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Is there a relationship between throbbing pain and arterial pulsations?

PainSci » bibliography » Mirza et al 2012
Tags: chronic pain, odd, fun, counter-intuitive, pain problems

One article on PainSci cites Mirza 2012: Pain is Weird

PainSci commentary on Mirza 2012: ?This page is one of thousands in the bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.

Is your pain a throbbing pain? Pain often has a pulsating quality, especially when it’s severe and acute. If you’ve ever thought about why it pulses, you probably assumed that it’s pulsating with your pulse. Heck, “pulsatile pain” is actually a clinical term used to describe throbbing pain that is assumed to be surging in time with the arterial pulse.

I have always particularly noticed the throbbing of little infections — like a hangnail that’s gotten out of hand — and I always thought that I was feeling the blood pushing through the ultra-sensitized tissue.

But Mirza et al. just checked that assumption… and got a fun science surprise.

They checked in a bunch of patients with jack-hammering dental pain, getting them to tap out the rhythm of their throbbing with a button… and discovered that their throbs were actually much slower than their heart rates, almost half the pace, just not in sync. They were clearly different rhythms! Not so pulsatile after all.

That’s a fascinating upset to conventional wisdom.

The authors cannot definitively explain what does set the rhythm of the throb, but they did take a crack at it: “an emergent property, or perception, whose “pacemaker” lies within the CNS." (Which is a bit of a hand wave. Perception and the brain can explain anything. Try it sometime!)

Reality is always more complicated than the conventional wisdom or a slam-dunk of a debunk. The safe bet is that there are several kinds of throbbing pain. I doubt anyone will be checking them all anytime soon, so we can just enjoy the uncertainty indefinitely. But I definitely suspect that some of our throbbing pains actually are pulsatile. Like that infected hangnail, maybe. Ow, ow, ow, ow, ow…

~ Paul Ingraham

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

Pain can have a throbbing quality, especially when it is severe and disabling. It is widely held that this throbbing quality is a primary sensation of one’s own arterial pulsations, arising directly from the activation of localized pain-sensory neurons by closely apposed blood vessels. We examined this presumption more closely by simultaneously recording the subjective report of the throbbing rhythm and the arterial pulse in human subjects of either sex with throbbing dental pain-a prevalent condition whose pulsatile quality is widely regarded a primary sensation. Contrary to the generally accepted view, which would predict a direct correspondence between the two, we found that the throbbing rate (44 bpm ± 3 SEM) was much slower than the arterial pulsation rate (73 bpm ± 2 SEM, p < 0.001), and that the two rhythms exhibited no underlying synchrony. Moreover, the beat-to-beat variation in arterial and throbbing events observed distinct fractal properties, indicating that the physiological mechanisms underlying these rhythmic events are distinct. Confirmation of the generality of this observation in other pain conditions would support an alternative hypothesis that the throbbing quality is not a primary sensation but rather an emergent property, or perception, whose “pacemaker” lies within the CNS. Future studies leading to an improved understanding of the neurobiological basis of clinically relevant pain qualities, such as throbbing, will also enhance our ability to measure and therapeutically target severe and disabling pain.

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