title: Impaired β-cell function attenuates training effects by reducing the increase in heart rate reserve in patients with myocardial infarction.
abstract: BACKGROUND
  Insulin resistance (IR) is characterized as a metabolic disorder syndrome that is upstream of hypertension, dyslipidemia, and diabetes mellitus (DM). This study investigated exercise training effects on the exercise tolerance and heart rate dynamics in patients with IR or pancreatic β-cell dysfunction.
  
  
  METHODS
  Seventy patients (mean age, 60.1 years) with myocardial infarction (MI) participating in a phase II cardiac rehabilitation program were studied. Patients diagnosed with DM were excluded. Homeostasis model-assessment indices were used to divide patients into three groups - A: IR; B: normal; and C: β-cell dysfunction. A cardiopulmonary exercise test (CPX) was performed and peak oxygen uptake (V˙O2) was measured. After baseline testing, subjects participated in a supervised, combined aerobic and resistance exercise program.
  
  
  RESULTS
  Peak V˙O2 at baseline was comparable among the three groups, and it improved after training in all groups (p<0.05). However, both the increase and percentage increase in peak V˙O2 were smaller in Group C than in Group A (p<0.05). Heart rate (HR) reserve (peak HR-rest HR), and HR recovery immediately 1min after exercise during CPX were calculated in 45 patients who were not taking negative chronotropic agents. Group C alone did not show any significant increase in HR reserve. HR reserve at both baseline and after training had significant positive correlations with peak V˙O2. HR recovery was 1.9 beats/min lower in group C than group A, but this was not significant. HR recovery in group C did not increase after cardiac rehabilitation.
  
  
  CONCLUSIONS
  Impaired HR reserve increase after training in patients with pancreatic β-cell dysfunction attenuates exercise training effects on functional capacity. Comprehensive treatment including vigorous exercise training will be needed in such prediabetic patients.
authors: Department of Cardiology, St. Marianna University Yokohama City Seibu Hospital, Yokohama, Japan. Electronic address: omiya@marianna-u.ac.jp.
authors: Kazuto
authors: K
authors: Omiya
authors: Department of Cardiology, St. Marianna University Yokohama City Seibu Hospital, Yokohama, Japan.
authors: Keisuke
authors: K
authors: Minami
authors: Department of Cardiology, St. Marianna University Yokohama City Seibu Hospital, Yokohama, Japan.
authors: Yukio
authors: Y
authors: Sato
authors: Department of Cardiology, St. Marianna University Yokohama City Seibu Hospital, Yokohama, Japan.
authors: Manabu
authors: M
authors: Takai
authors: Department of Cardiology, St. Marianna University Yokohama City Seibu Hospital, Yokohama, Japan.
authors: Eiji
authors: E
authors: Takahashi
authors: Department of Cardiology, St. Marianna University Yokohama City Seibu Hospital, Yokohama, Japan.
authors: Akio
authors: A
authors: Hayashi
authors: Department of Cardiology, St. Marianna University Yokohama City Seibu Hospital, Yokohama, Japan.
authors: Masahiro
authors: M
authors: Yamauchi
authors: Department of Cardiology, St. Marianna University School of Medicine, Kawasaki, Japan.
authors: Kengo
authors: K
authors: Suzuki
authors: Department of Cardiology, St. Marianna University School of Medicine, Kawasaki, Japan.
authors: Yoshihiro J
authors: YJ
authors: Akashi
authors: Department of Cardiology, St. Marianna University School of Medicine, Kawasaki, Japan.
authors: Naohiko
authors: N
authors: Osada
authors: Department of Rehabilitation Medicine, St. Marianna University School of Medicine Hospital, Kawasaki, Japan.
authors: Kazuhiro P
authors: KP
authors: Izawa
authors: Department of Rehabilitation Medicine, St. Marianna University School of Medicine Hospital, Kawasaki, Japan.
authors: Satoshi
authors: S
authors: Watanabe
mesh_terms: D000368:Aged; D003920:Diabetes Mellitus; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D050417:Insulin-Secreting Cells / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000503:physiopathology*; D010101:Oxygen Consumption; D064797:Physical Conditioning, Human
keywords: Cardiac rehabilitation; Heart rate recovery; Heart rate reserve; Insulin resistance; Pancreatic β-cell function