Week 21: (A) Breathing I - Static Forces Flashcards
What are the 2 physical forces that influence breathing?
Static and dynamic
What is static force?
Mechanical properties of the lung that influence gas flow but which are independent of volume change
What are the 3 types of static force?
Elasticity
Compliance
Surface tension
What is Dynamic force?
Mechanical properties affecting flow of air into and out of lung as volume changes with time
What are the 3 types of dynamic force?
Force
resistance
turbulence
What force will be focused on in this lecture?
static force
What is the pleural sac?
The thin space between 2 pleura of the lungs.
Filled with liquid
A pleura is a serous membrane which folds back onto itself to form a two-layered membranous pleural sac
What is barometric pressure?
measure of air pressure in a given area
pressure is the force of air on pressing down on something
What is the function of the pleural sac in the lungs?
links elastic forces in the chest wall and lung
What is elastic recoil?
Elastin in alveoli acts as an
inward “collapsing” force
What 2 factors contribute to the sub-atmospheric
intrapleural pressure?
elastic recoil of the alveoli
and the opposing elastic recoil of the ribs as an outward expanding force
What happens to alveolar pressure during an inhale?
inspire, alveolar P decreases below atmospheric (needs to happen to draw gas in)
equalises back to 0 cmH20 and the end of insp
What happens to pleural pressure during an inhale?
goes from -5 and decreases to the end on an inhale
gets more negative as the chest cavity increases in vol.
What is pleural pressure?
pressure surrounding the lung tether the lung movement to the rib cage
What happens to pleural pressure as lung vol increases?
Ppl decreases
from ~-5 start of inhale to ~-8 at the end
What pressure is Ppl always during quiet breathing?
sub-atmospheric
What aids the alveolar pressure to move in a negative direction?
Ppl being negative ~-5 cmH2O (pressure)
What drives expiration?
elastic forces, drive lung collapse/ return of lung to inspired state.
Elastic retraction enables alveolar pressure go above atmospheric
What happens to Alveolar pressure during exhalation?
increases so the pressure in the lungs increases to overcome the forces of the upper airways and then returns to 0 at the end of exhalation
What happens to Ppl during an exhalation?
increase from around -8 cmH2O to -5
What is the equation for compliance?
change in Volume L (lung) /
change in Ptp (transpulmonary pressure)
What is the compliance equation asking us?
How much work (pressure) lung vol do we need to do to achieve a change in lung volume.
What is the effect of a lung with high compliance on ability to distend?
a high compliance balloon is easily inflated as its elasticity is low