Mechanics of breathing Flashcards
Resistance
An opposing force that acts to reduce the flow of a gas or fluid through a conduit
The variable factors within the airway
Cross sectional area of the airway lumen
Airflow pattern
Hagen Poiseuille equation describes
relationship between resistance and the various properties of ariways and airflow
What is the resistance in the Haigen Poiseuille equation
Inversely proportional to cross sectional radius raised to power of 4
Decrease in radius
Produce a large increase in resistance
What pathological features can impact the cross sectional area of the airway lumen
Contraction of airway smooth muscle
Excessive mucus secretion
Oedema/swelling of airway tissue
Damage to the integrity of the airways structure
Effect of reducing the size of the lumen
Increase airway resistance
Decrease airflow
When does turbulence occur
High velocities of airflow are achieved
If there is a sudden decrease in luminal area such as obstructed airways
Airway patency
State of being open or unobstructed
Loss of patency
Closing/obstruction
What maintains the open structure of airways
Elastic fibres within wall of airway and radial traction
Transpulmonary pressure
Difference between pressure within the alveoli and intrapleural space
Determines level of force acting to expand or compress lungs
During inspiration
Increasing levels of negative intrapleural pressure are generated as lung volume increases due to elastic properties of lung tissue
Lung compliance
- Relationship between the change in lung volume produced by a change in transpulmonary pressure
- Describes how easily the lungs can be distended
Higher lung compliance
less elastic recoil = less force required to inflate = increase volume change per pressure change
Lower compliance
more elastic recoil = more force required to inflate = decrease volume change per pressure change
Compliance
Change in volume/change in pressure
Gradient of curve
Diseases that lower compliance
(Affect chest wall mechanics) Scoliosis Muscular dystrophy Obesity (affect elastin fibres) Fibrosis (Affect surface tension) NRDS - Neonatal respiratory distress syndrome
Diseases that increase compliance
(Affect elastin fibres)
COPD
Emphysema
Surface tension
Arises due to the strength of hydrogen bonds between water molecules - cause a collapsing force - generate pressure
Relationship between the pressure and radius
Inversely proportional - smaller = generate pressure greater pressure
Pulmonary surfactant function
- Prevent smaller alveoli collapsing into larger alveoli due to pressure gradients
- disrupt attractive forces between water molecules, reducing surface tension
- prevent alveolar oedema - excessive fluid being pulled from capillaries
Pulmonary surfactant structure
Phospholipoprotein - secreted by type II pneumocytes
Amphipathic - hydrophilic head, hydrophobic tail
Position themselves at air-liquid interface
As alveolar size increases
Concentration of surfactant at interface decreases
Net effect of pulmonary surfactant
Surface tension increases with increasing alveolar surface area
Air will move from large alveolar to small ones
NRDS
Occurs in infants born prematurely. Produce insufficient levels of pulmonary surfactant
NRDS results in respiratory failure due to
alveoli collapsing
Decreasing lung compliance
alveolar oedema reducing gas exchange
Treatment for NRDS
Artificial surfactant
Glucocoritcoids
