Lecture 14 - Lung mechanics and lung volumes Flashcards
What is occuring if Patm= 0 mmHg and Palv = 4 mmHg?
Air is flowing out of the lung
What work needs to be done in breathing?
Overcome elastic properties (or stiffness) of lung
Overcome airway resistance
What factors effect how hard is it to expand lungs?
• Compliance of lung
• Surfactant
What is lung compliance?
A measure of elastic property of the lung, compliance is the
inverse of stiffness
What is lung compliance defined by?
Defined as the magnitude of the change in the lung volume (ΔVL) produced by the given change in the transpulmonary pressure (ΔPtp)
CL = ΔVL ⁄ ΔPtp
What are the determinants of lung compliance?
1.Stiffness / elasticity of lung
2.Also need to overcome SURFACE TENSION at
the fluid gas interface - surfactant
What happens during emphysema?
Alveoli wall damage - big air pocket, smaller SA
“Floppy” lungs
High compliance (very stretchy)
- No effect on inspiration
Low elastic
recoil
- Requires more Energy During expiration
What happens during fibrosis?
“Stiff” lungs
Low compliance - more energy
for inspiration
High elastic recoil - No additional
energy required for expiration
Why is surfactant important?
Hydrogen/fluid attracted to each other so wants to come together. Bigger problem in smaller alveoli where things are closer.
Surfactant – reduces surface tension in alveoli
Where is surfactant produced?
alveolar type II cells
What is the major constituent of surfactant?
phospholipids
How does surfactant lower surface tension?
Reduces attractive forces between
fluid molecules lining alveoli - hydrophobic phospholipids
What occurs when there is a lack of surfactant/failure to produce adequate surfactant?
“stiff” lungs
Why do premature infants develop respiratory distress syndrome (RDS)?
Surfactant is absent in premature infants - Type II cells don’t differentiate until 34 weeks
In new-born RDS what happens to alveoli?
They become collapsed
Surfactant:
Lowers surface tension at the fluid-gas interface of the alveoli
Stabilizes the smaller alveoli, thereby preventing them from collapsing due to high pressure.
How is resistance to flow determined by?
Poiseuille’s Law
R = 8nl / πr4
What are important elements in airway resistance?
Bronchoconstriction / bronchodilation
Where is the main area of airway resistance?
BRONCHI
Most of the resistance to airflow arises in the the first 6 generations of the airway. Trachea - early bronchioles
Whys is resistance is higher in larger airways?
Resistance to air flow depends on the number of parallel pathways present - larger airways are are in parallel (bronchi)
What normal condition factors affect airway resistance?
Lung volume
Radial traction
How does lung volume effect airway resistance?
Lung volume:
- increases during inspiration (due to increase in transpulmonary pressure)
- airway radius becomes larger
- airway resistance lower
- lung expands
How does radial traction effect airway resistance?
Radial traction:
Pulling of adjacent alveoli – reduces airway resistance
What diseases affect airway resistance?
Asthma
Chronic obstructive pulmonary disease (COPD)
• Emphysema
• Chronic Bronchitis
