title: A six-month exercise intervention in subclinical diabetic heart disease: effects on exercise capacity, autonomic and myocardial function.
abstract: OBJECTIVE
  Autonomic dysfunction may contribute to the etiology and exercise intolerance of subclinical diabetic heart disease. This study sought the efficacy of exercise training for improvement of peak oxygen uptake (VO₂(peak)) and cardiac autonomic function in type 2 diabetic patients with non-ischemic subclinical left-ventricular (LV) dysfunction.
  
  
  METHODS
  Forty-nine type 2 diabetic patients with early diastolic tissue Doppler velocity >1 standard deviation below the age-based mean entered an exercise intervention (n=24) or usual care (n=25) for 6-months (controlled, pre-/post- design). Co-primary endpoints were treadmill VO₂(peak) and 5-min heart-rate variability (by the coefficient of variation of normal RR intervals [CVNN]). Autonomic function was additionally assessed by resting heart-rate (for sympathovagal balance estimation), baroreflex sensitivity, cardiac reflexes, and exercise/recovery heart-rate profiles. Echocardiography was performed for LV function (systolic/diastolic tissue velocities, myocardial deformation) and myocardial fibrosis (calibrated integrated backscatter).
  
  
  RESULTS
  VO₂(peak) increased by 11% during the exercise intervention (p=0.001 vs. -1% in controls), but CVNN did not change (p=0.23). Reduction of resting heart-rate in the intervention group (p<0.05) was associated with an improvement in the secondary endpoint of heart-rate variability total spectral power (p<0.05). However, baroreflex sensitivity, cardiac reflexes, and exercise/recovery heart-rate profiles showed no significant benefit. No effects on LV function were observed despite favorable reduction of calibrated integrated backscatter in the intervention group (p<0.05).
  
  
  CONCLUSIONS
  The exercise intolerance of subclinical diabetic heart disease was amenable to improvement by exercise training. Despite a reduction in resting heart-rate and potential attenuation of myocardial fibrosis, no other cardiac autonomic or LV functional adaptations were detected.
authors.affiliation: School of Human Movement Studies, University of Queensland, Brisbane, Australia; Baker IDI Heart and Diabetes Institute, Melbourne, Australia. Electronic address: julian.sacre@bakeridi.edu.au.
authors.forename: Julian W
authors.initials: JW
authors.lastname: Sacre
authors.affiliation: School of Medicine, University of Queensland, Brisbane, Australia.
authors.forename: Christine L
authors.initials: CL
authors.lastname: Jellis
authors.affiliation: School of Medicine, University of Queensland, Brisbane, Australia.
authors.forename: Carly
authors.initials: C
authors.lastname: Jenkins
authors.affiliation: School of Medicine, University of Queensland, Brisbane, Australia.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Haluska
authors.affiliation: School of Electrical & Electronic Engineering, University of Adelaide, Adelaide, Australia.
authors.forename: Mathias
authors.initials: M
authors.lastname: Baumert
authors.affiliation: School of Human Movement Studies, University of Queensland, Brisbane, Australia.
authors.forename: Jeff S
authors.initials: JS
authors.lastname: Coombes
authors.affiliation: School of Medicine, University of Queensland, Brisbane, Australia; Menzies Research Institute Tasmania, Hobart, Australia.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Marwick
mesh_terms: D000368:Aged; D001341:Autonomic Nervous System / Q000503:physiopathology*; D015415:Biomarkers; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000150:complications*; D058065:Diabetic Cardiomyopathies / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000628:therapy*; D042241:Early Diagnosis; D018618:Echocardiography, Doppler, Color; D015444:Exercise; D017079:Exercise Tolerance; D005260:Female; D005500:Follow-Up Studies; D006352:Heart Ventricles / Q000000981:diagnostic imaging / Q000294:innervation / Q000503:physiopathology*; D006801:Humans; D057194:Intention to Treat Analysis; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D010352:Patient Dropouts; D055070:Resistance Training; D012720:Severity of Illness Index; D018487:Ventricular Dysfunction, Left / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000628:therapy*
chemical_list: D015415:Biomarkers
keywords: Diabetic cardiomyopathies; Exercise tolerance; Heart rate; Left Ventricular function; Type 2 Diabetes mellitus