static mechanics of breathing Flashcards
what are the physical forces that influence breathing mechanics
static - influence gas flow, independent of volume change - elasticity, compliance, surface tension
dynamic - affecting flow of air into and out of lung as volume changes with time - flow, resistance, turbulence
describe what happens when you breath
when u breathe in rib cage expands outwards and upwards, lungs expand with expansion, air pressure falls below air pression in room creating vacuum causing air to move from mouth to lungs
breathe out - relax muscles in rib cage and let elastic recoil of lungs take over, recoil inwards of own elastic recoil creating air pressure that is slightly higher than air pressure in room, air moves out
what is meant by lung compliance
Lung with high compliance is easily distended
Lung with low compliance is difficult to distend
compliance varies inversely with lung elasticity
Static compliance is measured under conditions of NO GAS FLOW
what can affect compliance
diseases like pulmonary fibrosis decrease it
disease like emphysema increase it due to poor elastic structure
how do elastic forces link pleural pressure to alveolar pressure
elastic recoil - elastin in alveoli acts as an inward collapsing force
opposing elastic recoil of ribs acts as an outwards expanding force
balance of forces results in a sub-atmospheric intrapleural pressure
what is intrapleural pressure during quiet breathing
sub-atmospheric
what allows alveolar pressure to go above atmospheric during quiet breathing
elastic retraction
what is Pulmonary compliance / elastic recoil
produced by
elastic connective fibres - elastic mesh around alveoli
alveolar surface tension
how do you calculate compliance
change in volume/change in pressure
describe surface tension in the alveolus
resists alveolar stretch, so high surface tension decreases compliance reducing alveolar size and more energy required to inflate lungs
what does small variation in alveolar size/volume cause
as small diameter bubbles have higher surface tension that larger ones, variation causes small alveoli to collapse into larger ones -NOT GOOD
how do you calculate the pressure in bubble
(2 x surface tension) / radius of bubble