when does VQ mismatch occur?
when ventilation is blocked but perfusion continues - in otherwords blood is flowing through poorly ventilated areas
what is hypoxic pulmonary vasoconstriction?
when there are poorly ventilated alveoli, the local hypoxia triggers vasoconstriction of pulmonary arterioles
how does the body compensate for the V/Q mismatch with regards to hypoxic pulmonary vasoconstriction?
blood is diverted away from poorly ventilated regions towards better ventilated ones
explain the concept of interdependence of alveoli
alveoli share septa, meaning, the expansion or collapse of one alveolus affects its neighbouring alveoli
what is the advantages of interdependence of alveoli?
- local alveolar collapse is resisted by the mechanical pulling of adjacent alveoli and it helps to stabilize lung structure during disease states
which part of the airway is influenced by intrapleural pressures?
the lower airway and not the trachea and primary bronchi
what is transmural pressure?
the pressure difference inside vs the outside of the lungs
what is transpulmonary pressure?
its the transmural pressure across the alveoli
alveolar pressure - intrapleural pressure
what is airway transmural pressure?
airway pressure - surrounding tissue pressure
what is functional residual capacity? (FRC)
the volume of air in the lungs after a normal exhalation
what is expiratory reserve volume?
the amount of air that can be forcefully exhaled after a tidal expiration
what is residual volume?
the amount of air still in the lungs that cannot be exhaled
where is residual volume primarily located?
at the apex of the lungs
what are the pressure conditions at the end of expiration (FRC). (atmospheric, alveolar, intrapleural, and transpulmonary pressures)
Patm = 0 cmH2O
Palv = 0 cmH2O
Pip = approx -5 cmH2O
transpulmonary = +5 cmH2O
how is a balance of forces at FRC. in other words how is there an equilibrium at rest?
the inward recoil of the alveoli balances with the outward recoil of the chest wall
static vs dynamic conditions
static condition = no air flow
dynamic conditions = air is moving (either during inspiration or expiration)
what pressure changes occur during inspiration?
- intrapleural pressure becomes more negative
- transpulmonary pressure increases
- alveolar pressure decreases below atmospheric pressure (because air is flowing into the lungs)
alveolar pressure is composed of two opposing forces, what are they?
- outward pressure that pulls the alveoli open (the negative intrapleural pressure)
- inward pressure that pulls the alveoli closed (elastic recoil pressure from elastin and collagen)
during static conditions Palv always = Patm. how does these pressure differ with inspiration and expiration?
inspiration = Palv < Patm
expiration = Palv > Patm
