It seems there are really three types of double lung shots:
There seems to be a great deal of misunderstanding concerning how the animal actually dies in each case. For hunters it seems to me the "true" shot is what is of the most interest.
A friend indicated the key is to separate the lung from the diaphragm. You damage the lung then the diaphragm pulls it apart. If this is done the lung diaphragm can not pull on the lungs to inflate them and the deer will suffocate.
From my observations it seems this is not exactly true. It seems the double lung results in holes in both lungs which causes them to fill with blood and the animal begins to drown. I say this because it seems a great deal of blood usually exits out the nose and mouth when the animal is running away. It seems to me this is indicative of the respiratory system continuing to function until it is filled with blood.
Additionally, I know, on a human, an air choke takes approximately one minute to cause loss of consciousness and several minutes for death whereas a blood choke takes 8-10 seconds to lose consciousness and irreparable brain damage begins not long after. Assuming deer expire in similar times it would seem to me that the deer must die from blood being cut off from the brain, or at least the supply of newly oxygenated blood.
So it seems to me, the shot must remove the lungs ability to oxygenate blood which in return causes the deer to pass out in 8-10 seconds. By the time you catch up the deer is likely still alive, although unconscioous and unresponsive, but it may take several minutes for the deer to become totally brain dead.
I was thinking about this b/c I killed a deer with a double lung for the first time. It was inside 15 yards with a rifle, and i can't help but think there might be a better way.