Abstract: A method of determining whether an individual's breathing is obstructed. The method includes measuring a transthoracic impedance of the individual over a predetermined time interval, identifying a baseline impedance and selecting an impedance cycle. The method also includes identifying a maximum impedance during the selected impedance cycle, determining an upper difference between the maximum impedance and the baseline impedance, identifying a minimum impedance during the selected impedance cycle, and determining a lower difference between the minimum impedance and the baseline impedance. The method includes determining whether an amplitude of the upper difference is less than about seventy percent of an amplitude of the lower difference, and notifying an observer that the amplitude of the upper difference is less than about seventy percent of the amplitude of the lower difference.