Heart rate dynamics during cardio-pulmonary exercise testing are associated with glycemic control in individuals with type 1 diabetes

INTRODUCTION: This study investigated the degree and direction (k(HR)) of the heart rate to performance curve (HRPC) during cardio-pulmonary exercise (CPX) testing and explored the relationship with diabetes markers, anthropometry and exercise physiological markers in type 1 diabetes (T1DM). MATERIAL AND METHODS: Sixty-four people with T1DM (13 females; age: 34 ± 8 years; HbA(1c): 7.8 ± 1% (62 ± 13 mmol.mol(-1)) performed a CPX test until maximum exhaustion. k(HR) was calculated by a second-degree polynomial representation between post-warm up and maximum power output. Adjusted stepwise linear regression analysis was performed to investigate k(HR) and its associations. Receiver operating characteristic (ROC) curve was performed based on k(HR) for groups k(HR) < 0.20 vs. > 0.20 in relation to HbA(1c). RESULTS: We found significant relationships between k(HR) and HbA(1c) (β = -0.70, P < 0.0001), age (β = -0.23, P = 0.03) and duration of diabetes (β = 0.20, P = 0.04). Stepwise linear regression resulted in an overall adjusted R(2) of 0.57 (R = 0.79, P < 0.0001). Our data revealed also significant associations between k(HR) and percentage of heart rate at heart rate turn point from maximum heart rate (β = 0.43, P < 0.0001) and maximum power output relativized to bodyweight (β = 0.44, P = 0.001) (overall adjusted R(2) of 0.44 (R = 0.53, P < 0.0001)). ROC curve analysis based on k(HR) resulted in a HbA(1c) threshold of 7.9% (62 mmol.mol(-1)). CONCLUSION: Our data demonstrate atypical HRPC during CPX testing that were mainly related to glycemic control in people with T1DM.