L1 - Respiration - Airflow Flashcards
Which 4 factors have a role in determining air flow?
Type of air flow
Resistance of the pathway
Pressure gradients
Links between lung volume, resistance and airflow
What is laminar flow?
Steady flow down a tube in a uniform direction and speed
Flow rate is maximal in the centre but reduces towards the edge
During laminar flow movement of air into and out of the lungs is?
Proportional to the pressure gradient
Inversely proportional to the resistance
What is turbulent flow?
If flow rate moves beyond a critical value, irregular currents – vortices develop
Greater pressure gradient needed to obtain the same flow seen under laminar conditions – more effort
During turbulent flow the rate of gas movement is?
Proportional to square root of the pressure difference
What is transitional flow?
High numbers of bifurcations in the airways disrupt flow - creating eddies
What is determination of flow type governed by?
Reynolds number o r - radius o v - velocity o ρ - density of the gas o η - viscosity
Reynolds number equation
Re = 2rvp/n
If Re < 1000 what flow is seen?
Laminar flow
If Re is between 1000 and 1500 what flow is seen?
Flow switching between laminar and turbulent
If Re is > 1500 what flow is seen?
Turbulent flow
What is Poiseuilles law?
Airway resistance is proportional to gas viscosity
Length of the tube but is inversely proportional to the fourth power of the radius
Small changes in airway diameter have a big impact on the resistance and therefore flow rate
In a normal individual what is the airway resistance throughout the lung?
Total airway resistance is 1.5cm H2O .s.litres-1
- Pharynx-Larynx - 40%
- Airways >2mm diameter – 40%
- Airways <2mm diameter – 20%
In a COPD patient what is the airway resistance throughout the lung?
Total airway resistance is 5.0 H2O .s.litres-1
- Pharynx-Larynx - 12%
- Airways >2mm diameter – 18%
- Airways <2mm diameter – 70% (huge difference from normal patients)
What are the 2 factors impacting airway resistance?
Airway diameter
Lung volume