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- 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 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: 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).

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.