Mechanics of Breathing Flashcards
How does inspiration occur, and what muscles are involved?
Inspiration is an active process
The diaphragm is the most important muscle, followed by the external intercostals
Accessory muscles: scalenes, sternocleidomastoids (during exercise)
How does expiration occur, and what muscles are involved?
Passive during rest (lung and chest wall spring back)
Active during exercise or in respiratory distress
Abdominal muscles and internal intercostals
36 year old female with a history of lupus presents with chest pain, dyspnea, and orthopnea. Inspiratory pressures are low. Expiratory pressures are normal.
What muscles are weak?
Diaphragm or external intercostals
What pressure expands the lungs?
An intrapleural pressure that is negative compared to the pleural pressure will cause the lungs to expand.
What is low lung compliance? What condition is characterized by it?
Low compliance indicates a stiff lung and means extra work is required to bring in a normal volume of air.
This occurs as the lungs become fibrotic with Interstitial Fibrosis, lose their distensibility and become stiffer.
What is high lung compliance? What condition is characterized by it?
With high lung compliance, there is no difficulty in stretching the lungs, but the lungs lack elastic recoil, making it difficult to expire air from them.
This occurs with emphysema. Patients cannot exhale.
What is surfactant? What role does it play in elastic recoil of the lungs?
Pulmonary surfactant is a mixture of lipids and proteins which is secreted by the epithelial type II cells into the alveolar space. Its main function is to reduce the surface tension at the air/liquid interface in the lung.
By reducing surface tension, it increases compliance and decreases the work of breathing. It also promotes stability of the alveoli, and keeps the alveoli dry.
How are the alveoli at the top of the lung different than the alveoli at the bottom of the lung?
The lung has a weight, so the alveoli at the top of it are stretched open, while the alveoli at the base are smaller and more crowded.
What three factors is airway resistance dependent on?
- Gas viscosity
- Length of tube
- Radius of tube
What is the Equal Pressure Point?
EPP is reached at the point during expiration when the airway pressure equals the intrapleural pressure, at which point airways that are not supported by cartilage will collapse.
Why is flow decreased in COPD?
- Increased resistance (mucus/remodelling)
- Lung destruction causing loss of small airways
- Lower recoil pressure due to loss of elastic tissue
- Decreased radial traction on airways by lungs
What is Dynamic Hyperinflation?
Dynamic hyperinflation is a phenomenon that occurs when a new breath begins before the lung has reached the static equilibrium volume.
It refers to the increase in end-expiratory lung volume (EELV) that may occur in patients with airflow limitation when minute ventilation increases, causing stacking of air in the lungs.
What is the functional residual capacity?
FRC is the equilibrium volume at which the elastic recoil of the lung is balanced by the tendency for the chest wall to spring out.
