Compliance and Surface Tension

What is compliance in the context of lung expansion?

Compliance refers to the ease with which the lungs and chest wall expand to allow air in.

What does high compliance mean?

High compliance means the lungs and chest wall are easy to expand, similar to blowing up a thin balloon.

What does low compliance mean?

Low compliance means the lungs and chest wall are difficult to expand, like trying to blow up a thick balloon. This can lead to shallower and faster breathing.

What factors can interfere with lung compliance?

Factors that interfere with compliance include elasticity, surface tension, and factors like damaged respiratory muscles, bones, nerves, or fluid in the lungs.

How does elasticity affect lung compliance?

Elasticity refers to the lung’s ability to retain shape and recoil. If there is a loss of elastic fibers (e.g., from scar tissue), the lungs become stiffer, reducing compliance.

How does scar tissue affect lung compliance?

Scar tissue, caused by conditions like tuberculosis or fibrotic lung disease, destroys elastic fibers and makes it more difficult to expand the lungs, lowering compliance.

How does surface tension affect lung compliance?

Surface tension, the attraction between water molecules in the lungs, must be overcome during inhalation. It contributes to elastic recoil during exhalation, impacting lung expansion and compliance.

What is surfactant, and how does it affect compliance?

Surfactant is a substance secreted by type II alveolar cells that reduces surface tension, making it easier to expand the lungs and improving compliance. It is critical for proper lung function.

What happens if there is insufficient surfactant?

Insufficient surfactant, such as in respiratory distress syndrome (RDS), makes it harder to expand the lungs. RDS is often seen in premature infants due to underdeveloped lungs.

How does surface tension affect ventilation?

- ↑ Surface tension → ↓ Ventilation (more difficult to breathe)

- ↓ Surface tension → ↑ Ventilation (easier to breathe)

How can damage to the respiratory muscles, bones, or nerves affect compliance?

Damage to these structures can reduce lung and chest wall expansion, lowering compliance and making it harder to breathe.

How does fluid in the lungs affect compliance?

Fluid in the lungs, such as in pulmonary edema caused by left-sided heart failure (CHF), reduces compliance and makes it more difficult to expand the lungs.