The respiratory pump facilitates the return of blood to the heart by the respiratory pump facilitates the return of blood to the heart by squeezing blood from the rhythmic contraction of the diaphragm muscle decreasing the pressure gradient between abdominal and thoracic veins during expiration raising the pressure gradient between abdominal and thoracic veins during inspiration decreasing the pressure gradient between abdominal and thoracic veins during inspiration raising the pressure gradient between abdominal and thoracic veins during expiration