A spirometer is an instrument use in a hospital to measure lungs capacity of patient suffering from respiratory diseases the following are associated to air.

• Tidal air or tidal volume:  This is the volume of air which moves into and out of the lungs during normal breathing.
• Dead space air: It is air that remains in the respiratory passage when no gaseous exchange takeplace.
• Inspiratory reserve volume: It represent the maximum extent to which the lungs can expand.
• Expiratory reserve volume: It represent the maximum extent to which the lungs can contract.
• Residual volume(air): It is the volume of air that remains in the lungs when we forcefully breath out. Hence the lungs can never become completely empty.
• Vital capacity: It the maximum amount of air that one can send out after fully breathing in.
• Respiratory quotient: It is the ratio of the volume of carbon dioxide produce to the volume of oxygen taken in, in respiration during the same period of time. Respiration quotient indicate the type of food substrate use for respiration and were there respiration is aerobic or anaerobic.