Anatomy of Chest Wall and Mechanics of Breathing Flashcards
State Boyle’s Law
Pressure exerted by a gas is directly proportional to its volume
What are the two membranes of the pleural cavity
pariteral - sits inside the rib
Viscera - coats outer surface
What is the importance of the pleural fluid
allows gliding of the membranes
stops separation of thoracic cavity and the lungs
define pleurisy
inflammation of the lungs
What simple mechanism allows us to breath and why
thoracic cavity increases in volume, following Boyles law this means there is a decrease in pressure, causing air move from high pressure in the atmosphere to the low pressure in the lungs
What muscle are used for Inspiration?
Intercostal muscle
Diaphragm - contracts, flattening out
(both result in an increase in thoracic volume)
Scalene + sternomastoid - (help intercostal)
How is pneumothorax caused?
Break in the pleural membrane, allowing air in changing intrapleural pressure
While the recoil equilibrium created between thorasic cavity and lungs by the pleural membrane means the lung recoils and collapses
What is intrapleural pressure
pressure inside the pleural cavity
always negative
What muscles are used for expiration when you are respiring quickly e.g. through exercise and how?
internal intercostal muscles and abdominal muscles
abdominal muscles actively decreases thoracic dimensions this reduces duration of breathing cycle and allows more breaths/min.
How is asthma caused
Over reactive constriction of bronchial smooth muscle, increase resistance, expiration difficult
Define Intra-thoracic (Alveolar) Pressure
pressure inside the thoracic cavity, (essentially pressure inside the lungs).
How do you calculate transpulmonary pressure
difference between alveolar pressure and intra-pleural pressure
Why is transpulmonary pressure always positive
Intrapleural is always negative
and although alveolar pressure is negative during inspiration, Intrapleual pressure is always gonnna be more negative so transpulmonary pressure WILL always be POSITIVE
Why does intrapleural pressure need to be negative
As needs to be less that atmospheric pressure to allows oxygen into the lungs
and must oppose the pressure of the chest wall recoiling out while lungs recoil in
what is the major determinant in airway resistance
the radii of the airways
How do you calculate the bulk flow of air between the atmosphere and alveoli
the difference between atmospheric pressure and alveoli pressure
divided by airway reisitance
When does atmospheric pressure equal alveoli pressure
Between breaths at the end of an unforced expiration
What are the opposing elastic forces present in the lungs and thoracic cage
The lungs are stretched and are attempting to recoil, whereas the chest wall is compressed and attempting to move outward
What opposes the force of elastic recoil
transpulmonary pressure
what does the opposing elastic recoils create
a subatmospheric intrapleural pressure (keeping it negative and below atmospheric pressure) as allow the lungs to expand and pressure to decrease so air can move in
What two basic things does the lungs volume depend on?
transpulmonary pressure and how stretchable the lungs are
What occurs during expiration
Inspiratory muscles stop causing elastic recoil, therefore chest size returns to normal and compresses the alveolar air, raising alveolar pressure above atmospheric pressure and driving air out of the lungs
