Relationship Between Exercise Heart Rate Recovery and Circadian Blood Pressure Pattern

J Clin Hypertens (Greenwich). 2010;12:407–413. ^©2010 Wiley Periodicals, Inc. The aim of the present cross-sectional study was to evaluate heart rate recovery (HRR) in normotensive and hypertensive individuals with either nondipper or dipper type circadian rhythm of blood pressure. Eighty-five patients were divided into 4 groups according to the presence of hypertension and pattern of circadian blood pressure as follows: (1) normotensive/dipper, n=20; (2) normotensive/nondipper, n=21; (3) hypertensive/dipper, n=22; and (4) hypertensive/nondipper, n=22. HRR indices were calculated by subtracting first, second, and third minute heart rates from the maximal heart rate obtained during stress testing and designated as HRR1, HRR2, and HRR3. Mean HRR1 values (29.7±4.0 vs 26.6±3.7, P=.016) were significantly higher in the normotensive/dipper group than the normotensive/nondipper group. Mean HRR1 values (28.6±4.0 vs 24.8±4.6 beats per minute, P=.007) were higher in the hypertensive/dipper group than the hypertensive/nondipper group. Spearman’s correlation analyses revealed a positive correlation between degree of nighttime dipping and HRR1 (r=.600, P=.001). The correlation coefficient between degree of nighttime dipping and HRR1 was higher in the hypertensive group than the normotensive group (r=.676, P=.001 and r=.575, P=.001, respectively). Blunting of the nocturnal fall in blood pressure associates with a delayed recovery of heart rate after graded maximal exercise in both normotensive and hypertensive groups.     

Nocturnal diastolic blood pressure decline is associated with higher 25-hydroxyvitamin D level and standing plasma renin activity in a hypertensive population

Patients with nondipper hypertension are known to carry a high risk of cardiovascular complications. Vitamin D deficiency is associated with hypertension. Because vitamin D deficiency activates the renin–angiotensin–aldosterone system (RAAS), we hypothesized that this vitamin would interact with the RAAS to influence blood pressure (BP) in nondipper hypertensive patients. We performed a cross-sectional analysis of 1,007 outpatients with hypertension (HTN). Dipper and nondipper patterns were detected, and the two groups were matched for clinical, laboratory, 25-hydroxyvitamin D (25OHD) levels, and ambulatory blood pressure recording. Plasma renin activity (PRA), angiotensin II, and plasma aldosterone concentration (PAC) were assessed in 174 patients treated with calcium channel blockers or no medication. The mean 25OHD concentration in the entire study population was 12.3ng/dL, and the prevalence of vitamin D deficiency was 87.0%. Dipper and nondipper HTN were noted in 187 patients (24.6%) and 573 patients (75.4%). 25OHD levels were similar between nondipper and dipper HTN groups. Forward stepwise logistic regression analysis showed that BMI and age were independent predictors of nondipper HTN. Neither 25OHD levels nor RAAS components were included in the model. In correlation analyses, nocturnal decline of diastolic BP was positively associated with 25OHD levels and standing PRA (r = 0.152 p = 0.045, r = 0.165 p = 0.038, respectively). The present study showed that vitamin D deficiency was astonishingly prevalent in hypertensive subjects residing in Xinjiang, China. There may be a weakly association of nocturnal DBP decline with 25OHD levels and standing PRA levels. We found no association between vitamin D deficiency and nondipper HTN.     

QT Dispersion in Dipper- and Nondipper-Type Hypertension

The aim of this study was to identify the relationship of QT dispersion on 12-lead electrocardiograms and left ventricular mass index on echocardiograms associated with the circadian rhythm of blood pressure (BP). Heart rate and BP were monitored every 30 min for 48 h in 62 patients with essential hypertension using an ambulatory BP monitoring device. The patients were divided into four groups according to gender and circadian BP pattern (nocturnal BP dipper or nondipper). The patients were classified as dippers if their daytime BP decreased by at least 10% during the night and all the other subjects were classified as nondippers. Age, body mass index, and 48-h mean BP were similar among the four groups. During the night-rest period, the systolic and diastolic BP were significantly decreased in dipper-type hypertensives. The maximum QT_c interval and QT_c dispersion were longer in nondippers than in dippers. Left ventricular mass index (LVMI) had a tendency to increase in nondippers. The nocturnal reduction of BP significantly correlated with QT_c dispersion and LVMI. The QT_c dispersion significantly correlated with LVMI and interventricular septum thickness.     

Association Between Nondipper Behavior and Serum Calcium in Hypertensive Patients with Mild-to-Moderate Chronic Renal Dysfunction

A nondipping BP pattern has been shown to be predictive of end-organ damage, cardiovascular events, and mortality. The mechanisms of blunted nocturnal BP fall are multifactorial. We assessed whether total corrected serum calcium and ionic calcium (iCa) are associated with a blunted nocturnal BP fall in both treated and untreated hypertensive patients with stages 1–3 of the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (NKF KDOQI). Clinical data and 24-hour ambulatory blood pressure monitoring were obtained in a cohort of 231 essential hypertensive patients. Among the entire cohort, 107 were nondippers and 124 were dippers. Only in nondippers, we found significant correlations between iCa and 24-hour systolic blood pressure (SBP; r = 0.21, P < .03), diurnal SBP (r = 0.21, P < .03), and 24-hour pulse pressure (PP; r = 0.23, P < .02). The ambulatory arterial stiffness index (AASI) was significantly related with 24-hour PP in both dippers and nondippers after adjusting for age. Both AASI and 24-hour PP were higher in nondippers than in dippers. In addition, in nondippers, the prevalence of estimated glomerular filtration rate (eGFR) <60 mL/minute/1.73 m² was higher than in dippers (50% vs. 33.7%, P < .02). Logistic regression showed that patients with eGFR ≥60 mL/minute/1.73 m² had lower risk of nondipper status than patients with eGFR <60 mL/minute/1.73 m² (odds ratio = 2.445; 95% confidence interval = 1.398–4.277, P < .002). In conclusion, serum iCa could participate in the pathogenesis of nondipping pattern. Increased large artery stiffness may be a mechanism of the deleterious influence of nondipping on cardiovascular outcome. Hypertensive subjects with stage 3 of NKF KDOQI had a greater loss of circadian BP rhythm than those in stages 1 and 2.     

Oxidative Stress Impairs Endothelial Function in Nondipper Hypertensive Patients

Aims: Essential hypertension, as well as other established cardiovascular risk factors, is associated with endothelial dysfunction. Hypertensive patients with a nondipper circadian pattern have a greater risk of cerebrovascular and cardiovascular complications in comparison with those with a dipper circadian pattern. In this study, we evaluated the association between nondipper pattern and endothelial function in patients with essential hypertension. Methods: We evaluated the forearm blood flow (FBF) response to intraarterial acetylcholine (ACh), an endothelium‐dependent vasodilator, and sodium nitroprusside (SNP), an endothelium‐independent vasodilator, infusions in 190 hypertensive patients stratified according to dipper and nondipper status. The FBF was measured by strain‐gauge plethysmography. Effects of oxidative stress on FBF were evaluated by intraarterial infusion of vitamin C. Ambulatory BP monitorings were obtained by a validated oscillometric device (SpaceLabs 90207 Monitor Inc., Issaquah, WA, USA). Results: Systolic and diastolic blood pressures were higher during daytime and lower during night‐time in dipper subjects than in nondippers. The peak percent increase in ACh‐stimulated FBF was higher in dippers than in nondippers (473% vs. 228%, P < 0.001). The FBF responses to SNP were similar in dipper and nondipper patients. The FBF response to ACh during coinfusion of vitamin C was higher in nondippers rather than in dipper hypertensives. Conclusions: Present data demonstrate that endothelium‐dependent vasodilation is impaired in patients who have nondipper hypertension. The effects of vitamin C on impaired ACh‐stimulated vasodilation support the hypothesis that oxidative stress contributes to endothelial dysfunction of nondipper hypertensive patients.     

Relationships between new risk factors and circadian blood pressure variation in untreated subjects with essential hypertension

Recently a growing amount of interest has been focused on new risk factors for cardiovascular disease, such as insulin, leptin, homocysteine, and urinary albumin excretion (UAE). Furthermore, the absence of a nocturnal blood pressure (BP) decrease is emerging as an index for future target organ damage. In the present study we aimed to determine the relationship between these risk factors and circadian BP variations in essential hypertensive subjects.One hundred six patients, aged 54 ± 7 years, with stage I–II untreated hypertension were classified as dippers and nondippers according to the diurnal variation of >10% between mean daytime and nighttime systolic BP (SBP) and diastolic BP (DBP) in 24-h noninvasive ambulatory BP monitoring. Venous blood samples were drawn for determination of insulin, leptin, and homocysteine plasma levels, whereas UAE was evaluated in three consecutive 24-h urine samples. Nondippers compared to dippers had significantly greater hemodynamic load and higher UAE (by 17 mg/24 h, P < .05). The two groups did not differ regarding serum insulin, plasma leptin, and homocysteine levels. In the entire population, leptin was positively correlated with age, body mass index, 24-h DBP, fasting serum insulin, and plasma homocysteine levels, whereas homocysteine levels were significantly related to 24-h SBP and DBP values. Multiple linear regression analyses revealed that only UAE was significantly related with nocturnal SBP and DBP decrease (P < .05 for both). These findings suggest that the increased UAE observed in nondipper hypertensive subjects possibly represents a useful indicator for future target organ damage.     

Ambulatory blood pressure monitoring in secondary arterial hypertension due to adrenal diseases

The aim of this study was to evaluate ambulatory blood pressure monitoring in patients with essential hypertension and hypertension caused by adrenal pathology. Sixty-six patients with primary aldosteronism, 37 with pheochromocytomas, and 45 with adrenal incidentalomas were included. These patients were compared with 152 essential hypertensive patients and 64 normotensive subjects. Ambulatory blood pressure monitoring evaluated daytime and nighttime systolic and diastolic blood pressure and heart rate. The authors found that the "nondipper" phenomenon was present in 51.5% of patients with primary aldosteronism, 43.2% with pheochromocytomas, 42.2% with incidentalomas, 34.2% with hypertension, and 15% of subjects who were normotensive. In 58% of primary aldosteronism patients with idiopathic adrenal hyperplasia, there was an absence of the physiologic blood pressure nocturnal fall (nondipper), which was statistically significant (P<.001) compared with nondipper primary aldosteronism patients with adrenocortical adenoma (38%). In conclusion, the prevalence of the nondipping pattern was higher in patients with adrenal hypertension compared with patients with essential hypertension, suggesting an independent cardiovascular risk factor.     

Interventricular Septum and Posterior Wall Thickness Are Associated With Higher Systolic Blood Pressure

Elevated blood pressure (BP) is a known factor that affects the structure of the left ventricle. The association between left ventricular hypertrophy (LVH) and BP in normotensive individuals is poorly understood. All individuals who underwent routine echocardiography and BP measurements as aircrew candidates for the Israeli Air Force in the years 2006 to 2012 were identified. Participants with normal values were included. Associations between echocardiographic characteristics and BP were studied. A total of 2386 participants were included. Mean systolic BP was 125.31±11.18 mm Hg and mean diastolic BP was 68.69±9.02 mm Hg. Interventricular septal (IVS) thickness was positively correlated with systolic BP (P<.001, correlation coefficient 0.121) and significantly inversely correlated with heart rate and hematocrit level (P<.001 for both). Men with evidence of IVS or posterior wall thickening on echocardiography, even within the normal range, may require a closer follow‐up of BP.     

Age-Related Differences in the Mechanism of Nondipping Among Patients with Obstructive Sleep Apnea Syndrome

The frequency of nondipper (those lacking the normal drop in nocturnal blood pressure [BP]) is high in patients with obstructive sleep apnea syndrome (OSAS). The objective of this study is to investigate age-related differences in the nocturnal BP profile of patients with OSAS. The study subjects included 214 patients with polysomnography-diagnosed OSAS. The status of dipper or nondipper was determined by 24-hour ambulatory BP measurements. We divided the subjects into three groups by age (younger, middle-aged, and elderly) and compared the frequency and sleep profiles of nondippers in the different age groups. The prevalence of nondippers was significantly higher in the elderly OSAS group than in the younger and middle-aged OSAS groups (69% vs. 45%, 47%; P < .05). In the younger OSAS group, nondippers, when compared with dippers, were characterized by higher apnea–hypopnea index (AHI, 48.2 ± 27.1 vs. 37.4 ± 23.0 times/h, P < .05), whereas in the middle-aged and elderly OSAS groups, the AHI of nondippers was almost identical to that of dippers. On the other hand, in the elderly OSAS group, nondippers, when compared with dippers, had shorter periods of slow wave sleep as measured by nonrapid eye movement stage 3–4, whereas nondippers and dippers in the other two age groups were not different in terms of slow wave sleep. These results indicate age-related differences in major mechanisms leading to nondipping. Severe apnea causes nondipping only in young OSAS patients, whereas disturbance of sleep quality plays a more important role in elderly OSAS patients.     

INSULIN RESISTANCE IS ASSOCIATED WITH REDUCED NOCTURNAL FALLS OF BLOOD PRESSURE IN NORMOTENSIVE,NONOBESE TYPE 2 DIABETIC SUBJECTS

To assess the relationship between insulin resistance and ambulatory blood pressure (BP) pattern, we determined glucose infusion rate (GIR) as a marker of insulin resistance using a glucose clamp method, and measured 24-h BPs in 25 normotensive, nonobese type 2 diabetic subjects. They were divided into two groups: 11 dippers and 14 nondippers. Clinical characteristics were similar in the two groups except for orthostatic fall in systolic BP. The median GIR level was significantly lower in nondippers than in dippers (P < 0.05). Spearman's rank correlation revealed that the GIRs were negatively correlated with the systolic, diastolic and mean BPs during nighttime (P < 0.05 or less), but not with daytime or whole day BPs. Moreover, based on a logistic regression analysis, the GIR as well as orthostatic fall in systolic BP discriminated independently between dippers and nondippers. Thus, our results suggest that insulin resistance is associated with decreased nocturnal BP fall in type 2 diabetic subjects.     

Prevalence of gestational diabetes mellitus and the effect of weight on measures of insulin secretion and insulin resistance in third‐trimester pregnant rural women residing in the Central Region of Limpopo Province,South Africa

Aims To examine the prevalence of gestational diabetes in third‐trimester pregnant women as well as to assess their insulin secretion and insulin resistance (IR). Methods Third‐trimester pregnant women (n = 262) attending antenatal care at local clinics in the central region of the Limpopo Province underwent a 2‐h oral glucose tolerance test (OGTT) with blood collected at 0, 30 and 120 min. Glucose and insulin were measured. Results The prevalence of gestational impaired glucose tolerance (GIGT) and gestational diabetes mellitus (GDM) was 8.8% (7.3% GIGT; 1.5% GDM). Women with GIGT/GDM were significantly older and had more children compared with women with a normal response to the OGTT. Homeostasis model assessment (HOMA)‐IR and fasting insulin were lower in the GIGT/GDM group compared with the normal group, as were measures of insulin secretion (HOMA B‐cell function and insulinogenic index). Furthermore, women with body mass index (BMI) ≥ 30.0 kg/m² were significantly older and had higher parity, systolic and diastolic blood pressure measurements than those with BMI 25.0–29.9 kg/m² and BMI < 25.0 kg/m². However, increased BMI was not associated with an increased risk of GIGT/GDM. Conclusion The present study shows that there is a high prevalence of GIGT/GDM, with most women having IGT. The GIGT/GDM present in these women is characterized by increased insulin sensitivity accompanied by reduced pancreatic B‐cell function. Additionally, heavier women appear to have increased first phase insulin secretion, suggesting the presence of insulin resistance.     

Estradiol-17β reduces blood pressure and restores the normal amplitude of the circadian blood pressure rhythm in postmenopausal hypertension

After menopause, both systolic (SBP) and diastolic (DBP) blood pressure (BP) become higher in women than in men of the same age, suggesting that estrogen deficiency may influence the age-related increase in BP. We studied 30 postmenopausal women (mean age, 55 ± 5.7 years; time from menopause, 2–5 years) affected by mild hypertension with no target-organ complications by means of 24-h BP monitoring. None of the group were undergoing estrogen replacement therapy or taking antihypertensive drugs. According to a randomized, double-blind protocol, subjects received patches of transdermal estradiol-17β (E₂) or a matched placebo, with crossover after a 7-day washout period. In 12 patients the 24-h peak-to-trough variation in SBP and DBP amounted to less than 10% (nondippers). Administration of E₂ significantly decreased 24-h SBP and DBP in the whole cohort (P < .05). Furthermore, E₂ restored the expected reduction in BP during nighttime in the nondipper subgroup. It is well known that estrogen replacement therapy protects against the development of both cardiovascular diseases and stroke. Our data suggest that this activity could be attributed, at least in part, to the activity of E₂ in preserving physiologic circadian fluctuation of BP.     

The influence of ambulatory blood pressure profile on global and regional functions of the left and the right ventricles in orderly treated hypertensive patients

BACKGROUND: The association between nondipping profile and adverse cardiovascular outcome is still controversial. Tissue Doppler imaging (TDI), a new and useful addition to standard echocardiographic imaging techniques, permits a quantitative assessment of both global and regional function and timing of myocardial velocities. In this study, we aimed to assess whether a reduced nocturnal fall in blood pressure (BP) in orderly treated hypertensive patients with satisfactory BP control is related to more prominent structural and functional alterations of the ventricles. METHOD AND RESULTS: Sixty-nine hypertensive patients with adequate BP control were divided into two groups with respect to ambulatory BP profiles as dippers and nondippers. In addition to conventional echocardiographic parameters, in septal and lateral segments of left ventricle and free wall of right ventricle, peak systolic velocity (Sm), early (Em), and late (Am) diastolic velocities, isovolumic contraction time (ICTm), isovolumic relaxation time (IRTm), and ejection times (ETm) were measured, and modified myocardial performance index (MPIm) was calculated. Left ventricular (LV) and atrial dimensions, ejection fraction, transmitral early to late diastolic flow ratio, LV mass index, and LV hypertrophy ratio did not differ between groups. Both regional and mean LV Sm, Em/Am, MPIm and right ventricular Sm and MPIm were similar in both groups. CONCLUSION: In treated hypertensive patients with satisfactory BP control, there was no significant difference in cardiac structural and functional abnormalities among dipper and nondipper subjects.     

Which blood pressure measurement,systolic or diastolic,better predicts future hypertension in normotensive young adults?

The impact of age‐related differences in blood pressure (BP) components on new‐onset hypertension is not known. A follow‐up examination of 93 303 normotensive individuals (mean age 41.1 years) who underwent a health checkup in 2005 was conducted every year for 8 years. The primary end point was new‐onset hypertension (systolic BP [SBP]/diastolic BP [DBP] ≥140/90 mm Hg and/or the initiation of antihypertensive medications with self‐reported hypertension). During the mean 4.9 years of follow‐up, 14 590 subjects developed hypertension. The impact of DBP on the risk of developing hypertension compared with optimal BP (SBP <120 mm Hg and DBP <80 mm Hg) was significantly greater than that of SBP in subjects younger than 50 years (hazard ratios, 17.5 for isolated diastolic high‐normal vs 10.5 for isolated systolic high‐normal [P<.001]; 8.0 for isolated diastolic normal vs 4.1 for isolated systolic normal [P<.001]). Among the subjects 50 years and older, the corresponding effects of DBP and SBP were similar. Regarding the risk of new‐onset hypertension, high DBP is more important than SBP in younger adults (<50 years) with normal or high‐normal BP.     

原发性高血压病患者血压昼夜节律的临床意义探讨

目的 探讨原发性高血压病患者昼夜血压均值波动的节律与临床意义。方法 ９２例原发性高血压病人分成三组,单纯收缩压增高组（ＩＳＨ）３６例,收缩压和舒张压均增高认定为混合组（ＭＤＨ）,共３１例,二组均除外心,脑,肾损害。高血压合并左心室肥大（ＬＶＨ）组２５例。２０例正常个体为对照组,仪器采用美国Ｓｐａｃｅｌａｂｓ ９０２０７无创性携带式血压监测仪,获取２４小时平均收缩压（２４ｈＳＢＰ０和舒张压（２４ｈＤ     

Ambulatory blood pressure monitoring in patients with hyperthyroidism before and after control of thyroid function

BACKGROUND AND OBJECTIVE: Thyroid hormones have pronounced effects on the cardiovascular system. Thyrotoxicosis affects blood pressure (BP), modifying both diastolic (DBP) and systolic (SBP) pressures. There are no studies examining BP with ambulatory blood pressure monitoring (ABPM) in hyperthyroidism before and after control of thyroid function. Our aims were (1) to analyse ABPM in a group of normotensive hyperthyroid patients before and after normalizing circulating thyroid hormones and (2) to compare these results with those obtained in a group of euthyroid subjects. PATIENTS AND MEASUREMENTS: We studied 20 normotensive hyperthyroid subjects [18 women; age (mean +/- SEM) 49.0 +/- 3.0 years] and 15 healthy subjects. Patients were evaluated by ABPM over 24 h, at diagnosis and after therapy (n = 18). RESULTS: The average 24-h, daytime and night-time SBP was significantly greater in hyperthyroid patients than in controls with no significant differences in DBP. Circadian BP rhythm, estimated by the difference between mean values of SBP, DBP and mean BP during daytime and night-time, was unchanged. The average 24-h and daytime SBP significantly decreased after normalizing thyroid function in the 18 hyperthyroid evaluated patients. Daytime SBP and DBP were higher than night-time values both before and after control of thyroid function. However, no differences in circadian BP rhythm were observed. CONCLUSIONS: Normotensive hyperthyroid patients exhibit higher ambulatory SBP throughout 24 h than normotensive euthyroid subjects. Control of hyperthyroidism decreases ambulatory SBP values. Mean nocturnal fall in BP is comparable in normotensive hyperthyroid patients and control subjects.     

Diurnal Variation of Blood Pressure in Adolescents with Type 1 Diabetes: Dippers and Non-dippers

The study aimed to determine the prevalence of impaired nocturnal BP fall in adolescents with Type 1 diabetes. Thirty-six normoalbuminuric normotensive adolescents with Type 1 diabetes (19 males, 17 females) aged 14.4 ± 2.1 years (mean ± SD) with duration of 4.0 (2.6–7.5) years (median (25–75th percentile)) and 23 controls (11 males, 12 females) aged 15.0 ± 1.6 years were studied. Day/night BP variation was examined using Ambulatory Accutracker II Monitor (Raleigh, NC). Recordings were made at 30 min intervals during the day and 60 min intervals during the night. Time records were set according to individual diaries. There was no significant difference in day and night systolic or diastolic BP or in mean day/night BP variability between patients with Type 1 diabetes and control subjects. 15/36 patients compared to 3/23 controls (chi squared = 5.43, p < 0.02) were non-dippers defined as a nocturnal fall in either systolic (13/36) or diastolic (6/36) BP or both (4/36) of less than 10 %. These non-dippers had normal day–night ratio of heart rate when compared with the remainder of the patients or controls. In conclusion a significant number of young normotensive normoalbuminuric patients with Type 1 diabetes show an impaired fall in blood pressure at night, predominantly in systolic BP. These changes may be relevant to the long-term development of macrovascular or microvascular disease.     

The Relationship Between Nocturnal Blood Pressure and Hemorrhagic Stroke in Chinese Hypertensive Patients

To study the relationship between nocturnal blood pressure (BP) variation and spontaneous intracerebral hemorrhage (ICH) among Chinese hypertensive patients and its clinical significance, the authors retrospectively screened 371 patients with primary hypertension (189 patients with ICH, 182 patients without ICH) in Shanghai and analyzed their demographics, clinical information, nocturnal blood pressure variability and medication. Compared with the control group, the levels of blood glucose, triglycerides, and creatinine were significantly increased in the ICH group, along with a marked reduction in nocturnal BP drop (P<.05). Multivariate logistic regression indicated that blood glucose, creatinine, and nocturnal mean arterial pressure were risk factors for ICH, and the magnitude of nocturnal BP drop was negatively related to the risk for ICH. There was no significant difference in the prevalence of reverse dippers between the large hematoma volume group and the small hematoma volume group (χ²=2.529, P=.112), nor among the patients taking angiotensin‐converting enzyme inhibitors, angiotensin receptor blockers, or calcium channel blockers (χ²=1.981, P=.371). Reverse dipping is associated with the risk for ICH, suggesting that appropriate antihypertensive drug and chronotherapy might be effective to normalize the rhythm of abnormal circadian variation in hypertensive patients.     

Patients with renal dysfunction require a longer duration until blood pressure dips during the night

We have postulated that the diminished renal capacity to excrete sodium causes nocturnal blood pressure (BP) elevation, which enhances pressure natriuresis in compensation for impaired daytime natriuresis. If such a mechanism holds, high BP during sleep at night may continue until excess sodium is sufficiently excreted into urine. This study examined whether the duration, defined as "dipping time," until nocturnal mean arterial pressure began to fall to <90% of daytime average became longer as renal function deteriorated. Ambulatory BP measurements and urinary sodium excretion rates were evaluated for daytime and nighttime to estimate their circadian rhythms in 65 subjects with chronic kidney disease. Dipping time showed an inverse relationship with creatinine clearance (C(cr); rho=-0.61; P<0.0001) and positive relationships with night/day ratios of mean arterial pressure (rho=0.84; P<0.0001) and natriuresis (rho=0.61; P<0.0001), both of which were also inversely correlated with C(cr) (mean arterial pressure: r=-0.58, P<0.0001; natriuresis: r=-0.69, P<0.0001). When divided into tertiles by C(cr) (mL/min), hazard ratios of nocturnal BP dip adjusted for age, gender, and body mass index were 0.37 (95% CI: 0.17 to 0.79; P=0.01) for the second tertile (C(cr): 50 to 90) and 0.20 (95% CI: 0.08 to 0.55; P=0.002) for the third tertile (C(cr): 5 to 41) compared with the first tertile (C(cr): 91 to 164). These findings demonstrate that patients with renal dysfunction require a longer duration until BP falls during the night. The prolonged duration until BP dip during sleep seems an essential component of the nondipper pattern of the circadian BP rhythm.     

Autonomic dysfunction associates with prolongation of QT intervals and blunted night BP in obese women with visceral obesity

Prolonged QT intervals and a reduced fall of nocturnal blood pressure (BP) both predict an increased risk of cardiovascular events in obese subjects. We evaluated circadian BP variations (24-h ambulatory BP monitoring), autonomic function (power spectral analysis of RR interval oscillations) and cardiac repolarization times (QTc-dispersion and QTc interval) in 70 obese women, aged 25-44 yr, grouped by WHR into group A (WHR > 0.85, no.=38) and group B (WHR < or = 0.85, no.=32). Compared with non-obese age-matched women (no.=25, BMI=23+/-1.8) and obese women of group B, obese women of group A had higher values of QTc-d (p<0.05) and QTc (p<0.05), an altered sympathovagal balance (ratio of low-frequency/high-frequency power, p<0.01), and a blunted nocturnal drop in BP (p<0.01). In group A, QTc-d and the QTc interval correlated with diastolic night BP (p<0.01) and sympathovagal balance (p<0.01). WHR and plasma insulin levels correlated with QT intervals, reduced nocturnal fall in diastolic BP and sympathovagal balance (p<0.01). Prolongation of cardiac repolarization times and the reduction of nocturnal fall in BP coexist in obese women with visceral obesity, and might contribute to their raised cardiovascular risk. Autonomic dysfunction may be the common mechanism for this association.