Obesity hypoventilation syndrome in Japan and independent determinants of arterial carbon dioxide levels.

Abstract

[Background and objective]Obesity hypoventilation syndrome (OHS) prevalence was previously estimated at 9% in patients with obstructive sleep apnoea (OSA) in Japan. However, the definition of OSA in that study was based on an apnoea-hypopnoea index (AHI) of ≥ 20/h rather than ≥ 5/h. Therefore, the prevalence of OHS in OSA was not measured in the same way as for Western countries. Our study objectives were to investigate the characteristics of Japanese patients with OHS. [Methods]Nine hundred eighty-one consecutive patients investigated for suspected OSA were enrolled. At least 90% of them were from urban areas, including 162 with obese OSA (body mass index (BMI) ≥ 30 kg/m2 and AHI ≥ 5/h). [Results]The prevalence of OHS (BMI 36.7 ± 4.9 kg/m2) in OSA and that in obese OSA were 2.3% and 12.3%, respectively. Multiple regression analysis revealed that independent of age and BMI, arterial oxygen pressure (contribution rate (R2) = 7.7%), 4% oxygen desaturation index (R2 = 8.9%), carbon monoxide diffusing capacity/alveolar volume (R2 = 8.3%), haemoglobin concentration (R2 = 4.9%) and waist circumference (R2 = 4.9%) were independently associated with arterial carbon dioxide pressure. After 12.3 ± 4.6 months of CPAP treatment, more than 60% of OHS patients no longer had hypercapnia. [Conclusions]The prevalence of OHS in OSA in Japan was 2.3%. The mean BMI of patients with OHS in Japan was lower than that in Western countries (36.7 kg/m2 vs 44.0 kg/m2).