Suction against resistance: a new breathing technique to significantly improve the blood flow ratio of the superior and inferior vena cava

Objectives: Optimal contrast within the pulmonary artery is achieved by the maximum amount of contrast-enhanced blood flowing through the superior vena cava (SVC), while minimum amounts of non-contrasted blood should originate from the inferior vena cava (IVC). This study aims to clarify whether "suction against resistance” might optimise this ratio. Methods: Phase-contrast pulse sequences on a 1.5T MRI magnet were used for flow quantification (mean flow (mL/s), stroke volume (Vol) in the SVC and IVC in volunteers. Different breathing manoeuvers were analysed repeatedly: free breathing; inspiration; expiration; suction against resistance, and Valsalva. To standardise breathing commands, volunteers performed suction and Valsalva manoeuvers with an MR-compatible manometer. Results: Suction against resistance was associated with a significant drop of the IVC/SVC flow quotient (1.63 [range 1.3-2.0] p 0.05). Conclusions: Suction against resistance caused a significant drop in the IVC/SVC quotient. Theoretically, this breathing manoeuver might significantly improve the enhancement characteristics of CT angiography. Key Points: • Suction provokes reduction in blood flow in the inferior vena cava. • Ratio between the inferior and superior vena cava blood flow diminished during suction. • Manometer used during breathing standardises MR phase-contrast blood flow measurements