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Pulse oximeter is a simple medical device used to measure heart rate and blood oxygen level.
The pulse oximeter makes use of a technique called photoplethysmography (PPG) to measure the amount of light absorbed or reflected by the blood vessels. A typical pulse oximeter uses a light source and a photodetector to measure the amount of optical absorption or reflection and thus determine the blood volume and the oxygen content.
The key readings on a pulse oximeter include the SpO₂ (the oxygen saturation level) , pulse rate and a waveform showing your pulse.
Incident light is absorbed by tissue and bone, venous blood and arterial blood. However, we assume that optical absorption by other parts is constant and only the absorption by pulsatile volume of arterial blood varies, as shown in the PPG waveform. The amplitude of the PPG waveform is proportional to the blood pulse pressure, i.e. it changes with the systolic (heart muscle contracts) and diastolic (heart muscle relaxes) pressure in the arteries. With a higher blood volume in the arteries during systole, more light is absorbed and lower light intensity is detected. The frequency of the PPG waveform reflects the pulse rate.
SpO₂ is the ratio of oxyhemoglobin (hemoglobin that binds with oxygen) over all types of hemoglobin (mainly deoxyhemoglobin, hemoglobin without bound oxygen). The absorbance of oxyhemoglobin and deoxyhemoglobin are different at different wavelengths. Measuring the absorbance of oxyhemoglobin and deoxyhemoglobin allows us to calculate the ratio between oxyhemoglobin and deoxyhemoglobin. A side note is that it is important to choose 2 wavelengths in which the absorbance of oxyhemoglobin and deoxyhemoglobin do not overlap. A combination of red and near-infrared LEDs is usually used.
Pulse oximeter is a simple, non-invasive and convenient method to monitor heart and lung functions in a continuous manner. It is particularly useful in:
COVID-19 infections may lower your blood oxygen level and cause “silent hypoxia”. The current hypothesis is that the virus may affect our nervous system's sensitivity to the oxygen level, making our brain unaware of hypoxia. When the patients seek medical help, the situations are already worse than they think, and miss the golden period for treatment. According to the HK government’s guidelines for using a pulse oximeter at home for persons who tested positive for COVID-19, if the SpO₂ is 94% or below on two occasions (after taking a few breaths, and measuring on a different finger), you have to seek medical attention as soon as possible. If your it is consistently 92% or below, please go to the Accident and Emergency Department immediately.
Most pulse oximeters are designed to be clipped on fingertips. Follow these steps:
A normal resting heart rate for adults ranges from 60 to 100 beats per minute (bpm). You should consider seeking medical advice if you have the following conditions:
However, a well-trained athlete might have a lower resting heart rate than normal people, around 40 beats per minute.
An oxygen saturation level of 95% or higher is considered normal for most healthy people, while that of 92% or lower can indicate potential hypoxemia. According to the HK government’s guidelines for using a pulse oximeter at home for persons who tested positive for COVID-19, if the SpO₂ is 94% or below on two occasions (after taking a few breaths, and measuring on a different finger), you have to seek medical attention as soon as possible. If your it is consistently 92% or below, please go to the Accident and Emergency Department immediately.
In Hong Kong, a pulse oximeter can be purchased from medical device shops, pharmacies, electronic appliances stores and other retail outlets.
The key readings on a pulse oximeter include the SpO2 (the oxygen saturation level) , pulse rate and a waveform showing your pulse.
COVID-19 infections may lower your blood oxygen level and cause “silent hypoxia”, a life-threatening condition that can easily go unnoticed. A SpO2 lower than 95% is a warning sign to seek medical care immediately.
A normal resting heart rate for adults ranges from 60 to 100 beats per minute (bpm).
An oxygen saturation level of 95% or higher is considered normal for most healthy people.
This article was independently written by Healthy Matters and is not sponsored. It is informative only and not intended to be a substitute for professional medical advice, diagnosis or treatment. It should not be relied upon for specific medical advice.
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