Session 2: Lung Mechanics and Ventilation of the Lungs Flashcards
What is ventilation?
The mechanical process of inspiration and expiration The physical action of breathing and moving air into and out of the lung.
What is tidal volume?
Volume of air being moved during quiet** inspiration and expiration. Breathing is a rhythmic and **involuntary process.
Briefly explain how breathing is rhythmic and involuntary.
Neurones in respiratory centre of brain automatically generate impulses to inspiratory muscles.
What is Boyle’s law?
The inverse relationship between pressure and volume.
Briefly explain the process of inspiration.
Inspiration: An active process where air is drawn into the airways by active expansion of the thoracic cavity which expands the lungs. This leads to an increase in the volume of the lungs. The increase in volume means that the intrapulmonary pressure will decrease and decrease below atmospheric pressure. This leads to air going into the lungs.
Briefly explain the process of expiration.
Air is expelled passively from the airways by relaxing muscles used in inspiration. This is also an elastic recoil. This reduces the volume of the thoracic cavity and reduces the volume of the lungs. This means that the intrapulmonary pressure increase and air moves out of the lungs.
The lungs have a natural elastic recoil and a tendency of wanting to collapse in, especially when stretched. Then what keeps the lungs against the chest wall?
The pleural seal.
Explain what the pleural seal is.
There is pleural fluid between the visceral and parietal pleura in the intrapleural space. This fluid forms a seal between the lung and thoracic wall. This lets the lungs to expand with the thoracic cavity.
The surface tension between the pleural surfaces created by the presence of thin film of pleural fluid (the pleural seal) holds outer surface of the lung to inner surface of the chest wall.
Think of the analogy: A cup sticking to a coaster due to water between them.
Define inspiratory reserve volume (IRV).
The difference in the amount of air you can possible inhale (maximum inspiration) and when you normally inhale (quiet inspiration).
Define expiratory reserve volume (ERV).
The difference between the maximum amount you can possibly expire (maximum expiration) and the amount you normally expire (quiet expiration).
What is residual volume?
The amount of volume we cannot possible empty. This means after forced expiration there will still be a small amount left that cannot be emptied out. This is the residual volume.
What is inspiratory capacity?
End of quiet expiration to maximum inspiration.
This means it is inspiratory reserve + tidal volume.
What is functional residual capacity?
The volume of air in the lungs at the end of quiet expiration.
Expiratory reserve volume + residual volume.
What is vital capacity?
Inspiratory capacity + expiratory reserve.
Can also be thought of as:
Inspiratory reserve volume + tidal volume + Expiratory reserve volume.
What is total lung volume?
Vital capacity + residual volume
Explain what the anatomical dead space is.
Not all of the tidal volume will be available for gas exchange. This means that there will be air that fills the conducting airways as well, the part of the lungs and airways which do not diffuse air.
This volume, the volume of the conducting airways is known as anatomical dead space.
Explain what alveolar dead space is.
Damaged or alveoli which do not perfuse still fill with air. However they do not take part in the gas exchange. This means that ventilation of these alveoli are wasted.
The volume in such alveoli is known as alveolar dead space.
What is physiological dead space?
Anatomical dead space + alveolar dead space.
How do you calculate total pulmonary ventilation?
Tidal volume x respiratory rate
What happens to the intrapleural pressure during inspiration?
The intrapleural pressure which is already negative relative to the atmospheric pressure will become even more negative due to the expansion of the thorax.
