What term describes ventilation without perfusion?

Ventilation without perfusion refers to a situation where air reaches the alveoli (ventilation) but there is inadequate blood flow to those areas (perfusion). This condition is specifically termed "alveolar dead space." In this scenario, even though gas exchange is expected to occur, it does not happen efficiently because the perfusion component is compromised.

Alveolar dead space can result from various factors, such as a blocked blood vessel, pulmonary embolism, or some conditions that result in poor blood flow to parts of the lung. Essentially, the alveoli are ventilated and available for gas exchange, but because there is no blood to carry away the oxygen or bring in carbon dioxide, effective gas exchange cannot take place.

In contrast, an intrapulmonary shunt indicates that blood flows through the pulmonary circulation but does not adequately participate in gas exchange due to collapsed or filled alveoli. Vascular shunting involves blood bypassing the lungs altogether or some of the lung regions not delivering oxygen, and a high V/Q ratio typically relates to situations where ventilation exceeds perfusion, but still does not specifically denote the absence of perfusion in specific segments of the lung as alveolar dead space does. Therefore, alveolar dead space is the most accurate