PERSONAL HEALTH DATA COLLECTION

Abstract

The present application provides a personal hand-held monitor for the measurement of a subject's blood pressure and, optionally, one or more other vital signs, comprising a housing located on a personal hand-held computing device or a hand-held component of a computing system; a blood flow occlusion means located in the housing; a pressure sensor adapted to provide an electrical signal indicative of the pressure applied; a means for detecting the flow of blood in the body part of the subject when pressure is applied; and means for receiving electrical signals from the pressure sensor and the blood flow detecting means and for transmitting electrical signals indicative of the pressure and blood flow to the processor of the personal hand-held computing device or the computing system, wherein the processor of the personal hand-held computing device or computing system provide at least a measurement of the blood pressure of a subject. The processor is further adapted to carry out a process to measure a diastolic blood pressure value and a systolic blood pressure value.

Claims

1. A personal hand-held monitor (PHHM) for the measurement of a subject's blood pressure (BP) and, optionally, one or more other vital signs, comprising a housing located on a personal hand-held computing device (PHHCD) or a hand-held component of a computing system; a blood flow occlusion device located in the housing such that, when the housing is located on the PHHCD or the hand-held component, an open surface of the blood flow occlusion device is available to be pressed against a body part of the subject or to have a body part of the subject pressed against it; a pressure sensor adapted to provide an electrical signal indicative of the pressure applied to or by the open surface; an optical blood flow detecting device configured to detect the flow of blood in the body part of the subject when pressure is applied to or by the open surface; and a device configured to receive electrical signals from the pressure sensor and the optical blood flow detecting device and for transmitting electrical signals indicative of the pressure and blood flow to the processor of the PHHCD or the computing system, wherein: the processor of the PHHCD or computing system is adapted to process signals acquired by the pressure sensor and the optical blood flow detecting device to provide at least a measurement of the BP of a subject, the processor is adapted to calculate a ratio of the amplitude of the pressure fluctuations on each pulse to the optical signals on each pulse to provide an estimate of the rotation of the body part relative to the blood flow occlusion device; and the processor is further adapted to carry out a process to measure a diastolic blood pressure (DBP) value and a systolic blood pressure (SBP) value using the estimate; and either the DBP and the SBP values are estimated in such a way that the difference between the measured optical signals and those that would be generated by the estimation of the DBP and SBP values is minimized or the DBP and the SBP values are estimated in such a way that the difference between the measured incremental pressure signals and those that would be generated by the estimation of the DBP and SBP values is minimized.

2-117. (canceled)

118. The PHHM of claim 1, wherein the processor is adapted to take account of the difference in pressure at which the peak of the pressure fluctuations and the peak of the optical signals is detected.

119. The PHHM of claim 1, wherein the processor is adapted to measure the gradient of the absolute optical signal at systole as a function of the measured external pressure and to use the said slope in order to estimate the error due to a misplaced body part.

120. The PHHM of claim 1, wherein the processor is adapted to measure the relative amplitude of red and infrared optical signals as a function of the pressure measured by the pressure sensor and to use said ratio to estimate the error due to a misplaced body part.

121. The PHHM of claim 1, wherein the processor is adapted to derive from the measured pressure and optical signals other estimates of the degree to which the body part is displaced.

122. The PHHM of claim 1, wherein the processor is adapted to combine the results of the analysis defined in the previous claims, where each is available, to make an estimate of the error due to a misplaced body part.

123. The PHHM of claim 122, wherein the processor is adapted to use the misplacement to estimate and correct for the error in the estimated SBP and/or DBP due to the misplacing of the body part.

124. The PHHM of claim 123, wherein the error in the measured SBP is used to estimate and correct for the error in the measured DBP or vice versa.

125. The PHHM of claim 119, wherein the processor is adapted to use said gradient to determine if the body part is so misplaced as to render to resulting estimates of SBP and DBP unreliable and to warn the user by way of audible and/or visual signals.

126. The PHHM of claim 1, wherein the PHHM is further adapted to generate a correction factor based on the relative locations of the body part of the subject and the blood flow occlusion device, wherein said correction factor is used to increase the accuracy of estimation of the value of BP.

127. The PHHM of claim 1, wherein the body part is a finger.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0251] The present invention is further described below, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0252] FIG. 1 is a representation of a SAD incorporating a dam;

[0253] FIG. 2 is a representation of various saddle shapes for the open surface of a SAD;

[0254] FIG. 3 is sketched from a Magnetic Resonance Image of a finger pressed against a SAD;

[0255] FIG. 4 is a representation of a SAD incorporating a magnetic pressure sensor;

[0256] FIG. 5 is a representation of the electrical signals measured by a SAD;

[0257] FIG. 6 shows the waveforms of typical signals received from optical, pressure and electrical sensors of a SAD;

[0258] FIG. 7 shows the typical relationship between luminal area and pressure;

[0259] FIG. 8 shows a range of pressures encountered during the arterial cycle at various External Applied Pressures;

[0260] FIG. 9 shows a simulation of the difference between the luminal area at systole and diastole as a function of EAP;

[0261] FIG. 10 shows a measured version of the simulated curve of FIG. 9;

[0262] FIG. 11 shows a plot of the absolute PPG signal at diastole against the measured external pressure;

[0263] FIG. 12 shows the plot of FIG. 11 against time;

[0264] FIG. 13 shows a plot of the absolute PPG signal at systole against the measured external pressure;

[0265] FIG. 14 shows the instantaneous arterial pressure;

[0266] FIG. 15 shows the components of FIG. 13;

[0267] FIGS. 16 and 17 show embodiments of the display of the blood pressure results;

[0268] FIG. 18a shows a band around a typical smartphone;

[0269] FIG. 18b shows a break in the band shown in FIG. 18a to form two electrodes;

[0270] FIG. 19 shows typical data recorded from a SAD;

[0271] FIG. 20 shows a possible optical configuration of a holder;

[0272] FIG. 21 shows the typical spectral response of an inexpensive red LED;

[0273] FIG. 22 shows the typical spectral response of the two filters used to analyse an inexpensive red LED;

[0274] FIG. 23 shows the relative value of the signals from two photo-detectors;

[0275] FIG. 24 shows a typical response to LED heating;

[0276] FIG. 25 shows a cross-section of an embodiment of a SAD;

[0277] FIG. 26 shows a cross-section of a second embodiment of a SAD

[0278] FIG. 27 shows a cross-section of a third embodiment of a SAD;

[0279] FIG. 28 shows a cross-section of a fourth embodiment of a SAD;

[0280] FIG. 28 shows a cross-section of a fifth embodiment of a SAD;

[0281] FIG. 30a shows a PHHM with a SAD;

[0282] FIG. 30b shows a cross-section of the PHHM of FIG. 30a;

[0283] FIG. 30c shows a perspective view of a hand holding the PHHM of FIG. 30a;

[0284] FIG. 31 shows a location of a SAD on a smartphone;

[0285] FIG. 32 shows the position of the artery in a finger and a SAD;

[0286] FIG. 33 shows an alternative pressure sensor;

[0287] FIG. 34 shows a SAD located on a mouse;

[0288] FIG. 35 shows an embodiment of a holder;

[0289] FIG. 36 shows an embodiment of a socket; and

[0290] FIG. 37 shows an embodiment of a SAD and the location of a gel.

[0291] In all embodiments described below, unless otherwise stated, the PHHCD can be a cellphone, tablet computer or MP4 player and the hand-held component can be a component, such as a mouse or a remote controller, of a larger computer system such as a laptop, PC or TV.

DETAILED DESCRIPTION OF THE DRAWINGS

[0292] FIG. 25 shows a cross-section of a SAD 2500 as part of a PHHM for measuring BP, intended for use where the body part of the subject is a finger.

[0293] The SAD 2500 includes a housing 2504 made of a non-conductive plastic material. The length of the SAD 2500 is approximately 15 mm. The housing 2504 includes a well 2501 in which a flexible and essentially incompressible gel 2505 is located. The housing 2504 comprises electrical connectors 2514 located on the exterior lower surface of the housing 2504 to connect the SAD 2500 to a PHHCD or a hand-held component of a computing system. A pressure sensor 2507 is embedded in the gel 2505. The housing 2504 has embedded infra-red and visible LEDs 2508 and photo-detector 2509. The infra-red and visible LEDs 2508 and photo-detector 2509 access the body part of the subject via windows 2502 and 2503. The SAD 2500 includes a blood flow occlusion means in the form of the open top surface of the housing 2504 against which a finger of the subject can be pressed. The SAD 2500 includes receiving and transmitting means 2506 embedded in the housing 2504. In this particular embodiment, the receiving and transmitting means 2506 includes an ASIC and there is a separate bolometric temperature sensor 2510. Alternatively, the bolometric temperature sensor 2510 could be incorporated as part of the same ASIC 2506. The bolometric temperature sensor 2506 has a window 2509 in the top of the housing 2504 of the SAD 2500.

[0294] Preferably, the receiving and transmitting means 2506 is adapted to carry out signal conditioning, such as filtering, analog to digital conversion and amplification. These functions may be carried out by the ASIC, if present. Alternatively, the processor of the PHHM is adapted to carry out the signal conditioning.

[0295] The SAD includes one electrode 2512 adapted to be touched by the body part of the subject when it is pressed against the open surface of the housing 2504. Not shown is a further electrode which is adapted to make contact with another body part of the subject.

[0296] FIG. 26 shows a second SAD 2600. A flexible and essentially incompressible gel 2604 forms the entire housing, without being contained within a well. The open surface is entirely formed by gel 2604. The housing 2604 also comprises electrical connectors 2614 located on the exterior lower surface of its base 2601 to connect the SAD 2600 to a PHHCD or a hand-held component of a larger computing system. The SAD 2600 of FIG. 26 comprises an electrode (not shown) disposed on the open surface of the gel 2604. The electrode is adapted to transmit electrical signals from the body part of the subject pressed against the open surface of the gel 2604 to receiving and transmitting means 2606 via electrical connections (not shown) embedded in the gel 2604. In this particular embodiment, the receiving and transmitting means 2606 is adapted to carry out signal conditioning. The processing routines to obtain the BP of the subject are carried out in the processor of a PHHM. The SAD 2600 of FIG. 26 further comprises a pressure sensor 2607, infra-red and visible LEDs 2608 and photo-detector 2609 and a bolometric temperature sensor 2610 embedded in gel 2604. The infra-red and visible LEDs 2608 and photo-detector 2609 access the body part of the subject via the windows 2602 and 2603.

[0297] FIG. 27 shows a SAD 2700 according to a preferred embodiment of the present invention. The SAD of FIG. 27 comprises a housing 2704 which includes a well 2701 in which the flexible and essentially incompressible gel 2712a and 2712b is located. The housing 2704 comprises electrical connectors 2714 located on the exterior lower surface of the housing 2704 to connect the SAD 2700 to the processor of a PHHCD or a computing system. The open surface of the housing 2704 is coplanar with the upper surface of the gel 2712a at the open end of the well 2701. Gel is divided into two layers 2712a and 2712b. The upper layer 2712a is a hard gel, designed to provide a robust surface that will resist physical or chemical damage. Alternatively, the first layer may be a hard material, such as the same material as is used to form the housing. The lower layer 2712b, that extends from the interface between the two layers down to the pressure sensor 2707, is a softer gel which is still essentially incompressible but has low shear strength. An advantage of such a construction is that the shear forces that arise when the open surface is in contact with the body part of the subject are transmitted less well to the pressure sensor 2707. In this preferred embodiment, the receiving and transmitting means 2706 is adapted to carry out signal conditioning. The SAD 2700 of FIG. 27 also comprises an electrode (not shown) disposed on the open surface of the housing 2704. The electrode is adapted to transmit electrical signals from the body part of the subject pressed against the open surface of the housing 2704 to the receiving and transmitting means 2706 via electrical connections (not shown) embedded in the housing 2704. The processing routines to obtain the BP of the subject are carried out in the processor of a PHHCD or a computing system of which the SAD is a part. The SAD 2700 of FIG. 27 further comprises a pressure sensor 2707 embedded in lower layer 2712b, infra-red and visible LEDs 2708 and photo-detector 2709 and a bolometric temperature sensor 2710. The infra-red and visible LEDs 2708 and photo-detector 2709 are also embedded in the housing 2704 and access the body part of the subject via the windows 2702 and 2703.

[0298] FIG. 28 shows a representation of a SAD 2800 according to a preferred embodiment of the present invention. In this embodiment, the SAD of FIG. 28 comprises a housing 2804 which includes a well 2801 in which a flexible and essentially incompressible gel 2805 is located. The housing 2804 comprises electrical connectors 2814 located on the exterior lower surface of the housing 2804 to connect the SAD 2800 to the processor of a PHHCD or a computing system. The open surface of the gel 2805 is at the open end of the well 2801. In this embodiment, the housing 2804 forming the well 2801 is made of a conductive plastic material. The housing 2804 further comprises one or more electrically conductive pads 2813 in contact with the conductive plastic material. The electrode described with reference to FIGS. 25 to 27 is omitted in this embodiment. The electrical connections (not shown) from receiving and transmitting means 2806 now run to pads 2813 within the housing 2804. The conducting material is chosen so that the resistance between each one of the pads 2813 and the open surface of the housing 2804 is of the order of 50K ohms. This limits the current that would flow through the subject's body part in the event of a fault causing a voltage to be applied to the open surface of the housing 2804. The processing routines to obtain the blood pressure of the subject are carried out in the processor of a PHHCD or computing system integrated with the SAD of FIG. 28. The SAD of FIG. 28 further comprises a pressure sensor 2807 embedded in the gel, infra-red and visible LEDs 2808 and photo-detector 2809 and a bolometric temperature sensor 2810. The infra-red and visible LEDs 2808 and photo-detector 2809 access the body part of the subject via windows 2802 and 2803.

[0299] FIG. 29 shows a SAD 2900 according to an embodiment of the present invention. The SAD 2900 differs from the SAD 2500 of FIG. 25 in that the housing 2904 of the SAD 2900 comprises two cut-outs or slots 2901 and 2902 that allow it to be slid into a mounting guide in the PHHCD or the hand-held component of the computing system. The housing 2904 can conveniently be manufactured by cutting or punching individual devices out of a sheet. The sheet might be manufactured in several layers, with the slots 2901 and 2902 formed by omitting some material from one or more layers. In this case, it is beneficial to restrict the width of the slots to less than the full width of the device so that the layer(s) from which they are removed remains structurally robust. The mounting guide into which the SAD 2900 slides is a component of a PHHCD or hand-held component of a computing system and can include electrical connections that press against electrical connectors 2914 of the SAD. Alternatively, a flexible cable can be soldered to the electrical connectors 2914 and inserted into a socket in the PHHCD or hand-held component of the computing system (not shown).

[0300] FIG. 30a shows a PHHM 3000 according to an aspect of the invention. The PHHM 3000 comprises a SAD 3002 and a PHHCD 3001. The SAD 3002 is located on a surface of the PHHCD 3001. During measurement, it can be difficult to position the finger comfortably on the open surface of the SAD 3002 which has a saddle-shape open surface. The saddle-shaped open surface can affect the accuracy of the measurements because the natural reaction when the finger is forced into an uncomfortable position is to tension the muscles. The tense muscles can affect the pressure applied to the artery and can also affect the distribution of tissue between the bone and the skin, which can in turn affect the optical signals.

[0301] FIG. 30a shows a modification of the saddle-shape of the open surface wherein the concave section 3003 is not perpendicular to the body of the PHHCD 3001 and the convex section is asymmetric. FIG. 30b shows a plan view of the saddle and a cross-section along the bottom of the concave section.

[0302] FIG. 30c is a sketch showing a cellphone as the PHHCD 3001 being held in the right hand of the subject. The SAD 3002 is under the index finger, which falls naturally over the top of the mobile telephone. The concave section 3003 of the SAD 3002 is at an angle of approximately 70 degrees to the longer axis of the surface of the PHHCD 3001.

[0303] FIG. 31 shows a preferred embodiment of the present invention which is PHHM 3100. The PHHM 3100 comprises the SAD 3101 according to any of FIGS. 25 to 30 located on a PHHCD or on a hand-held component of a computing system 3102 comprising a user interface 3103. The electrical signals are transmitted from the receiving and transmitting means to a processor of the PHHCD or computing system or vice versa and the PHHM 3100 is adapted to process signals acquired by the SAD to provide at least a measurement of the BP of a subject.

[0304] The PHHM 3100 comprises a user interface 3103 which is a display which permits the subject to use the PHHM 3100 as a hand-held games console, used for interactive electronic games. The use of the PHHM 3100 as a hand-held games console provides a convenient way for the subject to operate the PHHM and also allows the results of the measurements of BP and, optionally, one or more other physiological vital signs to be exploited within the game. The steps that are required to operate the PHHM 3100 correctly might cause difficulties for some subjects if they have to read detailed instructions. Many subjects are familiar with playing interactive electronic games and are comfortable using a controller and electronic displays such as on a cellphone or tablet computer. Hence, it is possible to set the measurements made by the PHHM 3100 in a games context so that the subjects are automatically guided to make accurate measurements.

[0305] An exemplary game that could be used to derive a measurement of a subject's BP could be a game that represents some of the elements of a biathlon, requiring the player to remain calm when subject to physical or emotional stress. Alternatively, the interface could display two fighter aircraft in the sky. The pressure generated by the subject's finger on the pressure sensor controls the orientation of one of them. The position of the other aircraft is controlled by the pressure that the subject is applying over the SAD of the PHHM based on specific prompts shown to the subject via the user interface. In particular, if a missile is fired from the first aircraft on each pulse and the second aircraft rolls when hit by a missile, then the subject gets immediate feedback that the pressure is correct. This helps the user to adjust the pressure. The data obtained from that point are used even though it was not at the target pressure because it is still a valid data point and adds to the accuracy of the result. Subjects with no knowledge or training would be able to use this video game interface immediately to make accurate measurements of BP.

[0306] It is common for devices for monitoring vital signs to be purchased and used a few times but then for the subject to lose interest. An entertaining games interface would encourage the subject to continue monitoring his or her vital signs. Hence, the user interface using a game for some or all of the measurements can automatically guide the subject through the necessary steps and ensure that the device is being used correctly. Information and instructions would be included in the game.

[0307] The PHHM may be adapted to store different video games. These videogames could take many forms, such as bat and ball, fighting, shooting, role-play, strategy and pattern-matching such as mazes. The subject may select from a suite of games that are included in the PHHM and new games may be downloaded to the PHHM via the internet.

[0308] The PHHCD of the PHHM 3100 of FIG. 31 comprises a frontal camera 3104 and a rear camera (not shown). When the subject uses the index finger as the relevant body part, it is also advantageous to provide guidance to the user to locate the finger correctly with respect to the PHHM. The PHHM 3100 is adapted to interpret the images from the frontal camera 3104 and the rear camera located on the PHHCD. For example, a smartphone typically has two cameras, one facing away from the screen and one facing in the direction of the screen. If the SAD is located on the edge of the smartphone and the index finger is placed on the SAD, the hand and/or finger is in the field of view of both cameras or at least in the field of one of the cameras, typically the rear camera. The images from the cameras provide an indication of its position, and the accuracy of this indication may be further enhanced by relating it to the signals measured simultaneously by the pressure and optical sensor in the PHHM.

[0309] The indication of the position of the finger and/or hand so derived may be used by the processor of the PHHCD to generate audible and/or visual feedback to guide the subject to position the finger optimally on the SAD of the PHHM. Alternatively, the indications of position may be used to generate a correction factor to be applied to other measured data to improve the accuracy of the parameter related to health that is being measured.

[0310] FIG. 32 shows a representation of the key elements of a preferred embodiment which has a SAD 3203 according to any one of FIGS. 26 to 31, further comprising an additional pressure sensing element, i.e. the SAD 3203 comprises two pressure sensing elements 3204 and 3205. FIG. 32 shows a finger 3201 with artery 3202 pressing against the open surface of the SAD 3203. More pressure sensing elements could be integrated in the SAD.

[0311] The SADs disclosed in the present application operate by using the pressure between the open surface of the SAD and the finger of the subject to cause partial or total occlusion of an artery in the finger. It is assumed that the pressure to which the artery is subjected is the same as the pressure measured by the pressure sensing elements 3204 and 3205 in the SAD 3203. The accuracy of the measurement of pressure by the SAD can be reduced if there is a shear force between the finger and the SAD 3203. This shear force will cause a difference in the pressure measured by the two or more pressure sensing elements within the SAD, in particular for this embodiment, elements 3204 and 3205. The shear force can be obtained by analysing the measurements made by the two pressure sensing elements 3204 and 3205.

[0312] The estimation of the shear force can be used to increase the accuracy of estimation of the subject's BP and to reduce the magnitude of the shear force. An example of the provision of feedback to the subject based on the estimation of the shear force would be, for example, to display on the screen of a PHHCD a circle within which a spot is displayed. The position of the spot in the circle would be related to the magnitude and orientation of the measured shear force and the subject would adjust the force on the finger to move the spot towards the centre of the circle.

[0313] Pressure sensing elements 3204 and 3205 can also be used to locate the position of the artery 3202 with respect to the SAD 3203 so that, if the artery 3202 is not central, either the subject can be instructed to reposition the SAD 3203 against the body part of the subject so as to make it more central or the measured pressure can be corrected for the difference between it and the pressure at the artery 3206.

[0314] The two pressure sensing elements 3204 and 3205 in the SAD 3203 measure the pressure between the body part of the subject, e.g. finger 3201, and the SAD 3203. When the pulse reaches the artery, the artery expands and causes an increase in the pressure in the tissue of the finger 3201 surrounding the artery 3202. The magnitude of that pressure is smaller in the tissue further from the artery. Accordingly, the change in pressure measured at pressure sensing element 3204 will be greater than that measured at 3205. This difference is used to indicate whether the artery is centrally located with respect to the pressure sensing elements 3204 and 3205.

[0315] FIGS. 33a to 33d show an alternative pressure sensing element. The pressure sensing element shown in FIG. 33 can be used instead of the pressure sensing elements described in the SADs shown in FIGS. 25 to 30. The alternative pressure sensing element is a MEMS pressure sensor 3300. FIG. 33a shows a cross-section of a typical MEMS pressure sensor. It is made from a block of silicon 3301 typically 1 or 2 mm wide. The surface is etched to form a thin membrane 3302. This membrane 3302 deforms when it is subject to pressure.

[0316] Four resistive elements R1, R2, R3 and R4 are embedded into the membrane 3302. The resistance of these elements changes when they are strained by the deformation of the membrane 3302. The resistance of these four resistive elements also changes with the temperature of the membrane 3302.

[0317] A common way of constructing such a device is to incorporate the four resistive elements R1, R2, R3 and R4 connected as a bridge as shown in FIG. 33b. The four resistive elements R1, R2, R3 and R4 are arranged in a square pattern around the membrane 3302. The resistors are oriented so that, when the membrane 3302 is deformed by pressure, the resistance of one pair of the elements (R1 and R4) increases and the resistance of the other pair (R2 and R3) falls. The change in differential voltage (V1−V2) is, for small changes in resistance, proportional to the average strain on the membrane.

[0318] The resistance of each element is a function of temperature and the strain to which that element is subject. Making the simplifying assumptions that the resistance of the ith resistive element is given by:

R.sub.i=R.sub.i0(1+u.sub.iT+v.sub.iS.sub.i)

where: [0319] R.sub.i0 is the resistance at nominal temperature and no strain; [0320] T is the difference between the current temperature and the nominal temperature (assumed to be the same for all four resistive elements); [0321] S.sub.i is the strain of the ith resistive element; [0322] u.sub.i is the temperature sensitivity, where u.sub.iT1; and [0323] v.sub.i is the strain sensitivity, where v.sub.iS.sub.i1.

[0324] The strain of the ith resistive element S.sub.i is the sum of two contributions P+S.sub.gi where: [0325] P is the average strain across the four resistive elements (proportional to the average pressure on the membrane); and [0326] S.sub.gi is the local contribution due to the difference in pressure across the MEMS pressure sensor.

[0327] Assuming that to first order the difference in pressure across the MEMS pressure sensor 3300 is expressed as: [0328] a strain gradient G (corresponding to the pressure difference between the two sides of the MEMS pressure sensor 3300); and [0329] an orientation Θ corresponding to the angle between the axis of the pressure gradient and the axis of the MEMS pressure sensor 3300
and making the simplifying assumptions that the resistance of the ith resistive element is given by:

R.sub.i=R.sub.i0(1+u.sub.iT+v.sub.iS.sub.i)

then the resistance of each of the four resistance elements can be expressed as:

R.sub.1=R.sub.10(1+u.sub.1T+v.sub.1(P+G sin Θ))

R.sub.2=R.sub.20(1+u.sub.2T+v.sub.2(P+G cos Θ))

R.sub.3=R.sub.30(1+u.sub.3T+v.sub.3(P−G sin Θ))

R.sub.4=R.sub.40(1+u.sub.4T+v.sub.4(P−G cos Θ))

[0330] u and v may be determined by calibration under controlled conditions. Therefore, there are four equations with four measured values (R.sub.1 to R.sub.4) that must be solved to find the four unknowns T, P, G and Θ.

[0331] The difference in pressure across the MEMS pressure sensor 3300 may also be expressed to first order as two components, one aligned with one axis of the MEMS pressure sensor and the other aligned with a second axis. The transformation between this and the (G, Θ) first order representation is a matter of simple trigonometry.

[0332] In practice, it is simpler to measure voltages than resistance. MEMS pressure sensors are usually manufactured as in FIG. 33c. The left and right sides may be connected together to make the simple bridge or external resistors may be added to trim out the dependence on temperature. FIG. 33d shows an arrangement where two additional resistors R.sub.e have been added and four voltages can be measured and, by application of Ohm's law, the instantaneous resistance of each of the four resistive elements R.sub.1 to R.sub.4 can be found. It would be more effective to measure [(V.sub.ref/2)−V.sub.13] (and similarly for V.sub.24) because this will have a smaller dynamic range and therefore be measured more accurately.

[0333] Hence, independent measurements of the resistance elements R.sub.1, R.sub.2, R.sub.3 and R.sub.4 of the MEMS pressure sensor 3300 are combined to make an estimate of the temperature of the membrane 3302, the average pressure to which it is subject and the orientation and magnitude of the pressure gradient across the MEMS pressure sensor.

[0334] In practice, MEMS pressure sensors are designed to minimize their sensitivity to shear force. In an alternative embodiment, the strain of each resistive element R.sub.1 to R.sub.4 would be determined as far as possible by the local pressure on that element with the minimum electrical coupling between the resistive elements. It would also be designed so that the change in resistance of each element with respect to strain has the same sign.

[0335] The shear force may be estimated by a measurement of the magnitude and orientation of the instantaneous pressure gradient across the MEMS pressure sensor. This measurement can be used to estimate the shear force to increase the accuracy of the measurement of the subject's blood pressure and/or temperature, to reduce the shear force and to correct for the displacement of an artery as previously disclosed.

[0336] FIG. 34 shows a cross-section through the fingers of a subject and a mouse (a computer pointing device) 3411 as part of a PHHM that comprises a computer or laptop (not shown) and a computer pointing device 3411 (i.e. the mouse), where there is the index finger 3412, middle finger 3413, ring finger 3414 and little finger 3415. The SAD 3416 of the PHHM is incorporated in the body of the computer pointing device 3411 and the index finger 3412 rests against it. The computer pointing device 3411 can be another component, such as a remote controller for a TV or other domestic electronic appliance, that could enable a measurement of subject's BP and, if desired, some other vital signs, such as a subject's blood oxygen concentration, pulse rate, respiration rate or other physiological vital signs. The SAD 3416 is adapted to transmit electrical signals to the processor of the computing system to which the mouse is connected, either by means of a cable or by wireless means such as Bluetooth.

[0337] FIG. 35 shows an embodiment of a holder 3500 according to an aspect of the present invention. The holder 3500 is equipped to check that a SAD 3503 under test is functioning correctly before it is calibrated. FIG. 35 shows a sketch of a cross-section of the holder. The SAD 3503 under test is held against the holder body 3501 by a partial vacuum through pipe 3508. In FIG. 35, the SAD 3503 is shown displaced downwards to make the components clearer; in use, it is engaged into the shape of the underside of the holder, indicate by the two cut-outs 3502.

[0338] The holder 3500 comprises the fibre optic cable 3507 (as 2004 in FIG. 20) and the optical diffuser 3506 (as 2002 in FIG. 20). One or more spring-loaded connectors 3505 in the holder presses on the pad(s) (not shown) on the open surface of the SAD 3503 and permits the testing of the SAD through the calibration board. A spring-loaded probe 3504 is adapted to rest on the open surface in contact with the flexible and essentially incompressible gel (not shown) and the pressure signal is measured by the circuits of the calibration board. The pressure signal may be used to confirm that the pressure sensor of the SAD 3503 is functional and to make an estimate of its sensitivity. The signal from the probe 3504 measures the height of the essentially incompressible gel with respect to the open surface of the SAD 3503.

[0339] The same, or a similar, holder is also used to remove the SAD 3503 from the calibration board after calibration. The tests are repeated to check that the module has not failed during calibration. The test of the height of the essentially incompressible gel is repeated because the calibration of the pressure sensor is known after calibration and so the height of the essentially incompressible gel can be estimated more accurately. The holder 3500 is equipped with a mechanism (not shown in FIG. 35) to release mechanical retaining clips 3601 shown in FIG. 36 that hold the SAD 3503 under test to the socket within the calibration board and to remove the SAD 3503 using the partial vacuum to retain it against the holder 3500.

[0340] The SAD 3503 is inserted in a socket shown in FIG. 36 on the calibration board. FIG. 36 shows a socket 3600 to be used on the calibration board to hold and connect to each SAD under calibration test. FIG. 36 is a sketch of the socket 3600. There are spring-loaded connecting pins 3602 that press against the connectors of the SAD. The SAD is retained by mechanical retaining clips 3601 that snap into slots of the type shown in FIG. 29 in the side of the housing of the SAD. The SAD is located on a well 3603 that is slightly larger than the base of the SAD. A cut-out 3604 is provided in the side of the well in case it is necessary to test the SAD with their flexible connectors already attached. In this case, the pins 3602 press on flexible connector.

[0341] The socket provides electrical connections between an external computer and the SAD under test.

[0342] FIG. 37 shows a SAD comprising a gel 3701 surrounding a pressure sensor 3707 within a housing 3704. The gel consists of a flexible epoxy resin formed from EPICOL 295, a 2-component system for making a soft epoxy resin including a modified epoxy resin and a modified amine hardener, supplier by APM Technica. The hardened resin has a Durometer, measured on the Shore A scale at 25° C., of 60.

[0343] In an alternative embodiment, the gel consists of a cured silicone resin formed from Dow Corning Sylgard 160, a 2 component system for making a soft silicone resin including a silicone resin and a catalyst. The cured resin has a Durometer, measured on the Shore A scale at 25° C., of 56.

[0344] In other respects, the SAD is identical to the SADs described above.

[0345] The SAD as described above was incorporated into a cellphone such that the sensors in the SAD can receive signals from and transmit signals to the processor of the cellphone. The processor of the cellphone was programmed such that it can operate in accordance with all of the aspects of the present invention described above.

[0346] In an alternative embodiment, the SAD was incorporated into a pointing device (a mouse) connected by wire or wirelessly to a personal computer such that the sensors in the SAD can receive signals from and transmit signals to the processor of the personal computer via the pointing device. The processor of the personal computer was programmed such that it can operate in accordance with all of the aspects of the present invention described above.

[0347] The present invention has been described above by way of example only. The invention is not limited to the disclosures made above and is only limited by the spirit and scope of the invention as determined by the attached claims.