Department of Biomedical Engineering, Toyo University, Kawagoe-Shi, Saitama, Japan.
Clin Sci (Lond). 2013 Jul;125(1):37-44. doi: 10.1042/CS20120335.
The respiratory chemoreflex is known to be modified during orthostatic stress although the underlying mechanisms remain to be established. To determine the potential role of cerebral hypoperfusion, we examined the relationship between changes in MCA V(mean) (middle cerebral artery mean blood velocity) and ˙VE (pulmonary minute ventilation) from supine control to LBNP (lower body negative pressure; −45mmHg) at different CO(2) levels (0, 3.5 and 5% CO(2)). The regression line of the linear relationship between ˙V(E) and PETCO(2) (end-tidal CO(2)) shifted leftwards during orthostatic stress without any change in sensitivity (1.36+− 0.27 l/min per mmHg at supine to 1.06+− 0.21 l/min per mmHg during LBNP; P=0.087). In contrast, the relationship between MCA V(mean) and PETCO(2) was not shifted by LBNP-induced changes in PETCO2. However, changes in ˙V(E) from rest to LBNP were more related to changes in MCA V(mean) than changes in PETCO(2). These findings demonstrate for the first time that postural reductions in CBF (cerebral blood flow) modified the central respiratory chemoreflex by moving its operating point. An orthostatically induced decrease in CBF probably attenuated the ‘washout’ of CO(2) from the brain causing hyperpnoea following activation of the central chemoreflex.
已知在直立应激期间呼吸化学反射会发生变化，但其潜在机制仍有待确定。为了确定脑灌注不足的潜在作用，我们研究了在不同 CO2 水平（0、3.5 和 5% CO2）下，MCA Vmean（大脑中动脉平均血流速度）和 ˙VE（肺分钟通气量）从仰卧位对照到 LBNP（下体负压；−45mmHg）的变化之间的关系。在直立应激期间， ˙V(E) 和 PETCO2（呼气末 CO2）之间的线性关系回归线向左移动，而敏感性没有变化（仰卧位时为 1.36+−0.27 l/min per mmHg，LBNP 时为 1.06+−0.21 l/min per mmHg；P=0.087）。相比之下，LBNP 引起的 PETCO2 变化并未使 MCA V(mean)和 PETCO2 之间的关系发生移位。然而，从休息到 LBNP 的 ˙V(E)变化与 MCA V(mean)的变化比与 PETCO2 的变化更相关。这些发现首次表明，CBF（脑血流）的体位降低通过移动其操作点来改变中枢呼吸化学反射。CBF 的直立诱导降低可能减弱了 CO2 从大脑中的“冲洗”作用，从而导致中枢化学感受器激活后过度通气。
