Final answer:
Exudate in the alveoli during ARDS obstructs normal oxygenation and CO₂ removal by creating a physiological shunt and reducing the V/Q ratio. This leads to impaired gas exchange and decreased oxygen levels, as seen in conditions like pneumonia.
Step-by-step explanation:
When exudate enters the alveoli in Acute Respiratory Distress Syndrome (ARDS), it impedes the normal gas exchange process. The alveoli are tiny air sacs in the lungs where oxygenation of blood and the removal of carbon dioxide (CO₂) occur. If these alveoli fill with exudate, which is a fluid consisting of serum, white blood cells, and other inflammatory debris, they cannot effectively perform this exchange. A physiological shunt can develop, meaning that blood passes through these areas without being properly oxygenated because ventilation (airflow to the alveoli) is decreased but perfusion (blood flow to the alveoli) is not affected. This imbalance leads to a reduced V/Q ratio, where 'V' stands for ventilation and 'Q' for perfusion, resulting in impaired gas exchange and decreased oxygen levels in the bloodstream. During respiratory infections such as pneumonia, alveoli fill with fluid, inhibiting the exchange of gases with the blood and causing symptoms like coughing, chest pain, and difficulty breathing.