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Flashcards in Respiration 1 Deck (16)
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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



What reynolds number is needed to produce turbulent flow