It's possible to occlude the airway by extreme neck flexion -- try it yourself as you sit here. If you really bend your head down, you can feel the resistance to breathing increase.
However, there is no particular reason why a diver, suspended in water, will assume that extreme neck flexion position. That is a product of gravity, which is ameliorated by buoyancy. If you are retrieving an unconscious diver and ascending in a vertical orientation, there is some small amount of gravity encouraging neck flexion. But if you are sending someone up by flotation, there is no particular reason that they will remain in a position of neck flexion.
Airway occlusion is also variable, depending on whether you are trying to get air IN or OUT. Again, try this yourself -- flex your neck until it gets hard to inhale. Now exhale -- it's much easier, isn't it? Exhalation tends to expand the upper airway, where inhalation tends to collapse it. In cases of laryngospasm, patients may be able to exhale when they can't inhale at all.
But the bottom line is the one cerich keeps making. Someone who is at technical depths and is both unresponsive and not breathing is very unlikely to survive. Breathing is built deep into the brainstem; one of the tests for brain death is an apnea test. If someone is no longer making any respiratory efforts, the brainstem has been shut down, and that's really bad news. Either the brain isn't getting any circulation (likely) or the brain has been seriously depressed by hypoxia, hypercarbia, or possibly severe narcosis . . . although the stories I've read of people who are thought to have died from narcosis have indicated their tanks were empty, which suggests they continue to breathe long after they have lost the ability to conceive of an ascent.
The physiology is known . . . you just don't have much time to get an apneic patient to a place where circulation and ventilation can be restored. Each of us has to make an assessment of what risk to ourselves we are willing to take in such a situation, but make that assessment rationally -- don't assume that, if you blow off all your deco and use your carefully trained rescue skills, you're going to end up with a live, neurologically intact victim. Unless you witnessed the respiratory arrest event, it's vanishingly unlikely, and even if you did, it's not probable.
However, there is no particular reason why a diver, suspended in water, will assume that extreme neck flexion position. That is a product of gravity, which is ameliorated by buoyancy. If you are retrieving an unconscious diver and ascending in a vertical orientation, there is some small amount of gravity encouraging neck flexion. But if you are sending someone up by flotation, there is no particular reason that they will remain in a position of neck flexion.
Airway occlusion is also variable, depending on whether you are trying to get air IN or OUT. Again, try this yourself -- flex your neck until it gets hard to inhale. Now exhale -- it's much easier, isn't it? Exhalation tends to expand the upper airway, where inhalation tends to collapse it. In cases of laryngospasm, patients may be able to exhale when they can't inhale at all.
But the bottom line is the one cerich keeps making. Someone who is at technical depths and is both unresponsive and not breathing is very unlikely to survive. Breathing is built deep into the brainstem; one of the tests for brain death is an apnea test. If someone is no longer making any respiratory efforts, the brainstem has been shut down, and that's really bad news. Either the brain isn't getting any circulation (likely) or the brain has been seriously depressed by hypoxia, hypercarbia, or possibly severe narcosis . . . although the stories I've read of people who are thought to have died from narcosis have indicated their tanks were empty, which suggests they continue to breathe long after they have lost the ability to conceive of an ascent.
The physiology is known . . . you just don't have much time to get an apneic patient to a place where circulation and ventilation can be restored. Each of us has to make an assessment of what risk to ourselves we are willing to take in such a situation, but make that assessment rationally -- don't assume that, if you blow off all your deco and use your carefully trained rescue skills, you're going to end up with a live, neurologically intact victim. Unless you witnessed the respiratory arrest event, it's vanishingly unlikely, and even if you did, it's not probable.
