Characteristic patterns of circadian variation in plasma catecholamine levels, blood pressure and heart rate variability in Type 2 diabetic patients

Disrupted Circadian Rhythm of Epinephrine in Males With Youth-Onset Type 2 Diabetes

Context

Blood pressure and plasma catecholamines normally decline during sleep and rapidly increase in early morning. This is blunted in adults with type 2 diabetes (T2D).

Objective

We hypothesize that increased sympatho-adrenal activity during sleep differentiates youth with T2D from nondiabetic obese youth and lean youth.

Methods

Fasting spot morning and 24-hour urines were collected in obese adolescents with and without T2D, and normal-weight controls. Fractionated free urine catecholamines (epinephrine, norepinephrine, and dopamine) were measured, and the ratio of fasting spot morning to 24-hour catecholamines was calculated.

Results

Urinary 24-hour catecholamine levels were comparable across the 3 groups. Fasting morning epinephrine and the ratio of fasting morning/24-hour epinephrine were higher in youth with T2D (P = 0.004 and P = 0.035, respectively). In males, the ratio of fasting morning/24-hour epinephrine was also higher in youth with T2D (P = 0.005). In females, fasting morning norepinephrine and the ratio of fasting morning/24-hour dopamine were lower in obese youth with and without T2D (P = 0.013 and P = 0.005, respectively) compared with lean youth. Systolic blood pressure was higher in diabetic participants than other groups; males trended higher than females.

Conclusion

Circadian rhythm in catecholamines is disrupted in youth-onset T2D, with a blunted overnight fall in urinary epinephrine in males. Conversely, fasting morning norepinephrine and dopamine levels were lower in obese females with or without T2D. Higher nocturnal catecholamines in males with T2D might associate with, or predispose to, hypertension and cardiovascular complications. Lower catecholamine excretion in females with obesity might serve an adaptive, protective role.

Pronounced cortisol response to acute psychosocial stress in type 2 diabetes patients with and without complications

It is increasingly recognized that psychological stress is linked with type 2 diabetes mellitus and its late complications. Thus, the aim of the current study was to investigate the psychophysiological response to acute psychosocial stress in patients with type 2 diabetes. In total, 53 type 2 diabetes patients with complications, 16 type 2 diabetes patients without complications, and 47 age and gender matched non-diabetic participants underwent the Trier Social Stress Test. Subjective as well as biological parameters (i.e., blood levels of cortisol, adrenocorticotropic hormone (ACTH), norepinephrine, methylglyoxal) were assessed repeatedly before and after stress induction. Data were analyzed by means of multilevel regression. Patients with type 2 diabetes showed an exaggerated cortisol response to acute stress as compared to age matched control participants (diabetes*T2 est. = 1.23, p < .001), while stress-induced alterations of ACTH and subjective parameters did not differ. Norepinephrine levels were lower among patients (diabetes est. = -4.36, p = .044) and tended to decrease earlier than in controls. The subjective reaction of type 2 diabetes patients with complications was stronger than that of patients without complications (complication*T2 est. = -1.83, p = .032), while their endocrine response to stress was similar. Stress had no effect on methylglyoxal level, and there were no group differences regarding methylglyoxal response. These results show that the cortisol reactivity of patients with type 2 diabetes to acute psychosocial stress is increased compared to a control group. Thus, alterations of the hypothalamus-pituitary-adrenal axis - especially regarding its dynamic regulation - are a plausible link between psychological stress and type 2 diabetes and its complications.

Positive Relationship Between Precompetitive Sympathetic Predominance and Competitive Performance in Elite Extreme Sports Athletes

Elite athletes achieve superior performance under high pressure in competitive situations. Although it is known that such situations affect the precompetitive activity of their autonomic nervous system (ANS), the relationship between precompetitive ANS activity and performance remains controversial. Especially in extreme sports, it has been shown that cardiac sympathetic tone occurs in athletes before competition attempts. However, the relationship between precompetitive sympathetic tone and performance is unclear. To investigate this relationship in extreme sports, we organized a freestyle snowboard jumping competition and examined competitors' physiological states and performance during this event. The electrocardiograms (ECGs) of 20 elite snowboarders were measured 10 min before each jump in different competitive situations: practice, qualifying, and final sessions. The mean heart rate (HR), the low-frequency to high-frequency component ratio (LF/HF ratio), the logarithm of the HF (lnHF) component of the frequency-domain of the heart rate variability (HRV), the ratio of the standard deviation of all R-R intervals to the root mean square of successive differences of R-R intervals (SDNN/rMSSD ratio), and the rMSSD of the time-domain of the HRV were calculated from the ECG data. The results showed a significant increase in the mean HR as well as significant decreases in the lnHF component and rMSSD of the HRV as the sessions progressed. Interestingly, the mean HR, LF/HF ratio and SDNN/rMSSD ratio of the HRV showed significant positive correlations with competitive scores, and the lnHF component and rMSSD of the HRV showed significant negative correlations with the scores. Our results indicate that precompetitive ANS activity becomes predominantly sympathetic in elite extreme athletes, such as freestyle snowboarders, when the competition intensifies, and that this sympathetic predominance is positively related to competitive performance.

Complexities in cardiovascular rhythmicity: perspectives on circadian normality, ageing and disease

Biological rhythms exist in organisms at all levels of complexity, in most organs and at myriad time scales. Our own biological rhythms are driven by energy emitted by the sun, interacting via our retinas with brain stem centres, which then send out complex messages designed to synchronize the behaviour of peripheral non-light sensing organs, to ensure optimal physiological responsiveness and performance of the organism based on the time of day. Peripheral organs themselves have autonomous rhythmic behaviours that can act independently from central nervous system control but is entrainable. Dysregulation of biological rhythms either through environment or disease has far-reaching consequences on health that we are only now beginning to appreciate. In this review, we focus on cardiovascular rhythms in health, with ageing and under disease conditions.

The effects of DPP4 inhibitors on the levels of plasma catecholamines and their metabolites in patients with type 2 diabetes

AIMS

Dipeptidyl peptidase 4 inhibitors (DPP4Is) can increase sympathetic activity. We aimed to evaluate the direct association between serum DPP4 activity and sympathetic activity in humans.

METHODS

Fasting serum DPP4 activity and plasma levels of catecholamines and their metabolites were measured in 211 patients with type 2 diabetes mellitus (T2DM) treated with DPP4I (n = 146) or non-DPP4I therapy (n = 65) and in healthy control subjects (n = 30).

RESULTS

Although there were no differences in plasma levels of catecholamines and their metabolites between the DPP4I and non-DPP4I groups, the levels in both of these groups were lower than those in the healthy control group. In DPP4I-treated patients, serum DPP4 activity showed an inverse correlation with plasma levels of norepinephrine (NE) (r = -0.339, p < 0.01), metanephrine (MET) (r = -0.251, p < 0.01) and normetanephrine (r = -0.312, p < 0.001). In addition, plasma MET level showed a weak inverse correlation with serum DPP4 activity in the combined T2DM group. In DPP4I-treated patients, the inverse correlation between DPP4 activity and plasma NE remained significant even after multiple adjustments.

CONCLUSIONS

Our results suggest that although sympathetic activity is lower in patients with T2DM, the greater the suppression of DPP4 activity by DPP4I therapy, the greater the increase in sympathetic activity is, which may have clinical implications in high risk T2DM patients.

Catecholamines in Post-traumatic Stress Disorder: A Systematic Review and Meta-Analysis

Studies on the association between post-traumatic stress disorder (PTSD) and levels of catecholamines have yielded inconsistent results. The aim of this study was to conduct a systematic review and meta-analysis to assess whether concentrations of the catecholamines dopamine, norepinephrine, and epinephrine are associated with PTSD. This study searched relevant articles in the following databases: PubMed, Embase, Web of Science, and Psyc-ARTICLES. Each database was searched from its inception to September, 2018. Data related to catecholamine concentrations were extracted for patients with PTSD and the controls to calculate standardized mean differences and to evaluate effect sizes. A meta-analysis was then performed to compare the concentration of each catecholamine between the two groups in blood and/or urine samples. Heterogeneity was quantified using I² and its significance was tested using the Q statistics. Subgroup analyses of the types of controls, PTSD assessment tools, and assayed methods used in the studies were performed to explore sources of heterogeneity among studies. Random-effects models were used to combine results from selected studies. A total of 1,388 articles were identified, of which 27 were included in the final analysis. Heterogeneity was high; hence random-effects models were used to combine results of selected studies. Results revealed significantly higher norepinephrine levels in people with PTSD than in the controls [standardized mean difference (SMD) = 0.35, 95% confidence interval (CI): 0.13 to 0.57, p = 0.002]. No difference was found in dopamine and epinephrine concentrations between the two groups. Elevated norepinephrine levels may be an important indicator for PTSD.

Heart rate variability in type 2 diabetes mellitus: A systematic review and meta-analysis

BACKGROUND

Cardiac autonomic neuropathy in type 2 dibetes mellitus (T2DM) patients is frequent and associated with high cardiovascular mortality. Heart rate variability (HRV) is the gold standard to measure cardiac autonomic neuropathy. We aimed to conduct a systematic review and meta-analysis to evaluate the impact of T2DM on HRV parameters.

METHODS

The PubMed, Cochrane Library, Embase and Science Direct databases were searched on 1st October 2017 using the keywords "diabetes" AND ("heart rate variability" OR "HRV"). Included articles had to report HRV parameters in T2DM patients and healthy controls measured during 24 hours with a Holter-electrocardiogram. Measurements of HRV retieved were: RR-intervals (or Normal to Normal intervals-NN), standard deviation of RR intervals (SDNN), percetange of adjacent NN intervals differing by more than 50 milliseconds (pNN50), square root of the mean squared difference of successive RR intervals (RMSSD), total power, Low Frequency (LF), High Frequency (HF) and LF/HF ratio, as per Task Force recommendations.

RESULTS

We included twenty-five case-control studies with 2,932 patients: 1,356 with T2DM and 1,576 healthy controls. T2DM patients had significantly (P<0.01) lower RR-intervals (effect size = -0.61; 95%CI -1.21 to -0.01), lower SDNN (-0.65; -0.83 to -0.47), lower RMSSD (-0.92; -1.37 to -0.47), lower pNN50 (-0.46; -0.84 to -0.09), lower total power (-1.52; -2.13 to -0.91), lower LF (-1.08; -1.46 to -0.69]), and lower HF (-0.79; -1.09 to -0.50). LF/HF did not differ between groups. Levels of blood glucose and HbA1c were associated with several HRV parameters, as well as Time from diagnosis of T2DM.

CONCLUSIONS

T2DM was associated with an overall decrease in the HRV of T2DM patients. Both sympathetic and parasympathetic activity were decreased, which can be explained by the deleterious effects of altered glucose metabolism on HRV, leading to cardiac autonomic neuropathy.

Carotid atherosclerosis and the association between nocturnal blood pressure dipping and cardiovascular events

The impact of a nondipping blood pressure (BP) pattern, defined as (awake systolic BP - sleep systolic BP)/awake systolic BP < 0.1, on cardiovascular events in populations with different degrees of carotid atherosclerosis is uncertain. The authors hypothesized that a nondipping BP pattern would show differential predictive power for cardiovascular events, including total cardiovascular death, sudden death, nonfatal cardiovascular events, and nonfatal stroke, between populations with and without carotid atherosclerosis. To test this hypothesis, the authors analyzed 493 patients (mean age 67.9 years, 47.5% men) from the J-HOP (Japan Morning Surge-Home Blood Pressure) study for whom ambulatory BP monitoring and carotid intima-media thickness data were available. Twenty-nine cardiovascular events occurred during follow-up (1867 person-years). A nondipping BP pattern was independently associated with cardiovascular events in the population without carotid atherosclerosis, defined as carotid intima-media thickness < 1.1 mm after adjustment for other cardiovascular risk factors including age, sex, diabetes mellitus, chronic kidney disease, and 24-hour systolic BP (hazard ratio, 8.15; 95% confidence interval, 1.76-37.78 [P < .01]). This association was not found in the population with carotid intima-media thickness ≥ 1.1 mm. Therefore, in the hypertensive population without carotid atherosclerosis, physicians should consider ambulatory BP monitoring to determine the nocturnal BP pattern as an alternative approach to assessing cardiovascular events.

Consequences of Type 1 and 2 Diabetes Mellitus on the Cardiovascular Regulation During Exercise: A Brief Review

INTRODUCTION

One challenging problem in patients suffering from Diabetes Mellitus (DM) is the elevate incidence of cardiovascular events. Exercise has been proved useful in reducing cardiovascular risks in these patients. However, both type 1 and 2 DM significantly affect the cardiovascular response during exercise. Therefore, on one side exercise is considered to be a valid therapeutic tool for DM, whereas on the other side during exercise these patients may experience troubles in the cardiovascular regulation.

BACKGROUND

Several impairments at central and at peripheral level have been reported during exercise in both types of DM. For example, sympathetic dysfunctions have been demonstrated in type 1 and 2 DM. Furthermore, impairments in hemodynamics have been often reported. The purpose of the present paper is to briefly review the latest data on the role played by type 1 and 2 DM in the cardiovascular regulation during dynamic exercise.

CONCLUSION

Hemodynamic dysfunctions may develop in both type 1 and 2 DM during exercise. However, these cardiovascular dys-regulations are different between the two kinds of diabetes.

Heart rate responses induced by acoustic tempo and its interaction with basal heart rate

Many studies have revealed the influences of music on the autonomic nervous system (ANS). Since previous studies focused on the effects of acoustic tempo on the ANS, and humans have their own physiological oscillations such as the heart rate (HR), the effects of acoustic tempo might depend on the HR. Here we show the relationship between HR elevation induced by acoustic tempo and individual basal HR. Since high tempo-induced HR elevation requires fast respiration, which is based on sympatho-respiratory coupling, we controlled the participants’ respiration at a faster rate (20 CPM) than usual (15 CPM). We found that sound stimuli with a faster tempo than the individual basal HR increased the HR. However, the HR increased following a gradual increase in the acoustic tempo only when the extent of the gradual increase in tempo was within a specific range (around + 2%/min). The HR did not follow the increase in acoustic tempo when the rate of the increase in the acoustic tempo exceeded 3% per minute. These results suggest that the effect of the sympatho-respiratory coupling underlying the HR elevation caused by a high acoustic tempo depends on the basal HR, and the strength and the temporal dynamics of the tempo.

Sympathetic Tone Induced by High Acoustic Tempo Requires Fast Respiration

Many studies have revealed the influences of music, and particularly its tempo, on the autonomic nervous system (ANS) and respiration patterns. Since there is the interaction between the ANS and the respiratory system, namely sympatho-respiratory coupling, it is possible that the effect of musical tempo on the ANS is modulated by the respiratory system. Therefore, we investigated the effects of the relationship between musical tempo and respiratory rate on the ANS. Fifty-two healthy people aged 18–35 years participated in this study. Their respiratory rates were controlled by using a silent electronic metronome and they listened to simple drum sounds with a constant tempo. We varied the respiratory rate—acoustic tempo combination. The respiratory rate was controlled at 15 or 20 cycles per minute (CPM) and the acoustic tempo was 60 or 80 beats per minute (BPM) or the environment was silent. Electrocardiograms and an elastic chest band were used to measure the heart rate and respiratory rate, respectively. The mean heart rate and heart rate variability (HRV) were regarded as indices of ANS activity. We observed a significant increase in the mean heart rate and the low (0.04–0.15 Hz) to high (0.15–0.40 Hz) frequency ratio of HRV, only when the respiratory rate was controlled at 20 CPM and the acoustic tempo was 80 BPM. We suggest that the effect of acoustic tempo on the sympathetic tone is modulated by the respiratory system.

Prognostic significance of dipping in older hypertensive patients

BACKGROUND AND AIMS

Arterial hypertension doubles the risk of coronary heart disease, heart and kidney failure, and peripheral arterial disease. Less variation in diurnal ambulatory blood pressure monitoring (ABPM) patterns may affect mortality outcome. Therefore, as hypertension occurs in over 95% of older subjects, the prognostic value of dipping status in older hypertensive patients will be assessed.

METHOD

The retrospective study group consisted of 170 hypertensive patients, aged 75-84 years, enrolled in the years 2005 to 2007. Baseline measures included 24-h ABPM. Diurnal index and dipping status was calculated and stratified the group into dippers (40 patients, 23.5%), non-dippers (65 patients, 38.2%) and reverse-dippers (65 patients, 38.2%).

RESULTS

During a 5-year observation, after baseline we have observed 69 deaths (40.9%) from the whole group of 170 patients with 23 (35.4%) being non-dippers and 36 (55.4%) reverse-dippers. There were significant differences between the groups divided according to diurnal dipping status in survival time, number of recorded deaths and night mean blood pressure. We have identified and confirmed risk factors for the all-cause mortality: age, mean systolic and diastolic blood pressure, diurnal index and dipping status (dipping, non-dipping or reverse-dipping).

CONCLUSION

Reverse-dippers and non-dippers revealed worse prognosis compared with dippers.

Attenuated dopaminergic tone in the paraventricular nucleus contributing to sympathoexcitation in rats with Type 2 diabetes

The study was conducted to investigate the role for dopamine in the centrally mediated sympathoexcitatory response in rats with Type 2 diabetes (T2D). T2D was induced by a combination of high-fat diet (HFD) and low-dose streptozotocin (STZ). HFD/STZ treatment for 12-14 wk resulted in significant increase in the number of FosB-positive cells in the paraventricular nucleus (PVN) and rostral ventrolateral medulla (RVLM). In anesthetized rats, administration of exogenous dopamine (dopamine hydrochloride, 20 mM) in the PVN, but not in the RVLM, elicited decreases in renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) in control rats and but not in the T2D rats. Blocking the endogenous dopamine with dopamine D1/D5 receptor antagonist SCH39166 (2 mM) in the PVN and RVLM, resulted in increases in RSNA, MAP, and heart rate (HR) in both control and T2D rats. These responses were significantly attenuated in T2D rats compared with control rats (PVN - ΔRSNA: 21 ± 10 vs. 44 ± 2%; ΔMAP: 7 ± 3 vs. 19 ± 6 mmHg, ΔHR: 17 ± 5 vs. 32 ± 4 bpm, P < 0.05). There were no significant increases in response to dopamine D2/D3 receptor antagonist raclopride application in the PVN and RVLM of both control and T2D rats. Furthermore, there were decreased dopamine D1 receptor and D2 receptor expressions in the PVN of T2D rats. Taken together, these data suggest that reduced endogenous dopaminergic tone within the PVN may contribute to the sympathoexcitation in T2D.

Cardiac sympathetic dysfunction in the prehypertensive spontaneously hypertensive rat

Recent studies in prehypertensive spontaneously hypertensive rats (SHR) have shown larger calcium transients and reduced norepinephrine transporter (NET) activity in cultured stellate neurons compared with Wistar-Kyoto (WKY) controls, although the functional significance of these results is unknown. We hypothesized that peripheral sympathetic responsiveness in the SHR at 4 wk of age would be exaggerated compared with the WKY. In vivo arterial pressure (under 2% isoflurane) was similar in SHRs (88 ± 2/50 ± 3 mmHg, n = 18) compared with WKYs (88 ± 3/49 ± 4 mmHg, n = 20). However, a small but significant (P < 0.05) tachycardia was observed in the young SHR despite the heart rate response to vagus stimulation (3 and 5 Hz) in vivo being similar (SHR: n = 12, WKY: n = 10). In isolated atrial preparations there was a significantly greater tachycardia during right stellate stimulation (5 and 7 Hz) in SHRs (n = 19) compared with WKYs (n = 16) but not in response to exogenous NE (0.025-5 μM, SHR: n = 10, WKY: n = 10). There was also a significantly greater release of [(3)H]NE to field stimulation (5 Hz) of atria in the SHR (SHR: n = 17, WKY: n = 16). Additionally, plasma levels of neuropeptide Y sampled from the right atria in vivo were also higher in the SHR (ELISA, n = 12 for both groups). The difference in [(3)H]NE release between SHR and WKY could be normalized by the NET inhibitor desipramine (1 μM, SHR: n = 10, WKY: n = 8) but not the α2-receptor antagonist yohimbine (1 μM, SHR: n = 7, WKY: n = 8). Increased cardiac sympathetic neurotransmission driven by larger neuronal calcium transients and reduced NE reuptake translates into enhanced cardiac sympathetic responsiveness at the end organ in prehypertensive SHRs.

Influence of dietary behavior on the circadian rhythm of the autonomic nervous system as assessed by heart rate variability

BACKGROUND

Misalignment of circadian systems is detrimental to human health. However, only a few studies have examined the influence of late meals on the human circadian system. The purpose of this study was to investigate whether delayed meals affect circadian rhythm as assessed by heart rate variability (HRV).

METHODS

Seven healthy men (aged 22.4±0.4years) participated in this study, which involved delaying mealtimes by 5h for two weeks. Prior to this study, the regular mealtimes of participants were at 08:00, 13:00, and 18:00 (Baseline). During the intervention, each meal was provided at 13:00, 18:00 and 23:00 (Late mealtimes). Circadian variation was assessed by HRV based on R-R intervals calculated from a pulse at the rising phase of each spike in the QRS complex in a 24-h electrocardiograph record. The ratio of low frequency (LF) to high frequency (HF) power (LF/HF) and the ratio of HF power to total power (%HF) were calculated using spectral analysis. The phase and amplitude of HRV variables in a 24-h period were mathematically obtained with double cosinor analysis.

RESULTS

The acrophase and amplitude for LF power, HF power and %HF in a 24-h period were not significantly different between Baseline and Late mealtimes. On the other hand, the acrophase significantly differed between Baseline and Late mealtimes for heart rate (95%CI, 1.1-3.8h), standard deviation of R-R intervals (95%CI, 2.5-4.4h) and LF/HF (95%CI, 1.1-2.3h).

CONCLUSIONS

Our findings suggest that delayed mealtimes shift the phase of circadian rhythm of the autonomic nervous system.

Relationship of plasma neuropeptide Y with angiographic, electrocardiographic and coronary physiology indices of reperfusion during ST elevation myocardial infarction

OBJECTIVES

The co-transmitter neuropeptide Y (NPY) is released during high levels of sympathetic stimulation and is a potent vasoconstrictor. We defined the release profile of plasma NPY during acute ST elevation myocardial infarction, and tested the hypothesis that levels correlate with reperfusion measures after treatment with primary percutaneous coronary intervention (PPCI).

DESIGN

Prospective observational study.

SETTING

University hospital heart centre.

PATIENTS

64 patients (62.6±11.7 years-old, 73% male) presenting throughout the 24-h cycle of clinical activity with ST elevation myocardial infarction.

INTERVENTIONS

PPCI.

MAIN OUTCOME MEASURES

NPY was measured (ELISA) in peripheral blood taken before and immediately after PPCI and at 6, 24 and 48 h post-PPCI. Reperfusion was assessed by angiographic criteria, ST segment resolution, invasive measurement of coronary flow reserve and the index of microcirculatory resistance.

RESULTS

Plasma NPY levels were highest before PPCI (17.4 (8.8-42.2) pg/ml, median (IQR)) and dropped significantly post-PPCI (12.4 (6.5-26.7) pg/ml, p<0.0001) and after 6 h (9.0 (2.6-21.5) pg/ml, p=0.008). Patients with admission NPY levels above the median were significantly more hypertensive and tachycardic and were more likely to have diabetes mellitus. Patients with angiographic no-reflow (less than thrombolysis in myocardial infarction 3 flow and myocardial blush grade >2, n=16) or no electrocardiographic ST resolution (<70%, n=30) following PPCI had significantly higher plasma NPY levels. Patients with a coronary flow reserve <1.5 or index of microcirculatory resistance >33 also had significantly higher plasma NPY levels pre-PPCI and post-PPCI.

CONCLUSIONS

Plasma NPY levels correlate with indices of reperfusion and coronary microvascular resistance.

Diabetic cardiomyopathy: pathophysiological mechanisms and cardiac dysfuntion

Several experimental, pathological, epidemiological, and clinical studies have clearly depicted that diabetes mellitus results in cardiac functional and structural changes. Diabetic cardiomyopathy results in both structural and functional alterations in the myocardium. Several mechanisms have been implicated in the pathophysiology of diabetic cardiomyopathy. Of these, metabolic disturbances, myocardial fibrosis, small vessel disease, and cardiac autonomic neuropathy are the major players in the pathophysiology of diabetic cardiomyopathy. This review is intended to discuss various such pathophysiological mechanisms of diabetic cardiomyopathy. We have also described the systolic and diastolic dysfunctioning and its corelation to structural changes in diabetes.

Diurnal salivary cortisol and urinary catecholamines are associated with diabetes mellitus: the Multi-Ethnic Study of Atherosclerosis

The objective was to examine the cross-sectional association of diurnal salivary cortisol curve components and urinary catecholamines with diabetes status. Up to 18 salivary cortisol samples over 3 days and overnight urinary catecholamines were collected from 1002 participants in the Multi-Ethnic Study of Atherosclerosis. Diabetes was defined as a fasting blood glucose of at least 126 mg/dL or medication use. Cortisol curve measures included awakening cortisol, cortisol awakening response, early decline, late decline, and cortisol area under the curve (AUC). Urinary catecholamines included epinephrine, norepinephrine, and dopamine. Participants with diabetes had significantly lower cortisol awakening response (β = -0.19; 95% confidence interval [CI], -0.34 to -0.04) than those without diabetes in multivariable models. Whereas men with diabetes had a nonsignificant trend toward lower total AUC (β = -1.56; 95% CI, -3.93 to 0.80), women with diabetes had significantly higher total AUC (β = 2.62; 95% CI, 0.72 to 4.51) (P = .02 for interaction) compared with those without diabetes. Men but not women with diabetes had significantly lower urinary catecholamines compared with those without diabetes (P < .05). Diabetes is associated with neuroendocrine dysregulation, which may differ by sex. Further studies are needed to determine the role of the neuroendocrine system in the pathophysiology of diabetes.

Habituation of rapid sympathetic response to aversive timbre eliminated by change in basal sympathovagal balance

We studied the difference in the habituation of the rapid sympathetic response to slightly and highly aversive timbres in 68 males. We measured the decrease in the blood volume pulse amplitude (BVP response) as the rapid sympathetic response and the low- (0.04-0.15 Hz) to high- (0.15-0.40 Hz) frequency (LF/HF) ratio of heart rate variability as the sympathovagal balance. The BVP response was suppressed for slightly aversive timbres that had been presented once before, but not for a highly aversive timbre. In contrast, the prior presentation of a highly aversive timbre enhanced the BVP response to a slightly aversive timbre. Only a highly aversive timbre reduced the LF/HF ratio. We suggest that the lack of habituation of the rapid sympathetic response to an aversive timbre is the result of the balance between the effects of the increase caused by the change in sympathovagal balance to vagal dominance and the decrease caused by classical habituation.

The circadian pattern of cardiac autonomic modulation in a middle-aged population

Objectives

To examine the circadian pattern of cardiac autonomic modulation (CAM) and its attributes in general population.

Methods

We obtained 24-h beat-to-beat RR data using a high resolution 12-lead Holter ECG in a community-dwelling sample of 115 non-smokers. We performed heart rate variability (HRV) analysis on the normal RRs from each 5-min segment to obtain time-specific HRV indices: high (HF; 0.15–0.40 Hz) and low (LF; 0.04–0.15 Hz) frequency powers, standard deviation of RR intervals (SDNN), and the square root of the mean of the sum of the squared differences of the adjacent RR intervals (RMSSD). For each individual, we fit the segment-specific HRV data to a cosine periodic function, and estimated 3 individual-level cosine function parameters to quantify the circadian variation: the mean (M), amplitude (A), and acrophase (θ). We then used a random-effects meta-analysis to summarize the M, A, and θ, and their 95% confidence intervals (CI).

Results

The mean age was 56 (SD 8) years, with 63% female and 76% white. The averages of M, A and θ (95%CI) of log HF were 3.59 (3.43–3.76) ms², 0.61 (0.54–0.68) ms², and 3:10 (2:25–3:55) AM, respectively, and that of RMSSD were 22.3 (20.5–24.1) ms, 6.5 (5.4–7.5) ms, 3:45 (2:55–4:35) AM, respectively. Older age is associated with lower mean of HRV. Males have higher oscillation amplitude than females. The acrophase of LF/HF was earlier in females than in males, and in younger individuals than in older individuals.

Conclusions

The circadian pattern of CAM can be quantified by 3 cosine parameters of HRV, which are correlated with age and gender.

Increased heart rate variability during sleep is a predictor for future cardiovascular events in patients with type 2 diabetes

We aimed this study to test the hypotheses that heart rate (HR) variability, evaluated by ambulatory blood pressure monitoring (ABPM), predicts risk of incident cardiovascular disease (CVD) in patients with type 2 diabetes (T2DM). ABPM was performed in 200 normotensive or hypertensive subjects with T2DM and 257 hypertensive subjects without diabetes (the mean age: 66.9+/-9.2 years; 38% were male). All subjects were untreated at the time of ABPM, and were followed for 67+/-27 months. Various measures of HR variability-standard deviation (s.d.) of HR, the root-mean-square of successive differences (RMSSD) of HR, systolic blood pressure (SBP)-HR relationships evaluated by slope and coefficients of correlation between SBP and HR-were used for the analyses. Cox proportional hazard models were used to estimate hazard ratios and 95% confidence intervals, after controlling for age, sex, body mass index, serum creatinine and 24-h SBP. During follow-up, there were 34 cardiovascular events. Awake HR variability in diabetics was smaller than non-diabetics, but sleep HR variability was similar between the groups. In multivariable analyses, increased sleep HR variability evaluated by s.d. and RMSSD of sleep HR, and slope and correlation coefficient of SBP-HR each was independently associated with the increased risk of CVD in T2DM. For non-diabetics, decreased slope of 24 h SBP-HR, and decreased correlation of 24 h SBP-HR were associated with increased risk of CVD. In conclusion, increased HR variability during sleep was a predictor for incident CVD in T2DM, but not in non-diabetics. Increased HR variability at night would reflect pathophysiological mechanism of T2DM.

Effects of exenatide on systolic blood pressure in subjects with type 2 diabetes

BACKGROUND

The majority of patients with type 2 diabetes mellitus have blood pressure (BP) exceeding the recommended value of <130/80 mm Hg. Optimal control of hyperglycemia and hypertension has been shown to reduce the incidence of macrovascular and microvascular complications due to diabetes. Treatment with the GLP-1 receptor agonist exenatide, previously demonstrated to reduce hemoglobin A(1C) and weight in subjects with type 2 diabetes, was associated with BP reduction in several studies.

METHODS

This analysis explored the effects of exenatide vs. placebo or insulin on BP measurements in pooled data from six trials including 2,171 subjects studied for at least 6 months.

RESULTS

Overall, 6 months of exenatide treatment was associated with a significantly greater reduction in systolic BP (SBP) compared with placebo (least squares mean (s.e.): difference of -2.8 mm Hg (0.75); P = 0.0002) or insulin (difference of -3.7 mm Hg (0.85); P < 0.0001). No significant intergroup differences in diastolic BP (DBP) were observed. The majority of the intergroup difference was observed in subjects with SBP > or = 130 mm Hg (difference of -3.8 mm Hg (1.08) from placebo: P = 0.0004; difference of -4.0 mm Hg (1.01) from insulin; P < 0.0001). The largest intertreatment differences between exenatide and comparators were observed in subjects with SBP >/=150 mm Hg. Similar responses were observed in African-American subjects. A weak correlation between the amount of weight lost and reduction in SBP was found (r = 0.09, P = 0.002) for exenatide-treated subjects.

CONCLUSIONS

These results support the need for a prospective, randomized, controlled study of BP changes during exenatide treatment in patients with hypertension and type 2 diabetes.

24-hour variation in the reactivity of rate-pressure-product to everyday physical activity in patients attending a hypertension clinic

The exercise-related response of the rate-pressure-product (RPP) is a prognostic marker of autonomic imbalance, cardiovascular mortality, and silent myocardial ischemia in hypertension. In view of the well-known 24 h variation in out-of-hospital sudden cardiac events, our aim was to investigate whether the reactivity of RPP to everyday physical activities varies over the 24 h. Ambulatory measurements of systolic blood pressure (BP) and heart rate were recorded every 20 min for 24 h in 440 diurnally active patients attending a hypertension clinic. Wrist activity counts were summed over the 15 min that preceded a BP measurement. An RPP reactivity index was derived for each of twelve 2 h data bins by regressing the change in RPP against the change in logged activity counts. The RPP showed 24 h variation (p < 0.0005), with a peak of 11,004 (95% CI = 10,757 to 11,250) beat . min(-1) . mmHg occurring at 10:00 h (2 h after mean wake-time). The overall 24 h mean of RPP reactivity was 477 beat . min(-1) . mmHg . logged activity counts(-1) (95% CI = 426 to 529). The largest increase in RPP reactivity occurred within the first 2 h after waking (p < 0.0005). There were no subsequent significant differences in RPP reactivity up to 14 h after waking. The lowest RPP reactivity was found 18-20 h after waking, with a peak-to-trough variation of 593 beat . min(-1) . mmHg . logged activity counts(-1) (95% CI = 394 to 791, p < 0.0005). Although this variation was not moderated by BP status, age, or sex, less variability in RPP reactivity was found for the medicated individuals during the waking hours. These data suggest that under conditions of normal living, the reactivity of RPP to a given change in physical activity increases markedly during the first 2 h after waking from nocturnal sleep, the time when out-of-hospital sudden cardiac events are also most common. Therefore, these data add weight to the notion that reactivity of RPP to physical activity could be a prognostic marker of autonomic imbalance and cardiovascular mortality, although more research is needed to assess the specific prognostic value of 24 h ambulatory measurements of RPP and physical activity.

Non-dipping pattern in ambulatory blood pressure monitoring is associated with metabolic abnormalities in a random sample of middle-aged subjects

A reduction in the blood pressure decline at night (<10% from daytime systolic blood pressure (SBP)) during 24-h ambulatory blood pressure monitoring (ABPM) ('non-dipping pattern') is associated with cardiovascular morbidity. Our aim was to evaluate whether ABPM characteristics are associated with metabolic abnormalities in subjects without known hypertension or type 2 diabetes mellitus (T2DM). This is a cross-sectional population-based study on middle-aged subjects (n=462). Two distinct definitions of metabolic syndrome (MetS) were used: National Cholesterol Education Program-Third Adult Treatment Panel (NCEP-ATPIII) and International Diabetes Federation (IDF) criteria. Results suggested that subjects characterized by non-dipping in 24 h ABPM were more obese (P=0.014). After adjustment for body mass index, age and sex, non-dippers had higher very-low-density lipoprotein (VLDL)-cholesterol (P=0.003), total (P=0.029)-and VLDL-triglycerides (P=0.026) and oral glucose tolerance test 2 h blood glucose (P=0.027) compared with dippers. Non-dipping status was more common among subjects with MetS (P< or =0.01), impaired glucose tolerance (IGT) (P<0.05) and in those with the combination of IGT-T2DM (P< or =0.01) than among those without these abnormalities. ABPM non-dipping status was an independent predictor of IGT in multivariate models (P<0.05). With respect to MetS components, high triglycerides (P< or =0.005) and low high density lipoprotein-cholesterol (P<0.05) were associated with a non-dipping pattern. The percentage decline in blood pressure from day to night decreased with the number of metabolic abnormalities (P=0.012). In conclusion, ABPM non-dipping status is an independent predictor of glucose intolerance. It is also associated with several other metabolic abnormalities. Whether non-dipping pattern is causally related to these metabolic aberrations remains to be explored in a future prospective follow-up of this cohort.

Sleep-disordered breathing and 24-hour blood pressure pattern among older adults

BACKGROUND

To examine the association between sleep-disordered breathing (SDB) and 24-hour blood pressure (BP) pattern among community-dwelling older adults.

METHODS

A convenience sample of 70 community-dwelling older adults, recruited from senior housing, community centers, and learning centers, were admitted to General Clinical Research Center, Emory University Hospital, Atlanta, Ga. Information regarding demographic and clinical history was obtained using questionnaires. Twenty-four-hour BP monitoring in supine position was performed using Spacelabs model 20207. Breathing during sleep was monitored with the use of a modified sleep recording system (Embletta, PDS), which monitors nasal and oral airflow, chest and abdominal movements, and pulse oximetry. Night time-daytime (night-day) BP ratio (average night-time BP divided by daytime BP) was calculated both for systolic and diastolic BPs.

RESULTS

Sixty-nine participants, mean age 74.9 +/- 6.4 years (41 [57%] women), completed the study. The mean apnea-hypopnea index (AHI) was 13 +/- 13 per hour of sleep, and 20 participants (29%) had AHI > or =15 per hour of sleep, indicating moderate to severe SDB. Moderate to severe SDB (AHI > or =15 per hour of sleep) was significantly associated with nocturnal hypertension, whereas there was no statistically significant difference in wake-time BP between those with and without moderate to severe SDB. Stepwise multiple regressions showed that AHI independently predicted increased night-day systolic and night-day diastolic BP ratio, even after controlling for nocturia frequency.

CONCLUSIONS

The results indicate increased BP load associated with increased AHI in this group of older adults. This increased BP load may contribute to increased hypertension-related morbidity and disease burden.

Association between circadian rhythm of blood pressure and glucose tolerance status in normotensive, non-diabetic subjects

AIMS

To examine whether circadian rhythm of blood pressure (BP) is associated with glucose tolerance status in normotensive, non-diabetic subjects.

METHODS

A cross-sectional study recruited normotensive and non-diabetic subjects, aged 35-79 years. A 75 g oral glucose tolerance test (OGTT) and 24-h ambulatory blood pressure monitoring (24-h ABPM) were performed.

RESULTS

Among 31 impaired glucose tolerance (IGT) and 36 normal glucose tolerance (NGT) study subjects, the mean (+/-S.D.) diurnal-nocturnal differences of average systolic BP (SBP) were 7.1+/-6.9 and 9.9+/-6.2 mmHg, respectively (p=0.086). In a linear mixed-effects regression model, however, taking each measurement of BP as the outcome, nighttime reduction of SBP in the IGT group was 7.19 mmHg, which was significantly smaller compared to a reduction of 9.80 mmHg in the NGT group (p-value for IGT: nighttime interaction=0.0014). The prevalence of non-dipping BP pattern was 77.4% in the IGT group which was significantly higher than 52.8% of the NGT group (p=0.036). Logistic regression revealed a significant effect of IGT for predicting non-dipping pattern with an adjusted odds ratio of 3.71 (95% CI: 1.09, 12.66, p=0.029).

CONCLUSIONS

Among normotensive, non-diabetic subjects, the decreased nocturnal BP reduction was associated with impaired glucose tolerance status.

Hypertension and disrupted blood pressure circadian rhythm in type 2 diabetic db/db mice

Human Type 2 diabetes is associated with increased incidence of hypertension and disrupted blood pressure (BP) circadian rhythm. Db/db mice have been used extensively as a model of Type 2 diabetes, but their BP is not well characterized. In this study, we used radiotelemetry to define BP and the circadian rhythm in db/db mice. We found that the systolic, diastolic, and mean arterial pressures were each significantly increased by 11, 8, and 9 mmHg in db/db mice compared with controls. In contrast, no difference was observed in pulse pressure or heart rate. Interestingly, both the length of time db/db mice were active (locomotor) and the intensity of locomotor activity were significantly decreased in db/db mice. In contrast to controls, the 12-h light period average BP in db/db mice did not dip significantly from the 12-h dark period. A partial Fourier analysis of the continuous 72-h BP data revealed that the power and the amplitude of the 24-h period length rhythm were significantly decreased in db/db mice compared with the controls. The acrophase was centered at 0141 in control mice, but became scattered from 1805 to 0236 in db/db mice. In addition to BP, the circadian rhythms of heart rate and locomotor activity were also disrupted in db/db mice. The mean arterial pressure during the light period correlates with plasma glucose, insulin, and body weight. Moreover, the oscillations of the clock genes DBP and Bmal1 but not Per1 were significantly dampened in db/db mouse aorta compared with controls. In summary, our data show that db/db mice are hypertensive with a disrupted BP, heart rate, and locomotor circadian rhythm. Such changes are associated with dampened oscillations of clock genes DBP and Bmal1 in vasculature.

Molecular clocks, type 2 diabetes and cardiovascular disease

The westernised world is in the midst of an epidemic of type 2 diabetes and associated cardiovascular disease. These closely interlinked conditions have a common pathophysiological basis underpinned by insulin resistance and the metabolic syndrome. Contemporary changes in environmental factors on a background of genetic susceptibility are thought to account for the increases seen. Life on earth is governed by the 24-hour environment of light and darkness cycling with the rotation of the earth. Numerous metabolic and physiological pathways are coordinated to this 24-hour cycle by an endogenous clock. Recent epidemiological evidence and animal data suggest that disturbance of circadian rhythms through genetic and environmental influences on the molecular clock is pivotal in the pathogenesis of obesity, type 2 diabetes and cardiovascular disease. This review describes current knowledge on the topic.

Impaired diurnal blood pressure variation and all-cause mortality

BACKGROUND

Most healthy people exhibit a decrease in systolic blood pressure (SBP) at night. A drop of <10% from mean daytime values, "non-dipping," is associated with kidney disease and cardiovascular events. We hypothesized that non-dipping would predict all-cause mortality.

METHODS

Consecutive patients referred for ambulatory blood pressure (BP) monitoring at the Cleveland Clinic between 1994 and 2004 were included. Mean daytime (6 AM-11 PM) and nighttime (11 PM-6 AM) SBP values were calculated. We examined diurnal BP variation as a continuous variable, ((Mean daytime SBP - Mean nighttime SBP)/(Mean daytime SBP)) x 100%, and also as a categorical variable, defining "non-dipping" as a nocturnal SBP drop of <10%; subjects who exhibited non-dipping were defined as "non-dippers" and the others as "dippers." All-cause mortality was ascertained from the Social Security Death Index.

RESULTS

Of the 621 patients included in the study, 261 were dippers and 360 were non-dippers. Non-dippers were older (P < 0.0001), more likely to be non-white (P < 0.05), and had higher rates of smoking, diabetes, hypertension, coronary artery disease, congestive heart failure, and renal insufficiency (P < 0.01 for all). Over a mean follow-up of 6.3 years, 61 patients died, including 10 dippers (3.8%) and 51 non-dippers (14.2%). The unadjusted hazard ratio for death based upon a decrement in the dipping percentage from the 75th to 25th percentile was 2.22 (95% confidence interval 1.64-2.95; P < 0.0001). This was attenuated after adjustment for comorbid conditions, including mean 24-h SBP and renal function: adjusted hazard ratio 1.62 (1.14-2.24; P < 0.005).

CONCLUSIONS

Blunted diurnal BP variation is a strong predictor of death, but this may be accounted for, in large part, by its association with other cardiovascular risk factors.

Adrenal insufficiency, heart rate variability, and complex biologic systems: a study of 1,871 critically ill trauma patients

BACKGROUND

Reduction in integer heart rate variability (HRVi), one potential measurement of complex biologic systems, is common in ICU patients and is strongly associated with hospital mortality. Adrenal insufficiency (AI) and reduced HRVi are associated with autonomic dysfunction. Failure of the autonomic nervous system can be associated with loss of biologic complexity. We hypothesize decreased HRVi is associated with AI, and HRVi improves after treatment of AI, suggesting "recomplexification" (resumption of normal stress response to injury).

STUDY DESIGN

Of 4,116 trauma ICU admissions from December 2000 to November 2005, 1,871 patients had sufficient physiologic, laboratory, pharmacy, and demographic data for analysis. Seventy-five patients failing cosyntropin-stimulation testing were defined as AI; the remaining 1,796 were defined as no AI. HRVi was calculated as integer heart rate standard deviation over 5-minute intervals. HRVi 10th, 50th (median), and 90th percentiles were calculated over the 72 hours pre-, or poststeroid, or both administration (AI). HRVi percentiles in non-AI patients were evaluated at the same interval and compared with AI using Wilcoxon's rank-sum test. In patients with AI, daily HRVi was computed 3 days before and after steroid administration, and compared between survivors and nonsurvivors.

RESULTS

There were 2.9 million heart-rate intervals measured. HRVi stratified patients with AI (cosyntropin failure), and without AI. HRVi was similar in AI survivors and nonsurvivors before steroid treatment, but differed after treatment. HRVi increased substantially in survivors after steroid administration, yet did not change in nonsurvivors. HRVi does not increase in patients who are unresponsive to steroids and die.

CONCLUSIONS

Reduced heart-rate variability, a potential measurement of complex biologic systems, is associated with cosyntropin-confirmed AI; improved in patients responding to steroid therapy; and is a noninvasive, real-time biomarker suggesting AI.

Abnormal blood pressure circadian rhythm: a target organ damage?

Blood pressure (BP) varies according to cycles characterized by a reduction during sleep and an increase on awakening. The nighttime decrease is absent or blunted in some patients (termed "non-dippers"). Cross-sectional and prospective data have shown that non-dippers have more target organ damage than have dippers in normotensive and hypertensive subjects. We reviewed the English language literature regarding this association. A non-fortuitous association seems to exist between non-dipper status and cardiovascular risk such as stroke and cardiac events. Among diabetic patients, this phenomenon has been described to occur more often in individuals with autonomic neuropathy and with different degrees of diabetic nephropathy. In normoalbuminuric normotensive type I diabetic patients without any degree of autonomic dysfunction, according to traditional cardiovascular tests, diastolic BP (dBP) night/day ratio is associated with an increased glomerular filtration rate and an increased extracellular volume. The disruption of the circadian rhythm of sympathovagal activity in non-dipper patients was associated with higher levels in systolic BP (sBP) and dBP and with a reduced decline in sBP and dBP levels during the night. Therefore, the prognostic implications of the non-dipper status may be important since the overall 24-h blood pressure load is elevated in these individuals. These data suggest that patients in whom blood pressure decreases during the night incur less damage to their brain, kidneys, heart, and blood vessels than people with elevated nocturnal BP.

Brain natriuretic peptide and cardiac autonomic function in type 2 diabetic patients

The present study tested the hypothesis that increased plasma brain natriuretic peptide (BNP) levels are related to cardiac autonomic dysfunction in type 2 diabetic patients. A total of 32 consecutive Japanese patients with type 2 diabetes were assigned to either a high-BNP (>or=18 pg/ml) group (n=12; age 57+/-13 years, mean+/-S.D.) or a normal-BNP (<18 pg/ml) group (n=20; 59+/-10 years). No patient had any overt structural heart disease. Cardiac autonomic function was assessed by measurements of baroreflex sensitivity (BRS), heart rate variability (HRV) and cardiac (123)I-metaiodobenzylguanidine (MIBG) scintigraphic findings. BRS was lower (p<0.005) in the high-BNP group than in the normal-BNP group. However, the components of HRV, and the early and delayed myocardial uptake of (123)I-MIBG and percentage washout rate of (123)I-MIBG were not significantly different between the groups. The plasma level of BNP negatively correlated with BRS (r=0.35, p=0.049). These findings suggest that increased plasma BNP levels were related to cardiac reflex parasympathetic dysfunction in our Japanese type 2 diabetic patients.

Organization of circadian functions: interaction with the body

The hypothalamus integrates information from the brain and the body; this activity is essential for survival of the individual (adaptation to the environment) and the species (reproduction). As a result, countless functions are regulated by neuroendocrine and autonomic hypothalamic processes in concert with the appropriate behaviour that is mediated by neuronal influences on other brain areas. In the current chapter attention will be focussed on fundamental hypothalamic systems that control metabolism, circulation and the immune system. Herein a system is defined as a physiological and anatomical functional unit, responsible for the organisation of one of these functions. Interestingly probably because these systems are essential for survival, their function is highly dependent on each other's performance and often shares same hypothalamic structures. The functioning of these systems is strongly influenced by (environmental) factors such as the time of the day, stress and sensory autonomic feedback and by circulating hormones. In order to get insight in the mechanisms of hypothalamic integration we have focussed on the influence of the biological clock; the suprachiasmatic nucleus (SCN) on processes that are organized by and in the hypothalamus. The SCN imposes its rhythm onto the body via three different routes of communication: 1.Via the secretion of hormones; 2. via the parasympathetic and 3.via the sympathetic autonomous nervous system. The SCN uses separate connections via either the sympathetic or via the parasympathetic system not only to prepare the body for the coming change in activity cycle but also to prepare the body and its organs for the hormones that are associated with such change. Up till now relatively little attention has been given to the question how peripheral information might be transmitted back to the SCN. Apart from light and melatonin little is known about other systems from the periphery that may provide information to the SCN. In this chapter attention will be paid to e.g. the role of the circumventricular organs in passing info to the SCN. Herein especially the role of the arcuate nucleus (ARC) will be highlighted. The ARC is crucial in the maintenance of energy homeostasis as an integrator of long- and short-term hunger and satiety signals. Receptors for metabolic hormones like insulin, leptin and ghrelin allow the ARC to sense information from the periphery and signal it to the central nervous system. Neuroanatomical tracing studies using injections of a retrograde and anterograde tracer into the ARC and SCN showed a reciprocal connection between the ARC and the SCN which is used to transmit feeding related signals to the SCN. The implications of multiple inputs and outputs of the SCN to the body will be discussed in relation with metabolic functions.

Relation of diurnal blood pressure variation and triglyceride-to-high-density lipoprotein cholesterol ratio in patients without diabetes mellitus

A night-time decrease in systolic blood pressure that differs <10% from mean daytime values ("nondipping") is associated with increased rates of cardiovascular morbidity and mortality. We hypothesized that insulin resistance would be associated with nondipping in patients who did not have frank diabetes mellitus or hypertension. We included 106 consecutive outpatients who had been referred for 24-hour ambulatory monitoring of blood pressure. Our data suggest that insulin resistance, defined as a high ratio of triglyceride to high-density lipoprotein, is associated with blunted diurnal blood pressure variation (odds ratio 6.3, 95% confidence interval 2.6 to 16.4, p <0.0001) before the development of abnormal levels of fasting blood glucose.

Disparity of autonomic control in type 2 diabetes mellitus

AIMS/HYPOTHESIS

Acute insulinaemia activates the sympathetic drive in a nonuniform manner. The extent and nature of such activation in type 2 diabetic patients who do not have neuropathy have not yet been addressed despite evidence relating sympathetic activation to cardiovascular risk. We planned to determine the magnitude and extent of the sympathetic drive and its reflex responses in patients with type 2 diabetes and fasting hyperinsulinaemia.

METHODS

We measured resting muscle sympathetic nerve activity (MSNA) as the mean frequency of multi-unit bursts and single unit muscle sympathetic nerve activity (s-MSNA) in 17 overweight patients with type 2 diabetes and two matched normal control groups comprising 17 overweight and 16 normal-weight subjects. We also tested the MSNA and s-MSNA responses to cold pressor and isometric hand-grip tests, along with the effect of sympatho-vagal balance on heart period variability.

RESULTS

Both MSNA and s-MSNA in the group with type 2 diabetes (66+/-3.5 bursts/100 beats and 78+/-4.5 impulses/100 beats) were greater (at least p<0.0001) than in the overweight control group (42+/-2.6 bursts/100 beats and 48+/-3.4 impulses/100 beats) and normal-weight control group (43+/-6.2 bursts/100 beats and 51+/-7.1 impulses/100 beats), though the three groups had similar reflex responses, baroreflex sensitivity and sympatho-vagal balance controlling the heart period.

CONCLUSIONS/INTERPRETATION

The patients with type 2 diabetes had no evidence of impaired reflex or autonomic control of heart period variability at a time when there was central sympathetic activation to the periphery. Furthermore, being overweight itself was not associated with sympathetic activation.

Diabetic cardiomyopathy: evidence, mechanisms, and therapeutic implications

The presence of a diabetic cardiomyopathy, independent of hypertension and coronary artery disease, is still controversial. This systematic review seeks to evaluate the evidence for the existence of this condition, to clarify the possible mechanisms responsible, and to consider possible therapeutic implications. The existence of a diabetic cardiomyopathy is supported by epidemiological findings showing the association of diabetes with heart failure; clinical studies confirming the association of diabetes with left ventricular dysfunction independent of hypertension, coronary artery disease, and other heart disease; and experimental evidence of myocardial structural and functional changes. The most important mechanisms of diabetic cardiomyopathy are metabolic disturbances (depletion of glucose transporter 4, increased free fatty acids, carnitine deficiency, changes in calcium homeostasis), myocardial fibrosis (association with increases in angiotensin II, IGF-I, and inflammatory cytokines), small vessel disease (microangiopathy, impaired coronary flow reserve, and endothelial dysfunction), cardiac autonomic neuropathy (denervation and alterations in myocardial catecholamine levels), and insulin resistance (hyperinsulinemia and reduced insulin sensitivity). This review presents evidence that diabetes is associated with a cardiomyopathy, independent of comorbid conditions, and that metabolic disturbances, myocardial fibrosis, small vessel disease, cardiac autonomic neuropathy, and insulin resistance may all contribute to the development of diabetic heart disease.

Comparison of the effects of amlodipine and verapamil on autonomic activity in hypertensive patients

Background: Many studies have shown that autonomic activation is one of the major factors in the etiology of hypertension. Furthermore, sympathovagal imbalance may be responsible for arrhythmias and sudden cardiac death. The aim of the present study was to compare and to evaluate the effects of short-term therapy with amlodipine and verapamil on heart rate variability (HRV) in patients with essential hypertension. Methods: Forty patients with essential hypertension (11 men and 29 women, mean age 50.5+/-10.4 years) were included in the study. Patients with cardiac, metabolic, or any other systemic disease were excluded. Patients were randomized to receive either amlodipine (10 mg; n=20) or verapamil (240 mg; n=20). Patients underwent 24-h Holter monitoring assessment before treatment and after the 4-week treatment period. Standard deviation of normal RR intervals (SDNN), standard deviation of all 5-min mean normal RR intervals (SDANN), square root of the mean of the sum of the squares of differences between adjacent RR intervals (r-MSSD), and pNN50 (time domain variables) and TF, high-frequency power (HF), low-frequency power (LF), and sympathovagal balance (LF/HF; frequency domain variables) were analyzed before and after treatment. Results: Blood pressure (BP) was reduced to a similar degree, from 182/104 to 128/85 mmHg with verapamil and from 174/100 to 124/86 mmHg with amlodipine (verapamil p<0.001; amlodipine p<0.001). This study revealed that amlodipine had no significant effect on any of the time or frequency domain parameters. In contrast, in patients on verapamil, there were significant increases in all time domain parameters, and the LF/HF ratio was significantly decreased (p<0.05). Conclusions: These results suggest that verapamil may have additional positive effects on sympathico-parasympathetic control beyond lowering blood pressure compared with amlodipine, even after short-term treatment in hypertensive patients.

Impact of type 2 diabetes mellitus on sympathetic neural mechanisms in hypertension

BACKGROUND

Essential hypertension (EHT) is a major cardiovascular risk factor, and the additional presence of type 2 diabetes mellitus (DM2) increases this risk. However, although the sympathetic nerve hyperactivity of EHT is known to play a role in cardiovascular risk, the level of sympathetic nerve activity is known neither in DM2 nor in hypertensive type 2 diabetic patients (EHT+DM2). Therefore, we planned to quantify the vasoconstrictor sympathetic nerve activity in patients with EHT+DM2 and with DM2 relative to that in matched groups with EHT and normal blood pressure (NT).

METHODS AND RESULTS

In 68 closely matched subjects with EHT+DM2 (n=17), DM2 (n=17), EHT (n=17), and NT (n=17), we measured resting muscle sympathetic nerve activity as the mean frequency of multiunit bursts (MSNA) and of single units (s-MSNA) with defined vasoconstrictor properties. The s-MSNA in EHT+DM2 (97+/-3.8 impulses/100 beats) was greater (at least P<0.001) than in EHT (69+/-3.4 impulses/100 beats) and DM2 (78+/-4.1 impulses/100 beats), and all these were significantly greater (at least P<0.01) than in NT (53+/-3.3 impulses/100 beats) despite similar age and body mass index. The MSNA followed a similar trend. In addition, the level of insulin was also raised in EHT+DM2 (20.4+/-3.6 microU/mL) and DM2 (18.1+/-3.1 microU/mL; at least P<0.05) compared with HT or NT.

CONCLUSIONS

Patients with EHT+DM2, EHT, or DM2 had central sympathetic hyperactivity, although plasma insulin levels were raised only in EHT+DM2 and DM2. The combination of EHT and DM2 resulted in the greatest sympathetic hyperactivity and level of plasma insulin, and this hyperactivity could constitute a mechanism for the increased risks of this condition.

Are β-blockers as efficacious in patients with diabetes mellitus as in patients without diabetes mellitus who have chronic heart failure? A meta-analysis of large-scale clinical trials

BACKGROUND

Diabetes mellitus is a frequent comorbid condition in patients with chronic heart failure (CHF) and confers a worse prognosis. Furthermore, although patients with CHF derive considerable benefit from beta-blockers, these agents are thought by many physicians to be contraindicated in patients with diabetes mellitus. Most published studies on beta-blockers in CHF have been unable to reach definitive conclusions about the mortality benefits of these agents in patients with diabetes mellitus. We therefore performed a meta-analysis of beta-blocker trials that reported mortality outcomes in patients with diabetes mellitus who had CHF to pool all available trial evidence on the benefits (or otherwise) of these agents in this setting.

METHODS

All-cause mortality data on patients with diabetes mellitus were obtained from all completed beta-blocker CHF randomized placebo-controlled trials involving >100 patients exposed to beta-blockers, in which outcomes in patients with diabetes mellitus were described. When events were not directly reported, risk ratios (RRs) were derived from analysis of figures and other manuscript data. Results were pooled with the Mantel-Haenszel method.

RESULTS

A total of 24.6% of patients were reported to have diabetes mellitus in the 6 studies analyzed (Australia and New Zealand [ANZ]-Carvedilol, Beta-blocker Evaluation of Survival Trial [BEST], Carvedilol US Trials, Cardiac Insufficiency Bisoprolol Study [CIBIS-II], Carvedilol Prospective Randomized Cumulative Survival Trial [COPERNICUS], and Metoprolol Controlled-release Randomized Intervention Trial in Heart Failure [MERIT-HF]). Patients with diabetes mellitus had increased mortality rates overall compared with subjects without diabetes mellitus (RR, 1.25; 95% CI, 1.15-1.36; P <.001). Compared with placebo, beta-blocker therapy for CHF was beneficial in patients with diabetes mellitus (RR, 0.84; 95% CI, 0.73-0.96; P =.011) and in subjects without diabetes mellitus (RR, 0.72; 95% CI, 0.65-0.79; P <.001). The absolute risk reduction in mortality with beta-blocker therapy was greater in patients with heart failure but without diabetes mellitus than in patients with diabetes mellitus (P =.023).

CONCLUSIONS

Patients with diabetes mellitus and CHF appear to derive prognostic benefit from beta-blocker therapy, although the magnitude of that benefit is somewhat less than that observed in subjects without diabetes mellitus.