Recovery of cerebral autoregulation during the first three months after acute ischaemic stroke

Abstract

Recovery of cerebral autoregulation during the first three months after acute ischaemic stroke - A longitudinal study using transcranial Doppler ultrasonography by Dr Joseph Shiu Kwong Kwan Cerebral autoregulation (CA) is a mechanism that maintains a constant cerebral blood flow over wide ranges of blood pressure (BP). CA is impaired after stroke and changes in cerebral blood flow may become passive to changes in BP. Manipulation of BP after stroke may worsen regional cerebral blood flow with possible clinical implications. However, little is known about the recovery of CA soon after stroke. In this study, we used transcranial Doppler (TCD) to examine the recovery of CA after ischaemic stroke. We studied ten stroke patients and eleven controls. Each patient was examined within seven days, at six weeks, and at three months. For each examination, cerebral blood flow velocity (CBFV) and BP were continuously recorded by bilateral TCD and Finapres, respectively. We examined the relationship between spontaneous oscillations of BP and CBFV, and between induced BP oscillations (by rhythmic handgrip) and CBFV, using cross-spectral transfer function analysis (calculation of phase, gain, and coherence). We demonstrated that, using rhythmic handgrip, CA changes over the first three months after stroke, although no difference was found between patients and controls. Moreover, these changes appear to affect the hemisphere contralateral to the ischaemia, which suggests that disturbances in cerebral haemodynamics after stroke may be global in nature. We also found that the competence of CA was dependent on the frequency of BP oscillations. This indicates that CA behaves as a high-pass filter system, even after ischaemic stroke. The combination of TCD and rhythmic handgrip appear to be a useful non-invasive method of assessing CA after stroke. This technique may become a useful clinical tool in the future.</p