Complexity of autonomic control during cerebrovascular reactivity

Complexity of autonomic regulation affects the systemic vascular, but little is known about its influence on cerebrovascular regulation. In this study, we examine the complexity of neuromodulation by frequency and nonlinear heart rate variability (HRV) to cerebral reserve function during cerebrovascular reactivity (CVR) by breath holding induced - hypercapnia and subsequently, cerebral vasodilatation. Method: 16 healthy controls were monitored during CVR for arterial blood pressure (ABP), electrocardiography (EKG) and mean cerebral blood flow velocity (mCBFV) of middle cerebral arteries (MCA) with transcranial Doppler. Short term-one minute HRV was analyzed for LF/HF ratio, nonlinear of SD1/SD2 and SampEn. Result: An increase in LF/HF ratio from 0.79 ± 0.85 to 2.05 ± 1.38 (p<;0.05) was evident. Significant decrease of SD1/SD2 and SampEn during the experiment phase indicates predominant of parasympathetic activity associated with less irregularity. Less scatter signals of SD1 and SD2 with low value was illustrated from Poincaré plot. Significant increase in mCBFV during breath holding and recovery compared with baseline suggests hypercapnia induced-vasodilatation. Moreover, significant negative correlation between SD1/SD2 vs mCBFV suggests complexity of ANS control and cerebral blood flow. This is first report that nonlinear HRV is applied to physiological mechanism of vasodilatation triggered by hypercapnia from CVR. In conclusion, best fit of nonlinear HRV with frequency domain is proposed in CVR assessment which it will be applied to small artery stroke.