21 September 2011

Polysomnography: Measuring sleep!

Today let us talk about another interesting term, Polysomnography. Those who already know that the Latin word 'somnus' means sleep, can guess what polysomnography deals with. Yes, it is a standard procedure to evaluate sleep, mainly for the cure of sleep disorders.
Well, when I say 'measuring sleep' what actually are we measuring? Polysomnography is a multi-parametric test (means it measures different parameters connected to the sleep activity, lest you are frightened by the term multi-parametric) Mainly there are three parts in your body that responds directly to your sleep; brain, eyes and muscles. The study of activity in these three parts constitute the core of polysomnography. Measurements are carried out by placing electrodes on specific parts of the body and measuring the voltage change associated with the corresponding activity.
Now let us have a close look at the core parameters:
Brain activity:
It is studied by the ordinary EEG (Electro Encephalography) technique. It is based on measuring the bioelectric aactivity of brain by placing electrodes on the scalp of the person in sleep. EEG will look like a polygrah, the one you see in a seismogram record of earth quake. Like a random scribble made by a pen. But by looking at EEG, the researcher can understand the various stages of the person's sleep.
Eye movements:
It is studied by a technique called Electro Oculography (EOG). It is based on a rarely known fact that the front part of our eye called Cornea is electrically positive with respect to its hind part Retina. This voltage will obviously change when eye moves left, right, up or down. EOG is based on the measurement of this voltage, thereby giving an idea about the eye-movements.
Muscle activity:
This is studied by a technique called Electro Myogram (EMG). The movements of our muscles are a result of rapid electrical activity within the muscle tissues. EMG measures the voltage change associated with it. In polysomnography, EMG electrodes are usually placed over the chin muscles.

A sample polysomnogram
Along with these many similar activities in the body can also be studied for a very detailed analysis, three of them being  breathing, heart rate and contraction of leg muscles.

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