In vivo study for non-linear relationship between capillary blood flow and tissue pO_2 in skeletal muscle

我们验证了这样一种假说，即骨骼肌可能有一种简单的、内在的O2敏感机制来调节毛细血管血流，在这种机制中，毛细血管血流的启动和停止响应于一个阈值PO2。这一假说是通过活体显微镜测量毛细血管红细胞(RBC)的速度和毛细血管密度，以响应兔腱细肌灌流液中PO2水平的变化来验证的。红细胞流速和毛细血管密度均随灌流液中PO2浓度的升高而显著降低，但根据流速和密度数据计算的毛细血管血流量与灌流液中的PO2浓度之间呈非线性相关关系。这一数据表明，对于血氧饱和度在35-45托之间的灌流液，可能存在一个影响微血管血流调节的临界血氧饱和度。超过或低于这一临界值，毛细血管血流量急剧减少或增加。这些发现支持这样一种可能性，即小动脉在检测局部代谢需求方面发挥着重要作用，并通过影响其平滑肌的张力来直接调节毛细血管血流，而不需要从远端部位传递信号。

We tested the hypothesis that skeletal muscle may have a simple, intrinsic O_2-sensing mechanism for regulating capillary blood flow in which capillary flow is started and stopped in response to a threshold pO_2 value. This hypothesis was evaluated by measuring the capillary red blood cell (RBC) velocity and perfused capillary density in response to changes in the pO_2 level of suffusates in rabbit tenuissimus muscle using an intravital microscope. Both the RBC velocity and the capillary density significantly decreased as the pO_2 level of the suffusates was elevated, but the relationship between the capillary blood flow rate, calculated by the velocity and density data, and the pO_2 level of the suffusates displayed a non-linear correlation. This data suggests that a critical pO_2 value affecting microvascular blood flow regulation might exist for suffusates with a pO_2 of between 35 and 45 Torr. Above or below this critical threshold pO_2 level, capillary blood flow drastically decreases or increases. These findings support the possibility that the arterioles play an important role in detecting local metabolic demand and directly regulate capillary blood flow by influencing the tonus of their smooth muscle, without requiring signal transmission from a distal site.