Lung Mechanics 2 Flashcards
What do we need to measure to calculate lung compliance?
What instruments will we use for each of these?
Lung compliance = change in lung volume (V) / change in transpulmonary pressure (PL).
Transpulmonary pressure (PL) however = PA - PPL.
When not breathing, we can exploit the fact that PA = O
PPL has to be measured with an oesophageal balloon.
Volume is measured with a spirometer.
Explain the process of calculating lung compliance.
The patient is asked to breathe from RV to TLC in stages, holding their breath at set points so each time PA = 0.
The volume is measured at each of these points as well as the PPL and these are plotted against each other graphically to give a hysteresis display.
Lung compliance is the gradient of the steepest part of the graph. The steeper the gradient, the more compliant the lungs.
What is a typical/normal lung compliance value?
1.5L/kpa.
What condition would see a patients lung compliance increase highly due to lung fibrosis?
What causes this condition?
Emphysema
= destruction of the elastic tissue of the lung which causes flop pines and increased compliance.
What diseases is COPD a ‘blanket’ term for?
1) chronic bronchitis
2) emphysema
What happens to the airways in chronic bronchitis?
The airways become inflamed and excess muscles is produced which narrows the airways.
Key point = bronchitis is a NARROWING.
What happens to the airways in emphysema?
The elastic tissues of the lungs are destroyed and the alveoli begin to break down. It is the elastic tissues which help hold the airway open therefore destruction of these can cause airway collapse especially on exhalation.
What fluid makes up the air-fluid interface in the lungs?
Surfactant
What formula denotes the gas pressure needed to maintain equilibrium between the collapsing force of the alveolar surface tension and the gas?
Pressure (P) = 2T (surface tention) / R (radius of alveoli)
Which cells produce surfactant?
Type 2 alveolar cells.
What does surfactant aim to do?
Decrease the surface tension.
