EFFECTS OF MOUTH OPENING ON UPPER AIRWAY COLLAPSIBILITY IN NORMAL SLEEPING SUBJECTS

We investigated the influence of mouth opening on upper airway (UA) co llapsibility in six healthy sleeping volunteers. UA collapsibility was measured during continuous negative airway pressure trials that consi sted of the progressive decrease in pressure in a nasal mask, with sim ultaneous recording of esophageal pressure and instantaneous flow. Mea surements were made under two experimental conditions: mouth closed (M C), and mouth open (MO). Cephalometric measurements were obtained with subjects awake in the same position for both experimental conditions. UA critical pressure (Pcrit) was derived from the relationship betwee n the breath-by-breath values of the maximal inspiratory airflow and t he corresponding mask pressure. Pcrit was significantly less negative during MO than during MC (MO, -12.7 +/- 4.8 cm H2O; MC, -16.4 +/- 6 cm H2O, mean +/- SD; p = 0.03). Mouth opening was associated with a sign ificant increase in the total respiratory resistance (MO, 3.8 +/- 1.6 cm H2O/ml/s; MC, 3.0 +/- 1.6 cm H2O/ml/s(-1), p = 0.03). Besides an in crease in the distance between the teeth and a reduction in the distan ce between the hyoid bone and the mandible, no significant changes in cephalometric parameters were found between MO and MC. We conclude tha t mouth opening increases UA collapsibility during sleep and that mout h opening may contribute to the occurrence of sleep-related breathing abnormalities.