Long post, first theory then some expiriences.
My
theory is that it is possible to get pulmonary erection without going past RV depth.
I
speculate it is possible for a few reasons:
- Un-relexed ribcage (which can also happen in short periods due to not using a good mouthfill*).
- The fact that we train our pulmonary vessels to be flexible by doing deep dives and negatives/frc/reverse packs, so it takes less "pressure" to swell them.
- Elevated pulmonary blood pressure:
- We get peripheral vasoconstriction which means that more blood goes to the core, combined with the fact that we have one side of the heart that pumps blood exclusively to the lungs we get sudden pulses of blood pressure which also in cases of short ribcage resistance to pressure such as in bad mouthfill techniqe* could be a mecahnism to cause pulmonary erection (in my theory, I have no indication that this is true).
- I think that our body might have some reflex to increase pulmonary (and other) blood pressure in response to changing environment, for example in altitude sickness (to my weak recollection!) if I understood correctly, people who are prone to that get elevated pulmonary blood pressure which can lead to pulmonary edema (which might be considered as a subtle form of lung squeeze as fluid not equal blood). So maybe this exists in all humans but to a lesser extent. [On a side note: cerebral edema can also happen, which I will guess is due to elevated cerebral blood pressure. Those local changes in blood pressure seems pretty close to some of our apnea response, should we start getting worried of cerebral edema as well?
]
- We are inverted (though in water)
Pulmonary erection makes it much more likely that a capillary will burst due to some sort of physical pressure (contractions, sudden upper body movements, equalizations) because it means that the capillary walls are thinner at that given moment.
*any equalization that requires pushing air from the lungs will cause that, I'm am stating bad mouthfill as one can still do the mouthfill and operate ribcage muscles accidentaly while equalizing.
Theory aside, I got squeezed once (from TLC diving) at a site that was 25m max. Old spirometry tests from before I started freediving show that I was supposed to be far enough from RV at those depths, and I bet my RV/TLC ratio improved a lot since then - mostly the RV as I don't really pack (increases RV by some theories) and I know how to empty (and fill) my lungs
much better than when I took those tests.
I still don't know why it has happen, I speculate a combination of pulmonary erection and contractions at depth.
I started descending slower on my dives and try not to have many contractions at 20 and below (if I notice) and doing stretches before the session. It seemed to work even for a little deeper diving but I got a suspected squeeze last weekend again at that same site.
There was a barely noticeable amount of red in my spit after 2-3 of the last few dives (recrational dives). At the end of the session there wasn't any red in my spit. It felt like I had a chest infection for those last dives, also I had to cough underwater a few times because the urge to cough was so strong when I got inverted. The day after I took it easy and I felt fine - not peak performance but no blood, no hypoxia, no chest symptomes. I suspect a few other factors at that last incident.
One thing I'm still contemplating of is the relevance of the speed of ascent from moderate depth (25m meter and shallower) and from below RV depth to lung squeezes, assuming no packing.
All comments are welcome as lung squeeze is my main concern/limiting factor at the moment in freediving.
