Preserved heart rate variability in first-degree relatives of subjects with Type 2 diabetes mellitus without metabolic disorders

Comparison of cardiac autonomic function across complete glycaemic spectrum

OBJECTIVES

Autonomic imbalance is attributed as key mechanism altering metabolic regulation in diabetes mellitus. In view of controversial reports on autonomic function in FDRD and prediabetes, we aimed to assess and compare the autonomic function across the complete glycaemic spectrum in Indian population.

METHODS

Short term heart rate variability and cardiac autonomic reactivity tests - blood pressure and heart rate response to orthostatic tolerance and deep breathing exercise, and diastolic response to isometric handgrip exercise were recorded in normoglycemic apparently healthy individual, normoglycemic first degree relatives of diabetes, prediabetes and diabetes individuals.

RESULTS

Resting heart rate is significantly higher in FDRD, prediabetes and diabetes as compared to controls (control < FDRD = prediabetes = diabetes). Total power, LF power (control < FDRD < prediabetes = diabetes) and HF power (control < FDRD < prediabetes < diabetes) decreased along the glycaemic spectrum. Time-domain variables of HRV (SDNN, RMSSD, NN50, pNN50) were reduced as we move along the glycaemic spectrum (control < FDRD < prediabetes = diabetes). Cardiac autonomic function reactivity parameters such as 30:15 ratio and E:I ratio are decreased in prediabetes and diabetes group as compared to control and FDRD group (control = FDRD < prediabetes = diabetes). Diastolic response to isometric hand grip increases along the glycaemic spectrum starting from FDRD (control < FDRD < prediabetes = diabetes).

CONCLUSIONS

Autonomic dysfunction is observed even in first degree relatives of diabetes. Autonomic dysfunction increases as we move along the glycaemic spectrum (control < FDRD < prediabetes < diabetes).

Sympathovagal imbalance contributes to prehypertension status and cardiovascular risks attributed by insulin resistance, inflammation, dyslipidemia and oxidative stress in first degree relatives of type 2 diabetics

BACKGROUND

Though cardiovascular (CV) risks are reported in first-degree relatives (FDR) of type 2 diabetics, the pathophysiological mechanisms contributing to these risks are not known. We investigated the association of sympathovagal imbalance (SVI) with CV risks in these subjects.

SUBJECTS AND METHODS

Body mass index (BMI), basal heart rate (BHR), blood pressure (BP), rate-pressure product (RPP), spectral indices of heart rate variability (HRV), autonomic function tests, insulin resistance (HOMA-IR), lipid profile, inflammatory markers, oxidative stress (OS) marker, rennin, thyroid profile and serum electrolytes were measured and analyzed in subjects of study group (FDR of type 2 diabetics, n = 72) and control group (subjects with no family history of diabetes, n = 104).

RESULTS

BMI, BP, BHR, HOMA-IR, lipid profile, inflammatory and OS markers, renin, LF-HF (ratio of low-frequency to high-frequency power of HRV, a sensitive marker of SVI) were significantly increased (p<0.0001) in study group compared to the control group. SVI in study group was due to concomitant sympathetic activation and vagal inhibition. There was significant correlation and independent contribution of markers of insulin resistance, dyslipidemia, inflammation and OS to LF-HF ratio. Multiple-regression analysis demonstrated an independent contribution of LF-HF ratio to prehypertension status (standardized beta 0.415, p<0.001) and bivariate logistic-regression showed significant prediction (OR 2.40, CI 1.128-5.326, p = 0.002) of LF-HF ratio of HRV to increased RPP, the marker of CV risk, in study group.

CONCLUSION

SVI in FDR of type 2 diabetics occurs due to sympathetic activation and vagal withdrawal. The SVI contributes to prehypertension status and CV risks caused by insulin resistance, dyslipidemia, inflammation and oxidative stress in FDR of type 2 diabetics.