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(Chest. 2001;120:390-396.)
© 2001 American College of Chest Physicians

Abdominal Muscle Activity in Sleep Apnea During Continuous Positive Airway Pressure Titration*

Frédéric Lofaso, MD, PhD; Marie Pia d’Ortho, MD, PhD; Redouane Fodil, PhD; Christophe Delclaux, MD, PhD; Alain Harf, MD, PhD and Anne Marie Lorino, PhD

* From the Service de Physiologie, Explorations Fonctionnelles, Institut National de la Santé et de la Recherche Médicale, Créteil, France.

Correspondence to: Frédéric Lofaso, MD, PhD, Service de Physiologie, Explorations Fonctionnelles, Hôpital Raymond Poincaré, 92380 Garches, France; e-mail: f.lofaso{at}rpc.ap-hop-paris.fr

Study objectives: The aim of this study was to investigate whether presence of expiratory abdominal muscle activity (EAMA) in obstructive sleep apnea syndrome (OSAS) patients during nasal continuous positive airway pressure (nCPAP) is due to either nCPAP overprescription or nCPAP underprescription.

Design: Airflow, esophageal pressure (Pes), and gastric pressure (Pga) were routinely measured during polysomnography aimed at determining the optimal nCPAP level, and the magnitude of EAMA was evaluated in relation to the nCPAP level and to the conventional indexes of upper-airway obstruction used during nCPAP titration.

Patients: The study was performed 12 patients with OSAS.

Results: Six patients displayed sustained EAMA, ie, EAMA lasting > 3 min, and characterized by a decrease in abdominal diameter and a paradoxical rise in Pga during expiration. In all six patients, EAMA decreased gradually as nCPAP neared optimal levels, and then disappeared when the optimal nCPAP level was achieved. The decrease in EAMA as nCPAP increased was associated with an increase in minute ventilation, decreases in both inspiratory and expiratory resistance, a decrease in Pes swing, and the normalization of the inspiratory flow contour.

Conclusions: We conclude that the EAMA observed in some OSAS patients might be an indirect marker of upper-airway obstruction, and that the presence of EAMA during nCPAP titration might indicate a suboptimal nCPAP level rather than a deleterious effect of nCPAP.

Key Words: expiratory resistance • nCPAP • OSAS




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