Respiratory pressure and surfactant Flashcards
What are the types of lung pressure?
Intra-alveolar pressure, intrapleural pressure and transpleural pressure
What is intra-alveolar pressure?
Pressure inside the alveoli
What is the value of atmospheric pressure?
0 mmHg
What is the value of intra-alveolar pressure during inspiration and expiration?
Inspiration = -1 mmHg
Expiration = +1 mmHg
What is intrapleural pressure?
Pressure in the pleural space
What is the range of values of intrapleural pressure?
-6 (during inspiration) to -2.5 (during expiration) mmHg
-12 mmHg during deep inspiration
Average = -4mmHg
Under normal physiological conditions, intrapleural pressure is ALWAYS negative
Why is intrapleural pressure always negative in normal physiological conditions?
The value is negative because of the continuous tendency of the lung to recoil against the continuous tendency of the chest to expand
What is the Valsalva maneuver?
Forced expiration against closed glottis
During the maneuver:
* IPP = +50 mmHg
* Intra-alveolar pressure = +100mmHg
When is intrapleural pressure positive?
Valsalva maneuver
Pneumothorax (Tension, traumatic, primary spontaneous, secondary spontaneous, etc.)
What is transpulmonary pressure?
Difference in pressure across the lung wall
= intra-alveolar pressure - intrapleural pressure
What is the average value of transpulmonary pressure?
+4mmHg
Always a positive value
What does transpulmonary pressure measure?
TPP is the force that opposes the inward elastic recoil pressure of the lung at rest
What is the importance of intrapleural pressure?
DIC WOB
* Helps venous and lymphatic drainage
* Helps lung inflation during inspiration
* Prevents lung collapse
* Decreases the work of breathing
What are the types of cells of the alveolar wall?
Type I pneumocytes: 95% of the alveolar cell. Important in gas exchange.
Type II pneumocytes: 5% of the alveolar cell. It secretes surfactant.
What are the layers of the alveoli?
Outer to inner layers:
* Pneumocytes
* Fluid
* Surfactant
* Air
What are the components of surfactant?
Mixture of phospholipids (Dipalmatoyl-Phospatidyle-Choline) and Ca++
What is the surface tension in the alveoli?
Surface tension is a force exerted by fluid in alveoli to resist distension
Lungs secrete and absorb fluid, leaving a very thin film of fluid
This film of fluid causes surface tension
What is the function of surfactant?
STWOB PEC
Decrease surface tension of the fluid lining the alveoli
Decrease work of breathing
Prevents pulmonary edema by decreasing the filtration forces
Prevents collapse of alveoli during expiration
How does surfactant decrease surface tension?
It maintains lung expansion by:
* Monomolecular layer of surfactant at the interface between the fluid lining the alveoli and the air decreases surface tension
* Reduces attractive forces of hydrogen bonding by becoming interspersed between H2O molecules
What are the causes of surfactant deficiency?
Hyaline disease/Respiratory distress syndrome where newborns fail to secrete adequate amount of surfactant
