Lung resistances

Respiratory System

• Respiratory Distress Syndrome (RDS) is caused by the harmful effects of excess oxygen on surfactant function.

Compliance and Elastance

• Compliance refers to the degree to which the lungs and chest wall can expand.
• Compliance can be calculated as ΔV / ΔP.
• Elastance refers to the tendency of the lungs and chest wall to return to their original shape.
• Elastance affects the lungs' ability to expand and contract.
• Increased elastance means the lungs are stiffer and harder to expand.
• Elastance can be calculated as ΔP / ΔV.

Chest Wall Mechanics

• The static resistance of the chest wall refers to its tendency to expand outward.
• The force of movement of the chest wall is opposite to that of the lungs.
• The chest wall has a tendency to expand but is held by the surrounding tissues and bones.
• The unopposed expansion of the chest wall reaches 40% of the total lung capacity.
• When the thorax is intact and in equilibrium with the lungs, its resting level corresponds to the functional residual capacity (FRC).

Factors Affecting Chest Wall Movement

• Decreased flexibility/expansion of the chest wall can be caused by conditions such as ankylosing spondylitis.
• Paralysis, strain, or pain of the chest wall can be caused by conditions such as neuropathy or thoracic injury.
• Loss of elasticity in the chest wall can be caused by aging or disease.

Respiratory Passages and Airways

• Mucus or fluid can block the smaller respiratory passages.
• Raised abdominal pressure can cause decreased lung expansion.

Lung Collapse

• The primary factors contributing to the collapse of the lungs are surface tension and elastin and collagen in lung tissues.
• Elastin and collagen in lung tissues contribute approximately 1/3 of the resistance to lung collapse.
• Surface tension contributes approximately 2/3 of the resistance to lung collapse.
• Surface tension has a destabilizing effect on small alveoli, making them more prone to collapse.
• A decrease in radius makes it harder to open the alveoli, as the pressure required to open them increases.

Surfactant

• Surfactant is a lipid-protein complex that reduces surface tension in alveoli, preventing collapse.
• Surfactant benefits the lungs by allowing for easier expansion and reducing the work of breathing.
• One benefit of surfactant is that it helps maintain alveolar stability.
• Surfactant prevents alveoli from collapsing by reducing surface tension.
• Additional structures that aid surfactant in maintaining alveolar stability include the fibrous network of the lungs.

Disorders

• Respiratory Distress Syndrome (RDS) is characterized by a decrease in surfactant production and can occur in premature infants.
• Adult Respiratory Distress Syndrome (ARDS) is associated with a deficiency or dysfunction of surfactant in adults.

Elastance

• Elastance is important in the respiratory system because it affects the lungs' ability to expand and contract.