Whats the typical volume and pressure of residual air in the lungs.?

Question

When a person dies sometimes the residual air in the lungs is let out. It's under pressure so the body has less boyancy until this air is let out. If you weighed the body after this last breath is gone the scale would show a reduced weight.

Anyone know the pressure and volume?

Answer 1

Wonderful, a real science question! Creative idea but scientifically inviable I'm afraid. Review the effect of buoyancy force. To illustrate, consider a typical mylar balloon filled with air, and with air pressure inside about equal to the pressure outside (thus about the same air density inside and outside). The force pulling down on the balloon is the gravitational constant multiplied by the combined mass of the mylar film and trapped air. The force pulling up on the balloon is the buoyancy force, equal to the density of air multiplied by the balloon volume and gravitational constant.

If you sum the forces, and recognize that the mass of the air inside the balloon is equal to the density of air multiplied by the balloon volume, then you'll find that the mass of air cancels out of the equation. If you put the balloon on a very precise scale, the amount of air inside it will not change what the scale says. Only the mass of the mylar film makes a difference.

By the same token, air in the lungs is not going to change the measured weight of the body, due to buoyancy force canceling out the effect of the mass of air.

EDIT: By the way, if we assume the residual volume of air in the lungs is 1200 ml as another answerer said, that amount of air would have a mass of 1.6 grams. Not very much. A lungful of air would be about 6 liters, or about 7.8 grams.

Answer 2

There is about 1200mL of air left in the lungs after tital expiration.  The pressure is very close to the same at the atm.

Answer 3

No. The air pressure is always 1 Atm (atmospheres) The problem is that while you are living, your diaphragm is never totally relaxed, and when you die, all your muscles, including the diaphragm, relax. While it relaxes, it pushes on the lungs, making them have more pressure than in the outside. As for the buoyancy thing, it only matters when the internal gas is less or more dense than the outside gas, and your lungs and the air have the same gases, in the same proportion (at least when you are dead and not consuming oxigen).  If you fill a balloon with water, it will have the same buoyancy than the same empty balloon in water.