Wearable Heart Monitor Detects T1D Hypoglycemia

Heart rate variability occurs with hypoglycemia, used for early warning to people with impaired awareness of hypoglycemia

Mats Koeneman, Technical Physician with the REshape Center for Innovation at Radboud University Medical Center, The Netherlands

We spoke with Mats Koeneman, MSc and Technical Physician with the REshape Center for Innovation at Radboud University Medical Center, The Netherlands — — who co-authored a recent study in Diabetes Journal to get his thoughts on how wearables might help people with T1D who are hypo unaware.

Note: Technical Physician is a new designation in The Netherlands for a person trained as a doctor who has a deep understanding of applied technology.

“One of the most common adverse events seen in patients with type 1 diabetes is hypoglycemia because injected insulin is not subject to normal physiological feedback regulation.  On average, people with T1D have about two symptomatic hypoglycemia episodes each week.

“Early symptoms associated with hypoglycemia include heart palpitation, confusion, dizziness, fatigue, pallor, anxiety, and diaphoresis. Detection of early symptoms is critical to avoid severe hypoglycemia.

“These common symptoms of hypoglycemia go unnoticed, however, in patients with impaired awareness of hypoglycemia and this subset of people are six times more at risk of severe hypoglycemic events.

“Detecting a hypo is already delayed with a CGM because glucose levels in subcutaneous tissue are always 15-20 minutes behind the changes in glucose in the blood.

“Heart rate variability (HRV) is secondary to hypoglycemia due to the stimulation of the sympathetic nervous system and it is one of the measurable symptoms for early detection of hypoglycemia.  It is an independent indicator of hypoglycemia that does not have the delays endemic to CGM readings.

Study Description

“We tracked changes in HRV, sensed by a wearable monitor, to determine if these devices could help detect hypoglycemia in patients with type 1 diabetes.

  • A total of 29 T1D participants were included in this study
  • The minimum age for participants was 18
  • Patients with a history of cardiac arrhythmias or who are on medications causing changes in heart rate were excluded from this study


  1. Each participant wore a HealthPatch (VitalConnect, San Jose, CA —, which has a single-lead electrocardiogram recording, on their chest for 5 consecutive days.
  2. Participants were continuously measured and then data was transferred via Bluetooth to an Apple device.
  3. Awareness state was assessed using the Dutch modified version of the Clarke questionnaire, in which a score ≥3 classified as having impaired awareness of hypoglycemia.
  4. Glucose was measured by fingerstick and any glucose ≤70 mg/dL [≤3.9 mmol/L] was categorized as mild hypoglycemia, and glucose <54 mg/dL was categorized as serious hypoglycemia.
  5. Any hypoglycemic event with the time of occurrence was recorded by the participants. Also, patients were asked to record the presence or absence of additional symptoms, and prior exercise (if applicable).


“By using the paired sample t-tests, the average changes in heart rate before hypoglycemia were compared to heart rate changes at the time of hypoglycemia.

Results from data analysis showed that nine patients had impaired awareness of hypoglycemia.

There was a total of 66 hypoglycemic events, with a mean glucose level of 56 mg/dL recorded in this study. It was noted that 33% of those hypoglycemic events were considered serious.

Furthermore, typical HRV changes were observed in 36 (55%) of the recorded hypoglycemia event and 18 events (27%) showed an atypical pattern. There were 10 (15%) unclassified events, and two (3%) without any changes in HRV.

HRV changes, associated with hypoglycemia, consisted of an increase in low and high frequency (LF:HF) changes and a decrease in standard differences of successive R-R intervals (RMSSD). The opposite effects were also seen with HRV changes due to hypoglycemia.

Changes in HRV secondary to hypoglycemia were predominantly observed in patients with short diabetes duration and further influenced by gender, physical activity, and glucose peak level before and fall toward a hypoglycemic event.”


“Changes in HRV at the beginning of hypoglycemia could be detected by a wearable device to prevent a severe hypoglycemic event.

Commentary on Future

“SmartWatch technology currently measures heart rate every 3 minutes whereas the HealthPatch measures it each second, which is essential to our results.  Smartwatch sensors are advancing and Apple just released the ability to press your finger to the watch knob and measure your heart rate in real-time.

“Advances in Smartwatch sensors and battery life should eventually enable measuring real-time HRV but at the current time, sensors from VitalConnect or from Hexoskin are available.”

VitalConnect, which supplied the HealthPatch, provided this reply  when asked to comment on this article:

“At this point, we are focused on the clinical setting and addressing continuous monitoring of patients treated at home, in the hospital setting as well as trying to reduce readmissions. As our company evolves, we will look at other applications as well but our current priority is the clinical setting,” said Ravi Pendse, Director of Product Marketing at VitalConnect

To refine the hypo detection process and prevent false positive, Mats says that their next trial will integrate activity measures such as motion sensors so when someone’s heart rate elevates from exercise the algorithm won’t immediately signal the beginning of a hypo event.

Martin is the Founder of SelfRx Media and editor-in-chief of Insulin Nation. He's a passionate about sharing knowledge with those affected by Diabetes.

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