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Flashcards in Respiration 2 Deck (13)
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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.