Specific inhalation challenge

The Specific Inhalation Challenge (SIC) is defined as a diagnosis tool to assess airway responsiveness to "sensitizing" substances as opposed tononspecific stimuli such as pharmacological agents (i.e. histamine, methacholine),cold air and exercise. [ [http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=9426105&ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum Vandenplas and Malo, 1997] Vandenplas O, Malo JL. Inhalation challenges with agents causing occupational asthma. Eur Respir J 1997; 10:2612-29.] Subjects are exposed to a suspected occupational agent in a controlled way under close supervisionin a hospital laboratory. The specific inhalation challenges has been considered as thegold standard in confirming the diagnosis of occupational asthma. [ [http://www.chestjournal.org/cgi/content/abstract/102/2/402 Cloutier et al., 1992] Cloutier Y, Lagier F, Cartier A, Malo JL. Validation of an exposure system to particles for the diagnosis of occupational asthma. Chest 1992; 102: 402–407.]

SIC methods

One of the steps of SIC is to perform a challenge with the suspected asthmagen.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 1970's. [ [http://www.pulsus.com/Respir/11_01/yeun_ed.htm Occupational Asthma: The Past 50 years] Chan-Yeung M. Jan/Feb 2004, Volume 11, Number 01: 21-26] 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 attemptto 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 reductionin FEV₁. [ [http://www.pulsus.com/Respir/11_01/yeun_ed.htm Occupational Asthma: The Past 50 years] Chan-Yeung M. Jan/Feb 2004, Volume 11, Number 01: 21-26]

There are, however, disadvantages to the method. First, SIC is currently only conductedin 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 attacks. [ [http://erj.ersjournals.com/cgi/content/abstract/2/8/769 Cloutier et al., 1989] Cloutier Y, Lagier F, Lemieux R, Blais MC, St-Arnaud C, Cartier A, and Malo JL. New methodology for specific inhalation challenges with occupational agents in powder form. Eur Respir J 1989; 2: 769-777.] 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 minuteand extremely stable minimize the risk of exaggerated responses. [ [http://www.erj.ersjournals.com/cgi/content/full/23/2/300 Malo et al., 2004] Malo JL, Cartier A, Lemiere C, Desjardins A, Labrecque M, L'Archeveque J, Perrault G, Lesage J, Cloutier Y. Exaggerated bronchoconstriction due to inhalation challenges with occupational agents. Eur Respir J 2004; 23: 300–303.]

References

See also

*Occupational asthma

External links

* [http://www.sclmedtech.com/ SCL Medtech ] - For any questions on workplace asthma diagnosis, especially Specific Inhalation Challenge
* [http://www.occupationalasthma.com/default.aspx/ Occupational Asthma (UK)] - Created by some of the most important people in the field, in UK. For any questions/ help on Workplace asthma