Detection of expiratory flow limitation by evaluating the spontaneous flow pattern

In order to simplify the evaluation of expiratory flow limitation (EFL) in patients with respiratory disorders, we investigated a new method in which EFL was detected during spontaneous ventilation. The method is based on the evaluation of the mean derivative of the expiratory airflow signal (αm). The methodology was evaluated in 15 normal volunteers and 15 patients. This analysis revealed a linear correlation between αm and the EFL, as measured by the negative expiratory pressure technique (R= -0, 74; p<;0, 0001). The evaluation of the clinical usefulness showed that αm is sufficiently accurate for clinical use. We concluded that the developed method could be a useful tool for the evaluation of EFL.