Frequency-dependent baroreflex control of blood pressure and heart rate during physical exercise.

Background: It is widely recognised that during exercise vagal heart rate control is markedly impaired but blood pressure control may or may not be retained. We hypothesised that this uncertainty arose from the differing responses of the vagus (fast) and sympathetic (slow) arms of the autonomic effectors, and to differing sympatho-vagal balance at different exercise intensities.

Methods And Results: We studied 12 normals at rest, during moderate (50% maximal heart rate) and submaximal (80% maximal heart rate) exercise.

Autonomic modulation of heart rate during obstructive versus central apneas in patients with sleep-disordered breathing.

Sleep-disordered breathing is associated with an altered sympathovagal balance determined by the nocturnal cyclic alternating of apneas and hyperventilation. The aim of this study was to determine whether the autonomic modulation of heart rate during obstructive apneas (OA) and central apneas (CA) in patients with sleep-disordered breathing is different. Therefore, by using the time-varying Wigner-Ville transform spectral analysis we described, in 17 patients, the time course of the low-frequency (LF) and the high-frequency (HF) components of the interbeat interval (R-R interval) reflecting, at large, respectively, the sympathetic and the parasympathetic modulation, during OA (n = 185) and CA (n = 51) and during the postapneic hyperventilation.