Which conditions increase physiologic dead space?

Which conditions increase physiologic dead space?

• A. COPD
• B. Morbid obesity
• C. Pulmonary embolism
• D. All of the above

Answer: (D)

Physiologic dead space is the portion of each breath that is ventilated but does not participate in gas exchange because the alveoli receiving the air are not adequately perfused. It increases when ventilation exceeds perfusion in portions of the lung. COPD, especially emphysema, destroys alveolar walls and the surrounding capillary bed, creating more alveolar units that are ventilated but poorly perfused. That directly raises alveolar (physiologic) dead space. Pulmonary embolism blocks blood flow to ventilated regions, so air reaches alveoli that receive little or no blood for gas exchange. This also increases alveolar dead space. Morbid obesity alters chest wall mechanics and reduces lung volumes, leading to uneven ventilation and perfusion. Some regions may be adequately ventilated but relatively underperfused, increasing physiologic dead space. So all of the listed conditions can raise physiologic dead space.

Physiologic dead space is the portion of each breath that is ventilated but does not participate in gas exchange because the alveoli receiving the air are not adequately perfused. It increases when ventilation exceeds perfusion in portions of the lung.

COPD, especially emphysema, destroys alveolar walls and the surrounding capillary bed, creating more alveolar units that are ventilated but poorly perfused. That directly raises alveolar (physiologic) dead space.

Pulmonary embolism blocks blood flow to ventilated regions, so air reaches alveoli that receive little or no blood for gas exchange. This also increases alveolar dead space.

Morbid obesity alters chest wall mechanics and reduces lung volumes, leading to uneven ventilation and perfusion. Some regions may be adequately ventilated but relatively underperfused, increasing physiologic dead space.

So all of the listed conditions can raise physiologic dead space.