Question

Physiological dead space and alveolar ventilation.

Hint:

When calculating alveolar ventilation, subtract the physiological dead space from the total ventilation to get the volume of air available for effective gas exchange.

Answer 1

Step 1: Understanding Physiological Dead Space.
Physiological dead space refers to areas in the respiratory system where no gas exchange occurs. This includes both anatomical dead space (the airways where no exchange of gases happens, such as the trachea and bronchi) and alveolar dead space (alveoli that are ventilated but not perfused with blood, therefore not participating in gas exchange).

Step 2: Understanding Alveolar Ventilation.
Alveolar ventilation is the volume of fresh air that reaches the alveoli per minute, available for gas exchange. It is calculated by subtracting the dead space ventilation from the total ventilation.

Step 3: Relationship Between Dead Space and Alveolar Ventilation.
Alveolar ventilation can be reduced if the physiological dead space increases. This leads to a decrease in the effective ventilation available for gas exchange, even if the total ventilation remains the same. Increased dead space ventilation decreases the efficiency of breathing.

Step 4: Clinical Relevance.
In diseases like chronic obstructive pulmonary disease (COPD), the physiological dead space may increase due to alveolar damage and poor perfusion, which decreases effective alveolar ventilation and leads to inefficient gas exchange.