Which of the following disorders is least likely to be associated with V/Q mismatch?

Severe anemia is least likely to be associated with ventilation/perfusion (V/Q) mismatch because it primarily impacts the oxygen-carrying capacity of the blood rather than the distribution of blood flow and airflow within the lungs. In severe anemia, while the percentage of hemoglobin available for binding to oxygen is reduced, the ventilation of the alveoli and the perfusion of the pulmonary capillaries remain relatively normal. Therefore, the basic mechanics of gas exchange in terms of matching ventilation and perfusion are not disrupted.

On the other hand, conditions like asbestosis, pneumothorax, and acute respiratory distress syndrome (ARDS) directly affect lung function and can lead to significant V/Q mismatching. Asbestosis involves lung fibrosis, which can impair airflow and lead to uneven distribution of ventilation relative to perfusion. A pneumothorax can collapse part of a lung, leading to areas that are ventilated but not perfused, or vice versa, leading to a classic V/Q mismatch. Similarly, ARDS involves widespread inflammation and damage to the alveolar-capillary membrane, resulting in impaired gas exchange and significant positional mismatch of ventilation and perfusion.

Thus, severe anemia’s effect on oxygen transport via the blood, rather than on lung mechanics or