mechanics Flashcards
compliance
tendency to distort under pressure
change in V/change in P
elastance
tendency to recoil to original vol
retain its shape
change in P/change in V
COPD and compliance
more compliant
recoil forces don’t exist
Fluid filled lungs and compliance
same volume changes as air filled lungs
more compliant
start stretching immediately - water:water interface provides surface tension
from forces holding water together
alveoli without surfactant
a lot of force to bring air in
upward pressure from water - collapsing the lung
small airwasy collapse - force air into larger airways
alveoli with surfactant
surfactant break up tension - phospholipid
easier to ventilate
surfactant
made by Type 2 pneumocytes reduce collapsing pressure 80% polar phospholipids 10% non-polar lipids 10% protein increases compliance by reducing surface tension
law of Laplace
tension proportional to the radius
not linear
resistance through the generations
R inversely proportional to 4th power of the radius
reduces velocity - air not even moving in small airways
however exponential increase in cross sectional area from 7th generation - hydrostatic pressure decreases
conductance
how much conductancy airways offer
increases as lung vol increases
airways distorted under pressure
COPD resistance
increase
bronchoconstriction
excess mucous
bronchitis
ventilating with a snorkel
ventilation more forceful
against the dead space
effect of using a larger snorkel
breath the same air so deplete O2 and increase CO2 - breath faster - exacerbrate situation - die
deeper - increased hydrostatic pressure - resp muscles work harder to expand
poiseuille’s law - importance of radius for pressure
Boyle’s law - pressure is inversely proportional to volume
more effort to breathe
poiseulle’s law
R = 8nl/pi(r)to power of four
boyle’s law
Pgas (proportion symbol) 1/Vgas
mechanics of ventilation
as volume increases or decreases in lung - more pressure is needed to expel or inhale even more - huge effort to be ventilated
in expiration - low externally applied pressure, push pleura togeteher = increase in pleural pressure to -2
in inspiration- high externally applied pressure, pill pleura apart = pleural pressure decrease
volume and pressure relationship in COPD
height:width of curve change - lung more compliant - less pressure needed to change vol
vol and pressure relationship in restrictive lung
vital capacity reduced
stretch more - more effort to move in - wall less compliant
relationship between flow rate Palv, vol and Ppl
subtract vol from Ppl = curve for Palv and flow
Flow in collapsible tubes
pre-inspiration: no flow - func residual capacity - pleural pressure -2 because of recoil chest oppsoinbg force = partial vol
mid insp - decrease pressure in pl to -8, -2 in airway - transmural pressure +ve so airway open
end insp - airway pressue 0 - transmural still +ve (0–8)
hard expiration - pleural increase to +22 transmural pressure -ve (airway pressure 20) - would collapse but have cartilage support
mechanical forces in tidal vol
functional residual capacity at start
want to draw air in - use insp muscles
open lung
reduce pressure
create vacuum in lungs - pressure gradient - air in
pressures balance - atm 0cm H2O = no gradient
recoil of lung compress air - push it out
net change in vol is reversed
mechanical relationship with the chest wall
chest wall tendancy to spring out
lung tendency to spring in
these forces are in equilibrium at end tidal expiration - func residual capacity
neutral position of the intact chest
chest wall and lungs single unit
have own combination of physical properties - together dictate position, characteristics and behaviour of intact wall
chest wall and inspiration/expiration
in inspiration: insp muscle and chest recoil > lung recoil
expiration: chest recoil
Pleura
visceral pleura - on lungs
parietal - on chest wall
pleural cavity - gap with fixed vol, contains protein rich pleural fluid
lubricated movement - allow 2 things to work against each other
