Abstract: Inspiratory flow limitation (IFL) is involved in the pathophysiology of sleep-related breathing disorders. Since the definition of flow-limited cycle is based on a dissociation between flow and respiratory efforts, identification of IFL requires upper airway or intrathoracic pressure measurements. We examined the feasibility and accuracy of the analysis of the flow-volume loop of a tidal breath in identifying IFL. The tidal volume was obtained by integration of the instantaneous airflow signal, and the flow-volume loop was reconstructed for each breathing cycle by plotting the instantaneous flow and the tidal volume. The instantaneous inspiratory and expiratory flows were measured at a 50% of the respective (inspiratory or expiratory) portion of the tidal volume, and a breath-by-breath analysis of the mid tidal volume flow ratio (I/E ratio) was obtained. There was a positive significant relationship between I/E ratio and V.sub.