pulmonary ventilation Flashcards
what is pulmonary ventilation needed for
-maintain oxygen and co2 gradients between alveolar air and arterial blood
-allows sufficient level of gas exchange
-adequate blood supply
what is ventilation dependant on and what is the equation for ventilation
depth and rate of breath
ventilation = tidal volume x frequency
how much of the dead space volume is left in the respiratiry system
150mL
equation for alveolar air
Va= (Vt-Vd) x f
Vt = tidal volume
Vd= dead space volume ( volume of air remaining in respiratory system at the end of expiration )
Vt-Vd= the volume of fresh air entering each breath
brief overview of what happens in inspiration
-diaphragm contracts
-thoracic cavity expands
-alveolar pressure decreases
brief overview of what happens in expiration
-diaphragm relaxes
-lungs recoil
-thoracic cavity volume decreases
-alveolar pressure increases
at the end of expiration
P alveoli=P atmostphere
there is no movement of air
describe pressure changes in atmostphere and alveoli during inspiration
-higher atmostpheric pressure
-lower alveolar pressure
-air flows into alveoli
-outer surfaces of lungs are pulled outwards
describe pressure changes in alveoli and atmosphere during expiration
-lower pressure in atmosphere
-higher pressure in alveoli
-air flows out
-air within lungs is compressed
what is the pleural cavity
fluid filled space between membranes that line the chest wall and each lung
use of the pleural cavity
-reduces friction between lungs and chest during breathing
what are the properties of the pleural cavity
-sealed
-fluid filled
-sub atmospheric
what causes the pleural cavity to be sub atmospheric
the opposing elastic recoil of the chest wall (outwards) and the lungs (inwards ) makes the pressure in the pleural cavity sub atmospheric
what is negative pressure
lower number of molecules per volume which generates a collapsing force
what is positive pressure
increased number of molcules per volume which generates expanding force
outline inspiration
-respiratory muscles eg diaphragm, contract
-volume of thoracic cavity increases
-interpleural pressure becomes negative
-lungs expand, increasing volume
-p alv decreases below p atm
-air moves down pressure gradient , through airways into alveoli , expanding lungs
outline expiration
-respiratory muscles relax eg diaphragm
-volume of thoracic cavity decreases
-interpleural pressure increases
-lungs compressed , volume decreases
-p alv increases above p atm
-air moves down pressure gradient into atmosphere
what happens in forced expiration
compression of lungs due to increased interpleural pressure
what happens in quiet breathing
elastic recoil is sufficient to decrease lung volume
what happens if either pleura is ruptured
-air will enter pleural space because its sub atmospheric
-lung will recoil and collapse
-pneumothorax
-pressure gradient in pleural cavity and surrounding environment causes air to enter (pneumothorax) until intrapleural pressure = atmospheric pressure
