Intramyocellular Lipids, Insulin Resistance, and Functional Performance in Patients with Severe Obstructive Sleep Apnea

Abstract

Purpose

An increasing number of studies have linked the severity of obstructive sleep apnea (OSA) with metabolic dysfunction. However, little is known about the lipid compartments (intramyocellular [IMCL] and extramyocellular [EMCL] lipids) inside the musculature in these patients. The present study was designed to investigate the IMCL and EMCL, biochemical data, and functional performance in patients with severe OSA, and to examine the correlations between intramuscular lipid contents and test variables.

Participants and Methods

Twenty patients with severe OSA (apnea-hypopnea index [AHI]: ≥30/h; body mass index [BMI]: 26.05±2.92) and 20 age- and BMI-matched controls (AHI <5/h) were enrolled. Proton magnetic resonance spectroscopy was used to measure the IMCL and EMCL of the right vastus lateralis muscle. Biochemical data, including levels of fasting plasma glucose, insulin, lipid profiles, and high-sensitivity C-reactive protein (hsCRP), were measured. Insulin resistance index (IR) was calculated using the homeostasis model assessment method. Performance tests included a cardiopulmonary exercise test and knee extension strength and endurance measurements.

Results

Patients with severe OSA had significantly (P<0.05) lower values of IMCL (14.1±5.4 AU) and EMCL (10.3±5.8 AU) compared to the control group (25.2±17.6 AU and 14.3±11.1 AU, respectively). Patients with severe OSA had significantly higher hsCRP, IR, and dyslipidemia compared with controls (all P<0.05). Furthermore, IMCL was negatively correlated with AHI, cumulative time with nocturnal pulse oximetric saturation lower than 90% (TSpO₂<90%) (ρ=−0.35, P<0.05), IR (ρ=−0.40, P<0.05), glucose (ρ=−0.33, P<0.05), and insulin (ρ=−0.36, P<0.05), and positively correlated with lowest oximetric saturation (ρ=0.33, P<0.01).

Conclusion

Skeletal muscle dysfunction and metabolic abnormalities were observed in patients with OSA that did not have obesity. IMCL was positively correlated with aerobic capacity and muscular performance, but negatively correlated with AHI and IR. Large-scale clinical trials are required to explore the complicated mechanism among OSA, intramuscular metabolism, and insulin action.

Clinical Trial Registration

ClinicalTrials.gov Identifier: NCT00813852.

Keywords:

• ¹H magnetic resonance spectroscopy
• insulin resistance
• obstructive sleep apnea
• skeletal muscle

Data Sharing Statement

The authors do not intend to share individual deidentified participant data.

Acknowledgment

The authors thank the National Science Council (Taiwan) for financial support (NSC 96-2314-B-002-022-MY3). The authors also thank Professor Yunn-Jy Chen from Division of Prosthodontics, Department of Dentistry, National Taiwan University Hospital and Graduate Institute of Clinical Dentistry, School of Dentistry, College of Medicine, National Taiwan University, for his great contribution to this research.

Disclosure

None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript. The authors report no conflicts of interest in this work.