spirometer

• Air is drawn down the trachea during inspiration.
• Bronchi, bronchioles and alveoli are successively entered during inspiration.
• The diaphragm flattens and the internal intercostal muscles relax whilst the external intercostal muscles contract during inspiration, creating a greater cavity volume and reduced pressure so air is drawn in.
• In expiration, the diaphragm contracts, the external intercostal muscles relax and the internal intercostal muscles contract, creating a smaller volume in the cavity where air is forced out of the lungs.
• Pulmonary ventilation is the product of tidal volume and ventilation rate.
• Tidal volume is the volume of air in each breath.
• Ventilation rate is the number of breaths per minute.
• Forced expiratory volume is the maximum volume of air that can be breathed out in 1 second.
• Forced vital capacity is the maximum volume of air it is possible to breathe forcefully out of the lungs after a deep breath in.