Brent Cornell

    
Breathing is the active movement of respiratory muscles that enables the passage of air into and out of the lungs

• The contraction of respiratory muscles changes the volume of the thoracic cavity (i.e. the chest)

The mechanism of breathing occurs according to the principle of Boyle’s Law (pressure is inversely proportional to volume)

• When the volume of the thoracic cavity increases, pressure in the thorax decreases
• When the volume of the thoracic cavity decreases, pressure in the thorax increases

Gases will move from a region of high pressure to a region of lower pressure (similar to movement via concentration gradient)

• When the pressure in the chest is less than the atmospheric pressure, air will move into the lungs (inspiration)
• When the pressure in the chest is greater than the atmospheric pressure, air will move out of the lungs (expiration)

Principle Behind Negative Pressure Breathing

 

    
Respiratory muscles contract to change the volume of the thoracic cavity and hence alter the pressure in the chest

• Because muscles only do work via contraction, different groups of muscles are required to expand and contract chest volume

Changing chest volume creates a pressure differential between the chest and atmosphere – with air then moving to equalise

• Muscles that increase the volume of the chest cause inspiration (as chest pressure is less than atmospheric pressure)
• Muscles the decrease the volume of the chest cause expiration (as chest pressure is greater than atmospheric pressure)

Atmospheric pressure is lower at high altitudes, meaning a greater increase in chest volume is required before a pressure differential is formed – making it harder to breathe at high altitudes

• The body will adapt mechanisms to improve oxygen uptake under these conditions, which is why athletes will often undertake high altitude training prior to competitions

Negative Pressure Breathing