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Sophia Children’s Hospital Rotterdam, The Netherlands
Correspondence to: Peter J.F.M. Merkus, MD, PhD, Department of Pediatrics, Subdivision of Respiratory Medicine, Erasmus University and University Hospital/Sophia Children’s Hospital, Dr Molewaterplein 60, 3015 GJ Rotterdam, The Netherlands; e-mail: merkus{at}alkg.azr.nl
To the Editor:
We read with special interest the article by Sheikh et al (CHEST; July 1999),1 who studied infants using the rapid compression technique. They found an increase in forced expiratory flow (FEF) at 25% of the remaining tidal volume (VT) following the administration of albuterol in infants with a family history of asthma. The authors concluded that this was due to reversible bronchospasm, which seemed absent in infants who were exposed to maternal smoking and did not show such improvement, and they suggested that this technique could be used in recognizing different phenotypes of wheezy infants. If this interpretation is correct, this would have important practical implications.
However, some relevant issues are not addressed in the discussion. Higher FEFs at 25% of the remaining VT may be due to factors such as shifts in the inflation level of functional residual capacity (FRC) or to changes in VT itself. These changes may be induced by drugs but also may be induced by altered sleeping patterns. The review by Hayden et al2 concluded that no studies in which forced expirations were used to assess bronchodilator responsiveness in wheezy infants convincingly demonstrated that the maximal flow at FRC (VmaxFRC) was significantly improved following the inhalation of a bronchodilator. In contrast to the findings by Sheikh and colleagues, we found a mean decrease of VmaxFRC in 39 infants with dyspnea of various origins (eg, asthma, bronchopulmonary dysplasia, congenital abnormalities, diaphragm paralysis, and lung hypoplasia) following administration of 250 µg terbutaline (Fig 1 ). Subgroup analysis in 15 infants with asthma (2 passive smokers) showed a similar reduction of VmaxFRC (p < 0.01). In a subgroup of 16 infants, we could rule out a change in FRC as an explanation for the decrease.
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On the other hand, there seems to be a consensus that, clinically, some infants benefit from inhaled bronchodilator drugs. Therefore, it may still be possible that the net result of dynamic airway compression and bronchodilation following albuterol administration is improvement of airway patency, but that this effect differs between more central and more peripheral airways and does not improve VmaxFRC. We hope that Sheikh et al have enough data to rule out alterations of VT or inflation level and that they are able to correlate VmaxFRC with the ratio of FEF at 25% of FVC to peak forced expiratory flow before and after bronchodilation. If so, their data would add important new information on the pathophysiology of wheezy infants, indicating that attention should focus more on the shape of the (partial) forced expiratory flow-volume curves of infants with respiratory diseases.
References
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= asthma; • = other wheezing disorders. * = p < 0.02
(paired t test).