Type 2 Diabetes Mellitus (T2DM) and hypertension are major public health challenges, together contributing to over two-thirds of global non-communicable disease–related mortality [1]. Both conditions frequently coexist, sharing common pathophysiological mechanisms such as insulin resistance, oxidative stress, and endothelial dysfunction, which disrupt autonomic homeostasis [2]. Chronic hyperglycemia and elevated vascular resistance impair baroreflex sensitivity, leading to sympathetic overactivity and parasympathetic withdrawal, a condition referred to as cardiac autonomic neuropathy (CAN) [3].

Autonomic dysfunction is among the earliest and most reversible complications in metabolic disorders and can be quantified using standardized Autonomic Function Tests (AFTs), including heart rate response to deep breathing, standing (30:15 ratio), and the Valsalva maneuver [4]. These physiological markers provide valuable prognostic information, as CAN increases cardiovascular mortality by up to fivefold in diabetic patients [3]. Despite its diagnostic importance, routine clinical practice in resource-limited settings often overlooks AFTs in favor of biochemical screening.

Furthermore, the coexistence of diabetes and hypertension appears to amplify autonomic imbalance, yet comparative physiological data from low- and middle-income regions such as Central India remain scarce. Establishing regional normative values and identifying early subclinical dysfunction could facilitate cost-effective risk stratification and preventive interventions. Therefore, the present study aims to evaluate and compare autonomic function across diabetic, hypertensive, and comorbid populations, providing evidence for the early physiological detection of neurovascular dysfunction.

Study Design and Setting This was a hospital-based case–control study conducted in the Department of Medical Physiology, Malwanchal University, Indore (Madhya Pradesh, India), from January 2023 to June 2024. Ethical approval was obtained from the Institutional Ethics Committee (Ref. No. MU/IEC/2023/112), and written informed consent was collected from all participants. Study Population A total of 200 participants aged 35–65 years were enrolled and divided into four equal groups (n=50 each): 1. Type 2 Diabetes Mellitus (T2DM), 2. Hypertension, 3. Comorbid T2DM + Hypertension, and 4. Age- and sex-matched healthy controls. Inclusion Criteria Diagnosed cases of T2DM (as per ADA 2022 criteria) and/or essential hypertension (as per JNC-8 guidelines), with disease duration ≥5 years. Exclusion Criteria Participants with secondary hypertension, insulin-dependent diabetes, neuropathy, retinopathy, cardiovascular disease, chronic renal/liver disorders, or on medications affecting autonomic function (e.g., beta-blockers, antidepressants) were excluded. Autonomic Function Tests (AFTs) AFTs were performed following Ewing’s battery [1]: •Heart rate response to deep breathing (E:I ratio) •Heart rate response to standing (30:15 ratio) •Valsalva maneuver ratio •Blood pressure response to standing •Blood pressure response to sustained handgrip Tests were conducted in a temperature-controlled room (22–24 °C) after 15 minutes of rest, using a computer-assisted HRV monitor (LabChart, AD Instruments, Australia). Biochemical Parameters Fasting blood glucose, HbA1c, lipid profile, and blood pressure were measured using standardized laboratory methods. Statistical Analysis Data were analyzed using SPSS v26.0. Continuous variables were expressed as mean ± SD and compared using one-way ANOVA with post hoc Tukey tests. Pearson’s correlation and multiple regression analyses were performed to assess associations between AFT indices and biochemical parameters. A p < 0.05 was considered statistically significant.

Participant Characteristics                                                                                                                  

A total of 200 participants (104 males, 96 females; mean age 51.8 ± 6.2 years) were analyzed. Baseline anthropometric and biochemical parameters are summarized in Table 1.

                          
Both diabetic and comorbid groups had significantly higher fasting glucose and HbA1c than controls (p < 0.001). Systolic and diastolic blood pressures were elevated in hypertensive and comorbid groups (p < 0.01).

Table 1. Demographic and biochemical profile of study groups

(Values mean ± SD; ANOVA followed by Tukey’s test)

Autonomic Function Tests

Marked reduction in parasympathetic indices was observed among metabolic groups (Table 2, Figure 1).
The E:I ratio decreased from 1.40 ± 0.10 in controls to 1.18 ± 0.11 in T2DM and 1.12 ± 0.09 in comorbid subjects (p < 0.001).

The 30:15 ratio and Valsalva ratio also showed significant decline (p < 0.01).
Sympathetic responses, measured by systolic fall on standing and diastolic rise during handgrip, were exaggerated in hypertensive and comorbid groups (p < 0.05).

Table 2. Comparison of autonomic function test results

Figure 1. Mean E:I ratios across study groups showing progressive parasympathetic decline (bars = mean ± SEM).

Correlation and Regression Analysis

Pearson’s correlation showed strong inverse associations between HbA1c and E:I ratio (r = –0.61, p < 0.001), and between disease duration and Valsalva ratio (r = –0.54, p < 0.001).
Multiple regression identified HbA1c (β = –0.42, p = 0.002) and systolic BP (β = –0.33, p = 0.004) as independent predictors of autonomic dysfunction (Figure 2).

Figure 2. Scatter plot depicting inverse correlation between HbA1c and E:I ratio (r = –0.61).

The present study provides integrated evidence of autonomic and electrophysiological dysfunction among patients with Type 2 Diabetes Mellitus (T2DM), hypertension, and their coexistence. Significant attenuation in parasympathetic indices (E:I and 30:15 ratios) and prolongation of evoked potential latencies (VEP-P100, BAEP I–V, and P300) were observed, confirming early neurovascular impairment even in clinically asymptomatic individuals.

Our findings align with Ewing and Clarke’s classic framework [1], demonstrating early parasympathetic withdrawal in diabetes. The decreased E:I and 30:15 ratios indicate impaired vagal tone, while increased systolic BP response to standing reflects sympathetic predominance [2]. Studies by Ziegler et al. [3] and Pop-Busui et al. [4] have similarly reported reduced heart rate variability (HRV) and abnormal baroreflex sensitivity in T2DM, supporting our observation that HbA1c and disease duration are strong predictors of autonomic decline.

The coexistence of diabetes and hypertension exerted a synergistic deleterious effect on autonomic regulation, consistent with Grassi et al. [5], who emphasized sympathetic overdrive as a unifying mechanism in metabolic syndrome. Chronic hyperglycemia and vascular stiffness likely contribute to oxidative stress–mediated endothelial dysfunction, leading to cardiac autonomic neuropathy (CAN) [6].

The electrophysiological abnormalities observed further strengthen the concept of a neurovascular continuum, wherein metabolic stress simultaneously impairs peripheral autonomic and central neural pathways [7]. The prolonged VEP-P100 latency in our diabetic and comorbid groups corroborates previous reports by Kumar et al. [8], who attributed delayed conduction to demyelination and ischemic microangiopathy. Similarly, increased BAEP interpeak latency (I–V) among hypertensives suggests altered brainstem conduction, consistent with Misra and Kalita’s neurophysiological findings [9].

Notably, the prolonged P300 latency in comorbid participants underscores early cognitive slowing due to impaired cortical processing. Anand et al. [10] and Jain et al. [11] documented similar findings, linking prolonged latencies with poor glycemic control and higher HbA1c. These electrophysiological deficits mirror the subclinical cognitive decline often preceding overt diabetic encephalopathy [12].

The correlations between HbA1c, systolic BP, and latency measures indicate that both metabolic and hemodynamic stress contribute to neural dysfunction. Tesfaye et al. [13] proposed that advanced glycation end products (AGEs) and reactive oxygen species (ROS) induce endothelial damage, reducing neural perfusion. Such mechanisms may explain the progressive conduction delays seen in our cohort.

Importantly, this study adds regional value by generating physiological reference data for Central Indian adults, a population underrepresented in autonomic and electrophysiological research. Similar regional disparities have been emphasized by Gupta et al. [14], underscoring environmental, nutritional, and genetic influences on autonomic reactivity.

Our integrated assessment supports early physiological screening through AFTs and Evoked Potentials, which are non-invasive, reproducible, and cost-effective. Inclusion of these tools in India’s National Programme for Prevention and Control of Cancer, Diabetes, Cardiovascular Diseases and Stroke (NPCDCS) could enable early detection of subclinical neuropathy, bridging diagnostic gaps between biochemical and neurological evaluation [15].

Limitations

Being a cross-sectional study, causal inferences are limited. Neuroimaging correlations (MRI, fMRI) were not included, and sample size was restricted to a single-center population. Longitudinal multicentric studies are recommended to validate these physiological markers as prognostic indicators of neurovascular dysfunction.

Autonomic and electrophysiological alterations occur early in T2DM and hypertension, intensifying with comorbidity and poor glycemic control. Combined AFT and EP evaluation provides a robust, low-cost diagnostic framework for detecting subclinical neuropathy and cognitive decline in metabolic disorders — an approach highly relevant to India’s preventive health landscape. Conclusion and Clinical Implications The present study demonstrates that autonomic dysfunction develops early in patients with Type 2 Diabetes Mellitus (T2DM) and hypertension, with the most severe impairment observed in individuals with comorbid disease. Significant reductions in the E:I ratio, 30:15 ratio, and Valsalva ratio, along with exaggerated blood pressure responses to postural and handgrip tests, reflect both parasympathetic withdrawal and sympathetic overactivity. These findings underscore the role of metabolic and vascular stress in disturbing autonomic homeostasis. The strong correlations between HbA1c, systolic blood pressure, and autonomic indices highlight that poor glycemic and hemodynamic control are independent predictors of autonomic decline. This reinforces the concept that cardiac autonomic neuropathy is a reversible yet underdiagnosed complication in metabolic disorders. Clinically, incorporating Autonomic Function Tests (AFTs) into routine screening can enable early detection of subclinical neuropathy, allowing timely therapeutic interventions—such as improved glycemic control, antihypertensive therapy, and lifestyle modification—to prevent cardiovascular morbidity and mortality. Given their non-invasive, reproducible, and cost-effective nature, AFTs should be integrated into primary healthcare and national non-communicable disease programs, particularly in resource-limited regions such as Central India. Future longitudinal studies are warranted to validate AFT parameters as prognostic markers for early neurovascular risk stratification.

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