Effects of Autonomic Nervous System Modulation by Heart Rate Variability Biofeedback Training With Resonant Frequency Breathing on Glucose Metabolism in Individuals With Prediabetes

Approximately 20% of adults have prediabetes in Germany. Prediabetes is defined as a condition with glucose levels outside the normal range but not yet meeting the criteria for type 2 diabetes. The pathogenesis of prediabetes, as well as of type 2 diabetes, involves whole-body insulin resistance associated with inadequate insulin secretion. These two central processes of glucose regulation are modulated by the brain. The brain communicates via the autonomic nervous system (ANS) with metabolically important organs in the periphery to modulate insulin sensitivity and insulin secretion. These processes are impaired in individuals with prediabetes and diabetes. An ANS sympathovagal imbalance has also been observed in individuals with prediabetes. There are no specific therapeutic approaches to improve ANS sympathovagal imbalance. It is assumed that resonant frequency breathing (RFB) maximizes heart rate variability (HRV) through rhythmization of breathing, heartbeat, and blood pressure. Through this state of coherence, the activity of the parasympathetic nervous system is upregulated, and the activity of the sympathetic nervous system is suppressed, leading to an increase in modulation of ANS activity. Several studies have demonstrated that heart rate variability-biofeedback (HRV-BF) interventions improve HRV, reduce stress and anxiety, and alleviate symptoms in patients with various medical conditions. To the best of current knowledge, no study has investigated the effect of HRV-BF-RFB on glucose metabolism. Therefore, the proposed randomized controlled non-blinded trial aims to gain evidence about the effect of HRV-BF-RFB compared to an anti-stress program on glucose metabolism in individuals with prediabetes. Glucose metabolism is characterized using the 75 g oral glucose tolerance test. There are two potential mechanisms by which HRV-BF-RFB may improve glucose metabolism in individuals with prediabetes: (a) a 0°-phase relationship between heart oscillations and breathing, maximizing the amplitude of respiratory sinus arrhythmia (RSA), and (b) activation of the cholinergic anti-inflammatory pathway. The investigators hypothesized that in individuals with prediabetes, the HRV-BF-RFB intervention will improve glucose metabolism and glucose variability.


Eligibility Criteria:
Inclusion Criteria:

* Presence of prediabetes Fasting glucose: 100-125 mg/dl (5.6-6.9 mmol/L) and/or HbA1c in %: 5.7-6.4 (39-47 mmol/mol Hb) and/or 2-hour value of the 75 g OGTT: 140-199 mg/dl (7.8-11.0 mmol/L)

  * This is checked using a 75 g OGTT in a screening visit.
* Age between 18 and 65 years
* BMI between 20 and 40 kg/m²

Exclusion Criteria:

* Diabetes mellitus
* Malignant diseases within the last 5 years before randomization
* History of gastrointestinal surgery
* Pancreatic diseases other than pancreatic lipomatosis
* Acute diseases or infections
* Regular intake of cardiac drugs that affect heart rate within the last 4 weeks before the first measurement (e.g. beta-receptor blockers, antiarrhythmics, etc.)
* Intake of centrally acting drugs
* Medical contraindications to a meaningful interpretation of the heart rate analysis (e.g. patients with pacemakers, atrial fibrillation or other arrhythmias)
* Chronic diseases (particularly metabolic diseases, heart diseases, blood diseases)
* Endocrinological disease other than substituted hypothyroidism
* Mental illnesses
* Intake of drugs that can affect blood sugar metabolism (e.g. steroids)