Mayberg T S, Lam A M, Matta B F, Visco E
Department of Anesthesiology, University of Washington, Harborview Medical Center, Seattle, USA.
J Neurosurg Anesthesiol. 1996 Oct;8(4):268-72. doi: 10.1097/00008506-199610000-00002.
Transcranial Doppler (TCD) ultrasonography has been used in a variety of clinical contexts to assess cerebrovascular reserve by measuring carbon dioxide reactivity. Reproducibility with time and altered position of the patient is examined in the present study. Carbon dioxide reactivity was determined in 10 healthy volunteers using TCD. Hypocarbia was produced by voluntary hyperventilation, and hypercarbia was produced by rebreathing from a circuit primed with 7% carbon dioxide. Each patient was studied in the supine position twice (1 week apart) and once in the seated position. Carbon dioxide reactivity was determined from linear regression analysis of paired middle cerebral artery flow velocity and end-tidal carbon dioxide values. Analysis of covariance for repeated measures was used for statistical analysis. Both the absolute slope and the relative slope (absolute slope expressed as a percentage of flow velocity at 40 mm Hg) were compared. In the supine position, flow velocity, absolute and relative slopes, and mean arterial pressure were similar from one week to the next at all carbon dioxide levels. In contrast, flow velocity, mean arterial pressure (adjusted for hydrostatic gradient), and absolute slope were decreased in the seated position (p < 0.05). No difference was observed when the relative slope was used for comparison. We conclude that absolute carbon dioxide reactivity is reproducible over time but may be influenced by position. Relative reactivity (relative slope), however, was both time and position independent.
经颅多普勒（TCD）超声检查已在多种临床情况下用于通过测量二氧化碳反应性来评估脑血管储备。本研究检测了患者随时间及体位改变时的可重复性。使用TCD对10名健康志愿者测定二氧化碳反应性。通过自主过度通气产生低碳酸血症，通过从充有7%二氧化碳的回路中重复呼吸产生高碳酸血症。每位患者在仰卧位进行两次研究（间隔1周），并在坐位进行一次研究。根据大脑中动脉血流速度与呼气末二氧化碳值的线性回归分析确定二氧化碳反应性。采用重复测量的协方差分析进行统计分析。比较了绝对斜率和相对斜率（绝对斜率表示为40 mmHg时血流速度的百分比）。在仰卧位，所有二氧化碳水平下，一周到下一周的血流速度、绝对和相对斜率以及平均动脉压相似。相比之下，坐位时血流速度、平均动脉压（根据静水压梯度调整）和绝对斜率降低（p<0.05）。使用相对斜率进行比较时未观察到差异。我们得出结论，绝对二氧化碳反应性随时间具有可重复性，但可能受体位影响。然而，相对反应性（相对斜率）与时间和体位无关。
