PMC

Inspiratory airflow (V_Imax) response to increasing hypoglossal nerve stimulation current amplitude during non-REM sleep for stimulated and unstimulated breaths in the patient illustrated in . As stimulation current increased beyond the flow capture threshold, V_Imax increased linearly until the peak flow threshold was attained, at which point V_Imax plateaued as increasing stimulus current was applied. Note that inspiratory flow limitation persisted at intermediate current levels (closed circles). Further increases in current abolished inspiratory flow limitation (open circles).

Baseline (unstimulated) and peak (stimulated) maximal inspiratory airflow (V_Imax) during non-REM sleep. Maximal inspiratory airflow (V_Imax) with stimulation OFF (mean baseline unstimulated breaths) and ON (at peak flow threshold) is represented for each patient and for the group as a whole (means ± SEM). A significant increase in V_Imax was observed for the group as a whole (P < 0.001). At the peak flow threshold, flow limitation was eliminated in 17 of 30 patients (open circles, stimulation ON), and persisted in the remaining 13 patients (solid circles, stimulation ON).

Maximal inspiratory airflow (V_Imax) versus stimulation current (milliamperes) in groups with (solid circles) and without (open circles) inspiratory flow limitation at the peak flow threshold. The flow response slope in the non–flow-limited group was greater than that in the flow-limited subgroup (1241 ± 199 vs. 674 ± 167 ml/s/mA; n = 25; P < 0.05). Lower levels of stimulation current were required to achieve peak airflow in the non–flow-limited compared with flow-limited subgroup (1.23 ± 0.10 vs. 1.80 ± 0.20 mA; n = 25; P < 0.05), although peak inspiratory airflow did not differ between non–flow-limited and flow-limited subgroups (564 ± 58 vs. 438 ± 35 ml/s). Both groups attained normal or near normal levels during sleep of approximately 400 ml/s or greater (shaded region).

Representative polysomnographic recording examples of hypoglossal nerve stimulation (HGNS) response at low (1.7 mA, left panel), moderate (2 mA, middle panel), and high (2.5 mA, right panel) levels of stimulation in one patient. In each panel, two stimulated breaths are shown (stimulation marker signal at bottom and stimulus artifact in EMG_SM), and are bracketed by adjacent unstimulated breaths during stable non-REM sleep. Unstimulated breaths displayed evidence of severe inspiratory airflow limitation as characterized by an early plateau in inspiratory flow at a low level and high frequency mid-inspiratory oscillations in airflow, consistent with snoring. During unstimulated breaths, maximal inspiratory airflow did not change across all stimulation levels, indicating that severe inspiratory flow limitation persisted across stimulation levels. In contrast, a graded response in maximal inspiratory airflow (downward direction) was observed with increasing levels of maximal inspiratory airflow as current was increased. Inspiratory airflow limitation persisted at low (left panel) and mid-levels (middle panel) of stimulation, but was abolished at the highest stimulation level applied (right panel). Note time lags of respiratory impedance signal (HGNS [Z]) and stimulus current marker signal (STIM) of approximately 400 ms and approximately 250 ms, respectively, relative to the airflow and ABD signals caused by signal processing and transmission from the implanted neurostimulation device. ABD = abdominal piezoelectric gauge; EMG_SM = submental electromyogram; F4M1, C4M1, and O2M1 = electroencephalogram leads; FLOW = tidal airflow; HGNS (Z) = implanted respiratory impedance sensor; L. EOG = left electrooculogram; R. EOG = right electrooculogram; STIM = stimulation current marker signal.