Resp 2 - Ventilation Flashcards
What is Functional Residual Capacity (FRC)?
When the elastic inward recoil of the lungs and the outward recoil of the rib cage are in equilibrium.
Occurs at the end of tidal expiration.
What is the pleural cavity?
Space between parietal and visceral pleura. It is a fixed volume.
Contains protein rich pleural fluid.
It is at negative pressure
How does the pleura play a role in ventilation?
It is the negative pressure of the pleura that allows the chest wall to pull the lungs with it.
If chest wall/lung punctured, fixed volume of pleura is compromised - elastic recoil takes over and lung will collapse
What happens if the pleural cavity is breached?
Intrapleural bleeding may occur - haemothorax.
If there is a perforated chest wall - air enters pleural cavity = pneumothorax
Define tidal breathing.
Amount of inspiration/expiration that meets metabolic demand
What is residual volume?
Volume of air in the lungs that cannot (and should not) be expelled.
Explain:
- Total Lung Capacity (TLC)
- Vital Capacity (VC)
- Functional Residual Capacity (FRC)
- Inspiratory Capacity (IC)
- TLC = everything (including residual volume)
- VC = air within our maximal inspiration/expiration confines
(VC = TLC - RV) - Functional Residual Capacity (FRC) = Amount of air in the lungs at equilibrium
(FRC = ERV + RV) - Inspiratory Capacity (IC) = how much air you can take on top of FRC.
(IC = TV + IRV)
Transmural pressures?
Pressure across a tissue or several tisses
Transpulmonary pressure?
Difference between alveolar and intrapleural pressure
Transrespiratory pressure (important one)?
Tells us if Airflow into or out of lung
Negative pressure breathing vs positive pressure breathing?
Negative = normal breathing
Positive = ventilator / CPR
What is dead space?
Part of the airways and lung that doesn’t participate in gas exchange.
The conducting zone is dead space. What other dead space can there be?
Alveolar dead space = parts of the lung that can participate in gas exchange but do not.
What is physiological dead space equal to?
Physiological dead space = Anatomical Dead space + alveolar dead space.
In healthy adults, physiological dead space should roughy equal anatomical dead space (usually around 150mL)
In normal patients, FEV1/FVC ratio should be 75% ish.
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What is FET?
Forced Expiratory Time.
Time taken to expel all the air from the lungs
What is the pattern of Forced values for obstructive lung disease?
- FEV1 MUCH lower
- FET higher
- FVC lower
What is the pattern of Forced values for restrictive lung disease? (e.g. sarcoidosis)
- FVC lower
2. FEV1 relatively high
Difference between restrictive and obstructive disease?
Obstructive = mechanical obstruction to airflow
Restrictive = inability of chest to expand
What are flow-volume loop features of mild obstructive disease?
- Displaced to the left
2. Coving
What are flow volume loop features of a severe obstructive disease?
- Shorter curve
- Displaced to left
- Greater extent of coving
What are flow volume loop features of restrictive disease?
- Displaced to the right
2. Narrower loop
TLC may increase in people with obstructive disease. Why?
Air is trapped in the alveoli - because small airways linking alveoli to outside world have collapsed - causes increased residual volume.
Emphysema - degrades alveolar walls. Only a large alveolus instead of separate segments - increase in volume of the lungs.
If airway obstructed, flow rate can be limited. Explain how extrathoracic and intrathoracic obstructions differ.
Extrathoracic obstruction = inspiratory curve flatten
Intrathoracic obstruction = expiratory curve flattened
What does fixed airway obstruction do?
Both inspiratory and expiratory curves are blunted.
