What happens when intraalveolar pressure exceeds atmostpheric pressure?

When the intraalveolar pressure exceeds atmospheric pressure, it signifies a pathological condition known as positive airway pressure. This imbalance between the pressure within the alveoli and the surrounding environment leads to several consequences.

1. Alveolar Overinflation: The increased pressure causes the alveoli to overinflate, resulting in a condition known as emphysema. The overstretched alveoli lose their elasticity, leading to permanent damage and difficulty exchanging gases.

2. Air Trapping: Positive airway pressure hinders the normal expiration of air from the lungs. This causes air trapping, where old air remains in the alveoli, reducing the volume of fresh air that can enter during inspiration.

3. Increased Work of Breathing: Overcoming the elevated pressure requires more effort from the respiratory muscles, leading to increased work of breathing. This can put strain on the respiratory system and cause respiratory distress.

4. Barotrauma: Extreme positive airway pressure can cause barotrauma - damage to lung tissue due to overpressure. This can result in conditions such as pneumothorax (collapsed lung) or pneumomediastinum (air in the mediastinum).

5. Atelectasis: In certain cases, positive airway pressure can lead to atelectasis - collapse or closure of lung alveoli. This occurs when the pressure within the alveoli drops below atmospheric pressure, causing them to collapse.

Positive airway pressure can arise due to various factors, including mechanical ventilation, obstructive lung diseases (e.g., asthma, COPD), or certain medical procedures. Therefore, understanding and managing intraalveolar pressure is essential in respiratory medicine to prevent complications and ensure proper gas exchange.