The topic of a "Void" seems to pop up every year & on every bowhunting forum. The following is the best explanation I've seen to dispel the myth of a "void". It was submitted by Dr. Tom Gross, a pulmonologist (lung Dr.) & avid archer from Iowa.
"OK. Enough. I normally am strictly a lurker, but I can't take anymore. I am a Pulmonologist (Lung Dr) and avid archer. As a disclaimer, I am not privy to what others have seen or witnessed. I am only trained in normal mammalian anatomy. As such, I offer the following:
1) The lungs are not "glued" to the chest wall. That said, they are mechanically linked by fluid forces between the chest wall pleural surface and the lung pleural surface. The example I use for my students is to take a zip lock bag, put in a very small amount of fluid to "wet" the surfaces and close the bad squeezing out all the air. Then try to separate one bag surface from the other. Can't be done without ripping the bag or putting air into the system. During normal respiration, the chest wall expands a small amount and the lung expand to remain constantly in contact no matter how fast or sharply you breath in. The diaphragm moves up and down a good deal as well, but again, the lungs are in continual contact with the diaphragm. The lungs never separate from chest wall - pleural space is a "potential space" until disease causes fluid to accumulate (effusion), bleeding (hemothorax), or chest wall puncture or lung rupture (pneumothorax). There is no anatomic pr physiologic void.
2) the lungs of all large mammals have recesses that reach above the horizontal lowermost reach of the spinal column. I will gladly attach computer tomographic images (CT scan) from man, pig, sheep to demonstrate that you can not design a path that goes under the spine that will not puncture at least one lung (assuming we are talking about the chest cavity). Someone needs to tell me how to do this with a Mac - or I can email them to someone to do it for us.
3) Not all pneumothoraces are lethal. Even bilateral lung puncture can be survived if there is not a large "sucking chest wound" and/or the lung slices quickly seal up with blood clot. Most of these animals will die, but a few can travel a long way even with "double lung" hits if only the tops of the lungs are sliced.
So, there is no void except in the beliefs of some; you can hit an animal below the spine and not recover it.
One common misconception is that a pneumothorax (collapsed lung) is an all or nothing phenomena. This is not true. Now certainly with a big open chest wound, most certainly the lung will collapse completely, but this still happens on a breath by breath basis (breath in creates negative pressure drawing air through open wound) and can take many minutes (= many yards if running). Also, if chest wound seals up (narrow slit, fat, clot, etc), lung may only leak a little air during expiration (positive pressure in lung to get breath out) and only partially collapse. Humans and deer have two separate pleural cavities (one for each lung), so dropping one lung leaves the other relatively unscathed. The bison has a single pleural space and was relatively "easy" to kill with even a one lung shot. That said, I have heard that an arrow to the chest of a bison may still take large fractions of any hour to put it down.
In addition, remember your fluid dynamics and air flow resistance factors. A deer trachea (windpipe) provides a much bigger cross sectional area than most any broad head wound (area of circle vs intersecting slits). Thus, air will still follow path of least resistance and animal will be able to inspire until pressure in pleural space impedes air entry through normal channels. This scenario also presumes a "sucking" chest wound whereby entrained air through wound on inspiration does not escape on expiration (think ball valve). Very deadly. However, a true open pneumothorax (air in and out wound during respiratory cycle) can be tolerated for a very long time (ask many of our young men getting shrapnel wounds overseas or any trauma center doc) "
The entire discussion can be found at:
http://forums.bowsite.com/TF/bgforums/thread.cfm?threadid=316310&forum=4#1834833
