Contraction of the abdominal muscles compresses the abdominal contents and pushes up on the diaphragm, and that further decreases the thoracic volume, increasing thoracic pressure and pushing the air out.

腹部肌肉收缩压迫腹部内容物并向上推压膈肌，从而进一步减小胸腔容积，增加胸腔压力并将空气推出。

As the inferior vena cava passes through both abdominal and thoracic cavities, an increase in abdominal pressure together with a decrease in thoracic pressure squeeze the blood upward- toward the heart.

当下腔静脉同时通过腹腔和胸腔时，腹腔压力增加和胸腔压力降低会将血液向上挤压—流向心脏。