Sympathetic nervous system alterations in sleep apnea. The relative importance of respiratory disturbance, hypoxia, and sleep quality

Emerging role of metabolomics for biomarker discovery in obstructive sleep apnea

Obstructive sleep apnea (OSA) is characterized by the complete or partial blockage of the upper airway passage during sleep which causes repetitive breaks in sleep and may result in excessive daytime sleepiness. OSA has been linked to various metabolic disorders and chronic health conditions, such as obesity, diabetes, hypertension, and depression. Profiling of alterations in metabolites and their regulation in OSA has been hypothesized to be an effective approach for early diagnosis and prognosis of OSA. Several studies have characterized metabolic fingerprints associated with sleep disorders. There is a lack of understanding of metabolite contents and their alterations in OSA that may help to identify specific biomarkers. The information provided in this review will help update new methodologies and interventions of high throughput advanced molecular/metabolomics tools which may clarify the metabolic aspects and mechanisms for improved management and treatment of OSA.

Dynamics of ACTH and Cortisol Secretion and Implications for Disease

The past decade has seen several critical advances in our understanding of hypothalamic-pituitary-adrenal (HPA) axis regulation. Homeostatic physiological circuits need to integrate multiple internal and external stimuli and provide a dynamic output appropriate for the response parameters of their target tissues. The HPA axis is an example of such a homeostatic system. Recent studies have shown that circadian rhythmicity of the major output of this system-the adrenal glucocorticoid hormones corticosterone in rodent and predominately cortisol in man-comprises varying amplitude pulses that exist due to a subhypothalamic pulse generator. Oscillating endogenous glucocorticoid signals interact with regulatory systems within individual parts of the axis including the adrenal gland itself, where a regulatory network can further modify the pulsatile release of hormone. The HPA axis output is in the form of a dynamic oscillating glucocorticoid signal that needs to be decoded at the cellular level. If the pulsatile signal is abolished by the administration of a long-acting synthetic glucocorticoid, the resulting disruption in physiological regulation has the potential to negatively impact many glucocorticoid-dependent bodily systems. Even subtle alterations to the dynamics of the system, during chronic stress or certain disease states, can potentially result in changes in functional output of multiple cells and tissues throughout the body, altering metabolic processes, behavior, affective state, and cognitive function in susceptible individuals. The recent development of a novel chronotherapy, which can deliver both circadian and ultradian patterns, provides great promise for patients on glucocorticoid treatment.

Obstructive Sleep Apnea, Daytime Sleepiness, and Type 2 Diabetes

PURPOSE

The purpose of this article is to review the literature on obstructive sleep apnea, resultant daytime sleepiness, and type 2 diabetes mellitus, as the state of evidence exists.

METHODS

A search was conducted on Medline and CINAHL using the search terms sleep apnea syndromes, obstructive sleep apnea, disorders of excessive somnolence, type 2 diabetes mellitus, and insulin resistance. This review includes only published research studies in English, in adults aged 19 years or older. There were 109 citations when the terms were combined, 36 citations that were identified as research studies, no randomized clinical trials, and only 1 qualitative study.

RESULTS

Obstructive sleep apnea and type 2 diabetes share the risk factors of age and central abdominal obesity. Recent studies suggest that obstructive sleep apnea and type 2 diabetes not only frequently coexist but also have a bidirectional association wherein each condition exacerbates the other. The mechanism whereby obstructive sleep apnea affects glucose metabolism is likely repetitive hypoxia and sleep fragmentation, which cause a stress response with increased sympathetic nervous system activity, increased fatigue-causing cytokines, and altered leptin levels that result in weight gain. In addition, daytime sleepiness results in an impaired mood state that may impede diabetes management.

CONCLUSIONS

Type 2 diabetes is prevalent in persons with obstructive sleep apnea, although the direction of causality is unknown. More research, including randomized clinical trials, is needed to determine how obstructive sleep apnea and daytime sleepiness affect persons with type 2 diabetes.

Resistant hypertension and obstructive sleep apnea in the setting of kidney disease

OBJECTIVES

To explore the relationship between obstructive sleep apnea (OSA) and resistant hypertension in chronic kidney disease (CKD) and end-stage renal disease (ESRD).

METHODS

We examined sleep parameters and blood pressure (BP) in 224 community-based, non-CKD participants from the Sleep-SCORE study: 88 nondialysis-dependent CKD and 95 ESRD participants. Unattended home polysomnography with standardized scoring protocols and automated BP monitors were used. Resistant hypertension was defined as a BP of at least 140/90  mmHg despite at least three antihypertensive drugs.

RESULTS

Mean SBP of the CKD and ESRD groups were significantly higher than that of the non-CKD group [148.2 (23.8), 144.5 (26.7) vs. 132.2  mmHg (26.7), respectively; P < 0.0001] despite the use of more antihypertensive medications. The CKD and ESRD groups had higher rates of resistant hypertension than the non-CKD group (41.4, 22.6 vs. 6.7%, respectively; P < 0.0001). The severity of sleep apnea was associated with a higher risk of resistant hypertension. Although resistant hypertension was associated with severe sleep apnea in participants with ESRD [odds ratio (OR) 7.1, 95% confidence interval (CI) 2.2-23.2), there was no significant association in the non-CKD (OR 3.5, 95% CI 0.8-15.4) or CKD groups (OR 1.2, 95% CI 0.4-3.7) after accounting for case-mix.

CONCLUSION

The association between resistant hypertension and sleep apnea appeared robust in ESRD. OSA may contribute to resistant hypertension or both may be linked to a common underlying process such as volume excess. Future studies in patients with kidney disease should further characterize the resistant hypertension-OSA relationship and determine whether treatment of underlying mechanisms may improve outcomes.

Glucoregulatory consequences and cardiorespiratory parameters in rats exposed to chronic-intermittent hypoxia: effects of the duration of exposure and losartan

BACKGROUND

Obstructive sleep apnea (OSA) is associated with glucose intolerance. Both chronic sleep disruption and recurrent blood oxygen desaturations (chronic-intermittent hypoxia, CIH) may cause, or exacerbate, metabolic derangements.

METHODS

To assess the impact of CIH alone, without accompanying upper airway obstructions, on the counter-regulatory response to glucose load and cardiorespiratory parameters, we exposed adult male Sprague-Dawley rats to CIH or sham room air exchanges for 10 h/day for 7, 21, or 35 days and then, 1 day after conclusion of CIH exposure, conducted intravenous glucose-tolerance tests (ivgtt) under urethane anesthesia. Additional rats underwent 35 days of CIH followed by 35 days of regular housing, or had 35 day-long CIH exposure combined with daily administration of the type 1 angiotensin II receptor antagonist, losartan (15 mg/kg, p.o.), and then were also subjected to ivgtt.

RESULTS

Compared with the corresponding control groups, CIH rats had progressively reduced glucose-stimulated insulin release and impaired glucose clearance, only mildly elevated heart rate and/or arterial blood pressure and slightly reduced respiratory rate. The differences in insulin release between the CIH and sham-treated rats disappeared in the rats normally housed for 35 days after 35 days of CIH/sham exposure. The losartan-treated rats had improved insulin sensitivity, with no evidence of suppressed insulin release in the CIH group.

CONCLUSION

In adult rats, the glucose-stimulated insulin release is gradually suppressed with the duration of exposure to CIH, but the effect is reversible. Elimination of the detrimental effect of CIH on insulin release by losartan suggests that CIH disrupts glucoregulation through angiotensin/catecholaminergic pathways. Accordingly, treatment with continuous positive airway pressure may ameliorate pre-diabetic conditions in OSA patients, in part, by reducing sympathoexcitatory effects of recurrent nocturnal hypoxia.

Effects of selective slow-wave sleep deprivation on nocturnal blood pressure dipping and daytime blood pressure regulation

Nocturnal blood pressure (BP) decline or "dipping" is an active, central, nervously governed process, which is important for BP regulation during daytime. It is, however, not known whether the sleep process itself or, more specifically, slow-wave sleep (SWS) is important for normal dipping. Therefore, in the present study, healthy subjects (6 females, 5 males) were selectively deprived of SWS by EEG-guided acoustic arousals. BP and heart rate (HR) were monitored during experimental nights and the following day. Additionally, nocturnal catecholamine excretion was determined, and morning baroreflex function was assessed by microneurographic measurements of muscle sympathetic nerve activity (MSNA) and heart rate variability (HRV). Data were compared with a crossover condition of undisturbed sleep. SWS was successfully deprived leading to significantly attenuated mean arterial BP dipping during the first half (P < 0.05), but not during the rapid-eye-movement-dominated second half of total sleep; however, dipping still evolved even in the absence of SWS. No differences were found for nighttime catecholamine excretion. Moreover, daytime resting and ambulatory BP and HR were not altered, and morning MSNA and HRV did not differ significantly, indicating that baroreflex-mediated sympathoneural BP regulation was not affected by the preceding SWS deprivation. We conclude that in healthy humans the magnitude of nocturnal BP dipping is significantly affected by sleep depth. Deprivation of SWS during one night does not modulate the morning threshold and sensitivity of the vascular and cardiac baroreflex and does not alter ambulatory BP during daytime.

Diurnal variability of C-reactive protein in obstructive sleep apnea

OBJECTIVE

The objective of this study is to examine the diurnal variability of C-reactive protein (CRP) in obstructive sleep apnea (OSA).

METHODS AND MEASUREMENTS

Participants included 44 women and men with untreated OSA (mean apnea/hypopnea index = 37.5, SD +/- 28) and 23 healthy adults with no OSA. Sleep was monitored with polysomnography in the University of California San Diego General Clinical Research Center. Over a 24-h period, blood was collected every 2 h, and CRP levels were determined.

RESULTS

Adjusting for age, gender, and body mass index, a significant group by time interaction showed that patients with OSA had higher CRP levels during the daytime (8:00 a.m.-8:00 p.m.) versus the nighttime (10:00 p.m. until 6:00 p.m.; p < 0.001). Non-apneics showed no significant change in CRP levels during the 24 h.

CONCLUSIONS

The findings indicate that sleep apnea patients have disproportionately elevated CRP levels in the day versus the nighttime, possibly as a result of carryover effects of nighttime arousal into the daytime.

Catecholamine alterations in pediatric obstructive sleep apnea: effect of obesity

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) elicits increased sympathetic activity in adults and increased urinary catecholamines. Moreover, urinary catecholamine excretion is altered in obese patients. We hypothesized that morning urine catecholamine levels would be correlated with the severity of obstructive sleep apnea and degree of obesity in children.

METHODS

Children referred to the pediatric sleep center for habitual snoring underwent overnight polysomnography, and the first morning voided urine sample was collected. Urinary concentrations of norepinephrine, epinephrine and dopamine were measured and corrected for creatinine levels. In a subset of children, blood samples were drawn and gene expression of catecholamine-relevant genes analyzed by quantitative real-time PCR.

RESULTS

One hundred fifty-nine children were recruited and completed the protocol. Children with OSA had significantly higher urinary norepinephrine and epinephrine levels, but not dopamine, compared to habitual snorers (norepinephrine: 40.1 +/- 24.7 ng/mg creatinine vs. 31.6 +/- 16.2 ng/mg creatinine, P < 0.01; epinephrine: 6.4 +/- 10.5 ng/mg vs. 4.5 +/- 0.5 ng/mg, P < 0.01). There was a positive correlation between norepinephrine and epinephrine values and polysomnographic indices, but no effect of obesity on catecholamine levels. In addition, expression of several of the major genes involved in synthesis and transport of catecholamines, as well as in selected receptors were compatible with increased bioavailability of catecholamines.

CONCLUSIONS

In children with OSA, morning urinary norepinephrine and epinephrine levels are significantly higher than those without OSA, and correlate with the severity of the disease. Gene expression patterns are in agreement with such findings. Urine catecholamine levels do not appear to be influenced by the presence of obesity. Thus, altered sympathetic activity in OSA patients appears to occur independently of the presence of obesity.

Metabolic consequences of sleep-disordered breathing

There is increasing evidence of a causal relationship between sleep-disordered breathing and metabolic dysfunction. Metabolic syndrome (MetS), a cluster of risk factors that promote atherosclerotic cardiovascular disease, comprises central obesity, insulin resistance, glucose intolerance, dyslipidemia, and hypertension, manifestations of altered total body energy regulation. Excess caloric intake is indisputably the key driver of MetS, but other environmental and genetic factors likely play a role; in particular, obstructive sleep apnea (OSA), characterized by intermittent hypoxia (IH), may induce or exacerbate various aspects of MetS. Clinical studies show that OSA can affect glucose metabolism, cholesterol, inflammatory markers, and nonalcoholic fatty liver disease. Animal models of OSA enable scientists to circumvent confounders such as obesity in clinical studies. In the most widely used model, which involves exposing rodents to IH during their sleep phase, the IH alters circadian glucose homeostasis, impairs muscle carbohydrate uptake, induces hyperlipidemia, and upregulates cholesterol synthesis enzymes. Complicating factors such as obesity or a high-fat diet lead to progressive insulin resistance and liver inflammation, respectively. Mechanisms for these effects are not yet fully understood, but are likely related to energy-conserving adaptations to hypoxia, which is a strong catabolic stressor. Finally, IH may contribute to the morbidity of MetS by inducing inflammation and oxidative stress. Identification of OSA as a potential causative factor in MetS would have immense clinical impact and could improve the management and understanding of both disorders.

Relationship between the severity of obstructive sleep apnea and impaired glucose metabolism in patients with obstructive sleep apnea

BACKGROUND

The relationship between the severity of obstructive sleep apnea (OSA) and impaired glucose metabolism (IGM) has not yet been fully elucidated in patients with OSA. Accordingly, we sought to clarify this relationship in Japanese patients with OSA.

METHODS

The study population consisted of 129 Japanese patients with OSA (apnea-hypopnea index [AHI] > or = 5). A 75-g oral glucose tolerance test was performed in all patients who had not been diagnosed as diabetes mellitus (DM). IGM was defined as either diabetes mellitus (DM) or impaired glucose tolerance (IGT).

RESULTS

IGM was observed in 78 (60.5%) patients: DM in 39 (30.2%) and IGT in 39 (30.2%). The frequency of IGM was significantly different among patients with AHI > or = 30, those with 15 < or = AHI < 30, and those with AHI < 15 (72.1%; 53.7%; 35.0%; respectively, p=0.001). Univariate logistic regression analyses showed male sex, the BMI, the AHI, and the lowest SpO(2) to be significantly associated with IGM. A stepwise multivariate logistic regression analysis showed a male sex and the AHI to be independently associated with IGM.

CONCLUSION

IGM was observed in 60.5% of Japanese patients with OSA (AHI > or = 5), and the prevalence of IGM increased according to the severity of OSA. Furthermore, the AHI was independently associated with IGM, thus suggesting that OSA may contribute to the development of IGM.

Chronic intermittent hypoxia alters hypothalamic transcription of genes involved in metabolic regulation

Epidemiological studies show that the obstructive sleep apnea syndrome (OSAS) is strongly associated with obesity, hypertension and diabetes, the three conditions characteristic of the metabolic syndrome. Since metabolic disorders usually involve altered homeostatic mechanisms both centrally and peripherally, it is likely that so it is in OSAS, but the underlying mechanisms remain largely unknown. We used an established rodent model to test whether chronic intermittent hypoxia (CIH) similar to that experienced by OSAS patients leads to distinct and relevant for metabolic regulation transcriptional changes in the posterior hypothalamus. Using quantitative reverse transcription-polymerase chain reaction, we found that rats exposed to CIH for 35 days (n=9) had twice higher levels of the adrenergic alpha2A receptor mRNA than the rats simultaneously submitted to a matching sham treatment (n=9). The mRNA levels of three members of the family of signal transducers and activators of transcription, STAT1, STAT3 and STAT5b, were also increased 2-4 times. The increases occurred only in the perifornical region, whereas no changes were detected in the ventromedial region comprising the ventromedial and arcuate nuclei or the dorsomedial region comprising the dorsomedial and paraventricular nuclei. These results show that, at least at the transcriptional level, CIH exerts a distinct and regionally selective central effect on the expression of selected mRNAs involved in metabolic regulation through adrenergic, leptinergic and inflammatory pathways.

A case of sleep apnea syndrome manifesting severe hypertension with high plasma norepinephrine levels

A 55-year-old female was admitted to our hospital with severe hypertension (274/140 mmHg). Endocrinological examination revealed that her plasma levels of norepinephrine (NE) was elevated with high levels of urinary NE, normetanephrine and vanillylmandelic acid (VMA), suggesting the presence of pheochromocytoma. However, neither computed tomography nor MIBG scintigraphy detected any catecholamine-producing tumor in or outside the adrenal glands. She was screened with full polysomnography because of heavy snoring, and the diagnosis of severe obstructive sleep apnea syndrome (OSAS) was made. She was treated with calcium channel blocker for three weeks, but severe hypertension persisted. After treatment with nasal continuous positive airway pressure (CPAP) was added, her blood pressure gradually lowered week by week. Concomitantly, the levels of plasma and urinary NE, urinary normetanephrine and urinary VMA were normalized following nasal CPAP therapy for 2 weeks. Additional treatments with alpha-adrenergic blocker further decreased her home blood pressure. After a year, she continued nasal CPAP therapy and her blood pressure was nearly below 160/100 mmHg. Urinary NE level was slightly above normal range and other catecholamines stayed within the normal range. This case shows that patients with OSAS could develop severe hypertension through elevated sympathetic tone, mimicking pheochromocytoma. Nasal CPAP therapy is recommended not only to improve hypertension and catecholamine excess but also to distinguish the condition from pheochromocytoma.

Central Sympathetic Inhibition Augments Sleep-Related Ultradian Rhythm of Parasympathetic Tone in Patients With Chronic Heart Failure

BACKGROUND

Abnormal sleep dynamics in patients with heart failure is one of the mechanisms for the relative predominance of central sympathetic outflow over parasympathetic tone. This study was designed to examine whether central sympathoinhibition could improve the sympathovagal imbalance related to rapid-eye-movement (REM)/non-REM ultradian sleep rhythm in these patients.

METHODS AND RESULTS

Beat-by-beat RR intervals of overnight electrocardiogram were serially subject to power spectral analysis in 14 patients with chronic heart failure and 13 age-matched subjects with normal cardiac function. To assess autonomic sleep dynamics, the ultradian rhythm was extracted from all-night consecutive high-frequency (HF) components of heart rate variability (HRV) before and after administration of an (alpha2)-adrenergic agonist, guanfacine. Night-time HRV in heart failure was characterized by an attenuated ultradian rhythm of HF-components with a concomitant reduction in averaged HF power. Guanfacine reduced blood pressure, heart rate, and plasma norepinephrine concentrations by 7%, 8%, and 34% (p < 0.01), respectively. After guanfacine, HF power rose by 154% (p < 0.01) with a prominent augmentation of the all-night ultradian rhythm (+361%, p < 0.01).

CONCLUSIONS

Central sympathoinhibition augments a sleep-related ultradian rhythm of parasympathetic tone, suggesting a potential benefit to autonomic balancing and sleep quality in patients with chronic heart failure.

Insulin resistance and obstructive sleep apnea: is increased sympathetic stimulation the link?

The science of sleep is in early stages of development, and the biochemical consequences of obstructive sleep apnea (OSA) are slowly being identified. Only recently have investigators begun to identify the commonalities and interaction between OSA and insulin resistance, the underlying pathology of type 2 diabetes. Obesity and increasing age play important parts in the natural history of both conditions, which frequently coexist. The purpose of this article is, first, to examine the extent and strength of studies that have investigated the association between OSA and increased insulin resistance or type 2 diabetes and, second, to propose a model that explains the association and cyclical interaction between OSA, obesity, and insulin resistance.

Impact of sleep apnea on sympathetic nervous system activity in heart failure

OBJECTIVES

To compare and establish the relevance of the relative degree of sympathetic nervous system activity (SNSA) in groups of patients with congestive heart failure (CHF) and obstructive sleep apnea (OSA), and in a control group.

BACKGROUND

Elevated SNSA is a characteristic feature of CHF, as well as of OSA and nonhypercapnic central sleep apnea (CSA). OSA and CSA commonly occur with CHF; however, the relative contribution of apnea-related hypoxemia and sleep fragmentation to the SNSA of patients with CHF is not known.

METHODS

This was a prospective, controlled, observational trial in which the overnight urinary norepinephrine (UNE) level, which is a measure of integrated overnight SNSA while asleep, was measured in 15 healthy male volunteers, 15 male OSA patients who did not have CHF, and 90 CHF patients (77 men). CHF patients also had right heart pressure measurements and then were grouped by the presence of sleep apnea.

RESULTS

Compared with healthy individuals, the mean (+/- SD) UNE level was significantly elevated in the OSA group and was even further elevated in the CHF group (13.4 +/- 5.6 vs 19.7 +/- 12.3 vs 32.2 +/- 20.2 nmol/mmol creatinine, respectively; p < 0.001 [by analysis of variance]). Within the CHF group, the mean UNE levels were greatest in the CHF-CSA group compared with the CHF-OSA group and the CHF nonapnea group (43.9 +/- 24.1 vs 24.0 +/- 10.8 vs 22.4 +/- 8.9 nmol/mmol creatinine, respectively; p < 0.001). Using a multivariate regression model, the variance of the UNE level in the CHF group was predicted, in descending order, by pulmonary capillary wedge pressure (14% variance), rapid eye movement sleep (8%), and the mean sleep pulse oximetry level (7%).

CONCLUSIONS

Overnight SNSA is significantly greater in CHF patients than in OSA patients. Moreover, the hemodynamic severity of CHF contributes to the elevation of SNSA in CHF patients to a greater degree than apnea-related hypoxemia.

Invited review: Neural network plasticity in respiratory control

Respiratory network plasticity is a modification in respiratory control that persists longer than the stimuli that evoke it or that changes the behavior produced by the network. Different durations and patterns of hypoxia can induce different types of respiratory memories. Lateral pontine neurons are required for decreases in respiratory frequency that follow brief hypoxia. Changes in synchrony and firing rates of ventrolateral and midline medullary neurons may contribute to the long-term facilitation of breathing after brief intermittent hypoxia. Long-term changes in central respiratory motor control may occur after spinal cord injury, and the brain stem network implicated in the production of the respiratory rhythm could be reconfigured to produce the cough motor pattern. Preliminary analysis suggests that elements of brain stem respiratory neural networks respond differently to hypoxia and hypercapnia and interact with areas involved in cardiovascular control. Plasticity or alterations in these networks may contribute to the chronic upregulation of sympathetic nerve activity and hypertension in sleep apnea syndrome and may also be involved in sudden infant death syndrome.

Blood pressure variability in obstructive sleep apnea: role of sympathetic nervous activity and effect of continuous positive airway pressure

BACKGROUND

Many studies support a link between obstructive sleep apnea (OSA), increased blood pressure (BP) and/or BP variability, and sympathetic nervous system (SNS) activity. We assessed the relationship between SNS activity and 24-h BP variability in patients with OSA, and the effect of continuous positive airway pressure (CPAP) on BP variability.

DESIGN

Forty-one patients with a respiratory disturbance index (RDI) > 15 were randomized into CPAP or CPAP placebo groups for a 1-week trial.

METHODS

Ambulatory BP, 24-h urine norepinephrine (NE) and polysomnography were measured prior to treatment and after 1 and 7 days of treatment.

RESULTS

Neither RDI nor 24-h urine NE levels were related to 24-h mean BP levels. While RDI was associated only with night-time BP variability, daytime urine NE levels were associated with both night-time and daytime BP variability. After treatment, the BP variability decreased significantly but equally in both active and placebo CPAP groups.

CONCLUSIONS

Obstructive sleep apnea is more related to BP variability than BP. Sympathetic nervous activity, as inferred from daytime urine NE, is related to changes in BP variability in OSA patients. BP variability is not specifically affected by CPAP.

Nocturnal polyuria in type 2 diabetes: a symptom of obstructive sleep apnea

PURPOSE

Polyuria and nocturia in individuals with type 2 diabetes may be due to obstructive sleep apnea (OSA), a recently recognized etiology of excess nighttime urine production. This exploratory study examined the relationships among glucose control, OSA, and nocturnal urine production.

METHODS

A sample of community-dwelling older adults (20 nondiabetic subjects and 10 poorly controlled type 2 diabetes subjects) was recruited based on self-report of nocturia more than twice per night. Participants were monitored on a metabolic research unit for 24 hours to track intake/output, collect blood and urine samples, and conduct an overnight polysomnography sleep study.

RESULTS

None of the subjects had fasting serum glucose levels above the renal threshold. OSA was found in 65% of subjects. Those with moderate/severe OSA had significantly greater overnight urine production than subjects without OSA. Subjects with type 2 diabetes and moderate/severe OSA had the highest nocturnal urine production.

CONCLUSIONS

The high incidence of undetected OSA in subjects with type 2 diabetes with nocturia suggests that nocturia, OSA, and type 2 diabetes frequently coexist and may be interrelated.

Sleep-disordered breathing and insulin resistance in middle-aged and overweight men

Sleep-disordered breathing is a prevalent condition associated with impairment of daytime function and may predispose individuals to metabolic abnormalities independent of obesity. The primary objective of this study was to determine the metabolic consequences and community prevalence of sleep-disordered breathing in mildly obese, but otherwise healthy, individuals. One hundred and fifty healthy men, without diabetes or cardiopulmonary disease, were recruited from the community. Measurements included polysomnography, a multiple sleep latency test, an oral glucose tolerance test, determination of body fat by hydrodensitometry, and fasting insulin and lipids. The prevalence of sleep-disordered breathing, depending on the apnea-hypopnea index (AHI) cutoff, ranged from 40 to 60%. After adjusting for body mass index (BMI) and percent body fat, an AHI gt-or-equal, slanted 5 events/h was associated with an increased risk of having impaired or diabetic glucose tolerance (odds ratio, 2.15; 95% CI, 1.05-4.38). The impairment in glucose tolerance was related to the severity of oxygen desaturation (DeltaSa(O(2))) associated with sleep-disordered breathing. For a 4% decrease in oxygen saturation, the associated odds ratio for worsening glucose tolerance was 1.99 (95% CI, 1.11 to 3.56) after adjusting for percent body fat, BMI, and AHI. Multivariable linear regression analyses revealed that increasing AHI was associated with worsening insulin resistance independent of obesity. Thus, sleep-disordered breathing is a prevalent condition in mildly obese men and is independently associated with glucose intolerance and insulin resistance.

The sleep apnoea/hypopnoea syndrome depresses waking vagal tone independent of sympathetic activation

The modest daytime hypertension and sympathetic upregulation associated with the sleep apnoea/hypopnoea syndrome (SAHS), does not explain the relatively large increased risk of cardiac morbidity and mortality in the SAHS patients population. Therefore, efferent vagal and sympathetic activity was evaluated during wakefulness in SAHS subjects and matched healthy controls, in order to determine if vagal downregulation may play a role in the aetiology of cardiac disease in the SAHS. The awake autonomic nervous system function of 15 male subjects, with mild-to-moderate SAHS was compared to that of 14 healthy controls matched for age, body mass index, gender and blood pressure. All subjects were free from comorbidity. Vagal activity was estimated from measurements of heart rate variability high frequency power (HF) and sympathetic activity was measured from urine catecholamine excretion. The %HF power was significantly (p < 0.03) reduced in SAHS patients (10+/-1.6 (mean+/-SEM)) as compared to controls (17 +/- 3). In addition, HF power correlated with the apnoea/hypopnoea index in the SAHS subjects (R = -0.592, p = 0.02). There was no statistically significant difference in the daytime excretion of nonadrenaline between control (242 +/- 30 nmol x collection(-1)) and SAHS (316 +/- 46 nmol x collection(-1)) subjects (p = 0.38). In these sleep apnoea/hypopnoea syndrome patients there was limited evidence of increased waking levels of urine catecholamines. The principal component altering waking autonomic nervous system function, in the sleep apnoea/hypopnoea syndrome subjects, was a reduced daytime efferent vagal tone.

Sleep bruxism in patients with sleep-disordered breathing

The aim was to test the hypothesis of a direct association between sleep-disordered breathing and sleep bruxism. The frequency of masseter contraction (MC) episodes and rhythmic jaw movements (RJM) was measured in patients with mild and moderate obstructive sleep apnoea (OSA). The diagnosis of sleep bruxism was made from a combination of questionnaire, clinical observation and all-night polysomnographic recording which included masseter electromyography. A total of 21 patients (19 males/two females, mean age 40.0 years+/-9.2 SD) were randomly selected from a provisional diagnosis of snoring and OSA by a sleep physician. In the patients with mild OSA [n=11, mean apnoea hypopnoea index (AHI)=8.0+/-4.1 SD, body mass index (BMI)=29.1+/-5.0], the diagnosis of sleep bruxism was made in six out of 11 patients (54%); similarly, four out of 10 patients (40%) with moderate OSA (n=10, mean AHI=34.7+/-19.1, BMI=30.6+/-5.0) were identified as bruxists. Although the combination of clinical, subjective estimation and nocturnal electromyographic recording of masseter muscle might provide a more solid base for the diagnosis of sleep bruxism, the result is biased by the variation in the bruxing activity. MC episodes were associated with the termination of apnoea or hypopnoea episodes in only 3.5% of the mild group and 14.4% of the moderate group (p<0.05). It appears that sleep bruxism is rarely directly associated with apnoeic events, but is rather related to the disturbed sleep of OSA patients.

Does caffeine confound relationships among adrenergic tone, blood pressure and sleep apnoea?

The purpose of this study was to determine whether caffeine consumption confounds the relationship among adrenergic tone, as measured by urinary norepinephrine (NE), blood pressure (BP) and obstructive sleep apnoea (OSA). Data were analysed using correlation and regression analysis, analysis of covariance and t-tests. Subjects included normotensives and hypertensives with and without OSA: 38 men, 23 women, aged 30-60 y; 100-150% of ideal body weight; without other major illness. Patients were studied using polysomnography, caffeine consumption was assessed, 24-h urinary NE levels were examined and ambulatory BP was recorded. Patients with OSA (N=27) reported significantly greater caffeine consumption than those without OSA (N=34) (295 vs. 103 mg, P=0.010), but caffeine was not significantly correlated with their ambulatory BP. In contrast, NE excretion correlated with caffeine consumption (r=0.24, P=0.041), apnoea severity (r=0.65, P < 0.001) and BP (r=0.34, P < 0.005). Significant OSA-NE and BP-NE relationships remained even after controlling for caffeine consumption. Patients with OSA consumed nearly three times the amount of caffeine as patients without OSA. While caffeine partially explains the increased adrenergic tone in patients with OSA and the relationship between BP and NE, it does not appear to contribute significantly to the relationship between OSA and elevated BP.

Plasma epinephrine levels in hypertension and across gender and ethnicity

Epinephrine (E) infusions raise blood pressure and there is an excess incidence of hypertension among males and blacks. However, reports of E levels by ethnicity, gender, and blood pressure status are inconsistent. Insensitive assays, variability in plasma E levels within individuals, and the small size of most studies have contributed to these conflicting reports. We measured plasma E levels in a large diverse sample of subjects, using a highly sensitive assay. A total of 361 individuals participated in the study: 61% were men and 39% women, 74% were normotensive and 26% hypertensive, 59% were white and 41% were black. Except for difference in blood pressure and body mass index between the normotensives and hypertensives, subjects had similar baseline characteristics and took no antihypertensive medications for at least five days prior to sampling. All blood samples were collected after resting for a least 30 minutes following the insertion of an indwelling i.v. catheter. Catecholamine levels were determined using a radioenzymatic assay (assay sensitivities for E and norepinephrine were 6 pg/ml and 10 pg/ml, respectively). An ethnicity by gender interaction was found (F(1,315) = 5.126, p = .024). Subsequent analysis revealed that white women had significantly lower basal plasma E levels than white men (p <0.001) and black women (p = 0.036). There were no significant differences in E levels between black men and women or between white men and black men. Uncorrected E levels were lower in normotensive than hypertensive subjects (p = .009) but this difference was not significant when corrected for body mass index (BMI). Uncorrected norepinephrine levels were higher in women than men (p = .03) but the difference was no longer significant when corrected for BMI. Plasma E levels were significantly lower among white women than men or black women. In contrast to prior studies, E levels were lower in hypertensives, but this may reflect obesity among hypertensives.

Relationship of arousals from sleep to sympathetic nervous system activity and BP in obstructive sleep apnea

STUDY OBJECTIVE

Obstructive sleep apnea (OSA) patients have a high frequency of arousals. We hypothesized that arousals significantly influence tonic sympathetic nervous system function.

DESIGN

We examined the association of 11 variables measuring sympathetic activity, including plasma norepinephrine (NE), urinary NE, and BP measurements, with movement and cortical arousals.

PATIENTS

Sixty-seven subjects with various degrees of hypertension and OSA were evaluated. All patients were free from antihypertensive medications.

RESULTS

The age (range, 35 to 60 years), weight (range, 100 to 150% of ideal body weight), and diet of the subjects were similar. The movement arousal index was correlated with daytime baseline plasma NE (BNE), daytime urine NE, mean daytime diastolic BP, and systolic BP during rapid eye movement sleep (r = 0.39 to 0.53; p < or = 0.002). Cortical arousals did not correlate with any of the variables. A multiple regression procedure was performed to examine how well movement arousals predicted those variables with significant correlations. The respiratory disturbance index (RDI) and nighttime pulse oxyhemoglobin saturation were included in the regression equation due to their close association with movement arousals. Movement arousals independently predicted BNE (t [48] = 2.06; p < 0.05). No other variable independently predicted any of the measurements of sympathetic activity.

CONCLUSIONS

These findings suggest that movement arousals may influence daytime sympathetic tone independently of RDI and nighttime saturation.

Mechanisms of acute cardiovascular response to periodic apneas in sedated pigs

This study was designed to evaluate the importance of sympathoadrenal activation in the acute cardiovascular response to apneas and the role of hypoxemia in this response. In addition, we evaluated the contribution of the vagus nerve to apnea responses after chemical sympathectomy. In six pigs preinstrumented with an electromagnetic flow probe and five nonpreinstrumented pigs, effects of periodic nonobstructive apneas were tested under the following six conditions: room air breathing, 100% O2 supplementation, both repeated after administration of hexamethonium (Hex), and both repeated again after bilateral vagotomy in addition to Hex. With room air apneas, during the apnea cycle, there were increases in mean arterial pressure (MAP; from baseline of 108 +/- 4 to 124 +/- 6 Torr, P < 0.01), plasma norepinephrine (from 681 +/- 99 to 1,825 +/- 578 pg/ml, P < 0.05), and epinephrine (from 191 +/- 67 to 1,245 +/- 685 pg/ml, P < 0.05) but decreases in cardiac output (CO; from 3.3 +/- 0.6 to 2.4 +/- 0.3 l/min, P < 0.01) and cervical sympathetic nerve activity. With O2 supplementation relative to baseline, apneas were associated with small increases in MAP (from 112 +/- 4 to 118 +/- 3 Torr, P < 0.01) and norepinephrine (from 675 +/- 97 to 861 +/- 170 pg/ml, P < 0.05). After Hex, apneas with room air were associated with small increases in MAP (from 103 +/- 6 to 109 +/- 6 Torr, P < 0.05) and epinephrine (from 136 +/- 45 to 666 +/- 467 pg/ml, P < 0.05) and decreases in CO (from 3.6 +/- 0.4 to 3.2 +/- 0. 5 l/min, P < 0.05). After Hex, apneas with O2 supplementation were associated with decreased MAP (from 107 +/- 5 to 100 +/- 5 Torr, P < 0.05) and no other changes. After vagotomy + Hex, with room air and O2 supplementation, apneas were associated with decreased MAP (from 98 +/- 6 to 76 +/- 7 and from 103 +/- 7 to 95 +/- 6 Torr, respectively, both P < 0.01) but increased CO [from 2.7 +/- 0.3 to 3. 2 +/- 0.4 l/min (P < 0.05) and from 2.4 +/- 0.2 to 2.7 +/- 0.2 l/min (P < 0.01), respectively]. We conclude that sympathoadrenal activation is the major pressor mechanism during apneas. Cervical sympathetic nerve activity does not reflect overall sympathoadrenal activity during apneas. Hypoxemia is an important but not the sole trigger factor for sympathoadrenal activation. There is an important vagally mediated reflex that contributes to the pressor response to apneas.

Apnea syndrome in a patient with Alzheimer dementia under chlormethiazole treatment: a clinical experience report

Sleep apnea syndromes in conjunction with dementia have attracted considerable interest among geropsychiatrists in recent years. This clinical case report describes a demented and delirious elderly patient with a history of alcoholism who developed a sleep apnea syndrome under treatment with chlormethiazole. The risk of chlormethiazole treatment may be underestimated in vulnerable patients, e.g. those suffering from severe respiratory diseases or dementia. Alternative treatments for delirious states need to be evaluated instead.

Changes in urinary uric acid excretion in obstructive sleep apnea before and after therapy with nasal continuous positive airway pressure

STUDY OBJECTIVE

To assess the utility of urinary uric acid excretion as a marker of nocturnal hypoxia in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS) before and after the institution of nasal continuous positive airway pressure (CPAP).

DESIGN

Prospective, open.

SETTING

Sleep Disorders Laboratory, Veterans Affairs Medical Center.

PARTICIPANTS

Thirty consecutive male subjects, 20 with OSAHS and 10 without OSAHS.

MEASUREMENTS AND METHODS

Spot morning urine and venous blood samples were obtained in all subjects; samples were also obtained after the application of CPAP in those with OSAHS. Uric acid excretion, normalized to creatinine clearance, was calculated as the product of urinary uric acid and serum creatinine concentrations divided by urine creatinine concentration. In patients with OSAHS, uric acid excretion was 0.55+/-0.1 mg/dL before CPAP therapy and decreased to 0.30+/-0.01 mg/dL after CPAP therapy (p < 0.001). The latter value did not differ significantly from the mean value (0.32+/-0.03 mg/dL) in the control group. Uric acid excretion in OSAHS patients correlated significantly with the apnea-hypopnea index (r=0.42; p<0.0003).

CONCLUSION

Uric acid excretion is increased in OSAHS patients and normalizes after CPAP treatment, most likely reflecting differences in tissue oxygenation between the two conditions. Further studies in large number of patients may confirm the usefulness of this simple test for diagnosis and follow-up of patients with OSAHS.