Impact of type 2 diabetes on cardiac autonomic responses to sympathetic stimuli in patients with coronary artery disease

"Comparison of cardiovascular autonomic activity (heart rate variability and baroreceptor sensitivity) in young healthy females during fasting and hyperglycaemia"

BACKGROUND AND AIM

The present study compared cardiovascular autonomic activity and reactivity during fasting (FS) and hyperglycemia (HS) states in young healthy females.

METHODS

This case crossover study was conducted on 30 females recruited by convenient sampling. Blood glucose levels were measured in FS and after oral glucose load i.e., HS. Finger arterial blood pressure (BP) and ECG were recorded constantly to monitor baroreceptor sensitivity (BRS) and heart rate variability (HRV). Autonomic reactivity was tested with deep breathing (DB), Valsalva manoeuvre (VM), and head-up-tilt (HUT) test under FS and HS. HRV parameters not normally distributed were natural log (ln) transformed.

RESULTS

Significantly reduced Valsalva ratio and higher heart rate and BP were observed in HS that continued during HUT (P < 0.05). The lnSDNN (standard deviation of normal-to-normal intervals) and lnRMSSD (root mean square of successive differences) were significantly lower (p < 0.05) in HS during HUT. After HUT, lnRMSSD remained lower (P = 0.031), whereas lnLF/HF (low frequency/high frequency power) ratio (P = 0.042) and LFnu (normalized units) (P = 0.024) were higher in HS. BRS was significantly lower in supine position in HS compared to FS and further reduced in HUT position in both FS and HS (P < 0.05).

CONCLUSION

Compared to FS, the HS exhibited heightened sympathetic activity with attenuation of parasympathetic activity and this phenomenon was further accentuated by HUT. BRS was more sensitive indicator of autonomic effects of hyperglycemia in resting state. In addition to standard tests, autonomic reactivity in vulnerable young subjects could be useful to detect autonomic imbalance at an early stage.

The additional impact of type 2 diabetes on baroreflex sensitivity of coronary artery disease patients might be undetectable in presence of deterioration of mechanical vascular properties

Both deterioration of the mechanical vascular properties of barosensitive vessels and autonomic derangement lead to modification of baroreflex sensitivity (BRS) in coronary artery disease (CAD) individuals. Type 2 diabetes (T2D) reduces BRS as well even in absence of cardiac autonomic neuropathy. The aim of the study is to clarify whether, assigned the degree of mechanical vascular impairment and without cardiac autonomic neuropathy, the additional autonomic dysfunction imposed in CAD patients by T2D (CAD-T2D) decreases BRS further. We considered CAD (n = 18) and CAD-T2D (n = 19) males featuring similar increases of average carotid intima media thickness (ACIMT) and we compared them to age- and gender-matched healthy (H, n = 19) subjects. BRS was computed from spontaneous beat-to-beat variability of heart period (HP) and systolic arterial pressure (SAP) at supine resting (REST) and during active standing (STAND). BRS was estimated via methods including time domain, spectral, cross-spectral, and model-based techniques. We found that (i) at REST BRS was lower in CAD and CAD-T2D groups than in H subjects but no difference was detected between CAD and CAD-T2D individuals; (ii) STAND induced an additional decrease of BRS visible in all the groups but again BRS estimates of CAD and CAD-T2D patients were alike; (iii) even though with different statistical power, BRS markers reached similar conclusions with the notable exception of the BRS computed via model-based approach that did not detect the BRS decrease during STAND. In presence of a mechanical vascular impairment, indexes estimating BRS from spontaneous HP and SAP fluctuations might be useless to detect the additional derangement of the autonomic control in CAD-T2D without cardiac autonomic neuropathy compared to CAD, thus limiting the applications of cardiovascular variability analysis to typify CAD-T2D individuals. Graphical abstract Graphical representation of the baroreflex sensitivity (BRS) estimated from spontaneous fluctuations of heart period and systolic arterial pressure via transfer function (TF) in low frequency (LF) band (from 0.04 to 0.15 Hz). BRS was reported as a function of the group (i.e., healthy (H), coronary artery disease (CAD) and CAD with type 2 diabetes (CAD-T2D) groups) at REST (black bars) and during STAND (white bars). Values are shown as mean plus standard deviation. The symbol "*" indicates a significant difference between conditions within the same group (i.e., H, CAD, or CAD-T2D) and the symbol "§" indicates a significant difference between groups within the same experimental condition (i.e., REST or STAND). BRS cannot distinguish CAD and CAD-T2D groups both at REST and during STAND, while it is useful to distinguish experimental conditions and separate pathological groups from H subjects.

Childhood growth patterns and cardiovascular autonomic modulation in midlife: Northern Finland 1966 Birth Cohort Study

OBJECTIVES

To test the hypothesis that age and body mass index (BMI) at BMI peak during infancy and at BMI rebound in childhood are related to cardiovascular autonomic modulation in adulthood.

METHODS

At the age of 46 years, a sample (n = 5861) of the participants of the Northern Finland Birth Cohort 1966 took part in follow-up examinations. Heart rate variability (HRV), baroreflex sensitivity (BRS) and low-frequency oscillations of systolic blood pressure (LF_SBP) were measured during sympathetic stimulus by standing. BMI at various ages was calculated from frequent anthropometric measurements collected from child welfare clinical records. BRS and LF_SBP were available for 1243 participants with BMI peak data and 1524 participants with BMI rebound data, and HRV for 2137 participants with BMI peak data and 2688 participants with BMI rebound data.

RESULTS

Age at BMI rebound had a significant inverse association with LF_SBP (beta = -0.071, p = 0.006) after all adjustments (p < 0.001) and was also directly associated with BRS (beta = 0.082, p = 0.001) independently of birth and maternal factors (p = 0.023). BMI at BMI peak and at BMI rebound was inversely associated with high-frequency component of HRV (HF) (beta = -0.045, p = 0.036 for BMI at peak; beta = -0.043, p = 0.024 for BMI at rebound) and directly associated with the ratio of low- and high-frequency components of HRV (LF/HF ratio) (beta = 0.084, p = < 0.001 for BMI at peak; beta = 0.069, p < 0.001 for BMI at rebound). These associations remained significant after all adjustments (p < 0.05 for all).

CONCLUSIONS

This novel study shows that younger age at BMI rebound and higher BMI at BMI peak and at BMI rebound are associated with higher levels in markers suggestive of augmented sympathetic and reduced vagal cardiovascular modulation in midlife.

Association between Birth Characteristics and Cardiovascular Autonomic Function at Mid-Life

Background

Low birth weight is associated with an increased risk of cardiovascular diseases in adulthood. As abnormal cardiac autonomic function is a common feature in cardiovascular diseases, we tested the hypothesis that low birth weight may also be associated with poorer cardiac autonomic function in middle-aged subjects.

Methods

At the age of 46, the subjects of the Northern Finland Birth Cohort 1966 were invited to examinations including questionnaires about health status and life style and measurement of vagally-mediated heart rate variability (rMSSD) from R-R intervals (RRi) and spontaneous baroreflex sensitivity (BRS) in both seated and standing positions. Maternal parameters had been collected in 1965–1966 since the 16^th gestational week and birth variables immediately after delivery. For rMSSD, 1,799 men and 2,279 women without cardiorespiratory diseases and diabetes were included and 902 men and 1,020 women for BRS. The analyses were adjusted for maternal (age, anthropometry, socioeconomics, parity, gestational smoking) and adult variables (life style, anthropometry, blood pressure, glycemic and lipid status) potentially confounding the relationship between birth weight and autonomic function.

Results

In men, birth weight correlated negatively with seated (r = -0.058, p = 0.014) and standing rMSSD (r = -0.090, p<0.001), as well as with standing BRS (r = -0.092, p = 0.006). These observations were verified using relevant birth weight categories (<2,500 g; 2,500–3,999 g; ≥4,000 g). In women, birth weight was positively correlated with seated BRS (r = 0.081, p = 0.010), but none of the other measures of cardiovascular autonomic function. These correlations remained significant after adjustment for potential confounders (p<0.05 for all).

Conclusions

In men, higher birth weight was independently associated with poorer cardiac autonomic function at mid-life. Same association was not observed in women. Our findings suggest that higher, not lower, birth weight in males may contribute to less favourable cardiovascular autonomic regulation and potentially to an elevated cardiovascular risk in later life.

Long-term effects of baroreflex activation therapy on glucose metabolism

AIMS

Sympathetic overactivity is one critical factor associated with the development of arterial hypertension, impaired insulin secretion and resistance. Some antihypertensives exert beneficial effects on glucose metabolism, whereas others lead to an impairment of metabolic state with consecutive weight gain. In resistant hypertension, baroreflex activation therapy (BAT) reduces arterial blood pressure (BP) by inhibition of the sympathetic nervous system. The objective of this study was to evaluate whether BAT influences metabolic state in patients with resistant hypertension.

METHODS

Thirty patients with resistant hypertension (10 with known diabetes mellitus) were prospectively included into this study. Blood pressure, BMI, weight, fasting glucose, insulin, C-peptide, hemoglobin A1c, HOMA-IR, HOMA-β, ISQuickI, and glucose levels during oral glucose tolerance test were measured at baseline and 6 months after BAT activation.

RESULTS

Fasting glucose was significantly reduced after 6 months of BAT, whereas mean 2-h glucose levels during oral glucose tolerance test, fasting insulin levels, C-peptide levels, hemoglobin A1c, HOMA-IR, HOMA-β, ISQuickI, weight, and BMI remained unchanged.

CONCLUSION

Despite improvement in fasting glucose, BAT exerts neither sustained additional beneficial effects nor an impairment of metabolic state. Thus, chronic BAT might be an effective interventional method to reduce BP without metabolic disadvantages.

Acute post-exercise change in blood pressure and exercise training response in patients with coronary artery disease

We tested the hypothesis that acute post-exercise change in blood pressure (BP) may predict exercise training responses in BP in patients with coronary artery disease (CAD). Patients with CAD (n = 116, age 62 ± 5 years, 85 men) underwent BP assessments at rest and during 10-min recovery following a symptom-limited exercise test before and after the 6-month training intervention (one strength and 3-4 aerobic moderate-intensity exercises weekly). Post-exercise change in systolic BP (SBP) was calculated by subtracting resting SBP from lowest post-exercise SBP. The training-induced change in resting SBP was -2 ± 13 mmHg (p = 0.064), ranging from -42 to 35 mmHg. Larger post-exercise decrease in SBP and baseline resting SBP predicted a larger training-induced decrement in SBP (β = 0.46 and β = -0.44, respectively, p < 0.001 for both). Acute post-exercise decrease in SBP provided additive value to baseline resting SBP in the prediction of training-induced change in resting SBP (R(2) from 0.20 to 0.26, p = 0.002). After further adjustments for other potential confounders (sex, age, baseline body mass index, realized training load), post-exercise decrease in SBP still predicted the training response in resting SBP (β = 0.26, p = 0.015). Acute post-exercise change in SBP was associated with training-induced change in resting SBP in patients with CAD, providing significant predictive information beyond baseline resting SBP.

Sinoatrial node dysfunction induces cardiac arrhythmias in diabetic mice

BACKGROUND

The aim of this study was to probe cardiac complications, including heart-rate control, in a mouse model of type-2 diabetes. Heart-rate development in diabetic patients is not straight forward: In general, patients with diabetes have faster heart rates compared to non-diabetic individuals, yet diabetic patients are frequently found among patients treated for slow heart rates. Hence, we hypothesized that sinoatrial node (SAN) dysfunction could contribute to our understanding of the mechanism behind this conundrum and the consequences thereof.

METHODS

Cardiac hemodynamic and electrophysiological characteristics were investigated in diabetic db/db and control db/+ mice.

RESULTS

We found improved contractile function and impaired filling dynamics of the heart in db/db mice, relative to db/+ controls. Electrophysiologically, we observed comparable heart rates in the two mouse groups, but SAN recovery time was prolonged in diabetic mice. Adrenoreceptor stimulation increased heart rate in all mice and elicited cardiac arrhythmias in db/db mice only. The arrhythmias emanated from the SAN and were characterized by large RR fluctuations. Moreover, nerve density was reduced in the SAN region.

CONCLUSIONS

Enhanced systolic function and reduced diastolic function indicates early ventricular remodeling in obese and diabetic mice. They have SAN dysfunction, and adrenoreceptor stimulation triggers cardiac arrhythmia originating in the SAN. Thus, dysfunction of the intrinsic cardiac pacemaker and remodeling of the autonomic nervous system may conspire to increase cardiac mortality in diabetic patients.