Respiration Flashcards
Laminar flow
And sentence about proportions
Under conditions of laminar flow the movement of air into or out of the lungs is proportional to the pressure gradient and inversely proportionate to the resistance.
Laminar flow is steady flow down a tube in a uniform direction and speed.
The flow rate is maximal in the centre of the tube and reduced towards the edges.
What is turbulent flow and what causes it.
Pressure differences in turbulent and laminar
If the flow rate moves beyond a critical value an irregular current develops.
The rate of gas movement is proportional to the square root of pressure difference.
A greater pressure difference is needed to obtain the same flow as seen under laminar conditions.
Laminar flow needs less pressure to increase flow rate.
Laminar flow increases higher than turbulent even though the same pressure is applied.
Transitional flow
The high number of bifurcations in the lung creates eddies.
Laminar flow until the split is reached which creates turbulent.
How do we determine the flow type.
Reynolds number.
R= 2 x radius x velocity x gas density / viscosity
(2 x r x v x p) / n
If R is less than 1000 then it’s laminar.
If R is between 1000-1500 it’s unstable.
If R is above 1500 it’s turbulent.
Where do the rules of Reynolds number apply to.
Terminal bronchioles.
alveolar airways because there is a very high cross sectional area so the velocity is low. And the Reynolds number will be low.
the trachea because there is a low area and a high velocity so the Reynolds number is high and there is turbulent flow.
There is turbulent flow in all high airways except terminal alveoli.
What determines the resistance of flow.
Poiselles law.
Resistance is proportional to gas viscosity and the length of the tube but is inversely proportional to the fourth power of the radius.
R= (8/pie) x (nl/ r^4)
The main affecting factor of poiselles law.
Small changes in the radius have a big impact on resistance and hence flow rate.
Airway resistance of a normal person.
Which airways have the highest resistance
Percentages of each part of the lung that contribute to the total resistance
1.5cm H2O litres.
Larger airways.
Pharynx and larynx 40%
Airways with diameter bigger than 2mm-40%
Airways with diameter lower than 2mm-20%
Resistance in a COPD patient.
Total would be 5.0 H2O litres.
Pharynx and larynx 12%
Airways bigger than 2mm -18%
Airways smaller than 2mm - 70%
The airways smaller than 2mm have a large increase in resistance but the other parts of the lung keep their resistance proportionality the same.
How airway diameter impacts resistance
Increased mucus secretion will reduce diameter and increase resistance.
An odema is increased fluid retention in lung tissue which causes swelling and narrowing of airways which will increase resistance.
Inspiration and expiration pressure changes.
During inspiration there is forced expansion of some higher airways which decreases resistance.
During expiration there is forced collapse of some higher airways which increases resistance.
Airflow at the resting state.
No airflow and the lungs only contain the residual capacity.
Alveolar and external pressure are equal resulting in no movement of air as there is no pressure gradient.
The trans pulmonary pressure is +5.
Airflow pressure at inspiration
The airways dilate to create a low alveolar pressure and a decreased resistance . So air will travel into the lungs down the gradient.
The alveolar pressure is -15.
Trans pulmonary pressure is +5.
Airflow pressure at expiration.
There is constriction of airways to increase the pressure and resistance and make air leave the lungs down the gradient.
The alveolar pressure is +15.
Emphysema and how they breathe differently.
Airways compression is exaggerated.
Loss of elastic tissue and breakdown of alveolar walls.
The airways are flimsy during forced expiration and are less able to resist collapse.
To overcome this they exhale slowly and through pursed lips and take larger breaths.
