Physical Agents in Bronchial Provocation Tests: Nebulized Hyperosmolar Aerosol

Abstract

Probably the most important development leading to the recognition that abnormal osmolarity of the respiratory tract is a potent stimulus that can provoke airway narrowing was the introduction of ultrasonic nebulizers in the 1960s. Since these nebulizers produce dense aerosols (usually in excess of 3 ml of aerosol per minute), with a large proportion of respirable droplets [31], they were considered superior to the nebulizers and humidifiers available at that time [18–20]. However, it became apparent that inhalation of ultrasonically nebulized aerosols could be associated both with an increase in airway resistance [11, 22, 23, 30] and a decrease in arterial oxygen tension [23, 29] in patients with chronic bronchitis [11, 23], chronic obstructive airways disease [22, 29] and asthma [6, 11]. The use of ultrasonically nebulized aerosols specifically for the purpose of diagnosis and assessment of bronchial hyperresponsiveness was investigated in the 1970s by Allegra et al. [1, 3] and Allegra and Bianco [2], who used ultrasonically nebulized water to challenge patients with asthma. In 1981, Schoeffel et al. [25] extended these findings by demonstrating that the response to ultrasonically nebulized aerosols is largely determined by the osmolarity of the aerosol and that hyperosmolar aerosols are also potent agents for provoking airway narrowing in asthmatic subjects.