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The Pulse
Written by Tim Sheppard MBBS BSc. Last updated 19/6/09

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What is the pulse?

Most people probably know what the pulse is because you've felt it - even if you don't know it's called the pulse; and happily, even if you don't know what it is, it's very easy to understand. It's basically the bulging of an artery when blood is pushed through. So how does it work?

Imagine you have a rubber tube a bit like a hose pipe. If you tried to push a ball through it that was slightly bigger than the tube, you'll cause it to bulge as the ball goes through. Similarly, if you were to use a pump to push a large volume of liquid through the tube, the tube will probably bulge out every time the pump does its thing.

Well, this is what's going on with the pulse. The heart is the pump pushing blood forward, and every time the heart beats, a wave of blood flows out and through the arteries. If the artery is big enough, then you can feel the bulge as it goes through - this is particularly clear at the wrist, and in the neck. You can tell how regularly the heart is beating by counting the number of times you feel the pulse in a minute (the pulse rate).

It can sometimes also be useful to consider the rhythm of the pulse. If you get a regular beat (like drips from a tap that hasn't been turned off properly), then that's a good sign. Sometimes people have a pulse which is irregular (like someone who's not very good at playing the drums), and this could be a sign of atrial fibrilation.


What is the pulse character?

The pulse is clearly a useful sign, as it gives us clues about what's going on in the heart. However, it's not just the rate and rhythm which give us clues about this - you can sometimes get clues that the heart valves aren't working properly by feeling the way that the pulse passes your fingers - feeling the pulse character.

There's no particularly easy way to remember these, it's just a case of sitting down and learning them. However, they do make sense - there's a reason that a particular pulse character suggests a particular problem.

- A collapsing pulse (or water-hammer pulse) happens when you have aortic regurgitation; if the aortic valve isn't working and blood flows back into the heart every time it's in diastole, then you'll get a powerful forward flow when the heart beats, as with a normal pulse, but there'll be a kind of sucking back when the blood leaks through the aortic valve. You can feel this in a patient with aortic regurgitation - as you feel their radial pulse (at the wrist), lift their arm up and feel with your fingers around the front of the forearm. The pulse can be felt rising and snaking back down again where you're feeling the pulse, and the hand around the forearm should feel the muscles contracting to help the blood along.

- A slow rising pulse is seen in aortic stenosis and it works exactly as it sounds. Because the aortic valve is tightly shut, only allowing blood to squeeze through a small hole in the middle, you're not going to get the quick outflow of blood that you'd expect. Instead, as you feel the pulse it is slow to reach its peak (slow-rising) and then drops away again.

- A jerky pulse is seen in hypertrophic cardiomyopathy. Although this can feel normal to start with, you might be able to notice that the pulse feels jerky, and the patient should really be investigated further.

- A bounding pulse is classically the sign that you see with carbon dioxide retention. When the blood has too much carbon dioxide in it, you'll find the pulse has a bounding character, but unless you know what you're looking for, you could mistake it for increased blood volume, or exercise. Helpfully, carbon dioxide excess can also show up with other signs - you get warm, sweaty palms, and the hands will give a flapping tremor when held out in front.

- Pulses alternans is seen when the left ventricle isn't working properly, so it can't sustain strong impulses. You get alternating strong and weak pulsation and suggests that you've got a big problem with your heart.

- Pulsus paradoxus is where the pulse volume (and similarly blood pressure) falls with inspiration. In a normal, healthy person you will often find that breathing in causes a increase in pulse rate. Expanding the rib cage causes a decrease in the pressure in the thorax, leading to air flowing into the lungs and blood vessels around the lungs collect blood more easily. Less blood coming out of the lungs causes a drop in systolic blood pressure, so the pulse rate goes up. Normally. If there is pressure on the heart (e.g. pericardial effusions or constrictive pericarditis), or if the lungs don't inflate so well (e.g. severe bronchoconstriction from asthma) then the opposite might occur, hence pulsus paradoxus.

- Finally, pulsus bisferiens is where the pulses has two peaks. This comes when someone is suffering from both aortic stenosis and aortic regurgitation. The two waves are sometimes called percussion and tidal waves.


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