[RS] Q.5) Pressure related to respiration:

ans.

a)    Intrapleural pressure

b)    Alveolar pressure (Intrapulmonary pressure)

c)    Transpulmonary pressure

a)Intrapleural pressure:

·  It is the pressure of the fluid in between two layers of pleura.

·  It requires to prevent lungs collapse.

·  It is always negative due to continual absorption of fluid from the space into the capillaries. This absorption creates a partial vacuum and produce a negative
pressure.

·  Intrapleural pressure at different pleases of respiration:

Ø                 During resting level →(-5cm of H2O)

Ø                 Beginning of Inspiration → (-5cm of H2O)

Ø                 At the end of Inspiration → (-7.5cm H2O)

Ø                 During inspiration → (-5-7.5cm H2O) – ↑Lungs volume of 0.5 liter

Ø                 During expiration →↓ Lungs volume.

b) Alveolar pressure (Intrapulmonary pressure):

·  It is the pressure of the air inside the lung alveoli.

·  Alveolar pressures at different phase of the respiration are:

•      During inspiration → Negative (-1cm H2O) to atmospheric pressure this causes to pull 0.5 liter of air into the lungs.
•           At the end of inspiration →Zero (no gas flow)
•    During expiration →Positive (+ 1cm H2O) to atmospheric pressure this causes   0.5 liter of air (inspired) out of the lungs.

  c) Transpulmonary pressure:

It is the pressure difference between the alveolar pressure and pleural pressure.

It is the pressure difference between lung alveoli and that on the outer surface of the lungs.

Ø                 It is a measure of the elastic forces of the lungs.