Effect of CPAP on airway reactivity and airway inflammation in children with moderate-severe asthma.

BACKGROUND AND OBJECTIVE: Asthma is characterized by airway hyperreactivity and airway inflammation. We previously demonstrated that adults with mild well-controlled asthma exhibited a marked decrease in airway reactivity (PC20 increased >2-fold) after using nocturnal continuous positive airway pressure (CPAP) for 1 week. If CPAP produces a similar suppression of airway reactivity in children with moderate-severe asthma, who require chronic use of corticosteroids, then this non-pharmacological therapy might provide a beneficial alternative or supplemental therapy in these subjects. METHODS: Children aged 8-17 years with moderate-severe asthma were treated with 4 weeks of nocturnal CPAP (8-10 cm H2 O) or sham CPAP (<2 cm H2 O). Adherence was monitored with a modem installed in the equipment or by memory cards. Airway reactivity, assessed by methacholine bronchial challenge, was measured prior to and following treatment. RESULTS: The percentage of subjects adherent to treatment was similar in both groups (19/27 CPAP vs 19/28 sham, ~70%). There was a tendency for PC20 to increase with treatment in both groups (3.0-5.3 mg/mL CPAP vs 3.2 to 4.3 mg/mL sham, P = 0.083); however, the change did not differ significantly between groups (P = 0.569). CONCLUSION: We found that the 4-week treatment with nocturnal CPAP did not produce a twofold suppression of airway reactivity in children with moderate-severe asthma.

An alternative method to measure the diffusing capacity of the lung for carbon monoxide in infants.

BACKGROUND: Lung diffusion assessed by the uptake of carbon monoxide (DLCO ) and alveolar volume (VA ) by inert gas dilution are readily assessed in cooperative older subjects; however, obtaining these measurements in infants has been much more difficult. Our laboratory has measured DLCO and VA in sleeping infants using a mass spectrometer, which continuously measures gas concentrations, and demonstrated that infants with bronchopulmonary dysplasia (BPD) have lower DLCO , but no difference in VA compared to full-term controls. The mass spectrometer is expensive and lacks portability; therefore, we evaluated whether measurement of end-expiratory alveolar gas concentrations using a gas chromatograph would provide an alternative approach. METHODS: (1) Using our previously digitized data for infants with BPD and full-term controls, DLCO and VA were calculated at end-expiration rather than between 60 and 80% of expired volume, as previously reported. (2) In a new group of infants, DLCO and VA were measured using gas concentrations obtained at end-expiration with a mass spectrometer and a gas chromatograph. RESULTS: (1) Using end-expiratory concentrations, infants with BPD (n = 49) had significantly lower DLCO , but similar VA compared to healthy controls (n = 34) (DLCO : 4.2 vs 4.6 mL/min/mmHg, P = 0.047; VA : 614 vs 608 mL, P = 0.772). (2) Among newly evaluated infants (n = 28), DLCO and VA obtained with a mass spectrometer and a gas chromatograph were highly correlated (R2 = 0.94 and 0.99, respectively), and were not significantly different for the two analyzers. CONCLUSION: Measuring DLCO and VA at end-expiration using a gas chromatograph can provide an effective assessment of gas exchange in sleeping infants.