Respiratory volumes are the amount of air inhaled, exhaled and stored within the lungs at any given time.
Tidal Volume: The amount of air which enters the lungs during normal inhalation at rest. The average tidal volume is 500ml. The same amount leaves the lungs during exhalation.
Inspiratory Reserve Volume: The amount of extra air inhaled (above tidal volume) during a deep breath. This can be as high as 3000ml.
Expiratory Reserve Volume: The amount of extra air exhaled (above tidal volume) during a forceful breath out.
Residual Volume: The amount of air left in the lungs following a maximal exhalation. There is always some air remaining to prevent the lungs from collapsing.
Vital Capacity: The most air you can exhale after taking the deepest breath you can. It can be up to ten times more than you would normally exhale.
Total Lung Capacity: This is the vital lung capacity plus the residual volume and is the total amount of air the lungs can hold. The average total lung capacity is 6000ml, although this varies with age, height, sex and health.