How does perfusion pressure work?
Your heart’s pumping action constantly pushes blood throughout your body, with every heartbeat propelling blood out of your heart and into your arteries. Blood then flows from your arteries and to your capillaries, where the blood delivers oxygen to your cells. Once that part of the job is complete, the blood in the capillaries enters your veins and returns to your heart. This cycle repeats every time your heart beats.
How is perfusion detected?
Perfusion tests that don’t involve internal organs usually start with pulse oximetry. This test shines red and infrared light through your skin. Hemoglobin, a molecule in your blood that carries oxygen, absorbs light in different ways depending on whether or not it’s carrying oxygen at the time. That allows a pulse oximeter to calculate your blood oxygen level and if there’s enough blood perfusion in an area.
Pulse oximeters often look like a clip that attaches to your finger or a sticky patch with a sensor in it that can stick to the skin of a finger or somewhere else. Some alternate sites for a pulse oximeter include an earlobe or your forehead.
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What is the perfusion index?
The perfusion index measures how well blood circulates in a specific part of your body. The perfusion index does that using a comparison of the amount of oxygen-carrying blood in the area vs. the volume of blood not carrying oxygen.
The same capability that lets a pulse oximeter calculate blood oxygen also helps with the perfusion index. Measuring how much hemoglobin has oxygen makes it possible to measure how much new blood (which still carries oxygen) is flowing through the area in question.
The peripheral perfusion index is one way this principle helps healthcare providers assess and treat someone who may be sick. Lower numbers mean either your heart isn’t pumping enough blood, or something is making it harder for enough blood to reach parts of your body furthest from your heart.
What’s the difference between the perfusion index and blood pressure?
The perfusion index and blood pressure are both measures of how well your circulatory system is working, but they use different methods, and they aren't looking for the same thing.
- Perfusion index: This ratio shows how much blood is flowing through an area. The higher the number, the better blood can flow through. Lower numbers can signal health problems with your heart or blood vessels.
- Blood pressure: This measures the pressure on your blood vessels in millimeters of mercury (mm/Hg), with top and bottom numbers. The two numbers are for the pressure put on the arteries with every heartbeat (the systolic number, on top) and pressure on the arteries between heartbeats (the diastolic number, on the bottom).
