Background and Purpose- Breath holding (BH) and hyperventilation are used to assess abnormal cerebrovascular reactivity, often in relation to severity of small vessel disease and risk of stroke with carotid stenosis, but responses may be confounded by blood pressure (BP) changes. We compared effects of BP and end-tidal carbon dioxide (etCO2) on middle cerebral artery mean flow velocity (MFV) in consecutive transient ischemic attack and minor stroke patients. Methods- In the population-based, prospective OXVASC (Oxford Vascular Study) phenotyped cohort, change in MFV on transcranial Doppler ultrasound (ΔMFV, DWL-DopplerBox), beat-to-beat BP (Finometer), and etCO2 was measured during 30 seconds of BH or hyperventilation. Two blinded reviewers independently assessed recording quality. Dependence of ΔMFV on ΔBP and ΔetCO2 was determined by general linear models, stratified by quartiles. Results- Four hundred eighty-eight of 602 (81%) patients with adequate bone windows had high-quality recordings, more often in younger participants (64.6 versus 68.7 years; P<0.01), whereas 426 had hyperventilation tests (70.7%). During BH, ΔMFV was correlated with a rise in mean blood pressure (MBP; r2=0.15, P<0.001) but not ΔCO2 (r2=0.002, P=0.32), except in patients with ΔMBP <10% (r2=0.13, P<0.001). In contrast during hyperventilation, the fall in MFV was similarly correlated with reduction in CO2 and reduction in MBP (ΔCO2: r2=0.13, P<0.001; ΔMBP: r2=0.12, P<0.001), with a slightly greater effect of ΔCO2 when ΔMBP was <10% (r2=0.15). Stratifying by quartile, MFV increased linearly during BH across quartiles of ΔMBP, with no increase with ΔetCO2. In contrast, during hyperventilation, MFV decreased linearly with ΔetCO2, independent of ΔMBP. Conclusions- In older patients with recent transient ischemic attack or minor stroke, cerebral blood flow responses to BH were confounded by BP changes but reflected etCO2 change during hyperventilation. Correct interpretation of cerebrovascular reactivity responses to etCO2, including in small vessel disease and carotid stenosis, requires concurrent BP measurement.

中文翻译：

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在短暂性脑缺血发作或中风时，屏住呼吸或换气过度时，血压会混淆大脑血流速度。

背景与目的-屏气（BH）和过度换气常用于评估异常的脑血管反应性，通常与小血管疾病的严重程度和患有颈动脉狭窄的中风风险有关，但血压（BP）的变化可能会混淆反应。我们比较了连续短暂性脑缺血发作和轻度中风患者的血压和潮气末二氧化碳（etCO2）对大脑中动脉平均流速（MFV）的影响。方法-在以人群为基础的前瞻性OXVASC（牛津血管研究）表型队列中，在30秒内测量经颅多普勒超声（ΔMFV，DWL-DopplerBox），逐搏BP（Finometer）和etCO2的MFV变化BH或换气过度。两名盲人审稿人独立评估了录音质量。ΔMFV对ΔBP和ΔetCO2的依赖性由四分位数分层的通用线性模型确定。结果-602例（81％）骨窗充足的患者中有888例具有高质量的记录，在年轻参与者中更为频繁（64.6 vs 68.7岁； P <0.01），而426例进行了换气过度测试（70.7％）。在BH期间，ΔMFV与平均血压升高（MBP; r2 = 0.15，P <0.001）相关，但与ΔCO2（r2 = 0.002，P = 0.32）不相关，除了ΔMBP<10％（r2 = 0.13， P ＜0.001）。相反，换气过度时，MFV的下降与CO2的减少和MBP的减少类似（ΔCO2：r2 = 0.13，P <0.001；ΔMBP：r2 = 0.12，P <0.001），而当ΔMBP＜10％（r2 ＝ 0.15）。按四分位数分层，在BH期间，跨ΔMBP四分位数的MFV线性增加，ΔetCO2没有增加。相反，在换气过度时，MFV与ΔetCO2呈线性下降，而与ΔMBP无关。结论-在近期短暂性脑缺血发作或轻度中风的老年患者中，对BH的脑血流反应被BP变化所混淆，但反映了过度换气期间的etCO2变化。正确解释对etCO2的脑血管反应性反应，包括在小血管疾病和颈动脉狭窄中，需要同时进行血压测量。