Abstract

We studied the effects of repeated exercise and histamine challenge in asthmatic patients to determine the frequency and degree to which a state of refractoriness was induced by these stimuli. Twentynine patients performed three exercise tests, and on a separate day 16 of these patients had three histamine inhalational challenge tests. Forty minutes separated each challenge. Changes in airways resistance were measured using the peak expiratory flowrate (PEFR). The fall in PEFR (expressed as a percentage of the pre-challenge value) was used to quantify the response to challenge. Significant protection was defined as a fall in PEFR after a repeated challenge less than 50 of the fall observed on the first challenge. All patients had a fall in PEFR greater than 22 on the first challenge of the day. With repeated exercise 28 out of 29 patients had a fall in PEFR less than that observed on the first test and 12 had significant protection. The fall in PEFR after the third exercise challenge was not significantly different to the second challenge anda plateau effect was observed. There was no significant difference in the fall in PEFR after the first and second histamine challenge although two of the 16 patients were significantly protected from the effects of the same doseof histamine. Verf.-Referat (gekuerzt)