Naresh M. Punjabi

Prospective Study of Obstructive Sleep Apnea and Incident Coronary Heart Disease and Heart Failure The Sleep Heart Health Study

Background— Clinic-based observational studies in men have reported that obstructive sleep apnea is associated with an increased incidence of coronary heart disease. The objective of this study was to assess the relation of obstructive sleep apnea to incident coronary heart disease and heart failure in a general community sample of adult men and women. Methods and Results— A total of 1927 men and 2495 women ≥40 years of age and free of coronary heart disease and heart failure at the time of baseline polysomnography were followed up for a median of 8.7 years in this prospective longitudinal epidemiological study. After adjustment for multiple risk factors, obstructive sleep apnea was a significant predictor of incident coronary heart disease (myocardial infarction, revascularization procedure, or coronary heart disease death) only in men ≤70 years of age (adjusted hazard ratio 1.10 [95% confidence interval 1.00 to 1.21] per 10-unit increase in apnea-hypopnea index [AHI]) but not in older men or in women of any age. Among men 40 to 70 years old, those with AHI ≥30 were 68% more likely to develop coronary heart disease than those with AHI <5. Obstructive sleep apnea predicted incident heart failure in men but not in women (adjusted hazard ratio 1.13 [95% confidence interval 1.02 to 1.26] per 10-unit increase in AHI). Men with AHI ≥30 were 58% more likely to develop heart failure than those with AHI <5. Conclusions— Obstructive sleep apnea is associated with an increased risk of incident heart failure in community-dwelling middle-aged and older men; its association with incident coronary heart disease in this sample is equivocal.

Sleep-disordered breathing and mortality: A prospective cohort study

In a cohort of 6,441 volunteers followed over an average of 8.2 years, Naresh Punjabi and colleagues find sleep-disordered breathing to be independently associated with mortality and identify predictive characteristics.

Obstructive sleep apnea-hypopnea and incident stroke: the sleep heart health study.

RATIONALE Although obstructive sleep apnea is associated with physiological perturbations that increase risk of hypertension and are proatherogenic, it is uncertain whether sleep apnea is associated with increased stroke risk in the general population. OBJECTIVES To quantify the incidence of ischemic stroke with sleep apnea in a community-based sample of men and women across a wide range of sleep apnea. METHODS Baseline polysomnography was performed between 1995 and 1998 in a longitudinal cohort study. The primary exposure was the obstructive apnea-hypopnea index (OAHI) and outcome was incident ischemic stroke. MEASUREMENTS AND MAIN RESULTS A total of 5,422 participants without a history of stroke at the baseline examination and untreated for sleep apnea were followed for a median of 8.7 years. One hundred ninety-three ischemic strokes were observed. In covariate-adjusted Cox proportional hazard models, a significant positive association between ischemic stroke and OAHI was observed in men (P value for linear trend: P = 0.016). Men in the highest OAHI quartile (>19) had an adjusted hazard ratio of 2.86 (95% confidence interval, 1.1-7.4). In the mild to moderate range (OAHI, 5-25), each one-unit increase in OAHI in men was estimated to increase stroke risk by 6% (95% confidence interval, 2-10%). In women, stroke was not significantly associated with OAHI quartiles, but increased risk was observed at an OAHI greater than 25. CONCLUSIONS The strong adjusted association between ischemic stroke and OAHI in community-dwelling men with mild to moderate sleep apnea suggests that this is an appropriate target for future stroke prevention trials.

Meta-analyses of genome-wide association studies identify multiple loci associated with pulmonary function

Spirometric measures of lung function are heritable traits that reflect respiratory health and predict morbidity and mortality. We meta-analyzed genome-wide association studies for two clinically important lung-function measures: forced expiratory volume in the first second (FEV1) and its ratio to forced vital capacity (FEV1/FVC), an indicator of airflow obstruction. This meta-analysis included 20,890 participants of European ancestry from four CHARGE Consortium studies: Atherosclerosis Risk in Communities, Cardiovascular Health Study, Framingham Heart Study and Rotterdam Study. We identified eight loci associated with FEV1/FVC (HHIP, GPR126, ADAM19, AGER-PPT2, FAM13A, PTCH1, PID1 and HTR4) and one locus associated with FEV1 (INTS12-GSTCD-NPNT) at or near genome-wide significance (P < 5 × 10−8) in the CHARGE Consortium dataset. Our findings may offer insights into pulmonary function and pathogenesis of chronic lung disease.

Effects of sleep fragmentation on glucose metabolism in normal subjects

BACKGROUND Sleep disorders are increasingly associated with insulin resistance, glucose intolerance, and type 2 diabetes mellitus. Whether the metabolic toll imposed by sleep-related disorders is caused by poor-quality sleep or due to other confounding factors is not known. The objective of this study was to examine whether experimental sleep fragmentation across all sleep stages would alter glucose metabolism, adrenocortical function, and sympathovagal balance. METHODS Sleep was experimentally fragmented across all stages in 11 healthy, normal volunteers for two nights using auditory and mechanical stimuli. Primary outcomes included insulin sensitivity (S(I)), glucose effectiveness (S(G)), and insulin secretion, as determined by the intravenous glucose tolerance test. Secondary outcomes included measures of sympathovagal balance and serum levels of inflammatory markers, adipokines, and cortisol. RESULTS Following two nights of sleep fragmentation, S(I) decreased from 5.02 to 3.76 (mU/L)(-1)min(-1) (P < .0001). S(G), which is the ability of glucose to mobilize itself independent of an insulin response, also decreased from 2.73 x 10(-2) min(-1) to 2.16 x 10(-2) min(-1) (P < .01). Sleep fragmentation led to an increase in morning cortisol levels and a shift in sympathovagal balance toward an increase in sympathetic nervous system activity. Markers of systemic inflammation and serum adipokines were unchanged with sleep fragmentation. CONCLUSIONS Fragmentation of sleep across all stages is associated with a decrease in S(I) and S(G). Increases in sympathetic nervous system and adrenocortical activity likely mediate the adverse metabolic effects of poor sleep quality.

Intermittent Hypoxia Increases Insulin Resistance in Genetically Obese Mice

Obstructive sleep apnoea, a syndrome that leads to recurrent intermittent hypoxia, is associated with insulin resistance in obese individuals, but the mechanisms underlying this association remain unknown. We utilized a mouse model to examine the effects of intermittent hypoxia on insulin resistance in lean C57BL/6J mice and leptin‐deficient obese (C57BL/6J−Lepob) mice. In lean mice, exposure to intermittent hypoxia for 5 days (short term) resulted in a decrease in fasting blood glucose levels (from 173 ± 11 mg dl−1 on day 0 to 138 ± 10 mg dl−1 on day 5, P < 0.01), improvement in glucose tolerance without a change in serum insulin levels and an increase in serum leptin levels in comparison with control (2.6 ± 0.3 vs. 1.7 ± 0.2 ng ml−1, P < 0.05). Microarray mRNA analysis of adipose tissue revealed that leptin was the only upregulated gene affecting glucose uptake. In obese mice, short‐term intermittent hypoxia led to a decrease in blood glucose levels accompanied by a 607 ± 136 % (P < 0.01) increase in serum insulin levels. This increase in insulin secretion after 5 days of intermittent hypoxia was completely abolished by prior leptin infusion. Obese mice exposed to intermittent hypoxia for 12 weeks (long term) developed a time‐dependent increase in fasting serum insulin levels (from 3.6 ± 1.1 ng ml−1 at baseline to 9.8 ± 1.8 ng ml−1 at week 12, P < 0.001) and worsening glucose tolerance, consistent with an increase in insulin resistance. We conclude that the increase in insulin resistance in response to intermittent hypoxia is dependent on the disruption of leptin pathways.

Sleep-disordered breathing, glucose intolerance, and insulin resistance

Sleep-disordered breathing (SDB) is a common condition with prevalence estimates of 2-4% in the general population. Epidemiological data suggest that SDB is an independent risk factor for cardiovascular disease. Glucose intolerance and insulin resistance are also well-recognized risk factors for the development of cardiovascular disease. A number of recent clinic-based studies suggest that, independent of obesity, SDB may adversely affect glucose tolerance and insulin sensitivity. The purpose of this study was to systematically review the evidence for the link between SDB, glucose intolerance, and insulin resistance. A MEDLINE search for SDB and metabolic disorders was performed and 24 articles that met the inclusion criteria were identified. Population-based studies indicate that habitual snoring is independently associated with glucose intolerance and insulin resistance. Studies that have used objective measures of SDB (e.g. polysomnography) provide further support for an independent link between SDB, glucose intolerance, and insulin resistance. However, studies on the treatment of SDB with continuous positive airway pressure (CPAP) have yielded inconsistent results and overall do not reveal an improvement in the metabolic disturbance after treatment. Although population-based prospective data on the metabolic implications of SDB are still lacking, current data point to an independent association between SDB and impaired glucose homeostasis. Potential mediators of this association include altered adrenergic function, the direct effects of hypoxemia on glucose regulation, and release of proinflammatory cytokines that affect metabolism.

Intermittent Hypoxia Induces Hyperlipidemia in Lean Mice

Obstructive sleep apnea, a syndrome leading to recurrent intermittent hypoxia (IH), has been associated previously with hypercholesterolemia, independent of underlying obesity. We examined the effects of experimentally induced IH on serum lipid levels and pathways of lipid metabolism in the absence and presence of obesity. Lean C57BL/6J mice and leptin-deficient obese C57BL/6J-Lepob mice were exposed to IH for five days to determine changes in serum lipid profile, liver lipid content, and expression of key hepatic genes of lipid metabolism. In lean mice, exposure to IH increased fasting serum levels of total cholesterol, high-density lipoprotein (HDL) cholesterol, phospholipids (PLs), and triglycerides (TGs), as well as liver TG content. These changes were not observed in obese mice, which had hyperlipidemia and fatty liver at baseline. In lean mice, IH increased sterol regulatory element binding protein 1 (SREBP-1) levels in the liver, increased mRNA and protein levels of stearoyl–coenzyme A desaturase 1 (SCD-1), an important gene of TG and PL biosynthesis controlled by SREBP-1, and increased monounsaturated fatty acid content in serum, which indicated augmented SCD-1 activity. In addition, in lean mice, IH decreased protein levels of scavenger receptor B1, regulating uptake of cholesterol esters and HDL by the liver. We conclude that exposure to IH for five days increases serum cholesterol and PL levels, upregulates pathways of TG and PL biosynthesis, and inhibits pathways of cholesterol uptake in the liver in the lean state but does not exacerbate the pre-existing hyperlipidemia and metabolic disturbances in leptin-deficient obesity.

Effects of acute intermittent hypoxia on glucose metabolism in awake healthy volunteers.

Accumulating evidence suggests that obstructive sleep apnea is associated with alterations in glucose metabolism. Although the pathophysiology of metabolic dysfunction in obstructive sleep apnea is not well understood, studies of murine models indicate that intermittent hypoxemia has an important contribution. However, corroborating data on the metabolic effects of intermittent hypoxia on glucose metabolism in humans are not available. Thus the primary aim of this study was to characterize the acute effects of intermittent hypoxia on glucose metabolism. Thirteen healthy volunteers were subjected to 5 h of intermittent hypoxia or normoxia during wakefulness in a randomized order on two separate days. The intravenous glucose tolerance test (IVGTT) was used to assess insulin-dependent and insulin-independent measures of glucose disposal. The IVGTT data were analyzed using the minimal model to determine insulin sensitivity (S(I)) and glucose effectiveness (S(G)). Drops in oxyhemoglobin saturation were induced during wakefulness at an average rate of 24.3 events/h. Compared with the normoxia condition, intermittent hypoxia was associated with a decrease in S(I) [4.1 vs. 3.4 (mU/l)(-1).min(-1); P = 0.0179] and S(G) (1.9 vs. 1.3 min(-1)x10(-2), P = 0.0065). Despite worsening insulin sensitivity with intermittent hypoxia, pancreatic insulin secretion was comparable between the two conditions. Heart rate variability analysis showed the intermittent hypoxia was associated with a shift in sympathovagal balance toward an increase in sympathetic nervous system activity. The average R-R interval on the electrocardiogram was 919.0 ms during the normoxia condition and 874.4 ms during the intermittent hypoxia condition (P < 0.04). Serum cortisol levels after intermittent hypoxia and normoxia were similar. Hypoxic stress in obstructive sleep apnea may increase the predisposition for metabolic dysfunction by impairing insulin sensitivity, glucose effectiveness, and insulin secretion.

Sleep-disordered breathing and type 2 diabetes A report from the International Diabetes Federation Taskforce on Epidemiology and Prevention

Sleep-disordered breathing (SDB) has been associated with insulin resistance and glucose intolerance, and is frequently found in people with type 2 diabetes. SDB not only causes poor sleep quality and daytime sleepiness, but has clinical consequences, including hypertension and increased risk of cardiovascular disease. In addition to supporting the need for further research into the links between SDB and diabetes, the International Diabetes Federation Taskforce on Epidemiology and Prevention strongly recommends that health professionals working in both type 2 diabetes and SDB adopt clinical practices to ensure that a patient presenting with one condition is considered for the other.