Influence of time of day on plasma glucose responses to cardiopulmonary exercise testing in individuals with type 1 diabetes using insulin pump therapy. A retrospective pooled analyses of data from adults with type 1 diabetes.

BACKGROUND
Though cardiopulmonary exercise testing (CPET) is frequently performed in clincial research as part of a screening procedure, information on whether the time of day at which it is performed influences physiologic or metabolic outcomes and whether this needs consideration for pre-test preparatory guidelines and/or data intepretation in people with type 1 diabetes (T1D) is yet to be established.
AIM
To explore the influence of the time of day on plasma glucose dynamics during CPET in individuals with T1D using insulin pump therapy.
METHODS
Twenty-three adults with T1D using insulin pump, or hybrid closed-loop, therapy undertook an incremental CPET to volitional exhaustion on a cycle ergometer. Participants refrained from bolus insulin dose administration and meal consumption for at least 90 minutes prior to laboratory arrival. Venous-derived plasma glucose concentrations were obtained every 3 minutes during exercise as well as at peak and recovery periods. Participants were retrospectively stratified into groups based on commencing exercise during the morning (<1200 [AM]) or afternoon (≥1200 [PM] Table 1). Data were compared using general linear modelling techniques and independent t-tests with p values ≤0.05 accepted for statistical significance.
RESULTS
There were no differences between groups in any anthropometric- or diabetes-related characteristics (Table 1), nor were there differences in any cardiopulmonary responses to CPET. Plasma glucose levels remained equivalent to rested concentrations throughout testing regardless of time of day (F [1,21] = 0.142, p=0.71. Figure 1 A). However, the small decline in glucose with afternoon exercise differed significantly to the rise observed during morning tests (PM: -0.3±0.6 mmol.L-1 vs. AM: +0.5±1.1 mmol.L-1, p=0.04. Figure 1 B).
CONCLUSION
These data suggest that the expected change in glucose during CPET is neglectable, whether performed in the morning or afternoon. This information may serve useful for informing appropriate insulin therapy management of people with T1D ahead of CPET commencement.