Positive expiratory pressure breathing is a technique in which resistance to airflow is applied during exhalation, similar to what occurs during pursed-lip breathing, except that the patient breathes through a specially designed mouthpiece or mask that controls resistance to airflow. This breathing technique is used to hold airways open during exhalation to mobilize accumulated secretions and improve their clearance. Positive expiratory pressure breathing provides an alternative or adjunct to postural drainage which a patient can perform independently.

Procedure
Positive expiratory pressure breathing is performed in an upright position, preferably seated with the elbows resting on a table. The procedure can be performed against low or high pressure. A low pressure technique involves tidal inspiration and active, but not forced, expiration through a mouthpiece or mask. The patient inhales, holds the inspiration for 2 to 3 seconds, and then exhales, repeating the sequence for approximately 10 to 15 cycles. The patient removes the mouthpiece or mask, takes several “huffs” and then coughs to clear the mobilized secretions from the airways. The breathing sequence typically is repeated four to six times with a total treatment session lasting about 15 minutes.

Respiratory Resistance Training
The process of improving the strength or endurance of the muscles of ventilation is known as respiratory resistance training (RRT). Other descriptions used to denote this form of breathing exercises are ventilatory muscle training, inspiratory (or expiratory) muscle training, inspiratory resistance training, and flow-controlled endurance training. These techniques typically focus on training the muscles of inspiration, although expiratory muscle training also has been described. RRT is advocated to improve ventilation in patients with pulmonary dysfunction associated with weakness, atrophy, or inefficiency of the muscles of inspiration or to improve the effectiveness of the cough mechanism in patients with weakness of the abdominal muscles or other expiratory muscles.
With support from animal studies, it has been suggested that the principles of overload and specificity of training apply to skeletal muscles throughout the body, including the muscles of ventilation. In humans, it is not feasible to use invasive procedures to evaluate morphological or histochemical changes in the diaphragm that may occur as the result of strength or endurance training. Instead, strength or endurance changes must be assessed indirectly. Increases in respiratory muscle strength and endurance are determined by ultrasonographic meaurements of the thickness of the diaphragm, maximal voluntary ventilation, and decreased reliance on accessory muscles of inspiration. Respiratory muscle strength (either inspiratory or expiratory) also is evaluated indirectly with measurements of inspiratory capacity, forced expiratory volume, inspiratory mouth pressure using a spirometer, vital capacity, and increased cough effectiveness.

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