The work of breathing Flashcards
What is atm in reality and regarded as
Reality is 110kPA
We regard it as 0 when looking at movement of air in
+ out of lungs
Boyles law uses what kind of system
Closed system assuming that temp and amount of Gas molecules are kept constant
Inhalation
- Lung volume is increasing
- Pressure inside the lungs is
decreasing - Pressure outside the lung is now
greater than inside, so air
rushes in
Exhalation
- Lung volume is decreasing
- Pressure inside the lungs is
increasing - Pressure outside the lung is now
lower than inside, so air rushes
out
Two forces that need to be overcome to breathe
- Stiffness of the lungs
- Resistance of the airways to the lungs
Stiffness of the lungs
- Lungs must expand to take in air
- How compliant are the lungs?
- Surface tension holds lungs in place
Resistance of the airways to the lungs
- Need to move the air from outside to the
alveoli - How much resistance is the respiratory tract
putting on the movement of air?
What is a low compliance lung
Lots of elastic tissue = less stretch
What is lung compliance?
The amount of E/P needed to inflate lungs by a certain volume
Key characteristic of pulmonary fibrosis
The deposition of fibrotic tissue on the walls of the alveoli
- Needs more P to take the same amount of air as a normal person hence easier to take quick shallow breaths
What is surface tension?
tendency of a fluid surface to occupy the
smallest possible surface area
How is there surface tension in the lungs?
Fluid lines the walls of the alveoli and due to cohesion forces between the fluid molecules, it cause the alveoli to collapse
How can ST be overcome
Surfactant i.e phospholipids
What is phospholipids made by
Alveolar T2 pneumocytes
What does the surfactant in the lungs do?
-Forms a thin film on the surface of the alveolar cells
- Reduces cohesive forces between
fluid molecules lining alveoli and hence prevents the lungs from collapsing
- Easier to increase lung size i.e.
increased compliance
Why do premature infants have an increased risk of RDS
They do not produce surfactant
Where are the T2 pneumocytes found?
These large cells are found in between the smaller T1 epithelial alveolar cells
What causes mechanical resistance for the air as it moves through the airways
Friction exerted by the rapid branching of the alveoli from the 1st bronchii
Resistance to air flow in the lung system is through…
The bronchial radius
Where does most of the air resistance occur?
1st 6 generations of branching and mostly in the broncii
What is tidal volume?
Volume of air moved in and out during normal quiet breath
Inspiratory reserve volume (IRV)
Extra volume that can be inhaled over and above the tidal
volume
Expiratory reserve volume (ERV)
Extra volume that can be exhaled voluntarily after completion
of a normal, quiet respiratory cycle
Residual volume
Volume remaining in lungs after maximal exhalation
Minimal volume
Volume remaining in lungs if they collapsed
Vital capacity
Inspiratory reserve + Expiratory reserve + Tidal volume
Volume of air that can be moved in and out of your lungs
Total lung capacity
Vital capacity + Residual volume
Total volume in lungs when it is filled to max
Inspiratory capacity
Inspiratory reserve + Tidal volume
Total volume of air that can be inspired from rest
Functional residual capacity
Expiratory reserve + Residual volume
Volume remaining in lungs after normal exhalation
Forced expiratory volume in one second FEV1
How much of the forced vital capacity (FVC) comes out in first
second
FEV1/FVC ratio
Normal ~ 80%
< 0.70 indicates airways obstruction = increased airway resistance
Difference between obstructive and restrictive
Restrictive: the lung capacity is reduced but the lung is patent so wont necessarily have reduced FEV
Obstructive has dramatically reduced FEV due to obstruction in the airways
