Claydon Victoria E, Hainsworth Roger
Institute for Cardiovascular Research, University of Leeds, LS2 9JT, Leeds, UK.
Clin Auton Res. 2003 Oct;13(5):321-9. doi: 10.1007/s10286-003-0120-8.
Posturally related syncope (PRS) is a common and distressing problem, which frequently occurs in people with no apparent clinical disorder and is ultimately caused by a reduction in blood supply to the brain. The aim of this study was to compare cerebrovascular responses to orthostatic stress in otherwise healthy patients suffering from PRS, and who were shown to have a poor orthostatic tolerance (n=28), with those in healthy control subjects with good orthostatic tolerance (n=11). Responses of heart rate, arterial blood pressure, end tidal carbon dioxide and middle cerebral artery (MCA) blood flow velocity were determined during a progressive orthostatic stress test of combined head-up tilting and lower body suction, which was continued until presyncope. We assessed the efficiency of autoregulation of cerebral blood flow from the relationship between values of MCA velocity and pressure obtained over the expected range for autoregulation (> 55 mmHg). All patients with PRS had a significant correlation between MCA velocity and pressure, but this was seen in only two of the controls. Furthermore, the values of the correlation coefficients were significantly higher in patients than controls, (p<0.001). We interpret these data as indicating that autoregulation in patients with PRS is less effective than in controls and suggest that this provides evidence for a link between abnormalities of regulation of the cerebral circulation and predisposition to syncope.
体位性相关晕厥（PRS）是一个常见且令人苦恼的问题，常发生于无明显临床疾病的人群中，最终由脑供血减少所致。本研究的目的是比较患有PRS且体位耐受性差的健康患者（n = 28）与体位耐受性良好的健康对照者（n = 11）对直立位应激的脑血管反应。在头高位倾斜和下体负压联合的渐进性直立位应激试验过程中，测定心率、动脉血压、呼气末二氧化碳和大脑中动脉（MCA）血流速度的反应，试验持续至前驱晕厥。我们根据MCA速度与压力值在自动调节预期范围（> 55 mmHg）内的关系，评估脑血流自动调节的效率。所有PRS患者的MCA速度与压力之间均存在显著相关性，但仅在两名对照者中观察到这种情况。此外，患者的相关系数值显著高于对照者（p < 0.001）。我们将这些数据解释为表明PRS患者的自动调节比对照者更无效，并表明这为脑循环调节异常与晕厥易感性之间的联系提供了证据。
