Interrupter Technique

Abstract: In 10 acutely ill patients mechanically ventilated for management of acute respiratory failure, respiratory system mechanics were determined with the interrupter technique as described recently (J Appl Physiol 1984; 56:681–690). Flow, volume, and tracheal pressure were measured throughout a series of brief expiratory interruptions. A plateau in tracheal pressure during interruption was observed in all patients, indicating respiratory muscle relaxation as well as equilibration between alveolar and tracheal pressure. Measurement of the plateau in postinterruption tracheal pressure, corresponding volume, and preceding flow enabled determination of the passive elastic and flow-resistive properties of the total respiratory system. In general, the volume-pressure relationship was linear over the expired volume examined and did not necessarily pass through the origin, indicating deviation of the end-expiratory lung volume during mechanical ventilation from the equilibrium position of the respiratory system. Elas...

Abstract: Spirometry is considered the primary method to detect the air flow limitation associated with obstructive lung disease. However, air flow limitation is the end-result of many factors that contribute to obstructive lung disease. One of these factors is increased airway resistance. Airway resistance is traditionally measured by relating air flow and driving pressure using body plethysmography, thus deriving airway resistance (Raw), specific airway resistance (sRaw), and specific airway conductance (sGaw). Other methods to measure airway resistance include the forced oscillation technique (FOT), which allows calculation of respiratory system resistance (RRS) and reactance (XRS), and the interrupter technique, which allows calculation of interrupter resistance (Rint). An advantage of these other methods is that they may be easier to perform than spirometry, making them particularly suited to patients who cannot perform spirometry, such as young children, patients with neuromuscular disorders, or patients on mechanical ventilation. Since spirometry also requires a deep inhalation, which can alter airway resistance, these alternative methods may provide more sensitive measures of airway resistance. Furthermore, the FOT provides unique information about lung mechanics that is not available from analysis using spirometry, body plethysmography, or the interrupter technique. However, it is unclear whether any of these measures of airway resistance contribute clinically important information to the traditional measures derived from spirometry (FEV1, FVC, and FEV1/FVC). The purpose of this paper is to review the physiology and methodology of these measures of airway resistance, and then focus on their clinical utility in relation to each other and to spirometry.

Abstract: There is a need for quick, reliable, and noninvasive lung function tests to assess airway obstruction in preschool children both for pediatric pulmonary care as well as for research purposes. We studied feasibility, reproducibility, and validity of measurements of the respiratory system using the interrupter technique (interrupter resistance [Rint]) and obtained reference values in children from a general population, 2 to 7 yr of age. Accuracy was studied by comparisons of Rint with plethysmographic airway resistance (Raw) in 20 patients (7 to 14 yr) with mild to severe chronic airways obstruction and was satisfactory in patients with FEV 1 . 60% predicted. The technique proved sensitive enough to detect changes in airway caliber within a small group of 12 children who developed mild respiratory tract infections. Among children from a general population, subgroups with mild respiratory symptoms or mild respiratory disease had higher mean Rint values. Airway obstruction was better detected using expiratory rather than inspiratory interruptions, both programmed at peak tidal ventilatory flow. Reproducibility within subjects was satisfactory (intraclass correlation 0.82 and 0.79). The same applied to interobserver agreement (intraclass correlation 0.98). The interrupter technique proves to be a reliable and practical test of airway function, suitable for clinical and epidemiologic studies in preschool children. Reliable lung function testing in preschool children is difficult because little cooperation and coordination can be expected at this age. Spirometric reference values for children have

Abstract: In a 4-year prospective study, we evaluated specific airway resistance (sRaw) by whole-body plethysmography, respiratory resistance by the interrupter technique, and respiratory resistance and reactance at 5 Hz by the impulse oscillation technique combined with measurement of responsiveness to bronchodilators and cold air in 30 children (mean [range] age 57 [2 to 8] years) with cystic fibrosis (CF) Spirometry was done at school age Mean sRaw was consistently abnormal: the mean z score (SD) was 252 (202) (p < 0001) at the start and was unchanged 36 months later at 274 (202) Mean z score (SD) for FEV1 at first satisfactory measurement, at a mean age (range) of 61 (49–75) years was −12 (12) and was further reduced to −185 (12) 4 years from inclusion at a mean age (range) of 99 (68–12) years Neither respiratory resistance by the interrupter technique nor the impulse oscillation technique demonstrated consistent abnormal levels Patients with CF as a group did not differ from healthy subject