1. Factors that affect pulmonary ventilation: (air flow to the lung):
المحاضرة الثامنة
Resistance of the respiratory passage.
Pressure relationship in the thoracic cavity.
Surfactant.
Lung and chest compliance.
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. 2- Pressure relationship in the thoracic cavity:
these pressure are:
Intra pulmonary pressure.
Intra pleural pressure.
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 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. 3- Surfactant: Function of surfactant:
stability and fluid balance of the pulmonary alveoli.
Surfactant may activate and exert a stimulant effect of macrophages.
It has abecteriolyic effect rendering the bacteria susceptible to alveolar macrophages.
The phospholipids of surfactant may act directly on T-lymphocytes membranes to prevent excess immune response .
It assists ciliary movement in upper respiratory tract excess (the mucociliary escalatory).

4. It keeps the alveoli opened
It helps to keep the alveoli dry
Surfactant decrease in the following conditions:
Respiratory distress syndrome.
Cigarette smoking decrease surfactant.
After cardiac surgery
4- Lung Compliance :
Compliance is a measure of stretchbility-elasticity-expansibility distensibility of the lungs.
It is refined as volume change per unit pressure change.