The Magnitude of the Postural Challenge Impacts on the Exponential Decay of the Baroreflex Impulse Response

Alberto Porta1, Francesca Gelpi2, Vlasta Bari2, Beatrice Cairo1, Beatrice De Maria3, Anielle Takahashi4, Aparecida Catai4
1Department of Biomedical Sciences for Health, University of Milan, 2Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, 3IRCCS Istituti Clinici Scientifici Maugeri, 4Department of Physical Therapy, Federal University of S�o Carlos


The magnitude of postural challenge is associated with baroreflex engagement. The rapidity of heart period (HP) response to changes of systolic arterial pressure (SAP) is linked to the bandwidth of the frequency response of the cardiac arm of the baroreflex. We recorded beat-to-beat HP and SAP variability in 17 healthy humans aged from 21 to 36 yrs (median = 29 yrs; 8 males) during graded head-up tilt (T) at 0, 15, 30, 45, 60, 75 and 90 degrees (T0, T15, T30, T45, T60, T75 and T90). A supine resting period preceded each T session. A bivariate autoregressive model with exogenous input was utilized to describe the dependence of HP variations on SAP changes. The model coefficients were estimated via traditional least squares approach solved via Choleski decomposition and the model order was optimized via Akaike figure of merit in the range from 4 to 14. The transfer function from SAP to HP was estimated and its impulse response was computed. The exponential decay constant (EDC) was calculated by fitting the absolute value of the impulse response with a mono-exponential function. A greater EDC indicates a faster response and a wider bandwidth of the cardiac baroreflex. The association between EDC and T angles was assessed via Pearson correlation coefficient r and type I error probability p was computed. EDC was 0.72±0.19 during T0 and progressively declined toward 0 with T angle (r=–0.426, p=2.85×10‒8). The decrease of EDC compared to T0 was significant during T45, T60, T75 and T90. The trend suggests that a reduced bandwidth of the cardiac baroreflex is associated with a more important postural challenge in agreement with the gradual vagal withdrawal and sympathetic activation. Bandwidth can be utilized to monitor the degree of involvement of cardiac baroreflex control with promising applications in pathological subjects.