Mechanics of Breathing Flashcards
What is Lung Compliance and what are the factors which effect it?
A measure of the lung’s ability to stretch and expand (distensability of elastic tissue). Effected by - Chest wall mechanics (major effector) + Alveolar surface tension + Elastin fibres (elasticity). How much each one effects compliance varies depending on standing/laying down etc.
**Decreased compliance occurs in restrictive diseases.
How is the diaphragm responsible for lowering pressure in your lungs?
*Direction ribs move in when inhaling
Diaphragm separates thorax from abdomen, when relaxed it is floppy and long and its dome shaped. It acts like the syringe plunger to stretch air molecules and lower pressure in lungs. After this lung recoils due to its elastic properties.
*Front ribs move upwards and outwards (like bucket handle), back ribs move upwards.
Why does the pleura cavity not expand?
Pleura (Visceral and Parietal) are liquid filled and therefore do not expand. Pleura can be broken (pneumothorax) this allows air into pleura and causes collapse.
**The lung WANTS TO collapse because it has so much recoil.
Do low/high compliance lungs require MORE or LESS pressure to get the same volume?
Low compliance lung requires MORE pressure to get to same volume
High compliance lung requires LESS pressure to get to same volume
**There is a plateaus because lungs have a maximum capacity.
What contributes to lung compliance?
50% elastin fibres around alveoli + 50% liquid in alveoli.
How do COPD + Emphysema + Fibrosis effect compliance?
COPD increases compliance because elastin is degraded and fluid in alveoli is lost.
Emphysema lung is very easy to fill but hard to empty because no recoil. People with emphysema need to forcefully exhale.
Fibrosis reduces compliance. The elastin fibres are replaced with collagen which is less elastic (occurs with scarring). Elastin side of recoil is lost; however, disease eventually obliterates alveoli.
What are the 4 ways pulmonary surfactant aids stability in the lung?
- Pulmonary surfactant allows alveoli to inflate at lower pressures than required.
- Pulmonary surfactant stabilises adjacent alveoli
- Pulmonary surfactant prevents alveolar collapse - Tightly packed surfactant molecules act more like a solid therefore preventing collapse.
- Pulmonary surfactant helps prevent fluid accumulating in alveoli - because water is pulled into ECF by the higher surface tension.
How do different diseases effect each component of lung compliance?
Chest wall mechanics (50% of compliance). E.g. Scliosis, Muscular Dystrophy and Obesity. Alveolar surface tension (25% of compliance). E.g. Respiratory distress of newborn. Elastin fibres (25% of compliance). E.g. Fibrosis and COPD. **Note: Lung diseases are obstructive or restrictive
Identify all possible trends and waves on a lung volumes graph.
VT – tidal volume (varies with breathing pattern)
ERV – expiratory reserve volume (max expiration)
RV – residual volume (you can’t blow this out)
IRV – inspiratory reserve volume (max inspiration)
VC – vital capacity (difference between max expiration and inspiration).
FRC – Functional residual capacity (ERV + RV)
TLC – Total lung capacity
Define airway resistance.
How hard it is for air to move down airways. Increased resistance occurs in obstructive diseases. If blocked (e.g. by mucus) air does not get into lungs. So, lung compliance is irrelevant at this point.
*This is the problem with asthma.
What is the equation for resistance?
Resistance = (8 x viscosity x length of tube)/(pi x radius^4)
**Note: Small change in radius causes major change in resistance. Most air flow in lungs is turbulent flow due to the branching of the airways.
What are the main sites of airway resistance?
Upper airway makes (anything above the larynx) up 50% of resistance (mainly turbulent flow and lower airways make up the other 50% (mainly laminar flow). Site of airway resistance occurs mainly in segmental bronchioles.
