Correlation between Baroreflex Sensitivity and Cerebral Autoregulation Index in Healthy Subjects

Francesca Gelpi1, Vlasta Bari1, Beatrice Cairo2, Beatrice De Maria3, Davide Tonon4, Gianluca Rossato4, Luca Faes5, Alberto Porta2
1Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, 2Department of Biomedical Sciences for Health, University of Milan, 3IRCCS Istituti Clinici Scientifici Maugeri, Milan, 4IRCCS Sacro Cuore Don Calabria Hospital, 5University of Palermo


Dynamic cerebral autoregulation (CA) is the physiological mechanism that maintains cerebral blood flow relatively constant despite transient changes in blood pressure. Its interaction with the baroreflex has been suggested but the functional relationship between the two mechanisms remains controversial. In this study we investigate this relationship in a healthy population undergoing an orthostatic challenge. Thirteen healthy subjects (age: 27 ± 8 yrs; 5 males) underwent electrocardiogram, arterial pressure (AP) and cerebral blood flow velocity (CBFV) recordings at supine resting and during 60° head-up tilt. CA was assessed via the autoregulation index (ARI) for spontaneous variations of mean AP and mean CBFV. ARI was computed by comparing the original mean CBFV series with that generated by the Tiecks’ model of CA driven by the original mean AP. The response of the Tiecks’ model was ranked according to its ability to maintain mean CBF relatively constant in spite of mean AP changes. The cardiac control and baroreflex were evaluated via autoregressive power spectral and transfer function analyses applied to systolic AP (SAP) and heart period (HP) variability. The power of HP variability in the high frequency (HF) band (HFHP), the power of SAP variability in the LF band (LFSAP) and the baroreflex sensitivity (BRS) in LF and HF bands were computed. The results show that HFHP and BRS decreased, while LFSAP increased with the orthostatic challenge. Conversely, ARI remained unvaried. At supine resting, we found a borderline positive correlation between ARI and LFSAP (r=0.578, p=4.90×10-2) and a stronger negative correlation with HFHP (r=-0.797, p=1.90×10-3) and BRS markers in LF (r=-0.897, p=7.76×10-5) and HF (r=-0.821, p=1.05×10-3). During head-up tilt, the correlations were lost. Our data indicated 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.