The interrupter technique--a renaissance of a non-invasive approach for lung function testing in infants and children

The analysis of the postocclusional rapid oscillatory mouth pressure transients pao(t) after expiratory flow interruption during 100 ms features additional information to the conventional interrupter technique. The analysis focuses on the sudden oscillatory rise in pressure after flow interruption and the following damped oscillation. By calculating the first derivative of pao(t) ( = change in pressure), the frequency omega 0 and damping characteristic d of the pressure swings reflecting the inertive and elastic properties of the thoracopulmonary system can be computed. The interrelationship between omega 0 respectively d and different sizes of lung volume respectively characteristics of airway mechanics (airway resistance (Raw) and/or maximal expiratory flow at 50% vital capacity (MEF50)) was evaluated in 5 healthy adult subjects (28-37 y) and 10 healthy children (7-14 y). The measured frequency was statistically significantly related to lung volume (p < 0.05) and varied between 66 Hz in healthy adults and 91 Hz in children. The damping factor d increased with increasing airway resistance (n.s.) and decreasing MEF50 (p < 0.005). These findings add further arguments to the conjecture previously intimated that development of the viscoelastic properties of the lung are defined by characteristics of airway mechanics in close relationship to lung growth. In consequence, alterations in mechanical properties observed in diseased lungs have functionally closely be evaluated in relation to actual lung volumes (pulmonary hyperinflation, restrictive lung disease).