Birch A A, Dirnhuber M J, Hartley-Davies R, Iannotti F, Neil-Dwyer G
Department of Medical Physics and Medical Engineering, Southampton General Hospital, Shirley, UK.
Stroke. 1995 May;26(5):834-7. doi: 10.1161/01.str.26.5.834.
The aim of this study was to test the hypothesis that the phase difference that occurs between an induced oscillation in blood pressure and the resultant oscillation in middle cerebral artery (MCA) flow velocity could reflect the competence of cerebral autoregulation.
Fourteen volunteers performed 19 cycles of 10 seconds of squatting followed by 10 seconds of standing. Peak MCA velocity was measured with transcranial Doppler ultrasound, and blood pressure was measured with a servo-controlled finger plethysmograph held level with the head. Waveforms from each cycle were added to obtain averaged waveforms of arterial blood pressure and MCA velocity. These results were processed by Fourier analysis to extract the phase difference between the fundamental components of velocity and pressure. Each volunteer performed the exercise three times: first breathing normally, secondly hyperventilating (hypocapnia), and finally while breathing air containing 5% carbon dioxide (hypercapnia). Under these conditions the volunteers were expected to have normal, enhanced, and impaired auto-regulation, respectively.
The measurements made with normal breathing showed a phase lead of velocity ahead of pressure of 46 +/- 14 degrees (mean +/- SD). We noted a highly significant reduction in phase lead with hypercapnia (P < .00015) (Wilcoxon signed rank test, two-tailed) and a highly significant increase in phase lead with hypocapnia (P < .002).
The results support our hypothesis and may lead to a technique for assessing the competence of cerebral autoregulation.
本研究旨在验证以下假设，即血压诱发振荡与大脑中动脉（MCA）血流速度产生的振荡之间出现的相位差能够反映脑自动调节功能。
14名志愿者进行了19个周期的试验，每个周期包括10秒深蹲，随后10秒站立。采用经颅多普勒超声测量MCA峰值流速，并用与头部平齐的伺服控制手指体积描记器测量血压。将每个周期的波形相加，以获得动脉血压和MCA流速的平均波形。通过傅里叶分析对这些结果进行处理，以提取流速和压力基本成分之间的相位差。每位志愿者进行三次该运动：第一次正常呼吸，第二次过度通气（低碳酸血症），最后一次呼吸含5%二氧化碳的空气（高碳酸血症）。在这些条件下，预计志愿者分别具有正常、增强和受损的自动调节功能。
正常呼吸时的测量结果显示，流速相位超前压力46±14度（平均值±标准差）。我们注意到，高碳酸血症时相位超前显著降低（P<.00015）（Wilcoxon符号秩检验，双侧），低碳酸血症时相位超前显著增加（P<.002）。
结果支持我们的假设，并可能带来一种评估脑自动调节功能的技术。
