Flashcards in Lung Mechanics Deck (78)
How does air flow during inspiration?
Alveolar pressure is less than atmospheric so air can flow in
How does air flow during expiration?
Alveolar pressure is greater than atmospheric so air can flow out
What are the muscles of inspiration?
What are the muscles of expiration?
How do the muscles act on inspiration?
The diaphragm flattens and moves downward, expanding the thorax vertically.
The external intercostals move the ribs up and out enlarging the thorax lateral as well as anterior and posteriorly.
How do the muscles act on expiration?
Expiration is a mostly passive process in quiet breathing.
What is the action of the external intercostals similar to?
Lifting the handle of a bucket
How do the muscles act on forced expiration?
The internal intercostals contract and pull down on the ribs and make the thoracic cavity smaller
What are the accessory inspiratory muscles?
How do the muscles act on forced inspiration?
The accessory inspiratory muscles raise the sternum and elevate the first 2 ribs in order to expand the chest cavity further. Only occurs during forced inspiration.
What is the Tidal Volume (Vt) of the lung?
It is the change in volume during quiet breathing
What is the Inspiratory Reserve Volume (IRV) of the lung?
It is the additional amount of air that can be inhaled in addition to the Tidal Volume.
What is the Expiratory Reserve Volume (ERV) of the lung?
It is the additional amount of air that can be exhaled in addition to the Tidal Volume.
What is the Residual Volume (RV) of the lung?
It is the volume remaining in the lungs after forced expiration and it cannot be exhaled.
What volume of the lung cannot be measured with spirometry?
Residual Volume as it is not physically blown out from the lungs.
What is the Inspiratory Capacity?
IC = IRV +Vt
It is the volume that can be inhaled after all respiratory muscles are relaxed.
What is the Functional Residual Capacity?
FRC = ERV + RV
It is the volume of air in the lungs when all of the respiratory muscles are relaxed.
What is the Vital Capacity?
VC = IRV + Vt + ERV
It is the maximum amount of air that can be moved when going from deep inspiration to deep expiration.
What is the Total Lung Capacity?
TLC = IRV + VT + ERV + RV
It is the total volume of air held by the lungs.
How can the FRC be measured?
It can be done by helium dilution.
How does the compliance of the lung change with its volume of air?
At volumes near the FRC, the compliance of the lung is maximized, but the compliance decreases as the volume of the lung increases.
What is the difference between specific lung compliance and lung compliance?
The specific lung compliance adjusts for different lung volumes so that they can be compared to each other, such as in the case of a child vs an adult. Specific compliance will not change with volume.
The lung compliance found is divided by its volume.
What is the normal compliance of the adult lung?
0.2 L/cm H2O
What forces must the inflation of the lung overcome?
-Viscoelastic properties of lung stretching
-Surface tension of the lungs
What happens to the compliance in emphysema?
It will increase the compliance as the disease will eat away at the elastin and collagen so that alveoli will stretch more but also have less surface area.
The FRC will increase and the intrapleural pressure will increase as well due to less recoil of the lungs.
What happens to the compliance in fibrosis?
The compliance decreases due to the scarring resulting in fibrotic tissue that is stiffer and also thickens the gas diffusion pathway.
The FRC decreases due to increased lung recoil and the intrapleural pressure becomes more negative.
What is hysteresis?
Dissipating energy between inflation and deflation
When does the compliance of the lung drastically decrease?
When the lung is inflated close to the TLC or deflated below the FRC.
Describe the movement of the lung and chest wall from deflation to inflation.
With shallow inflations from FRC to the equilibrium position of the chest wall, the lung is stretched and the chest wall relaxed.
With deep inflations from FRC to above the equilibrium position of the chest wall, both the chest wall and lung are stretched out.
With deflations of any volume below FRC, the chest wall is always stretched inward.