Pain prevention through faux-stress responses
When you see that something painful is coming your way, it’s pretty common to tense up and brace yourself for the unpleasant experience. If you hold your breath at those moments, you may be doing yourself a service, reducing the amount of pain you’ll end up feeling from the experience of say, getting a shot at the doctor.
When your body is stressed, your blood pressure increases, preparing you for possible fight or flight responses. You can’t stay in this state of alert indefinitely though, and pressure sensors in your lungs activate, telling your brain to calm things down after a while. In addition to lowering your blood pressure again, part of that de-escalation dampens your nervous system, and thus your sensitivity to pain.
Fortunately, you don’t have to feel you’re in peril to benefit from this idea when dealing with safer scenarios. Holding your breath seems to trigger the aforementioned pressure sensors in the lungs, starting the de-escalation process and dulling your pain sensitivity. It won’t undo pain already in progress, and it generally only changed test subjects pain experience a little bit, but that doesn’t mean it wouldn’t be a welcome option for people in for some hurt. If it ‘scales up,’ and can be applied to more intense pain, like a contraction during birth, it may be a very useful technique to coach people on.
Source: Hold your breath to dampen the pain of an injection by Jessica Hamzelou, New Scientist