Which statement about the respiratory pump and venous return is correct?

• A. Inhalation lowers intrathoracic pressure and increases venous return.
• B. Exhalation raises intrathoracic pressure and increases venous return.
• C. Inhalation raises intrathoracic pressure and increases venous return.
• D. Exhalation raises intrathoracic pressure and decreases venous return.

Answer: (A)

During inhalation the diaphragm contracts and moves downward while the chest expands, which makes intrathoracic (intra-thoracic) pressure more negative. That drop in pressure creates a stronger pressure gradient that draws blood from the peripheral veins toward the heart, increasing venous return to the right atrium. The abdominal cavity is compressed a bit, helping push blood upward into the thorax as part of the respiratory pump.

During exhalation the chest volume decreases and intrathoracic pressure rises, narrowing that gradient and reducing venous return. So the statement that inhalation lowers intrathoracic pressure and increases venous return is correct.