This study compared spontaneous baroreflex sensitivity (BRS) estimates obtained from an identical set of data by 11 European centers using different methods and procedures. Noninvasive blood pressure (BP) and ECG recordings were obtained in 21 subjects, including 2 subjects with established baroreflex failure. Twenty-one estimates of BRS were obtained by methods including the two main techniques of BRS estimates, i.e., the spectral analysis (11 procedures) and the sequence method (7 procedures) but also one trigonometric regressive spectral analysis method (TRS), one exogenous model with autoregressive input method (X-AR), and one Z method. With subjects in a supine position, BRS estimates obtained with calculations of alpha-coefficient or gain of the transfer function in both the low-frequency band or high-frequency band, TRS, and sequence methods gave strongly related results. Conversely, weighted gain, X-AR, and Z exhibited lower agreement with all the other techniques. In addition, the use of mean BP instead of systolic BP in the sequence method decreased the relationships with the other estimates. Some procedures were unable to provide results when BRS estimates were expected to be very low in data sets (in patients with established baroreflex failure). The failure to provide BRS values was due to setting of algorithmic parameters too strictly. The discrepancies between procedures show that the choice of parameters and data handling should be considered before BRS estimation. These data are available on the web site (http://www.cbi.polimi.it/glossary/eurobavar.html) to allow the comparison of new techniques with this set of results.

Heart rate variability is a recognized parameter for assessing autonomous nervous system activity. Fourier transform, the most commonly used method to analyze variability, does not offer an easy assessment of its dynamics because of limitations inherent in its stationary hypothesis. Conversely, wavelet transform allows analysis of nonstationary signals. We compared the respective yields of Fourier and wavelet transforms in analyzing heart rate variability during dynamic changes in autonomous nervous system balance induced by atropine and propranolol. Fourier and wavelet transforms were applied to sequences of heart rate intervals in six subjects receiving increasing doses of atropine and propranolol. At the lowest doses of atropine administered, heart rate variability increased, followed by a progressive decrease with higher doses. With the first dose of propranolol, there was a significant increase in heart rate variability, which progressively disappeared after the last dose. Wavelet transform gave significantly better quantitative analysis of heart rate variability than did Fourier transform during autonomous nervous system adaptations induced by both agents and provided novel temporally localized information.

Beat-by-beat variations in blood pressure and RR-interval are interrelated by the actions of baroreflex and non-baroreflex responses. This study had two purposes: (1) to examine the spontaneous relationships between RR-interval and systolic blood pressure to determine the relative occurrence of baroreflex and non-baroreflex responses in humans, and (2) to compare the beat-sequence method with a cross spectral estimate of the baroreflex response slope. Eight healthy men were studied during 10 h of quiet, seated rest, and six men and three women were studied during rest, rest plus fixed pace breathing, and a cold pressor test. RR-interval and continuous, non-invasive arterial blood pressure were measured with a computerized system. A baroreflex sequence was defined by a series of at least three consecutive heart beats in which systolic pressure and the following RR-interval either both increased or both decreased. A non-baroreflex relationship was defined by sequences of at least three beats by opposite directional changes of RR-interval and systolic pressure of that beat. The results showed that there were approximately 30% as many non-baroreflex compared to baroreflex slopes. Individual subject mean baroreflex and non-baroreflex slopes were highly correlated (r = 0.72, P < 0.001). Absolute slope values were not different, and they were unaffected by time, fixed pace breathing, or cold pressor test. The data showed the relatively simple beat-by-beat sequence method to yield spontaneous baroreflex response slopes that were quantitatively similar to, and highly correlated with (r = 0.85-0.94), baroreflex response slopes calculated by spectral analysis methods.

Non-technical summary It is still unknown how the autonomic nervous system influences the fractal dynamics of cardiovascular signals. We show that in supine volunteers vagal and sympathetic outflows contribute differently to the fractal structures of heart rate and blood pressure. The vagal outflow contributes with a 'white-noise' component to the heart rate dynamics, indirectly influencing also the fractal dynamics of blood pressure. The sympathetic outflow contributes with a Brownian motion component to the heart rate dynamics, increasing long-term fractal coefficients, without affecting long-term coefficients of blood pressure. Results are explained by the different distribution and dynamics of acetylcholine receptors and of α-and β-adrenergic receptors. Our findings may allow better delineating alterations of cardiovascular fractal dynamics in physiological and pathophysiological settings.Abstract How the autonomic nervous system influences the fractal dynamics of heart rate (HR) and blood pressure (BP) remains unclear. The purpose of our study was to separately assess cardiac vagal and sympathetic (cardiac vs. vascular) influences on fractal properties of HR and BP as described by scale exponents of detrended fluctuation analysis (DFA). R-R intervals, systolic and diastolic BP were measured in nine supine volunteers before and after administration of autonomic blocking agents (atropine, propranolol, atropine + propranolol, clonidine). Spectra of DFA scale exponents, α(t), were calculated for scales between 5 and 100 s. HR and BP scale structures differed at baseline, being α(t) of HR <1, with a minimum between 10 and 20 s followed by a higher plateau between 40 to 80 s, while α(t) of BP decreased with t from values >1. Comparison of atropine and propranolol with baseline and combined cardiac parasympathetic and sympathetic blockade (atropine + propranolol) indicated opposite influences of vagal and cardiac sympathetic outflows on HR exponents. The vagal outflow adds white-noise components, amplifying differences with BP exponents; the cardiac sympathetic outflow adds Brownian motion components at short scales and contributes to the plateau between 40 and 80 s. Overall sympathetic inhibition by clonidine decreased short-and long-term exponents of HR, and short-term exponents of BP, so that their α(t) spectra had different means but similar profiles. Therefore, cardiac vagal, cardiac sympathetic and vascular sympathetic outflows contribute differently to HR and BP fractal structures. Results are explained by different distribution and dynamics of acetylcholine receptors and of α-and β-adrenergic receptors between heart and vasculature. Abbreviations BP, blood pressure; DBP, diastolic blood pressure; DFA, detrended fluctuation analysis; HF, high frequency; HR, heart rate; LF, low frequency; MAP, mean arterial pressure; SBP, systolic blood pressure; VLF, very low frequency.