TLDR;
This video by Ninja Nerd explains the concept of compliance in the lungs and chest wall, differentiating it from elasticity. It details the factors affecting compliance, including elasticity of the lungs and chest wall, surface tension, and neuromuscular function. The video also uses clinical correlations to explain how changes in volume and pressure affect compliance in real-life scenarios, such as pulmonary fibrosis, emphysema, and pneumothorax.
- Compliance is the measure of stretchability or distensibility.
- Elasticity is the resistance to stretch.
- Factors affecting compliance include elasticity of the lungs, surface tension, and elasticity of the chest wall.
Introduction to Compliance and Elasticity [0:07]
Compliance is defined as the change in volume of the lungs or chest wall in relation to the change in pressure. It measures how easily something stretches, while elasticity is the resistance to that stretch, representing the tendency to recoil. Compliance is directly proportional to the change in volume and inversely proportional to the change in pressure. Conversely, elasticity is directly proportional to the change in pressure and inversely proportional to the change in volume.
Factors Affecting Normal Compliance [4:11]
Three main factors affect compliance: the elasticity of the lungs, surface tension, and the elasticity of the chest wall. The lungs are naturally compliant but also possess elasticity, allowing them to expand easily and recoil. The chest wall also exhibits compliance and elasticity, maintaining a dynamic interplay to ensure equilibrium.
Elasticity of the Lungs and Pulmonary Fibrosis [5:53]
In conditions like pulmonary fibrosis, the development of fibrous tissue reduces the lungs' ability to stretch, decreasing compliance and increasing elasticity. This makes it difficult for the lungs to inflate. Conversely, in emphysema, the breakdown of elastic tissue increases compliance but reduces elasticity, making it hard for the lungs to recoil and expel air.
Elasticity of the Chest Wall and Related Conditions [11:45]
The chest wall is generally compliant, with an outward recoil that helps maintain negative intrapleural pressure. Conditions like ankylosing spondylitis, kyphosis, scoliosis, and ossification of rib cartilage can decrease chest wall compliance, making it difficult to inhale. If the chest wall becomes too flexible, compliance increases, allowing more air to be inhaled.
Surface Tension and Surfactant [17:09]
Surface tension, caused by the air-water interface in the alveoli, tends to shrink the alveoli. Surfactant, a protein-lipid complex produced by type II alveolar cells, reduces surface tension, allowing the alveoli to expand more easily. In conditions like infant respiratory distress syndrome, a lack of surfactant increases surface tension, decreasing compliance and increasing the work of breathing.
Neuromuscular Problems and Mucus Buildup [21:59]
Neuromuscular problems, such as diaphragm injuries or paralysis of external intercostal muscles, can decrease compliance by impairing the ability to expand the lungs. Conditions like ALS, which damages motor neurons, can also reduce compliance. Mucus buildup in the bronchioles can obstruct airflow, leading to underventilation of the alveoli and decreased compliance.
Pneumothorax, Hemothorax, and Atelectasis [25:58]
If the chest wall is punctured, introducing air into the pleural cavity (pneumothorax), the intrapleural pressure increases, potentially collapsing the lung (atelectasis). Similarly, the accumulation of blood (hemothorax) or other fluids in the pleural cavity can compress the lung, reducing compliance.
