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

我们验证了骨骼肌可能具有一种简单的、内在的o_2感知机制来调节毛细血管血流，其中毛细血管血流在阈值pO_2的响应下启动和停止。通过活体显微镜下测量兔腱肌内弥漫性积液中pO_2水平变化对毛细血管红细胞（RBC）速度和灌注毛细血管密度的影响，对该假说进行了验证。红细胞流速和毛细血管密度随着pO_2浓度的升高而显著降低，但由流速和密度计算的毛细血管血流速率与pO_2浓度呈非线性相关。这些数据表明，pO_2在35 ~ 45 Torr之间时，可能存在影响微血管血流调节的临界pO_2值。高于或低于临界阈值pO_2水平，毛细血管血流量急剧减少或增加。这些发现支持了一种可能性，即小动脉在检测局部代谢需求方面发挥重要作用，并通过影响其平滑肌张力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.