One day, on the eve of the 1st of April I played great doctor friend. I decided to pay him back. He "sat" in the district hospital on the electrocardiograph, and my first thought was using the tool that I had little knowledge of electrical engineering, change his testimony.
I had to turn in the library decent weight medical literature from which I learned nothing, except that this device picks up electrical impulses working muscles of the heart and displays them in graphical form. But the nature of the disease is judged mainly on the amplitude and pulse shape measured from different points.
In the first place it was necessary to collect the generator with a repetition rate of from 50 to 150 pulses per minute. For this purpose I used the multivibrator circuit, for reasons of its simplicity and small size (Fig.1). When powered from battery "Krona" (9), a trimming resistor R3 pulse frequency was varied within the limits of. Verifying on the oscilloscope in the form of pulses, I was convinced that it is far from rectangular.
Fig.1
The pulses had a smooth rise and sharp decline (Fig.2). The output of the multivibrator I directly hooked up to electrodes that are placed on the hips. The dimensions of the electrodes was chosen so that the amplitude of the added pulses in the attachment of sensors cardiograph does not exceed the amplitude of the pulses of the heart muscle. Structurally, the entire circuit arranged in a matchbox and put it in the heat (because they do not need to remove the examination). The electrodes used plates from white tinplate size 60x40 mm, with rounded corners (so as not to injure the skin) and curved shape of the thigh (for better contact). The electrodes are also sewed in melting on the sides.
Fig.2
For better current flow I used salt solution (30%). In this case, in the contact area with the electrodes felt a slight tingling sensation. The side of the electrodes that is in contact with the body, must be honored, otherwise the sheet is rapidly oxidized. The positive electrode should be on the left thigh, otherwise the polarity of the pulses will be opposite the heart.
And now, fully "equipped", I go to the clinic, explain that she felt "something was wrong" with the heart. My friend looked at me a little suspiciously (I never complained), but did not deny.
Then came my "finest hour"! After the first inspection of the entire medical staff of the clinic was smitten. Gathered all experts, though little understood in cardiology. I have a very long discussed in uncontrollable astonishment. Listening, tapping and listening again, they made a conclusion about my chronic heart failure, heard some noise and incomplete closure (or opening?!) valve ventricle right atrium.
Accurate diagnosis of me so no one could supply. And immediately gave direction to the hospital for further examination. I decided to stick it out. For several days I repeatedly checked, tested, fed vitamins and forced to do therapeutic exercises.
It was terribly boring, and my passion to "outdo" medical bodies quickly extinguished. Began to think of ways to "waste". Fortunately, was rescued by the battery. She gradually "sat", and the amplitude of the false pulses become smaller. I was told that things are on the mend. Finally I'm completely "cured", and I was solemnly sent home. You should have seen then the face of my friend when I told him everything and showed "artificial heart"!
Fig.3
For reference in Fig.3 here is the ECG of a healthy heart, and in Fig.4 - with the multivibrator, where one can see the characteristic triangular pulses coming a little to the beat of a heart. This is the main disadvantage of this scheme. By and large, it was necessary to synchronize the generator with the heart rhythm, but this is a special conversation.
Fig.4
In addition, when you move the sensors of the apparatus on a body varies with the amplitude of false pulses, which makes it quite easy to localize the location of the source signals.
Author: V. Yakovlev, Petrikov, Gomel region; Publication: N. Bolshakov, rf.atnn.ru