Mechanics Flashcards
Intrapleural pressure
Pressure in the pleural space
Always neg in normal breathing but can become pos during forced, prolonged expiration
Intrapulmonary pressure
Pressure in the alveoli ranges from neg to pos during the different phases of respiration
(Neg in inspiration and pos in expiration)
Transpulmonary pressure
Intrapulmonary pressure - intrapleural pressure
Creates the suction to keep the lungs inflated:
Alveolar distention get pressure
Air flow from:
High to low pressure
If Palv = Patm no flow
Palv > Patm air flows out
Palv
Primary muscles of inspiration
Diaphragm
External intercostal muscles
Accessory muscles of inspiration
Sternocleidomastoid
Scalene
Inspiration causes an increase in pleural cavity volume which in turn causes
Intrapleural pressure to become more negative
Therefore, transpulmonary pressure increases - dis tending pressure causes alveoli to open
When alveoli expand, what occurs next?
Intrapulmonary pressure drops below atmospheric pressure and air flows into alveoli until Palv and Patm equilibrates
During expiration, pleural cavity volume decreased causing
Intrapleural pressure to increase
Transpulmonary pressure decreases and and the alveoli collapse
When the alveoli collapse during expiration, what happens next?
Intrapulmonary pressure increases above Patm and air flows out until Palv and Patm equilibrate.
What muscles are used during forced expiration
Internal intercostal, and abdominal wall muscles
What can cause a pneumothorax?
Trauma that penetrates/disrupts pleura
Bullouse emphysema- build up in pressure in bulla, burst -> air flows out into pleura
Procedures in which catheterize patients, may accidentally hit the lung.
Treatment for pneumothorax vs partial pneumothorax
Chest tub- hooked up to neg pressure
Partial- leave them be
Which factors affect ventilation
Compliance
Airway resistance
Compliance of lung and chest wall are ___ correlated with their elastic properties.
Inversely
When is compliance greatest
At lower lung volumes
Steeper slope in pressure volume loop
Pressure volume loop
C (L) = change in volume / change in pressure
Factors affecting compliance
Elasticity
Decrease in surface tension by surfactant
Mobility of the chest wall
In emphysema, do you have increased or decreased compliance.
Increased
Destruction of alveolar septa and elastic tissue
Alveoli are floppy and collapse but are easily distendable
Hysteresis
Caused by surface tension
Difference between inspiration and expiration curve on the volume pressure loop
LaPlace law
Pressure in the alveoli is directly proportional to surface tension and inversely proportional to radius.
The effect of surfactant is greater when
The alveolar are smaller because the ratio of surfactant to air is greater
What are the two factors that stabilize the alveoli
Reduced surface tension
Alveolar interdependance
respiratory distress syndrome of the newborn. Treatment?
More common in infants
FRC
Volume left in lungs when lung and chest walls are balanced (equal and opposite)
At what volume do the lungs feel most comfortable?
The lung wants to collapse- 0
At what volume does the chest wall feel most comfortable?
Halfway between FRC and TLC
~70% of TLC
Below this value, it wants to expand
When will the chest wall want to compress down
When the lungs are fully hyperexpanded
Changes in chest wall compliance
Less common than changes in lung compliance
Causes:
Increase intra-abdominal pressure:
Pregnancy and ascites
Reduced movement of rib cage:
Kyphosis
Broken ribs
Air flow =
Difference in pressure (alveoli and mouth) / airway resistance
Laminar flow is seen in ___ airways and is more dependent on ___.
Smaller
Viscosity
Extremely dependent on radius
R = (8 X viscosity X length) / radius ^4
Turbulent is seen in ____ airways and is more dependent on ___.
Larger
Density
Occurs when Reynolds number is high
Reynold number= (density X velocity X diameter) / viscosity
What is transitional flow and where do you see it?
Combination of laminar and turbulent flow
Branch points
Vast majority of flow in the lung is
Transitional
Resistance is greatest at ____ lung volumes
Lower
In emphysema, what happens to resistance
Resistance begins at higher lung volumes
Work
Pressure needed to overcome resistance of airflow and elastic recoil of the lungs X volume of air moved in and out of the lungs (Vt)
