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Daytime Hypercapnia in Obstructive Sleep Apnea Syndrome^*

^* From the Department of Respirology, Graduate School of Medicine, Chiba University, Chiba, Japan.

Correspondence to: Koichiro Tatsumi, MD, Department of Respirology, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuou-ku, Chiba 260-8670, Japan; e-mail: tatsumi{at}faculty.chiba-u.jp

Abstract

Background: The pathogenesis of daytime hypercapnia (PaCO₂ 45 mm Hg) may be directly linked to the existence of obstructive sleep apnea syndrome (OSAS) per se, although only some patients with OSAS exhibit daytime hypercapnia.

Objective: To investigate the prevalence of daytime hypercapnia in patients with OSAS; the association of daytime hypercapnia and obesity, obstructive airflow limitation, restrictive lung impairment, and severity of sleep apnea; and the response to continuous positive airway pressure (CPAP) therapy in a subset of subjects.

Methods: The study involved 1,227 patients with OSAS who visited a sleep clinic and were examined using polysomnography. As for the response to CPAP therapy, the patients were considered good responders if their daytime PaCO₂ decreased 5 mm Hg and poor responders if it decreased < 5 mm Hg.

Results: Fourteen percent (168 of 1,227 patients) exhibited daytime hypercapnia. These patients had significantly higher body mass index (BMI) and apnea-hypopnea index (AHI) values compared with normocapnic patients, while percentage of predicted vital capacity (%VC) and FEV₁/FVC ratio did not differ between the two groups. Logistic regression analysis showed that only AHI was a predictor of daytime hypercapnia (p < 0.0001), while BMI (p = 0.051) and %VC (p = 0.062) were borderline predictors of daytime hypercapnia. Daytime hypercapnia was corrected in some patients (51%, 19 of 37 patients) with severe OSAS after 3 months of CPAP therapy.

Conclusion: The pathogenesis of daytime hypercapnia may be directly linked to sleep apnea in a subgroup of patients with OSAS.

Key Words: continuous positive airway pressure • hypercapnia • hypoventilation • obesity • sleep apnea

Related Editorial

Hypercapnic Obstructive Sleep Apnea: An Underappreciated Marker of Severity

Clifford Zwillich and Carolyn H. Welsh
Chest 2007 132: 1729-1730. [Full Text] [PDF]

This article has been cited by other articles:

				A. BaHamman, K. Tatsumi, and N. Kawata Positive Airway Pressure Therapy and Daytime Hypercapnia in Patients With Sleep-Disordered Breathing Chest, July 1, 2008; 134(1): 218 - 219. [Full Text] [PDF]

				C. Zwillich and C. H. Welsh Hypercapnic Obstructive Sleep Apnea: An Underappreciated Marker of Severity Chest, December 1, 2007; 132(6): 1729 - 1730. [Full Text] [PDF]