Association of sleep-disordered breathing and the occurrence of stroke

Obstructive sleep apnea and cardiovascular disease: a perspective and future directions

Data from animal and human studies provide a biological plausibility to the notion that obstructive sleep apnea activates pathways that lead to insulin resistance, atherosclerosis and hypertension. Sleep apnea thus activates the same pathways as does obesity. That obstructive sleep apnea is a risk factor for cardiovascular disease is supported by epidemiological association studies. Longitudinal cohort studies also provide evidence that patients with untreated severe sleep apnea have an increased rate of cardiovascular events. But these studies, while highly suggestive, do not provide the evidence needed to convince the skeptic. This would only be obtained by randomized treatment trials with hard cardiovascular endpoints such as cardiac events and deaths. While such studies are in the planning stages, they will be challenging. There are issues about randomizing individuals with severe sleep apnea and excessive sleepiness into no therapy, since they are at known increased risk for car crashes. Thus, lack of therapy puts others on the road at risk as well as the subject with sleep apnea. There is, moreover, the concern that treating obstructive sleep apnea in very obese individuals will have little impact, since any effect of therapy for OSA will be overwhelmed by the effects of obesity itself. Data from randomized treatment trials for cardiovascular endpoints will likely not be available for many years. In the interim, physicians need to consider how to treat such patients. It is proposed that given that CPAP treatment for obstructive sleep apnea is highly effective and essentially totally safe, and that the evidence is suggestive that sleep apnea is a risk factor for cardiovascular disease, then we propose all patients with severe sleep apnea should be treated to reduce cardiovascular risk.

What the electroconvulsive therapy practitioner needs to know about obstructive sleep apnea

Obstructive sleep apnea (OSA) is common and increasingly so in countries experiencing an epidemic of obesity. The rate of OSA is likely as high or higher in psychiatric patients and patients receiving electroconvulsive therapy (ECT) as compared with the general population. Obstructive sleep apnea can be detected by maintaining a high degree of suspicion in patients with risk factors, symptoms, and typical physical findings. Failure to detect OSA can lead to serious long-term problems with cardiovascular health, excessive sleepiness, and increased risk of motor vehicle accidents. It is unknown whether failure to treat OSA could promote failure to respond to ECT or greater cognitive problems with ECT, but failure to recognize and manage the risk for OSA in patients receiving ECT might expose them to anesthetic difficulties. Ideally, patients with suspected OSA should have a sleep laboratory evaluation and a definitive treatment plan in place before ECT, but, sometimes, psychiatric urgency and lack of access to resources in developing countries would make this unworkable. At a minimum, steps can be taken during the ECT procedure to manage airway obstruction in suspected or known patients with OSA.

Excessive daytime sleepiness is an independent risk indicator for cardiovascular mortality in community-dwelling elderly: the three city study

BACKGROUND AND PURPOSE

Excessive daytime sleepiness, one of the most frequent sleep complaints in the elderly, may affect survival, but inconsistent results have been observed in that population so far. We therefore estimated the risk of mortality for excessive daytime sleepiness (EDS) in community-dwelling elderly participating in the Three City Study.

METHODS

The Three City Study is a French population-based multicenter prospective study including 9294 subjects (60% women) aged >or=65 years at recruitment between 1999 to 2001. At baseline, 8269 subjects rated EDS and nocturnal sleep complaints as never, rare, regular, and frequent in response to an administered questionnaire and provided information on medication use for sleep or anxiety. Hazard ratios (HR) of EDS (regular or frequent) for mortality over 6 years were estimated by a Cox proportional hazard model.

RESULTS

At baseline, 18.7% of the study participants had regular or frequent EDS. After 6 years of follow-up, 762 subjects had died including 260 from cancer and 196 from cardiovascular disease. EDS was associated with a significant 33% increased risk of mortality (95% CI: 1.13 to 1.61) after adjustment for age, gender, study center, body mass index, previous cardiovascular disease, Mini Mental State Examination score, and cardiovascular risk factors. Further adjustment for current use of medication for sleep and for depressive symptoms slightly diminished the HRs. EDS was equally predictive of mortality in those who snored loudly and in those who did not. EDS was related to cardiovascular mortality but not to mortality attributable to cancer.

CONCLUSIONS

EDS might be independently associated with total and cardiovascular mortality in community-dwelling elderly.

Obstructive sleep apnea, insulin resistance, and steatohepatitis in severe obesity

RATIONALE

Obstructive sleep apnea is associated with insulin resistance and liver injury. It is unknown whether apnea contributes to insulin resistance and steatohepatitis in severe obesity.

OBJECTIVES

To examine whether sleep apnea and nocturnal hypoxemia predict the severity of insulin resistance, systemic inflammation, and steatohepatitis in severely obese individuals presenting for bariatric surgery.

METHODS

We performed sleep studies and measured fasting blood glucose, serum insulin, C-reactive protein, and liver enzymes in 90 consecutive severely obese individuals, 75 women and 15 men, without concomitant diabetes mellitus or preexistent diagnosis of sleep apnea or liver disease. Liver biopsies (n = 20) were obtained during bariatric surgery.

MEASUREMENTS AND MAIN RESULTS

Obstructive sleep apnea with a respiratory disturbance index greater than 5 events/hour was diagnosed in 81.1% of patients. The median respiratory disturbance index was 15 +/- 29 events/hour and the median oxygen desaturation during apneic events was 4.6 +/- 1.8%. All patients exhibited high serum levels of C-reactive protein, regardless of the severity of apnea, whereas liver enzymes were normal. Oxygen desaturation greater than 4.6% was associated with a 1.5-fold increase in insulin resistance, according to the homeostasis model assessment index. Histopathology data suggested that significant nocturnal desaturation might predispose to hepatic inflammation, hepatocyte ballooning, and liver fibrosis. Fasting blood glucose levels and steatosis scores were not affected by nocturnal hypoxia. There was no relationship between the respiratory disturbance index and insulin resistance or liver histopathology.

CONCLUSIONS

Hypoxic stress of sleep apnea may be implicated in the development of insulin resistance and steatohepatitis in severe obesity.

Sleep-disordered breathing: autonomic mechanisms and arrhythmias

Obstructive sleep apnea (OSA) is present in at least 2% to 4% of the general population. Central sleep apnea (CSA), though less common, is highly prevalent in patients with heart failure. Both forms of sleep apnea exert strong modulatory effects on the autonomic nervous system at night through a number of mechanisms including central respiratory-cardiac coupling in the brainstem, chemoreflex stimulation, baroreflexes, and reflexes relating to lung inflation. Arousals also contribute to the autonomic disturbance. Although sleep is normally a time when parasympathetic modulation of the heart predominates and myocardial electrical stability is enhanced, OSA and CSA disturb this quiescence, creating an autonomic profile in which both profound vagal activity leading to bradyarrhythmias, and sympatho-excitation favoring ventricular ectopy are observed. The resulting tendency toward cardiac arrhythmia may directly contribute to sudden cardiac death and premature mortality in patients with sleep apnea. Therapy consists largely of treatment with continuous positive airway pressure, which has been shown to improve autonomic profile and reduce nocturnal arrhythmias.

Obstructive sleep apnoea and its cardiovascular consequences

Obstructive sleep apnoea (OSA) is a common disorder in which repetitive apnoeas expose the cardiovascular system to cycles of hypoxia, exaggerated negative intrathoracic pressure, and arousals. These noxious stimuli can, in turn, depress myocardial contractility, activate the sympathetic nervous system, raise blood pressure, heart rate, and myocardial wall stress, depress parasympathetic activity, provoke oxidative stress and systemic inflammation, activate platelets, and impair vascular endothelial function. Epidemiological studies have shown significant independent associations between OSA and hypertension, coronary artery disease, arrhythmias, heart failure, and stroke. In randomised trials, treating OSA with continuous positive airway pressure lowered blood pressure, attenuated signs of early atherosclerosis, and, in patients with heart failure, improved cardiac function. Current data therefore suggest that OSA increases the risk of developing cardiovascular diseases, and that its treatment has the potential to diminish such risk. However, large-scale randomised trials are needed to determine, definitively, whether treating OSA improves cardiovascular outcomes.

Impaired cerebral autoregulation in obstructive sleep apnea

Obstructive sleep apnea (OSA) increases the risk of stroke independent of known vascular and metabolic risk factors. Although patients with OSA have higher prevalence of hypertension and evidence of hypercoagulability, the mechanism of this increased risk is unknown. Obstructive apnea events are associated with surges in blood pressure, hypercapnia, and fluctuations in cerebral blood flow. These perturbations can adversely affect the cerebral circulation. We hypothesized that patients with OSA have impaired cerebral autoregulation, which may contribute to the increased risk of cerebral ischemia and stroke. We examined cerebral autoregulation in patients with and without OSA by measuring cerebral artery blood flow velocity (CBFV) by using transcranial Doppler ultrasound and arterial blood pressure using finger pulse photoplethysmography during orthostatic hypotension and recovery as well as during 5% CO2 inhalation. Cerebral vascular conductance and reactivity were determined. Forty-eight subjects, 26 controls (age 41.0±2.3 yr) and 22 OSA (age 46.8±2.3 yr) free of cerebrovascular and active coronary artery disease participated in this study. OSA patients had a mean apnea-hypopnea index of 78.4±7.1 vs. 1.8±0.3 events/h in controls. The oxygen saturation during sleep was significantly lower in the OSA group (78±2%) vs. 91±1% in controls. The dynamic vascular analysis showed mean CBFV was significantly lower in OSA patients compared with controls (48±3 vs. 55±2 cm/s; P <0.05, respectively). The OSA group had a lower rate of recovery of cerebrovascular conductance for a given drop in blood pressure compared with controls (0.06±0.02 vs. 0.20±0.06 cm·s−2·mmHg−1; P <0.05). There was no difference in cerebrovascular vasodilatation in response to CO2. The findings showed that patients with OSA have decreased CBFV at baseline and delayed cerebrovascular compensatory response to changes in blood pressure but not to CO2. These perturbations may increase the risk of cerebral ischemia during obstructive apnea.

Gender differences in obstructive sleep apnea and treatment implications

Obstructive sleep apnea (OSA) is a common cause of daytime sleepiness for millions of Americans. It is also a disease associated with an increased likelihood of hypertension, cardiovascular disease, stroke, daytime sleepiness, motor vehicle accidents, and diminished quality of life. A number of population-based studies have shown that OSA is more common in men than in women and this discrepancy is often evident in the clinical setting. There are a number of pathophysiological differences to suggest why men are more prone to the disease than women. Although the exact mechanisms are unknown, differences in obesity, upper airway anatomy, breathing control, hormones, and aging are all thought to play a role. The purpose of this review was to examine the literature on gender differences in OSA and to analyze whether or not these differences in pathogenic mechanisms affect diagnosis or treatment.

The pathophysiology, clinical impact, and management of nasal congestion in allergic rhinitis

BACKGROUND

Nasal congestion is a cardinal symptom of allergic rhinitis (AR). It is difficult to treat and is associated with decreased quality of life.

OBJECTIVE

This article reviews the clinical features of nasal congestion, its complex pathophysiology in the context of AR, its clinical impact, and the strengths and weaknesses of available treatments.

METHODS

Primary studies and reviews in the peer-reviewed, English-language literature were identified through searches of MEDLINE (1966-2008) and the Cochrane Library (1996-2008) using the terms nasal congestion, allergic rhinitis, pathophysiology, quality of life, and burden. Additional references were obtained by searching the reference lists of the identified articles. Abstracts from the 2006 and 2007 meetings of the American Academy of Allergy, Asthma, and Immunology were also searched. Pertinent articles were included in the review if they were recently published and patient-focused, and if their authors were recognized leaders in the field.

RESULTS

A survey of 2355 patients with AR or their guardians found that almost half of respondents rated nasal congestion the most bothersome symptom; in a survey of 2500 adults with AR, 78% rated nasal congestion either extremely or moderately bothersome. Histamine and leukotrienes are major mediators of the allergic inflammation associated with nasal congestion, as indicated by reductions in nasal cross-sectional area in response to histamine challenge (P<0.001) and increases in nasal airway resistance in response to leukotriene challenge (P<0.05).Therapy for nasal congestion in AR is often hampered by limitations associated with the individual agents; for example, decongestants are effective in the control of nasal congestion, but their use is restricted by their adverse-event profiles. A meta-analysis of 16 controlled studies involving 2267 patients with AR found that intranasal corticosteroids provided significantly greater relief of nasal congestion than oral antihistamines (95% CI for combined standardized mean difference, -0.73 to -0.53). The results of several clinical trials have suggested that leukotriene-receptor antagonists may be associated with reduced nasal congestion; however, no agents in this class are currently approved for the treatment of nasal congestion in AR.

CONCLUSION

There is a need for therapies that are well tolerated and effective in relieving nasal congestion in AR.

Additive effects of obstructive sleep apnea and hypertension on early markers of carotid atherosclerosis

Obstructive sleep apnea (OSA) has emerged as an independent risk factor for atherosclerosis. However, OSA is frequently associated with several risk factors for atherosclerosis, including hypertension (HTN). The impact of OSA and HTN alone compared with the association of both conditions on carotid atherosclerosis is not understood. We studied 94 middle-aged participants free of smoking and diabetes mellitus who were divided into 4 groups: controls (n=22), OSA (n=25), HTN (n=20), and OSA+HTN (n=27). All of the participants underwent polysomnography and carotid measurements of intima-media thickness, diameter, and distensibility with an echo-tracking device. Compared with controls, intima-media thickness and carotid diameter were similarly higher in OSA (713+/-117 and 7117+/-805 microm), and HTN groups (713+/-182 and 7191+/-818 microm), with a further significant increase in OSA+HTN patients (837+/-181 and 7927+/-821 microm, respectively; P<0.01). Carotid distensibility was significantly lower in HTN (P<0.05) and OSA+HTN subjects (P<0.001) compared with controls. In the OSA+HTN group, carotid distensibility was significantly lower than in the OSA group and controls (P<0.05 for each comparison). Multivariate analysis showed that intima-media thickness was positively related to systolic blood pressure and apnea-hypopnea index. Apnea-hypopnea index was the only factor related to carotid diameter. Age and systolic blood pressure were independently related to carotid distensibility. In conclusion, the association of OSA and HTN has additive effects on markers of carotid atherosclerosis. Because early markers of carotid atherosclerosis predict future cardiovascular events, including not only stroke but also myocardial infarction, these findings may help to explain the increased risk of cardiovascular disease in patients with OSA.

Assessment of sleep in ventilator-supported critically III patients

OBJECTIVES

In critically ill patients, sleep derangements are reported to be severe using Rechtschaffen and Kales (R&K) methodology; however, whether such methodology can reliably assess sleep during critical illness is unknown. We set out to determine the reproducibility of 4 different sleep-assessment methods (3 manual and 1 computer-based) for ventilator-supported critically ill patients and also to quantify the extent to which the reproducibility of the manual methods for measuring sleep differed between critically ill and ambulatory (control) patients.

DESIGN

Observational methodologic study.

SETTING

Academic center.

PATIENTS

Critically ill patients receiving mechanical ventilation and age-matched controls underwent polysomnography.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Reproducibility for the computer-based method (spectral analysis of electroencephalography [EEG]) was better than that for the manual methods: R&K methodology and sleep-wakefulness organization pattern (P = 0.03). In critically ill patients, the proportion of misclassifications for measurements using spectral analysis, sleep-wakefulness organization pattern, and R&K methodology were 0%, 36%, and 53%, respectively (P < 0.0001). The EEG pattern of burst suppression was not observed. Interobserver and intraobserver reliability of the manual sleep-assessment methods for critically ill patients (kappa = 0.52 +/- 0.23) was worse than that for control patients (kappa = 0.89 +/- 0.13; P = 0.03). In critically ill patients, the overall reliability of the R&K methodology was relatively low for assessing sleep (kappa = 0.19), but detection of rapid eye movement sleep revealed good agreement (kappa = 0.70).

CONCLUSIONS

Reproducibility for spectral analysis of EEG was better than that for the manual methods: R&K methodology and sleep-wakefulness organization pattern. For assessment of sleep in critically ill patients, the use of spectral analysis, sleep-wakefulness organization state, or rapid eye movement sleep alone may be preferred over the R&K methodology.

Ventilatory and cerebrovascular responses to hypercapnia in patients with obstructive sleep apnoea: effect of CPAP therapy

The purpose of this study was to assess whether the cerebrovascular response to hypercapnia is blunted in OSA patients and if this could alter the ventilatory response to hypercapnia before and after CPAP therapy. We measured the cerebrovascular, cardiovascular and ventilatory responses to hypercapnia in 8 patients with OSA (apnoea-hypopnoea index=101+/-10) before and after 4-6 weeks of CPAP therapy and in 10 control subjects who did not undergo CPAP therapy. The cerebrovascular and ventilatory responses to hypercapnia were not different between OSA and controls at baseline or follow-up. The cardiovascular response to hypercapnia was significantly increased in the OSA group by CPAP therapy (mean arterial pressure response: 1.30+/-0.16 vs. 2.04+/-0.36 mmHg Torr(-1); p=0.007). We conclude that in normocapnic, normotensive OSA patients without cardiovascular disease, the ventilatory, cerebrovascular, and cardiovascular responses to hypercapnia are normal, but the cardiovascular response to hypercapnia is heightened following 1 month of CPAP therapy.

[Stroke prevention outside the pharmacy : risk factors and lifestyle]

Advice on modifiable risk and lifestyle factors for stroke prevention should be an established component of medical consultation. It is most important to explain that alterations to the lifestyle can be highly efficient with respect to the individual risk profile. The following review describes the importance of lifestyle factors such as nutrition, smoking, alcohol consumption, psychiatric condition, sport, dental hygiene and sleep disturbances for the risk of stroke using current data. It provides evidence that lifestyle modifications are highly effective with respect to stroke prevention. Corresponding recommendations and preventive strategies are presented.

Acceptance, effectiveness and safety of continuous positive airway pressure in acute stroke: a pilot study

OBJECTIVES

To evaluate the acceptance, effectiveness in preventing upper airways obstruction, and haemodynamic effects of continuous positive airway pressure (CPAP) in acute stroke.

METHODS

Twelve patients (4 M, and 8 F; mean (SD), 75.2 (5.5) years) within 48 h of acute stroke onset underwent: (1) sleep studies (1st night: auto-CPAP mode; 2nd night: diagnostic); (2) nocturnal non-invasive blood pressure studies (1st night during CPAP; 2nd night during spontaneous breathing (SB)); and (3) daytime cerebral blood flow velocity measurement in middle cerebral artery (FV) with transcranial Doppler during SB and with CPAP (5, 10, 15 cm H(2)O).

RESULTS

Ninety percent, 60% and 50% of stroke patients had a respiratory disturbance index (RDI) of >or=5, >or=10 and >or=15 events per hour, respectively (18.2 (11.3)). CPAP acceptance was 84%; 42% used CPAP more than 6h and 42% between 1-3h with a mean use of CPAP of 5.2h (4.0). Compared to SB, CPAP reduced, though not significantly, RDI, time with SaO(2)<90%, mean blood pressure and mean blood pressure dips (10 mm Hg)/h. Compared with SB, any level of CPAP progressively and significantly reduced systolic and mean FV; drop in diastolic FV was significant at CPAP10 and CPAP15. The partial pressure of end-tidal CO(2) was significantly lowered by all levels of CPAP.

CONCLUSIONS

According to this pilot study, CPAP is reasonably well tolerated by patients with acute stroke for at least one night. Despite its possible beneficial effect on obstructive sleep-disordered breathing and blood pressure variability, CPAP use in acute stroke should be still considered with caution due to possible harmful haemodynamic effects at higher pressures.

Heavy snoring as a cause of carotid artery atherosclerosis

STUDY OBJECTIVES

Previous studies have suggested that snoring and obstructive sleep apnea hypopnea syndrome may be important risk factors for the development of carotid atherosclerosis and stroke. However, it is not clear if snoring per se is independently related to the risk of developing carotid atherosclerotic plaque.

DESIGN

Observational cohort study.

SETTING

Volunteer sample examined in a sleep laboratory.

PARTICIPANTS

One hundred ten volunteers (snorers and nonsnorers with only mild, nonhypoxic obstructive sleep apnea hypopnea syndrome) underwent polysomnography with quantification of snoring, bilateral carotid and femoral artery ultrasound with quantification of atherosclerosis, and cardiovascular risk factor assessment. Subjects were categorized into 3 snoring groups: mild (0%-25% night snoring), moderate (> 25%-50% night snoring), and heavy (> 50% night snoring).

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

The prevalence of carotid atherosclerosis was 20% with mild snoring, 32% with moderate snoring, and 64% with heavy snoring (P < 0.04, X2). Logistic regression analysis was used to determine the independent effect of snoring on the prevalence of carotid and femoral atherosclerosis. After adjustment for age, sex, smoking history, and hypertension, heavy snoring was significantly associated with carotid atherosclerosis (odds ratio 10.5; 95% confidence interval 2.1-51.8; P = 0.004) but not with femoral atherosclerosis.

CONCLUSIONS

Heavy snoring significantly increases the risk of carotid atherosclerosis, and the increase is independent of other risk factors, including measures of nocturnal hypoxia and obstructive sleep apnea severity. Considering the high prevalence of snoring in the community, these findings have substantial public health implications for the management of carotid atherosclerosis and the prevention of stroke.

Increased risk of stroke in patients with coronary artery disease and sleep apnea: a 10-year follow-up

BACKGROUND

The effect of sleep apnea on mortality and cardiovascular morbidity is mainly unknown. We aimed to study whether sleep apnea is related to stroke, death, or myocardial infarction in patients with symptomatic coronary artery disease.

METHODS AND RESULTS

A total of 392 men and women with coronary artery disease referred for coronary angiography were examined by use of overnight sleep apnea recordings. Sleep apnea, defined as an apnea-hypopnea index >or=5, was recorded in 54% of the patients. All patients were followed up prospectively for 10 years, and no one was lost to follow-up. Stroke occurred in 47 (12%) of 392 patients during follow-up. Sleep apnea was associated with an increased risk of stroke, with an adjusted hazard ratio of 2.89 (95% confidence interval 1.37 to 6.09, P=0.005), independent of age, body mass index, left ventricular function, diabetes mellitus, gender, intervention, hypertension, atrial fibrillation, a previous stroke or transient ischemic attack, and smoking. Patients with an apnea-hypopnea index of 5 to 15 and patients with an apnea-hypopnea index >or=15 had a 2.44 (95% confidence interval 1.08 to 5.52) and 3.56 (95% confidence interval 1.56 to 8.16) times increased risk of stroke, respectively, than patients without sleep apnea, independent of confounders (P for trend=0.011). Death and myocardial infarction were not related to sleep apnea. Intervention in the form of coronary artery bypass grafting or percutaneous coronary intervention was related to a longer survival but did not affect the incidence of stroke.

CONCLUSIONS

Sleep apnea is significantly associated with the risk of stroke among patients with coronary artery disease who are being evaluated for coronary intervention.

Sleep disordered breathing and mortality: eighteen-year follow-up of the Wisconsin sleep cohort

BACKGROUND

Sleep-disordered breathing (SDB) is a treatable but markedly under-diagnosed condition of frequent breathing pauses during sleep. SDB is linked to incident cardiovascular disease, stroke, and other morbidity. However, the risk of mortality with untreated SDB, determined by polysomnography screening, in the general population has not been established.

METHODS

An 18-year mortality follow-up was conducted on the population-based Wisconsin Sleep Cohort sample (n = 1522), assessed at baseline for SDB with polysomnography, the clinical diagnostic standard. SDB was described by the number of apnea and hypopnea episodes/hour of sleep; cutpoints at 5, 15 and 30 identified mild, moderate, and severe SDB, respectively. Cox proportional hazards regression was used to estimate all-cause and cardiovascular mortality risks, adjusted for potential confounding factors, associated with SDB severity levels.

RESULTS

All-cause mortality risk, adjusted for age, sex, BMI, and other factors was significantly increased with SDB severity. The adjusted hazard ratio (HR, 95% CI) for all-cause mortality with severe versus no SDB was 3.0 (1.4,6.3). After excluding persons who had used CPAP treatment (n = 126), the adjusted HR (95% CI) for all-cause mortality with severe versus no SDB was 3.8 (1.6,9.0); the adjusted HR (95% CI) for cardiovascular mortality was 5.2 (1.4,19.2). Results were unchanged after accounting for daytime sleepiness.

CONCLUSIONS

Our findings of a significant, high mortality risk with untreated SDB, independent of age, sex, and BMI underscore the need for heightened clinical recognition and treatment of SDB, indicated by frequent episodes of apnea and hypopnea, irrespective of symptoms of sleepiness.

Correlation between severity of obstructive sleep apnea and prevalence of silent cerebrovascular lesions

STUDY OBJECTIVES

We investigated the prevalence of silent cerebrovascular lesions in patients with obstructive sleep apnea (OSA) and the correlation between OSA severity and prevalence of silent cerebrovascular lesions in Japanese patients.

METHODS

Study subjects were 192 polysomnography (PSG)-confirmed patients who visited the sleep disorders clinic in our university hospital. None had a history of cerebrovascular disease (CVD). We performed a cross-sectional study on OSA severity and the prevalence of silent cerebrovascular lesions detected by brain MRI analysis.

RESULTS

The control (AHI < 5/h) group included 19 subjects with a mean AHI of 1.7 +/- 1.6/h, the mild OSAS (AHI 5 to < 15/h) group included 25 patients with a mean AHI of 9.5 +/- 3.7/h, the moderate OSAS (AHI 15 to < 30/h) group included 35 patients with a mean AHI of 22.0 +/- 7.0/h while the severe OSAS (AHI > or = 30/h) group included 113 patients with a mean AHI of 59.9 +/- 20.5/h. A larger percentage of patients with severe OSAS had a higher BMI and hyperglycemia than those with mild or moderate OSAS and control subjects (p < 0.05). Silent lacunar infarction was identified in 4 (21.1%) control subjects, 3 (12.0%) patients with mild OSA, 17 (48.6%) with moderate OSA and 61 (54.0%) with severe OSA. Among control subjects and the mild, moderate, and severe OSA groups, 4 (21.1%), 5 (20.0%), 19 (54.3%) and 61(54.0%), respectively, had periventricular hyperintensity (PVH); most PVH was mild to moderate.

CONCLUSION

Results indicate that patients with moderate to severe (AHI > or = 15/h) OSA have a higher prevalence of silent cerebrovascular lesion than those with less severe OSA.

Obstructive sleep apnea and cardiovascular disease: role of the metabolic syndrome and its components

Although obstructive sleep apnea and cardiovascular disease have common risk factors, epidemiologic studies show that sleep apnea increases risks for cardiovascular disease independently of individuals' demographic characteristics (i.e., age, sex, and race) or risk markers (i.e., smoking, alcohol, obesity, diabetes, dyslipidemia, atrial fibrillation, and hypertension). Individuals with severe sleep apnea are at increased risk for coronary artery disease, congestive heart failure, and stroke. The underlying mechanisms explaining associations between obstructive sleep apnea and cardiovascular disease are not entirely delineated. Several intermediary mechanisms might be involved including sustained sympathetic activation, intrathoracic pressure changes, and oxidative stress. Other abnormalities such as disorders in coagulation factors, endothelial damage, platelet activation, and increased inflammatory mediators might also play a role in the pathogenesis of cardiovascular disease. Linkage between obstructive sleep apnea and cardiovascular disease is corroborated by evidence that treatment of sleep apnea with continuous positive airway pressure reduces systolic blood pressure, improves left ventricular systolic function, and diminishes platelet activation. Several systematic studies are necessary to explicate complex associations between sleep apnea and cardiovascular disease, which may be compounded by the involvement of diseases comprising the metabolic syndrome (i.e., central obesity, hypertension, diabetes, and dyslipidemia). Large-scale, population-based studies testing causal models linking among sleep apnea, cardiovascular morbidity, and metabolic syndrome are needed.

Epidemiology of Obstructive Sleep Apnea: a Population-based Perspective

This review summarizes the recent literature on the epidemiology of adult obstructive sleep apnea (OSA) from various population-based studies. Despite methodologic differences, comparisons have yielded similar prevalence rates of the OSA syndrome in various geographic regions and amongst a number of ethnic groups. Risk factors for OSA including obesity, aging, gender, menopause, and ethnicity are analyzed. We also provide discussion on adverse medical conditions associated with OSA including hypertension, stroke, congestive heart failure, coronary artery disease, cardiovascular mortality, insulin resistance, and neurocognitive dysfunction. Finally with the progression of the global obesity epidemic, we focus on the economic health care burden of OSA and the importance of recognizing the largely undiagnosed OSA population with emphasis on strategies to improve access to diagnostic resources.

Obstructive sleep apnea, cardiovascular disease, and pulmonary hypertension

With the growing epidemic of obesity in an aging population, obstructive sleep apnea (OSA) is increasingly encountered in clinical practice. Given the acute cardiopulmonary stressors consequent to repetitive upper airway collapse, as well as evidence for cardiovascular homeostatic dysregulation in subjects with sleep apnea, there is ample biologic plausibility that OSA imparts increased cardiovascular risk, independent of comorbid disease. Indeed, observational studies have suggested strong associations with multiple disorders, such as systemic hypertension, heart failure, cardiac arrhythmias, and pulmonary hypertension. Further data in the form of longitudinal cohort studies and randomized controlled trials are accruing to add to the body of evidence. This review examines pathophysiologic mechanisms and explores current concepts regarding the impact of OSA and its treatment on selected clinical disease states.

Pharmacologic therapy for sleep-related breathing disorders

Sleep-related breathing disorders (SRBDs) are characterized by disruptions in normal breathing patterns, typically caused by increased upper airway resistance or diminished ventilatory drive. SRBDs are often accompanied by impairment in sleep continuity and wakefulness. The full spectrum of features associated with SRBD syndromes can be divided into three components, each of which can be a target for pharmacological intervention: the sleep-breathing event and its immediate physiological consequences; the adverse effects of these events on sleep continuity; and impairment in daytime waking function. A number of pharmacologic agents have been studied for their ability to reduce upper airway resistance or increase ventilatory drive. Other medications have been tested for their ability to treat one or more of the symptoms of sleep or wakefulness in SRBD patients. The purpose of this article is to provide a review of the status of research related to the pharmacologic treatment of SRBDs.

Unilateral ablation of pre-Botzinger complex disrupts breathing during sleep but not wakefulness

RATIONALE

In adult rats, bilateral ablation of pre-Bötzinger complex (preBötC) neurokinin 1-expressing (NK1R) neurons leads to a progressive and irreversible disruption in breathing pattern, initially during sleep, eventually resulting in an ataxic breathing pattern during wakefulness.

OBJECTIVES

Here we determine whether ablation of fewer preBötC NK1R neurons leads to a persistent pattern of disordered breathing during sleep but not during wakefulness.

METHODS

Adult male Sprague-Dawley rats (n = 12) were instrumented to record diaphragmatic, abdominal, and neck EMG, and EEG. Fourteen days later, a second surgery was performed to stereotaxically microinject into the preBötC on one side the toxin saporin conjugated to substance P (SP-SAP), which selectively ablates NK1R neurons.

MEASUREMENTS AND MAIN RESULTS

Postinjection, rats were monitored within a plethysmograph until they were killed (Days 21-51). At Days 6-9 post-unilateral SP-SAP injection, respiratory pattern during sleep, particularly REM sleep, became increasingly disordered, characterized by an increase in frequency of central sleep apnea and hypopneas (36.8 +/- 7.4 episodes/h of REM vs. 6 +/- 2.0 episodes/h in preinjection controls; P < 0.05), whereas breathing during resting wakefulness remained stable. Unlike bilateral SP-SAP-injected rats, an ataxic breathing pattern did not develop during wakefulness. Rats that were monitored up to 51 days post-SP-SAP injection continued to have sleep-disordered breathing; breathing during wakefulness remained relatively stable. Histologic analysis of the ventrolateral medulla confirmed that NK1R neurons within the preBötC on the injected but not on the contralateral side of the medulla were ablated.

CONCLUSIONS

Gradual loss of preBötC NK1R neurons may be an underlying factor of sleep-disordered breathing, in particular of central sleep apnea.

Sleep disordered breathing in hospitalized patients

STUDY OBJECTIVE

There is a relatively small body of literature looking at sleep disordered breathing (SDB) in acutely ill inpatients. The aim of this study was to assess the frequency of SDB in acutely ill patients admitted to tertiary care centers referred for an inpatient polysomnogram and to identify associations between SDB and patient characteristics.

METHODS

The study was a retrospective chart review of 100 polysomnograms and medical records of all patients who had polysomnography while hospitalized at 2 tertiary care centers between January 2003 and September 2004. Main outcome measures included the frequency of and the association between SDB and specific characteristics, including age, sex, body mass index, and admission disease condition.

RESULTS

There was a high frequency of SDB in the sample (77%). There was an increase in the odds ratio (OR) of SDB with increasing body mass index (OR 1.08; 95% confidence interval; 95% CI 1.02, 1.15). Increasing BMI categories were associated with more severe SDB (p = 0.005). Adjusting for age and BMI, men had a reduced OR of sleep apnea, as compared with women (OR 0.32; 95% CI 0.10, 1.0), and women with SDB were more likely to have more severe disease than men (p = 0.003). There was a significant association of SDB with decompensated CHF (p = 0.01).

CONCLUSIONS

There is a high frequency of SDB in hospitalized patients referred for polysomnography, especially in patients with underlying cardiopulmonary disease. Further investigation of the impact of SDB on acute exacerbations of cardiopulmonary disease is needed, given the high frequency of SDB in hospitalized patients.

Gender differences in Saudi patients with obstructive sleep apnea

Obstructive sleep apnea (OSA) remains under-recognized in women possibly due to differences in clinical presentation, difference in tolerance to symptoms, and rate of usage and referral to sleep services. No reports have addressed OSA in women in the Middle Eastern (Arab) population. Therefore, we conducted this study to assess the differences in demographics, clinical presentation, and polysomnographic (PSG) findings between Saudi women and men diagnosed to have (OSA). The study group comprised 191 consecutive Saudi women and 193 consecutive men who were referred to the Sleep Disorders Centre and were found by in-laboratory PSG to have OSA. Demographic and clinical data were obtained by personal interviews. Women were significantly older than men (53.9 and 43.0 years, respectively; p < 0.001). Similarly, their body mass index was significantly higher than men (p < 0.001). Insomnia was more common among women (39.8%) compared to men (25.9%; p = 0.005). Other sleep symptoms including witnessed apnea, and excessive daytime sleepiness did not show any statistical difference between the two groups. Women were more likely than men to be diagnosed with hypothyroidism, diabetes, hypertension, cardiac disease, and asthma. Apnea-hypopnea index (AHI) was statistically higher in men compared to women; however, most of apnea/hypopnea events in women occurred during rapid eye movement sleep, and the mean duration of hypopnea and apnea was significantly lower in women (p = 0.004). Sleep efficiency was lower in women (71.5% vs. 77.7%) in men (p < 0.001). The desaturation index was higher in men (p = 0.01), but no difference was found in lowest SaO2 or time with SaO2 less than 90%. The present study showed important clinical and PSG differences between Saudi women and men with OSA. Clinicians need to be aware of these differences when assessing women for the possibility of OSA as they may be symptomatic at a lower AHI and have significant comorbid conditions that can be adversely affected if their OSA was not timely managed.

Cerebrovascular response to arousal from NREM and REM sleep

STUDY OBJECTIVE

To determine the effect of arousal from sleep on cerebral blood flow velocity (CBFV) in relation to associated ventilatory and systemic hemodynamic changes.

PARTICIPANTS

Eleven healthy individuals (6 men, 5 women).

MEASUREMENTS

Pulsed Doppler ultrasonography was used to measure CBFV in the middle cerebral artery with simultaneous measurements of sleep state (EEG, EOG, and EMG), ventilation (inductance plethysmography), heart rate (ECG), and arterial pressure (finger plethysmography). Arousals were induced by auditory tones (range: 40-80 dB; duration: 0.5 sec). Cardiovascular responses were examined beat-by-beat for 30 sec before and 30 sec after auditory tones.

RESULTS

During NREM sleep, CBFV declined following arousals (-15% +/- 2%; group mean +/- SEM) with a nadir at 9 sec after the auditory tone, followed by a gradual return to baseline. Mean arterial pressure (MAP; +20% +/- 1%) and heart rate (HR; +17% +/- 2%) increased with peaks at 5 and 3 sec after the auditory tone, respectively. Minute ventilation (VE) was increased (+35% +/- 10%) for 2 breaths after the auditory tone. In contrast, during REM sleep, CBFV increased following arousals (+15% +/- 3%) with a peak at 3 sec. MAP (+17% +/- 2%) and HR (+15% +/- 2%) increased during arousals from REM sleep with peaks at 5 and 3 sec post tone. VE increased (+16% +/- 7%) in a smaller, more sustained manner during arousals from REM sleep.

CONCLUSIONS

Arousals from NREM sleep transiently reduce CBFV, whereas arousals from REM sleep transiently increase CBFV, despite qualitatively and quantitatively similar increases in MAP, HR, and VE in the two sleep states.

Exhaled breath condensate cytokine level as a diagnostic tool for obstructive sleep apnea syndrome

BACKGROUND

Relationships between exhaled breath condensate (EBC) and serum cytokines and apnea-hypopnea index (AHI) in patients with excessive daytime sleepiness and loud snoring were evaluated for their potential to predict the severity of obstructive sleep apnea syndrome (OSAS).

METHODS

Non-smoking patients with suspected OSAS who had undergone polysomnography (PSG) were selected until 22 non-OSAS, and 22 mild, 22 moderate and 24 severe OSAS cases based on AHI were achieved. Ten healthy smokers served as a smoker control group. Interleukin-6 (IL-6), interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-alpha), and 8-isoprostane were measured in EBC and serum on the morning after PSG and related to OSAS severity using linear discriminant analysis (LDA) and logistic regression (LR).

RESULTS

Biomarker levels, in both EBC and serum, differed significantly across the four groups. Classification by LDA using IL-10 in EBC showed the highest agreement with AHI classification (kappa=0.88). LR distinguished moderate and severe OSAS from mild OSAS and non-OSAS perfectly using IL-6 in EBC and almost perfectly using IL-10 in EBC (area under the ROC curve=0.997). The levels of biomarkers among smokers overlapped with mild to severe OSAS patients.

CONCLUSIONS

Among non-smoker OSAS suspects, EBC IL-6 and IL-10 have potential to predict severity of OSAS.

Pharyngeal motor control and the pathogenesis of obstructive sleep apnea

The upper airway in patients with obstructive sleep apnea (OSA) is thought to collapse during sleep at least in part, because of a sleep related reduction in upper airway dilator muscle activity. Therefore, a comprehensive understanding of the neural regulation of these muscles is warranted. The dilator muscles can be classified in two broad categories; those that have respiratory related activity and those that fire constantly throughout the respiratory cycle. The motor control of these two groups likely differs with the former receiving input from respiratory neurons and negative pressure reflex circuits. The activity of both muscle groups is reduced shortly after sleep onset, indicating that both receive input from brainstem neurons involved in sleep regulation. In the apnea patient, this may lead to pharyngeal airway collapse. This review briefly describes the currently proposed sleep and respiratory neural pathways and how these circuits interact with the upper airway dilator muscle motorneurones, including recent evidence from animal studies.