Respiration 1 Flashcards
What is compliance
Change in Volume/ Change in Pressure
What defines low compliance
Harder to inflate the lungs - more work to inspire - pulmonary fibrosis
What defines high compliance
Harder to expire - emphysema
What is the equilibrium position of the lungs
When the collapsing force of the lungs = expanding force of the chest wall
What do you need to apply to keep the lungs inflated
Positive pressure
How do you overcome the tendancy for the chest wall to expand
Apply a negative pressure
When volume is less than FRC there is a smaller volume in the lung - what happens to forces acting on collapse and chest wall
Forces favouring collapse are low
Forces favouring chest expansion are high
Overall the system wants to expand
What generates surface tension
generated by the differing forces acting on air and water molecules at the interface between the two
Why would surface tension normally lead to collapse of small alveoli
Because in Laplace’s equation P=2T/r so larger sacs have small pressures so air would tend to flow from small sacs into larger causing them to collapse.
What is surfactant and where is it produced
Produced by type 2 pneumocytes - acts to reduce surface tension by giving water molecules an upward moment - high density at start of inspiration which depletes as the lungs expand
What is laminar flow
Steady flow in a uniform direction - fastest flow in the centre and slows towards the periphery of the tube
What is turbulent flow
Vortices develop - greater pressure gradient needed to obtain the same flow rate
How is flow determined
Reynolds number
What is Reynolds number
2rvp/n where r = radius, v = velocity, p = density of gas and n = viscosity
What Reynolds number is needed to produce laminar flow
<1000
