Do you think perhaps you are “over-thinking” it? That just maybe the way it has been done for thousands of years isn’t all that contaminating.
Have you actually looked at the lungs of chickens that have been killed using different methods so you could compare, say chop block versus killing cone? With your medical training you should have an idea what you are looking at.
I have given a lot of thought to this, probably "over-thinking"....LOL. I think everyone agrees that the better the bleedout, the better in terms of the quality of the meat.
The neck-wringing that our parents/grandparents did resulted in the chicken's head being in their hand(if done properly) with the rest of the bird flopping around. Same with the hatchet.....except the head ends up on the ground. In both instances, the chicken bled. After each of those procedures, the heart would continue to beat for a period of time, probably a couple of minutes tops, because of the heart's intrinsic conduction system that is independent of the control of the brain/brainstem. The flapping of the chickens wings from random nerve impulses following severing of the spinal cord would further help with the bleedout, but then the chicken would be hung upside down to continue draining.
Could blood get into the lungs with all of the flapping around...certaintly, though respiration
does stop with the severing of the spinal cord because it separates the body from the brainstem, which completely controls respiration. Does it affect the quality of the meat? I doubt it. If blood goes into the trachea(windpipe) and is aspirated into the lungs, it would follow the route that air would take. The avian respiratory system is very different from humans. A small amount of air goes into the lungs, but most of the air goes into the air sacs of the body, some of which are in the neck, and some of which are even in the abdomen. SO, if blood goes into the trachea, the bulk of it would go into the air sacs, and could remain there. The issue of the blood would come into play during processing. If the air sacs are full of blood, and are in the neck, chest, and abdomen, then when we remove them, there is blood leakage, which is messy....but we have water hoses to rinse that out of the chest and abdominal cavities. We promptly process and remove those, so the meat should not be affected.
Now, many feel that a bleedout by severing the carotid artery(better bleedout than with just severing the jugular vein because of the heart pumping) is the most humane, and I have no intention of debating that. The spinal cord is not severed, so respiration will continue briefly, though the bird is unconscious within seconds, followed quickly by death.
The long and short of this, following my "overthinking"...LOL is that any of these procedures, if done properly, achieves the same results: the bird is dead quickly, the blood is drained from the body, and we have a wonderful, tasty food source,