Re: Why do we sigh and is it related to yawning?

What do sighing and yawning have to do with each other? A lot of research 
has been done on the purposes of yawning and not much at all on sighing. 
Let's look at both yawning and sighing and see if there is any connection.

Yawning is still somewhat of a mystery. A yawn is a deep inspiration and 
expiration through a wide open mouth. There are a number of theories as to 
why people yawn, and yawns may have several different functions. In fact, 
nearly all vertebrates -- fish, reptiles, birds, mammals -- yawn. And 
yawns are contagious, at least among people. The main theories as to why 
people yawn are:


1.)Yawning is a form of social communication. It signals the state of an 
individual to the group and, because yawns are contagious, can help 
coordinate the state of the group. In a sense it strengthens group 
cohesion and helps synchronize the group. (Laughter, which is also 
contagious, can do the same thing.)

2.) Yawning can be a sign of tiredness.

3.) Yawning can be a sign of boredom.

4.) Yawning can be a sign of mild stress, anxiety or conflict. For 
example, atheletes may yawn before an event and participants in a meeting 
may yawn in response to disagreement or tension.

5.) Yawning may be a form of stretching. Many people yawn when waking up. 
In these cases, the yawn is associated with generalized stretching of the 
arms and upper body.

Sighing is in many ways different from yawning. While it is, like yawning, 
a deep inspiration and expiration, it is done either though the nose with 
the mouth closed or with the mouth only partly open -- not widely open as 
in the yawn. Sighing occurs in a number of situations:

1.) Sighing can be a response to low O2 and high CO2 in the body. A sigh 
increases the amount of air entering the lungs. Infants often do this 
while sleeping. Adults do this sometimes after a long period of low-
volume, tidal breathing. (Yawning was once though to perform the same 
function but tests have shown that it has nothing to do with this.)

2.) Sighs are emotional responses to a number of situations. Sighs can 
express longing or yearning or wistfulness or relief or disappointment or 
even pleasure. 

3.) A sigh can be a means of relieving stress. This may be part of #2 
above.

So are yawning and sighing related? Not really. They both can signal 
emotional states, but they tend to signal different states. And unlike 
yawning, sighing is not contagious.