Hyperpnea: The common stimulus for bronchospasm in asthma during exercise and voluntary isocapnic hyperpnea

S. Kivity, J. F. Souhrada

Research output: Contribution to journalArticlepeer-review

Abstract

The observation that different forms of exercise can induce varying degrees of bronchoconstriction in asthmatic patients remains to be explained. The aim of this study was to determine whether the degree of bronchoconstriction is dependent on the level of hyperpnea as recorded during different forms of exercise. 9 asthmatics (10-16 years of age) performed treadmill walking, arm peddling and leg cycling on 3 separate days. On the 4th study day, all patients performed voluntary hyperpnea under isocapnic conditions. Each challenge, i.e. exercise and/or hyperpnea, lasted 10 min. The subject breathed room (19-23°C, 7-14% relative humidity) air through the mouth. The following variables were continuously monitored: ventilation (V(E) end-tidal and mixed expiratory PCO2, and heart rate. The pulmonary functions measured before and at 7-15 min after challenge included spirometry, MEFV curve and SG(aw). It was found that: (1) all four forms of challenges when matched for minute ventilation (a mean of 42.3 ± 0.2 liters/min) induced a comparable degree of bronchoconstriction. This was measured by all pulmonary function variables including V(max) at 70% TLC and SG(aw). The voluntary isocapnic hyperpnea is an equally strong stimulus to bronchospasm when compared to absolute exercise hyperpnea, regardless of the method of exercise. (2) Both ventilatory response and oxygen consumption measured during leg cycling were significantly increased in asthmatics when compared to normal range. (3) Each individual showed a dose-response-like relationship between minute ventilation measured during exercise and the degree of bronchoconstriction following this challenge, as measured by pulmonary functions.

Original languageEnglish
Pages (from-to)169-177
Number of pages9
JournalRespiration
Volume40
Issue number4
DOIs
StatePublished - 1980
Externally publishedYes

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