Bronchial inhalation challenge by plethysmography in asthmatic children

A new technique for breath-by-breath controlled bronchial inhalation test is described, using the body plethysmographic method. The values of airway resistance (Raw) and of thoracic gas volume at resting expiratory level (TGV) have been compared to the data of total pulmonary flow resistance (R1), measured with the intraesophageal catheter method, and of functional residual capacity (FRC). The dynamic lung compliance (C1 dyn) was calcualted, too; the mechanical parameters of breathing (R1; Raw; C1 dyn) have been investigated on the same breathing cycles before, during and after respiratory challenges in symptom-free asthmatic children. Regarding the breath-to-breath variation of the parameters, a respiratory challenge is usually considered as positive, if the R1 or Raw values increase 100% or more. Out of 39 assays, "positive" challenges were observed in 14 casis regarding R1 values and in 11 cases regarding Raw values. "Doubtful" tests - i.e. +50% less than or equal to R1 or Raw less than 100% - were observed in 5 assays regarding R1 and in 7 cases regarding Raw. A decrease of more than 40% of C1 dyn was observed in 12 out of the 19 'positive' or 'doubtful-positive' challenges; the largest spontaneous breath-to-breath variation being +/- 25%. Such a decrease of C1 dyn is suggested as a sign of peripheral bronchial obstruction. An increase of more than 25% of TGV was observed in 11 out of 19 assays, considered "positive" or "doubtful-positive". A correlation being observed between C1 dyn decrease and TGV increase this latter parameter is suggested to be an additional sign of bronchial obstruction. Beside the practical problem of the interpretation of a respiratory challenge, these results are discussed from the phatophysiological point of view.