Mechanics of breathing Flashcards
What does the rate of airflow into the lungs depend on?
The rate of airflow depends on the pressure
gradient & level of airway resistance
What is ohm’s law(airflow)?
Airflow(V)= change in pressure(P)/Resistance(R)
What is the hagen poiseuille equation?
Resistance(R) is proportional to 1/radius^4
What happens as airways radius decreases?
As an airway’s radius decreases, the resistance
increases (and the airflow decreases) dramatically
What can airway resistance be further increased by?
Airway resistance is further increased
by turbulent airflow
What does elastin in healthy alveoli provide and why is that?
Elastin in surrounding
alveoli provides radial
traction to splint
bronchioles against
positive Palv
What does a lack of or no elastin due to COPD result in alveoli?
Without radial traction,
bronchioles collapse
What does lung compliance quantify?
Lung compliance quantifies the relationship between the level of expansive force applied to the lung and the resulting change in lung volume
What is the equation fro transpulmonary pressure?
Transpulmonary pres. (Ptp) = Alveolar pres. (Palv) – Intrapleural pres. (Pip)
What is transpulmonary pressure?
the level of force acting to expand the lung
What is lung compliance calculated by?
Lung compliance is calculated by dividing a change in lung
volume by the associated change in transpulmonary pressure
-Compliance(CL)=change in volume/change in pressure
What does the gradient of the transpulmonary pressure against lung volume graph represent?
Compliance is expressed as the gradient of the curve.
What does a steeper curve in a transpulmonary pressure against lung volume graph represent?
Steeper curve = Greater level of lung compliance
What does it mean by a greater lung compliance?
‘Looser’/easier to inflate lung = greater lung
compliance
What does it mean by a lower lung compliance?
Stiffer/harder to inflate lung = lower lung compliance
What factors and diseases affect lung compliance by impacting chest wall mechanics?
- Scoliosis
- Muscular dystrophy
- Obesity
-These decrease CL
What factors and diseases affect lung compliance by impacting alveolar surface tension?
NRDS
-Neonatal respiratory distress syndrome
-Increased alveolar surface tension
-This decreases CL
What factors and diseases affect lung compliance by impacting elastin fibres?
-Fibrosis(decreases CL)
-COPD(Increases CL)
What do air liquid interfaces generate and what do they resist?
Air-liquid interfaces (e.g. alveoli) generate
surface tension, which resists inflation
What are alveoli lined with?
Alveoli are lined with fluid to enable gas exchange (the gas molecules
dissolve into water before diffusing.
What arises and is exerted by the bubble formed by the water-air interface?
Within the bubble formed by the water-air interface, surface tension
arises due to H-bonds between the water molecules, exerting a
collapsing force toward the centre of the bubble.
What does laplace’s law describe in relation to pressure?
The Law of Laplace describes the pressure
generated by the surface tension within a bubble
What is the equation that describes the amount of pressure within a specific bubble?
P=2T/r
P is the pressure
T is surface tension
r is radius of bubble
If T is constant, what does that mean for the P=2T/r equation?
If T remains constant, then P is proportional to 1/r
-The smaller the alveoli, the larger the pressure generated
What is alveolar surface tension reduced by?
Alveolar surface tension is reduced by the presence of
pulmonary surfactant,
What is pulmonary surfactant secreted by?
Secreted by type 2 pneumocytes
How does pulmonary surfactant work?
Attractive forces at surface disrupted, reducing surface tension
What are the 2 type of cells that the surface of alveoli primarily consist of?
-Type 1 is responsible for gas exchange
-Type 2 secretes pulmonary surfactant
What does pulmonary surfactant act to equalise across varying alveoli?
Pulmonary surfactant acts to equalise
pressure & volume across varying alveoli
What happens as to surface tension as alveoli expand and due to what?
As alveoli expand, the concentration of
surfactant molecules decreases, increasing
surface tension.
What helps with consistent inflation of the lungs?
Now, larger alveoli tend to collapse into
smaller ones, helping consistent inflation of
the lungs.
What does pulmonary surfactant help to prevent?
Pulmonary surfactant helps to prevent
alveolar oedema
How is alveolar oedema prevented by pulmonary surfactant?
-Pulmonary surfactant helps to prevent
alveolar oedema
Surface tension produced at the air-liquid interface also reduces
hydrostatic pressure. Fluid is then pulled out of surrounding
capillaries and into the alveoli.
-By reducing surface tension, pulmonary surfactant helps to prevent
alveolar oedema, as observed in patients with insufficient surfactant.
What is neonatal respiratory distress syndrome(NRDS) caused by?
Neonatal respiratory distress syndrome is caused
by insufficient production of pulmonary surfactant
What are the steps involved in neonatal respiratory distress?
Premature birth, maternal diabetes, congenital
developmental issues
↓
Insufficient surfactant production
↓
Stiff (low compliance) lungs, alveolar collapse, oedema
↓
Respiratory failure
↓
Hypoxia
↓
Pulmonary vasoconstriction, endothelial damage,
acidosis, pulmonary + cerebral haemorrhage.
