Pleural Pressure

1. How negative pressure is
maintained in pleura?
discuss tHe clinical
significance of pleural
pressure.
Hare Ram Karn
14-05-2011

2. Interpleural
Pressure
• Pressure inside the pleural cavity i.e.
between parital & visceral layer of pleura.
• Also k/a Intrathoracic pressure.
• Mainly exerted by ‘Suction Effect’ caused
by recoiling of lung

3. • As the lungs recoils elastically pulling force
in the plural cavity decreases pressure
inside it.

4. Normal Value
During Inspiration : - 6 mmHg
During Expiration : -2 mmHg

5. Negative Plural
Pressure
• Negative force is always required to keep the lungs
expanded.
• Maintained by negative pressure in plural space.
• Negative plural pressure is basically caused by
pumping out plural fluid
• Plural fluid is pumped out by lymphatics.

6. Lymphatic Drainage
• Lymph from the parietal pleura is drained into the
lymph node of thoracic wall.
• Medistinum
• Lateral surfaces of the perital pleura
• Superior surface of Diaphragm

7. Lymph from visceral pleura is drained
into deep pulmonary plexus

8. • Pressure at Artrial end of capillary 15-25mmHg
• Fluid diffused into interstital space is reabsorbed at
venous end.
• Remainig fluid after venous reabsorption is carried
away by lymphatics present over that area.

9. • Venous capillaries are more numerous & permeable
than arterial capillaries.
• About nine tenth of fluid is absorbed at venous end .
• Only one tenth is drained by lymphatics into
circulating blood.

10. • Normally when the fluid enters the terminal
lymphatics capillaries, the lymph vessels walls
automatically contract for a few seconds and pump
the fluid into blood circulation.
The pleural membrane is a
porous, mesenchymal, serous membrane through
which small amount of interstital fluid transude
continuously into plural space.This over all processes
maintains the negative pleural pressure.

11. Clinical significance
Due to negative pressure thoracic region the larger veins
and venacava becomes dilated.
The negative pressure acts as suction pump and pulls
the blood from lower part of body against gravity.
Hence, responsible for venous return and termed as
respiratory pump.
Prevent collapsing tendency of the lungs caused by
elastic recoiling of lung tissues.

12. • In some of the pathological conditions such as
Pneumothorax
Hydrothorax
Hemothorax
Pyothorax
Tends to be more positive.
-In Valsalva Maneuver pleural pressure becomes more
positive.
-In reverse Valsalva/Mueller’s Maneuver pleural
pressure becomes less positive.