psychological state of a patient are known in the art. Examples include US 4,625,732 and GB 2310377. This latter document also includes an alternative way of determining the emotional state of a person in that it discloses an image recognition system.

US 6,102,847 discloses a method of using eye movements to gain an indication of the level of stress in a person. Such a device may be adapted to be used with the apparatus, according to the invention.

Another alternative is to use the fluctuation of brain waves to gain an indication of the psychological condition of a patient, as indicated in US 6,129,681.

A second aspect of the invention provides a kit for attaching to a blood pressure monitoring apparatus, the blood pressure monitoring apparatus comprising blood pressure monitoring equipment, the kit comprising stress measurement equipment for determining the level of stress in a patient and processing means for comparing the measurement of stress determined by the stress measurement equipment with the blood pressure of a patient identified by the blood pressure monitoring equipment to produce a corrected blood pressure reading.

Preferably, the blood pressure monitoring equipment, stress measuring equipment and processing means are as indicated for the first aspect of the invention. The kit may also include a display for displaying the corrected blood pressure reading or both the corrected blood pressure reading and the actual blood pressure reading from the blood pressure monitoring equipment.

Means for connecting the kit to suitable recording equipment, such as a computer, directly or via a remote link, such as a telephone or mobile telephone, may also be provided.

A third aspect of the invention provides a method of determining a corrected blood pressure value for a patient comprising:

(i) Measuring the blood pressure of a patient to determine the actual blood pressure of the patient;

(ii) Measuring one or more physiological or psychological parameters to obtain an indication of the level of stress of the patient; and

(iii) Comparing the actual blood pressure of the patient with the indication of the level of stress of the patient to produce a corrected value for the blood pressure of the patient.

Preferably, the level of stress is compared with a predetermined standard set of values relating the level of stress against the effect of that level of stress on the blood pressure. This enables a correction factor to be determined for the level of stress recorded for the patient. The correction value can then be applied to the actual blood pressure reading to correct it to account for the level of stress observed for the patient.

The method of measuring the blood pressure, level of stress and comparing the actual blood pressure with the level of stress are preferably as indicated for the first aspect of the invention.

The inventor has also realised that as stress is related to blood pressure, measuring stress could be used to deliver feedback for therapy given to the patient to reduce the level of stress recorded by that patient. Accordingly, a fourth aspect of the invention provides a physiological monitoring device for monitoring the effectiveness of stress therapy comprising stress measurement equipment to determine the level of stress in a patient at predetermined intervals of time, processing means for comparing the level of stress recorded by the stress measuring equipment at each predetermined time interval, and display means for indicating the change in the level of stress recorded by the stress measurement equipment between each time interval.

The therapy to lower stress could be a conventional, pharmaceutical-based therapy for reducing stress. Preferably, however, the therapy is a fault challenging therapy which involves altering the cognitive behaviour of a patient. The device allows the patient to self-monitor the effect of the therapy on their levels of stress. This is particularly useful for anxious, such as suicidal-type and self-harm-type, patients for whom it has conventionally been difficult to monitor the stress levels and for monitoring the effect of the behavioural therapy on the patient.

Preferably, the stress measurement equipment is the same as that for the first aspect of the invention. Processing means may be a suitable microprocessor or computer.

The display means may be in the form of a digital display of the level of stress or indeed could be in the form of a graphical display to give an indication of increased or decreased stress levels in the patient.

A fifth aspect of the invention comprises the apparatus according to the first aspect of the invention adapted so that the stress measuring equipment determines the level of stress in a patient at predetermined intervals of time, the processing means compares the level of stress recorded by the stress measuring equipment at each predetermined time interval and further comprises an indicator for indicating the change in the level of stress measurement between each time interval. The apparatus of any of the aspects of the invention may comprise one or more indicators to indicate the absolute level of stress encountered by a patient. Further more the indicator or indicators may indicate any relative change in stress levels. Such an indicator or indicators would provide a clear signal to an operator, e.g. medical staff, regarding the absolute level of stress or a relative change in stress levels.

By absolute stress level we mean the actual level of stress measured in a patient at a given time point.

By relative change in stress levels we mean:

(a) the difference between (i) the level of stress measured in a patient in a non-clinical or other non-stressful environment and (ii) the level of stress measured in a patient in a clinical or other stressful environment, or

(b) the difference between (i) the level of stress measured in a patient when they initially enter a clinical or other stressful environment and (ii) the level of stress measured in a patient some time period after the initial entry into the clinical or other stressful environment. Relative changes in stress levels may be monitored over a period of minutes, hours, days or weeks.

Suitable indicators include lights, (which may be light emitting diodes (LED)), audible tones or other signals. A light-based indicator may comprise a series comprising at least one green light and at least one red light. The series may further comprise at least one amber light.

An indicator may comprise one green, one amber and one red light: under low stress levels the green light would be in an 'on' state' and the amber and red lights would be in an 'off state; under moderate stress levels the amber light would be in an 'on' state and the green and red lights would be in an 'off state and under high stress levels the red light would be in an 'on' state' and the green and amber lights would be in an 'off state. Optionally, high or very high stress levels may be indicated by a flashing red light. Alternatively, the series may comprise more than one of each of red and green and optionally amber lights. Such a series would allow the indication of finer increments of stress levels.

A light indicator may provide a continuous or intermittent, e.g. flashing, signal.

Provision of more than one set or series of indicators would enable stress levels measured over a period of time to be displayed

Furthermore, it will be appreciated that different coloured lights, i.e. other than green, amber and red, may be used. The choice of colours may be for aesthetic reasons or may aid visualisation of the signal, e.g. in a clinical environment.

Lights may be arranged in a linear, curved, circular or geometric arrangement.

Alternatively, the indicator or indicators may comprise audible signals. For example: under low stress levels no audible signal would be emitted; under moderate stress levels a quiet audible signal would be emitted and under high stress levels a louder audible signal would be emitted.

As an alternative to varying the loudness of an audible signal to reflect the stress level, other features of the audible signal may be varied e.g. pitch. Alternatively, under low stress levels a continuous tone may be emitted; under moderate stress levels an intermittent tone may be emitted and under high stress levels a faster intermittent tone may be emitted.

The tone may be audible to the medical staff only or to both a patient and medical staff. For a tone audible to medical staff only, the tone may be delivered by a suitable earpiece worn by the medical staff. For example, the signal may be delivered to the medical staff by a wired or wire-free system as described previously.

The visual and audible signals described above may be combined. For example, a low stress level may be indicated by a green light in an 'on' state, a moderate stress level may be indicated by an amber light in an On' state and a high stress level may be indicated by an audible tone optionally accompanied by a 'red' light in an 'on' state.

Apparatus may be adapted to provide one or more of the following in isolation or in combination:

(i) a quantitative measurement of the extent to which the stress level encountered by a patient is predicted to raise or lower a blood pressure value. Such a quantitative measurement would be displayed to a user, for example, in terms of mm Hg (ii) a qualitative measurement of the stress level encountered by a patient. Such a qualitative measurement would be indicated to a user, for example by the movement of at least one green, amber or red light from an 'off state to an 'on' state as described previously to indicate low, moderate and high stress levels, respectively.

Furthermore, apparatus maybe adapted to provide one or more of the following in isolation or in combination:

(i) a qualitative measurement of the extent to which the stress level encountered by a patient is predicted to raise or lower a blood pressure value. Such a qualitative measurement would be displayed to a user, for example, by the movement of at least one green, amber or red light from an 'off state to an 'on' state as described previously to indicate that the blood pressure is expected to decrease, to be substantially unaffected or to increase, respectively

(ii) a quantitative measurement of the stress level encountered by a patient. Such a quantitative measurement would be indicated to a user, for example, by a numerical indicator.

Both the measurement of the extent to which the stress level encountered by a patient is predicted to raise or lower a blood pressure value and the measurement of the stress level encountered by a patient may be indicated by qualitative measurements. Both the measurement of the extent to which the stress level encountered by a patient is predicted to raise or lower a blood pressure value and the measurement of the stress level encountered by a patient may be indicated by quantitative measurements.

Alternatively or in addition to displaying a quantitative measurement of the extent to which the stress level encountered by a patient, a corrected blood pressure reading corrected to may be displayed. A 'corrected blood pressure reading' is understood as the reading which reflects the true blood pressure and takes into account the increase in blood pressure induced by stress.

An initial measurement of the stress level encountered by a patient may be taken to determine whether there is likely to be a stress-induced alteration of blood pressure, such as that caused by white-coat hypertension. This measurement could be displayed, preferably by a qualitative indication, e.g. a coloured light or audible tone as described previously. Alternatively, the stress level may be indicated quantitatively. If a moderate or high level of likely stress is indicated, a quantitative measurement of the extent to which the stress level encountered by a patient is predicted to raise or lower a blood pressure value would be displayed. Such a quantitative measurement would be displayed to a user, for example, in terms of mm Hg. The indication of stress level and display of measurement of the extent to which the stress level encountered by a patient is predicted to raise or lower a blood pressure may be displayed simultaneously or consecutively.

The invention will now be described by way of example only, with reference to the following figures:

Figure 1 shows a schematic diagram indicating the arrangement of the blood pressure monitoring apparatus according to the invention.

Figure 2 shows a schematic diagram showing the psychological monitoring device according to the invention. Initial experimentation has demonstrated that there is correlation between the level of stress and the blood pressure observed in a patient. Accordingly, it is possible to create a standard curve or graph of stress against blood pressure. This enables a stress measurement to be associated with a predetermined blood pressure value, and allows a correction factor to be determined to take into account of a level of stress observed in a patient.

Figure 1 shows a schematic diagram indicating a preferred embodiment of the invention. Blood pressure is recorded by blood pressure monitoring apparatus known in the art. This produces a reading which is sent to a suitable software algorithm. A measure of stress may be obtained by any suitable stress measuring equipment. Preferably, the stress measuring equipment is a skin-conductance apparatus which uses sensors for determining the conductance of at least one area of an individual's skin, for example the palm of the hand or sole of the feet of a patient. This level of conductance is sent to the software algorithm where it is used as an indication of the level of stress in a patient. This is then compared with a standard curve of stress against blood pressure to create a correction value. The correction value is then applied to the actual blood pressure recorded, to produce the corrected reading which takes into account the level of stress observed by the patient. This corrected reading may be displayed by any suitable display means, for example a liquid crystal display or on a computer monitor. The actual blood pressure observed for a patient may also be displayed to enable a doctor to have an indication of the effect of the stress on the patient's blood pressure.

The connection of the stress measurement equipment and the blood pressure monitoring equipment may be direct through suitable electrical cabling. Alternatively, the processing means with its associated software may be remote from the blood pressure monitoring apparatus and the stress measurement equipment, and the information may be sent by, for example, telephone or a wireless system, such as, via a mobile telephone, to the processor. This enables information regarding the patient to be determined and processed remotely.

Two or more different stress measuring devices may be used to produce a more accurate indication of the level of stress for the patient. This level is used by the software to produce a value of the level of the stress of the patient, and thereby to create a corrected blood pressure reading.

Psychological monitoring device, according to the invention

This is shown schematically in Figure 2.

The level of stress is recorded by suitable stress measuring equipment at predetermined time intervals. A suitable microprocessor or computer compares the stress levels at each time interval and is used to produce an indication of increased or decreased levels of stress over time. This indication can be used to show whether therapeutic treatment is correctly being used by a patient or carried out by a patient. This may be used for conventional pharmaceutically based treatments to see whether the drug is having an effect on the levels of stress observed by the patient. Alternatively, it may be used in behavioural treatments, such as thought challenging treatments, to demonstrate to a patient or a doctor whether the treatment is being correctly followed by a patient or is being of use to the patient.

Claims

n-Claims

1. A blood pressure monitoring apparatus comprising blood pressure monitoring equipment for determining the real-time blood pressure of a patient; stress measuring equipment for determining the level of stress of the patient; and processing means for comparing the level of stress indicated by the patient with said real-time blood pressure of the patient, to generate a corrected blood pressure value.

2. An apparatus according to claim 1 wherein the processing means is adapted to generate a correction factor for blood pressure, by comparing the level of stress indicated for the patient with a predetermined calibration function relating stress level and blood pressure.

3. An apparatus according to any preceding claim which comprises a display to show the corrected blood pressure value.

4. An apparatus according to any preceding claim which comprises a display to show the real-time blood pressure.

5. An apparatus according to any preceding claim and adapted to display a comparison of the real-time blood pressure and the corrected blood pressure value.

6. Use of a device according to any of claims 3 to 5 adapted such that the display means is in the form of a digital display.

7. Use of a device according to any of claims 3 to 6 adapted such that the display means is in the form of a graphical display.

8. An apparatus according to any preceding claim and adapted for connection to a processing means to enable the real-time blood pressure and corrected blood pressure to be recorded.

9. An apparatus according to any of claims 1 to 8 and adapted for connection to a processing means to enable the real-time blood pressure or corrected blood pressure to be recorded.

10. An apparatus according to any preceding claim wherein the processing means is a computer.

11. An apparatus according to any of claims 8 to 10 and adapted to send one or both blood pressure values to a remote location.

12. An apparatus according to claim 11 wherein values are sent by one of telephone line, radio-link and mobile telephone communication.

13. An apparatus according to any preceding claim wherein the blood pressure monitoring equipment is a cuff-based system.

14. An apparatus according to any of claims 1 to 13 wherein the blood pressure monitoring equipment is invasive.

15. An apparatus according to any preceding claim wherein the stress measuring equipment is a biofeedback device.

16. An apparatus according to any preceding claim wherein the stress measuring equipment is adapted to generate measurements of one or more of: heart rate, skin conductivity, eye movement, muscle movement, brain waves and behavioural patterns.

17. An apparatus according to claim 16 and adapted such that combining two or more of the heart rate, skin conductivity, eye movement, muscle movement, brain waves and behavioural pattern measurements to improve the accuracy of the indication of the stress level of the patient.

18. A kit for attaching to a blood pressure monitoring apparatus to generate a corrected blood pressure value, the kit comprising stress measurement equipment for determining the level of stress in a patient and processing means for comparing the measurement of stress determined by the stress measurement equipment with real-time blood pressure of a patient identified by the blood pressure monitoring equipment.

19. A kit according to claim 18 and adapted such that one or more of the blood pressure monitoring equipment, stress measuring equipment or processing means is as defined in any one of claims 1 to 17.

20. A kit according to claim 18 or 19 and adapted such that a display shows the corrected blood pressure value.

21. A kit according to claim 18 or 19 and adapted such that a display shows the corrected blood pressure value and the real-time blood pressure value.

22. A kit according to any of claims 18 to 21 further comprising one or more connectors for connecting the kit to recording equipment.

23. A kit according to claim 22 and adapted such that the connector forms a direct connection between the kit and the recording equipment.

24. A kit according to claim 22 and adapted such that the connecting means forms a remote link between the kit and the recording equipment.

25. A kit according to any of claims 22, 23 and 24 and adapted such that the recording equipment is a computer.

26. A kit according to any of claims 22 to 25 and adapted such that the connecting means is a telephone, mobile telephone or radio-link.

27. A method for determining a corrected blood pressure value for a patient comprising: (i) monitoring blood pressure of a patient to determine real-time blood pressure of the patient; (ii) measuring one or more physiological or psychological parameters to obtain an indication of stress level of the patient; (iii) comparing the real-time blood pressure of the patient with the indication of the stress level of the patient to generate a corrected blood pressure value.

28. A method according to claim 27 comprising generating a correction factor for converting real-time blood pressure to corrected blood pressure by comparing the stress level indicated for the patient with a predetermined calibration function of stress level and blood pressure.

29. A method according to any of claims 27 or 28 including causing the corrected blood pressure value to take into account stress produced in the patient by being in a clinic or hospital.

30. A method according to any of claims 27 to 30 including providing a biofeedback device to obtain the indication of the level of stress of the patient.

31. A method according to any of claims 27 to 31 comprising using the stress measuring equipment to measure one or more of: heart rate, skin conductivity, eye movement, muscle movement, brain waves and behavioural patterns.

32. A method according to claim 31 comprising combining two or more of the heart rate, skin conductivity, eye movement, muscle movement, brain waves and behavioural pattern measurements to improve the accuracy of the indication of the stress level of the patient.

33. A method according to any of claims 27 to 32 comprising using the apparatus according to any of claims 1 to 17 to determine the corrected blood pressure value.

34. The apparatus according to claim 1 adapted so that the stress measuring equipment determines the level of stress in a patient at predetermined intervals of time, the processing means compares the level of stress recorded by the stress measuring equipment at each predetermined time interval and further comprising an indicator for indicating the change in the level of stress measurement between each time interval.

35. Apparatus, device or kit according to any of claims 1 to 26 and 34, further comprising an indicator adapted to attach to stress monitoring equipment of any preceding claim, for indicating the stress level of a patient.

36. An indicator according to claim 35 for indicating the stress level of a patient.

37. An indicator according to claim 35 for indicating the blood pressure of a patient.

38. An indicator according to any of claims 35, 36 and 37 comprising at least one red light and at least one green light.

39. An indicator according to claim 38 further comprising at least one amber light.

40. An indicator according to any of claims 35 to 39 comprising a device for emitting at least one audible tone.

41. Use of a device according to any of claims 34 to 40 adapted in which the stress therapy is a fault challenging therapy which involves altering the cognitive behaviour of a patient.

42. Use of a device according to any of claims 34 to 40 adapted in which the stress therapy is a pharmaceutical-based therapy.

43. Use of a device according to any of claims 34 to 42 in which the stress measuring equipment is according to any of claims 15, 16 and 17.

44. Use of a method, apparatus or kit according to any preceding claim to identify the correct blood pressure value for a patient suffering from White Coat Hypertension.