Forced Expiration Technique (FET)
Forced expiration technique consists of one or two huffs from mid to low lung volume followed by a period of breathing control to reduce any bronchospasm the huffs may have engendered (Tannenbaum 1995; Hardy 1994; ACPRC 1996; Webber & Pryor 1993; Webber 1990).
The technique may be performed in postural drainage positions but is commonly performed in sitting or high side lying . The patient is instructed to take a medium sized breath in, followed by a lightly forced expiration through an open mouth and glottis (Webber & Pryor 1993). The huff should not be sharply forced or too prolonged as coughing may result. It is usual to perform one or two huffs followed by a period of breathing control to avoid inducement of bronchospasm. The cycle of huffs and breathing control may be repeated until secretions reach the proximal airways when a cough or short huff from high lung volume may remove them (Webber & Pryor 1993).
Forced expiratory technique may also be used as part of the active cycle of breathing technique. In patients with marked instability of the airways, forced expiratory technique is more effective than a cough at removing peripheral secretions, as coughing tends to completely close airways above the equal pressure point and therefore obstructs airflow (Hardy 1994).
The purpose of the technique is to mobilize secretions from the more peripheral airways towards the proximal airways in order that they be removed either by a huff from high lung volume or by a cough. The physiological basis of the technique centres around the equal pressure point (EPP) in airways where the pressure within the airway is equal to intrapleural pressure (Tannenbaum 1995; Schoni 1989). Downstream (towards the mouth) of the equal pressure point, the airways are dynamically squeezed and secretions are moved proximally (Tannenbaum 1995; Webber & Pryor 1993). At successively lower lung volumes, the equal pressure point moves more peripherally, mobilizing secretions at lobar and segmental bronchi (Webber & Pryor 1993).
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