Perfusion Pressure

What is perfusion pressure?

Perfusion pressure is how much pressure it takes to push blood through all the blood vessels in a specific area. As long as this pressure is high enough, blood will continue to flow through those vessels. That means that perfusion pressure is a critical part of how your body’s circulatory system works.

When perfusion pressure in certain areas drops too low, that can lead to major problems. The two most critical areas where this can happen are your heart and brain. When either of these organs isn't getting enough blood flow, it can lead to serious or life-threatening conditions.

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.

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).

How does perfusion pressure work in your heart?

Your heart is a muscle that has to work non-stop your entire life. To do that, your heart needs a steady supply of oxygen, which it gets from the coronary arteries. Your heart uses about 70% to 80% of the oxygen in the blood that passes through those arteries. No other organ uses that much of the oxygen in its blood supply.

Coronary perfusion pressure keeps blood flow through those arteries moving. When that pressure is low, your heart doesn’t get enough blood and oxygen, which can have life-threatening effects.

How to find it

Coronary perfusion pressure doesn’t use pulse oximetry. To find this pressure, healthcare providers have to take two other measurements and use those to calculate your coronary perfusion pressure. Taking these measurements is possible with echocardiography or with a heart catheterization.

• Aortic diastolic pressure: This is the pressure on your aorta between heartbeats. The aorta is the largest artery in your body, carrying blood out of your heart and into the rest of your body. Finding this involves taking your blood pressure. The lower number of your blood pressure is the aortic diastolic pressure.
• Left ventricular end-diastolic pressure: This is the pressure inside the left ventricle, one of the heart's two lower chambers, between heartbeats.

To find the coronary perfusion pressure, do the following:

• Aortic diastolic pressure – left ventricular end-diastolic pressure = coronary perfusion pressure.

How does perfusion pressure work in the brain?

The other organ with the highest oxygen demand, aside from your heart, is your brain. Cerebral perfusion pressure ensures enough blood flow to all areas of the brain. Without constant blood flow to your brain, you would pass out in a matter of seconds.

How to find it

Calculating cerebral perfusion pressure involves two different tests.

• Blood pressure: The first is taking blood pressure, which healthcare providers then use to calculate mean arterial pressure. Mean arterial pressure is the average pressure in your arteries during a cardiac cycle (this is one squeeze of the heart and the following resting pause). To calculate the mean arterial pressure, take the diastolic blood pressure (the lower number) and double it. Add the doubled number to the systolic blood pressure (the top number). Take the number you get from adding those together and divide it by 3.
• Intracranial pressure: Intracranial means “inside the skull.” Between your brain and the bone of your skull is a layer of cerebrospinal fluid. Intracranial pressure is the total pressure on the inside of your skull because of your brain and its blood, plus the cerebrospinal fluid. Taking this involves

To calculate the cerebral perfusion pressure, do the following:

• Mean arterial pressure – intracranial pressure = cerebral perfusion pressure.

What are the common conditions and disorders that happen because of perfusion pressure problems?

Ischemia is the main concern when there’s not enough perfusion pressure somewhere in your body. When ischemia happens on one of your limbs, it can cause areas of the affected limb to die. That can cause gangrene, infections and more. If it affects a major organ, that organ may start to die, leading to even more serious or deadly complications.

Conditions that happen because of, or that involve, perfusion pressure problems include:

• Heart attack.
• Heart failure.
• Coronary artery disease.
• Stroke.
• Cardiogenic shock.
• Cerebral hypoxia (lack of oxygen leading to brain injury).
• Atherosclerosis.
• Leg and foot ulcers.
• Reynaud’s disease.

What can I do to make sure my perfusion pressure is at safe levels?

Your perfusion pressure, especially in your heart or brain, is usually not an issue unless you develop specific health conditions that involve your heart and circulatory system. It’s possible to prevent or delay these conditions by doing the following:

• Reach and maintain a healthy weight.
• Eat a healthy diet.
• Quit tobacco products (including smokeless tobacco products and vaping).

The best way to catch any problems affecting perfusion pressure is to get an annual physical examination with a healthcare provider. Also known as a wellness check, this visit to a healthcare provider includes simple medical tests that can often detect serious problems long before you have symptoms. Early detection means you can get treatment and act to prevent permanent damage or limit its impact.

If you have conditions that affect perfusion pressure, be sure to see a healthcare provider regularly to monitor your condition and treat it if needed. You should also follow your provider's guidance and take medication as prescribed. If you have questions or need resources, your provider is also the best person to help you.

A note from Cleveland Clinic

Perfusion pressure is a key part of how every part and organ in your body functions. Without perfusion, blood wouldn't circulate to all the places it should go. That lack of blood flow can have major consequences over time or lead to severe or life-threatening complications. If you want to know more about perfusion pressure and how it affects you, be sure to talk to a healthcare provider. They are the best ones to determine what you need and how you can act to take care of yourself. That way, you can take care of your health and devote time to what matters most to you.