Chest
Standardization of Inhalation Provocation Tests: Dose vs Concentration of Histamine
Section snippets
Subjects
Fifteen subjects with asthma5 were selected from the Respiratory Clinic at the University Hospital in Saskatoon. All subjects were in stable state. None had history of allergen exposure or respiratory infection for four weeks prior to testing, none smoked and the baseline forced expired volume in one second (FEV1) on the two days varied less than 10 percent. Bronchodilator drugs were withheld for eight hours, steroids were continued in the same dosage, and no subject was using antihistamines.
Histamine Inhalation Tests
RESULTS
The geometric mean two min PC20 was 0.8 mg/ml and the geometric mean 30 sec PC20 was 2.9 mg/ml, 3.6-fold greater than the mean two min PC20. The paired t-test comparison of the 30 sec PC20 and 4 × 2 min PC20 revealed no significant difference (t = 0.9, p > 0.2).
The two min PC20 and 30 sec PC20 are compared graphically in Figure 1 with the line of “dose identity” and the range of reproducibility (± one doubling dose)7 shown as references. Ten of 15 subjects fell within this range of “dose
DISCUSSION
This investigation has documented that the “dose” of inhaled histamine is more important than the “concentration” of histamine in determining the response. The histamine inhalation test we currently employ uses two min inhalations of doubling concentrations of histamine up to 8 mg/ml.6,7 This was adapted from the method of de Vries et al9 in which 30 sec inhalations of up to 32 mg/ml histamine were used. It was thought that two min inhalations might prove more reproducible than 30 sec
ACKNOWLEDGMENTS
The authors wish to thank Mrs. R. Day and Mr. A. Campbell for help in preparing the manuscript and Ms. K. Y. Murdock for technical assistance.
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Supported by Grant No MA-7051 from the Medical Research Council of Canada.
Manuscript received March 22; revision accepted June 1.