By using a simplified model for cardiovascular system which consists of the cardiac resistance R_h, the artery C_a, the vein C_b and the peripheral vessel R_s, the ratio of the arteriovenous pressure difference Δp to the maximum arteriovenous pressure difference Δp_M was defined as the circulatory ratio θ ≡Δp ⁄ Δp_M. It was shown that the circulatory ratio θ was θ=1 ⁄ 2 regardless of the exercise. It was revealed that this regulation is done by keeping R_h ⁄ R_s constant and the ratio is equal to the arterial compliance fraction k_a.

A 24-year-old woman had been injured in an automobile accident. The chest X-ray showed widening of the mediastinum and computed tomography showed mediastinal hematoma around the aortic arch. Aortic rupture was suspected, so we performed aortography, which revealed pseudoaneurysm of the descending aorta. Moreover, she also had splenic rupture and pelvic fracture. She underwent an emergency operation 4 hours after the accident. Medial tear of the descending aorta was replaced with a graft under temporary bypass without heparin. Simultaneously, splenectomy was performed. Her postoperative course was uneventful. We consider that temporary bypass without heparin is a useful method during repair of the descending aortic rupture due to trauma.