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Basic principal on working of Pulse Oximeter. Importance of Pulse Oximeter in coronavirus COVID-19

Updated: Aug 3




A pulse oximeter is a device that is used to quickly and easily monitor a patient’s oxygen saturation,This means that it can measure the level of oxygen within the blood specifically in arterial blood without using any invasive means

A Pulse Oximeter is a device which is used to monitor oxygen saturation (SO2) or amount of oxygen carried in a person’s body. The sensor digital device is placed on thin part of a person’s body; generally a fingertip or earlobe is considered for such process or may be across a foot for a child (infant). The oximeter device emits light which consists of two wavelengths that passes through the patient’s body to a photo detector. These two lights of different wavelength beams in the small vessels or capillaries which consist of blood (circulating blood) and these light beams are responsible for determination of amount of oxygen present in the blood along with the current pulse rate in a person’s body. The pulse oximeter measures the change that is observed by the light of emitted wavelength which is the basic working principle. This measurement allows the determination of absorbance due to pulsing arterial blood only excluding the venous blood, skin, bone, fat and muscle

The Pulse Oximeter works on two basic physical principle

  1. The presence of a pulsatile signal generated by your artery (The beating sensation you feel at the bottom of your palm.

  2. The fact your Oxyhemoglobin (O2Hb) and reduced hemoglobin (Hb) blood have different absorption spectra.

How does pulse oximeter measure the oxygen levels?

The pulse oximeter has 2 LED installed in it that produce 2 types of light rays infrared (940 nm) and red (690 nm) light.

  1. fully oxygenated hemoglobin in your artery (O2Hb) will absorb infrared light more readily

  2. Reduced hemoglobin (Hb) in your veins will absorb more red light

The relative absorbance of the light is used to determine the oxygen concentration in your body,

When the device is placed in your finger the two lights pass through your finger

The light passes through your tissue bed and blood vessels over to a receiver which is on the other side of the pulse oximeter you can see that

As the red and infrared light passes through the tissue bed the hemoglobin which is fully oxygenated and deoxygenated will absorb amounts of light

Bypassing this information about how much light is absorbed both infrared and red light the Machine will be able to calculate the percentage of fully saturated hemoglobin.

Fractional oxygen Saturation= Saturation in HbO2 (in Artery) X 100/ [HbO2 (Artery) + Hb (Vein)]

Pulse Oximeter & corona virus (covid-19)

Pulse Oximeter has suddenly come into prominence during this COVID-19 pandemic due to the fact that unlike conventional pneumonia where difficulty in breathing due to a fall in the oxygen saturation in the blood is an early symptom and a warning sign and in COVID-19 infection the pneumonia causes a ‘silent hypoxia ‘or a dangerous drop in the oxygen saturation without any associated breathing difficulties. Thus despite the patient having significant pneumonia does not feel ill a presents late to the hospital. The way to detect this hypoxia would be to use a pulse oximeter and treatment initiated immediately before the lung conditions deteriorate.

You know? Nowadays many fitness and smartphone bands are also equipped with an oximeter feature which uses a similar technology perhaps how much they are accurate is a question too.

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