We’ve all seen that small clip-like device that is added on to our fingers during a visit to the hospital. Finger-tip Pulse Oximeters are devices that basically measure the oxygen concentration in blood. In this post, let’s look at what they are, what do they measure and why we need them.
How is Oxygen transported?
It is common knowledge that the cells that compose our body need oxygen to survive. Oxygen that enters the body is carried all through the body by the circulatory system. Wondering how the gas gets transported everywhere? Alveoli is the answer. The Oxygen that is taken in by the body enters the air sacs a.k.a Alveoli and dissolves into the plasma inside the capillaries. Then comes our hero – RBC (Red Blood Cells) or Erythrocytes that attach themselves to the oxygen molecules.
RBC contain a protein called Hemoglobin, whose ‘Heme’ component binds to Oxygen molecules. Oxy-Hemoglobin (Hemoglobin saturated with oxygen) now moves through the body’s circulatory system and gives up Oxygen based on partial pressure. When these RBCs move through tissues where there is low content of Oxygen, they give up their Oxygen molecule and become Deoxy-Hemoglobin, turning from red to purple.
Did you know?
Every RBC contains 270 million Hemoglobin molecules. Imagine the amount of Oxygen that is carried every minute!
What does a Pulse Oximeter do?
A Pulse Oximeter effectively measures the oxygen saturation in blood. In order to do that, it comes equipped with a photodetector and 2 light emitting diodes. The moment the light is emitted by the diodes, it is absorbed by the tissues. The photodetector detects the amount of light absorbed and calculates the hemoglobin concentration.
Principle of Pulse Oximetry
In principle, the oxy-hemoglobin and deoxy-hemoglobin absorbs different amounts of light and at different wavelengths. Oxy-hemoglobin absorbs more light at 600-800 nm and deoxy-hemoglobin absorbs more at 800 -1000 nm.
While one diode emits at red spectrum, one diode emits light at infrared spectrum and thus the amount of light absorbed by the tissue is analysed by photo detectors. By looking at the different wavelengths, the respective concentration of hemoglobin is arrived at.
Pulse Oximeters and Perfusion Index
In few of the Pulse Oximeters, there is an index called PI. Perfusion Index is a measure for physicians to check if a sensor site has good pulse strength. A sensor site can be your fingertip, earlobe etc. It is the ratio of the pulsatile blood flow to the non-pulsatile static blood flow in a peripheral tissue.
What should you check for when you buy a pulse oximeter?
A good Pulse Oximeter displays SpO2 recordings along with a graph. When buying a Pulse Oximeter for home use, see if the display is clear and also check for accuracy. While most Pulse Oximeters measure higher recordings accurately, most fail during lower SpO2 measurements. A Pusle Oximeter that comes with a PI indication comes in handy for the physician to better assess your condition.
BPL Pulse Oximeters are equipped with four direction display in bigger fonts and is with ±2% accuracy. PI recordings are displayed along with the graph. BPL iOxy also comes with Bluetooth enabled function that lets you connect to a mobile app and store your measurements. The trend thereby stored serves as an important tool for the physician.