The Electrocardiograph

The Electrocardiograph is also called the ECG or EKG machine [kardia means heart, graphein, to write).

The electrocardiograph is an instrument that measures electrical activity spreading over the heart during each contraction and relaxation. The first electrocardiograph was devised by William Einthoven (1860-1927) of the University of Leyden in the Netherlands.

This is how Einthoven described his invention in 1903:

"This instrument the string galvanometer is essentially composed of a thin silver-coated quartz filament, which is stretched like a string, in a strong magnetic field. When an electric current is conducted through this quartz filament, the filament reveals a movement which can be observed and photographed by means of considerable magnification . . ."

Einthoven's original machine weighed 600 pounds and required five people to operate. Over the next decades this instrument was greatly simplified and now fits into a small box the size of a laptop computer. The tracings obtained are referred to as electrocardiograms, ECG's for short, or EKG's.

ECG tracings include several waves, arbitrarily called P Q R S T by Einthoven.

P waves record the spreading of the electrical impulse through the right and left atria (the heart's upper chambers).

Q waves are a recording of the same impulse going down the right and left bundle.

R and S waves result from the depolarization of the ventricles (the heart's lower chamber)

T waves reflect the repolarization of the ventricles.

By analyzing electrocardiograms, physicians are able to diagnose cardiac disorders, in particular arrhythmia (rhythm disorders) and myocardial infarctions, also known as heart attacks.

Myocardial infarctions begin with peaked P waves, then with ST segment elevations, on to Q wave development and T wave inversion. These changes may occur over periods of several hours or of several days.

Sphygmomanometer

A sphygmomanometer is an instrument designed to measure arterial blood pressure. The word is a combination of: sphygmos, "pulse" in Greek and manometer, another Greek term meaning "measuring device."

The arterial blood pressure was first measured in 1773 by the Rev. Stephen Hales, an English pastor interested in the physical sciences. In 1896 a mercury manometer, essentially the prototype of today's model, was introduced by the Italian Scipione Riva Rocci.

It was not until 1905 that the Russian Mikolai Korotkoff distinguished between:

1. The first sound, heard over an artery, when the constriction blocking an artery is gradually diminished, allowing blood to go through. This corresponds to the period of maximum ejection called systole.

2. The second sound, or in fact, the absence of sound which occurs during diastole, that fraction of time when the heart is at rest between two heartbeats.

The more important of these two measurements is the diastolic blood pressure. A normal blood pressure is 120/80 mm. of mercury (120 systolic and 80 diastolic). A diastolic pressure between 90 and 100 mm. of mercury is considered borderline and one above 100 is considered high blood pressure. High blood pressure may result in vascular accidents in the smaller and more fragile arteries in the body, as in cerebrovascular accidents in the brain, also called strokes.