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Mouth-opening Increases Upper-airway Collapsibility without Changing Resistance during Midazolam Sedation

¹ Nagasaki University Graduate School of Biomedical Science, Dept. of Clinical Physiology, 1-7-1 sakamoto Nagasaki-shi, 852-8588, Japan; and
² The Johns Hopkins School of Medicine, Division of Pulmonary and Critical Care Medicine and Johns Hopkins Sleep Disorders Center, Baltimore, MD, USA;

View larger version (25K): [in a new window]   Figure 1. Diagram of experimental techniques.

View larger version (112K): [in a new window]   Figure 2. A representative polysomnographic recording is illustrated, showing the change in nasal pressure (Pn) (fourth channel from top) and upper inspiratory airflow (VI) (fifth channel from top). As shown, progressively sub-atmospheric levels of nasal pressure (Pn) were applied in a stepwise manner (left to right) and kept constant at each pressure level for 5 or 6 breaths. At negative Pn values, below –3 cm H2O, inspiratory flow limitation ensued, as indicated by a flattening of the inspiratory airflow contour (see downward arrow from left), while the esophageal pressure (Pes) continued to become increasingly more negative. We obtained maximal inspiratory flow (VImax) by taking the difference between zero inspiratory flow and maximal inspiratory flow, as illustrated by the dotted lines. Of note, electroencephalograms (EEG), bilateral electro-oculograms (EOG), and submental electromyograms (EMG) (Channels 1–3 from top) indicate that moderate sedation was maintained throughout the experiment. Similar findings were observed in all subjects.

View larger version (16K): [in a new window]   Figure 3. A representative example of the nasal pressure (Pn) vs. inspiratory flow (VImax) relationship in one subject. Nasal resistance (Rua) was defined as the reciprocal of the slope of the relationship between VImax and Pn, and Pcrit as the x intercept of the regression line as illustrated. In the mouth-closed condition (open circle), Pcrit was –9.4 cm H2O and Rua was 15.8 cm H2O/L/sec. In the moderate mouth-open condition (black circle), Pcrit was –7.0 cm H2O and Rua was 17.0 cm H2O/L/sec, while in the maximal mouth-open condition (open square), Pcrit was –4.0 cm H2O and Rua was 34.6 cm H2O/L/sec.