Obstructive sleep apnea is associated with increased high-sensitivity cardiac troponin T levels

BACKGROUND

Obstructive sleep apnea (OSA) is associated with increased cardiovascular risk. Stress imposed on the myocardium by repeated severe hypoxemia and/or BP surges during sleep may result in subclinical myocardial injury. A high-sensitivity cardiac troponin T (hs-cTnT) assay has been developed. We hypothesized that the severity of OSA, as assessed by the apnea-hypopnea index (AHI), is associated with circulating levels of hs-cTnT in the general population.

METHODS

Five hundred five subjects drawn from the general population (age range, 30-65 years; 45% women) underwent in-hospital polysomnography and had morning blood samples drawn. Oversampling of subjects at high risk of OSA was performed.

RESULTS

Overall, hs-cTnT was detectable (≥ 3 ng/L) in 216 subjects (42.8%). After categorizing subjects according to AHI cutoffs that correspond to no, mild to moderate, and severe OSA, the proportion of subjects with detectable hs-cTnT levels increased with increasing severity of OSA (P for trend < .001). Multivariate logistic regression with detectable hs-cTnT as the dependent variable was used to further assess the association between OSA and troponin T. After adjustment for significant univariate predictors of detectable hs-cTnT, the association between AHI and hs-cTnT was no longer statistically significant.

CONCLUSIONS

The prevalence of detectable hs-cTnT increases in proportion to OSA severity, but this association is likely to be caused by a clustering of cardiovascular risk factors among subjects with OSA.

Association between QRS duration and obstructive sleep apnea

BACKGROUND

Both obstructive sleep apnea (OSA) and prolonged QRS duration are associated with hypertension, heart failure, and sudden cardiac death. However, possible links between QRS duration and OSA have not been explored.

METHODS

Cross-sectional study of 221 patients who underwent polysomnography at our center. Demographics, cardiovascular risk factors and ECG were collected to explore a relationship between OSA and QRS duration.

RESULTS

The apnea-hypopnea index (AHI) was positively correlated with QRS duration (r = 0.141, p = 0.03). Patients were divided into 3 groups: AHI < 5 (61), AHI 5-29 (104), and AHI > 30 (55). The mean QRS duration prolonged significantly as OSA worsened (AHI < 5, 85 ± 9.5; AHI 5-29, 89 ± 11.9; and AHI > 30, 95 ± 19.9 ms, p = 0.001). QRS ≥ 100 ms was present in 12.7% of patients with severe OSA compared with 0% in the rest of the sample (p < 0.0001). After adjustment for age, race, and cardiovascular risk factors, this association remained significant in women but not in men.

CONCLUSION

QRS duration and OSA were significantly associated. Severity of OSA independently predicted prolonged QRS in women but not men. Nevertheless, prolongation of QRS duration in either sex may potentiate arrhythmic risks associated with OSA.

Risk perception of obesity and bariatric surgery in patients seeking treatment for obesity

Bariatric surgery (BSx) produces clinically relevant weight loss that translates into improved quality of life, decreased mortality, and reduction in medical comorbidities, including cardiovascular (CV) risk. Little is known about patients' decision-making process to undergo BSx, but risk perception is known to influence medical decision-making. This study examined CV and BSx risk perception in obese subjects undergoing BSx (n = 268) versus those managed medically (MM) (n = 273). This retrospective population-based survey of subjects evaluated for BSx had 148 (55%) and 88 (32%) responders in the BSx and MM groups, respectively. Survey questions assessed risk perceptions and habits prior to weight loss intervention. CV risk was calculated using the Framingham Risk Score (FRS). At baseline, BSx subjects had a greater body mass index and greater prevalence of diabetes and depression. Follow-up mean weight loss was greater in the BSx group. BSx subjects perceived obesity as a greater risk to their overall health than the surgical risk. FRS declined in the BSx group (10 to 5%; p < 0.001) while there was no change in the MM group (8 to 8%; p = 0.54). Those without a measurable decrease in CV risk had a greater tendency to perceive the risk of BSx as greater than that of obesity. Obese subjects undergoing BSx are more likely than MM subjects to perceive obesity as a greater risk to their health than BSx. MM subjects generally underestimate their CV risk and overestimate the risk of BSx. Active discussion of CV risk using the FRS and the perception of risk associated with bariatric surgery can enhance patients' ability to make an informed decision regarding their management.

Impaired endothelial function in persons with obstructive sleep apnoea: impact of obesity

OBJECTIVE

Obstructive sleep apnoea (OSA) and obesity are both associated with endothelial dysfunction, which precedes the development of atherosclerosis. As obesity is highly prevalent in OSA, we wanted to test the hypothesis that OSA is associated with endothelial dysfunction independently of obesity.

DESIGN

Cross-sectional, population-based study.

SETTING

Norwegian university hospital.

PATIENTS

Seventy-one subjects (median age 44 years, 35% female) were recruited from a population-based study in Norway. Participants were categorised as obese (body mass index (BMI) ≥30 kg/m(2)), non-obese (BMI<30 kg/m(2)) with OSA (apnoea-hypopnoea index (AHI)≥10), or non-obese without OSA (AHI<5).

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Endothelial function measured by brachial artery ultrasound and expressed as percentage of flow-mediated dilation (FMD%).

RESULTS

When non-obese subjects without OSA were used as the reference (FMD% (mean±SD) 10.1±6.3), endothelial function was found to be impaired in subjects with OSA (FMD% 6.4±3.2) (p=0.003). FMD% did not differ between obese (6.0±3.4) and non-obese (6.7±3.1) OSA subjects (p=0.3). By univariate linear regression analysis, AHI, BMI, gender and baseline brachial artery diameter were significantly associated with FMD%. When these variables were entered into a multivariate model, only AHI was significantly associated with FMD%.

CONCLUSIONS

OSA is associated with endothelial dysfunction independently of obesity and conventional risk factors.

Baroreflex sensitivity after adenotonsillectomy in children with obstructive sleep apnea during wakefulness and sleep

STUDY OBJECTIVES

Children with obstructive sleep apnea have blunted baroreflex sensitivity and increased blood pressure variability. The aim of the study was to test the hypothesis that treatment of sleep apnea by adenotonsillectomy results in significant improvement of baroreflex sensitivity, lowering of blood pressure and blood pressure variability and increase vagal heart rate modulation.

STUDY DESIGN

One hundred ninety-four children aged 9.6 ± 2.3 years were enrolled; 133 had obstructive sleep apnea and 61 were healthy controls. For children with sleep apnea, polysomnography with 3-lead electrocardiography and continuous blood pressure was performed before adenotonsillectomy, then 6 weeks and 6 months postoperatively. Controls underwent the same assessment at study entry and 6 months later. Spontaneous baroreflex sensitivity was measured in the time and frequency domains. Data analyses were performed for available and complete cases.

RESULTS

Children with sleep apnea experienced postoperatively an increase in baroreflex sensitivity and decrease in blood pressure variability during wakefulness and sleep. A decrease in blood pressure during sleep and in heart rate during wakefulness was also measured. The improvement in baroreflex sensitivity was predicted by the change in the apnea-hypopnea and arousal indices. A normal pattern of rising baroreflex sensitivity during the night was restored in children with severe apnea after surgery. However, baroreceptor sensitivity did not completely normalize after treatment.

CONCLUSION

Treatment of obstructive sleep apnea in children by adenotonsillectomy is associated with gradual improvement in known risk factors for cardiovascular disease. Complete normalization of baroreceptor sensitivity was not achieved 6 months postoperatively.

Type D personality is associated with increased prevalence of ventricular arrhythmias in community-residing persons without coronary heart disease

BACKGROUND

Type D personality may be a risk factor for poor outcome in patients with cardiovascular disease. The biological mechanisms underlying this association are poorly understood. The objective of the study was to test the hypotheses that Type D personality is associated with biological markers for sympathetic dysregulation.

DESIGN

Cross-sectional community-based study.

METHODS

Type D personality was evaluated by DS-14 in 450 persons (46% men), aged between 30 and 65 years. From a Holter-recording, (mean length 18.3 hours), long-term heart rate, ventricular arrhythmias, and heart rate variability (HRV) were registered as markers of sympathetic dysregulation. Traditional cardiovascular risk factors, apnoea-hypopnoea index, medication, and anxiety symptoms were adjusted for.

RESULTS

Type D persons had higher long-term averaged heart rate (74 vs. 71 beats/min, p = 0.003), but this difference was attenuated and not significant in the multivariate model (p = 0.078)). There was an increased prevalence of complex ventricular ectopy (bigeminy, trigeminy, or non-sustained ventricular tachycardia; 14 vs. 6%, p = 0.005 in multivariate model). HRV indices did not differ significantly between those with or without Type D personality. Anxiety symptoms did not confound these associations.

CONCLUSIONS

Type D personality is independently associated with a higher likelihood of ventricular arrhythmias, which may be implicated in the increased cardiovascular risk observed in persons with Type D personality.

Effects of weight gain and weight loss on regional fat distribution

BACKGROUND

Normal-weight adults gain lower-body fat via adipocyte hyperplasia and upper-body subcutaneous (UBSQ) fat via adipocyte hypertrophy.

OBJECTIVES

We investigated whether regional fat loss mirrors fat gain and whether the loss of lower-body fat is attributed to decreased adipocyte number or size.

DESIGN

We assessed UBSQ, lower-body, and visceral fat gains and losses in response to overfeeding and underfeeding in 23 normal-weight adults (15 men) by using dual-energy X-ray absorptiometry and abdominal computed tomography scans. Participants gained ∼5% of weight in 8 wk and lost ∼80% of gained fat in 8 wk. We measured abdominal subcutaneous and femoral adipocyte sizes and numbers after weight gain and loss.

RESULTS

Volunteers gained 3.1 ± 2.1 (mean ± SD) kg body fat with overfeeding and lost 2.4 ± 1.7 kg body fat with underfeeding. Although UBSQ and visceral fat gains were completely reversed after 8 wk of underfeeding, lower-body fat had not yet returned to baseline values. Abdominal and femoral adipocyte sizes, but not numbers, decreased with weight loss. Decreases in abdominal adipocyte size and UBSQ fat mass were correlated (ρ = 0.76, P = 0.001), as were decreases in femoral adipocyte size and lower-body fat (ρ = 0.49, P = 0.05).

CONCLUSIONS

UBSQ and visceral fat increase and decrease proportionately with a short-term weight gain and loss, whereas a gain of lower-body fat does not relate to the loss of lower-body fat. The loss of lower-body fat is attributed to a reduced fat cell size, but not number, which may result in long-term increases in fat cell numbers.

Impact of diagnosing metabolic syndrome on risk perception

OBJECTIVES

To determine the effect of using the diagnosis of metabolic syndrome (MetSx) on risk perception.

METHODS

We randomized 74 participants to receive either the diagnosis of MetSx or the diagnosis of individual cardiovascular risk factors. The MetSx group was subdivided into those receiving written patient education material or written patient education plus educational videos.

RESULTS

At 6 weeks, participants receiving the diagnosis of MetSx were more likely to increase their health concerns, perceived risk of myocardial infarction, and their motivation toward health behavior.

CONCLUSION

Sharing the diagnosis of MetSx increases risk perception and motivation toward a healthier behavior.

Leptin signaling in adipose tissue: role in lipid accumulation and weight gain

RATIONALE

The link between obesity, hyperleptinemia, and development of cardiovascular disease is not completely understood. Increases in leptin have been shown to impair leptin signaling via caveolin-1-dependent mechanisms. However, the role of hyperleptinemia versus impaired leptin signaling in adipose tissue is not known.

OBJECTIVE

To determine the presence and significance of leptin-dependent increases in adipose tissue caveolin-1 expression in humans.

METHODS AND RESULTS

We designed a longitudinal study to investigate the effects of increases in leptin on adipose tissue caveolin-1 expression during weight gain in humans. Ten volunteers underwent 8 weeks of overfeeding, during which they gained an average weight of 4.1±1.4 kg, with leptin increases from 7±3.8 to 12±5.7 ng/mL. Weight gain also resulted in changes in adipose tissue caveolin-1 expression, which correlated with increases in leptin (rho=0.79, P=0.01). In cultured human white preadipocytes, leptin increased caveolin-1 expression, which in turn impaired leptin cellular signaling. Functionally, leptin decreased lipid accumulation in differentiating human white preadipocytes, which was prevented by caveolin-1 overexpression. Further, leptin decreased perilipin and fatty acid synthase expression, which play an important role in lipid storage and biogenesis.

CONCLUSIONS

In healthy humans, increases in leptin, as seen with modest weight gain, may increase caveolin-1 expression in adipose tissue. Increased caveolin-1 expression in turn impairs leptin signaling and attenuates leptin-dependent lowering of intracellular lipid accumulation. Our study suggests a leptin-dependent feedback mechanism that may be essential to facilitate adipocyte lipid storage during weight gain.

Abstract 440: Regional Differences in Fat Loss Following Weight Gain in Normal Adults

Background: Normal weight adults gain leg fat gain via adipocyte hyperplasia and upper body subcutaneous (UBSQ) fat gain via adipocyte hypertrophy.

Objective: To understand whether regional fat loss mirrors fat gain and whether leg fat loss results in decreased adipocyte number vs. size.

Design: We assessed UBSQ, leg and visceral fat gain and loss in response to over- and underfeeding in 23 young, healthy normal weight adults (15 men). Participants gained ∼5% weight over 8 weeks and lost ∼80% of gained fat over the following 8 weeks. We measured abdominal subcutaneous and femoral adipocyte size and number after weight gain and loss.

Results: Volunteers gained 3.1 ± 2.1 kg of body fat with overfeeding and lost 2.4 ± 1.7 kg with calorie restriction. Although upper body subcutaneous (UBSQ) fat and visceral fat gains were completely reversed with weight loss, leg fat had not yet returned to baseline values by 8 weeks. Abdominal and femoral adipocyte size decreased significantly with weight loss, but the number of adipocytes did not decrease. Abdominal adipocyte size decreases correlated (rho= 0.76, p = 0.001) with UBSQ fat mass decreases and femoral adipocyte size decreases correlated (rho= 0.49, p=0.05) with leg fat mass decreases.

Conclusion: UBSQ and visceral fat depots increase and decrease proportionately with short term weight gain and loss, whereas gain and loss of leg fat are less well linked. Loss of lower body fat is due to reduced fat cell size, not number, which may result in long-term increases in leg fat cell number. This may have implications for long-term weight control.

Circulating cytokine concentrations are not associated with major depressive disorder in a community-based cohort

OBJECTIVE

The objective was to test the hypotheses that cytokine levels are elevated in community-residing persons at high risk for obstructive sleep apnea with major depressive disorder (MDD) compared to nondepressive persons and that cytokine levels show stronger correlations with somatic than psychological symptoms of depression.

METHOD

A case-control study within the cross-sectional Akershus Sleep Apnea Project was performed. Two controls matched for age, gender, metabolic syndrome and obstructive sleep apnea were drawn for each case of MDD.

RESULTS

Group comparisons revealed no significant difference in the levels of 17 cytokines [interleukin-1β, -2,-4, -5, -6, -7, -8, -10, -12(p70), -13 and -17; tumor necrosis factor-α; interferon-γ; granulocyte colony-stimulating factor; granulocyte-monocyte colony-stimulating factor; macrophage chemoattractant protein-1 and monocyte inhibitory protein-1β] between persons with (n=34) and without MDD (n=68). There was no association between cytokines levels and MDD in multivariate regression analyses. The concentration of interleukin-4 was significantly more positively correlated with psychological than somatic symptoms (r=0.046 vs. -0.143, respectively, P=0.024), while no different correlations were observed for other cytokines.

CONCLUSION

The cytokine levels were not elevated in MDD, and cytokine levels were not more strongly associated with somatic than psychological symptoms of depression. The depression-specific effect on inflammation may be weak in community-based samples with prevalent somatic comorbidity.

Relation of natriuretic peptide concentrations to central sleep apnea in patients with heart failure

BACKGROUND

Central sleep apnea (CSA) is frequent among patients with heart failure (HF) and associated with increased morbidity and mortality. Elevated cardiac filling pressures promote CSA and atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) secretion. We hypothesized that circulating natriuretic peptide concentrations predict CSA.

METHODS

Consecutive patients with HF (n = 44) with left ventricular ejection fraction (LVEF) ≤ 35% underwent polysomnography for detection of CSA. CSA was defined as an apnea-hypopnea index ≥ 15 with ≥ 50% central apneic events. The relation of natriuretic peptide concentrations to CSA was evaluated by estimation of ORs and receiver operator characteristics (ROCs).

RESULTS

Twenty-seven subjects (61%) had CSA, with men more frequently affected than women (73% vs 27%; OR, 7.1; P = .01); given that only three women had CSA, further analysis was restricted to men. Subjects with CSA had higher mean ANP (4,336 pg/mL vs 2,510 pg/mL, P = .03) and BNP concentrations (746 pg/mL vs 379 pg/mL, P = .05). ANP and BNP concentrations were significantly related to CSA (OR, 3.7 per 3,000 pg/mL, P = .03 and OR, 1.5 per 200 pg/mL, P = .04, respectively), whereas age, LVEF, and New York Heart Association functional class were not. Concentrations of ANP and BNP were predictive of CSA as ROC demonstrated areas under the curve of 0.75 and 0.73, respectively.

CONCLUSIONS

Risk of CSA is related to severity of HF. ANP and BNP concentrations performed similarly for detection of CSA; low concentrations appear associated with low risk for CSA in men.

Validity of weight loss to estimate improvement in body composition in individuals attending a wellness center

The accuracy of weight loss in estimating successful changes in body composition (BC), namely fat mass (FM) loss, is not known and was addressed in our study. To assess the correlation between change in body weight and change in FM, fat% and fat-free mass (FFM), 465 participants (41% male; 41 ± 13 years), who met the criteria for weight change assessment at a wellness center, underwent air-displacement plethysmography (ADP). Body weight and BC were measured at the same time. We categorized the change in body weight, FM and FFM as an increase if there was >1 kg gain, a decrease if there was >1 kg loss and no change if the difference was ≤1 kg. We estimated the diagnostic performance of weight change to identify improvement in BC. After a median time of 132 days, there was a mean weight change was 2.4 kg. From the 255 people who lost >1 kg of weight, 216 (84.7%) had lost >1 kg of FM, but 69 (27.1%) had lost >1 kg of FFM. Of the 143 people with no weight change, 42 (29.4%) had actually lost >1 kg of FM. Of the 67 who gained >1 kg of weight at follow-up, in 23 (34.3%) this was due to an increase in FFM but not in FM. Weight change had a NPV of 73%. Our results indicate that favorable improvements in BC may go undetected in almost one-third of people whose weight remains the same and in one-third of people who gain weight after attending a wellness center. These results underscore the potential role of BC measurements in people attempting lifestyle changes.

Cardiac arrhythmias in obstructive sleep apnea (from the Akershus Sleep Apnea Project)

Increased prevalence of cardiac arrhythmias has been reported in patients with severe obstructive sleep apnea (OSA), but this may not be generalizable to patients from the general population with a milder form of the condition. The aim of this study was to assess the association between cardiac arrhythmias and OSA of mainly mild and moderate severity. In total, 486 subjects (mean age 49 years, 55% men) recruited from a population-based study in Norway underwent polysomnography for OSA assessment and Holter recordings for arrhythmia assessment. Of these, 271 patients were diagnosed with OSA (apnea-hypopnea index [AHI] ≥5, median AHI 16.8, quartiles 1 to 3 8.9 to 32.6). Mean nadir oxygen saturations were 82% and 89% in patients with and without OSA, respectively. Ventricular premature complexes (≥5/hour) were more prevalent in subjects with OSA compared to subjects without OSA (median AHI 1.4, quartiles 1 to 3 0.5 to 3.0) during the night (12.2% vs 4.7%, p = 0.005) and day (14% vs 5.1%, p = 0.002). In multivariate analysis after adjusting for relevant confounders, AHI was independently associated with an increased prevalence of ventricular premature complexes at night (odds ratio per 1-U increase of log-transformed AHI 1.5, 95% confidence interval 1.1 to 2.0, p = 0.008) and during the day (odds ratio 1.37, 95% confidence interval 1.0 to 1.8, p = 0.035). In conclusion, the prevalence of ventricular premature complexes is increased in middle-aged patients with mainly mild or moderate OSA, suggesting an association between OSA and ventricular arrhythmias even in mild OSA.

Sleep-disordered breathing and excessive daytime sleepiness in patients with atrial fibrillation

BACKGROUND

An important consequence of sleep-disordered breathing (SDB) is excessive daytime sleepiness (EDS). EDS often predicts a favorable response to treatment of SDB, although in the setting of cardiovascular disease, particularly heart failure, SDB and EDS do not reliably correlate. Atrial fibrillation (AF) is another highly prevalent condition strongly associated with SDB. We sought to assess the relationship between EDS and SDB in patients with AF.

METHODS

We conducted a prospective study of 151 patients referred for direct current cardioversion for AF who also underwent sleep evaluation and nocturnal polysomnography. The Epworth Sleepiness Scale (ESS) was administered prior to polysomnography and considered positive if the score was ≥ 11. The apnea-hypopnea index (AHI) was tested for correlation with the ESS, with a cutoff of ≥ 5 events/h for the diagnosis of SDB.

RESULTS

Among the study participants, mean age was 69.1 ± 11.7 years, mean BMI was 34.1 ± 8.4 kg/m(2), and 76% were men. The prevalence of SDB in this population was 81.4%, and 35% had EDS. The association between ESS score and AHI was low (R(2) = 0.014, P = .64). The sensitivity and specificity of the ESS for the detection of SDB in patients with AF were 32.2% and 54.5%, respectively.

CONCLUSIONS

Despite a high prevalence of SDB in this population with AF, most patients do not report EDS. Furthermore, EDS does not appear to correlate with severity of SDB or to accurately predict the presence of SDB. Further research is needed to determine whether EDS affects the natural history of AF or modifies the response to SDB treatment.

Effects of renal sympathetic denervation on blood pressure, sleep apnea course, and glycemic control in patients with resistant hypertension and sleep apnea

Percutaneous renal sympathetic denervation by radiofrequency energy has been reported to reduce blood pressure (BP) by the reduction of renal sympathetic efferent and afferent signaling. We evaluated the effects of this procedure on BP and sleep apnea severity in patients with resistant hypertension and sleep apnea. We studied 10 patients with refractory hypertension and sleep apnea (7 men and 3 women; median age: 49.5 years) who underwent renal denervation and completed 3-month and 6-month follow-up evaluations, including polysomnography and selected blood chemistries, and BP measurements. Antihypertensive regimens were not changed during the 6 months of follow-up. Three and 6 months after the denervation, decreases in office systolic and diastolic BPs were observed (median: -34/-13 mm Hg for systolic and diastolic BPs at 6 months; both P<0.01). Significant decreases were also observed in plasma glucose concentration 2 hours after glucose administration (median: 7.0 versus 6.4 mmol/L; P=0.05) and in hemoglobin A1C level (median: 6.1% versus 5.6%; P<0.05) at 6 months, as well as a decrease in apnea-hypopnea index at 6 months after renal denervation (median: 16.3 versus 4.5 events per hour; P=0.059). In conclusion, catheter-based renal sympathetic denervation lowered BP in patients with refractory hypertension and obstructive sleep apnea, which was accompanied by improvement of sleep apnea severity. Interestingly, there are also accompanying improvements in glucose tolerance. Renal sympathetic denervation may conceivably be a potentially useful option for patients with comorbid refractory hypertension, glucose intolerance, and obstructive sleep apnea, although further studies are needed to confirm these proof-of-concept data.

Advanced heart failure and nocturnal hypoxaemia due to central sleep apnoea are associated with increased serum erythropoietin

AIMS

Central sleep apnoea (CSA) and increased serum erythropoietin (EPO) concentration have each been associated with adverse prognosis in heart failure (HF) patients. The aim of this study was to examine the relationship between nocturnal hypoxaemia due to CSA and the serum EPO concentration in patients with HF.

METHODS AND RESULTS

Heart failure subjects (n = 33) and healthy controls (n = 18) underwent polysomnography (PSG) for diagnosis of CSA and identification and quantification of hypoxaemia. Blood collection for measurement of EPO was performed immediately post-PSG. For the analysis, HF subjects were dichotomized into subgroups defined by the presence or absence of CSA and by HF severity. Multivariate analyses were performed to evaluate the relationships of hypoxaemia and advanced HF to EPO concentration. Mean EPO concentration was 62% higher for HF subjects with CSA than for healthy controls (P = 0.004). The magnitude of nocturnal hypoxaemia was significantly and positively related to EPO concentration (r = 0.45, P = 0.02). Advanced HF was also significantly and positively related to EPO concentration (r = 0.43, P = 0.02). On multivariate analysis, the presence of combined nocturnal hypoxaemia and advanced HF yielded greater correlation to EPO concentration than either factor alone (r = 0.57, P = 0.04 and P = 0.05, respectively). Linear regression demonstrated that the combination of New York Heart Association Class and CSA was strongly associated with EPO concentration (P < 0.0001).

CONCLUSION

In non-anaemic HF patients, advanced HF and hypoxaemia due to CSA may each be independently associated with increased serum EPO concentration.

A Norwegian population-based study on the risk and prevalence of obstructive sleep apnea. The Akershus Sleep Apnea Project (ASAP)

The Berlin Questionnaire (BQ) is a widely used screening tool for obstructive sleep apnea (OSA), but its performance in the general population setting is unknown. The prevalence of OSA in middle-aged adults is not known in Norway. Accordingly, the aims of the current study were to evaluate the utility of the BQ for OSA screening in the general population and to estimate the prevalence of OSA in Norway. The study population consisted of 29,258 subjects (aged 30-65 years, 50% female) who received the BQ by mail. Of these, 16,302 (55.7%) responded. Five-hundred and eighteen subjects were included in the clinical sample and underwent in-hospital polysomnography. Screening properties and prevalence were estimated by a statistical model that adjusted for bias in the sampling procedure. Among the 16,302 respondents, 24.3% (95% confidence interval (CI)=23.6-25.0%) were classified by the BQ to be at high-risk of having OSA. Defining OSA as an apnea-hypopnea index (AHI) ≥5, the positive predictive value of the BQ was estimated to be 61.3%, the negative predictive value 66.2%, the sensitivity 37.2% and the specificity 84.0%. Estimated prevalences of OSA were 16% for AHI≥5 and 8% for AHI≥15. In conclusion, the BQ classified one out of four middle-aged Norwegians to be at high-risk of having OSA, but the screening properties of the BQ were suboptimal. The estimated prevalence of OSA was comparable to previous estimates from general populations in the USA, Australia and Europe.

Diagnostic accuracy of the Berlin Questionnaire in detecting sleep-disordered breathing in patients with a recent myocardial infarction

BACKGROUND

The Berlin Questionnaire (BQ) has been used to identify patients at high risk for sleep-disordered breathing (SDB) in a variety of populations. However, there are no data regarding the validity of the BQ in detecting the presence of SDB in patients after myocardial infarction (MI). The aim of this study was to determine the performance of the BQ in patients after MI.

METHODS

We conducted a cross-sectional study of 99 patients who had an MI 1 to 3 months previously. The BQ was administered, scored using the published methods, and followed by completed overnight polysomnography as the "gold standard." SDB was defined as an apnea-hypopnea index of ≥ 5 events/h. The sensitivity, specificity, and positive and negative predictive values of the BQ were calculated.

RESULTS

Of the 99 patients, the BQ identified 64 (65%) as being at high-risk for having SDB. Overnight polysomnography showed that 73 (73%) had SDB. The BQ sensitivity and specificity was 0.68 and 0.34, respectively, with a positive predictive value of 0.68 and a negative predictive value of 0.50. Positive and negative likelihood ratios were 1.27 and 0.68, respectively, and the BQ overall diagnostic accuracy was 63%. Using different apnea-hypopnea index cutoff values did not meaningfully alter these results.

CONCLUSION

The BQ performed with modest sensitivity, but the specificity was poor, suggesting that the BQ is not ideal in identifying SDB in patients with a recent MI.

Effect of weight gain on cardiac autonomic control during wakefulness and sleep

Obesity has been associated with increased cardiac sympathetic activation during wakefulness, but the effect on sleep-related sympathetic modulation is not known. The aim of this study was to investigate the effect of fat gain on cardiac autonomic control during wakefulness and sleep in humans. We performed a randomized, controlled study to assess the effects of fat gain on heart rate variability. We recruited 36 healthy volunteers, who were randomized to either a standardized diet to gain ≈4 kg over 8 weeks followed by an 8-week weight loss period (n=20) or to serve as a weight-maintainer control (n=16). An overnight polysomnogram with power spectral analysis of heart rate variability was performed at baseline, after weight gain, and after weight loss to determine the ratio of low-frequency to high-frequency power and to examine the relationship between changes in heart rate variability and changes in insulin, leptin, and adiponectin levels. Mean weight gain was 3.9 kg in the fat gain group versus 0.1 kg in the maintainer group. Low frequency/high frequency increased both during wakefulness and sleep after fat gain and returned to baseline after fat loss in the fat gain group and did not change in the control group. Insulin, leptin, and adiponectin also increased after fat gain and fell after fat loss, but no clear pattern of changes was seen that correlated consistently with changes in heart rate variability. Short-term fat gain in healthy subjects is associated with increased cardiac sympathetic activation during wakefulness and sleep, but the mechanisms remain unclear.

Combined effect of cardiorespiratory fitness and adiposity on mortality in patients with coronary artery disease

BACKGROUND

High cardiorespiratory fitness and body mass index (BMI) are associated with decreased mortality in patients with coronary artery disease. Our objective was to determine the joint impact of fitness and adiposity measures on all-cause mortality in this subgroup.

METHODS

Coronary artery disease patients (n = 855) enrolled in the Mayo Clinic cardiac rehabilitation program from 1993 to 2007 were included. Fitness levels were determined by cardiopulmonary exercise testing. Patients were divided into low and high fitness by sex-specific median values of peak oxygen consumption and total treadmill time. Adiposity was measured through BMI and waist-to-hip ratio (WHR).

RESULTS

There were 159 deaths during 9.7 ± 3.6 years of mean follow-up. After adjusting for potential confounding factors, low fitness, shorter treadmill time, low BMI, and high WHR were significantly associated with increased mortality. Using low WHR-high fitness group as reference, significantly increased mortality was noted in low WHR-low fitness (hazard ratio 4.2, 95% CI, 1.8-9.8), centrally obese-high fitness (2.3, 1.0-5.4), and centrally obese-low fitness (6.1, 2.7-13.6) groups. Overweight-high fitness (2.2, 0.63-7.4), obese-high fitness (3.2, 0.88-11.4), and obese-low fitness (3.3, 0.96-11.4) subjects did not have a significantly different mortality as compared with the reference group of normal weight-high fitness subjects, whereas normal weight-low fitness (9.6, 2.9-31.8) and overweight-low fitness (6.8, 2.1-22.2) groups had significantly increased mortality.

CONCLUSIONS

Low fitness and central obesity were independently and cumulatively associated with increased mortality in coronary artery disease patients attending cardiac rehabilitation. The association of BMI with mortality is complex and altered by fitness levels.