The measurement of autoregulatory delay by near-infrared spectroscopy (NIRS) has been proposed as an alternative technique to assess cerebral autoregulation, which is routinely assessed via transcranial Doppler sonography (TCD) in most centers. Comparitive studies of NIRS and TCD, however, are largely missing. We investigated whether cerebrovascular reserve (CVR), as assessed via TCD, correlates with the delay of the autoregulatory response to changes in arterial blood pressure (ABP) as assessed by NIRS, i.e., if impaired upstream vasomotor reactivity is reflected by downstream cortical autoregulation. Twenty patients with unilateral high-grade steno-occlusion of the middle cerebral artery (MCA) underwent bilateral multichannel NIRS of the cortical MCA distributions over a period of 6 min while breathing at a constant rate of 6 cycles/min to induce stable oscillations in ABP. The phase shift φ between ABP and cortical blood oxygenation was calculated as a measure of autoregulatory latency. In a subgroup of 13 patients, CO2 reactivity of the MCAs was determined by TCD to assess CVR in terms of normalized autoregulatory response (NAR). Mean phase shift between ABP and blood oxygenation was significantly increased over the hemisphere ipsilateral to the steno-occlusion (n = 20, p = 0.042). The interhemispheric difference Δφ in phase shift was significantly larger in patients with markedly diminished or exhausted CVR (NAR < 10) than in patients with normal NAR values (NAR ≥ 10) (p = 0.007). Within the MCA core distribution territory, a strong correlation existed between Δφ and CO2 reactivity of the affected MCA (n = 13, r = -0.78, p = 0.011). NIRS may provide an alternative or supplementary approach to evaluate cerebral autoregulation in risk assessment of ischemic events in steno-occlusive disease of cerebral arteries, especially in patients with insufficient bone windows for TCD.
Keywords: Cerebral autoregulation; Cerebrovascular reserve; Middle cerebral artery; Near-infrared spectroscopy; Steno-occlusive disease.