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Induced and spontaneous hemodynamic oscillations in cerebral and extracerebral tissue for coherent hemodynamics spectroscopy

机译：相干血流动力学光谱法在脑和脑外组织中诱发和自发的血流动力学振荡

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We report preliminary results of a study for investigating the spatial homogeneity of induced and spontaneous oscillations in the concentration of oxyhemoglobin on the scalp/skull layer of two human subjects. Hemodynamic oscillations were induced by modulation of arterial blood pressure, which triggers the cerebral autoregulation mechanism. Induced hemodynamic oscillations are used in coherent hemodynamics spectroscopy to derive physiological parameters of interest for medical diagnostics. For example, our dedicated mathematical model translates typical near-infrared spectroscopy observables, like the amplitude and phase relationship of the oscillations of oxy- and deoxyhemoglobin concentrations into capillary and venous blood transit times, cutoff frequency of the autoregulation process, and other parameters related to microvascular blood volume. In this study, we focused on the phase relationship between the oscillations of oxyhemoglobin concentrations in three optical channels, two of which feature a short (5 mm) source-detector separation (sampling the scalp/skull only) and the third one features a long (30 mm) source-detector separation (sampling both extracerebral and cerebral tissues). The two main goals of the study were: a) to compare the coherence of induced and spontaneous oscillations; b) to assess if induced and spontaneous oscillations may be assumed to be uniform in the extracerebral layer. This was assessed by studying the phase relationship of oscillations in oxyhemoglobin concentration at the two short source-detector separations. About point a) we verified that induced oscillations have a higher incidence of coherence than spontaneous oscillations: 74% for induced oscillations, and 30% for spontaneous oscillations. About point b) the results show an overall trend for both spontaneous and induced oscillations to be homogeneous or "quasi-homogeneous" in the extracerebral tissue; however, we observed cases where a significant non-zero phase difference was measured, indicating spatial heterogeneity. We propose a method for taking into account the possible inhomogeneous behavior of the oscillations in the scalp/skull in order to increase the accuracy of measurements of cerebral hemodynamic oscillations.
机译：我们报告了研究的初步结果，用于调查两个人类受试者的头皮/头骨层上氧合血红蛋白浓度的诱导和自发振荡的空间均匀性。动脉血压的调节引起血流动力学振荡，从而触发脑自动调节机制。诱导的血流动力学振荡被用于相干血流动力学光谱中，以导出医学诊断所需的生理参数。例如，我们专用的数学模型将典型的近红外光谱观测结果转化为可观测的数据，例如氧合和脱氧血红蛋白浓度的振荡的幅度和相位关系到毛细血管和静脉血的通过时间，自动调节过程的截止频率以及其他与微血管血容量。在这项研究中，我们重点研究了三个光学通道中氧合血红蛋白浓度的振荡之间的相位关系，其中两个具有短（5毫米）的源-检测器间隔（仅对头皮/头骨进行采样），第三个具有长的特征（30毫米）源探测器分离（对脑外和脑组织都采样）。该研究的两个主要目标是：a）比较诱发和自发振荡的相干性； b）评估在脑外层是否可以假定诱发和自发振荡是否均匀。通过研究两个短暂的源-检测器分离处氧合血红蛋白浓度的振荡的相位关系来评估这一点。关于点a），我们验证了诱导振荡比自发振荡具有更高的相干发生率：诱导振荡为74％，自发振荡为30％。关于点b），结果显示出在脑外组织中自发性振动和诱导性振动均质性或“准均质性”的总体趋势；但是，我们观察到测量到显着的非零相位差的情况，表明存在空间异质性。我们提出了一种方法，考虑到头皮/头骨中振荡的可能不均匀行为，以提高脑血流动力学振荡测量的准确性。

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