title: Dynamic blood pressure control and middle cerebral artery mean blood velocity variability at rest and during exercise in humans.
abstract: OBJECTIVE
  Cardiac failure and ischaemic heart disease patients receive standard of care cardiac beta(1)-adrenergic blockade medication. Such medication reduces cardiac output and cerebral blood flow. It is unknown whether the beta(1)-adrenergic blockade-induced reduction of cardiac output in the presence of an exercise-induced reduction in cardiac-arterial baroreflex gain affects cerebral blood flow variability. This study evaluated the influence of cardiac output variability on beat-to-beat middle cerebral artery mean blood velocity (MCA V(mean)) during exercise with and without cardiac beta(1)-adrenergic blockade.
  
  
  METHODS
  Eight men (22 +/- 1 years; mean +/- SE) performed 15 min bouts of moderate (105 +/- 11 W) and heavy (162 +/- 8 W) intensity cycling before and after cardio-selective beta(1)-adrenergic blockade (0.15 mg kg(-1) metoprolol). The relationship between changes in cardiac output or mean arterial pressure (MAP) and MCA V(mean) as well as cardiac-arterial baroreflex gain were evaluated using transfer function analysis.
  
  
  RESULTS
  Both exercise intensities decreased the low frequency (LF) transfer function gain between cardiac output and MCA V(mean) (P < 0.05) with no significant influence of beta(1)-blockade. In contrast, the LF transfer function gain between MAP and MCA V(mean) remained stable also with no significant influence of metoprolol (P > 0.05). The LF transfer function gain between MAP and HR, an index of cardiac-arterial baroreflex gain, decreased from rest to heavy exercise with and without beta(1)-blockade (P < 0.05).
  
  
  CONCLUSIONS
  These findings suggest that the exercise intensity related reduction in cardiac-arterial baroreflex function at its operating point does not influence the dynamic control of MCA V(mean), even when the ability of exercise-induced increase in cardiac output is reduced by cardiac beta(1)-adrenergic blockade.
authors.affiliation: Department of Integrative Physiology, University of North Texas Health Science Center, Fort Worth, TX 76107, USA. sogoh@hsc.unt.edu
authors.forename: S
authors.initials: S
authors.lastname: Ogoh
authors.forename: M K
authors.initials: MK
authors.lastname: Dalsgaard
authors.forename: N H
authors.initials: NH
authors.lastname: Secher
authors.forename: P B
authors.initials: PB
authors.lastname: Raven
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000328:Adult; D000704:Analysis of Variance; D017704:Baroreflex; D001783:Blood Flow Velocity / Q000187:drug effects; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000187:drug effects / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000379:methods; D006706:Homeostasis; D006801:Humans; D008297:Male; D008790:Metoprolol / Q000494:pharmacology; D020768:Middle Cerebral Artery; D010807:Physical Endurance / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D017585:Ultrasonography, Doppler, Transcranial
chemical_list: D000319:Adrenergic beta-Antagonists; D008790:Metoprolol