Sleep Breath 2002; 06(1): 011-018
DOI: 10.1055/s-2002-23151

Copyright © 2002 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel.: +1(212) 584-4662

Hypercapnia in Overlap Syndrome: Possible Determinant Factors

Onofrio Resta1 , Maria Pia Foschino Barbaro2 , Caterina Brindicci1 , Maria Cristina Nocerino1 , Gennaro Caratozzolo1 , Monica Carbonara3
  • 1Centre of Sleep Breathing Disorders, Department of Clinical Methodology and Medical Surgery Technology, University of Bari, Bari, Italy
  • 2Department of Respiratory Disease, University of Foggia, Foggia, Italy
  • 3Public and Internal Medicine Department, University of Bari, Bari, Italy
Further Information

Publication History

Publication Date:
26 March 2002 (online)


We retrospectively evaluated data from 213 consecutive patients; 152 were affected by obstructive sleep apnea (OSA), 29 had OSA associated with chronic obstructive pulmonary disease (COPD), also known as overlap syndrome, and 32 had COPD. Patients with obesity-hypoventilation syndrome were not included. The aims of the study were to evaluate the anthropometric, pulmonary, and polysomnographic characteristics of patients affected by overlap syndrome compared to ``simple'' OSA and to COPD subjects and to analyze the determinants of hypercapnia in overlap syndrome. In the comparison between overlap and OSA patients, the overlap group had a significantly higher PaCO2 (44.59 vs. 39.22 mm Hg; p < 0.01), in the presence of a similar AHI (40.46 vs. 41.59/h). Comparing overlap to COPD patients, overlap showed a significantly higher PaCO2 value (44.59 vs. 39.63 mm Hg; p < 0.005) and had significantly less severe obstructive impairment (FEV 162.93 vs. 47.31%; FEV1/FVC ratio 66.71 vs. 59.25%; p < 0.005). Anthropometric, pulmonary function, and polysomnographic data did not differ between normo- and hypercapnic overlap patients. The best model (stepwise multiple regression analysis) for predicting PaCO2 in overlap patients showed r2 value 0.65: PaO2 contributed to 38%, FEV1 to 15%, and weight to 12%. In conclusion, the occurrence of hypercapnia in overlap patients is only partially explained by the combination of overweight and reduced respiratory function, supporting the hypothesis of a multifactorial genesis.


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