Breathing Mechanics Flashcards
How is breathing related to Boyle’s Law?
Inspiration - diaphragm contracts. Thoracic volume increases. Pressure decreases.
Expiration - diaphragm relaxes. Thoracic volume decreases. Pressure increases.
What muscles are required for breathing?
Inspiration - external intercostal muscles and the diaphragm.
Expiration - passive at rest. During severe respiratory load, internal intercostal muscles and abdominal muscles are used.
What happens to the airways during breathing?
Inspiration - airways are pulled open via the physical forces of inspiration.
Expiration - airways are compressed via the physical forces of inspiration.
This can aggravate asthma.
What motions increase the dimensions of the rib cage?
The intercostal muscles elevate the rib cage.
‘Pump handle’ - increases anterior-posterior dimension.
‘Bucket handle’ - increases lateral dimension.
Define alveolar pressure.
The pressure inside the thoracic cavity / lungs.
Can be positive or negative compared to atmospheric pressure.
Define intra-pleural pressure.
The pressure inside the pleural cavity.
Typically negative compared to atmospheric pressure.
Define transpulmonary pressure.
The difference between alveolar pressure and intra-pleural pressure.
Typically positive, because intra-pleural pressure is typically negative.
What factors affect the flow of air between the atmosphere and the alveoli?
Proportional to the difference between atmospheric pressure and alveolar pressure.
Inversely proportional to the airway resistance.
What occurs between breaths at the end of expiration?
No air flows.
The lungs are stretched and are attempting to recoil; the chest wall is compressed and attempting to expand.
Describe the pressures formed at the end of expiration.
The lungs and thoracic cage are stable, as a result of opposing elastic forces.
This forms a negative intra-pleural pressure, therefore creating a positive transpulmonary pressure (that opposes elastic recoil).
