The Respiratory Fluctuation Index: A global metric of nasal airflow or thoracoabdominal wall movement time series to diagnose obstructive sleep apnea

•A new global measure, the respiratory fluctuation index, to assess obstructive sleep apnea.•This parameter considers both degree and frequency of respiratory drops without the need for hand-counting episodes.•Generalized quantification of thoracic or abdominal respiratory effort as well as nasal airflow.•Respiratory fluctuation index from nasal airflow has a good efficacy to diagnose obstructive sleep apnea.