Mechanics of breathing Flashcards
What happens in quiet respiration?
Inspiration is active, expiration is passive
What happens in increased tidal volume?
Breathe out below functional residual capacity
What is functional residual capacity?
Volume left in lungs when breathe out
What are the components of the chest wall?
Ribcage, diaphragm & abdomen
What do the external and internal intercostal muscles do?
External - help move ribs up in inspiration
Internal - help move ribs down in expiration
What is the principle muscle of respiration and how is it innervated?
Diaphragm - phrenic (C3,4,5)
What are the muscles involved in inspiration and expiration?
Inspiration - scalenes, external intercostals, diaphragm
Expiration (active) - abdominal muscles, internal intercostals, pectoral girdles
What lines the lungs?
The visceral pleura, which is covered by the parietal pleura
What is in between the parietal & visceral pleura?
The pleural cavity - filled with pleural fluid
Why is the pleural seal important?
The pleural fluid acts as a lubricant so movements of the chest wall + diaphragm permit expansion of the lungs.
The pleural seal brings the chest into an equilibrium
What happens if the integrity of the seal is broken?
Lung collapse –> pneumothorax
What is compliance?
Willingness of the lungs to expand
What is elastance?
Willingness of lungs to return to resting position
When are the lungs least compliant (most stiff)?
At extremes of volume - start of inspiration & expiration
Does emphysema increase or decrease compliance?
Increase
Does fibrosis increase or decrease compliance?
Decrease
What do type II pneumocytes secrete?
Surfactant
What are the functions of surfactant?
- Reduce surface tension
- Stabilise lung structure
- Reduce tendency for fluid transudation
- Lipid component has antioxidant activity
- Proteins A + D have immune responses
What is respiratory distress syndrome?
Premature infants born before 28 weeks when surfactant secretion begins - lack surfactant.
Can also occur in adults due to damage of lungs.
What are the 3 resistances that help to fill the lungs?
- Elastic recoil of the lungs
- Resistance of airways to flow of air
- Frictional forces arising from movement of lung relative to chest wall → tissue resistance
Where is the greatest resistance in the pulmonary airways?
Medium sized bronchi
What 3 factors affect resistance in the lungs?
- ANS
- Lung volume - increased volume increases airway diameter
- Turbulent vs laminar flow
How can lung function be tested in clinical practice?
PEFR
Spirometry
