What is the effect of pneumonia on the ventilation/perfusion ratio?

Pneumonia typically affects the ventilation/perfusion (V/Q) ratio by causing a decrease in it. This is primarily due to the accumulation of inflammatory fluid and exudate within the alveoli, which impairs gas exchange. In the case of pneumonia, the areas of the lung affected often have adequate blood flow (perfusion) but reduced ventilation due to the buildup of fluid, mucus, or inflammation blocking airflow.

As a result, there is a mismatch where the blood passing through the pulmonary capillaries does not receive adequate oxygen because the alveoli are not functioning properly. This leads to regions of the lung that are well perfused but poorly ventilated, resulting in a lowered V/Q ratio overall. Understanding this relationship is crucial in recognizing how diseases like pneumonia can impact the efficiency of gas exchange in the lungs and subsequently influence treatment strategies in critical care scenarios.