The objectives of this study were to 1) compare the strength of associations between sleep duration and BMI in middle childhood, early and late adolescence; 2) determine whether sleep duration in middle childhood predicts BMI in early or late adolescence; 3) examine the consistency of these associations by sex.
Subjects included 313 children/adolescents aged 8–19 participating in a longitudinal cohort study on sleep and health. Participants were assessed at three time points approximately 4 years apart: ages 8–11, 12–15 and 16–19. BMI z-score (BMIz) was calculated using age and sex normative data from the Centers for Disease Control. Sleep duration was reported by the parent (ages 8–15) or the adolescent (ages 16–19).
Half of the participants were male and 79% were Caucasian. Sleep duration had a negative linear association with BMIz for boys but not girls, and the magnitude of this association decreased with age. Sleep duration at age 8–11 predicted BMIz in early and late adolescence for boys but not girls, and associations were largely attenuated after adjusting for BMIz at age 8–11. The strongest predictor of adolescent BMIz was BMIz at age 8–11 for both boys and girls.
We conclude that the association between sleep duration and BMIz varies by sex and age, with stronger associations in boys and in middle childhood compared to adolescence.
Adolescents; BMI; Children; Obesity; Sleep
Pharyngeal muscle dilators are important in obstructive sleep apnea pathogenesis because the failure of protective reflexes involving these muscles yields pharyngeal collapse. Conflicting results exist in the literature regarding the responsiveness of these muscles during stable non-rapid eye movement sleep. However, variations in posture in previous studies may have influenced these findings. We hypothesized that tongue protruder muscles are maximally responsive to negative pressure pulses during supine sleep, when posterior tongue displacement yields pharyngeal occlusion.
We studied all subjects in the supine and lateral postures during wakefulness and stable non-rapid eye movement sleep by measuring genioglossus and tensor palatini electromyograms during basal breathing and following negative pressure pulses.
Upper-airway physiology laboratory of Sleep Medicine Division, Brigham and Women’s Hospital.
17 normal subjects.
Measurements and Results
We observed an increase in genioglossal responsiveness to negative pressure pulses in sleep as compared to wakefulness in supine subjects (3.9 percentage of maximum [%max] ± 1.1 vs 4.4 %max ± 1.0) but a decrease in the lateral decubitus position (4.1 %max ± 1.0 vs 1.5 %max ± 0.4), the interaction effect being significant. Despite this augmented reflex, collapsibility, as measured during negative pressure pulses, increased more while subjects were in the supine position as compared with the lateral decubitus position. While the interaction between wake-sleep state and position was also significant for the tensor palatini, the effect was weaker than for genioglossus, although, for tensor palatini, baseline activity was markedly reduced during non-rapid eye movement sleep as compared with wakefulness.
We conclude that body posture does have an important impact on genioglossal responsiveness to negative pressure pulses during non-rapid eye movement sleep. We speculate that this mechanism works to prevent pharyngeal occlusion when the upper airway is most vulnerable to collapse eg, during supine sleep.
pharynx; posture; sleep; breathing; genioglossus; lung; tensor palatini; respiration; upper airway; vestibular
Sleeping more than 7 to 8 hours per day has been consistently associated with increased mortality. Whether this association is causal and what pathways explain this association are unknown. We sought to identify factors that could potentially explain the association between long sleep and mortality.
Cross-sectional epidemiologic survey.
Middle-aged women (n = 60,028) participating in the Nurses Health Study II who reported a habitual sleep duration of 7 hours or more.
Multiple sclerosis (odds ratio [OR] = 3.7, 95% confidence interval [3.0–4.5]), antidepressant use (OR = 3.1, [2.9–3.3]), benzodiazepine use (OR = 3.0 [2.6–3.3]), and systemic lupus erythematosus (OR = 2.9, [2.3–3.6]) were the factors most strongly associated with prolonged sleep. Combining these data with prevalence information and a range of plausible associations with mortality, the confounding rate ratio was estimated. This parameter is the ratio of the unadjusted long sleep–mortality rate ratio to the rate ratio adjusted for the factor and measures the extent that the factor can alter the long sleep—mortality association, either through confounding or as a causal intermediate. Based on this parameter, psychiatric and socioeconomic factors have the greatest potential to influence the long sleep–mortality relationship. Assuming each factor doubles mortality risk, the confounding rate ratios for depression, antidepressant use, and unemployment were 1.10, 1.18, and 1.12. Lesser influential factors were benzodiazepine use, poverty, low societal status, sedentary lifestyle, and obesity.
Depression and low socioeconomic status are strong candidates for producing the statistical association between long sleep and mortality, either as confounders or as causal intermediates. Future causal research on the effects of long sleep should include a detailed assessment of psychiatric disease and socioeconomic status.
Sleep duration; long sleep; depression
Physiologic studies suggest that sleep restriction has metabolic effects that predispose to weight gain. The authors investigated the association between self-reported usual sleep duration and subsequent weight gain in the Nurses’ Health Study. The 68,183 women who reported habitual sleep duration in 1986 were followed for 16 years. In analyses adjusted for age and body mass index, women sleeping 5 hours or less gained 1.14 kg (95% confidence interval (CI): 0.49, 1.79) more than did those sleeping 7 hours over 16 years, and women sleeping 6 hours gained 0.71 kg (95% CI: 0.41, 1.00) more. The relative risks of a 15-kg weight gain were 1.32 (95% CI: 1.19, 1.47) and 1.12 (95% CI: 1.06, 1.19) for those sleeping 5 and 6 hours, respectively. The relative risks for incident obesity (body mass index: >30 kg/m2) were 1.15 (95% CI: 1.04, 1.26) and 1.06 (95% CI: 1.01, 1.11). These associations remained significant after inclusion of important covariates and were not affected by adjustment for physical activity or dietary consumption. These data suggest that short sleep duration is associated with a modest increase in future weight gain and incident obesity. Further research is needed to understand the mechanisms by which sleep duration may affect weight.
obesity; sleep deprivation; weight gain; women
Obstructive sleep apnea (OSA) is two to three times more common in men as in women. The mechanisms leading to this difference are currently unclear but could include gender differences in respiratory stability [loop gain (LG)] or upper airway collapsibility [pharyngeal critical closing pressure (Pcrit)]. The aim of this study was to compare LG and Pcrit between men and women with OSA to determine whether the factors contributing to apnea are similar between genders. The first group of 11 men and 11 women were matched for OSA severity (mean ± SE apnea-hypopnea index = 43.8 ± 6.1 and 44.1 ± 6.6 events/h). The second group of 12 men and 12 women were matched for body mass index (BMI; 31.6 ± 1.9 and 31.3 ± 1.8 kg/m2, respectively). All measurements were made during stable supine non-rapid eye movement sleep. LG was determined using a proportional assist ventilator. Pcrit was measured by progressively dropping the continuous positive airway pressure level for three to five breaths until airway collapse. Apnea-hypopnea index-matched women had a higher BMI than men (38.0 ± 2.4 vs. 30.0 ± 1.9 kg/m2; P = 0.03), but LG and Pcrit were similar between men and women (LG: 0.37 ± 0.02 and 0.37 ± 0.02, respectively, P = 0.92; Pcrit: 0.35 ± 0.62 and –0.18 ± 0.87, respectively, P = 0.63). In the BMI-matched subgroup, women had less severe OSA during non-rapid eye movement sleep (30.9 ± 7.4 vs. 52.5 ± 8.1 events/h; P = 0.04) and lower Pcrit (–2.01 ± 0.62 vs. 1.16 ± 0.83 cmH2O; P = 0.005). However, LG was not significantly different between genders (0.38 ± 0.02 vs. 0.33 ± 0.03; P = 0.14). These results suggest that women may be protected from developing OSA by having a less collapsible upper airway for any given degree of obesity.
pharyngeal critical closing pressure; loop gain; gender
Acoustic pharyngometry represents a simple, quick, non-invasive method for measuring upper airway dimensions which are predictive of sleep apnea risk. In this study we sought to assess the genetic basis for upper airway size as obtained by pharyngometry.
Participants over age 14 y in the Cleveland Family Study underwent three acoustic pharyngometry measurements. Variance component models adjusted for age and sex were used to estimate heritability of pharyngometry-derived airway measures.
A total of 568 of 655 subjects (87%) provided quality pharyngometry curves. Although African-Americans tended to have narrower airways compared to Caucasians, heritability patterns were similar in these two groups. Minimum cross-sectional area had a heritability of 0.34 (p=0.004) in Caucasians and 0.39 (p<0.001) in African-Americans, suggesting that 30-40% of the total variance in this measure is explained by shared familial factors. Estimates were unchanged after adjustment for body mass index or neck circumference. In contrast, oropharyngeal length did not have significant heritability in either ethnic group.
The minimum cross-sectional area in the oropharynx is a highly heritable trait suggesting the presence of an underlying genetic basis. These findings demonstrate the potential utility of acoustic pharyngometry in dissecting the genetic basis of sleep apnea.
sleep apnea; upper airway; oropharynx; pharyngometry; genetic epidemiology; heritability
The recent obesity epidemic has been accompanied by a parallel growth in chronic sleep deprivation. Physiologic studies suggest sleep deprivation may influence weight through effects on appetite, physical activity, and/or thermoregulation. This work reviews the literature regarding short sleep duration as an independent risk factor for obesity and weight gain.
A literature search was conducted for all articles published between 1966 and January 2007 using the search “sleep” AND (“duration” OR “hour” OR “hours”) AND (“obesity” OR “weight) in the MEDLINE database. Additional references were identified by reviewing bibliographies and contacting experts in the field. Studies reporting the association between sleep duration and at least one measure of weight were included.
Thirty-six publications (31 cross-sectional, 5 prospective, and 0 experimental) were identified. Findings in both cross-sectional and cohort studies of children suggested short sleep duration is strongly and consistently associated with concurrent and future obesity. Results from adult cross-sectional analyses were more mixed with 17 of 23 studies supporting an independent association between short sleep duration and increased weight. In contrast, all 3 longitudinal studies in adults found a positive association between short sleep duration and future weight. This relationship appeared to wane with age.
Short sleep duration appears independently associated with weight gain, particularly in younger age groups. However, major study design limitations preclude definitive conclusions. Further research with objective measures of sleep duration, repeated assessments of both sleep and weight and experimental study designs that manipulate sleep are needed to better define the causal relationship of sleep deprivation on obesity.
sleep; sleep duration; sleep deprivation; risk factor; weight
Obesity and obstructive sleep apnea each have a substantial genetic basis and commonly co-exist in individuals. The degree to which the genetic underpinnings for these disorders overlap has not been previously quantified.
A total of 1802 individuals from 310 families in the Cleveland Family Study underwent home sleep studies as well as standardized assessment of body mass index and circumferences at the waist, hip, and neck. In 713 participants with laboratory sleep studies, fasting blood samples were assayed for leptin, adiponectin, and resistin. Variance component models were used to estimate heritability and genetic correlations.
The heritability of the apnea hypopnea index was 0.37 ± 0.04 and 0.33 ± 0.07 for home and laboratory sleep studies respectively. The genetic correlations between apnea hypopnea index and anthropomorphic adiposity measures ranged from 0.57 to 0.61 suggesting obesity can explain nearly 40% of the genetic variance in sleep apnea. The magnitude of the genetic correlations between apnea severity and adipokine levels was substantially less than those with anthropomorphic measures, ranging from 0.11–0.46. After adjusting for body mass index, no significant genetic correlation with apnea severity was observed for any of the other adiposity measures.
Substantial but not complete overlap in genetic bases exist between sleep apnea and anthropomorphic indices of adiposity, and this overlap accounts for more than one third of the genetic variance in apnea severity. These findings suggest that genetic polymorphisms exist that importantly influence sleep apnea susceptibility through both obesity-dependent and obesity-independent pathways.
obesity; sleep apnea; genetics; heritability; genetic correlation
Noninvasive positive pressure ventilation (NPPV) can improve outcomes of critically ill patients. Early and simple predictors of NPPV outcome could improve clinical management of patients with respiratory failure.
Materials and Methods
A prospective observational study was conducted in a medical intensive care unit (ICU) of a tertiary medical center. Patients requiring NPPV were included and followed. Clinical data including respiratory mechanics at the time of NPPV initiation, and clinical outcomes were recorded. Data were analyzed to identify variables that distinguished NPPV success or failure.
A total of 133 patients were included in the study. NPPV success rate was 41%. Patients diagnosed with malignancy had only 29% NPPV success rate. Among patients without malignancy, higher oxygen saturation, oxygen saturation/FiO2 (SF) ratios, and SF/minute ventilation (MV) ratios were associated with NPPV success. Receiver operating curve analyses identify SF < 98.5 to be a specific (89% specificity, P=0.013) predictor of NPPV failure. Furthermore, for patients requiring at least 24hr of NPPV support, tidal volume (TV)/predicted body weight (PBW) ratio inversely correlated with respiratory improvement.
For patients without malignancy, SF ratios at the time of NPPV initiation discriminated NPPV success and failure, and could be used to help guide the management of critically ill patients who require ventilatory support.
Mechanical ventilation; Respiratory Insufficiency; Non-Invasive Positive-Pressure Ventilation; Clinical Markers; Hypoxemia; Critical Care
Because obstructive sleep apnea (OSA) is associated with increased levels of inflammatory cytokines, we examined the relationship between OSA and polymorphisms for interleukin-6 (IL-6).
6 single nucleotide polymorphisms (SNPs) within IL-6 were genotyped in 259 African-Americans from the Cleveland Family Study with replication conducted in the Cardiovascular Health Study (n=124). OSA was dichotomized into apnea hypopnea index (AHI)>15 or on treatment vs. absent: AHI<5. Logistic regression was conducted, adjusting for age and sex in models with and without body mass index (BMI).
SNP IL6-6021 was associated with a decreased risk of OSA after adjusting for BMI (Odds Ratio for T allele 0.24; 95%CI [0.09–0.67]; p=0.006; q=0.07) under an additive model. This same allele was associated with increased BMI. The results from the replication sample were consistent in direction though not statistically significant (p=0.23). The SNPs were studied in European-Americans, although the minor allele frequency in IL6-6021 was too low (4%) for meaningful comparisons.
A synonymous SNP within the IL-6 coding region was protective of OSA in African-Americans; with qualitatively similar findings observed in another cohort. This suggests that variants in IL-6 may influence the risk of OSA in a pathway that is not explained by obesity.
Rationale: Obstructive sleep apnea (OSA) is hypothesized to be influenced by genes within pathways involved with obesity, craniofacial development, inflammation, and ventilatory control.
Objectives: We conducted the first candidate gene study of OSA using family data from European Americans and African Americans, selecting biologically plausible genes from within these pathways.
Methods: A total of 1,080 single nucleotide polymorphisms (SNPs) were genotyped in 729 African Americans and 505 SNPs were genotyped in 694 European Americans. Coding for SNPs additively, association testing on the apnea-hypopnea index (AHI) as a continuous trait, and OSA as a dichotomous trait (AHI ≥15) was conducted using methods that account for familial correlations in models adjusted for age, age-squared, and sex, with and without body mass index.
Measurements and Main Results: In European Americans, variants within C-reactive protein (CRP) and glial cell line–derived neurotrophic factor (GDNF) were associated with AHI (CRP: β = 4.6; SE = 1.1; P = 0.0000402) (GDNF: β = 4.3; SE = 1; P = 0.0000201) and with the dichotomous OSA trait (CRP: odds ratio = 2.4; 95% confidence interval, 1.5–3.9; P = 0.000170) (GDNF: odds ratio = 2; 95% confidence interval, 1.4–2.89; P = 0.0000433). In African Americans, rs9526240 within serotonin receptor 2a (HTR2A: odds ratio = 2.1; 95% confidence interval, 1.5–2.9; P = 0.00005233) was associated with OSA.
Conclusions: This candidate gene analysis identified the potential role of genes operating through intermediate disease pathways to influence sleep apnea phenotypes, providing a framework for focusing future replication studies.
sleep apnea; body mass index; genetics; candidate gene study
Rationale: Individuals with sleep-disordered breathing (SDB) are at increased cardiovascular risk, possibly due to SDB-related stresses contributing to atherosclerosis.
Objectives: We postulate that pathways associated with a prothrombotic potential are up-regulated in SDB.
Methods: Morning and evening plasminogen activator inhibitor-1 (PAI-1), morning fibrinogen, and morning D-dimer were measured in 537 Cleveland Family Study adults. Piecewise multivariable linear mixed models estimated relative mean change or mean change in the biomarker per 5-unit increase in apnea-hypopnea index (AHI) in two groups: AHI less than 15 and AHI greater than or equal to 15, and hypoxia defined as percentage of sleep time with SaO2 less than 90% (< 2%, ≥ 2%).
Measurements and Main Results: Nonlinear associations were demonstrated: morning and evening PAI-1 increased by 12% (95% confidence interval [CI], 5–20%; P < 0.001) and 11% (95% CI, 2–20%; P = 0.01), respectively per 5-unit AHI increase until an AHI of 15, when no further increase in PAI-1 was demonstrated. The association between AHI and morning PAI-1 remained significant after adjusting for evening PAI-1 level (10%; 95% CI, 3–17%; P < 0.01). Morning fibrinogen increased on average by 8.4 mg/dl (95% CI, 3.12–13.65; P = 0.002) per five-unit AHI increase until an AHI of 15. There was no association between AHI and morning D-dimer. Hypoxia severity was not associated with thrombotic marker levels.
Conclusions: PAI-1 and fibrinogen levels increase monotonically with AHI at degrees of SDB considered mildly to moderately abnormal, suggesting that even mild SDB levels may increase prothrombotic processes. There may be a plateau in this effect, occurring at levels considered to reflect only moderate SDB severity. These relationships with mild-to-moderate SDB were not observed with D-dimer.
sleep apnea; thrombosis; cardiovascular disease
Increased variability in ventilation may contribute to the pathogenesis of obstructive sleep apnea (OSA) by promoting ventilatory instability, fluctuations of neuromuscular output to the upper airway, and pharyngeal collapsibility. We assessed the association of a measure of ventilatory variability measured at the wake-sleep transition with OSA and associated covariates.
485 participants in the Cleveland Family Study underwent overnight polysomnography with independent derivation of the Ventilatory Variability Index and the Apnea Hypopnea Index. The Ventilatory Variability Index was calculated from the variability in the power spectrum of the abdominal inductance signal over a 2-minute period beginning at sleep onset.
The Ventilatory Variability Index was strongly correlated with the Apnea Hypopnea Index (r=0.43, p<0.001). After adjusting for age, body mass index, sex, and race, the Ventilatory Variability Index remained significantly associated with Apnea Hypopnea Index (p<0.001). The adjusted odds ratio for obstructive sleep apnea (Apnea Hypopnea Index ≥ 15) with each half standard deviation increase in Ventilatory Variability Index was 1.41 [1.25–1.59]. In a subgroup analysis of obese snorers, to limit analyses to those with a presumed anatomic predisposition for apnea, Ventilatory Variability Index remained associated with an elevated Apnea Hypopnea Index.
Increased ventilatory variability may be a useful phenotype in characterizing obstructive sleep apnea.
Sleep apnea syndromes; sleep disordered breathing; polysomnography; apnea
Reduced sleep has been reported to predict obesity in children and young adults. However, studies based on self-report have been unable to identify an association in older populations. In this study, the cross-sectional associations between sleep duration measured objectively and measures of weight and body composition were assessed in two cohorts of older adults.
Wrist actigraphy was performed for a mean (SD) of 5.2 (0.9) nights in 3055 men (age: 67–96 years) participating in the Osteoporotic Fractures in Men Study (MrOS) and 4.1 (0.8) nights in 3052 women (age: 70–99 years) participating in the Study of Osteoporotic Fractures (SOF). A subgroup of 2862 men and 455 women also underwent polysomnography to measure sleep apnea severity.
Compared to those sleeping an average of 7–8 hours per night, and after adjusting for multiple risk factors and medical conditions, a sleep duration of less than 5 hours was associated with a body mass index (BMI) that was on average 2.5 kg/m2 (95% CI: 2.0–2.9) greater in men and 1.8 kg/m2 (95%CI: 1.1–2.4) greater in women. The odds of obesity (BMI ≥ 30 kg/m2) was 3.7-fold greater (95% CI: 2.7–5.0) in men and 2.3-fold greater in women (95% CI: 1.6–3.1) who slept less than 5 hours. Short sleep was also associated with central body fat distribution and increased percent body fat. These associations persisted after adjusting for sleep apnea, insomnia, and daytime sleepiness.
In older men and women, actigraphy-ascertained reduced sleep durations are strongly associated with greater adiposity.
sleep duration; sleep deprivation; obesity; central obesity; geriatrics; insomnia; sleepiness
Stature (adult body height), and body mass index (BMI) have a strong genetic component explaining observed variation in human populations, however, identifying those genetic components has been extremely challenging. It seems obvious that sample size is a critical determinant for successful identification of quantitative trait loci (QTL) that underlie the genetic architecture of these polygenic traits. The inherent shared environment and known genetic relationships in family studies provide clear advantages for gene mapping over studies utilizing unrelated individuals. To these ends, we combined the genotype and phenotype data from four previously performed family-based genome-wide screens resulting in a sample of 9.371 individuals from 3.032 African-American and European-American families and performed variance-components linkage analyses for stature and BMI. To our knowledge, this study represents the single largest family-based genome-wide linkage scan published for stature and BMI to date. This large study sample allowed us to pursue population-and sex-specific analyses as well. For stature we found evidence for linkage in previously reported loci on 11q23, 12q12, 15q25 and 18q23 as well as 15q26 and 19q13 which have not been linked to stature previously. For BMI we found evidence for two loci: one on 7q35 and another on 11q22 both of which have been previously linked to BMI in multiple populations. Our results show both the benefit of 1) combining data to maximize the sample size and 2) minimizing heterogeneity by analyzing subgroups where within-group variation can be reduced and suggest that the latter may be a more successful approach in genetic mapping.
Body Height; Body Mass Index; Linkage mapping; Quantitative Trait Loci
Stature (adult body height) and body mass index (BMI) have a strong genetic component explaining observed variation in human populations; however, identifying those genetic components has been extremely challenging. It seems obvious that sample size is a critical determinant for successful identification of quantitative trait loci (QTL) that underlie the genetic architecture of these polygenic traits. The inherent shared environment and known genetic relationships in family studies provide clear advantages for gene mapping over studies utilizing unrelated individuals. To these ends, we combined the genotype and phenotype data from four previously performed family-based genome-wide screens resulting in a sample of 9.371 individuals from 3.032 African-American and European-American families and performed variance-components linkage analyses for stature and BMI. To our knowledge, this study represents the single largest family-based genome-wide linkage scan published for stature and BMI to date. This large study sample allowed us to pursue population- and sex-specific analyses as well. For stature, we found evidence for linkage in previously reported loci on 11q23, 12q12, 15q25 and 18q23, as well as 15q26 and 19q13, which have not been linked to stature previously. For BMI, we found evidence for two loci: one on 7q35 and another on 11q22, both of which have been previously linked to BMI in multiple populations. Our results show both the benefit of (1) combining data to maximize the sample size and (2) minimizing heterogeneity by analyzing subgroups where within-group variation can be reduced and suggest that the latter may be a more successful approach in genetic mapping.
body height; body mass index; linkage mapping; quantitative trait loci
Depletion of the circulating actin-binding protein, plasma gelsolin (pGSN) has been described in septic patients and animals. We hypothesized that the extent of pGSN reduction correlates with outcomes of septic patients and that circulating actin is a manifestation of sepsis.
We assayed pGSN in plasma samples from non-surgical septic patients identified from a pre-existing database which prospectively enrolled patients admitted to adult intensive care units at an academic hospital. We identified 21 non-surgical septic patients for the study. Actinemia was detected in 17 of the 21 patients, suggesting actin released into circulation from injured tissues is a manifestation of sepsis. Furthermore, we documented the depletion of pGSN in human clinical sepsis, and that the survivors had significantly higher pGSN levels than the non-survivors (163±47 mg/L vs. 89±48 mg/L, p = 0.01). pGSN levels were more strongly predictive of 28-day mortality than APACHE III scores. For every quartile reduction in pGSN, the odds of death increased 3.4-fold.
We conclude that circulating actin and pGSN deficiency are associated with early sepsis. The degree of pGSN deficiency correlates with sepsis mortality. Reversing pGSN deficiency may be an effective treatment for sepsis.
Previous studies have demonstrated that lung volume during wakefulness influences upper airway size and resistance, particularly in patients with sleep apnea. We sought to determine the influence of lung volume on the level of continuous positive airway pressure (CPAP) required to prevent flow limitation during non-REM sleep in subjects with sleep apnea. Seventeen subjects (apnea–hypopnea index, 42.6 ± 6.2 [SEM]) were studied during stable non-REM sleep in a rigid head-out shell equipped with a positive/negative pressure attachment for manipulation of extrathoracic pressure. An epiglottic pressure catheter plus a mask/pneumotachometer were used to assess flow limitation. When lung volume was increased by 1,035 ± 22 ml, the CPAP level could be decreased from 11.9 ± 0.7 to 4.8 ± 0.7 cm H2O (p < 0.001) without flow limitation. The decreased CPAP at the same negative extrathoracic pressure yielded a final lung volume increase of 421 ± 36 ml above the initial value. Conversely, when lung volume was reduced by 732 ± 74 ml (n = 8), the CPAP level had to be increased from 11.9 ± 0.7 to 17.1 ± 1.0 cm H2O (p < 0.001) to prevent flow limitation, with a final lung volume decrease of 567 ± 78 ml. These results demonstrate that relatively small changes in lung volume have an important effect on the upper airway in subjects with sleep apnea during non-REM sleep.
airflow limitation; continuous positive airway pressure; lung volume; sleep apnea; upper airway
The study of change in intermediate phenotypes over time is important in genetics. In this paper we explore a new approach to phenotype definition in the genetic analysis of longitudinal phenotypes. We utilized data from the longitudinal Framingham Heart Study Family Cohort to investigate the familial aggregation and evidence for linkage to change in systolic blood pressure (SBP) over time. We used Gibbs sampling to derive sigma-squared-A-random-effects (SSARs) for the longitudinal phenotype, and then used these as a new phenotype in subsequent genome-wide linkage analyses.
Additive genetic effects (σ2A.time) were estimated to account for ~9.2% of the variance in the rate of change of SBP with age, while additive genetic effects (σ2A) were estimated to account for ~43.9% of the variance in SBP at the mean age. The linkage results suggested that one or more major loci regulating change in SBP over time may localize to chromosomes 2, 3, 4, 6, 10, 11, 17, and 19. The results also suggested that one or more major loci regulating level of SBP may localize to chromosomes 3, 8, and 14.
Our results support a genetic component to both SBP and change in SBP with age, and are consistent with a complex, multifactorial susceptibility to the development of hypertension. The use of SSARs derived from quantitative traits as input to a conventional linkage analysis appears to be valuable in the linkage analysis of genetically complex traits. We have now demonstrated in this paper the use of SSARs in the context of longitudinal family data.
Using the longitudinal Framingham Heart Study data on blood pressure, we analyzed the reproducibility of linkage measures from serial cross-sectional surveys of a defined population by performing genome-wide model-free linkage analyses to systolic blood pressure (SBP) and history of hypertension (HTN) measured at five separate time points.
The heritability of SBP was relatively stable over time, ranging from 11.6 to 23.5% (coefficient of variation = 25.7%). However, the variability in linkage results was much greater. The average correlation in LOD scores at any pair of time points was 0.46 for HTN (NPL All LOD) and 0.17 for SBP (Variance Components LOD). No evidence of reproducible linkage results was found, with a mean κ of 0.02 for linkage to HTN and -0.03 for SBP linkage. At loci with potential evidence for linkage (LOD > 1.0 at one or more time points), the correlation was even lower. The coefficient of variation at loci with potential evidence of linkage was 126% for HTN and 135% for SBP. None of 15 chromosomal regions for HTN and only one of 28 regions for SBP with potential evidence for linkage had a LOD > 1.0 at more than two of the five time points.
These data suggest that, although heritability estimates at different time points are relatively robust, the reproducibility of linkage results in serial cross-sectional samples of a geographically defined population at successive time points is poor. This may explain in part the difficulty encountered in replicating linkage studies of complex phenotypes.
Although obstructive sleep apnea (OSA) is known to have a strong familial basis, no genetic polymorphisms influencing apnea risk have been identified in cross-cohort analyses. We utilized the National Heart, Lung, and Blood Institute (NHLBI) Candidate Gene Association Resource (CARe) to identify sleep apnea susceptibility loci. Using a panel of 46,449 polymorphisms from roughly 2,100 candidate genes on a customized Illumina iSelect chip, we tested for association with the apnea hypopnea index (AHI) as well as moderate to severe OSA (AHI≥15) in 3,551 participants of the Cleveland Family Study and two cohorts participating in the Sleep Heart Health Study.
Among 647 African-Americans, rs11126184 in the pleckstrin (PLEK) gene was associated with OSA while rs7030789 in the lysophosphatidic acid receptor 1 (LPAR1) gene was associated with AHI using a chip-wide significance threshold of p-value<2×10−6. Among 2,904 individuals of European ancestry, rs1409986 in the prostaglandin E2 receptor (PTGER3) gene was significantly associated with OSA. Consistency of effects between rs7030789 and rs1409986 in LPAR1 and PTGER3 and apnea phenotypes were observed in independent clinic-based cohorts.
Novel genetic loci for apnea phenotypes were identified through the use of customized gene chips and meta-analyses of cohort data with replication in clinic-based samples. The identified SNPs all lie in genes associated with inflammation suggesting inflammation may play a role in OSA pathogenesis.
. The National Heart, Lung, and Blood Institute’s Candidate Gene Association Resource (CARe), a planned cross-cohort analysis of genetic variation in cardiovascular, pulmonary, hematological, and sleep-related traits, comprises more than 40,000 participants representing four ethnic groups in nine community-based cohorts. The goals of CARe include the discovery of new variants associated with traits using a candidate gene approach and the discovery of new variants using the genome-wide association mapping approach specifically in African Americans.
Methods and Results
. CARe has assembled DNA samples for more than 40,000 individuals self-identified as European-American, African-American, Hispanic, or Chinese-American, with accompanying data on hundreds of phenotypes that have been standardized and deposited in the CARe Phenotype Database. All participants were genotyped for seven single-nucleotide polymorphisms (SNPs) selected based on prior association evidence. We performed association analyses relating each of these SNPs to lipid traits, stratified by gender and ethnicity and adjusted for age and age2. In at least two of the ethnic groups, SNPs near CETP, LIPC, and LPL strongly replicated for association with high-density lipoprotein cholesterol concentrations, PCSK9 with low-density lipoprotein cholesterol levels, and LPL and APOA5 with serum triglycerides. Notably, some SNPs showed varying effect sizes and significance of association in different ethnic groups.
. The CARe Pilot Study validates the operational framework for phenotype collection, SNP genotyping, and analytical pipeline of the CARe project and validates the planned candidate gene study of ~2,000 biologic candidate loci in all participants and genome-wide association study in ~8,000 African-American participants. CARe will serve as a valuable resource for the scientific community.
Genetics; lipids; diabetes; blood pressure; epidemiology