A community study of the risk for obstructive sleep apnea and respiratory inflammation in an adult Chinese population

Association between preserved ratio impaired spirometry and sleep apnea in a Chinese community

OBJECTIVE

This study investigated the association between obstructive sleep apnea (OSA) and preserved ratio impaired spirometry (PRISm) in a community population.

METHODS

Baseline data from a prospective cohort study, the Predictive Value of Combining Inflammatory Biomarkers and Rapid Decline of FEV1 for COPD (PIFCOPD), were used for cross-sectional analysis. Participants aged 40-75 years were recruited from the community and their demographic information and medical history were collected. The STOP-Bang questionnaire (SBQ) was used to assess the risk of OSA. Pulmonary function tests were performed using a portable spirometer (COPD-6) and forced expiratory volume in 1 s (FEV1) and 6 s (FEV6) were measured. Routine blood, biochemical, high-sensitivity C-reactive protein (hs-CRP), and interleukin-6 tests were also performed. The pH of the exhaled breath condensate was determined.

RESULTS

A total of 1183 participants were enrolled, of which 221 with PRISm and 962 with normal lung function. The neck circumference, waist-to-hip ratio, hs-CRP concentration, proportion of males, cigarette exposure, number of current smoker, high risk of OSA, and prevalence of nasal and ocular allergy symptoms were significantly higher in the PRISm group than in the non-PRISm group (p < .05). Logistic regression showed that the risk of OSA (odds ratio, 1.883; 95% confidence interval, 1.245-2.848), waist-to-hip ratio, current smoking, and prevalence of nasal allergy symptoms were independently associated with PRISm after correcting for age and sex.

CONCLUSION

These findings showed that OSA prevalence is independently associated with PRISm prevalence. Further studies should confirm the relationship between systemic inflammation in OSA, localized inflammation of the airways, and impaired lung function.

Anorexigenic Effects of Intermittent Hypoxia on the Gut-Brain Axis in Sleep Apnea Syndrome

Sleep apnea syndrome (SAS) is a breathing disorder characterized by recurrent episodes of upper-airway collapse, resulting in intermittent hypoxia (IH) during sleep. Experimental studies with animals and cellular models have indicated that IH leads to attenuation of glucose-induced insulin secretion from pancreatic β cells and to enhancement of insulin resistance in peripheral tissues and cells, such as the liver (hepatocytes), adipose tissue (adipocytes), and skeletal muscles (myocytes), both of which could lead to obesity. Although obesity is widely recognized as a major factor in SAS, it is controversial whether the development of SAS could contribute directly to obesity, and the effect of IH on the expression of appetite regulatory genes remains elusive. Appetite is regulated appropriately by both the hypothalamus and the gut as a gut-brain axis driven by differential neural and hormonal signals. In this review, we summarized the recent epidemiological findings on the relationship between SAS and feeding behavior and focused on the anorexigenic effects of IH on the gut-brain axis by the IH-induced up-regulation of proopiomelanocortin and cocaine- and amphetamine-regulated transcript in neuronal cells and the IH-induced up-regulation of peptide YY, glucagon-like peptide-1 and neurotensin in enteroendocrine cells and their molecular mechanisms.

Circulating C-reactive protein levels in patients with suspected obstructive sleep apnea

STUDY OBJECTIVES

To assess determinants of CRP in a cohort of patients referred for investigation of OSA and to determine whether overlap of OSA and COPD (overlap syndrome, OVS) is associated with higher levels of CRP.

METHODS

This was a cross-sectional study that included 2352 patients seen at the West Australian Sleep Disorders Research Institute between 2006 and 2010. All patients had circulating CRP levels, and spirometry performed. OSA was defined apnea-hypopnea index (AHI) ≥ 5 events per hour and COPD defined as FEV1/FVC ratio <0.70 and age > 40 years. Univariate and multivariate regression analysis were used to identify CRP determinants.

RESULTS

Mean age was 51 years (60% male), median (AHI) was 27 events/h, median 3% oxygen desaturation index (ODI3%) was 24 events/h, mean FEV₁ was 88% predicted, and median CRP was 3.0 mg/L. In multivariate analyses: age, body mass index, female sex, neck circumference, AHI, and desaturation markers (nadir and mean oxygen saturation) were independently associated with higher CRP. Spirometric variables were not predictors. There was no significant difference in CRP among OSA patients with or without co-existing COPD.

CONCLUSIONS

Markers of OSA severity (AHI and oxygenation), age, BMI, neck circumference and female sex were independent predictors of circulating CRP levels. OSA overlapping with COPD was not associated with increased CRP compared to either condition alone, suggesting other mechanisms for the increased CVD risk in OVS. Identification of factors that predict CRP will help identify patients at higher risk of CVD and aid risk stratification.