The Mechanics Of Breathing Flashcards
Why is the fall in alveolar pressure large enough to be observed?
There is a delay in pressure change as it takes time for the air to move
What does impaired airway function lead to?
Insufficient ventilation
What does the rate of airflow depend on?
The pressure gradient and level of airway resistance
What happens to resistance as airway radius decreases?
Increases (and airflow decreases) massively
What is airway resistance increased by (apart from small radius?)
Turbulent airflow
What is patency?
State of being open (ie not collapsing/flat)
What can cause airway obstruction?
Loss of airway patency due to degredation of structure
What maintains patency in a healthy alveoli?
Elastin in surrounding alveoli provides radical traction to splint bronchioles against positive alveolar pressure
What happens to the alveoli in COPD?
There is a reduction in radial traction, so the bronchioles collapse
What does lung compliance quantise?
The relationship between the level of expansive force applied to the lung and the resulting change in lung volume
What is trans pulmonary pressure?
The level of force acting to expand the lung
What is trans pulmonary pressure made up of?
Alveolar pressure - intrapleural pressure
How is lung compliance calculated?
By dividing a change in lung volume by the associated change in trans pulmonary pressure
What is compliance expressed as on a graph?
The gradient
What does it mean if there’s a steeper curve?
Greater level of lung compliance
What does it mean if there’s a greater lung compliance?
Looser/easier to inflate lung
What does a low lung compliance mean?
It’s stiffer/ harder to inflate the lung
What factors affect lung compliance(3)?
Chest wall mechanics Alveolar surface tension Elastin fibres (density)
What diseases affect the chest wall mechanics?
Scoliosis
Muscular dystrophy
Obesity
What disease affects the alveolar surface tension?
Neonatal respiratory distress syndrome
What diseases affect the elastin fibre density?
Fibrosis (increases density)
COPD (decreases density)
What do air-liquid interfaces generate?
Surface tension
Why are alveoli lined with fluid?
To enable gas exchange
What does laplaces law describe?
The pressure generated by the surface tension within a bubble
What would happen if two different sized alveoli were connected via airways and what is this force overcome by?
Pressure gradients being created between the alveoli, resulting in smaller alveoli emptying into larger ones
Overcome by pulmonary surfactants
What is a pulmonary surfactant?
Cocktail of different phospholipids and phospholipoproteins
What are pulmonary surfactants secreted by?
Type two pneumocytes
What do pulmonary surfactants do?
They disrupt the attractive forces and reduce surface tension (So lungs expand easier)
Also equalise pressure and volume across varying alveoli
What happens to the concentration of pulmonary surfactant as the alveoli expand and why does it happen?
Decreases, which increase surface tension
Set amount of surfactant in each alveoli
What does surfactant mean for the distribution of air in the alveoli?
Larger alveoli collapse into smaller ones
How does surfactant prevent alveolar oedema?
- surface tension produced at the air-liquid interface reduces hydrostatic pressure. It is then pulled out of the surrounding capillaries into the alveoli
What is neonatal respiratory distress syndrome caused by?
Insufficient production of pulmonary surfactant
What is the pathway of neonatal respiratory distress syndrome?
Premature birth, maternal diabetes, congenital developmental issues
- > insufficient surfactant production
- > stiff lungs, alveolar collapse, oedema
- > respiratory failure
- > hypoxia
Causes of death for neonatal respiratory distress syndrome
Pulmonary vasoconstriction, endothelial damage, acidosis, pulmonary + cerebral haemorrhage
