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.
Liu
Lei
L
Department of Public Health Sciences at the University of Virginia, Charlottesville, VA.
Teague
W Gerald
WG
Department of Pediatrics, Emory University, Atlanta, GA.
Erzurum
Serpil
S
Department of Pathobiology, the Cleveland Clinic, Cleveland, OH; Department of Pulmonary, Allergy, and Critical Care Medicine, the Cleveland Clinic, Cleveland, OH.
Fitzpatrick
Anne
A
Department of Pediatrics, Emory University, Atlanta, GA.
Mantri
Sneha
S
Department of Pediatrics, Charlottesville, VA.
Dweik
Raed A
RA
Department of Pathobiology, the Cleveland Clinic, Cleveland, OH; Department of Pulmonary, Allergy, and Critical Care Medicine, the Cleveland Clinic, Cleveland, OH.
Bleecker
Eugene R
ER
Department of Medicine, Wake Forest University, Winston-Salem, NC.
Meyers
Deborah
D
Department of Medicine, Wake Forest University, Winston-Salem, NC.
Busse
William W
WW
Department of Medicine, University of Wisconsin, Madison, WI.
Calhoun
William J
WJ
Department of Medicine, University of Texas, Galveston, TX.
Castro
Mario
M
Department of Medicine, Washington University, St. Louis, MO.
Chung
Kian Fan
KF
Imperial College, London, England.
Curran-Everett
Douglas
D
National Jewish Hospital, Denver, CO.
Israel
Elliot
E
Brigham and Women's Hospital, Boston, MA.
Jarjour
W Nizar
WN
Department of Medicine, University of Wisconsin, Madison, WI.
Moore
Wendy
W
Department of Medicine, Wake Forest University, Winston-Salem, NC.
Peters
Stephen P
SP
Department of Medicine, Wake Forest University, Winston-Salem, NC.
Wenzel
Sally
S
University of Pittsburgh, Pittsburgh, PA.
Hunt
John F
JF
Department of Pediatrics, Charlottesville, VA.
Gaston
Benjamin
B
Department of Pediatrics, Charlottesville, VA. Electronic address: Bmg3g@virginia.edu.
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