Touching Lives - June 2007
The pulse on the wrist provides information about how fast and how regularly the heart is beating — the ‘strength’ of the pulse, to the experienced tester, is some indication of blood pressure and how vigorously the heart is working.The stethoscope picks up sounds related to the flow of blood and how well the valves are functioning. Next to these, the electrocardiogram, a signal not apparent to any of the human senses, is probably the most frequent diagnostic measurement applied to hospital patients.
At the beginning of the 20th century, one might occasionally have seen a patient with the left foot and each hand in a bowl or bucket of salt water, all connected to a pre-electronic recording device.What was being measured was the electrical activity of the heart.When a muscle contracts, this is accompanied by an electrical signal and this applies also when an impulse is conducted along a nerve.
There are basically three phases in the operation of the heart as a pump, (really two pumps, the one on the right side pumping blood through the lungs, the other and stronger one, through the muscles and organs of the body). In the first phase (P) the atria fill with blood, and in turn fill the muscular ventricles, which do the actual work. In the second phase (QRS) the ventricles contract and expel most of their contents into the circulation. During the third phase (T) the muscles recharge themselves with energy.The relative timing of these events, the magnitude and direction of the electrical signals allows conclusions to be drawn about the health of the heart.
These days, the electrical connections are stuck on the limbs and chest and there are more of them. Recording from different combinations is like being able to look at the heart from different directions.The diagram on the left shows a rather stylised ECG, illustrating the major features. TL