The postural reduction in middle cerebral artery blood velocity is not explained by PaCO2
The postural reduction in middle cerebral artery blood velocity is not explained by PaCO2
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DOI：
10.1007/s00421-006-0136-6
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发表时间：
2006-03-01
影响因子：
3
通讯作者：
van Lieshout, JJ
中科院分区：
文献类型：
--
作者：
Immink, RV;Secher, NH;van Lieshout, JJ
在正常二氧化碳浓度范围内，大脑中动脉平均速度 (MCA V-mean) 的变化类似于动脉血中每毫米汞柱二氧化碳张力 (PaCO2) 3.5% 的变化，PaCO2 的降低将通过血管收缩（大脑的 CO2 反应性）减少脑血流量。当站立时，MCA V 平均值和潮气末二氧化碳张力 (PETCO2) 降低，表明 PaCO2 有助于 MCA V 平均值的降低。在固定体位时，PETCO2 跟踪 PaCO2 的变化，但当采取直立位置时，心输出量 ((Q) 点上) 减少，其在肺部的分布发生变化，而通气量 ((V) 点 (E) 上) 增加，表明 PETCO2 比 PaCO2 下降更多。本研究评估了 PaCO2 姿势性下降是否是 MCA V 平均值姿势性下降的原因。从仰卧位到直立位，对 7 名受试者进行了 (V)over dotE、(Q)over dot、PETCO2、PaCO2、MCA V 平均值和近红外分光光度法测定的脑组织氧合 (CO(2)Hb)。站立时，MCA V 平均值（从 65.3 +/- 3.8 至 54.6 +/- 3.3 cm s(-1) ；平均值 +/- SEM；P < 0.05）和 cO(2)Hb (-7.2 +/- 2.2 mu mol 1(-1) ；P < 0.05) 下降。同时，随着 PETCO2 姿势的减少高估了 PaCO2 的下降，(V) 过点 (E)/(Q) 过点比率增加了 49 +/- 14% (P < 0.05)（-4.8 +/- 0.9 mmHg 与 -3.0 +/- 1.1 mmHg；P < 0.05）。当采取直立姿势时，MCA V 平均值的姿势下降似乎可以通过 PETCO2 的减少来解释，但 PaCO2 的小幅下降使得 MCA V 平均值的姿势下降不太可能仅由脑 CO2 反应性来解释。
In the normocapnic range, middle cerebral artery mean velocity (MCA V-mean) changes similar to 3.5% per mmHg carbon-dioxide tension in arterial blood (PaCO2) and a decrease in PaCO2 will reduce the cerebral blood flow by vasoconstriction (the CO2 reactivity of the brain). When standing up MCA V-mean and the end-tidal carbon-dioxide tension (PETCO2) decrease, suggesting that PaCO2 contributes to the reduction in MCA V-mean. In a fixed body position, PETCO2 tracks changes in the PaCO2 but when assuming the upright position, cardiac output ((Q)over dot) decreases and its distribution over the lung changes, while ventilation ((V)over dot(E)) increases suggesting that PETCO2 decreases more than PaCO2. This study evaluated whether the postural reduction in PaCO2 accounts for the postural decline in MCA V-mean. From the supine to the upright position, (V)over dotE, (Q)over dot, PETCO2, PaCO2, MCA V-mean, and the near-infrared spectrophotometry determined cerebral tissue oxygenation (CO(2)Hb) were followed in seven subjects. When standing up, MCA V-mean (from 65.3 +/- 3.8 to 54.6 +/- 3.3 cm s(-1) ; mean +/- SEM; P < 0.05) and cO(2)Hb (-7.2 +/- 2.2 mu mol 1(-1) ; P < 0.05) decreased. At the same time, the (V)over dot(E)/(Q)over dot ratio increased 49 +/- 14% (P < 0.05) with the postural reduction in PETCO2 overestimating the decline in PaCO2 (-4.8 +/- 0.9 mmHg vs. -3.0 +/- 1.1 mmHg; P < 0.05). When assuming the upright position, the postural decrease in MCA V-mean seems to be explained by the reduction in PETCO2 but the small decrease in PaCO2 makes it unlikely that the postural decrease in MCA V-mean can be accounted for by the cerebral CO2 reactivity alone.