Advances in the use of inhalation provocation tests in clinical evaluation

Recent advances in the use of inhalation provocation tests in the clinical evaluation of asthma have been made with methacholine and histamine tests. The tests can be better standardized and the results more accurately interpreted. The ease of stimulation of bronchoconstriction by methacholine and histamine (bronchial responsiveness) relates closely to the presence and the degree of variable airflow obstruction that occurs spontaneously or is triggered by natural stimuli. Responsiveness can be heightened by bronchial infection and by exposure to allergens or sensitizing chemicals, such as toluene diisocyanate, and can be reduced by treatment. These observations indicate three uses of the tests in clinical practice. First, they can be used to validate the presence of hyperresponsiveness which, when spirometric study is normal, is synonymous with the presence of asthma. Second, they can be used to quantify the severity of hyperresponsiveness which relates closely to the amount of bronchodilator required to treat asthma. Finally, they can be used to measure a change in responsiveness, which is useful to document occupational asthma (defined as hyperresponsiveness caused by materials at work), and to optimize the treatment required to reverse or reduce hyperresponsiveness as much as possible.

Physical properties of aerosols produced by several jet- and ultrasonic nebulizers

In order to estimate the administered dose of inhaled drugs from aqueous aerosols, we have examined the output characteristics of eleven jet- and nine ultrasonic nebulizers. Under various operating conditions we measured driving pressure, airflow, solution- and solute output of the nebulizers, particle concentration and size distribution in the aerosol. The particle size distributions were determined of the dry particles from evaporated droplets of aerosolized 9 mg X ml-1 NaCl solutions by using a mobility aerosols spectrometer. These physical properties of the aerosols were found to vary considerably between nebulizers (even among specimens of the same type). Solution output per litre of air from the ultrasonic devices was 2 to 10 times larger than that from the jets, being dependent on electric power and driving pressure respectively. The jet nebulizers showed the largest particle concentration per litre of air. The volume median aerodynamic diameter of the droplets generated by the jet nebulizers was about 1.5-4 microns. With the exception of the Siemens TV 6000 and the Bosch Halomed, this diameter ranged between 3 and 7 microns among the ultrasonic nebulizers, being dependent on the frequency of the ultrasonic vibrations. The output characteristics appeared also to be affected by extension tubes, air vents, solute concentration and airflow. Solute output varied nonproportionally with solution output, which confirms the comparative merit of output measurements by weighing. The results of the present study can be used to estimate the administered dose of therapeutic or provocative agents by nebulizer equipment. Actual drug output can only be quantified by careful calibration of each separate set-up.

The physical properties of a jet-nebulizer and their relevance for the histamine provocation test

We have examined the physical properties of eight specimens of a frequently used jet-nebulizer (Wiesbadener Doppelinhalator). For each nebulizer, under various conditions we measured driving pressure, solution output, solute output, particle concentration and size distribution in the aerosol, and the change of solute concentration in the storage vessel. Using histamine acid phosphate solutions in distilled water, there was considerable variability between the nebulizers in solute output (range about a factor 3). Solute output was strongly related to driving pressure (r2 = 0.89), to solution output (r2 = 0.96) and to particle concentration (r2 = 0.87). The particle size distributions of the eight nebulizers were very similar. The volume median aerodynamic diameter (VMAD) of the stable evaporated particles was on average 0.33 micrograms (geometric standard deviation of 1.78), which implies a VMAD of the primary droplets of about 3.2 micrograms. In fifteen subjects with bronchial hyperreactivity, a twofold increase of histamine output of the nebulizer without a change in particle size resulted on average in a twofold decrease of the histamine concentration that caused a 20 per cent fall (PC20) in FEV1. At constant histamine output the administration of dry particles instead of direct nebulization of (partly) saturated droplets into the mouth increased PC20 by a factor 2. This difference could not be explained by a changed deposition in the hypopharynx. There were large interindividual differences in the response to the altered aerosol characteristics. We conclude that the physical properties of the administered aerosols should be carefully controlled since they influence the biological response to inhaled histamine. The solute output of the investigated jet-nebulizer can satisfactorily be validated by weighing, for which an equation is given. In bronchial provocation testing, administration of dry particles is recommended.