Patent Publication Number: US-2020281484-A1

Title: An apparatus for monitoring the pulse of a person and a method thereof

Description:
FIELD OF THE INVENTION 
     The current invention relates to devices and methods for measuring heart rate, and particularly devices providing electrocardiogram (ECG), ballistocardiogram (BCG) and photoplethysmogram (PPG) measurements. 
     BACKGROUND 
     Heart rate measurement is done typically using electrocardiogram (ECG) by placing electrodes on the body, about and around the heart. The electrodes monitor electrical signals which are then used to chart a signal, which shows the stages of a heartbeat, typically the contraction and relaxation of the different heart chambers. 
     However, applying electrodes to a person to obtain an ECG is not practical for long term, round-the-clock monitoring, as the person has to remain by the ECG machine to which the electrodes are attached. Furthermore, the application of electrodes onto the body is done using adhesive tape which irritates the skin. The tape tend to fall off after a while, which can disrupt the ECG reading. 
     Yet, it would be useful to monitor some people with high risk of cardiac arrest for long, extended periods of time, either for preventative care or for academic research. 
     Therefore, it is desirable to provide an apparatus and accompanying methods by which a person may be monitored for his ECG over a relatively long period of time. 
     Furthermore, in using ECG or PPG to monitor the pulse of a person, there is an underlying assumption that blood flow or cardiac performance observed from one part of the body is representative of the whole body. However, this is not quite the case in reality. For example, blood clot problems such as thrombosis are localised problems, but these locations are not discoverable by typical application of ECG or PPG. 
     Hence, it is also desirable to improve the applications of ECG and PPG technologies, in novel and inventive applications to bring about better health monitoring. 
     STATEMENTS OF INVENTION 
     In a first aspect, the invention proposes an apparatus for measuring the heart rate of a person, comprising a piece of vestment suitable for being worn on the body of the person; the vestment has two sleeves, each suitable for the person&#39;s respective arms to be inserted through; each of the sleeves having a tightened band for hugging the bicep of the respective arm, the tightening provided by a resilient material; one or more electrode for contacting the skin of the respective bicep in the band of each of the sleeves; an electrical conductor extending across the vestment connecting the electrodes of the band of each of the sleeves. 
     In a second aspect, the invention proposes an apparatus for measuring the heart rate of a person, comprising a piece of vestment suitable for being worn on the body of the person; the vestment has at least one sleeve suitable for one of the person&#39;s two arms to be inserted through; the sleeves having a tightened band for hugging the bicep of the arm, the tightening provided by a resilient material; an photoplethysmogram (PPG) sensor in the band; such that the resilient material urges the photoplethysmogram (PPG) into contact with the skin of the bicep. 
     In a third aspect, the invention proposes an apparatus for measuring the heart rate of a person, comprising a piece of vestment suitable for being worn on the body of the person; the vestment has two sleeves, each suitable for the person&#39;s respective arms to be inserted through; each of the sleeves having a tightened band for hugging the bicep of the respective arm, the tightening provided by a resilient material; one or more electrode for contacting the skin of the respective bicep in the band of each of the sleeves; an electrical conductor extending across the vestment connecting the electrodes of the band of each of the sleeves. 
     In a fourth aspect, the invention proposes an apparatus for measuring the heart rate of a person, comprising a piece of vestment suitable for being worn on the body of the person; the vestment has at least one sleeve suitable for one of the person&#39;s two arms to be inserted through; the sleeves having a tightened band for hugging the bicep of the arm, the tightening provided by a resilient material; an photoplethysmogram (PPG) sensor in the band; such that the resilient material urges the photoplethysmogram (PPG) into contact with the skin of the bicep. 
     The movements of the user do not dislocate the electrocardiogram (ECG) or the photoplethysmogram (PPG) from contacting his skin. As tee-shirts are not easily seen, especially if worn as an undergarment, and is less prone to collecting sweat as in the leather band of a watch, the embodiments allow twenty-four hour wearing and monitoring of the heartbeat of the wearer. Advantageously, subtle information such as heart rate variations (HRV) can be monitored for a person round the clock. Even if there were data obtained by embodiments during moments which could render the data inaccurate, such as when the person wearing the tee-shirt adjusts the sleeves, the round-the-clock data means the person is better off over-sampled than not. The person making deductions or analysis based on the data can reject any clearly inaccurate data and would still have data made over disconnected but continual, lengthy periods of observations. Such continuous monitoring is crucial for monitoring people with high risk of sudden cardiac arrests, or for research purposes. 
     An apparatus for monitoring the pulse of a person, comprising a piece of clothing suitable for being worn on the body of the person; the clothing having two sleeves, each suitable for the person&#39;s respective limbs to be inserted through; along each of the sleeves is a stretchable neck for hugging the respective limb; one or more electrodes in each neck; an electrical conductor connecting the electrodes of each neck; wherein the neck urges the electrodes of each of the sleeve into contact with the skin of the respective limb. 
     An electrocardiogram (ECG) monitor in the form of a wearable clothing or vestment allows a person to wear it over a long period of time to have his pulse monitored, even for a couple of days. The stretchable neck provides a sort of band around the arm which presses the electrodes against the skin, maintaining consistent and reliable contact in spite of any movements of the person or any flexing of the arm. 
     An apparatus for monitoring the pulse of a person, comprising a piece of clothing suitable for being worn on the body of the person; the clothing having least one sleeve suitable for at least one of the person&#39;s limbs to be inserted through; the at least one sleeve having a resilient neck for hugging the limb; one or more photoplethysmogram (PPG) sensors in the neck; such that the neck urges the one or more photoplethysmogram (PPG) sensors into contact with the skin of the limb. 
     In this aspect, the stretchable neck provides a sort of band around the arm which presses the photoplethysmogram (PPG) sensors against the skin, maintaining consistent and reliable contact in spite of any movements of the person or any flexing of the arm. This permits round the clock use of photoplethysmogram (PPG) sensors to monitor the pulse of the person. 
     Preferably, the clothing comprises at least two sleeves, each sleeve for the respective opposite limbs of the person to be inserted through. 
     This provides the possibility of having a photoplethysmogram (PPG) device on each opposite limb. This provides that information on the pulse transit time in each limb to be monitored. Pulse transit time is the time taken for the surge of blood caused by a heartbeat to reach a limb. Additionally, this allows the shape, the spread and the amplitude of the pulses can be compared. 
     Typically, the limbs are the arms of the person. Alternatively, the limbs are legs of the person. Therefore, ‘sleeves’ in this description is not limited to sleeves of clothing of the upper body, but ‘sleeves’ also include the legs of clothing intended to be worn on the lower body. 
     Preferably, the neck of each sleeve further comprises an electrocardiogram (ECG) electrode; an electrical conductor connecting the electrodes of each neck to form a closed circuit across the person&#39;s body; and the neck of each sleeve urging the electrocardiogram (ECG) electrode into contact with the skin of the limb. 
     Furthermore, it is also preferable, that the apparatus comprises a ballistocardiogram (BCG) sensor. 
     Furthermore, it is also preferable, that the apparatus comprises a microcontroller configured to identify the electrocardiogram (ECG) pulse and photoplethysmogram (PPG) pulses as being from the same heartbeat. 
     Typically, the device comprises a microcontroller configured to identify the ballistocardiogram (BCG) pulse and photoplethysmogram (PPG) pulses as being from the same heartbeat. 
     The limbs are typically the arms of the person. Alternatively, the limbs are the legs of the person. 
     In yet another aspect, the invention proposes a method of monitoring heart pulses of a person, comprising the steps of: obtaining the left pulse of a heartbeat in the left limb; obtaining the right pulse of the same heartbeat in the right limb; observing a difference between the pulses in one or more of the following pulse characteristic: i) the pulse-transit-time of the pulse; ii) the spread of the pulse; iii) the trough to peak amplitude of the pulse; iv) the shape of the pulse. 
     Preferably, the left pulse of a heartbeat in the left limb is obtained by photoplethysmogram (PPG), and the right pulse of the same heartbeat in the right limb is obtained by photoplethysmogram (PPG). 
     This method is not limited to any specific apparatus which has to be worn as a piece of clothing. Two wrist-worn photoplethysmogram (PPG) sensors may be used instead, as long as pulses can be identified as being of the same heartbeat. This is possible because heartbeat propagation into the limbs is never so slow that the pulse of one heartbeat is still reaching the extremity of a limb when a subsequent heartbeat commences. The photoplethysmogram (PPG) sensors can have wireless transceiver to send data to a common processing apparatus such as smartphone to compare the pulses. 
     Preferably, the method further comprises the step of: obtaining an electrocardiogram (ECG) pulse of the same heartbeat by electrocardiogram (ECG); wherein the pulse-transit-time of the left pulse is referenced from the electrocardiogram (ECG) pulse; the pulse-transit-time of the right pulse is referenced from the electrocardiogram (ECG) pulse. 
     If both sides of the body have similar constrictions, artery clogging and so on, there may be no difference in the pulses on the two limbs. In this case, the absolute pulse-transit-time may shed light on potential problem in the body as a whole. 
     Preferably, the method further comprises the steps of: obtaining a ballistocardiogram (BCG) pulse of the same heartbeat by ballistocardiogram (BCG); wherein the pulse-transit-time of the left pulse is referenced from the ballistocardiogram (BCG) pulse; the pulse-transit-time of the right pulse is referenced from the ballistocardiogram (BCG) pulse. 
     Typically, the limbs are the arms of the person. Alternatively, however, the left limb is the left leg of the person; and the right limb is the right leg of the person, in particular, the left pulse of a heartbeat in the left limb is obtained from the left calf; and the right pulse of the same heartbeat in the right limb is obtained from the left calf. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention, in which like integers refer to like parts. Other embodiments of the invention are possible, and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention. 
         FIG. 1  shows an embodiment of the invention; 
         FIG. 2  shows a second embodiment of the invention; 
         FIG. 3  shows a third embodiment of the invention; 
         FIG. 4  shows readings which may be obtained by the embodiment of  FIG. 3 ; 
         FIG. 5  shows further possible readings which may be obtained by the embodiment of  FIG. 3 ; 
         FIG. 5 a    shows further possible readings which may be obtained by the embodiment of  FIG. 3 ; 
         FIG. 6  shows a variation to the embodiment of  FIG. 3 ; 
         FIG. 6 a    shows a further variation to the embodiment of  FIG. 3 ; 
         FIG. 7  shows a variation of the embodiment of  FIG. 5 ; 
         FIG. 8  shows a variation to the embodiment of  FIG. 3 ; 
         FIG. 9  shows an alternative embodiment to that of  FIG. 3 ; and 
         FIG. 10  shows data obtained by the embodiment of  FIG. 9 . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows an embodiment  100  of the invention, which is a tee-shirt, for obtaining the electrocardiogram (ECG) of the person wearing it. The tee-shirt  100  has two short sleeves  101 . The edge of each of the sleeves  101  is lined with a resilient, stretchable material, such as an elastic band or Lycra (an elastic polyurethane fibre or fabric used especially for close-fitting sports clothing, also known as Spandex). 
     In the edge of each sleeve  101  is placed an ECG electrode  103 . The electrode  103  is held in close contact with the skin of any one who is wearing the tee-shirt. This allows movement of the user&#39;s arm, including repositioning and flexing of the muscles, without causing the electrode  103  to become out of contact with the person&#39;s skin. 
     The view of  FIG. 1  is the back of the tee-shirt  100  instead of the front, which is why only the back collar is seen. A conductive element, such as a wire  105 , is shown connecting the electrodes  103  to a flexible printed circuit board  107 . Hence, the printed circuit board  107  lays against the upper back of the person, where the printed circuit board  107  is the least likely to be in the way of most of the person&#39;s movements. 
     The printed circuit board  107  is preferably provided with a battery for operation of the electrodes  103  and any processor in the printed circuit board  107 , as well as any wireless communication transceiver for communicating with a smart phone, computer or a remote server. 
     Having an electrode  103  on both biceps connected by the wire  105  creates a closed circuit through the electrodes  103  across the body and heart of the person wearing the tee-shirt. The closed circuit is then useable for monitoring heart related electric signals to obtain an ECG. 
     The wire connecting the electrode  103  to the flexible printed circuit board  107  is preferably of the type that is thin and thread like, such that it may be woven into the fabric of the tee-shirt to behave as an integral, flexible part of the tee-shirt. 
     Wires can be made as thin as required depending on the choice of metals or alloys in an actual product embodying the invention. Gold has the highest conductivity and can be spun into very thin wires, but gold is expensive. Copper is one of the best wire material because it is very ductile and conductive. Another choice is silver, which is also very ductile and conductive. Yet another alternative is aluminium. Aluminium is less conductive than copper, having only about 61% of the conductivity of copper, but makes up for this shortcoming by being relatively lighter in weight. 
     The form of the wire can a cable with a circular cross section, however, flat wire strips (not illustrated) can also be used if a certain amount of rigidity is preferred. Flat wire strips are only easily bent about the flat face of the wire but not about the edge. Hence, flat wires can be used to provide some structure to the tee-shirt and prevent the wire from running away from its installed position. For example, all around the edge of the sleeve  101  can be lined with a flat wire. This will prevent the sleeve  101  from turning up, and cutting off contact between the wire and the person&#39;s skin 
     The fabric which the tee-shirt is made of is preferably woven or knitted fabric such as jersey, which allows the tee-shirt to be stretchable and body hugging. This allows the wires threaded into the tee-shirt to be held as closely to the body as possible, preventing dislocation of the wires, and also preventing any abrasion. Having said that, this preference is not a necessary one. The bulk of the tee-shirt does not have to be stretchable and body hugging, as long as the resilient material in the sleeves  101  consistently maintains electrode  103  contact with the skin of the person wearing the tee-shirt. 
     An advantage of using resilient and stretchable material to provide the bands lining the edge of the sleeves  101  is that the resilient material can accommodate flexing of muscles without letting the electrodes  103  lift away from the skin. 
       FIG. 2  shows another embodiment  200  of the invention wherein, instead of the ECG, the device placed in the band in the sleeve  101  of the tee-shirt is a photoplethysmogram (PPG) sensor  203 . As the skilled reader would know, a PPG sensor  203  monitors the pulsation of blood in the body by monitoring absorption and dispersion of light which has been sent into the skin and tissue of the body. As the content of blood in skin and tissue surges along with the pumping of the heart, the absorption of light varies in accordance to the fullness or depletion of blood in skin and tissue. Typically, any wavelength of light maybe used, from infra-red to visible light. However, it appears that green light and infrared light is the best choices for the purpose of reading blood volume surges. One advantage of using PPG is that unlike ECG there is no need to form a closed circuit across the heart of the person. Hence, in the simplest embodiments, only one sleeve  101  may be provided with an elastic band in which a PPG sensor  203  is embedded. 
     In  FIG. 2 , the tee-shirt has a wire extending from the printed circuit board  107  to the PPG, for controlling the PPG and collecting data from the PPG. 
     In both embodiments, the movements of the user do not dislocate the ECG or the PPG from contacting his skin. As tee-shirts are not easily seen if worn as an undergarment, the embodiments allow twenty four hours wearing and monitoring of the heartbeat of the person. This is particularly possible in a dry temperate or cold climate as the skin remains dry despite regular perspiration. 
     In a further embodiment shown in  FIG. 3 , each sleeve  101  of the tee-shirt has a PPG sensor  203  as well as the electrodes  103  of for obtaining an ECG. Hence, for each bicep, an ECG can be obtained as well as a PPG. The ECG tells when a heartbeat takes place, while the PPG on each bicep shows how long does it take for the surge of blood to travel from the heart to the respective bicep, i.e. the pulse-transit-time to the bicep. 
     Anomalies in the left and right main arteries of the upper body may be monitored by observing the difference between the left and right pulse-transit-times. 
     Generally, the length of the blood vessels from the heart to the bicep may be assumed to be virtually the same for both biceps. Hence, left and right pulse-transit-times should be similar in a healthy individual. If the left and right pulse-transit-times are different by a significant amount, it may be indicative of blockage in some of the blood vessels, and it is suggesting an increased risk of heart disease and stroke. Alternatively, it could represent a tumour blocking blood flow. Furthermore, it could be indicative of uneven constriction between the left and right sides of the upper body. Yet further, it could mean the muscles on one side of the body have been overused or over-exercised. Such information is useful for doctors to zoom in on any left and right side imbalance, and also to physical trainers, chiropractors and osteopaths. 
       FIG. 4  illustrates how any anomaly between the left and right sides of a person may be observed using the embodiment. 
       FIG. 4  is a chart of the pulse of a person wearing the embodiment of  FIG. 3 . The top line  401  in the chart shows his ECG. The middle line  403  shows his PPG down the left bicep. The bottom line  405  shows his PPG down the right bicep. The ECG chart  401  is virtually instantaneous with his heartbeat. However, the PPG charts  403 ,  405  are time delayed because the surge of blood created by the heartbeat needs time to reach the biceps and extremities of the limbs, i.e. pulse-transit-time. 
     The pulse-transit-time between the PPG pulse down the left bicep  403  and the ECG  401  is shown as d 1 . The pulse-transit-time between the PPG pulse down the right bicep  405  and the ECG  401  is shown as d 2 . The peak  411  monitored by ECG and the peaks  407 ,  409  monitored by PPG all belong to the same heartbeat. If the person is healthy, d 1  might equal d 2 . 
     It is possible to measure the time difference (i.e. d 1 −d 2 ) between the PPG signals  403 ,  405  down both biceps directly, i.e. observe the peak  407  of the pulse on the right bicep and the peak  409  of the pulse on the left bicep and take their time difference to obtain d 1 −d 2 , without measuring their time difference with respect to the ECG peak  411 . Nevertheless, it is preferable to monitor the pulses down each bicep  407 ,  409  with reference to the ECG peak  411  as time zero. This is because it is easier to identify an ECG peak in order to anticipate the corresponding PPG pulses  407 ,  409  down both biceps. Furthermore, if both sides of the body are just as blocked or constricted, there may not be any significant difference between d 1  and d 2 , but the absolute pulse-transit-time between each PPG pulse  403 ,  405  and the ECG pulse  401  might show significant time lag, indicating a health warning. 
       FIG. 5  shows another way in which the PPG pulses  403 ,  405  between the two biceps may be compared. Whereas the chart in  FIG. 4  shows how lag time between two PPG pulses  407 ,  409  may be used to observe differences between the left and right sides of the person&#39;s body, the chart in  FIG. 5  shows how the intensity of the PPG pulses  403 ,  405  may be used. The example in  FIG. 5  shows the trough-to-peak amplitude D 1  of a pulse in the left bicep  403  being smaller than the trough-to-peak amplitude D 2  of the pulse in the right bicep  405 . In this example, no time lag is observed between the PPG peaks,  407 ,  409 . This is possible in some cases because constriction in arteries may not necessarily translate into a slowing down of the pulse. A constriction may simply dampen the intensity of the pulse, leading to a weaker pulse signal. Physically, this means less blood content is pumped by each beat of the heart, hence the smaller amplitude. In  FIG. 5 , the pulse down the left bicep  403  is shown to have smaller trough-to-peak amplitude, whereas the pulse down the right bicep  405  has relatively greater trough-to-peak amplitude. The peak  411  of the ECG  401  is still useful as a trigger to anticipate the peaks  407 ,  409  of both PPG pulses  403 ,  405 , ensuring that they are all of the same heartbeat. 
       FIG. 5 a    shows yet another way in which the PPG pulses  403 ,  405  between the two biceps may be compared. Whereas the chart in  FIG. 4  shows how lag time between two PPG pulses  403 ,  405  may be used to observe difference between the left and right sides of the person&#39;s body, and whereas the chart in  FIG. 5  shows how the intensity of the PPG pulses  403 ,  405  may be used,  FIG. 5 a    shows how the difference in the spread of the pulses  403 ,  405  in the two biceps may be different and subject to comparison.  FIG. 5 a    illustrates that the spread δ 1  of the pulse  403  in the left bicep is less than the spread δ 2  of the pulse  405  in the right bicep. This is possible because constriction in arteries may cause a pulse to be released into a bicep or limp in a drawn-out, spread pulse. 
     Besides comparing the time of the PPG pulses, or the spread of the pulses  403 ,  405 , or the trough-to-peak amplitude of the pulses  403 ,  405 , it is also possible to simply compare the shape of the pulses  403 ,  405 . The peaks  407 ,  409  of the pulses can be easily classified into different categories of shape by using signal cross-correlation methods (not illustrated), wherein the template of a standard shape is applied to the pulses. If the shape of a pulse is a match to the template, a mathematical value of unity can be calculated. In this way, the shape of pulses down the left and right limb of the same heartbeat can be measured, characterised and compared. Cross-correlations methods are well-known signal processing techniques and do not require elaboration here. 
       FIG. 6  shows a variation of the embodiment of  FIG. 3 . Instead of a tee-shirt, the embodiment is now a diver&#39;s suit  601 .  FIG. 6  only shows the upper body part of the suit. As the diver&#39;s suit has long sleeves  101 , mid-way along each sleeve  101  about the position of the bicep is a PPG sensor  203  as well as the electrodes  103  of for obtaining an ECG, in similar positions to the PPG sensors  203  and electrodes  103  in  FIG. 3 . 
       FIG. 6 a    shows a further variation of the embodiment of  FIG. 3 . The embodiment comprises a full body undergarment  603  having leggings  605 . Along each legging  605  of the full body undergarment, about the position of the calf, is a resilient, stretchable, elastic band encircling the perimeter of the legging. Installed in the elastic band are a PPG sensor  203  as well as an electrode  103  of for obtaining an ECG. 
     Having an electrode  103  on both calves creates a closed circuit through the electrodes  103  across the body and heart of the person. The closed circuit is then useable for monitoring heart related electric signals. As in  FIG. 3 , a wire  105  is shown connecting the electrodes  103  to a flexible printed circuit board  107 . The full body undergarment  603  has a wire extending from the printed circuit board  107  to the PPG in each legging, for controlling the PPG and collecting data from the PPG. 
     Accordingly, for each calf, an ECG can be obtained as well as a PPG. The ECG represents the time the heart beat producing the pulse takes place, and the PPG on each calf shows how long does it take for the pulse to travel from the heart to the calf, i.e. pulse-transit-time to the calf. 
     Any anomaly in the calf arteries may be monitored by the user wearing the full body undergarment, by observing differences in pulse-transit-time to each calf, the difference in amplitude between the pulses of the left leg and the right leg, the difference in spread between the pulses of the left leg and the right leg, and/or the difference in shape of the pulses of the left leg and the right leg, in the same manner as illustrated in  FIG. 4 ,  FIG. 5  and  FIG. 5 a    for the upper limbs. 
     One useful application of this embodiment is in the quantification of ‘pins-and-needles’ or numbness suffered in the legs. 
     In another embodiment of the invention, a ballistocardiogram (BCG) sensor is placed on the clothing in place of the ECG. Alternatively the BCG sensor is placed in addition to the ECG. As the skilled man knows, a BCG sensor measures vibrational activity of the heart, i.e. ballistic forces. Generally, blood is ejected out from the heart into the ascending aorta and pulled into the heart from the inferior cava vein, in regular pumping motions. For both ejecting blood and pulling blood, according to Newton&#39;s 3rd Law, the force exerted on the blood by the heart is matched by an equal and opposite force on the body. These forces, or accelerations, can be detected by a sensitive accelerometer placed on the body, and the pumping of the blood can be deduced from the forces, to provide a chart which is the BCG. 
       FIG. 7  is a modification of  FIG. 4 , showing additionally two BCG signals. The BCG signals are modified from an actual chart in http://www.cs.tut.fi/sqn/SSSAG/BCG.htm, observed from a person seated in a chair that is slide-able with very low resistance. The top BCG  701  shows the acceleration of vibrations sensed by an accelerometer in in the back of a seat the person is seated on. The bottom BCG  701  shows the acceleration of vibrations sensed concurrently with the top BCG, but by an accelerometer located in the back of the same seat. The fluctuation of the baseline is caused by the person&#39;s normal breathing. 
       FIG. 8  shows the embodiment of  FIG. 3  modified to include a BCG sensor, which is typically an accelerometer  801 . BCG sensor in this embodiment is placed at the back of the tee-shirt, where the upper back is. The BCG can then be used to compare with the PPG signals down one or both biceps of the person. The time lapse between the pulse observed in the BCG and the pulse observed by the PPGs of either bicep can be used to calculate pulse-transit-time, and deduce health, constriction and blockage in the arteries down the biceps. 
       FIG. 9  shows one of the simplest embodiments of the invention, comprising only two wrist-worn PPG sensors  203 . The PPG sensors  203  are in wireless communication with a mobile phone  901 . The pulses read by each of the PPG sensors  203  are used to measure the time difference between them, as illustrated in  FIG. 10 , where d 3  labels the time lag. In other words, the pulse-transit-time in each hand is not measured but the difference between the pulse-transit-times of both hands is measured directly. As the skilled man understands, the pulse in each hand must be created by the same heartbeat. Other comparisons of the PPPG pulse down each wrist may be made in the manner as described for  FIG. 5  and  FIG. 5 a   , for comparing the trough-to-peak amplitudes, and the spread of the pulses, as well as comparing the shapes of the pulses (not illustrated). In this embodiment, there is no ECG for a reference point by which to measure pulse-transit-time. 
     Embodiments have been described some of which comprises an apparatus for monitoring the pulse of a person, comprising a piece of clothing suitable for being worn on the body of the person; the clothing having two sleeves, each suitable for the person&#39;s respective limbs to be inserted through; along each of the sleeves is a stretchable neck  101  (the band in the sleeve  101  of  FIG. 1 ,  FIG. 2  or  FIG. 3 ) for hugging the respective limb; one or more electrodes  103  in each neck  101 ; an electrical conductor  105  connecting the electrodes  103  of each neck  101 ; wherein the neck  101  urges the electrodes  103  of each of the sleeve into contact with the skin of the respective limb. 
     Furthermore, embodiments have been described some of which comprises an apparatus for monitoring the pulse of a person, comprising a piece of clothing suitable for being worn on the body of the person; the clothing having least one sleeve suitable for at least one of the person&#39;s limbs to be inserted through; the at least one sleeve having a resilient neck  101  for hugging the limb; one or more PPG sensors  203  in the neck  101 ; such that the neck  101  urges the one or more PPG sensors  203  into contact with the skin of the limb. 
     Also, embodiments have been described some of which comprises a method of monitoring heart pulses of a person, comprising the steps of: obtaining the left pulse of a heartbeat in the left limb; obtaining the right pulse of the same heartbeat in the right limb; observing a difference between the pulses in one or more of the following pulse characteristic: i. the pulse-transit-time of the pulse; ii. the spread of the pulse; iii. the trough to peak amplitude of the pulse; and/or iv. the shape of the pulse. 
     While there has been described in the foregoing description preferred embodiments of the present invention, it will be understood by those skilled in the technology concerned that many variations or modifications in details of design, construction or operation may be made without departing from the scope of the present invention as claimed. 
     For example, even though a tee-shirt has been described in most embodiments, any other kind of clothing such as jackets, formal shirts, overalls, pullovers and so on can be used as long as an elastic, resilient or stretchable part or parts are provided which strangle or hug the biceps, wrists, calves, ankles, fingers, toes, of the person in order to observe his pulses. 
     Although PPG has been described for measuring pulses in a person&#39;s limbs or extremities, other methods of observing the shape of a pulse is within the contemplation of the invention. For example, an atomic force microscope which uses a very sensitive cantilever for detecting the physical profile of a surface can be used to observe the shape of a pulse.