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Autonomic nervous system control of the heart
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1995
Year
HypertensionHeart FailureDiastolic FunctionAutonomic Nervous SystemKinesiologyExerciseSympathetic Nervous SystemApplied PhysiologyCardiologyAutonomic Nervous System AnatomyCardiac MechanicHealth SciencesEndurance Exercise TrainingAutonomic SystemNervous SystemReflex TachycardiaPhysiologyExercise PhysiologyBody Negative PressureElectrophysiologyCardiovascular PhysiologyMedicineArrhythmia
The study assessed how selective parasympathetic, sympathetic, and combined autonomic blockade affected hemodynamic responses to lower body negative pressure before and after eight months of endurance training in eight young men. Eight months of endurance training raised VO₂max by 27 % and blood volume by 16 %, lowered resting heart rate from 66 to 57 bpm, and enhanced vagal tone, while attenuating reflex tachycardia during LBNP and producing similar heart‑rate responses to LBNP under selective autonomic blockade, though beta‑1 blockade post‑training further reduced stroke volume. Abstract truncated at 250 words.
The purpose of this study was to assess hemodynamic responses to lower body negative pressure (LBNP) to -45 torr with selective cardiac parasympathetic (using atropine sulphate), sympathetic efferent (using metoprolol tartrate), and combined (atropine+metoprolol) blockade prior to and following 8 months of endurance exercise training in eight young men. Training resulted in significant increases of maximal oxygen uptake (27%) and blood volume (16%) and a decrease of baseline heart rate (HR, from 66 +/- 4 to 57 +/- 4 bpm). This training related bradycardia was exclusively determined by an enhanced vagal tone as there was no significant difference in intrinsic HR pre- to post-training and only atropine (pre: 100 +/- 3 vs post: 101 +/- 3 bpm), not metoprolol (pre: 56 +/- 3 vs post: 49 +/- 4 bpm), abolished the HR difference. The reflex tachycardia in the control experiment was significantly diminished following training. However, the increase in HR at LBNP -45 torr between pre- and post-training was similar after either atropine (+13 +/- 2 vs +14 +/- 1 bpm) or metoprolol (+8 +/- 1 vs +8 +/- 1 bpm). Reflex tachycardia was greater during atropine than metoprolol blockade and the sum of the HR increase during selective blockade (21 and 22 bpm) was greater when compared with the control (no blockade, 16 +/- 2 vs 11 +/- 2 bpm). There was no difference pre- to post-training in SV or Qc response to -45 torr LBNP during the control condition. However, selective beta 1-receptor blockade resulted in a greater decrease in SV to -45 torr LBNP post-training compared to pre-training (P < 0.05). (ABSTRACT TRUNCATED AT 250 WORDS)