Summarize this article in one sentence.
Respiratory rate is how many breaths you take in a minute. At birth, the average human respiratory rate ranges from 30 60 breaths per minute, whereas its much lower at 12 20 breaths per minute in adults. Tidal volume is the amount of air inhaled or exhaled during normal respiration (breathing), which amounts to about 0.5 L in both men and women. Tidal volumes increase during deep sleep and with relaxation, but decrease with stress, nervousness and panic attacks. In contrast, residual lung volume does not fluctuate with states of consciousness or mood. Men have slightly higher residual lung volumes because they tend to have larger bodies and lungs. When you exhale while breathing normally, the volume of air left in your lungs is called the functional residual capacity, which is NOT your residual volume. Instead, the residual volume is the air left in your lungs after a forced exhalation, which indirectly measures the strength of your respiratory muscles (diaphragm, intercostal muscles, etc.) as well as the health of your lung tissues. Shallow breathing (due to asthma, for example) results in a larger functional residual capacity, whereas a larger residual lung volume is a sign of good fitness and healthy lung tissue. Average functional residual capacity is about 2.3 L of air in men and 1.8 L in women. In contrast, residual lung volume is always lower than functional residual capacity 1.2 L for men and 1.1 L for women. Although residual lung volume is the amount of air left in your lungs after you completely breathe out, the reality is that it's practically impossible to do so on your own. As such, residual lung volume isn't measured like tidal volume is, for example; instead its calculation has to be done via indirect methods such as closed circuit dilution (including helium dilution), nitrogen washout and body plethysmography. In absence of special testing, residual lung volume can be estimated based on a proportion of body mass or vital capacity, as well as a person's height, weight and age; however, these estimates are not particularly accurate and not as helpful for determining lung diseases. Residual lung volume is reduced with restrictive lung disease, but it also changes somewhat in response to pregnancy, significant weight gain and muscle weakness due to aging.

Summary:
Realize that residual lung volume is not your tidal volume. Know that residual lung volume is not the same as functional residual capacity. Remember that residual lung volume is not easy to measure.