Positive- and Negative-Pressure Ventilation

by Greg Crowther

Anatomy and physiology students all know that the lungs are important for bringing in oxygen and getting rid of carbon dioxide. However, they are often unclear on exactly HOW air moves into and out of the lungs. There are two main mechanical options, as outlined below....

From evolution and engineers,
Not one but two different forms of ventilation have appeared.
One of them expands the chest,
And one delivers air from some container that becomes compressed.

Do the lungs suck or not?
If so, then negative-pressure ventilation is just what you've got.
Or is the air forced on down?
If so, then positive-pressure ventilation is just what you've found.

• sheet music (with melody play-back)

Songs like this one can be used during class meetings and/or in homework assignments. Either way, the song will be most impactful if students DO something with it, as opposed to just listening.

An initial, simple follow-up activity could be to answer the study questions below. A more extensive interaction with the song might entail (A) learning to sing it, using an audio file and/or sheet music as a guide, and/or (B) illustrating it with pictures, bodily poses, and/or bodily movements. The latter activity could begin with students identifying the most important or most challenging content of the song, and deciding how to illustrate that particular content.

(1) Name one group of organisms that naturally inflate their lungs via positive-pressure ventilation.

(2) Which form of ventilation operates by helping the inspiratory muscles expand the chest?

(3) Another way of contrasting the two forms of ventilation is to say that in one of them, air is pushed into the lungs, whereas in the other, air is pulled into the lungs. Which is which?