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.
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
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