Lecture 4 (Respiration 1) Flashcards
What factors have a role in determining air flow? (4)
-Type of air flow
-Resistance of the pathway
-Pressure gradients generated across the airways.
-Links between lung volume, resistance and airflow
What are the 3 types of airflow?
Laminar
Unstable
Turbulent
What determines air flow type?
Reynolds number (Re)
What are the Reynolds number (Re) values for laminar, unstable and turbulent flow?
-Re < 2000 – laminar flow
-Re between 2000 and 3000 - flow is unstable switching between laminar and turbulent
-Re >3000 – turbulent flow
What influences Reynolds number in terms off fluid? (2)
Viscosity and Density
What state is airflow usually in?
Turbulent
(laminar sometimes in terminal airways)
How is laminar flow proportional to pressure and resistance? (2)
-Proportional to the pressure gradient
-Inversely proportional to the resistance
Where is the flowrate maximum?
In the center
Describe the pressure gradient in alveoli when breathing in and out? (2)
-Pressure in alveoli is sub atmospheric when breathing in
-Pressure in alveoli is greater than atmospheric when breathing out
Describe the relationship between flow rate and pressure difference in turbulent flow state?
Under conditions of turbulent flow, the flow rate is proportional to square root of the pressure difference
Describe the relationship between flow rate and pressure difference in laminar flow state?
Under conditions of turbulent flow, the flow rate is proportional to the pressure difference
What is transitional airflow?
As air reaches branching points goes from laminar to turbulent back to laminar
What is airway generation number?
More branches of airways going deeper into lungs
How does CSA in airways affect velocity at trachea, further down branches and terminal airways? (3)
-Small CSA at trachea / bronchioles so high velocity
-Further down branches CSA increases so velocity drops as you go down generations
-Velocity drops down to nearly 0 at terminal airways
What is COPD?
Chronic Obstructive Pulmonary Disease (COPD)
What is COPD?
Group of progressive obstructive lung diseases characterised by an increase in airway resistance and decrease in airflow
What are 2 examples of COPD? (2)
Chronic Bronchitis – long standing inflammation of the bronchi and bronchioles
Emphysema – destruction of alveoli walls
How do you manage COPD?
A progressive disease – no cure – control the symptoms
Bronchodilators – anticholinergics or 𝛃2 adrenorecptor agonists.
Glucocorticosteroids (reduce inflammation in airways)
How does COPD cause reduced airflow? (2)
-Inflation in lumen causes in to narrow
-Destruction of alveoli walls affects elasticity of airways and makes them flimsy)
What is the impact of resistance on flow is determined by?
Poiseuille’s law
What is Poiseuille’s law?
Airway resistance is proportional to gas viscosity and the length of the tube but is inversely proportional to the fourth power of the radius
What is resistance proportional?
Resistance is proportional to 1 / radius of fourth power
What are the percentages of air way resistance for : (3)
Pharynx-Larynx -
Airways >2mm diameter –
Airways <2mm diameter –
Pharynx-Larynx - 40%
Airways >2mm diameter – 40%
Airways <2mm diameter – 20%
How does COPD affect these values: (2)
Pharynx-Larynx - 40%
Airways >2mm diameter – 40%
Airways <2mm diameter – 20%
Total airway resistance - 1.5cm H2O .s.litres-1
-Huge increase in airway resistance for small airways and total resistance due to inflammation
-Pharynx and Larynx both contribute the same to the resistance
Pharynx-Larynx - 12%
Airways >2mm diameter – 18%
Airways <2mm diameter – 70%
Total airway resistance - 5.0 H2O .s.litres-1
What is the normal total airway resistance?
1.5cm H2O .s.litres-1
What factor affects airways resistance?
How can this be affected? (2)
Airway Diameter:
Increased mucus secretion will effectively reduce airway diameter – increased resistance.
Oedema – increased fluid retention in the lung tissue will cause swelling and narrowing of the airways – increased resistance.
What happens to higher airways during inspiration and expiration? (2)
During inspiration – forced expansion of some higher airways
During expiration – forced collapse of some higher airways
How do you keep lungs from collapsing?
To keep lungs from collapsing you have a sub-atmopsheric pressure in the interpleural space
What is Transmural pressure?
Transmural pressure is difference of pressure in airways and atmospheric
What is Transpulmonary pressure?
Transpulmonary pressure is link between interpleural pressure and atmospheric pressure
How does inspiration affect pressure in airways? (2)
Pressure in airways becomes more sub atmospheric
Create big pressure gradient in alveoli which allows air to rush into lungs
Force that pulls airways out in inspiration and decreases in airways resistance
(During inspiration there is dilation of airways and decreases in airway resistance)
How does emphysema affect alveoli? (3)
Mechanical tethering affect keeps alveoli open
In emphysema alveoli walls are broken down
Airways become flimsy as affect to keep airways open is now lost
During forced expiration it is harder to resist these airways collapsing
How does airway resistance affect lung inflation?
When resistance is increased inflation is impaired
How does COPD affect time constant?
You reach 63% volume when healthy after 0.2 second
You reach 63% volume with COPD after 1 second
How much air do you need to take in for 1 breath?
500ml
How does COPD affect you when exercising?
Large drop of in tidal volume for patients with COPD due to high airway resistance
What’s the equation to calculate Reynolds number?
Re = (2 x radius x velocity x density) / viscosity
