Specific Inhalation Challenge
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The specific inhalation challenge (SIC) is a diagnosis tool to assess airway responsiveness to "sensitizing" substances as opposed to nonspecific stimuli such as pharmacological agents (i.e. histamine, methacholine), cold air and exercise. Subjects are exposed to a suspected occupational agent in a controlled way under close supervision in a hospital laboratory. The specific inhalation challenges has been considered as the gold standard in confirming the diagnosis of
occupational asthma Occupational asthma is new onset asthma or the recurrence of previously quiescent asthma directly caused by exposure to an agent at workplace. It is an occupational lung disease and a type of work-related asthma. Agents that can induce occupationa ...
.


Methods

One of the steps of SIC is to perform a challenge with the suspected
asthmagen An asthmagen is a substance that can cause asthma in exposed people. Workplace asthmagens induce what is called occupational asthma. A 2016 study of occupational asthmagens in Australia identified 277 in 27 groups, including ammonia, latex, pestic ...
. Then, FEV1 is subsequently measured using another device and compared to a baseline. A positive response is usually a decrease in baseline FEV1 of 15 to 20 percent.


Realistic method

The realistic method was developed in the 1970s. The patient enters a sealed chamber and is exposed to the suspected agent in a controlled, non-work, test environment. The asthmagen can be water-soluble and nebulized. If the agent is non-soluble, the patient tips the agent from one tray to another in an attempt to mimic the work environment. This method has the advantage of being able to assess, albeit highly subjectively, ocular and nasal symptoms as well as a reduction in FEV1. There are, however, disadvantages to the method. First, SIC is currently only conducted in specialty facilities because the facilities and equipment are rare and expensive. Second, the realistic method may exposed the patient to huge concentrations of particles, resulting in unduly severe
asthma Asthma is a common long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wh ...
attacks. Alternately, the agent can be delivered using the recently developed closed-circuit technique.


Closed-circuit method

This test requires the patient to breathe aerosols of the suspected agent (asthmagen) through an oro-facial mask or mouth piece. These asthmagens are aerosolized using closed-circuit chambers, and the quantities and concentrations administered being minute and extremely stable minimize the risk of exaggerated responses.


See also

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Occupational asthma Occupational asthma is new onset asthma or the recurrence of previously quiescent asthma directly caused by exposure to an agent at workplace. It is an occupational lung disease and a type of work-related asthma. Agents that can induce occupationa ...


References

{{reflist Asthma Occupational safety and health