Using Cross-Correlation Function to Assess Dynamic Cerebral Autoregulation in Response to Posture Changes for Stroke Patients

In this study, time-domain cross-correlation function was applied to evaluate the relationship between blood pressure and cerebral blood flow velocity signals acquiring from healthy subjects and stroke patients both in supine and head-up tilt positions to evaluate the effect of posture change. 10 stroke patients and 11 healthy subjects were included in this study. Results revealed that the mean arterial blood pressure (MABP) values of stroke patients in response to posture changes were reduced. However, MABP values in healthy subjects were become higher in head-up tilt position. Both of MABP values of healthy subjects in supine and head-up tilt were significantly lower than those in stroke patients (p<0.05). On the other hand, mean cerebral blood flow velocity (MCBFV) in healthy subjects remain constant. However, the values in stroke patients reduced in response to head-up tilt. In the results of cross-correlation function (CCF) analysis, max CCF values in healthy subjects were significantly higher than those in stroke patients (p<0.05) in both supine and head-up tile positions. It might indicate correlation of MABP and MCBFV was higher in healthy subjects. The max CCF index in stroke patients were close to 0 second in both positions (supine: 0.35 +/- 3.36 sec; head-up tilt: -0.29 +/- 3.20 sec). In healthy subjects, max CCF values should be around 2 seconds. Hence, it indicated the phase difference almost did not exist between MABP and MCBFV. This reveals the buffer function of CA were lower in stroke patients. Therefore, CA in stroke patients might be impaired by the results in response to posture changes.