How smart watches, sports trackers and other gadgets to measure the pulse? Part 2

Hello everyone!





Continue a fascinating journey into the world of heart rate meter. In the first part of we talked about methods of measurement based on ECG and plethysmography - the most popular on the market. Optical plethysmography method applied in our project EMVIO - hours that measure your stress.

Company project starts EMVIO platform Kickstarter March 17, 2015. We have nearly completed all the organizational work is underway on the final page layout Kick. You can subscribe to the newsletter promo-site of the project that would be up to date with all the news.

Offer support our project. All the details and price proposals will be presented in a separate post before us. For the first (Early bird) Baker, we have prepared a limited number of hours EMVIO for $ 129 USD.

And now continue. How else can you measure the pulse?

1. Measurement on the basis of sphygmography h4> This method is known to all, just not all know what he's called. Sphygmography registration method implements arterial pulse by deformation of the vessel wall of the artery. The result is a curve similar plethysmography. Pulse registration should be carried out in areas where the artery come close to the skin surface, such as the back of the wrist or upper arm, where the radial artery is one trunk. The beating of the artery wall is very small, so to amplify the signal at the end of the 19th century, was invented an original way: clamping the artery to the point where the artery blood flow still missing, but an obstacle shock wave of blood. In this case, a strong pulsation, which can be fixed by mechanical means.

Main photo post rendered image of the first device - smigmografa adjusted to practical application. It looks like a dart thrower Van Helsing. The invention of the French physiologist Etienne-Jules Mare. Almost wearable gadget 1863 release. Apparatus artery pressed down by an adjusting mechanism, mechanically strengthened, and the amplitude of the pulse wave produced fountain mechanical vibrations on recording paper. This was the prototype of a familiar pressure cuff.



Here here look animated working principle of this device and its design in 3D i>

In general, the processes that occur in the blood vessels artery in her cross-clamping, are quite complex. The study of these issues is overdue, if you want to measure the pressure. When do you need a pulse, the registration scheme can be simplified: remove the cuff, an acoustic sensor (microphone) or conventional stethoscope replace mechanical sensor - piezo. This element works in direct mode piezoelectric effect (deformation - & gt; polarization) and is capable of detecting the strain at micrometers.

pezosensorov
The idea of ​​the method based on the piezoelectric element is disclosed in good Wrist plethysmograph US 20070287923 A1. In the picture shows a diagram of the device. The sensor operates on the entire structure of the device - strap provides a tensile force on the edges of the piezoelectric transducer and serves as a kind of cuff body gives the necessary rigidity and support.



The patented method of recording pulse based on the piezoelectric transducer. I>

Calculation for pulse sphygmograms same as in plethysmography as pulse curves obtained are almost identical.
In the practical implementation may be nuances associated with individual characteristics. There is an interesting study , in which the dependence of the amplitude of the pulse signal from the pressure force piezosensor individual parameters hands of patients etc. Was fed to the wrist sensor stepper motor with feedback and thus normalized pressing force. The article states that the individual variation in pressure is quite high, as well as problems with the registration of people who are overweight with increased thickness of subcutaneous fat layer. There is work to do.

HealBe
The principle of the mechanical pulse is implemented in the sensational bracelet HealBe Go .



Bracelet HealBe Go uses pezodatchk Pulse. I>

According to the stated parameters of the pulse wave signal read out from the wrist by a piezoelectric pressure sensor. In scientific and technical report developers HealBe example pulse curve from the sensor, the waveform is quite typical for plethysmography and sphygmography . What is interesting in any gadget known to us this method is not used. So we can say HealBeGo pioneers.

Flexible sensors
There are concepts and research on the use of such sensors. Here's an example article, which describes the implementation of ultra-thin flexible sensor based on gold nanotubes.



If there is a bend sensor surface delta current. This delta is sufficient to capture the dynamic component of the pressure of 13 Pa (for comparison: 1 Pa (N / m2) is 7, 50062 mm Hg) (otsyuda , mix of figure 1 and 6). i>

The sensor is fixed on the skin in the area of ​​the wrist and detects the pulse wave. Investigation probe showed that the amplitude of the signal is affected by the current level of background noise, such as voice and music that is to be expected.

Here's another example of a sensor-based 2D-array pezoyacheek.



Microtechnology in action ( here , taken from figure 1). < / i>

This sensor is more perfect and functionally complete: contains the primary circuit gain and has terminals for connection. Here are examples of stickers sensor to various parts of the body.



The sensor access to any point ( here , taken from figure 4) < / i>

If you remove the signal from the wrist and neck, it is possible to implement a method of measuring blood pressure by calculating the relative velocity of the pulse wave (pulse wave velocity (PWV)) between the artery and the artery on the neck to the wrist (from the phase shift between the signals). Actually the article sensor positioned to tackle this problem. Here you have good ideas for future gadgets, heart rate monitor.

Perhaps we will soon see flexible translucent bracelets Pulse. Flexible batteries already appeared.

2. Measurement on the basis of ballistocardiography h4> ballistocardiography method uses the effect of detonation of the body from the shock when pumping blood through the vessels. In clinical practice, not used for measuring heart rate, and for the analysis of dynamic blood flow.



Another megadevays from the past. Scary? (Picture taken here ) i>

Signal are mechanical vibrations of the body under the action of the shock wave from pumping blood through the vessels. I think many, lying in bed, noticed this effect. Here тут very simple demonstration of the principle of work in the photos.

At the present stage, this method has been implemented in the form of smart pads Darma to control posture. Since the days of the institute in my memory ballistocardiography associated with bulky device, and I was pleasantly surprised by this project in the choice of ways to register a pulse. The project is well made on Kickstarter.



A girl in a green dress watches his posture using Darma. Feel the difference with a man on a rocking table for that we love such projects. I>

Pulse acts more as an additional parameter, the main thing - is to control the correct posture. In their promotional material shows a typical view ballistokardiogrammy (BCG) and its singular points. Heart rate calculated between the local maxima (point J). An interesting device, but if you are constantly twists and squirms in his chair, this solution is not for you.

Here's another gadget Beddit . It is designed as a belt and placed on a bed under a person's body during sleep.



A girl in a white and gadget Beddit. For men - black version dramatically. I>

The device is positioned as a monitor sleep. It can detect heart rate, respiration curve, phase of sleep. Also implemented "smart alarm clock." Here's what his signal.



The signal ballistokardiogrammy with Beddit. Against the background of the respiratory oscillations seen detonation heart (taken from the отчета.) I>

In principle, such devices can be integrated directly into mattresses or perform as diapers, blankets, etc. For two-bedroom options can be zoned area registration. Waking vibration motor.

3. Measurement on the basis of fonokardioskopii h4> The method is based on the detection of acoustic noise in a heartbeat and its valves. With this method diagnose disorders of the heart and valve. The simplest realization - attach a microphone or a conventional stethoscope to the heart, fix it and listen to the bass beats, noises.



Listen to the heart beats. Scene from the movie "The Diamond Arm." I>

In principle, for the registration of the pulse is sufficient to assume acoustic shock, but there is a small caveat. Fonokardioskopii signal contains a so-called tone - oscillations associated with the systole-diastole of the heart, the work of its valves and simply non-periodic noise. For each cardiac cycle normally there are several colors, usually providing 4 colors (they represent in Roman numerals). Key: I tone - the beginning of diastole, II tone - the beginning of systole. In English literature distinguish segments S1 (first heart sound) - the beginning of systole and S2 (second heart sound) - the beginning of diastole. Depending on the listening position relative amplitude tones may vary. Here is an example of the signal.



Examples of signal fonokardioskopii: Left synchronously with the ECG and basic colors (отсюда), Right example of automated segmentation of the signal is normal. (отсюда)

Over, now that the ultrasound machine with diagnostic method based on the Doppler effect has become a common medical device, available at any clinic and hospital, phonocardiography few lost its clinical significance.

However, stethoscopes have not gone away and is the most popular and affordable means of the initial examination. It is therefore natural that the developers took gadgets for them. You do not have a stethoscope bluetooth? Then we go to you! The market offers many such devices.

Here is an example of such a hybrid gadget from the company Thinklabs Medical LLC .



Version smart stethoscopes Thinklabs: from imitation classics to minimalism. I>

A big plus of this method is that this functionality is available in almost any phone. The sensor microphone already on board. Why then stethoscope? Not surprisingly, the program has been developed for IPhone, called iStethoscopePro.



Screens iStethoscopePro (developer Peter_J._Bentley ). I>

It turned out that it is quite popular application, and what is most interesting, according to Peter Bentley, it is used by doctors, because It allows you to record and play sounds of the heart. Can test how it works. Here is an example of the program SKEEPER Heart Rate under Android.



Screens SKEEPER Heart Rate. Press down and listen. I>

Still wondering how smartphones are gradually absorb the functionality that was not originally planned. In the next section, you will see a fantastic example of the possibility of using a smartphone to register a pulse.

4. Measurement on the basis of bioradiolokatorov h4> A very original and one can say boldly innovative method of recording pulse.



Perhaps a medical tricorder in Star Trek was equipped with a sensor that way. (Footage from the series Star Trek: The Original Series) i>

Uses the classic radar technology based on ultra-wideband (Ultra-Wide Band) signals. Emitted light, it is reflected from internal organs of the 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.



A model of the temporal characteristics of the reflected UWB signal in the thorax ( here ). I>

Analyzing the low-frequency periodic modulation of the delay can be identified respiratory and pulse component. Type of signal and its power spectral density shown in Fig. Signal is generated by the first derivative of the Gaussian function.



UWB signal and borders spectral range ( here ). I>

One of the first patents on such a device is dated 1996. Author Thomas E. McEwan US 5573012 A Body monitoring and imaging apparatus and method .



The functional diagram of a pulse radar and the type of output signals. I>

To date, work on the study of the application of UWB radars in medicine being released regularly. You can zaguglit UWB heart rate radar .

In Russia, there is a group UWBgroup.ru , on the basis of the Research Center for Ultra-Wideband technologies of the Moscow Aviation Institute (SRC UWB MAI), which develops medical radar. Group work can be viewed at публикациям on their website. Here is an example of such a prototype radar to measure heart rate, which is developed by members of this research group.



The appearance and location of the UWB radar (from abstracts ). I>

Now this theme is very popular, considering that in itself is very promising band UWB to transfer data at gigabit speeds (ultra-wideband communication) and appeared on the market low-cost radio transmission modules.

The result - a truly fantastic opportunity! Monitoring heart rate through the walls! Search people alive under the rubble. Using your smartphone as a probing signal generator! Antiterrorist multibeam systems for the detection of suspicious persons.



bioradiolocation for special use. The smartphone can be used as a generator of the probe radio signal (отсюда). Of course this is just an idea.
I>
Dogs trend. B>
To date, we have found only one such device, adjusting for mass product. This dog bracelet Voyce .



bracelet collar to monitor the health of your dog. I>

For the people there is nothing of the sort offered. Apparently, there is a problem with the certification of such emitters for use by people, but maybe it's a temporary problem. In general, dogs and other domestic pets can wear already.

Well, almost all. Technology does not stand still, and we'll be sure to see the unusual and original solutions "reading" of the classical methods for detecting pulse on your wrist. B>

PS: Yes, another pulse can be measured by ultrasound, monitor the reduction of the walls of the heart. It is a standard feature of any cardiac ultrasound machine, but wearable gadget is not yet used, although there are portable, the size of a small hair a >. Still, it is almost a full-fledged unit for clinical diagnostics.

Bye! All good health! B>
And once again prigashaem you on our project website . I>

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