Wearable device measuring HRV helps detect hypoglycaemia

A wearable device measuring real-time heart rate variability (HRV) could be an effective way of detecting hypoglycaemia in type 1 diabetes (T1D) patients with impaired awareness of hypoglycaemia (IAH), according to a recent study.

“[H]ypoglycaemia-induced changes in HRV are retained in the majority of people with T1D and IAH, despite almost complete blunting of symptomatic perception of hypoglycaemia,” the researchers said, noting “that these changes in HRV can be detected by a wearable device. Considering developments in wearable devices and data analytics, real-time HRV seems usable for detection of hypoglycaemia in patients with IAH.”

Using the VitalConnect HealthPatch, the researchers measured HRV in real-time in 12 T1D patients (mean age 57±12 years, eight women), who underwent a modified hyperinsulinaemic euglycaemic hypoglycaemic clamp. HRV was measured as the root mean square of successive differences (RMSSD) and low-to-high frequency (LF:HF) ratio.

During the clamp procedure, the absolute LF:HF ratio increased significantly from 1.33 during euglycaemia to 1.48 during hypoglycaemia (p<0.001). Normalized to euglycaemia, the increase of LF:HF ratio during hypoglycaemia was 1.09 (95 percent confidence interval [CI], 1.07–1.11; p<0.001). [J Diabetes Sci Technol 2021;doi:10.1177/19322968211007485]

Meanwhile, absolute RMSSD dropped from 26.1 ms during euglycaemia to 24.7 ms during hypoglycaemia. This change was notable but not statistically significant (p=0.198). Normalizing to euglycaemia, however, showed that the increase during hypoglycaemia averaged 1.03 ms (95 percent CI, 1.01–1.06; p=0.009), suggesting a significant jump.

In terms of individual participants, six showed a significant increase in LF:HF ratio while they were in hypoglycaemia; of these, three also demonstrated a statistically significant drop in RMSSD at the same time. Inversely, four participants had significantly higher RMSSD, of whom one also experienced a decrease in LF:HF ratio.

Of all the participants included, only two had no detectable response in either HRV measure. These patients also showed no or minimal symptoms during hypoglycaemia, and the changes in adrenaline level were within normal values.

“IAH is a clinical diagnosis, characterized by absence of timely perception of hypoglycaemia by the affected person—although family members often retain recognition of its symptoms—and suppression of sympathetic nervous system activation as its underlying mechanism,” the researchers explained.

“Our finding that most participants with IAH had a measurable HRV response during hypoglycaemia indicates … that such suppression is seldomly complete and … that even very low levels of sympathetic activation are sufficient for HRV to change,” they added.

Importantly, such subtle changes in sympathetic activation can be detected by wearable devices, suggesting their potential utility in monitoring hypoglycaemia in people with IAH, the researchers said.