Correlation between Decreased Parasympathetic Activity and Reduced Cerebrovascular Reactivity in Patients with Lacunar Infarct

Reduced cerebrovascular reactivity (CVR) was found in patients with recent lacunar infarct. However, its mechanisms were controversial. The breath holding maneuver as a vasodilatory stimulus is clinically useful for an estimation of cerebrovasomotor reactivity in well co-operative patients. Patients with lacunar infarct have no higher cortical dysfunction and remain well co-operation. The breath holding maneuver is feasible and safe to perform in patients with lacunar infarct. Autonomic nervous system regulates systemic vascular activity. Regulation of autonomic function to cerebrovascular reactivity has been reported in the literature. We examined the correlation between autonomic functions with frequency and nonlinear heart rate variability (HRV) and cerebrovascular reactivity in patients with lacunar infarct by application of breath holding maneuver. Fifteen patients with lacunar infarct (8 women, age 65.6 ± 13.61) and 16 healthy controls (11 women, age 27.33 ± 3.85) were continuously monitored at baseline before maneuver (basal phase), during CVR induction (experimental phase) with breath holding maneuver and after maneuver (recovery phase), for arterial blood pressure (ABP), electrocardiography (EKG), mean cerebral blood flow velocity (mCBFV) of middle cerebral arteries (MCA) by transcranial doppler (TCD). The short term-one minute HRV was analyzed from EKG signals for low frequency (LF)/ high frequency (HF) ratio, nonlinear of standard deviation 1 (SD1), standard deviation 2 (SD2), cardiac Sample Entropy (SampEn) and Shannon Entropy. Significant increasing in mCBFV, LF/HF ratio, SD2/SD1, Shannon Entropy and inversely decreasing SampEn during breath holding maneuver compared with baseline were found in both groups (p<0.05). The trend of cerebrovascular reactivity is similar in both groups. However, there were differences of mCBFV, systolic blood pressure (SysBP) in the whole phases (basal, experiment and recovery) between patients and controls (p<0.05). Less scattered signals of SD1 with low value in patient group were illustrated from Poincaré (p<0.05). This indicated less degree of parasympathetic drive in the patients compared to the controls. Moreover, significant positive correlation between systolic bloods pressure and mCBFV in patients suggests impact of autonomic control and cerebral blood flow on the patho-physiological mechanism of vasodilatation, triggered by hypercapnia from breath holding maneuver in patients with lacunar infarct. Reduction of cerebrovascular reactivity in patients with lacunar infarct may relate with decreased parasympathetic activity. Further study is required to demonstrate whether these findings mean mechanisms of lacunar infarct or the effect of hypertensive response.