Click on image to view larger version.
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.
