dead space

dead space [AS, dead; L, spatium] , 1. a cavity that remains after the incomplete closure of a surgical or traumatic wound, leaving an area in which blood can collect and delay healing. 2. the amount of lung in contact with ventilating gases but not in contact with pulmonary blood flow. Alveolar dead space is characterized by alveoli that are ventilated by the pulmonary circulation but are not perfused. The condition may exist when pulmonary circulation is obstructed, as by a thromboembolus. Anatomical dead space is an area in the trachea, bronchi, and air passages containing air that does not reach the alveoli during respiration. As a general rule, the volume of air in the anatomical dead space in milliliters is approximately equal to the weight in pounds of the individual affected. Certain lung disorders, such as emphysema, increase the amount of anatomical dead space. Physiological dead space is an area in the respiratory system that includes the anatomical dead space together with the space in the alveoli occupied by air that does not contribute to the oxygen–carbon dioxide exchange.