Unit 2, L2, Lung Mechanics A Flashcards
Why does air flow in and out of alveoli?
Air flows down a pressure gradient, so during inspiration, alveolar pressure is below atmospheric pressure and air flows in. During expiration, alveolar pressure is above atmospheric pressure and air flows out
How are the lungs connected to the chest
Not through any ligaments or tendons, its all through controlling pressure in pleural space
What is Boyle’s law
At a fixed temperature, the volume of a gas is inversely proportional to the pressures exerted by the gas
What is the equation for Boyle’s law
P = 1/V
Thoracic cavity is separated by what from the abdominal cavity
Diaphragm
Major muscles of inspiration
External intercostals and diaphragm
Muscles of active expiration
Internal intercostal muscles and abdominal musclees
Accessory muscles of inspiration
Scalenus and sternocleidomastoid
The diaphragm
Stimulated by phrenic nerve, accounts for 75% of increase in thorax cavity volume, its a major inspiratory muscle. Stimulation causes the muscle to flatten and move downward, enlarges the cavity in the vertical direction
External intercostal muscles
Stimulated by the intercostal nerves, stimulation causes the ribs to move up and outward, enlarges the cavity in both lateral and anteroposterior directoin
Deep forceful inspiration uses what muscles and what is different from a tidal inspiration
Needs to engage the accessory inspiratory muscles, so contraction of the neck muscles raises the sternum and elevates the first two ribs, enlarges the upper portion of the thorax
Expiration is active or passive
Mostly passive, inspiratory muscles relax. Diaphragm relaxes, allowing the muscle to assume its natural dome shape, and intercostal muscles relax, causing the rib cage to fall down due to gravity
Forced expiration is active or passive
Active, requires contraction of expiratory muscles. Abdominal muscle contraction increases abdominal pressure and pushes the diaphragm upward. The internal intercostal muscles contraction flatten the rib cage by pulling the ribs downward and inwards
What determines the volume of air in the lungs?
Balance between elastic properties of the lung and properties of the muscles of the chest wall
Elastic properties of the lung are primarily dependent on two factors
Surface tension of airways and elastic properties of cells and tissue. Both of these are an inward directed force
RV is
Residual volume
Positive side of 0, in terms of pressure, will do what to the lungs
They will want to collapse, want to get smaller when you release them
Negative side of 0, in terms of pressure, will do what to the lungs
Make them want to get bigger when you release them
For most of our volume, the chest wall is at a (negative or positive) expanding force
Negative
Lungs always have a (expanding or collapsing) force
Collapsing, lungs don’t give a shit, they just wanna collapse and end this life
What is FRC
Functional residual capacity, is the equilibrium point of the lungs and the chest wall, pulling equally on each other, also the volume left after a tidal exhale
Transmural pressure is what
Pressure inside relative to pressure outside of a compartment
Transmural pressure across the lung wall
PL (translung or transpulmonary pressure) = PA (alveolar pressure) - PpI (pleural pressure) so 760-756 = 4 mmHg
Transmural pressure across the chest wall
Pw (Pressure across the chest wall) = Ppl (pleural pressure) - Pb (Barometic pressure, atmospheric pressure) so 756-760 = - 4 mmHg
Pressure across respiratory system equation
Prs (pressure across respiratory system) = PL (translung, transpulmonary pressure) + Pw (pressure across the chest wall), which can be simplified down to be PA (alveolar pressure) - Pb (atmospheric pressure)
Puncture any barrier in the lungs and what will happen
Pneumothorax, lungs will collapse
Pleural space is an (open or closed) system
Closed, there is no airflow. Changes in volume change pressure with no dissipation
Alveolar space is (closed or open) system
Open, there is air flow. Changes in volume will change pressure transiently, but air flow will return pressure to steady-state
