INTRODUCTION: Unintentional leaks, patient-ventilatory asynchrony, and obstructive or central events (either residual or induced by NIV) occur in patients treated by non-invasive positive pressure ventilation (NPPV). The impact of ventilator settings on these disturbances is yet little explored. OBJECTIVES: To study the impact of back-up respiratory rate (BURR) settings on efficacy of ventilation, sleep structure, subjective sleep quality and respiratory events in a group of patients with obesity-hypoventilation syndrome (OHS). METHODS: 10 stable OHS patients treated by long term nocturnal NPPV underwent polysomnographic recordings (PSG) and transcutaneous capnography on 3 consecutive nights with 3 different settings for BURR in random order: spontaneous "S" mode, low BURR and high BURR. No other ventilator parameter was modified. RESULTS: "S" mode was associated with the occurrence of a highly significant increase in respiratory events, mainly of central and mixed origin when compared to both "S/T" modes. Accordingly, oxygen desaturation index was significantly higher in "S" mode than in either "S/T" modes. Results of nocturnal PtcCO2 (Mean value, time spent with PtcCO2 > 50 mmHg) were similar over the 3 consecutive nocturnal recordings. Quality of sleep was perceived as slightly better, and number of perceived arousals as lower with low versus high BURR ("S/T") mode. CONCLUSIONS: In a homogenous group of patients treated by long term NPPV for obesity-hypoventilation, changing BURR from an "S/T" mode with a high or low BURR to an "S" mode was associated with the occurrence of a highly significant increase in respiratory events, of mainly central and mixed origin.

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