title: Insulin levels and HOMA index are associated with exercise capacity in patients with type 2 diabetes and coronary artery disease.
abstract: BACKGROUND
  Previous studies on type 2 diabetes have shown an association between exercise capacity and insulin resistance. In patients with coronary artery disease (CAD) exercise capacity is often reduced due to exercise-induced ischemia. We have investigated the association between glucometabolic control, including the homeostatic model assessment (HOMA) of insulin resistance, and exercise capacity in patients with type 2 diabetes and CAD with and without exercise-induced ischemia.
  
  
  METHODS
  In 137 patients (age 63.1 ± 7.9) cardiopulmonary exercise testing on treadmill was performed using a modified Balke protocol. The highest oxygen uptake (VO2peak) was reported as 30-s average. Fasting blood samples were drawn for determination of glucose, insulin and HbA1c. Insulin resistance (IR) was assessed by the HOMA2-IR computer model. Exercise-induced ischemia was defined as angina and/ or ST-depression in ECG ≥ 0.1 mV during the exercise test.
  
  
  RESULTS
  HOMA2-IR was inversely correlated to VO2peak (r = -0.328, p < 0.001), still significant after adjusting for age, gender, smoking and BMI. Patients with HOMA2-IR above the median value (1.3) had an adjusted odds ratio of 3.26 (95 % CI 1.35 to 7.83, p = 0.008) for having VO2peak below median (23.8 mL/kg/min). Insulin levels were inversely correlated to VO2peak (r = -0.245, p = 0.010), also after adjusting for age and gender, but not after additional adjustment for BMI. The correlation between HOMA2-IR and VO2peak was also significant in the subgroups with (n = 51) and without exercise-induced ischemia (n = 86), being numerically stronger in the group with ischemia (r = -0.430, p = 0.003 and r = -0.276, p = 0.014, respectively). Fasting glucose and HbA1c were not correlated with VO2peak or AT.
  
  
  CONCLUSIONS
  Insulin resistance, as estimated by fasting insulin and the HOMA index, was inversely associated with exercise capacity in patients with type 2 diabetes and CAD, the association being more pronounced in the subgroup with exercise-induced ischemia. These results indicate that insulin resistance is related to exercise capacity in type 2 diabetic patients with CAD, possibly even more so in patients with exercise-induced ischemia compared to those without.
authors.affiliation: Center for Clinical Heart Research, Department of Cardiology, Oslo University Hospital Ulleval, PO box 4956, Nydalen N-0424, Oslo, Norway. rune.byrkjeland@ous-hf.no.
authors.forename: Rune
authors.initials: R
authors.lastname: Byrkjeland
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Edvardsen
authors.forename: Ida Unhammer
authors.initials: IU
authors.lastname: Njerve
authors.forename: Harald
authors.initials: H
authors.lastname: Arnesen
authors.forename: Ingebjørg
authors.initials: I
authors.lastname: Seljeflot
authors.forename: Svein
authors.initials: S
authors.lastname: Solheim