Sleep disorders and the failure to lower nocturnal blood pressure

Does Respiratory Sinus Arrhythmia Increase Nocturnal Blood Pressure?

By ambulatory blood pressure monitoring (ABPM), nocturnal blood pressure (BP) may increase before heart rate (HR), but the details are unknown.Among 102 participants who underwent ABPM, > 90% on hypertension treatment, the averaged BP (HR) data were examined for the time at which the BP (HR) increased significantly above the mean midnight BP (HR) between 3:00 AM - 9:00 AM in all patients and in subgroups divided by clinical variables. Participants were also divided according to the respiratory sinus arrhythmia (RSA) index, which is the ratio of the longest and shortest RR intervals obtained under normal breathing, and the effects of RSA on the nocturnal hemodynamics were examined.The average age of the patients was 70 ± 11 years, and there were 47 (46.1%) males. After midnight, the BP increased and was significantly greater than the midnight BP at 5:00 AM. The time of significant increase in BP was affected by clinical variables and the RSA index; an RSA index < 5% (> 10%) was associated with the earliest (latest) time of BP increase. However, the HR remained unchanged until 7:00 AM or later. According to the ABPM data, a discordant time course between BP and HR and the effect of RSA were evident during the nocturnal period.BP increased earlier than HR toward dawn, and this phenomenon was affected by clinical variables. A low RSA index facilitated the onset of BP increase. The underlying mechanisms and clinical significance of the role of RSA in circulatory regulation remain to be investigated.

Bidirectional correlation between gastroesophageal reflux disease and sleep problems: a systematic review and meta-analysis

Objectives

Gastroesophageal reflux disease (GERD) and sleep problems are highly prevalent among the general population. Both them are associated with a variety of psychiatric disorders such as depression and anxiety, which is highlighting an underexplored connection between them. This meta-analysis aims to explore the association between sleep problems and GERD.

Methods

We conducted a comprehensive search on PubMed, Cochrane Library, Embase, and Web of Science, using Medical Subject Headings (MeSH) and keywords, covering articles from the inception of the databases until August 2023. Stata statistical software, version 14.0, was utilized for all statistical analyses. A fixed-effects model was applied when p > 0.1 and I2 ≤ 50%, while a random-effects model was employed for high heterogeneity (p < 0.1 and I2 > 50%). Funnel plots and Egger's test were used to assess publication bias.

Results

Involving 22 studies, our meta-analysis revealed that insomnia, sleep disturbance, or short sleep duration significantly increased the risk of GERD (OR = 2.02, 95% CI [1.64-2.49], p < 0.001; I2 = 66.4%; OR = 1.98, 95% CI [1.58-2.50], p < 0.001, I2 = 50.1%; OR = 2.66, 95% CI [2.02-3.15], p < 0.001; I2 = 62.5%, respectively). GERD was associated with an elevated risk of poor sleep quality (OR = 1.47, 95% CI [1.47-1.79], p < 0.001, I2 = 72.4%), sleep disturbance (OR = 1.47, 95% CI [1.24-1.74], p < 0.001, I2 = 71.6%), or short sleep duration (OR = 1.17, 95% CI [1.12-1.21], p < 0.001, I2 = 0).

Conclusion

This meta-analysis establishes a bidirectional relationship between four distinct types of sleep problems and GERD. The findings offer insights for the development of innovative approaches in the treatment of both GERD and sleep problems.

Blood Pressure Increases Before Pulse Rate During the Nocturnal Period in Hypertensive Patients

Ambulatory blood pressure monitoring (ABPM) is used for the evaluation of out-of-office blood pressure (BP), however, knowledge concerning the detailed behavior of nocturnal blood pressure (BP) and pulse rate (PR) is limited.A total of 190 participants (64 ± 15 years, 46.3% males) underwent ABPM for diagnosis of hypertension or evaluation of hypertensive therapy. BP and PR were measured automatically by the oscillometric method. From the hourly average ABPM values, the nocturnal time courses (0 AM to 6 AM) of SBP and PR were determined and compared to each other.In general, SBP fell to the lowest level at around midnight and started to increase progressively towards dawn while PR stayed unchanged until 7 AM. Age and gender affected the time course of SBP, most distinctly in the female patients aged ≥ 60 years. The time course of the increase of SBP was very similar in the patients, with BP dipping and non-dipping. The cardiothoracic ratio (CTR) slightly and renal dysfunction modestly facilitated the increase of nocturnal SBP. The nocturnal increase in SBP was not accompanied by an increase of PR in any group or subgroup. The pathophysiology and clinical significance of the early and exclusive increase in nocturnal BP need to be investigated.Average ABPM values in these hypertensive patients showed that BP starts to increase toward dawn without an increase in PR and that this discrepant behavior between BP and RP was most distinct in females 60 or older. The mechanism and clinical significance of such a discordant variation in BP and PR need to be elucidated.

Sleep-Wake Cycling and Energy Conservation: Role of Hypocretin and the Lateral Hypothalamus in Dynamic State-Dependent Resource Optimization

The hypocretin (Hcrt) system has been implicated in a wide range of physiological functions from sleep-wake regulation to cardiovascular, behavioral, metabolic, and thermoregulagtory control. These wide-ranging physiological effects have challenged the identification of a parsimonious function for Hcrt. A compelling hypothesis suggests that Hcrt plays a role in the integration of sleep-wake neurophysiology with energy metabolism. For example, Hcrt neurons promote waking and feeding, but are also sensors of energy balance. Loss of Hcrt function leads to an increase in REM sleep propensity, but a potential role for Hcrt linking energy balance with REM sleep expression has not been addressed. Here we examine a potential role for Hcrt and the lateral hypothalamus (LH) in state-dependent resource allocation as a means of optimizing resource utilization and, as a result, energy conservation. We review the energy allocation hypothesis of sleep and how state-dependent metabolic partitioning may contribute toward energy conservation, but with additional examination of how the loss of thermoregulatory function during REM sleep may impact resource optimization. Optimization of energy expenditures at the whole organism level necessitates a top-down network responsible for coordinating metabolic operations in a state-dependent manner across organ systems. In this context, we then specifically examine the potential role of the LH in regulating this output control, including the contribution from both Hcrt and melanin concentrating hormone (MCH) neurons among a diverse LH cell population. We propose that this hypothalamic integration system is responsible for global shifts in state-dependent resource allocations, ultimately promoting resource optimization and an energy conservation function of sleep-wake cycling.

Intermittent hypoxia exacerbates increased blood pressure in rats with chronic kidney disease

Kidney injury and sleep apnea (SA) are independent risk factors for hypertension. Exposing rats to intermittent hypoxia (IH) to simulate SA increases blood pressure whereas adenine feeding causes persistent kidney damage to model chronic kidney disease (CKD). We hypothesized that exposing CKD rats to IH would exacerbate the development of hypertension and renal failure. Male Sprague-Dawley rats were fed a 0.2% adenine diet or control diet (Control) until blood urea nitrogen was >120 mg/dl in adenine-fed rats (14 ± 4 days, mean ± SE). After 2 wk of recovery on normal chow, rats were exposed to IH (20 exposures/h of 5% O₂-5% CO₂ 7 h/day) or control conditions (Air) for 6 wk. Mean arterial pressure (MAP) was monitored with telemeters, and plasma and urine samples were collected weekly to calculate creatinine clearance as an index of glomerular filtration rate (GFR). Prior to IH, adenine-fed rats had higher blood pressure than rats on control diet. IH treatment increased MAP in both groups, and after 6 wk, MAP levels in the CKD/IH rats were greater than those in the CKD/Air and Control/IH rats. MAP levels in the Control/Air rats were lower than those in the other three groups. Kidney histology revealed crystalline deposits, tubule dilation, and interstitial fibrosis in both CKD groups. IH caused no additional kidney damage. Plasma creatinine was similarly increased in both CKD groups throughout whereas IH alone increased plasma creatinine. IH increases blood pressure further in CKD rats without augmenting declines in GFR but appears to impair GFR in healthy rats. We speculate that treating SA might decrease hypertension development in CKD patients and protect renal function in SA patients.

Heart rate phenotypes and clinical correlates in a large cohort of adults without sleep apnea

BACKGROUND

Normal sleep is associated with typical physiological changes in both the central and autonomic nervous systems. In particular, nocturnal blood pressure dipping has emerged as a strong marker of normal sleep physiology, whereas the absence of dipping or reverse dipping has been associated with cardiovascular risk. However, nocturnal blood pressure is not measured commonly in clinical practice. Heart rate (HR) dipping in sleep may be a similar important marker and is measured routinely in at-home and in-laboratory sleep testing.

METHODS

We performed a retrospective cross-sectional analysis of diagnostic polysomnography in a clinically heterogeneous cohort of n=1047 adults without sleep apnea.

RESULTS

We found that almost half of the cohort showed an increased HR in stable nonrapid eye movement sleep (NREM) compared to wake, while only 13.5% showed a reduced NREM HR of at least 10% relative to wake. The strongest correlates of HR dipping were younger age and male sex, whereas the periodic limb movement index (PLMI), sleep quality, and Epworth Sleepiness Scale (ESS) scores were not correlated with HR dipping. PLMI was however significantly correlated with metrics of impaired HR variability (HRV): increased low-frequency power and reduced high-frequency power. HRV metrics were unrelated to sleep quality or the ESS value. Following the work of Vgontzas et al, we also analyzed the sub-cohort with insomnia symptoms and short objective sleep duration. Interestingly, the sleep-wake stage-specific HR values depended upon insomnia symptoms more than sleep duration.

CONCLUSION

While our work demonstrates heterogeneity in cardiac metrics (HR and HRV), the population analysis suggests that pathological signatures of HR (nondipping and elevation) are common even in this cohort selected for the absence of sleep apnea. Future prospective work in clinical populations will further inform risk stratification and set the stage for testing interventions.

Chemoreceptors, baroreceptors, and autonomic deregulation in children with obstructive sleep apnea

Obstructive sleep apnea (OSA) is highly prevalent sleep disorder of breathing in both adults and children that is fraught with substantial cardiovascular morbidities, the latter being attributable to a complex interplay between intermittent hypoxia (IH), episodic hypercapnia, recurrent large intra-thoracic pressure swings, and sleep disruption. Alterations in autonomic nervous system function could underlie the perturbations in cardiovascular, neurocognitive, immune, endocrine and metabolic functions that affect many of the patients suffering from OSA. Although these issues have received substantial attention in adults, the same has thus far failed to occur in children, creating a quasi misperception that children are protected. Here, we provide a critical overview of the evidence supporting the presence of autonomic nervous system (ANS) perturbations in children with OSA, draw some parallel assessments to known mechanisms in rodents and adult humans, particularly, peripheral and central chemoreceptor and baroreceptor pathways, and suggest future research directions.

Sympathetic and catecholaminergic alterations in sleep apnea with particular emphasis on children

Sleep is involved in the regulation of major organ functions in the human body, and disruption of sleep potentially can elicit organ dysfunction. Obstructive sleep apnea (OSA) is the most prevalent sleep disorder of breathing in adults and children, and its manifestations reflect the interactions between intermittent hypoxia, intermittent hypercapnia, increased intra-thoracic pressure swings, and sleep fragmentation, as elicited by the episodic changes in upper airway resistance during sleep. The sympathetic nervous system is an important modulator of the cardiovascular, immune, endocrine and metabolic systems, and alterations in autonomic activity may lead to metabolic imbalance and organ dysfunction. Here we review how OSA and its constitutive components can lead to perturbation of the autonomic nervous system in general, and to altered regulation of catecholamines, both of which then playing an important role in some of the mechanisms underlying OSA-induced morbidities.

Rotating night shift work and disparate hypertension risk in African-Americans

OBJECTIVE

Hypertension disproportionally affects black compared with white Americans, even after accounting for known risk factors. Circadian disruption as encountered by rotating night shift workers has been associated with an increased risk for hypertension. Because blood pressure responds differently to sleep alterations in blacks compared with whites, we hypothesized that rotating night shift work may be a stronger risk factor for hypertension among blacks.

METHODS

We prospectively examined the association between rotating night shift work and the risk of hypertension in 1510 black and 94 142 white female participants of the Nurses' Health Study II who were nonhypertensive at baseline in 1991. We used Cox proportional hazards models to control for potential confounders.

RESULTS

During 16 years of follow-up (1991-2007), we identified 580 incident cases of hypertension in blacks and 23 360 cases in whites. In blacks, the multivariable hazard ratio for incident hypertension among women who worked rotating night shift for more than 12 months in the previous 2 years was 1.81 [95% confidence interval (CI) 1.14-2.87], compared with those working none. By contrast, in whites, we observed no increase in risk (hazard ratio 0.99, 95% CI 0.93-1.06). The association between shift work and hypertension varied significantly by race (P interaction = 0.01). In secondary analyses, the multivariable hazard ratio for incident hypertension in black women who ever performed rotating night shift work was 1.46 (95% CI 1.07-1.99), compared with those never working rotating night shifts. In whites, there was no increase in risk (hazard ratio 0.97, 95% CI 0.93-1.01) (P interaction < 0.01).

CONCLUSION

Rotating night shift work is independently associated with an increased risk of hypertension in blacks but not in whites.

Orexins, feeding, and energy balance

In this chapter, we give an overview of the current status of the role of orexins in feeding and energy homeostasis. Orexins, also known as hypocretins, initially were discovered in 1998 as hypothalamic regulators of food intake. A little later, their far more important function as regulators of sleep and arousal came to light. Despite their restricted distribution, orexin neurons have projections throughout the entire brain, with dense projections especially to the paraventricular nucleus of the thalamus, the arcuate nucleus of the hypothalamus, and the locus coeruleus and tuberomammillary nucleus. Its two receptors are orexin receptor 1 and orexin receptor 2. These receptors show a specific and localized distribution in a number of brain regions, and a variety of different actions has been demonstrated upon their binding. Our group showed that through the autonomic nervous system, the orexin system plays a key role in the control of glucose metabolism, but it has also been shown to stimulate sympathetic outflow, to increase body temperature, heart rate, blood pressure, and renal sympathetic nerve activity. The well-known effects of orexin on the control of food intake, arousal, and wakefulness appear to be more extensive than originally thought, with additional effects on the autonomic nervous system, that is, to increase body temperature and energy metabolism.

Oxygen-dependent regulation of nitric oxide production by inducible nitric oxide synthase

Inducible nitric oxide synthase (iNOS) catalyzes the reaction that converts the substrates O(2) and l-arginine to the products nitric oxide (NO) and l-citrulline. Macrophages, and many other cell types, upregulate and express iNOS primarily in response to inflammatory stimuli. Physiological and pathophysiological oxygen tension can regulate NO production by iNOS at multiple levels, including transcriptional, translational, posttranslational, enzyme dimerization, cofactor availability, and substrate dependence. Cell culture techniques that emphasize control of cellular PO(2), and measurement of NO or its stable products, have been used by several investigators for in vitro study of the O(2) dependence of NO production at one or more of these levels. In most cell types, prior or concurrent exposure to cytokines or other inflammatory stimuli is required for the upregulation of iNOS mRNA and protein by hypoxia. Important transcription factors that target the iNOS promoter in hypoxia include hypoxia-inducible factor 1 and/or nuclear factor κB. In contrast to the upregulation of iNOS by hypoxia, in most cell types NO production is reduced by hypoxia. Recent work suggests a prominent role for O(2) substrate dependence in the short-term regulation of iNOS-mediated NO production.

Effects of sleep on the cardiovascular and thermoregulatory systems: a possible role for hypocretins

Sleep influences the cardiovascular, endocrine, and thermoregulatory systems. Each of these systems may be affected by the activity of hypocretin (orexin)-producing neurons, which are involved in the etiology of narcolepsy. We examined sleep in male rats, either hypocretin neuron-ablated orexin/ataxin-3 transgenic (narcoleptic) rats or their wild-type littermates. We simultaneously monitored electroencephalographic and electromyographic activity, core body temperature, tail temperature, blood pressure, electrocardiographic activity, and locomotion. We analyzed the daily patterns of these variables, parsing sleep and circadian components and changes between states of sleep. We also analyzed the baroreceptor reflex. Our results show that while core temperature and heart rate are affected by both sleep and time of day, blood pressure is mostly affected by sleep. As expected, we found that both blood pressure and heart rate were acutely affected by sleep state transitions in both genotypes. Interestingly, hypocretin neuron-ablated rats have significantly lower systolic and diastolic blood pressure during all sleep stages (non-rapid eye movement, rapid eye movement) and while awake (quiet, active). Thus, while hypocretins are critical for the normal temporal structure of sleep and wakefulness, they also appear to be important in regulating baseline blood pressure and possibly in modulating the effects of sleep on blood pressure.

Short sleep duration is associated with a blood pressure nondipping pattern in type 1 diabetes: the DIAPASOM study

OBJECTIVE

To assess whether nocturnal blood pressure dipping status in type 1 diabetes is correlated with specific sleep characteristics and differences in nocturnal glycemic profiles.

RESEARCH DESIGN AND METHODS

Twenty type 1 diabetic adult patients underwent sleep studies with simultaneous 24-h ambulatory blood pressure monitoring and continuous nocturnal glucose monitoring.

RESULTS

Altogether, 55% of patients exhibited blunted blood pressure dipping. They did not differ from the dipper group in age, BMI, or systolic (SBP) and diastolic (DBP) blood pressure. Total sleep period (TSP) was higher in the dipper group (497 +/- 30 vs. 407 +/- 44 min for dippers and nondippers, respectively, P < 0.001). TSP was correlated with SBP and DBP day-night differences (r = 0.44 and 0.49, respectively). Periods of nocturnal hypoglycemia (i.e., % of TSP with glycemia <70 mg/dl) were longer in the dipper group (8.1 +/- 10.7 vs. 0.1 +/- 0.4% for dippers and nondippers, respectively, P = 0.02).

CONCLUSIONS

Dipping status in type 1 diabetes was associated with longer sleep duration and with hypoglycemia unawareness.

Ambulatory blood pressure and physical activity in heart failure

This observational study used repeated measures over 24 hr to investigate ambulatory blood pressure (BP) and physical activity (PA) profiles in community-based individuals with heart failure (HF). The aims were to (a) compare BP dipping and PA between two groups of HF patients with different functional statuses, and (b) determine whether the strength of the association between ambulatory BP and PA varies by functional status in HF. Ambulatory BP was measured every 30 min with a SpaceLabs 90207; a Basic Motionlogger actigraph was used to measure PA minute-by-minute. Fifty-six participants (54% female, age 66.96 + or - 12.35 years) completed data collection. Functional status was based on New York Heart Association (NYHA) ratings. Twenty-seven patients had no limitation of PA (NYHA Class I HF), whereas 29 had some limitation of PA but no discomfort at rest (NYHA Class II or III HF). Patients with Class I HF had a significantly greater degree of BP dipping than those with Class II/III HF after controlling for left ventricular ejection fraction. In a mixed-model analysis, PA was significantly related to ambulatory systolic and diastolic BP and mean arterial pressure. The strength of the association between PA and BP was not significantly different for the two groups of patients. These findings demonstrate differences between Class I and Class II/II HF in BP dipping status and ambulatory BP but not PA. Longitudinal research is recommended to improve understanding of the influence of disease progression on changes in 24-hr PA and BP profiles of patients with HF.

Sleep quality among relatively younger patients with initial diagnosis of hypertension: Dippers versus non‐dippers

BACKGROUND

Sleep is a basic physiological process. Normal sleep yields decrease in sympathetic activity, blood pressure (BP) and heart rate. Those, who do not have expected decrease in their BP are considered "non-dippers". We aimed to determine if there was any association between the non-dipping status and sleep quality, designed a cross-sectional study, and enrolled and evaluated the sleep quality of relatively young patients with an initial diagnosis of hypertension.

METHODS

Seventy-five consecutive patients, diagnosed to have stage 1 hypertension by their primary physicians, were referred to our study. Patients had newly diagnosed with stage 1 hypertension. Patients with a prior use of any anti-hypertensive medication were not included. Eligible patients underwent the Pittsburgh Sleep Quality Index (PSQI), which has an established role in evaluating sleep disturbances. All patients underwent ambulatory BP monitoring.

RESULTS

There were 42 non-dipper patients (mean age = 47.5+/-11.9 years, 24 male/18 female), as a definition, 31 dipper hypertensive patients (mean age = 48.5+/-12.8 years, 21 male/10 female) and two with white coat hypertension. Daytime systolic and diastolic mean BPs were not significantly different between the two groups. Night-time mean systolic and diastolic BPs were significantly higher in non-dippers compared with dippers. PSQI scores, globally, were significantly higher in non-dippers compared with dippers. Total PSQI score was not correlated with body mass index. It was noticed that, individually, sleep quality, sleep efficiency and sleep disturbance scores were significantly higher in non-dippers. Being a poor sleeper in terms of high PSQI score (total score>5) was associated with 2.955-fold increased risk of being a non-dipper (95% confidence interval 1.127-7.747).

CONCLUSION

We showed that the risk of having non-dipping hypertension, a risk factor for poor cardiovascular outcomes among hypertensive individuals, was tripled (odds ratios) among poor sleepers. We think that evaluating sleeping status and sleep quality among the hypertensive population may help unmask non-dipper hypertension, enabling physicians to treat appropriately.

Time-dependent adaptation in the hemodynamic response to hypoxia

In rats, acute exposure to hypoxia causes a decrease in mean arterial pressure (MAP) caused by a predominance of hypoxic vasodilation over chemoreflex-induced vasoconstriction. We previously demonstrated that exposure to chronic intermittent hypoxia (CIH) impairs hypoxic vasodilation in isolated resistance arteries; therefore, we hypothesized that the acute systemic hemodynamic responses to hypoxia would be altered by exposure to CIH. To test this hypothesis, rats were exposed to CIH for 14 days. Heart rate (HR) and MAP were monitored by telemetry. On the first day of CIH exposure, acute episodes of hypoxia caused a decrease in MAP (-9+/-5 mmHg) and an increase in HR (+45+/-4 beats/min). On the 14th day of CIH exposure the depressor response was attenuated (-4+/-1mmHg; 44% of the day 1 response) and the tachycardia was enhanced (+68+/-2 beats/min; 151% of the day 1 response). The observed time-dependent modulation of the acute hemodynamic responses to hypoxia may reflect important changes in neurocirculatory regulation that contribute to CIH-induced hypertension.

PSYCHOSOCIAL FACTORS IN PATIENTS WITH CHRONIC KIDNEY DISEASE: Sleepiness, Sleeplessness, and Pain in End-Stage Renal Disease: Distressing Symptoms for Patients

Symptoms are increasingly recognized as problematic for patients with end-stage renal disease (ESRD) treated with dialysis. Sleep disorders are common in ESRD patients treated with dialysis and are associated with patients' perceptions of quality of life, assessed by diverse measures, as well as depressive affect. Sleep disorders appear to be equally prevalent in peritoneal dialysis (PD) and hemodialysis (HD) patients. Treatment for sleep disorders in dialysis patients depends on establishing the diagnosis, often in a sleep laboratory, using polysomnography. Reversing coexistent medical and psychological disorders is important. The sleep apnea syndrome (SAS) can be treated with continuous positive airway pressure in dialysis patients, but conventional hemodialytic techniques have little effect on its severity. In contrast, nocturnal HD and transplantation appear to have important beneficial effects on sleep disordered breathing in ESRD patients. Although pain has been appreciated as a problem for ESRD patients for more than 20 years, few studies exist on this subject. Pain appears to be an underappreciated problem for ESRD patients. More research must be performed on the problem of pain in patients with chronic kidney disease (CKD).

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.

Longitudinal association of sleep-disordered breathing and nondipping of nocturnal blood pressure in the Wisconsin Sleep Cohort Study

STUDY OBJECTIVES

The association of sleep-disordered breathing (SDB) and blunting of normal nocturnal lowering of blood pressure (BP) (nondipping) has only been examined cross-sectionally. The purpose of this study is to investigate whether SDB is prospectively associated with nondipping.

METHODS

The longitudinal association between SDB and incident nondipping was examined in a subsample of 328 adults enrolled in the Wisconsin Sleep Cohort Study who completed 2 or more 24-hour ambulatory BP studies over an average of 7.2 years of follow-up. SDB identified by baseline in-laboratory polysomnography was defined by apnea-hypopnea index (AHI) categories. Systolic and diastolic nondipping was defined by systolic and diastolic sleep-wake BP ratios > 0.9. All models were adjusted for age, sex, body mass index at baseline and follow-up, smoking, alcohol consumption, hypertension, sleep time, length of follow-up time, and antihypertensive medication use.

RESULTS

There was a dose-response increased odds of developing systolic nondipping in participants with SDB. The adjusted odds ratios (95% confidence interval) of incident systolic nondipping for baseline AHI 5 to < 15 and AHI > or = 15, versus AHI < 5, were 3.1 (1.3-7.7) and 4.4 (1.2-16.3), respectively (P trend = 0.006). The adjusted odds ratios (95% confidence interval) of incident diastolic nondipping for corresponding SDB categories were not statistically significant: 2.0 (0.8-5.6) and 1.3 (0.2-7.1).

CONCLUSIONS

Our longitudinal findings of a dose-response increase in development of systolic nondipping of BP with severity of SDB at baseline in a population-based sample provide evidence consistent with a causal link. Nocturnal systolic nondipping may be a mechanism by which SDB contributes to increased cardiovascular disease.

NFATc3 is required for intermittent hypoxia-induced hypertension

Sleep apnea, defined as intermittent respiratory arrest during sleep, is associated with increased incidence of hypertension and peripheral vascular disease. Exposure of rodents to brief periods of intermittent hypercarbia/hypoxia (H-IH) during sleep mimics the cyclical hypoxia-normoxia of sleep apnea. Endothelin-1, an upstream activator of nuclear factor of activated T cells (NFAT), is increased during H-IH. Therefore, we hypothesized that NFATc3 is activated by H-IH and is required for H-IH-induced hypertension. Consistent with this hypothesis, we found that H-IH (20 brief exposures per hour to 5% O(2)-5% CO(2) for 7 h/day) induces systemic hypertension in mice [mean arterial pressure (MAP) = 97 +/- 2 vs. 124 +/- 2 mmHg, P < 0.05, n = 5] and increases NFATc3 transcriptional activity in aorta and mesenteric arteries. Cyclosporin A, an NFAT inhibitor, and genetic ablation of NFATc3 [NFATc3 knockout (KO)] prevented NFAT activation. More importantly, H-IH-induced hypertension was attenuated in cyclosporin A-treated mice and prevented in NFATc3 KO mice. MAP was significantly elevated in wild-type mice (Delta = 23.5 +/- 6.1 mmHg), but not in KO mice (Delta = -3.9 +/- 5.7). These results indicate that H-IH-induced increases in MAP require NFATc3 and that NFATc3 may contribute to the vascular changes associated with H-IH-induced hypertension.

Predictors of mortality in patients with type 2 diabetes with or without diabetic nephropathy: a follow-up study

OBJECTIVE

To evaluate the prognostic significance of cardiovascular risk factors including 24-h ambulatory blood pressure level and rhythm for all-cause mortality in type 2 diabetic patients.

METHODS

In a prospective observational study, 104 patients with type 2 diabetes were followed: 51 patients with diabetic nephropathy and 53 patients with persistent normoalbuminuria. At baseline, 24-h ambulatory blood pressure, left ventricular hypertrophy, glomerular filtration rate and cardiac autonomic neuropathy were measured. Blood samples were taken and patients answered a World Health Organization questionnaire. Dipping was calculated as the average nocturnal reduction in systolic and diastolic blood pressure.

RESULTS

Mean follow-up was 9.2 years (range 0.5-12.9). During follow-up, 54 of 104 patients died. Sixteen patients (15%) had higher blood pressure at night than during the day (reversed pattern); 14 of these patients died (88%), compared to 40 of 88 patients (45%) with reduced dipping or normal dipping; log rank P = 0.001. In a Cox regression analysis, predictors of all-cause mortality were: age, male sex, presence of left ventricular hypertrophy, glycated haemoglobin A1c (HbA1c), daytime systolic blood pressure, cardiac autonomic neuropathy, glomerular filtration rate and dipping (1% increase; hazard ratio 0.97, 95% confidence interval 0.94-0.998, P = 0.033).

CONCLUSION

Type 2 diabetes patients with non-dipping of night blood pressure were at higher risk of death as compared to dippers, independent of known cardiovascular risk factors. Since non-dipping has a high prevalence in patients with diabetic nephropathy, 24-h ambulatory blood pressure should be used to assess a full risk profile and blood pressure-lowering therapy in these patients.

Symptoms and their correlates in chronic kidney disease

While there is a significant body of literature documenting the impairments in health-related quality of life (HRQOL) experienced by patients with end-stage renal disease (ESRD), recent work has helped to elucidate the mediators of impaired well-being in this patient group. Physical and emotional symptoms have been shown to be common, frequently severe, and directly linked with impaired HRQOL. The following review explores the process of symptom assessment in patients with chronic kidney disease (CKD), presents an overview of the composite burden and importance of symptoms in patients with ESRD, highlights particularly common and distressing symptoms for which existing treatment strategies may be applicable, and discusses future directions for efforts to address and alleviate symptoms in the growing population of patients who suffer from CKD.

Effects of nasal continuous positive airway pressure and oxygen supplementation on norepinephrine kinetics and cardiovascular responses in obstructive sleep apnea

Obstructive sleep apnea (OSA) is characterized by noradrenergic activation. Nasal continuous positive airway pressure (CPAP) is the treatment of choice and has been shown to effectively reduce elevated norepinephrine (NE) levels. This study examined whether the reduction in NE after CPAP is due to an increase in NE clearance and/or a decrease of NE release rate. Fifty CPAP-naive OSA patients with an apnea-hypopnea index >15 were studied. NE clearance and release rates, circulating NE levels, urinary NE excretion, and blood pressure and heart rate were determined before and after 14 days of CPAP, placebo CPAP (CPAP administered at ineffective pressure), or oxygen supplementation. CPAP led to a significant increase in NE clearance ( P ≤ 0.01), as well as decreases in plasma NE levels ( P ≤ 0.018) and daytime ( P < 0.001) and nighttime ( P < 0.05) NE excretion. NE release rate was unchanged with treatment. Systolic ( P ≤ 0.013) and diastolic ( P ≤ 0.026) blood pressure and heart rate ( P ≤ 0.014) were decreased in response to CPAP but not in response to oxygen or placebo CPAP treatment. Posttreatment systolic blood pressure was best predicted by pretreatment systolic blood pressure and posttreatment NE clearance and release rate ( P < 0.01). The findings indicate that one of the mechanisms through which CPAP reduces NE levels is through an increase in the clearance of NE from the circulation.

Relation of nocturnal blood pressure dipping to cellular adhesion, inflammation and hemostasis

BACKGROUND

Subjects who fail to dip their nocturnal blood pressure (BP) are at substantially increased risk for cardiovascular diseases. The pathogenetic mechanisms of this relationship have not been elucidated. We investigated whether non-dipping would relate to procoagulant and proinflammatory activity.

DESIGN

Study participants were 76 unmedicated normotensive and hypertensive subjects (44 male, 32 female; 41 white, 35 black; mean age, 36 +/- 8 years) who underwent 24-h outpatient ambulatory BP monitoring. Based on whether their average nocturnal systolic BP relative to their average daytime systolic BP declined by less than 10%, 34 subjects were categorized as non-dippers. D-dimer, plasminogen activator inhibitor-1, von Willebrand factor, soluble intercellular adhesion molecule-1, and interleukin-6 were measured in plasma.

RESULTS

Multivariate analyses showed that D-dimer (median/interquartile range, 242/162-419 ng/ml versus 175/132-254 ng/ml; P=0.041), plasminogen activator inhibitor-1 (36/19-61 ng/ml versus 17/6-44 ng/ml; P=0.010), von Willebrand factor (122/91-179% versus 92/66-110%; P=0.001), and soluble intercellular adhesion molecule-1(227/187-291 ng/ml versus 206/185-247 ng/ml; P=0.044) were all higher in non-dippers than in dippers. Adjustment for gender, ethnicity, age, body mass index, smoking status, hypertension status, and social class revealed independent effects of non-dipping. Non-dippers continued to have higher D-dimer (P=0.030) and von Willebrand factor (P=0.034) than dippers. A similar trend not reaching statistical significance emerged for soluble intercellular adhesion molecule-1 (P=0.055). In contrast, dipping status had no effect on interleukin-6.

CONCLUSION

Nocturnal BP non-dipping is associated with elevated levels of molecules related to endothelial dysfunction and atherosclerosis. The finding provides one possible mechanism linking non-dipping with cardiovascular disease.

Blood pressure and progression of chronic kidney disease: Importance of systolic, diastolic, or diurnal variation

Several studies show that systolic blood pressure is an important predictor of renal disease progression, just as it is linked with cardiovascular consequences in hypertension. In contrast, particularly in older patients, diastolic blood pressure was not independently associated with risk of kidney disease progression in the same studies. Pulse pressure has been shown to be equivalent in predicting renal outcomes, but might not have added value after adjusting for systolic blood pressure. Several cross- sectional studies present a strong correlation of ambulatory blood pressure monitoring values with microalbuminuria, compared with office-based blood pressure measurements. Small, prospective studies have shown an association between loss of nocturnal blood pressure decline and outcomes, including microalbuminuria, accelerated kidney disease progression, and mortality.