Circadian blood pressure variation in diabetic patients with autonomic neuropathy

Examining the Pre- and Post-percutaneous Coronary Intervention Blood Pressure Variability Using Ambulatory Blood Pressure Monitoring in Patients With Stable and Unstable Coronary Artery Disease

Introduction The World Health Organization has drawn attention to the fact that coronary artery disease (CAD) is our modern "epidemic." Nowadays, sudden death during sleep has become prevalent due to a lack of oxygen supply to the heart. CAD causes more deaths and disabilities and incurs greater economic costs than any other illness in the developed world. The prevalence of cardiovascular disorders and heart disease is on the rise in India. Hypertension is one of the leading risk factors for all cardiovascular diseases. This study aims to compare blood pressure variability before and after percutaneous coronary intervention (PCI), using ambulatory blood pressure monitoring (ABPM) in patients with stable and unstable CAD. Materials and methods This prospective observational study was conducted among 52 patients with stable and unstable CAD, admitted to the medicine department, who required PCI at a tertiary care hospital. Before and after PCI, the same antihypertensive drugs were orally administered. ABPM was performed before PCI and one day after PCI. ABPM was conducted every 30 minutes during the day and every 60 minutes during the night over a 24-hour period using a mobil-o-graph (IEM, Germany). The results of the observed parameters were analyzed using the HMS Client-Server 4.0 system (Informer Technologies, Inc., Los Angeles, USA). The collected data were analyzed using SPSS Statistics version 21.0 software (IBM Corp. Released 2012. IBM SPSS Statistics for Windows, Version 21.0. Armonk, NY: IBM Corp.). Results Out of 52 patients, 28 (53.8%) had stable CAD and 24 (46.2%) had unstable CAD. The mean age of patients with stable and unstable CAD was 56.64±9.44 and 57.04±12.36 years, respectively. The majority of patients with stable (67.9%) and unstable CAD (62.5%) were males. Various other variables were considered, such as lipid profile, blood sugar, cardiac troponin-I, and medical history, including hypertension and type 2 diabetes mellitus. Among stable CAD patients, a comparison between pre- and post-PCI systolic blood pressure (SBP) did not show a significant difference in all SBP measurements (p>0.05). However, the mean diurnal index was significantly lower following PCI compared to before PCI (p=0.019). Among unstable CAD patients, a comparison between pre- and post-PCI SBP showed a significant change in peak daytime, average daytime, and diurnal index (p<0.05). For all other SBP measurements, the difference between pre- and post-PCI measurements was not statistically significant (p>0.05). In patients with stable CAD, a statistically significant change in diastolic blood pressure (DBP) following PCI was observed for peak daytime, peak nighttime, and average nighttime values. In contrast, for patients with unstable CAD, a statistically significant change in DBP following PCI was observed for peak daytime, peak nighttime, and minimum daytime values (p<0.05). Statistically, post-PCI, there was no significant difference between the two groups for SBP and DBP measurements (p>0.05). Additionally, there was no significant difference between the two groups pre- and post-PCI in the pattern of dipping. Conclusion A comparison of the ABPM before and after PCI showed that, within 48 hours post-PCI, the ambulatory blood pressure indicators did not differ statistically from those before PCI.

The recommendations of a consensus panel for the screening, diagnosis, and treatment of neurogenic orthostatic hypotension and associated supine hypertension

Neurogenic orthostatic hypotension (nOH) is common in patients with neurodegenerative disorders such as Parkinson’s disease, multiple system atrophy, pure autonomic failure, dementia with Lewy bodies, and peripheral neuropathies including amyloid or diabetic neuropathy. Due to the frequency of nOH in the aging population, clinicians need to be well informed about its diagnosis and management. To date, studies of nOH have used different outcome measures and various methods of diagnosis, thereby preventing the generation of evidence-based guidelines to direct clinicians towards ‘best practices’ when treating patients with nOH and associated supine hypertension. To address these issues, the American Autonomic Society and the National Parkinson Foundation initiated a project to develop a statement of recommendations beginning with a consensus panel meeting in Boston on November 7, 2015, with continued communications and contributions to the recommendations through October of 2016. This paper summarizes the panel members’ discussions held during the initial meeting along with continued deliberations among the panel members and provides essential recommendations based upon best available evidence as well as expert opinion for the (1) screening, (2) diagnosis, (3) treatment of nOH, and (4) diagnosis and treatment of associated supine hypertension.

Administration-time differences in effects of hypertension medications on ambulatory blood pressure regulation

Specific features of the 24-h blood pressure (BP) pattern are linked to progressive injury of target tissues and risk of cardiovascular disease (CVD) events. Several studies have consistently shown an association between blunted asleep BP decline and risk of fatal and nonfatal CVD events. Thus, there is growing focus on ways to properly control BP during nighttime sleep as well as during daytime activity. One strategy, termed chronotherapy, entails the timing of hypertension medications to endogenous circadian rhythm determinants of the 24-h BP pattern. Significant and clinically meaningful treatment-time differences in the beneficial and/or adverse effects of at least six different classes of hypertension medications, and their combinations, are now known. Generally, calcium channel blockers (CCBs) are more effective with bedtime than morning dosing, and for dihydropyridine derivatives bedtime dosing significantly reduces risk of peripheral edema. The renin-angiotensin-aldosterone system is highly circadian rhythmic and activates during nighttime sleep. Accordingly, evening/bedtime ingestion of the angiotensin-converting enzyme inhibitors (ACEIs) benazepril, captopril, enalapril, lisinopril, perindopril, quinapril, ramipril, spirapril, trandolapril, and zofenopril exerts more marked effect on the asleep than awake systolic (SBP) and diastolic (DBP) BP means. Likewise, the bedtime, in comparison with morning, ingestion schedule of the angiotensin-II receptor blockers (ARBs irbesartan, olmesartan, telmisartan, and valsartan exerts greater therapeutic effect on asleep BP, plus significant increase in the sleep-time relative BP decline, with the additional benefit, independent of drug terminal half-life, of converting the 24-h BP profile into a more normal dipping pattern. This is the case also for the bedtime versus upon-awakening regimen of combination ARB-CCB, ACEI-CCB, and ARB-diuretic medications. The chronotherapy of conventional hypertension medications constitutes a new and cost-effective strategy for enhancing the control of daytime and nighttime SBP and DBP levels, normalizing the dipping status of their 24-h patterning, and potentially reducing the risk of CVD events and end-organ injury, for example, of the blood vessels and tissues of the heart, brain, kidney, and retina.

Effects of restricted fructose access on body weight and blood pressure circadian rhythms

High-fructose diet is known to produce cardiovascular and metabolic pathologies. The objective was to determine whether the timing of high fructose (10% liquid solution) intake affect the metabolic and cardiovascular outcomes. Male C57BL mice with radiotelemetric probes were divided into four groups: (1) 24 h water (control); (2) 24 h fructose (F24); (3) 12 h fructose during the light phase (F12L); (4) 12 h fructose during the dark phase (F12D). All fructose groups had higher fluid intake. Body weight was increased in mice on restricted access with no difference in total caloric intake. Fasting glycemia was higher in groups with restricted access. F24 mice showed a fructose-induced blood pressure increase during the dark period. Blood pressure circadian rhythms were absent in F12L mice. Results suggest that the timing of fructose intake is an important variable in the etiology of cardiovascular and metabolic pathologies produced by high fructose consumption.

Circadian rhythms in blood pressure regulation and optimization of hypertension treatment with ACE inhibitor and ARB medications

Specific features of the 24 h-blood pressure (BP) pattern are linked to the progressive injury of target tissues and risk of cardiac and cerebrovascular events. Studies have consistently shown an association between blunted asleep BP decline and increased incidence of fatal and nonfatal cardiovascular events. Thus, there is growing interest in how to achieve better BP control during nighttime sleep in addition to during daytime activity, according to the particular requirements of each hypertension patient. One approach takes into consideration the endogenous circadian rhythm-determinants of the 24-h BP pattern, especially, the prominent day-night variation of the renin-angiotensin-aldosterone system, which activates during nighttime sleep. A series of clinical studies have demonstrated a different effect of the angiotensin-converting enzyme (ACE) inhibitors benazepril, captopril, enalapril, lisinopril, perindopril, quinapril, ramipril, spirapril, and trandolapril when routinely ingested in the morning vs. the evening. In most cases, the evening schedule exerts a more marked effect on the asleep than awake BP means. Similarly, a once-daily evening, in comparison to morning, ingestion schedule of the angiotensin receptor blockers (ARBs) irbesartan, olmesartan, telmisartan, and valsartan exerts greater therapeutic effect on asleep BP, plus significant increase in the sleep-time relative BP decline, with normalization of the circadian BP profile toward a more dipping pattern, independent of drug terminal half-life. Chronotherapy, the timing of treatment to body rhythms, is a cost-effective means of both individualizing and optimizing the treatment of hypertension through normalization of the 24-h BP level and profile, and it may constitute an effective option to reduce cardiovascular risk.

Exercise training augments the dynamic heart rate response to vagal but not sympathetic stimulation in rats

We examined the transfer function of autonomic heart rate (HR) control in anesthetized sedentary and exercise-trained (16 wk, treadmill for 1 h, 5 times/wk at 15 m/min and 15-degree grade) rats for comparison to HR variability assessed in the conscious resting state. The transfer function from sympathetic stimulation to HR response was similar between groups (gain, 4.2 ± 1.5 vs. 4.5 ± 1.5 beats·min(-1)·Hz(-1); natural frequency, 0.07 ± 0.01 vs. 0.08 ± 0.01 Hz; damping coefficient, 1.96 ± 0.55 vs. 1.69 ± 0.15; and lag time, 0.7 ± 0.1 vs. 0.6 ± 0.1 s; sedentary vs. exercise trained, respectively, means ± SD). The transfer gain from vagal stimulation to HR response was 6.1 ± 3.0 in the sedentary and 9.7 ± 5.1 beats·min(-1)·Hz(-1) in the exercise-trained group (P = 0.06). The corner frequency (0.11 ± 0.05 vs. 0.17 ± 0.09 Hz) and lag time (0.1 ± 0.1 vs. 0.2 ± 0.1 s) did not differ between groups. When the sympathetic transfer gain was averaged for very-low-frequency and low-frequency bands, no significant group effect was observed. In contrast, when the vagal transfer gain was averaged for very-low-frequency, low-frequency, and high-frequency bands, exercise training produced a significant group effect (P < 0.05 by two-way, repeated-measures ANOVA). These findings suggest that, in the frequency domain, exercise training augments the dynamic HR response to vagal stimulation but not sympathetic stimulation, regardless of the frequency bands.

Autonomic blood pressure control in children and adolescents with type 1 diabetes mellitus

INTRODUCTION

Increased daytime blood pressure and reduced nocturnal dipping can already be found in children with type 1 diabetes mellitus. We hypothesized that impaired baroreflex sensitivity can cause this abnormal blood pressure behavior in children and adolescents with type 1 diabetes, reflecting an early stage of diabetic autonomic neuropathy.

METHODS

In the present study, we monitored beat-to-beat blood pressure and pulse interval non-invasively with portapres in 38 patients with type 1 diabetes (7-18 yr) and 14 non-diabetic subjects (5-17 yr). The Trigonometric Regressive Spectral Analysis was used to assign spontaneous oscillations of blood pressure and pulse interval to defined frequency bands between 0.003 and 1.0 Hz and to calculate baroreflex sensitivity. Correlations with diabetes-specific data like hemoglobin A1c (HbA1c) and with 24-h blood pressure measurements were calculated.

RESULTS

The diabetic subjects displayed significantly less variance of blood pressure and pulse interval in the high frequency (HF) bands and a lower BRS. BRS decreased with higher HbA1c and daily insulin dose. We also saw significant changes in spectral variance of blood pressure and pulse interval with these parameters. Patients with higher sympathetic activity (LF/HF-ratio) during daytime measurements displayed more nocturnal dipping.

CONCLUSION

Our data evidence impaired baroreflex sensitivity in children and adolescents with type 1 diabetes mellitus. We suggest spectral analysis of spontaneous blood pressure and pulse interval oscillations during night sleep to further pursue the role of baroreflex sensitivity in the etiology of the non-dipping phenomenon in diabetic patients.

Pulsatile intravenous insulin therapy: the best practice to reverse diabetes complications?

In the basal state and after oral ingestion of carbohydrate, the normal pancreas secretes insulin into the portal vein in a pulsatile manner. The end organ of the portal vein is the liver, where approximately 80% of pancreatic insulin is extracted during first pass. In Type 1 diabetes, pancreatic insulin secretion is nearly or completely absent whilst in Type 2 diabetes the normal pattern is absent, abnormal, or blunted. Exogenous subcutaneous insulin treatment results in plasma insulin concentrations that are not pulsatile and a fraction of normal portal vein levels. Oral hypoglycemic agents also do not result in normal pulsatile response to a glucose load. Due to hypoglycemia risk, intensive treatment is not recommended after serious complications develop. Consequently, no conventional therapy has proved effective in treating advanced diabetes complications. Beta-cell replacement using whole pancreas or islet transplantation has been utilized to treat certain problems in Type 1 diabetic patients, but still unavailable for all diabetics. Pulsatile intravenous insulin therapy (PIVIT) is an insulin therapy, which mimics the periodicity and amplitude of normal pancreatic function. Numerous studies show PIVIT effective in preventing, reversing, and reducing the severity and progression of diabetes complications, however, the mechanisms involved with the improvement are not clearly understood. Here, we review the cellular basis of normal and abnormal insulin secretion, current treatments available to treat diabetes, the physiologic basis of PIVIT and possible mechanisms of action.

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.

Effects of reduced coronary flow reserve on left ventricular function in type 2 diabetes

AIMS

Diabetic patients without clinical evidence of cardiovascular disease may develop left ventricular (LV) dysfunction. The present study was designed to test the hypothesis that coronary microvascular dysfunction affects LV function in type 2 diabetic patients.

METHODS

The study subjects were 20 type 2 diabetic patients and 15 controls, who had been angiographically determined to have normal coronary arteries. LV ejection fraction (LVEF) and the percentage change in LVEF during dobutamine infusion (DeltaLVEF) were measured as an index of LV function. In order to evaluate coronary flow reserve, coronary flow velocity was recorded using a Doppler guide wire.

RESULTS

There were no significant differences in LVEF. DeltaLVEF was significantly lower in the diabetic patients than in the control subjects (p<0.01). Although there was no significant difference in the baseline coronary volumetric flow between the two groups, values during maximal hyperemia were significantly less in the diabetic patients than in the controls (p<0.05). Consequently, coronary flow reserve was significantly lower (p=0.0001). A significant positive correlation between coronary flow reserve and DeltaLVEF was exhibited (r=0.68, p=0.0009).

CONCLUSIONS

Coronary flow reserve, an indicator of coronary microvascular function, is significantly reduced in type 2 diabetes, and this is reflected in impairment of myocardial contractile reserve.

Circadian variability of blood pressure in obese children

BACKGROUND AND AIMS

The aim of the present study was to evaluate the circadian rhythm of blood pressure pattern in obese children, and to investigate if the lack of normal diurnal rhythm of blood pressure is associated with cardiovascular risk factors.

METHODS AND RESULTS

73 obese children (body weight [mean+/-SD]: 89.0+/-17.8 kg; age [mean+/-SD]: 14.2+/-2.3 years), 42 dippers and 31 non-dippers were investigated. Following ambulatory blood pressure monitoring (ABPM), physical fitness testing was performed on a treadmill. Physical working capacity at 130, -150, -170 beat/min (PWC-130, -150, -170), resting and peak oxygen consumption (VO(2)rest, VO(2)peak) were determined. Forty-two percent of obese children were non-dipper. PWC-130 (74.8+/-48.8 watts; 48.0+/-38.5 watts), PWC-150 (132.9+/-52.1 watts; 104.2+/-49.3 watts), PWC-170 (185.9+/-49.5 watts; 154.9+/-53.4 watts) and VO(2)rest, ([mean+/-SD]: 0.29+/-0.08 L/min; 0.26+/-0.07 L/min), and VO(2) peak (2.77+/-0.61 L/min; 2.44+/-0.62 L/min) were significantly lower in the non-dipper group, as compared to dippers (p<0.05). The prevalence of hypertension, on the basis of ABPM, was significantly higher in the non-dipper group (45.2% vs 83.9%, p<0.001). This is due to increased prevalence of masked hypertension in the non-dipper group (19.0% vs 32.3%, p<0.001).

CONCLUSION

The normal circadian variation of the blood pressure is frequently absent in obese children. Most of the non-dipper obese children are hypertensive, and their physical fitness is decreased.

Perturbed autonomic nervous system function in metabolic syndrome

The metabolic syndrome is characterized by the clustering of various common metabolic abnormalities in an individual and it is associated with increased risk for the development of type 2 diabetes and cardiovascular diseases. Its prevalence in the general population is approximately 25%. Central fat accumulation and insulin resistance are considered as the common denominators of the abnormalities of the metabolic syndrome. Subjects with metabolic syndrome have autonomic nervous system dysfunction characterized by predominance of the sympathetic nervous system in many organs, i.e. heart, kidneys, vasculature, adipose tissue, and muscles. Sympathetic nervous system activation in metabolic syndrome is detected as increased heart rate and blood pressure, diminished heart rate variability, baroreceptor dysfunction, enhanced lipolysis in visceral fat, increased muscle sympathetic nerve activity, and high urine or plasma catecholamine concentrations as well as turnover rates. The augmented sympathetic activity in individuals with metabolic syndrome worsens prognosis of this high-risk population. The mechanisms linking metabolic syndrome with sympathetic activation are complex and not clearly understood. Whether sympathetic overactivity is involved in the development of the metabolic syndrome or is a consequence of it remains to be elucidated since data from prospective studies are missing. Intervention studies have demonstrated that the autonomic disturbances of the metabolic syndrome may be reversible.

Circadian variation of blood pressure: the basis for the chronotherapy of hypertension

Ambulatory blood pressure (BP) measurements present a close correlation with target organ damage and cardiovascular events, including myocardial infarction, stroke and cardiovascular mortality. With the use of this measurement technique, a significant circadian variation has been shown to characterize BP. This circadian BP variation, although affected by a variety of external factors, represents the influence of internal factors such as ethnicity, gender, autonomic nervous system tone, vasoactive hormones, and hematologic and renal variables. In most individuals, BP presents a morning increase, a small post-prandial valley, and a deeper descent during nocturnal rest. However, under certain pathophysiological conditions, the nocturnal BP decline may be reduced or even reversed. This cannot be determined by traditional clinical or home BP assessments. Subjects with a diminished nocturnal BP decline (non-dipper pattern) have a significantly worse prognosis than the ones with a normal dipper pattern. In particular, the non-dipper circadian BP pattern represents a risk factor for left ventricular hypertrophy, microalbuminuria, cerebrovascular disease, congestive heart failure, vascular dementia and myocardial infarction. The normalization of the circadian BP pattern to a dipper profile is a novel therapeutic goal, and accumulating medical evidence suggests this can delay the progression towards the renal and cardiovascular pathology known to be a consequence of the non-dipper BP pattern. The features of the circadian BP profile have direct implications for improving the drug-delivery of antihypertensive therapies as well as the qualification of patients for medication trials and assessment.

Prolonged (48-hour) modest hyperinsulinemia decreases nocturnal heart rate variability and attenuates the nocturnal decrease in blood pressure in lean, normotensive humans

CONTEXT

Heart rate variability (HRV), an index of cardiac vagal activity, is decreased in individuals with metabolic disease. The relationship between decreased HRV and metabolic disease is unclear.

OBJECTIVE

The objective of this study was to determine whether experimentally induced glucose intolerance decreases HRV in a circadian relevant manner in healthy individuals.

DESIGN

This was a within-subject, randomized design study with subjects infused for 48 h with saline (50 ml/h) or 15% glucose (200 mg/m2.min). HRV was evaluated using time domain measurements taken over the 48-h period. Blood pressure and heart rate were monitored, and blood samples were taken.

SETTING

This study was performed at the General Clinical Research Center of the Hospital of the University of Pennsylvania.

PATIENTS

Sixteen healthy subjects (eight men and eight women; 18-30 yr old; mean body mass index, 21.7 +/- 1.6 kg/m2) were studied.

RESULTS

After glucose infusion, mean plasma glucose was increased by 16.8% (P < 0.0001), and plasma insulin was increased by 99.4% (P < 0.0001) compared with after saline infusion. Significant decreases in homeostasis model assessment indicated a decrease in insulin sensitivity (saline, 0.52 + 0.13; glucose, 0.34 + 0.12; P < 0.0001). The nocturnal root mean square successive difference, an index of cardiac vagal activity, was significantly decreased (P < 0.01), and nocturnal HR (P < 0.001) and blood pressure were significantly elevated (saline, 107.4 +/- 2.7; glucose, 112.5 +/- 3.3 mm Hg; P < 0.05) compared with the saline control. The change in homeostasis model assessment due to glucose infusion was significantly correlated with the change in root mean square successive difference (r = 0.48; P < 0.01).

CONCLUSIONS

Prolonged mild hyperinsulinemia disrupts the circadian rhythm of cardiac autonomic activity. Early changes in the neural control of cardiac activity may provide a potential mechanism mediating the pathophysiological link between impaired glucose tolerance and cardiovascular disease.

Vascular dysfunction and autonomic neuropathy in Type 2 diabetes

AIMS

To test the hypothesis that arterial dysfunction in Type 2 diabetes is related to autonomic neuropathy.

METHODS

Arterial function and autonomic neuropathy were assessed over two consecutive days in 45 Type 2 diabetic and control subjects. Systemic arterial compliance (SAC), arterial stiffness (pulse-wave velocity, PWV) and carotid intima thickness (IMT) were assessed; these markers reflect early vascular disease and predict clinical vascular events. Autonomic neuropathy was assessed using heart rate variability with continuous ECG recording during various breathing and postural manoeuvres and an overall autonomic score was generated. Fasting metabolic parameters including glucose, insulin, HbA(1c) and lipid profile were measured.

RESULTS

Autonomic neuropathy tests were all repeatable in diabetic subjects. Compared with controls, diabetic subjects had arterial dysfunction with increased PWV (P = 0.009), IMT (P < 0.001) and reduced SAC (P = 0.053). After adjustment for age, central PWV correlated with fasting insulin (r(2) = 0.45, P < 0.05) and autonomic score (r(2) = 0.44, P < 0.05), peripheral PWV correlated with autonomic score (r(2) = 0.51, P < 0.005) and IMT correlated with fasting insulin (r(2) = 0.5, P < 0.005). The presence of autonomic neuropathy correlated with fasting insulin (P = 0.015), but not age, duration diabetes, lipids or blood pressure.

CONCLUSION

Using repeatable measures of autonomic neuropathy and vascular function in Type 2 diabetic subjects, we have demonstrated associations between autonomic neuropathy, vascular dysfunction and hyperinsulinaemia. This may help to explain the excess cardiovascular mortality seen in diabetic subjects with autonomic neuropathy.

Blood pressure and cardiac autonomic function in relation to risk factors and treatment perspectives in Type 1 diabetes

The cumulative incidence of diabetic nephropathy in Type 1 diabetes mellitus is in the order of 25 30%. The recognition that elevated blood pressure (BP) is a major factor in the progression of these patients to end-stage renal failure has led to the widespread use of antihypertensive therapy in order to preserve glomerular filtration rate and ultimately to reduce mortality. The routine measurement of microalbuminuria allows early identification of the subgroup of patients at increased risk of developing clinical nephropathy. Microalbuminuric Type 1 diabetic patients show a number of characteristic pathological abnormalities. In addition to elevated BP and abnormal circadian rhythm, there are also associated abnormalities of vagal function, lipid profile and endothelial function, as well as an increased prevalence of retinopathy. The first section of this two-part review focusses on the early changes associated with renal involvement in Type 1 diabetes. It addresses the associations between urinary albumin excretion, glycaemic control, smoking, BP, circadian BP variation, QT interval abnormalities and autonomic function in three groups of patients; those with normoalbuminuria, those progressing towards microalbuminuria and those with established low-grade microalbuminuria.

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

AIMS

To investigate whether Type 2 diabetic patients exhibit characteristic patterns of circadian variation in plasma levels of catecholamines, blood pressure (BP) and heart rate variability (HRV).

METHODS

Ten Type 2 diabetic and eight control in-patients were studied. Blood for catecholamine measurement was collected every 4 h, and non-invasive ambulatory BP and heart rate were monitored throughout the day. HRV was determined using frequency domain methods.

RESULTS

Diabetic patients showed a different pattern of circadian variation in BP and HRV from that of controls, the diurnal-nocturnal differences (D-N) being significantly smaller. The mean 24-h HRV levels were reduced in diabetic subjects. The mean 24-h plasma noradrenaline level of 1.36 +/- 0.12 nmol/l in diabetic patients was significantly lower than the 2.03 +/- 0.20 nmol/l in controls (P < 0.01). In contrast, no significant difference in adrenaline levels was observed. The mean 24-h plasma noradrenaline level demonstrated a significant positive correlation with D-N in systolic BP (r = 0.49, P = 0.0153).

CONCLUSIONS

The present study demonstrated distinctive patterns of circadian variation in plasma noradrenaline level, BP and HRV in Type 2 diabetic patients, associated with an abnormal circadian pattern of sympathovagal modulation.

Increased QTc dispersion is related to blunted circadian blood pressure variation in normoalbuminuric type 1 diabetic patients

A reduced nocturnal fall in blood pressure (BP) and increased QT dispersion both predict an increased risk of cardiovascular events in diabetic as well as nondiabetic subjects. The relationship between these two parameters remains unclear. The role of diabetic autonomic neuropathy in both QT dispersion and circadian BP variation has been proposed, but data have been conflicting. The aim of the present study was to describe associations between QT dispersion and circadian BP variation as well as autonomic function in type 1 diabetic patients. In 106 normoalbuminuric (urinary albumin excretion <20 microg/min) normotensive patients, we performed 24-h ambulatory BP (Spacelabs 90207) and short-term (three times in 5 min) power spectral analysis of RR interval oscillations, as well as cardiovascular reflex tests (deep breathing test, postural heart rate, and BP response). No patient had received (or had earlier received) antihypertensive or other medical treatment apart from insulin. In a resting 12-lead electrocardiogram, the QT interval was measured by the tangent method in all leads with well-defined T-waves. The measurement was made by one observer blinded to other data. The QT interval was corrected for heart rate using Bazett's formula. The QTc dispersion was defined as the difference between the maximum and the minimum QTc interval in any of the 12 leads. When comparing patients with QTc dispersion below and above the median (43 ms), the latter had significantly higher night BP (114/67 vs. 109/62 mmHg, P < 0.003/P < 0.001), whereas day BP was comparable (129/81 vs. 127/79 mmHg). Diurnal BP variation was blunted in the group with QTc dispersion >43 ms with significantly higher night/day ratio, both for systolic (88.8 vs. 86.2%, P < 0.01) and diastolic (83.1 vs. 79.5%, P < 0.01) BP. The association between QTc dispersion and diastolic night BP persisted after controlling for potential confounders such as sex, age, duration of diabetes, urinary albumin excretion, and HbA1c. Power spectral analysis suggested an altered sympathovagal balance in patients with QTc dispersion above the median (ratio of low-frequency/high-frequency power: 1.0 vs. 0.85, P < 0.01). In normoalbuminuric type 1 diabetic patients, increased QTc dispersion is associated with reduced nocturnal fall in BP and an altered sympathovagal balance. This coexistence may be operative in the ability of these parameters to predict cardiovascular events.

[Nephropathy, nycthemeral variability and pulse pressure in patients with type 2 diabetes mellitus]

BACKGROUND

The loss of the blood pressure nictemeral rhythm and the elevated pulse pressure are considered independent cardiovascular risk factors that can be related with the microvascular damage of patients with type 2 diabetes mellitus.

PATIENTS AND METHOD

We carried out an observational, tranverse study, of a population of patients with type 2 diabetes mellitus. The variables are calculated by means of 24 hour ambulatory registry of blood pressure. The results are compared with the diverse degrees ofnephropathy.

RESULTS

A total of 61 patients is studied; 31 have a behavior "non dipper". The "non dipper" proportion increased with the urinary albumin excretion (p = 0.024). The pulse pressure was higher inpatients with macroalbuminuria (p = 0.004).

CONCLUSIONS

Theresults demonstrate a more frequent loss of the nictemeral rhythm and higher pulse pressure among the patients with type 2 diabetes mellitus and nephropathy.

Sympathetic nervous system, diabetes, and hypertension

Hypertension is twice as frequent in diabetic patients than in the general population. Its prevalence is higher in Type 2 than in Type 1 diabetes: in the former, the onset of hypertension often precedes the diagnosis of diabetes, whereas, in the latter it is strictly related to the presence of nephropathy. Sympathetic nerve overactivity is crucial in the pathogenesis of hypertension in diabetes. It can be related to the activation of the renin-angiotensin-aldosterone (RAA) system in Type 1 diabetic patients with chronic renal failure, or to a condition of insulin resistance/hyperinsulinemia in Type 2 patients with the metabolic syndrome. In patients with early autonomic neuropathy, vagal impairment can lead to a relative predominance of sympathetic activity in the sympatho-vagal balance. In these patients, the onset of hypertension is frequently preceded by reduced nocturnal dipping. Sympathetic overactivity stimulates RAA activity, promotes sodium reabsorption, and increases heart rate, stroke volume and peripheral vascular resistance, thus inducing hypertension and increasing cardiovascular risk. A number of drugs acting either directly or indirectly on sympathetic activity are available for the treatment of hypertension in diabetic subjects. Opinions on the potential advantages of the metabolic profile of some of these drugs are as yet conflicting.

Chronic intermittent intravenous insulin therapy: a new frontier in diabetes therapy

The limited success achieved in controlling diabetes and its complications with conventional insulin therapy suggests the need for reevaluation of the appropriateness of insulin administration protocols. Indeed, conventional subcutaneous insulin administration produces slowly changing blood insulin levels and suboptimal hepatocyte insulinization resulting in impaired hepatic capacity for processing incoming dietary glucose. The novel approach to insulin administration known as chronic intermittent intravenous insulin therapy (CIIIT) delivers insulin in a pulsatile fashion and achieves physiological insulin concentration in the portal vein. Done as a weekly outpatient procedure combined with daily intensive subcutaneous insulin therapy, this procedure has been shown to (1) significantly improve glycemic control while decreasing the incidence of hypoglycemic events, (2) improve hypertension control, (3) slow the progression of overt diabetic nephropathy, and (4) reverse some manifestations of diabetic autonomic neuropathy (e.g., abnormal circadian blood pressure pattern, severe postural hypotension, and hypoglycemia unawareness).

Diurnal blood pressure variation in progressive autonomic failure

To investigate the role of the autonomic nervous system (ANS) in the generation of the circadian blood pressure (BP) variation, the degree of impairment of the ANS was related to the results of ambulatory BP recordings in 212 patients with progressive autonomic failure due to familial amyloid polyneuropathy. On the basis of BP and/or heart rate (HR) responses to the Valsalva maneuver, 60 degrees head-up tilting, deep-breathing tests, and plasma norepinephrine levels, 4 groups of patients were distinguished. In all patients and in 38 age-matched control subjects, ambulatory BP was monitored. Patients of group I (n=40, aged 32+/-3 y), with no evidence yet of impairment of their ANS, had circadian BP and HR variations indistinguishable from controls. Patients of group II (n=41, aged 34+/-5 y) had a variable degree of impairment of their parasympathetic ANS, but their sympathetic ANS was still intact. Twenty-four-hour HR was higher in these patients than in controls (88+/-11 versus 78+/-7 bpm, P<0.01). Their circadian HR variation was maintained, but their circadian BP variation was diminished (10+/-6/11+/-4 versus 17+/-6/16+/-4 mm Hg in controls, P<0.01) because of an attenuation of the nocturnal BP decline. Patients of group III (n=69, aged 36+/-6 y), with parasympathetic failure and intermediate sympathetic dysfunction, had a blunted diurnal BP variation, whereas patients of group IV (n=62, aged 38+/-6 y), with parasympathetic failure and severe sympathetic dysfunction, had an absent diurnal BP variation. In patients of groups III and IV, a decrease in daytime BP accounted for the blunted circadian BP variation. This extensive study in progressive autonomic failure confirms the important role of the ANS in the generation of circadian BP variation. For the maintenance of a normal circadian BP pattern, not only an intact sympathetic but also an intact afferent parasympathetic ANS is a prerequisite.

Clinical value of ambulatory blood pressure monitoring

Ambulatory blood pressure monitoring (ABPM) has now become an established clinical tool. It is appropriate to take stock and assess the situation of this technique. UPDATE ON EQUIPMENT: Important improvements in equipment have occurred, with reductions in weight, in awkwardness and in noisiness of the machines, better acceptability and tolerance by the patients, and better reliability. Validation programmes have been proposed and should be referred to. Limitations of the technique persist with intermittent recording in current practice. The reproducibility is limited in the short-term while recording over 24 h is acceptable. DIAGNOSIS AND PROGNOSIS: White-coat effect (WCE) is manifested as a transient elevation in blood pressure during the medical visit The frequency of this phenomenon, the size of the effect, age, sex and level of blood pressure (BP) or the situation of occurrence (general practitioner, specialist or nurse) have been interpreted differently. It does not seem that WCE predicts cardiovascular morbidity or mortality. White-coat hypertension (WCH) is diagnosed on the evidence of abnormal clinical measures of BP and normal ABPM. The latest upper limits of normality by ABPM recommended by the JNCVI are < 135/85 mmHg while patients are awake and < 120/75 mmHg while patients are asleep. If we accept these upper limits of normality in ABPM, WCH does not appear to be a real problem as regards risk factors or end-organ effects. In terms of prognosis, data are limited. Cardiovascular morbidity seems low in WCH but identical to that of hypertensive subjects in these studies. However, further studies are needed to confirm these results. WCH does not appear to benefit from anti-hypertensive treatment. It is obvious that the lower the BP regarded as the limit of normality, the less likely the occurrence of secondary effects of metabolism, or end-organ effects or complications in those classified as hypertensive. 24 HOUR CYCLE: One of the most specific characteristics of ABPM is the possibility of being able to discover modification or alteration of the 24 h cycle of BP. Non-dippers are classically defined as those who show a reduction in BP of less than 10/5 mmHg or 10% between the day (06.00-22.00 h) and the night, or an elevation in BP. In contrast, extreme dippers are those in whom the BP reduction is greater than 20%. CARDIOVASCULAR SYSTEM: The data remain inconclusive with regard to the existence of a consistent relationship between the lack of a nocturnal dip in blood pressure and target organ damage. As regards prognosis, it seems that an inversion of the day-night cycle is of pejorative significance. CEREBROVASCULAR SYSTEM: Almost all studies have shown that non-dippers had a significantly higher frequency of stroke than dippers. In contrast, too great a fall in nocturnal BP may be responsible for more marked cerebral ischaemia. RENAL SYSTEM: Non-dippers have a significantly elevated median urinary excretion of albumin. There is a significant correlation between the systolic BP and nocturnal diastolic BP, and urinary excretion of albumin. Various studies have confirmed the increased frequency of change in the 24 h cycle in hypertensive subjects at the stage of renal failure.

DIABETES

BP abnormalities should be considered as markers of an elevated risk in diabetic subjects but cannot be considered at present as predictive of the appearance of micro-albuminuria or other abnormalities. ABPM is thus of interest in type I or type II diabetes both in the initial assessment and in the follow-up and adaptation of treatment. PHARMACO-THERAPEUTIC USES: The introduction of ABPM has truly changed the means and possibilities of approach to the study of the effects of anti-hypertensive medications, with new possibilities of analysis such as trough-peak ratio smoothness index, etc.

Nocturnal blood pressure in young patients with insulin-dependent diabetes mellitus: correlation with cardiac function

Lack of a decline in nocturnal blood pressure is associated with an adverse effect on end organs in adults with insulin-dependent diabetes mellitus (IDDM). The role of the decline in nocturnal blood pressure in young patients with IDDM is not known. We studied 25 white subjects with IDDM (age = 20.8 +/- 3.7 years, mean +/- SD), 8 of whom were female. The duration of IDDM in these subjects was 12.9 +/- 5.4 years (mean +/- SD). We determined the values for glycosylated hemoglobin (HgbA1), 24-hour ambulatory blood pressure, diastolic cardiac function (the ratio of peak E wave to peak A wave velocity (E/A) and indexed peak filling rate ¿PFR/SV¿ by Doppler echocardiography), and albumin excretion rate. The HgbA1 level was 10.9% +/- 1.9% (mean +/- SD; normal range = 4.5%-8.5%). The HgbA1 concentration was inversely correlated (p < 0.005) with the decline in systolic (r = 0.57) and diastolic (r = -0.55) nocturnal blood pressure. Diastolic cardiac dysfunction ¿E/A ratio [r = 0.42, p < 0.03) and PFR/SV (r = 0.52, p < 0.01)¿ correlated with a smaller decrease in nocturnal diastolic blood pressure. An inverse correlation between decline in nocturnal systolic blood pressure and log albumin excretion rate (r = -0.37, p = 0.07) approached statistical significance. We conclude that poor glycemic control adversely affects nocturnal blood pressure and that the latter may play an important role in cardiac and possibly renal dysfunction in early IDDM.

Autonomic nervous activity in elderly dipper and non-dipper patients with essential hypertension

The pathogenetic mechanisms of the blunted nocturnal fall in blood pressure, frequently observed in elderly patients with essential hypertension, are unclear. The aim of this study was to evaluate the autonomic nervous system in elderly dipper and non-dipper hypertensive subjects. The study group consisted of twelve non-dipper and twelve dipper hypertensive patients (mean age 77.7 and 73.8 years, respectively). Non-dippers were defined as subjects whose nocturnal fall in systolic blood pressure (SBP), evaluated by means of Ambulatory Blood Pressure Monitoring, was less than 10% of diurnal SBP. All the patients underwent the following cardiovascular tests to explore autonomic function: Tilt Table, Valsalva Maneuver, Deep Breathing, Cough. The tests were performed under standard conditions, and heart rate and blood pressure were continuously recorded. Valsalva ratio (VR), Expiration/Inspiration Ratio (E/IR) and Cough Test Ratio (CTR) were calculated. Mann Whitney's and chi 2 tests were used for comparison between groups. Relationships were assessed by univariate and multivariate analyses. Non-dipper hypertensive subjects showed significantly lower scores in VR (11.1 +/- 0.08 vs 1.28 +/- 0.14), E/IR (1.11 +/- 0.07 vs 1.21 +/- 0.10), and CTR (1.07 +/- 0.02 vs 1.15 +/- 0.07). During the tilt test, a significant decrease in SBP and a late increase in heart rate were observed in non-dippers. The day-night difference in SBP was significantly related to VR, CTR and maximal SBP drop during tilting. The findings confirm that non-dippers show an impairment in autonomic nervous drive, which is characterized mainly by decreased parasympathetic activity. These observations may explain the increase in cardiovascular risk in non-dippers.

Ambulatory blood pressure monitoring. Application to clinical medicine and antihypertension medication trials

The wide use of ABPM has resulted in greater appreciation of the circadian time structure of BP variability and its clinical relevance. It is now recognized that the day-night change in BP results from an interplay of circadian rhythms in neurohumoral mechanisms coupled with temporal patterns in physical activity and mental load. The composite effect and balance of these endogenous and exogenous cyclic phenomena give rise to elevated BP during diurnal activity and reduced BP during nighttime repose in both normotension and uncomplicated essential hypertension. The balance is frequently disturbed in complicated and secondary forms of hypertension causing gross alteration of the 24-hour BP profile. ABPM also reveals the efficiency of antihypertensive treatment throughout the 24 hours and as a function of drug administration time. The pharmacokinetics and/or pharmacodynamics of antihypertensive medications have been demonstrated to vary with ingestion time. Such time-dependencies arise from circadian rhythms in BP and underlying mechanisms. The effect of antihypertensive medications is not simply superimposed upon endogenous bioperiodicities. Rhythms in neurohumoral mechanisms of BP control may modulate treatment effect. Certain aspects of the shape of the 24-hour BP profile, such as the magnitude of the morning surge and nocturnal decrease, have been implicated as determinants of morbid and mortal cardiovascular events. One large clinical multicenter investigation, known as the CONVINCE (Controlled Onset Verapamil Investigation of Clinical Endpoints) trial, is aimed at assessing the impact (cardiovascular morbidity and mortality) of verapamil chronotherapy over standard diuretic or beta anatagonist treatment in hypertensive patients with at least one risk factor of coronary heart disease. ABPM will help ascertain to what extent depression of the morning surge in BP relates to reduction in cardiac morbidity and mortality in this as well as other such trials. In any event, the importance of ABPM and the indices derived from its application are just beginning to be appreciated and explored.

Circadian blood pressure variation in non-insulin-dependent diabetes mellitus with nephropathy

We studied a circadian blood pressure variation in relation to the progression of diabetic nephropathy in patients with non-insulin-dependent diabetes mellitus (NIDDM). Age, duration of diabetes, body mass index and glycemic control did not differ among the groups of patients with normo-, micro- and macroalbuminuria. None of the patients received antihypertensive drugs. There were no differences in renal and autonomic functions between normo- and microalbuminuric groups, but these functions were impaired in the macroalbuminuric group. The rise in blood pressure was more apparent in 24-h ambulatory blood pressure (AMBP), especially during night-time, as compared with casual blood pressure. Such blood pressure rise was in accordance with the progression of nephropathy. However, pulse rate did not differ among the three groups. The nocturnal fall in blood pressure was blunted in the micro- and macroalbuminuria groups, but evident in the normoalbuminuric group. In the latter, daytime systolic blood pressure (SBP) was significantly higher than night-time SBP (123 +/- 5 mmHg vs. 113 +/- 3 mmHg, P = 0.002). In contrast, in the former two groups of patients, there were no significant differences in SBP between daytime and night-time (134 +/- 9 mmHg vs. 134 +/- 9 mmHg, ns, for microalbuminuria and 159 +/- 8 mmHg vs. 165 +/- 7 mmHg, ns, for macroalbuminuria). Urinary albumin excretion was significantly correlated with night-time SBP (r = 0.48, P = 0.015), but not with daytime SBP (r = 0.30, ns).(ABSTRACT TRUNCATED AT 250 WORDS)