Respiratory pressure and surfactant

Question 1

What are the types of lung pressure?

Answer 1

Intra-alveolar pressure, intrapleural pressure and transpleural pressure

Question 2

What is intra-alveolar pressure?

Answer 2

Pressure inside the alveoli

Question 3

What is the value of atmospheric pressure?

Answer 3

0 mmHg

Question 4

What is the value of intra-alveolar pressure during inspiration and expiration?

Answer 4

Inspiration = -1 mmHg
Expiration = +1 mmHg

Question 5

What is intrapleural pressure?

Answer 5

Pressure in the pleural space

Question 6

What is the range of values of intrapleural pressure?

Answer 6

-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

Question 7

Why is intrapleural pressure always negative in normal physiological conditions?

Answer 7

The value is negative because of the continuous tendency of the lung to recoil against the continuous tendency of the chest to expand

Question 8

What is the Valsalva maneuver?

Answer 8

Forced expiration against closed glottis
During the maneuver:
* IPP = +50 mmHg
* Intra-alveolar pressure = +100mmHg

Question 9

When is intrapleural pressure positive?

Answer 9

Valsalva maneuver
Pneumothorax (Tension, traumatic, primary spontaneous, secondary spontaneous, etc.)

Question 10

What is transpulmonary pressure?

Answer 10

Difference in pressure across the lung wall
= intra-alveolar pressure - intrapleural pressure

Question 11

What is the average value of transpulmonary pressure?

Answer 11

+4mmHg

Always a positive value

Question 12

What does transpulmonary pressure measure?

Answer 12

TPP is the force that opposes the inward elastic recoil pressure of the lung at rest

Question 13

What is the importance of intrapleural pressure?

Answer 13

DIC WOB
* Helps venous and lymphatic drainage
* Helps lung inflation during inspiration
* Prevents lung collapse
* Decreases the work of breathing

Question 14

What are the types of cells of the alveolar wall?

Answer 14

Type I pneumocytes: 95% of the alveolar cell. Important in gas exchange.
Type II pneumocytes: 5% of the alveolar cell. It secretes surfactant.

Question 15

What are the layers of the alveoli?

Answer 15

Outer to inner layers:
* Pneumocytes
* Fluid
* Surfactant
* Air

Question 16

What are the components of surfactant?

Answer 16

Mixture of phospholipids (Dipalmatoyl-Phospatidyle-Choline) and Ca++

Question 17

What is the surface tension in the alveoli?

Answer 17

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

Question 18

What is the function of surfactant?

Answer 18

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

Question 19

How does surfactant decrease surface tension?

Answer 19

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

Question 20

What are the causes of surfactant deficiency?

Answer 20

Hyaline disease/Respiratory distress syndrome where newborns fail to secrete adequate amount of surfactant