How smart watches, sports trackers and other gadgets measure the pulse? Part 2
Hello to all!
We continue an exciting journey into the world of pulse meters. In the first part, we talked about measurement methods based on ECG and plethysmography - the most popular on the market. The method of optical plethysmography is applied in our project EMVIO - watches that measure your stress.
The EMVIO project company will start on the Kickstarter platform on March 17, 2015. We have almost completed all the organizational work, now the final layout of the Kickstarter page is underway. You can subscribe to the newsletter on the promotional site of the project, to keep abreast of all the news.
')
We offer to support our project. All the details and price offers will be presented in a separate post before the start of the company. For the very first (Early bird) backers, we prepared a limited number of EMVIO watches for $ 129 USD.
Now let's continue. How else can you measure the pulse?
This method is known to all, without exception, just not everyone knows that it is so called. The method of sphygmography realizes the registration of arterial pulses by deformation of the arterial vessel wall. The result is a curve similar to plethysmography. Pulse recording should be carried out in places where the arteries come close to the skin surface, for example, from the back of the wrist or above the elbow, where the radial artery goes along one trunk. The beating of the artery wall is very small, so the original method was invented to enhance the signal at the end of the 19th century: clamping the artery to a level where the artery still allows blood flow, but creates an obstacle to the shock wave of blood. In this case, there were strong pulsations that can be fixed by mechanical means.
On the main photo of the post rendered image of the first device - smigograph, brought to practical use. Looks like a Van Helsing javelin thrower. The invention of the French physiologist Etienne-Jules Mare. Almost wearable gadget 1863 release. The device pressed the artery with the help of an adjusting mechanism, mechanically amplified the amplitude of the pulse wave and produced a pen recording of mechanical vibrations on the paper. It was a prototype of the familiar cuff for measuring pressure.
Here look at the animated principle of operation of this device and its design in 3D
In general, the processes that occur in the arteries when they are clamped are quite complex. The study of these issues is relevant if you want to measure pressure. When you just need a pulse, you can simplify the registration scheme: remove the cuff, acoustic sensor (microphone) or a regular stethoscope to replace with a mechanical sensor - a piezo element. This element operates in the direct piezoelectric effect mode (deformation -> polarization) and is capable of detecting deformations at the level of micrometers.
Piezosensor
The idea of the method based on the piezoelectric element is well disclosed in the patent Wrist plethysmograph US 20070287923 A1. The picture shows the scheme of the device. The whole device design works on the sensor - the strap provides tensile force at the edges of the piezo sensor and acts as a kind of cuff, the case gives the necessary rigidity and support.
Patented method of pulse registration based on piezo sensor.
The calculation of the pulse using a sphygmogram is the same as in plethysmography, since the resulting pulse curves are almost identical.
In practical implementation, there may be nuances associated with individual characteristics. There is an interesting study in which the dependence of the amplitude of the pulse signal on the pressure force of the piezo sensor, individual parameters of the patient's hand, etc. was studied. The sensor was brought to the wrist with a stepper motor with feedback and, thus, the force of pressing was normalized. The article indicates that the variation of individual pressures is quite high, and also there are problems with the registration of overweight people with an increased thickness of the subcutaneous fat layer. There is work to do.
Healbe
The principle of mechanical measurement of the pulse is implemented in the acclaimed bracelet HealBe Go .
The HealBe Go bracelet uses a piezo sensor to measure heart rate.
According to the declared parameters, the pulse wave signal is read from the wrist using a piezoelectric pressure sensor. The scientific and technical report of the HealBe developers gives an example of the pulse curve from the sensor, the waveform is quite typical for plethysmography and sphygmography. That is interesting, in one gadget known to us such method is not used. So HealBeGo can say the pioneers.
Flexible sensors
There are concepts and research on the use of such sensors. Here is an example of an article where the implementation of an ultrathin flexible sensor based on gold nanotubes is described.
When the sensor bends the surface, a delta current appears. This delta is enough to fix the dynamic pressure component from 13 Pa (for comparison: 1 Pa (N / m2) is 7.50062 µm Hg) ( hence , the mix from figure 1 and 6).
The sensor is fixed on the skin in the wrist area and registers the pulse waves. The study of the sensor showed that the amplitude of the signal is affected by the level of the current background sound, such as voice and music, which is quite expected.
Here is another example of a sensor based on a 2D array of piezocells.
Microtechnologies in action ( hence , taken from figure 1).
This sensor is more advanced and functionally complete: it contains a primary amplification circuit and has contacts for connection. Here are some examples of sticker sticks to various parts of the body.
Any points are available to the sensor ( from here , taken from figure 4)
If you take a signal from the wrist and neck, you can implement a method of measuring blood pressure based on calculating the relative pulse wave velocity (PWV) between the artery on the neck and the artery on the wrist (by the phase shift between the signals). Actually in the article, the sensor is positioned to solve this particular problem. Here are some good ideas for future heart rate monitor gadgets.
Perhaps soon we will see flexible translucent bracelets for measuring the pulse. Flexible batteries have already appeared.
The method of ballistocardiography uses the effect of the detonation of the body from the shock wave when pumping blood through the vessels. In clinical practice, it was used not for the sake of pulse measurement, but for analyzing dynamic blood flow indicators.
Another megadevise from the past. Fearfully? (picture taken from here )
The signal is the mechanical oscillations of the body under the action of the shock wave from the flow of blood through the vessels. I think many, lying in bed, noticed this effect. Here is a very simple demonstration of the principle of work in photographs.
At the present level, this method has been implemented as a smart Darma pad for controlling posture. Since the institute, in my memory, ballistocardiography has been associated with a bulky device, and I was pleasantly surprised by this project in terms of choosing the method for registering a pulse. The project performed well on Kickstarter.
A girl in a green dress is monitoring her posture with the help of Darma. Feel the difference with the guy on the swinging table, for this we love such projects.
Pulse appears rather as an additional parameter, the main thing is control of correct posture. Their promotional materials show the characteristic form of a ballistocardiogram (BCG) and its specific points. Pulse values are calculated between local maxima (point J). An interesting device, but if you constantly turn around and fidget in your chair, this solution is not for you.
Here is another Beddit gadget. It is made in the form of a belt and is placed on the bed under the body of a person during sleep.
The girl in white and the Beddit gadget. For men - a version of the radically black.
The device is positioned as a sleep monitor. It can record the pulse, breathing curve, sleep phases. Also implemented a “smart alarm clock”. This is what his signal looks like.
Ballistocardiogram with Beddit. Against the background of respiratory vibrations, heart detonations are visible (taken from the report. )
In principle, such devices can be embedded directly in mattresses or carried out in the form of baby diapers, blankets, etc. For double options you can zone registration areas. Wake with a vibration motor.
The method is based on the registration of acoustic noise during the heartbeat and the operation of its valves. Using this method, diagnostics of abnormalities in the heart and valves is performed. The simplest implementation is to attach a microphone or an ordinary stethoscope to the heart, fix it and listen to low-frequency beats-noises.
Listen to how the heart beats. Shot from the movie “The Diamond Hand.”
In principle, for the registration of the pulse, it is enough to consider acoustic shocks, but there is a small nuance. The phonocardioscopy signal contains the so-called tones - oscillations associated with heart systole-diastole, the work of its valves and simply non-periodic noise. Normally, there are several tones for each cardiac cycle, usually 4 tones are distinguished (they are denoted by Roman numerals). Basic: I tone - the beginning of systole, II tone - the beginning of diastole. In the English-language literature, there are S1 segments (first heart sound) - the beginning of systole and S2 (second heart sound) - the beginning of diastole. Depending on the listening position, the relative amplitude of tones may vary. Here is an example of a signal.
Examples of phonocardioscopy signal: on the left, synchronously with the ECG and pitch ( from here ), on the right, the example of automated signal segmentation is normal. ( from here )
Of course, now that an ultrasound machine with a diagnostic method based on the Doppler effect has become a common medical device available at any clinic and hospital, phonocardiography has somewhat lost its clinical significance.
However, stethoscopes have not gone away and are the most popular and affordable means of initial examination. Therefore, it is only natural that the developers of the gadgets took on them. Do you have bluetooth in your stethoscope? Then we go to you! There are many such devices on the market.
Here is an example of such a hybrid gadget from the company Thinklabs Medical LLC .
Versions of smart Thinktobs stethoscopes: from imitation of classic to minimalism.
A big plus of this method is that this functionality is available in almost any phone. Sensor microphone is already on board. Why then a stethoscope? Not surprisingly, a program has already been developed for the IPhone, called iStethoscopePro.
Screens iStethoscopePro (developer Peter_J._Bentley ).
It turned out that this is quite a popular application, and what is most interesting, according to Peter Bentley, doctors use it, because it allows you to record and reproduce the noises of the heart. You can experience how it works. Here is an example of the program SKEEPER Heart Rate for Android.
Screens SKEEPER Heart Rate. Press and listen.
Still, it is interesting how smartphones gradually incorporate functionality that was not originally planned. In the next section, you will see an example of the fantastic possibility of using a smartphone to register a pulse.
A very original and, we can say boldly, innovative way to register the pulse.
Perhaps the medical tricorder in Startrek was equipped with just such a sensor. (Still from Star Trek: The Original Series)
Uses classical radar technology based on Ultra-Wide Band signals. The signal is emitted, it is reflected from the internal organs, chest and heart, respectively, the time of arrival (time-of-fight) of the reflected signal will depend on the distance to the antenna, the mobility of the chest and heart.
Model of formation of the temporal characteristics of the reflected UWB signal in the chest ( hence ).
Analyzing the low-frequency periodic modulation of the delay, you can select the respiratory and pulse components. The type of signal and its power spectral density are shown in the figure. The signal is generated by the first derivative of the Gauss function.
UWB signal and the boundaries of the spectral range ( from here ).
One of the first patents for such a device is dated 1996. Author Thomas E. McEwan US 5573012 A Body monitoring and imaging apparatus and method .
Functional diagram of the pulse radar device and the type of output signals.
To date, research work on the use of UWB radar in medicine is published regularly. You can google UWB heart rate radar .
In Russia, there is a group of UWBgroup.ru , based on the Research Center for Ultra Wideband Technologies of the Moscow Aviation Institute (SIC UWB MAI), which is developing medical radars. The work of the group can be viewed on the publications on their website. Here is an example of a prototype of such a radar for measuring pulse, which is developed by the participants of this scientific group.
The appearance and location of the UWB radar (from theses ).
Now this topic is very popular, given the fact that the UWB range itself is very promising for transmitting data at gigabit speeds (ultra-wideband communication) and inexpensive radio transmitting modules have appeared on the market.
In the end - truly fantastic features! Monitor your pulse through the walls! Search for living people under the rubble. Use smartphones as a sounding signal generator! Anti-terrorism multipath systems for identifying suspicious individuals.
Bioradar for special applications. A smartphone can be used as a sounding signal generator ( from here ). Of course, this is just an idea.
Dogs in trend.
To date, we managed to find only one such device, brought to the mass product. This is a Voyce doggy bracelet.
A collar bracelet to monitor your dog's health.
For people, nothing like this is being proposed. Apparently, there are problems with the certification of such emitters for use by people, but perhaps these are temporary problems. In general, dogs and other pets can already be worn.
Well, almost everything. Technology does not stand still, and we will definitely see unusual solutions and the original “reading” of the classic pulse registration methods on our wrists.
PS: Yes, another pulse can be measured using ultrasound, monitoring the contraction of the walls of the heart. This is a regular function of any cardiological ultrasound machine, but it is not yet used in wearable gadgets, although there are portable ones the size of a small hairdryer . Still, this is almost a full-fledged apparatus for clinical diagnosis.
Until! All good health!
And once again we invite you to the site of our EMVIO project.
We continue an exciting journey into the world of pulse meters. In the first part, we talked about measurement methods based on ECG and plethysmography - the most popular on the market. The method of optical plethysmography is applied in our project EMVIO - watches that measure your stress.
The EMVIO project company will start on the Kickstarter platform on March 17, 2015. We have almost completed all the organizational work, now the final layout of the Kickstarter page is underway. You can subscribe to the newsletter on the promotional site of the project, to keep abreast of all the news.
')
We offer to support our project. All the details and price offers will be presented in a separate post before the start of the company. For the very first (Early bird) backers, we prepared a limited number of EMVIO watches for $ 129 USD.
Now let's continue. How else can you measure the pulse?
1. Pulse measurement based on sphygmography
This method is known to all, without exception, just not everyone knows that it is so called. The method of sphygmography realizes the registration of arterial pulses by deformation of the arterial vessel wall. The result is a curve similar to plethysmography. Pulse recording should be carried out in places where the arteries come close to the skin surface, for example, from the back of the wrist or above the elbow, where the radial artery goes along one trunk. The beating of the artery wall is very small, so the original method was invented to enhance the signal at the end of the 19th century: clamping the artery to a level where the artery still allows blood flow, but creates an obstacle to the shock wave of blood. In this case, there were strong pulsations that can be fixed by mechanical means.
On the main photo of the post rendered image of the first device - smigograph, brought to practical use. Looks like a Van Helsing javelin thrower. The invention of the French physiologist Etienne-Jules Mare. Almost wearable gadget 1863 release. The device pressed the artery with the help of an adjusting mechanism, mechanically amplified the amplitude of the pulse wave and produced a pen recording of mechanical vibrations on the paper. It was a prototype of the familiar cuff for measuring pressure.
Here look at the animated principle of operation of this device and its design in 3D
In general, the processes that occur in the arteries when they are clamped are quite complex. The study of these issues is relevant if you want to measure pressure. When you just need a pulse, you can simplify the registration scheme: remove the cuff, acoustic sensor (microphone) or a regular stethoscope to replace with a mechanical sensor - a piezo element. This element operates in the direct piezoelectric effect mode (deformation -> polarization) and is capable of detecting deformations at the level of micrometers.
Piezosensor
The idea of the method based on the piezoelectric element is well disclosed in the patent Wrist plethysmograph US 20070287923 A1. The picture shows the scheme of the device. The whole device design works on the sensor - the strap provides tensile force at the edges of the piezo sensor and acts as a kind of cuff, the case gives the necessary rigidity and support.
Patented method of pulse registration based on piezo sensor.
The calculation of the pulse using a sphygmogram is the same as in plethysmography, since the resulting pulse curves are almost identical.
In practical implementation, there may be nuances associated with individual characteristics. There is an interesting study in which the dependence of the amplitude of the pulse signal on the pressure force of the piezo sensor, individual parameters of the patient's hand, etc. was studied. The sensor was brought to the wrist with a stepper motor with feedback and, thus, the force of pressing was normalized. The article indicates that the variation of individual pressures is quite high, and also there are problems with the registration of overweight people with an increased thickness of the subcutaneous fat layer. There is work to do.
Healbe
The principle of mechanical measurement of the pulse is implemented in the acclaimed bracelet HealBe Go .
The HealBe Go bracelet uses a piezo sensor to measure heart rate.
According to the declared parameters, the pulse wave signal is read from the wrist using a piezoelectric pressure sensor. The scientific and technical report of the HealBe developers gives an example of the pulse curve from the sensor, the waveform is quite typical for plethysmography and sphygmography. That is interesting, in one gadget known to us such method is not used. So HealBeGo can say the pioneers.
Flexible sensors
There are concepts and research on the use of such sensors. Here is an example of an article where the implementation of an ultrathin flexible sensor based on gold nanotubes is described.
When the sensor bends the surface, a delta current appears. This delta is enough to fix the dynamic pressure component from 13 Pa (for comparison: 1 Pa (N / m2) is 7.50062 µm Hg) ( hence , the mix from figure 1 and 6).
The sensor is fixed on the skin in the wrist area and registers the pulse waves. The study of the sensor showed that the amplitude of the signal is affected by the level of the current background sound, such as voice and music, which is quite expected.
Here is another example of a sensor based on a 2D array of piezocells.
Microtechnologies in action ( hence , taken from figure 1).
This sensor is more advanced and functionally complete: it contains a primary amplification circuit and has contacts for connection. Here are some examples of sticker sticks to various parts of the body.
Any points are available to the sensor ( from here , taken from figure 4)
If you take a signal from the wrist and neck, you can implement a method of measuring blood pressure based on calculating the relative pulse wave velocity (PWV) between the artery on the neck and the artery on the wrist (by the phase shift between the signals). Actually in the article, the sensor is positioned to solve this particular problem. Here are some good ideas for future heart rate monitor gadgets.
Perhaps soon we will see flexible translucent bracelets for measuring the pulse. Flexible batteries have already appeared.
2. Pulse measurement based on ballistocardiography
The method of ballistocardiography uses the effect of the detonation of the body from the shock wave when pumping blood through the vessels. In clinical practice, it was used not for the sake of pulse measurement, but for analyzing dynamic blood flow indicators.
Another megadevise from the past. Fearfully? (picture taken from here )
The signal is the mechanical oscillations of the body under the action of the shock wave from the flow of blood through the vessels. I think many, lying in bed, noticed this effect. Here is a very simple demonstration of the principle of work in photographs.
At the present level, this method has been implemented as a smart Darma pad for controlling posture. Since the institute, in my memory, ballistocardiography has been associated with a bulky device, and I was pleasantly surprised by this project in terms of choosing the method for registering a pulse. The project performed well on Kickstarter.
A girl in a green dress is monitoring her posture with the help of Darma. Feel the difference with the guy on the swinging table, for this we love such projects.
Pulse appears rather as an additional parameter, the main thing is control of correct posture. Their promotional materials show the characteristic form of a ballistocardiogram (BCG) and its specific points. Pulse values are calculated between local maxima (point J). An interesting device, but if you constantly turn around and fidget in your chair, this solution is not for you.
Here is another Beddit gadget. It is made in the form of a belt and is placed on the bed under the body of a person during sleep.
The girl in white and the Beddit gadget. For men - a version of the radically black.
The device is positioned as a sleep monitor. It can record the pulse, breathing curve, sleep phases. Also implemented a “smart alarm clock”. This is what his signal looks like.
Ballistocardiogram with Beddit. Against the background of respiratory vibrations, heart detonations are visible (taken from the report. )
In principle, such devices can be embedded directly in mattresses or carried out in the form of baby diapers, blankets, etc. For double options you can zone registration areas. Wake with a vibration motor.
3. Pulse measurement based on phonocardioscopy
The method is based on the registration of acoustic noise during the heartbeat and the operation of its valves. Using this method, diagnostics of abnormalities in the heart and valves is performed. The simplest implementation is to attach a microphone or an ordinary stethoscope to the heart, fix it and listen to low-frequency beats-noises.
Listen to how the heart beats. Shot from the movie “The Diamond Hand.”
In principle, for the registration of the pulse, it is enough to consider acoustic shocks, but there is a small nuance. The phonocardioscopy signal contains the so-called tones - oscillations associated with heart systole-diastole, the work of its valves and simply non-periodic noise. Normally, there are several tones for each cardiac cycle, usually 4 tones are distinguished (they are denoted by Roman numerals). Basic: I tone - the beginning of systole, II tone - the beginning of diastole. In the English-language literature, there are S1 segments (first heart sound) - the beginning of systole and S2 (second heart sound) - the beginning of diastole. Depending on the listening position, the relative amplitude of tones may vary. Here is an example of a signal.
Examples of phonocardioscopy signal: on the left, synchronously with the ECG and pitch ( from here ), on the right, the example of automated signal segmentation is normal. ( from here )
Of course, now that an ultrasound machine with a diagnostic method based on the Doppler effect has become a common medical device available at any clinic and hospital, phonocardiography has somewhat lost its clinical significance.
However, stethoscopes have not gone away and are the most popular and affordable means of initial examination. Therefore, it is only natural that the developers of the gadgets took on them. Do you have bluetooth in your stethoscope? Then we go to you! There are many such devices on the market.
Here is an example of such a hybrid gadget from the company Thinklabs Medical LLC .
Versions of smart Thinktobs stethoscopes: from imitation of classic to minimalism.
A big plus of this method is that this functionality is available in almost any phone. Sensor microphone is already on board. Why then a stethoscope? Not surprisingly, a program has already been developed for the IPhone, called iStethoscopePro.
Screens iStethoscopePro (developer Peter_J._Bentley ).
It turned out that this is quite a popular application, and what is most interesting, according to Peter Bentley, doctors use it, because it allows you to record and reproduce the noises of the heart. You can experience how it works. Here is an example of the program SKEEPER Heart Rate for Android.
Screens SKEEPER Heart Rate. Press and listen.
Still, it is interesting how smartphones gradually incorporate functionality that was not originally planned. In the next section, you will see an example of the fantastic possibility of using a smartphone to register a pulse.
4. Pulse measurement based on bio radar
A very original and, we can say boldly, innovative way to register the pulse.
Perhaps the medical tricorder in Startrek was equipped with just such a sensor. (Still from Star Trek: The Original Series)
Uses classical radar technology based on Ultra-Wide Band signals. The signal is emitted, it is reflected from the internal organs, chest and heart, respectively, the time of arrival (time-of-fight) of the reflected signal will depend on the distance to the antenna, the mobility of the chest and heart.
Model of formation of the temporal characteristics of the reflected UWB signal in the chest ( hence ).
Analyzing the low-frequency periodic modulation of the delay, you can select the respiratory and pulse components. The type of signal and its power spectral density are shown in the figure. The signal is generated by the first derivative of the Gauss function.
UWB signal and the boundaries of the spectral range ( from here ).
One of the first patents for such a device is dated 1996. Author Thomas E. McEwan US 5573012 A Body monitoring and imaging apparatus and method .
Functional diagram of the pulse radar device and the type of output signals.
To date, research work on the use of UWB radar in medicine is published regularly. You can google UWB heart rate radar .
In Russia, there is a group of UWBgroup.ru , based on the Research Center for Ultra Wideband Technologies of the Moscow Aviation Institute (SIC UWB MAI), which is developing medical radars. The work of the group can be viewed on the publications on their website. Here is an example of a prototype of such a radar for measuring pulse, which is developed by the participants of this scientific group.
The appearance and location of the UWB radar (from theses ).
Now this topic is very popular, given the fact that the UWB range itself is very promising for transmitting data at gigabit speeds (ultra-wideband communication) and inexpensive radio transmitting modules have appeared on the market.
In the end - truly fantastic features! Monitor your pulse through the walls! Search for living people under the rubble. Use smartphones as a sounding signal generator! Anti-terrorism multipath systems for identifying suspicious individuals.
Bioradar for special applications. A smartphone can be used as a sounding signal generator ( from here ). Of course, this is just an idea.
Dogs in trend.
To date, we managed to find only one such device, brought to the mass product. This is a Voyce doggy bracelet.
A collar bracelet to monitor your dog's health.
For people, nothing like this is being proposed. Apparently, there are problems with the certification of such emitters for use by people, but perhaps these are temporary problems. In general, dogs and other pets can already be worn.
Well, almost everything. Technology does not stand still, and we will definitely see unusual solutions and the original “reading” of the classic pulse registration methods on our wrists.
PS: Yes, another pulse can be measured using ultrasound, monitoring the contraction of the walls of the heart. This is a regular function of any cardiological ultrasound machine, but it is not yet used in wearable gadgets, although there are portable ones the size of a small hairdryer . Still, this is almost a full-fledged apparatus for clinical diagnosis.
Until! All good health!
And once again we invite you to the site of our EMVIO project.
Source: https://habr.com/ru/post/377255/
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