This study aimed to determine the glycemic responses to cardiopulmonary exercise testing (CPET) in individuals with type 1 diabetes (T1D) and to explore the influence of starting blood glucose (BG) concentrations on subsequent CPET outcomes.
This study was a retrospective, secondary analysis of pooled data from three randomized crossover trials using identical CPET protocols. During cycling, cardiopulmonary variables were measured continuously, with BG and lactate values obtained minutely via capillary earlobe sampling. Anaerobic threshold was determined using ventilatory parameters. Participants were split into (i) euglycemic ([Eu] >3.9 to ≤10.0 mmol·L−1, n = 26) and (ii) hyperglycemic ([Hyper] >10.0 mmol·L−1, n = 10) groups based on preexercise BG concentrations. Data were assessed via general linear modeling techniques and regression analyses. P values of ≤0.05 were accepted as significant.
Data from 36 individuals with T1D (HbA1c, 7.3% ± 1.1% [56.0 ± 11.5 mmol·mol−1]) were included. BG remained equivalent to preexercise concentrations throughout CPET, with an overall change in BG of −0.32 ± 1.43 mmol·L−1. Hyper had higher HR at peak (+10 ± 2 bpm, P = 0.04) and during recovery (+9 ± 2 bpm, P = 0.038) as well as lower O2 pulse during the cool down period (−1.6 ± 0.04 mL per beat, P = 0.021). BG responses were comparable between glycemic groups. Higher preexercise BG led to greater lactate formation during exercise. HbA1c was inversely related to time to exhaustion (r = −0.388, P = 0.04) as well as peak power output (r = −0.355, P = 0.006) and O2 pulse (r = −0.308, P = 0.015).
This study demonstrated 1) stable BG responses to CPET in patients with T1D; 2) although preexercise hyperglycemia did not influence subsequent glycemic dynamics, it did potentiate alterations in various cardiac and metabolic responses to CPET; and 3) HbA1c was a significant factor in the determination of peak performance outcomes during CPET.