We assessed the ability of innovative lung function tests to detect bronchial obstruction induced by methacholine bronchial challenge. Fifty-five recurrently wheezy infants (mean age 16 +/- 5.2 months) free of respiratory symptoms underwent baseline lung function tests. Forty-two completed the methacholine challenge. Maximal flow at functional residual capacity (VmaxFRC) was obtained using the squeeze technique; compliance and resistance of the respiratory system (Crs, Rrs) was measured with the passive expiatory flow volume technique; tidal volume breathing patterns were analyzed from recordings of respiratory rate (RR), tidal volume (VT), and inspiratory time divided by total cycle of duration (Ti/Ttot). Expiratory tidal flow volume (V/VT) curves were described with multiple indices such as the ratio of expiratory time necessary to reach peak tidal expiratory flow (Fpet) to expiratory time (Tme/Te). Transcutaneous oxygen tension (PtCO2) was measured as an indicator of response to methacholine challenge. Of 42 infants 41 responded to methacholine by a change > or = 2 standard deviations from baseline values. The mean SD unit changes were 9.8 in PtCO2, 3.7 for VmaxFRC, 2.8 for Crs, 2.09 for Rrs, 3.1 for RR, 1.6 for Ti/Ttot, 2.2 for Tme/Te 3.9 for PFVt. We conclude that these noninvasive lung function tests, especially VmaxFRC and Fpet, can be used to detect minor or moderate airway obstruction. Further studies are needed to determine the value of the tests in assessing bronchial disease and effects of its treatment.

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The aim of the study was to evaluate the effects of inhaled steroids (IS) on the improvement of clinical asthma symptoms and on the decrease in bronchial hyperreactivity (BHR). Twenty-four children with severe asthma were given 1,000 micrograms beclomethasone dipropionate (BDP) daily and compared with ten asthmatic control children. The study included the evaluation of daily clinical score, of exercise induced asthma, of bronchial obstruction (forced expiratory volume in 1 sec, FEV1), and of BHR at months 0, 1, 2-3, and 4-5 (M0, M1, M2-3, and M4-5). BHR was assessed by standardized inhaled carbachol provocation measuring plethysmographic specific airway resistance (SRaw). The carbachol dose causing a 40% decrease in specific conductance (SGaw) was determined (PD40 SGaw). Clinical scores decreased at M1 (P less than 0.01) and throughout the study. FEV1 increased at M1 (P less than 0.05), M2-3 (P less than 0.01), and M4-5 (P less than 0.05) compared to M0. PD40 SGaw only increased significantly at M1 and M2-3. No individual correlation was found between clinical scores and PD40 SGaw at any testing, or between the decrease of clinical scores and the decrease of BHR. We conclude that bronchoconstrictive challenge tests do not adequately assess the clinical efficacy of IS. In clinical practice non-specific BHR should be preferentially measured for diagnosing atypical forms of asthma.

Drs Ventura and Brooke comment:We thank Dr Bell and her colleagues for their comments. We were unaware of their paper when we submitted ours. There may well be differences in plasma amino acids depending on the type of preterm formula used, just as there will be differences if one formula is fed at different volumes.The purpose of our paper was not to compare formulasonly two infants were fed on formulas other than SMA Low Birthweight-but to examine the effects of a relatively high protein intake (in comparison with, for example, banked breast milk) in verv low birthweight infants. The infants in our study were appreciably smaller than those studied by Bell and her colleagues. but even so no potentially hazardous amino acid concentrations were detected.