CMS pulse oximeters are medical gadgets that help medical professionals determine, somewhat indirectly, if a patient is getting enough oxygen. The devices clip onto the finger, the earlobes or, in infants, a foot. What they actually measure is the amount of hemoglobin that is fully loaded up with oxygen. In most people, this figure should be at least 95% or more.

It isn't obvious how a non-invasive instrument can measure with any degree of accuracy something down to the molecular level. Without getting too technical, oximetry works on the principle that different substances absorb light differently. Two different wavelengths of light are passed through the patient and the instrument is able to determine the absorbance, and therefore the concentration, of oxygen in pulsating arterial blood.

While this technology can reveal the oxygen saturation of a person's hemoglobin, it is at best an indirect means of finding out how much actual oxygen is circulating in the bloodstream. To measure this directly, it is necessary to sample the blood passing through the arteries in real time. This involves placing a needle into an artery.

They need a good reason to measure arterial oxygen levels because placing the needle into an artery is very painful to the patient. This is fine if the person is unconscious, as if they were under an anesthetic or unconscious. If they are awake and aware, it feels like someone is plunging a needle directly into bone.

One of the circumstances where pulse oximetry is employed is during sleep studies. These investigations require an overnight stay in the hospital and are done for the purpose of finding out if someone has a condition called sleep apnea. This is when a person periodically stops breathing during the night. At best, they wake up drowsy and fuzzy-headed. At worst, it is a risk factor for life-threatening conditions like heart attack and stroke.

There are two categories of sleep apnea, neurological and obstructive. Obstructive sleep apnea (OSA) is more common than neurological sleep apnea, but no less dangerous. Treatments may include a device that is prescribed by a dentist to keep the mouth partially open at night, continuous positive airway pressure (CPAP) or, in extreme cases, surgery to correct an anatomic deformity that makes the airway unable to open.

Central, or neurological sleep apnea, is less common and harder to treat than OSA. Instead of stopping the breathing process, the brain doesn't attempt it. There is often a serious condition underlying neurological OSA that affects the brain stem. This is the brain area that is responsible for breathing and heart rate. Neurological sleep apnea can happen by itself or in combination with OSA.

Anybody can be diagnosed with either form of sleep apnea. The principal risk factors are age over 40, obesity and being male. This is a particularly heart-breaking condition in young babies, who can sometimes stop breathing for periods as long as 20s. This is frightening for new parents. Fortunately, alarms are available that can sound an alert when the baby has an apnea episode. CMS pulse oximeters may also be purchased for use at home for both adult and child use.