Measurement of Respiratory Mechanics during Partial Ventilatory Support: The Interrupter Technique
First described by Von Neergard and Wirtz in 1927 , the interrupter technique has been extensively used to measure respiratory resistance in spontaneously breathing non-intubated subjects. The basic principle involves a short mechanical interruption of the airflow at the mouthpiece: the airway pressure (Paw) measured just proximally to the occlusion site equilibrates then rapidly to a value very close to the alveolar one (Palv). The resistive pressure drop (DPint) can then be easily computed as the difference between Paw (the airway pressure before the taking place of the occlusion) and Palv (which is supposed equal to the airway pressure immediately following the occlusion). If flow (Vi) is known, respiratory resistance (Rint) is directly obtained as DPint/Vi. These principles have been validated by different authors using both the esophageal balloon and the body plethismography techniques as reference methods [2–6]. To measure Palv very brief occlusions suffice, in the range of a few hundred msec, so that the maneuver is not usually perceived by the patient and the breathing pattern is not significantly altered. Major improvements have been obtained by reducing upper airway compliance  and by introducing back- extrapolation to the time of interruption in the estimate of Palv .
KeywordsRespiratory Mechanic Pressure Support Ventilation Inspiratory Effort Control Mechanical Ventilation Respiratory Resistance
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