Orthostatic test shows higher systolic blood pressure and sympathetic response in uncomplicated type 1 diabetes patients with normal V̇O vs. healthy controls.

Purpose: Cardiovascular autonomic neuropathy remains underdiagnosed in type 1 diabetes mellitus, posing a risk for severe complications, particularly in patients with lowered V̇O, compared to controls. This study aimed to determine whether heart rate variability during cardiovascular autonomic reflex tests reveals early signs of cardiovascular autonomic neuropathy in patients with uncomplicated type 1 diabetes mellitus and normal cardiovascular fitness, compared to healthy controls.

Methods: A type 1 diabetes mellitus group (n = 14) with no other diagnosed diseases (diabetes duration 15 ± 7 years) and a control group (n = 31) underwent deep breathing test, passive orthostatic test, and cardiopulmonary exercise test. Participants were assessed for heart rate variability, heart rate, blood pressure, and V̇O (mL/min/kg).

Results: Participant characteristics, including V̇O (mL/min/kg), showed no significant differences. The type 1 diabetes mellitus group had higher systolic blood pressure during the supine phase of the orthostatic test than healthy controls (131.6 ± 14.7 mmHg vs. 122.4 ± 10.8 mmHg, p = 0.022). After 5 mins in the upright position, systolic blood pressure (132.2 ± 20.6 mmHg vs. 118.7 ± 11.7 mmHg, p = 0.036), heart rate (85 (76; 89) bpm vs. 75 (72; 83) bpm, p = 0.013), and the root mean square of successive RR interval differences (20.22 (11.22; 27.42) vs. 27.11 (19.90; 35.52), p = 0.033) were significantly different compared to controls.

Conclusion: Patients with uncomplicated type 1 diabetes mellitus, despite having normal cardiorespiratory fitness, exhibited higher systolic pressure and greater sympathetic activation in orthostatic tests, suggesting subclinically altered cardiovascular autonomic function.