Evaluation of the interrupter technique for the use of assessing airway obstruction in children

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Abstract
The purpose of this study was to determine if the interrupter technique, a noninvasive method for measuring airflow resistance, could be used to assess airway obstruction in children. In 107 children (74 with asthma, 12 with cystic fibrosis, and 21 without lung disease) conductance (mostly of airways) measured with the interrupter technique (Gint) was correlated with both forced expiratory volume in 1 second (FEV1) and the forced expired flow rate between 25% and 75% of vital capacity (FEF25–75. In addition, 17 children with significant airway obstruction due to asthma also had airway resistance measured by body plethysmography (Raw) before and after treatment. Resistance and conductance measurements made with the interrupter technique were subdivided into inspiratory (Rint-insp, Gint-insp) and expiratory (Rint-exp Gint-exp) values. In the 107 children, a high degree of linear correlation was found between Gint-exsp and FEV1 for Gint-insp, r = 0.77 (P < 0.001), and for r = 0.76 (P < 0.001). There was also good linear correlation between Gin, and FEF25–75 for r = 0.70 (P < 0.001), and for Gint-insp, r = 0.67 (P < 0.001). In the 17 asthmatic children who were tested before and after treatment of their airway obstruction, Rint correlated highly with Raw; for Rint-exp, r = 0.91 (P < 0.001), and for Rint-insp, r = 0.83 (P < 0.001). The pre- to posttreatment changes in R, and Raw were similar. We conclude that the interrupter technique can be used to assess changes in airway obstruction, but normal values must be established and further investigation is required before the complete extent of its clinical utility will be known. Pediatr Pulmonol. 1994; 17:211–217.