Respiration 2 Flashcards
What is Poiseulle’s law
Airway resistance is proportional to gas viscosity and tube length but is inversely proportional to the fourth power of the radius - increases in radius have a large impact on resistance
Where does the majority of resistance come from in the airways
Pharynx and larynx = 40%
Airways >2mm = 40%
How do upper airways resist
In series
How do lower airways resist
In parallel
What happens to airway diameter in COPD patients
Half in diameter due to inflammation of the lower airways
What three factors affect airway resistance
1 - Airway diameter
2 - Tissue oedema
3 - Airway collapse
What happens at rest - FRC
Forces are balanced - no net movement of air
No pressure gradient between barometric and alveolar air
Intrapleural pressure is slightly negative
Transmural pressure is +5 so resists collapse
What happens during inspiration
Intrapleural pressure becomes more negative
Alveolar pressure initially drops to sub atmospheric pressure
Transmural pressure increases along length - airways dilate causing a decrease in resistance to airflow
What happens during expiration
Intrapleural pressure becomes greater than barometric
as does alveolar
Transmural pressure becomes negative promoting collapse of the airway and increased resistance to airflow
What happens to tethering between adjoining airspaces in emphysema
It is reduced
What happens to the airways of an emphysema patient
They become more flimsy and liable to collapse - especially in expiration - this is overcome by slower expiration through pursed lips
What defines a COPD patients airways
Resistance is higher at all volumes
How do breaths of a normal patient differ to that of a COPD sufferer
In normal patient after half a breath the max inspiration volume is achieved - in exercise they are able to quadruple their resp rate and maintain the 500ml tidal volume whereas in COPD patients after 2.5s still havent reached 500ml and an increase in respiratory rate causes a large knock off in tidal volume.
