Abstract
We studied the bronchial hyperreactivity in neonates and early infants by measuring transcutaneous oxygen pressure (tcPO2) during histamine inhalation challenge tests.
The subjects were 157 infants (74 boys and 83 girls) who had been admitted to Neonatal Intensive Care Unit in Niigata City General Hospital. The mean age was 45 days (6-179 days) old and the mean birth weight was 2, 143g (665g-4, 440g). For the 41 of the subjects, the same tests were performed again after certain intervals to clarify the changes in bronchial hyperreactivity.
As a marker of bronchial responsiveness we used respiratory threshold of histamine (abbreviated as Th) defined as the minimal concentration of histamine solution needed to induce a more than 10% fall in tcPO2. Histamine solution was prepared for inhalation challenge tents at serially doubling concentrations (39, 78, 156, 313, 625, 1, 250, 2, 500, 5, 000, and 10, 000 μg/ml), and we expressed each concentration as integral numbers 1 through 9 respectively from the lowest. To show the respiratory threshold, we used those numbers instead of absolute concentrations for statistical convenience. In case the tcPO2 did not fall more than 10% even at 10, 000 μg/ml, the Th was expressed as 10.
The mean value of Th in all 157 infants was 5.8±2.2 (m±SD). There existed definite relationships between Th and the following factors; 1) presence of allergic disorders within a third degree family, 2) history of respiratory distress syndrome, and 3) oxygen and mechanical ventilation therapy in the newborn period.
About the 41 subjects who underwent the histamine inhalation challenge tests twice, the mean value of Th in the second tests was 7.7, which was significantly greater than that in the first tests, 5.3. Individually, most of the subjects who showed much smaller Th in the second tests compared to that in the first had a history of wheezing.
