Download Pressure relationship in the thoracic cavity

Factors that affect pulmonary ventilation:
(air flow to the lung):
‫المحاضرة‬
1. Resistance of the respiratory passage.
2. Pressure relationship in the thoracic cavity.
3. Surfactant.
4. Lung and chest compliance.
‫الثامنة‬
1- Resistance of the air passage:
The resistance to air flow depends on the
diameter of the respiratory passage which is
affected by:
i) Bronchial muscle tone
ii) Bronchial mucosa
iii) pressure gradient
2- Pressure relationship in the thoracic cavity:
these pressure are:
1) Intra pulmonary pressure.
2) Intra pleural pressure.
3) Intra thoracic pressure.
Intrapleural pressure (IPP) :
It is the pressure inside the pleural cavity.
•Causes of negativity of intrapleural pressure:
1- Elastic recoil of lungs-against
2- Rigid chest wall
Function of negativity of IPP :
1- Helps more venous return 2- Helps more lymph return.
3- Helps expansion of alveoli during inspiration.
4- Helps blood flow in the pulmonary vessels.
3- Surfactant:
Function of surfactant:
1. stability and fluid balance of the pulmonary alveoli.
2. Surfactant may activate and exert a stimulant effect
of macrophages.
3. It has abecteriolyic effect rendering the bacteria
susceptible to alveolar macrophages.
4. The phospholipids of surfactant may act directly on
T-lymphocytes membranes to prevent excess
immune response .
5. It assists ciliary movement in upper respiratory tract
excess (the mucociliary escalatory).
6. It keeps the alveoli opened
7. It helps to keep the alveoli dry
Surfactant decrease in the following conditions:
1. Respiratory distress syndrome.
2. Cigarette smoking decrease surfactant.
3. After cardiac surgery
4- Lung Compliance :
-Compliance is a measure of stretchbility-elasticityexpansibility distensibility of the lungs.
-It is refined as volume change per unit pressure change.
V
Compliance 
P