Lung statics 2 Flashcards
What are the 3 determinants of lung volume?
- pulmonary compliance
- chest wall compliance
- respiratory muscles
Define the following:
Pao
Pbs
Palv
Ppl
Pab
Pao: Pressure at the airways opening (mouth)
Pbs: Pressure on the body surface
Palv: Alveolar pressure
Ppl: Intrapleural pressure
Pab: Abdominal pressure
Define:
trans-pulmonary pressure
trans-lung pressure
trans-chest wall pressure
trans-respiratory system pressure
- Trans-pulmonary pressure: Pao-Ppl
- Trans-lung pressure: Palv-Ppl
- Trans-chest wall pressure: Ppl - Pbs
- Trans-respiratory system pressure: Pao-Pbs
What is compliance?
A measure of stiffness. It is the slope of the pressure-volume curve.
What is the stiffness of highly compliant lungs?
What is the stiffness of non-compliant lungs?
Greater compliance = looser lung
Lower compliance = stiffer lung
What is the formula for compliance?
Compliance is the slope of the pressure-volume curve:
C = ΔV/ΔP
When there is no flow, the pressure at the airway opening should be the same as …
alveolar pressure
Compliance is obtained using the … pressure.
transpulmonary (Ptp) (Pao-Ppl)
Transpulmonary pressure (Ptp) is used as a measure of…
the elastic recoil pressure (Pel) of the lungs and airways
What instrument is used to measure compliance? How does it work?
An esophageal balloon (compliance) catheter is swallowed and measures the pressure inside the esophagus, since the esophageal pressure reflects the pleural pressure.
Which requires more pressure to exert a change in volume in the lungs?
a) inspiration
b) expiration
a) inspiration
(see graph in your slides!)
Why is the pressure-volume curve different between inspiration and exhalation? What is this difference called?
It takes significantly more pressure to exert a change in volume in the lungs during inspiration compared to expiration. This difference is called “hysteresis”.
How does emphysema/COPD affect elastic recoil of the lungs?
Emphysema/COPD are obstructive diseases that lead to a reduction in the elastic recoil of the lungs (i.e. increased compliance). Therefore, it takes less pressure to exert a change in volume of the lungs
Make sure you can draw the emphysema PV curve compared to normal.
How does pulmonary fibrosis affect elastic recoil of the lungs?
Pulmonary fibrosis leads to the thickening and stiffening of lung tissue, resulting in increased lung stiffness (i.e. decreased compliance). Therefore, it takes more pressure to exert a change in volume of the lungs.
Make sure you can draw the pulmonary fibrosis PV curve compared to normal.
What are the 3 determinants of compliance?
- Tissue forces (lung)
- Surface tension
- Compliance of the chest wall
What do tissue forces in the lung arise from?
From the elastin-collagen-proteoglycan network of the lung tissue and the elastic recoil of the lung tissue.
Lungs have a tendency to want to…
deflate
What can decrease tissue forces in the lung?
Destruction of lung parenchymal architecture by diseases like emphysema. Lung tissue loses its elastic recoil and becomes more compliant.
What can increase tissue forces in the lung?
Lung scarring (fibrosis). Lung parenchyma thickens and stiffens due to fibrosis, making it stiffer and less compliant.
Surface tension occurs at the …. of the alveoli.
air-liquid interface
Surface tension arises from…
the tendency of the liquid molecules to stick together rather than to associate with air molecules - will cause the alveoli to collapse.
What prevents the alveoli from collapsing under their surface tension?
Pulmonary surfactant, which modifies surface tension
What is surfactant composed of?
Small layer of phospholipids in the alveoli which reduces surface tension.
What happens when lungs are filled with saline?
When lungs are filled with saline rather than air, the air-liquid interface in the alveoli is absent, so surface tension does not develop. The collapsing pressure in the alveoli is therefore reduced, making it easier to inflate the lungs.
In other words, elastic recoil decreases, making the lung more compliant.