Figure 3From: Observational study on efficacy of negative expiratory pressure test proposed as screening for obstructive sleep apnea syndrome among commercial interstate bus drivers - protocol study Measurements techniques for upper airway collapsibility evaluated as expiratory volume in 0.2s (V 0.2 - percent of the mean inspiratory volume of the three breaths preceding NEP application) and as the flow drop (Δ V ˙ - expressed as the percent of the peak flow).Back to article page