Respiratory Cycle Mechanics Flashcards
What is intrapleural pressure?
- intrathoracic pressure
- pressure everywhere in the thorax except lumen of blood vessels, lymphatics, or airways
What is a normal intrapleural pressure at rest?
-5 cm water
What is alveolar pressure?
- pressure within alveoli (759-761 mm Hg)
- decrease to -1 cm water during inhalation and increases to +1 cm water during exhalation
What is tidal volume?
volume of air per normal breath
normal is 500 mL
What is alveolar ventilation?
- process by which gas moves b/w alveoli and external environment
- tidal volume minus dead space
What is minute ventilation?
- volume of air inhaled every minute
- normal is 7L/min
-tidal volume multiplied by RR
What is transpulmonary pressure?
-the pressure difference b/w the air spaces (alveolar pressure) and the pressure surrounding the lung (pleural pressure)
Delineate how ventilation occurs, using volume and pressure.
- ctx of inspiratory muscles causes thoracic volume to increase, thus pressure decreases and air enters lungs
- relaxation causes thoracic volume to decrease, thus pressure increases and air exits lungs
How does intrapleural pressure change during the course of one breath?
- intrapleural pressure begins at -5 cm water during rest
- decreases to -8 cm water during inhalation
How does the alveolar pressure change during the course of one breath?
- begins at 0 cm water at rest
- decreases to -1 cm water during inhalation
- decreases to +1 cm water during exhalation
What is minute alveolar ventilation?
- volume of air that enters the alveoli per minute
- (tidal volume minus dead space) multiplied by RR
- dead space is body weight in lbs … in mL
What is anatomical dead space?
- space in respiratory system other than alveoli
- 1 mL per 1 lb of body weight
What is alveolar dead space?
- alveoli that receive air, but not blood
- should be almost nothing in a health person b/c most alveoli have a capillary by them
What is physiological dead space?
-air that functionally doesn’t participate in gas exchange
True or False: lungs inflate and deflate following the same pattern
False
True or False: lung compliance is low at low lung volumes
True, at low lung volumes, lungs must worker harder to get only a little increase in volume
-harder to stretch the lungs
True or False: compliance of the lungs is higher during the mid-point of inhalation
True, once there’s a little more air in the lungs, a little pressure will produce a large volume change
-easier to stretch the lungs
True or False: lung compliance is low at high lung volumes
True, as lung expands towards TLC, it becomes difficult to stretch again
-small change in pressure only produces a small change in volume
What is lung compliance?
the ability of the lung to stretch
- opposite of elasticity
- change in volume divided by the change in pressure
What is lung elasticity?
- lung’s ability to recoil
- opposite of compliance
If the lungs were not coupled to the chest wall, what would be the lungs normally tendency?
-lungs on their own want to collapse
If the chest wall wasn’t coupled to the lungs, what would be its normal tendency?
-chest wall on its own wants to expand
At what point during the respiratory cycle do the recoil of the lungs exactly balance out the tendency of the chest wall to expand?
FRC, the volume at the end of a normal exhalation
What does the FEV1/FVC ratio look like in obstructive lung diseases vs. restrictive lung diseases?
- FEV1/FVC ratio is decreased in obstructive diseases
- FEV1/FVC ratio is normal (or maybe increased) in restrictive diseases
Why might the FEV1/FVC ratio in restrictive diseases increase?
- exhalation may be favored
- FVC may be decreased
Describe what interdependence does for small airways and alveoli.
- structural stability depends on all connecting airways and alveoli
- elastic recoil in one alveolus is countered by the recoil of alveoli with shared walls
Describe what work is done during breathing.
- work is done to overcome the elastic recoil of lungs
- work is done to overcome resistance to air flow
-work done to overcome elastic recoil is greater than the work to overcome resistive forces
