Mechanics of breathing, pressure and work Flashcards
How does inspiration/expiration work?
- Lungs and chest wall elastic structures
- Lungs are stretched when we inhale (‘stretchiness’ is termed lung compliance)
- They recoil on exhalation (Term: elastic recoil)
- This is balanced by the chest wall tendency to recoil in opposite direction
- At end of quiet expiration pressures balance
What are the inspiratory muscles?
- Diaphragm (75% change in volume)
- External intercostals
- bucket-handle
- Accessory muscles
- scalene
- sternomastoids
How does inspiration work?
- Contraction of inspiratory muscles increases intrathoracic volume
- This causes a decrease in intrapleural pressure (usually -2.5 -6 mmhg)
- Lungs are pulled into more expanded position and the pressure in the airways becomes negative. Air moves in (Patm>Palv)
- At end of inspiration pressures are equal
- Recoil of lungs and chest wall then occur
Which part of the graph is inhalation and which part is exhalation?
What is transpulmonary pressure?
- The chest wall exerts a distending pressure on the pleural space, which is transmitted to the alveoli to increase its volume, lower its pressure, and generate airflow inwards
- This distending pressure is called the trans pulmonary pressure (Ptp).
What anatomical component is responsible for chest expansion?
Muscles
Under physiological conditions:
The Ptp is always _______
The Ppl is always ________
Positive
Negative
What is Ppl?
Note: Ppl is variably called pleural or intrapleural pressure
What is Ptp?
Transpulmonary pressure
What is the relationship between transpulmonary pressure and elastic recoil pressure?
For a given lung volume, the transpulmonary pressure is equal and opposite to the elastic recoil pressure of the lung.
Label which line is Total, Lung and Chest Wall Compliance
What graph is this?
Lung Compliance (pressure volume curve)
Label each line
What does the compliance of the lung depend on?
The compliance of the lung depends how inflated or not it is
What is hysteresis?
The compliance curves are different for inspiration and exhalation. This difference is called hysteresis (frictional resistance changes)
Is the lung more or less compliant at higher volumes?
lung is less compliant at higher volumes
What does each picture show?
What is compliance like in normal lung?
Compliance is just right. Good compliance for low work of inhalation, and good retention of elasticity of alveolar units to allow effective exhalation.
What is compliance like in interstitial fibrosis?
Compliance is decreased due to more stiff alveolar walls from scarring (called fibrosis).
What is compliance like in emphysema?
Compliance is increased due to loss of alveolar interdependence.
What does a P/V curve in emphysema show?
In emphysema the P-V curve demonstrates lungs with increased compliance
‘Loss of elastic recoil à easy to inflate, but difficult to exhale’
What does a P/V curve in pulmonary fibrosis show?
In pulmonary fibrosis the P-V curve demonstrates stiff lungs
‘Increase in elastic recoil -> difficult to inflate the lungs’