Author(s): LÉO, D., LESPAGNOL, L., PARENT, P., BALESTRA, C., HERMANS, M.P., FONTAINE, P., BERTHOIN, S., GAMELIN, F.X., MELIN, A., VAMBERGUE, A., RABASA-LHORET, R., HEYMAN, E., Institution: UNIVERSITÉ DE LILLE, Country: FRANCE, Abstract-ID: 572

INTRODUCTION:
Reduced heart rate variability (HRV) is an early marker of cardiac autonomic impairment in type 1 diabetes (T1D)1 and has been implicated in the “dead-in-bed” hypothesis of sudden nocturnal death2. Exercise training and higher habitual physical activity (PA) improve HRV3, but single vigorous or prolonged PA bouts can transiently depress parasympathetic activity during the subsequent night3. In T1D, days included these types of bouts are often accompanied by large hypo- and hyperglycaemic excursions4. Outside of the context of PA these glycaemic fluctuations are known to acutely disturb autonomic function5. Whether, in everyday life, the combination of acute PA and glycaemic excursions reflects in altered nocturnal HRV in adults with T1D remains unstudied.
METHODS:
This secondary pooled analysis included adults with T1D (18-65 years) without known autonomic neuropathy monitored for 1-2 weeks in France and Belgium. Daytime PA was measured by hip-worn accelerometer, glycaemia by continuous glucose monitoring, and overnight R-R intervals by heart rate monitor. For each night, HRV was derived from a single 5-min slow-wave sleep segment. Glycaemic exposure was quantified for an upstream period (wake-up to the HRV segment) and the concomitant 5-min segment using time spent <3.9 and <3.0 mmol/L and >10 and >13.9 mmol/L. Linear mixed models with participant random intercepts tested associations of same-day moderate-to-vigorous PA (MVPA), usual MVPA, and glycaemic metrics with nocturnal HRV, adjusting for age, sex, diabetes duration, and HbA1c.
RESULTS:
Forty-three participants contributed 173 nights. Higher usual MVPA was associated with higher nocturnal vagal and global HRV. In contrast, higher same-day MVPA predicted lower RMSSD, HF power, SD1, and SDNN during the subsequent night. Greater upstream exposure to level 2 hyperglycaemia (>13.9 mmol/L) was associated with lower RMSSD, HF power, SD1, and SDNN. Other upstream or concomitant hyperglycaemia and hypoglycaemia measures showed no consistent associations.
CONCLUSION:
In adults with T1D without clinical autonomic neuropathy, higher habitual PA is associated with better nocturnal cardiac vagal modulation, whereas higher acute MVPA is followed by transient overnight reductions in parasympathetic activity and global HRV. Severe daytime hyperglycaemia is also independently associated with lower nocturnal HRV, supporting CGM-guided strategies that minimize marked hyperglycaemia on high-PA days.
References:
1 Ewing DJ, et al. BMJ 1982
2 Reno CM, et al. Diabetes 2019.
3 Sandercock GRH, et al. Medicine & Science in Sports & Exercise 2005
4 Riddell MC, et al. The Lancet Diabetes & Endocrinology 2017
5 Koivikko ML, et al. Diabetes 2005