Flashcards in Ventilation Deck (22):
What are the two components of the chest-wall?
Independent rib cage and muscles
What is Functional Residual Capacity?
FRC = ERV + RV
It is the volume of air remaining in the lungs at the end of a tidal breath. At FRC, the recoil inwards of the lungs and the recoil outwards of the chest wall are in equilibrium.
Describe how the pleural cavity allows the chest wall and the lungs to move in unison.
The pleural cavity has a fixed volume and is at negative pressure. This means that when the chest wall expands, the lung gets pulled with it.
How may the fixed volume of the pleural cavity be compromised?
The pleural lining could get punctured in the case of a haemothorax or pneumothorax.
Which volumes make up each of the following capacities:
Total Lung Capacity
Functional Residual Capacity
Total Lung Capacity - all the volumes together
Vital Capacity - expiratory reserve volume, inspiratory reserve volume + tidal volume
Functional Residual Capacity - ERV + RV
Inspiratory Capacity - TV + IRV
Define Tidal Volume.
The amount of inspiration and expiration that meets metabolic demands.
Why can't we totally expel all air from our lungs?
The surfactant in the alveoli prevent the alveoli from collapsing and so you can't expel all the air from the lungs.
What unit is commonly used when describing lung pressures?
Unit: cm H2O
What are the three main lung pressures involved in respiratory mechanics? Define them.
Transthoracic = pressure difference between pleural cavity and the atmosphere
Transpulmonary Pressure = difference between alveolar and intrapleural pressure
Transrespiratory Pressure = tells us the direction of airflow in the airways
These are collectively known transmural pressures
Give two examples of positive pressure breathing.
CPR and Ventilators
What is the difference in alveolar pressure between the end of a tidal expiration and the end of tidal inspiration? Explain your answer.
NO DIFFERENCE - during inspiration, the thoracic cavity expands and so the alveoli expand and the pressure decreases. Air is drawn in to the alveoli and the pressure becomes the same as it was at the end of expiration.
Define Dead Space.
Parts of the airways and lungs that do not participate in gas exchange.
What are the two different types of dead space?
Anatomical Dead Space and Alveolar Dead Space
What is the normal physiological dead space of a healthy individual?
150 mL - physiological dead space is usually equivalent to anatomical dead space because normal healthy people don't have alveolar dead space
State two reversible procedures that can change dead space.
Tracheostomy and ventilators
Explain the chest wall relationship diagram (volume against pressure).
Expanding the chest wall to 6 L takes relatively little pressure because its natural tendency is to expand. Expanding the lungs to 6 L takes a lot more effort and pressure because its natural tendency is to recoil inwards.
Define FVC, FEV1 and FET.
Forced Vital Capacity - volume of air that can be expelled from the lungs after a full inspiration
Forced Expiratory Volume 1 - maximum volume of air that can be expired within 1 second
Forced Expiratory Time - time taken to fully empty the lungs (except residual volume)
How would these values change for a) someone with obstructive lung disease, b) someone with restrictive lung disease?
Obstructive lung disease: FVC = decrease, FEV1 = decrease, FET = higher
Restrictive lung disease: FVC = decrease, FEV1 = high
State normal FEV1/FVC values for a normal person, someone with obstructive lung disease and someone with restrictive lung disease.
Normal = 73,
Obstructive = 53,
Restrictive = 87
Describe the general arrangement of a flow-volume loop.
Flow rate against volume - distance from the x axis indicates flow rate. Positive y direction indicates that the air is moving out (expiration) and a negative y direction suggests that the air is moving in (inspiration).
Describe how the flow-volume loop changes for a) mild obstructive disease, b) severe obstructive disease and c) restrictive disease.
Mild Obstructive - the loop would move to the left because there is an increase in residual volume. The top right line will be indented.
Severe Obstructive - same as mild obstructive but the top right line will be even more indented.
Restrictive - the loop will be narrower and it may move to the right.