The purpose is to increase oxygen saturation in tissues where the saturation levels are too low due to illness or injury.

It is a device for measuring the oxygen saturation of arterial blood.

Oxygen saturation is the extent to which the blood is carrying as much oxygen as it is capable of doing. It is measured as a percentage. Oxygen saturation is the percentage of oxygen in the blood stream. Doctors become concerned when that percentage drops below 90%. It simple terms, at 82%, your brain other other organs are not receving enough oxygen to properly function. Anyone's oxygen saturation level varies from one moment in time to another. If you had a full copy of your sleep study report you might see reference to peak saturation (the highest saturation seen during the study), average saturation, saturation nadir (the lowest saturation recorded during the study), among other terms.

I'm assuming you're referring to saturation of oxygen in the blood. If the temperature is increased, oxyhemoglobin curve is shifted to the right, meaning hemoglobin realeses oxygen more readily, thus increasing blood oxygen saturation.

A pulse oximeter measures the body's oxygen saturation with a small clip.