title: Calcium and magnesium in exhaled breath condensate of children with endogenous and exogenous airway acidification.
abstract: OBJECTIVE
  Regulation of pH in the airways is of physiological importance. As acidification of the airways causes bronchoconstriction, the aim of the present study was to find out whether there is any difference in calcium and magnesium in exhaled breath condensate (EBC) of children with uncontrolled asthma (i.e., with endogenous acidification) and children with gastroesophageal reflux disease, GERD (i.e., with exogenous acidification).
  
  
  METHODS
  A total of 142 children were included in the study: children with uncontrolled asthma (N = 51), children with GERD (N = 61), and healthy controls (N = 30). In addition, according to the pH cut-off value children with asthma and GERD were divided into two subgroups, that is, patients with pH ≤ 6.93 (subgroup A) and patients with pH > 6.93 (subgroup B).
  
  
  RESULTS
  The mean EBC pH was significantly lower in children with asthma than in children with GERD (6.791 ± 0.374 vs. 7.002 ± 0.361, p = .006). Concentration [median and interquartile range-M (IQR)] of total magnesium, but not calcium, was lower in both asthmatic [(10 (10-40) μmol/L, p = .016)] and GERD children [(20 (10-40) μmol/L, p = .012)] in comparison with controls (47 ± 27 μmol/L). There was no statistically significant difference in EBC calcium and magnesium concentrations between asthmatic and GERD children. In asthmatic children a positive correlation was confirmed between forced expiratory volume in the first second (FEV1) and magnesium in EBC (r = 0.307; p = .030), and negative correlation was found between FEV1 and calcium/magnesium ratio (r = -0.290; p = .047). In addition, positive correlation was confirmed between fractional concentration of exhaled NO and calcium/magnesium ratio (r = 0.360; p = .018). In GERD patients a negative correlation (r = -0.404; p = .003) was found between magnesium and pH values. Concentration of calcium was higher in the GERD subgroup A children [(50 (30-90) μmol/L)] than in the subgroup B children [(30 (20-45) μmol/L, p = .031)]. In addition, concentration of magnesium was higher in the GERD subgroup A children [(30 (20-70) μmol/L)] than in the subgroup B children [(10 (10-20) μmol/L, p < .001)].
  
  
  CONCLUSIONS
  The present study indicates that decreased total magnesium concentration may be found in EBCs, irrespective of whether the acidification is the result of endogenous pathomechanisms or reflux-induced mechanisms. In children with GERD, EBC pH-metry should be performed after acute coughing episode. Future research is needed to investigate the mechanisms of onset and dynamics of these changes.
  
  
  CONCLUSIONS
  Lower concentration of magnesium may indicate its role in bronchoconstiction.
authors.affiliation: Department for Clinical Laboratory Diagnosis, Srebrnjak Children's Hospital, Zagreb, Croatia.
authors.forename: S
authors.initials: S
authors.lastname: Banović
authors.forename: M
authors.initials: M
authors.lastname: Navratil
authors.forename: Z
authors.initials: Z
authors.lastname: Vlašić
authors.forename: R Zrinski
authors.initials: RZ
authors.lastname: Topić
authors.forename: S
authors.initials: S
authors.lastname: Dodig
mesh_terms: D000293:Adolescent; D001249:Asthma / Q000378:metabolism*; D015415:Biomarkers / Q000032:analysis; D001944:Breath Tests; D016084:Bronchoconstriction / Q000502:physiology; D002118:Calcium / Q000032:analysis*; D002648:Child; D003430:Cross-Sectional Studies; D045853:Exhalation; D005260:Female; D005764:Gastroesophageal Reflux / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000032:analysis*; D008297:Male
chemical_list: D015415:Biomarkers; D008274:Magnesium; D002118:Calcium