Correlation Between Baroreflex Sensitivity and Cerebral Autoregulation Index in Healthy Subjects

Despite the acknowledged interaction between baroreflex and cerebral autoregulation (CA), their functional relationship remains controversial. The study investigates this relationship in a healthy population undergoing an orthostatic challenge. Thirteen healthy subjects (age:
$27\pm 8$
yrs; 5 males) underwent electrocardiogram, arterial pressure (AP) and cerebral blood flow velocity (CBFV) recordings at supine resting (REST) and during 60° head-up tilt (TILT). CA was assessed via the autoregulation index (ARI) from spontaneous variations of mean AP and mean CBFV. The cardiac control and baroreflex were evaluated via frequency domain and transfer function analyses applied to systolic AP and heart period variability. We found at REST a borderline positive correlation between ARI and indexes of sympathetic modulation and a stronger negative correlation with markers of vagal modulation and baroreflex sensitivity. Correlations were lost during TILT. Our data support the hypothesis that, when sympathetic drive is limited, vagal control and cardiac baroreflex have a compensatory effect on CA and sympathetic control could play a favorable role on CA.