Spontaneous baroreflex sensitivity estimates during graded bicycle exercise: a comparative study.

In the literature, several methods have been proposed for the assessment of the baroreflex sensitivity from spontaneous variability of heart period and systolic arterial pressure. The present study compares the most utilized approaches for the evaluation of the spontaneous baroreflex sensitivity (i.e. sequence-based, spectral, cross-spectral and model-based techniques) over a protocol capable of inducing a progressive decrease of the baroreflex sensitivity in the presence of a relevant respiratory drive (i.e. a stepwise dynamic bicycle exercise at 10%, 20% and 30% of the maximum nominal individual effort) in 16 healthy humans. Results demonstrated that the degree of correlation among the estimates is related to the structure of the model explicitly or implicitly assumed by the method and depends on the experimental condition (i.e. on the physiological mechanisms contemporaneously active with baroreflex, e.g. cardiopulmonary reflexes). However, even in the presence of a significant correlation, proportional and/or constant biases can be present, thus rendering spontaneous baroreflex estimates not interchangeable. We suggest that the comparison among different baroreflex sensitivity estimates might elucidate physiological mechanisms responsible for the relationship between heart period and systolic arterial pressure.

Multimodal signal processing for the analysis of cardiovascular variability.

Cardiovascular (CV) variability as a primary vital sign carrying information about CV regulation systems is reviewed by pointing out the role of the main rhythms and the various control and functional systems involved. The high complexity of the addressed phenomena fosters a multimodal approach that relies on data analysis models and deals with the ongoing interactions of many signals at a time. The importance of closed-loop identification and causal analysis is remarked upon and basic properties, application conditions and methods are recalled. The need of further integration of CV signals relevant to peripheral and systemic haemodynamics, respiratory mechanics, neural afferent and efferent pathways is also stressed.

Comparison of BRS estimates during mild dynamical exercise and recovery.

Ten estimates of baroreflex sensitivity (BRS) were compared during progressive graded exercise: they were computed from sequence method, spectral and cross-spectral analysis methods, and parametric model-based methods. Results showed baroreflex control of heart rate (HR) changes as a function of the intensity of exercise, as well as the resetting phenomenon. Sequence, spectral and cross-spectral methods generally provided higher estimates than parametric model-based ones. This bias was particularly evident during exercise, and in the high frequency (HF) respiratory band. Results may suggest that the interaction of respiration and baroreflex function play an important in the cardiovascular adaptation from rest to exercise and from exercise to the recovery period.

Heart rate and vasomotor control during exercise.

Spontaneous baroreflex function and vascular changes were assessed in young adults during dynamical mild exercise. Windkessel time constant was assessed by two different methods: two-element windkessel model, and by an autoregressive (AR) model, while the baroreflex sensitivity (BRS, ms/mmHg) was assessed by the sequence method. Results showed a change in the baroreflex control of heart rate (HR) with the severity of exercise, as well as the resetting phenomenon. Methods used to estimate the windkessel time constant were poorly correlated. Subject by subject correlation was found between the BRS and the time constant derived from the AR model within exercise and recovery period. These results may suggest that reflex mechanisms controlling HR may also participate in controlling peripheral circulation or, viceversa, BRS is influenced by vascular tone.