Comparison between hypertonic and isotonic saline-induced sputum in the evaluation of airway inflammation in subjects with moderate asthma.

BACKGROUND

Hypertonic saline-induced sputum has recently been used for the evaluation of airway inflammation in asthma.

OBJECTIVE

To assess the effect of hypertonicity on airway inflammation.

METHODS

We compared the inflammatory cell composition of hypertonic saline-induced sputum with that of isotonic saline-induced sputum in 21 asthmatic subjects and, at baseline and 30 min after each sputum induction, we measured bronchial hyper-responsiveness to methacholine as an indirect marker to detect increased airway inflammation. On two different days, the patients inhaled hypertonic saline (3-5% NaCl) or isotonic saline (0.9% NaCl) for 30 min via an ultrasonic nebulizer, while monitoring FEV1. Sputum was collected for inflammatory cell analysis.

RESULTS

There was no difference in inflammatory cell percentages obtained with the two methods. Eosinophils were > 1% in 20 subjects after hypertonic saline and in 16 subjects after isotonic saline, but this difference was not statistically significant. Intraclass correlation coefficients for sputum inflammatory cells obtained with the two methods were +0.642 for eosinophils, +0.644 for neutrophils, +0.544 for lymphocytes and +0.505 for macrophages. Hypertonic saline induced bronchoconstruction in a significantly greater number of subjects than isotonic saline. Also, hypertonic saline increased bronchial responsiveness to methacholine, while isotonic saline did not.

CONCLUSION

We conclude that hypertonicity does not affect sputum cell composition, suggesting that inflammatory cells in hypertonic saline-induced sputum are probably preexisting and not acutely recruited in the airways by the hypertonic stimulus. However, the bronchoconstriction and the increase in bronchial hyper-responsiveness after hypertonic saline inhalation may imply the release of inflammatory mediators. This fact must be considered in the evaluation of soluble markers of inflammation in hypertonic saline-induced sputum.