Breathing

Ventilation

Inspiration

• Intercostal and diaphragm muscles contract
• This causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thorax (the space where the lungs are)
• As the volume of the thorax increases the lung pressure decreases (to below atmospheric pressure)
• This causes air to flow into the lungs
• It is an active process - requires energy

Expiration

• The intercostal and diaphragm muscles relax
• The ribcage moves downards and inwards and the diaphragm becomes curved again
• The thorax volume decreases, causing the air pressure to increase (to above atmospheric pressure)
• Air is forced out of the lungs
• It is a passive process - doesn't require energy. 

Spirometer

• Tidal Volume - the volume of air in each breath (0.4 dm3)
• Vital Capacity - the maximum volume of air that…