Role of venous blood flow from exercising muscles in regulation of circulation during exercise

本研究的目的是阐明运动时静脉流出在血液循环调节中的作用。为此，在运动过程中，肱静脉和动脉的血流量进行了测定。6名女性受试者（年龄; 26.3±3.8岁），仰卧位，分别以10%，30%，50%，70%MVC进行5 s的握力训练，50%MVC进行1 min的节律性握力训练，频率为15次/min。同时测量前臂肌肉的血压（Finapres）和肌肉氧合（NIRS）。静脉流出增加肌肉收缩开始时，而动脉流入增加收缩后立即。动脉血流量随运动强度变化显著，静脉血流量随运动强度变化不显著。当手握练习重复1毫米静脉和动脉血流量，和速度波动与肌肉收缩和放松。20 s后，随着运动时间的延长，其含量逐渐增加。然而，动脉和静脉血流量的增加并没有以类似的方式改变，前者显着超过后者，并导致肌肉血容量的增加，在运动前臂肌肉测量的近红外光谱。这些结果表明，在低强度运动开始时，运动肌肉的静脉流出将与动脉流入平衡。随着运动强度的增加和运动时间的延长，它们之间的平衡逐渐失衡，运动肌肉中的血容量增加。运动时血容量增加对循环调节的影响还有待研究。

The purpose of this study was to clarify the role of venous out flow in regulation of blood circulation during exercise. For this purpose, the blood flow was determined in brachial vein and artery during exercise. Six female subjects (age; 26.3±3.8 yrs) performed handgrip exercise of two different protocols in a supine position; 1) 5-s handgrip exercise at 10%, 30%, 50% and 70% MVC, 2) 1-min rhythmic handgrip exercise at 50% MVC, at the frequency of 15 times /min. Blood flow volume and velocity were measured using M-mode ultrasound and Doppler ultrasound methods. Blood pressure (Finapres) and muscle oxygenation (NIRS) in forearm muscles were measured simultaneously. Venous outflow increased at the onset of muscle contraction, whereas arterial inflow increased immediately after contraction. Significant blood flow changes with exercise intensity were found in artery but not in vein. When handgrip exercises were repeated for 1-mm both venous and arterial blood flow, and velocity fluctuated with muscle contraction and relaxation. They gradually increased with exercise duration after 20s. However, the increase in arterial and venous blood flow did not change in the similar manner, and the former exceeded significantly the latter and resulted in the increase in muscle blood volume in the exercising forearm muscles measured by NIRS. These results suggest that venous outflow from exercising muscle would be balanced with arterial inflow at the beginning of exercise at low intensity. When exercise intensity became higher and exercise duration was prolonged, they became to be out of balance and the blood volume in exercising muscles increased. The effect of blood volume increase on circulatory regulation during exercise remains to be studied.