Determinants of exhaled breath condensate pH in a large population with asthma.
BACKGROUND
Exhaled breath condensate (EBC) pH is 2 log orders below normal during acute asthma exacerbations and returns to normal with antiinflammatory therapy. However, the determinants of EBC pH, particularly in stable asthma, are poorly understood. We hypothesized that patients with severe asthma would have low EBC pH and that there would be an asthma subpopulation of patients with characteristically low values.


METHODS
We studied the association of EBC pH with clinical characteristics in 572 stable subjects enrolled in the Severe Asthma Research Program. These included 250 subjects with severe asthma, 291 with nonsevere asthma, and 31 healthy control subjects.


RESULTS
Overall, EBC in this population of stable, treated study subjects was not lower in severe asthma (8.02; interquartile range [IQR], 7.61-8.41) or nonsevere asthma (7.90; IQR, 7.52-8.20) than in control subjects (7.9; IQR, 7.40-8.20). However, in subjects with asthma the data clustered below and above pH 6.5. Subjects in the subpopulation with pH < 6.5 had lower fraction of exhaled NO (FeNO) values (FeNO = 22.6 ± 18.1 parts per billion) than those with pH ≥ 6.5 (39.9 ± 40.2 parts per billion; P < .0001). By multiple linear regression, low EBC pH was associated with high BMI, high BAL neutrophil counts, low prebronchodilator FEV(1) ratio, high allergy symptoms, race other than white, and gastroesophageal reflux symptoms.


CONCLUSIONS
Asthma is a complex syndrome. Subjects who are not experiencing an exacerbation but have low EBC pH appear to be a unique subpopulation.
Department of Public Health Sciences at the University of Virginia, Charlottesville, VA.
Lei
L
Liu
Department of Pediatrics, Emory University, Atlanta, GA.
W Gerald
WG
Teague
Department of Pathobiology, the Cleveland Clinic, Cleveland, OH; Department of Pulmonary, Allergy, and Critical Care Medicine, the Cleveland Clinic, Cleveland, OH.
Serpil
S
Erzurum
Department of Pediatrics, Emory University, Atlanta, GA.
Anne
A
Fitzpatrick
Department of Pediatrics, Charlottesville, VA.
Sneha
S
Mantri
Department of Pathobiology, the Cleveland Clinic, Cleveland, OH; Department of Pulmonary, Allergy, and Critical Care Medicine, the Cleveland Clinic, Cleveland, OH.
Raed A
RA
Dweik
Department of Medicine, Wake Forest University, Winston-Salem, NC.
Eugene R
ER
Bleecker
Department of Medicine, Wake Forest University, Winston-Salem, NC.
Deborah
D
Meyers
Department of Medicine, University of Wisconsin, Madison, WI.
William W
WW
Busse
Department of Medicine, University of Texas, Galveston, TX.
William J
WJ
Calhoun
Department of Medicine, Washington University, St. Louis, MO.
Mario
M
Castro
Imperial College, London, England.
Kian Fan
KF
Chung
National Jewish Hospital, Denver, CO.
Douglas
D
Curran-Everett
Brigham and Women's Hospital, Boston, MA.
Elliot
E
Israel
Department of Medicine, University of Wisconsin, Madison, WI.
W Nizar
WN
Jarjour
Department of Medicine, Wake Forest University, Winston-Salem, NC.
Wendy
W
Moore
Department of Medicine, Wake Forest University, Winston-Salem, NC.
Stephen P
SP
Peters
University of Pittsburgh, Pittsburgh, PA.
Sally
S
Wenzel
Department of Pediatrics, Charlottesville, VA.
John F
JF
Hunt
Department of Pediatrics, Charlottesville, VA. Electronic address: Bmg3g@virginia.edu.
Benjamin
B
Gaston
D000328:Adult; D001249:Asthma / Q000378:metabolism*; D015415:Biomarkers / Q000032:analysis; D001944:Breath Tests / Q000379:methods*; D016022:Case-Control Studies; D045853:Exhalation; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D016014:Linear Models; D008297:Male; D010641:Phenotype; D012307:Risk Factors; D012720:Severity of Illness Index
D015415:Biomarkers