title: Frequency-dependent baroreflex control of blood pressure and heart rate during physical exercise.
abstract: 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.
  
  
  RESULTS
  We studied 12 normals at rest, during moderate (50% maximal heart rate) and submaximal (80% maximal heart rate) exercise. The carotid baroreceptors were stimulated by sinusoidal neck suction at the frequency of the spontaneous high- (during moderate exercise) and low-frequency (during submaximal) fluctuations in heart period and blood pressure. The increases in these oscillations induced by neck suction were measured by autoregressive spectral analysis. At rest neck stimulation increased variability at low frequency (RR: from 6.99+/-0.24 to 8.87+/-0.18 ln-ms2; systolic pressure: from 3.05+/-1.7 to 4.09+/-0.17 ln-mm Hg2) and high frequency (RR: from 4.67+/-0.25 to 6.79+/-0.31 ln-ms2; systolic pressure: from 1.93+/-0.2 to 2.67+/-0.125 ln-mm Hg2) (all p<0.001). During submaximal exercise RR variability decreased but systolic pressure variability rose (p<0.01 vs rest); during submaximal exercise low-frequency neck stimulation increased the low-frequency fluctuations in blood pressure (2.35+/-0.51 to 4.25+/-0.38 ln-mm Hg2, p<0.05) and RR. Conversely, neck suction at high frequency was ineffective on systolic pressure, and had only minor effects on RR interval during moderate exercise.
  
  
  CONCLUSIONS
  During exercise baroreflex control is active on blood pressure, but the efferent response on blood pressure and heart rate is only detected during low frequency stimulation, indicating a frequency-dependent effect.
authors.affiliation: Dipartimento di Medicina Interna IRCCS S. Matteo and University of Pavia, Italy.
authors.forename: Giammario
authors.initials: G
authors.lastname: Spadacini
authors.forename: Claudio
authors.initials: C
authors.lastname: Passino
authors.forename: Stefano
authors.initials: S
authors.lastname: Leuzzi
authors.forename: Felice
authors.initials: F
authors.lastname: Valle
authors.forename: Massimo
authors.initials: M
authors.lastname: Piepoli
authors.forename: Alessandro
authors.initials: A
authors.lastname: Calciati
authors.forename: Peter
authors.initials: P
authors.lastname: Sleight
authors.forename: Luciano
authors.initials: L
authors.lastname: Bernardi
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology*; D017536:Carotid Artery, Common / Q000502:physiology; D004562:Electrocardiography; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D011311:Pressoreceptors / Q000502:physiology; D012016:Reference Values; D012143:Respiratory Physiological Phenomena; D012146:Rest / Q000502:physiology