Occupational asthma

　　The causes of occupational asthma are divided into two types: high molecular weight biological substances and low molecular weight chemical substances, among which the majority are occupational asthma-inducing agents, and a few are irritants. There are currently more than 250 recorded asthma-inducing factors, and there are still many suspected factors yet to be determined.

　　1. Plant materials

　　Grain dust, flour, soybeans, sesame seeds, coffee beans, tea leaves, tobacco leaves, vegetable gums, cotton seeds, flax seeds, and so on.

　　2. Animal body components and excretions

　　Laboratory animals, birds, eggs, milk, crabs, shrimps, and so on.

　　3. Insects

　　House dust mites, grain mites, bird mites, silkworms, cockroaches, bees, and so on.

　　4. Enzymes

　　Papain, subtilisin, pancreatin, pepsin, trypsin, fungal amylase, and so on.

　　5. Vegetable gums

　　Gum Arabic, Atractylodes macrocephala gum, karaya gum, and so on.

　　6. Isocyanate derivatives

　　Such as toluene diisocyanate (TDI), methyl diisocyanate, hexamethylene diisocyanate, and so on.

　　7. Phthalic anhydride derivatives

　　Such as phthalic anhydride, o-phthalic anhydride, and triphenyl hexanoic anhydride, and so on.

　　8. Drug

　　Such as penicillin, cephalosporin, spiramycin, tetracycline, piperazine citrate, and so on.

　　9, Wood dust

　　Such as sawdust from wood such as桃花心木, cedar, maple, oak, etc.

　　10, Metal

　　Such as platinum, nickel, chromium, cobalt, etc.

　　Among them, 1-5 are high molecular weight biological substances, 6-11 are low molecular weight compounds. The scope of occupational asthma stipulated in China currently includes isocyanates, phthalic anhydride, amines, platinum complexes, and sisal, which can be divided into high molecular weight allergic type and low molecular weight allergic type according to the difference in asthma triggers. They can also be divided into immunomediated type and non-immunomediated type according to the different pathophysiological mechanisms. The onset of immunomediated type patients has an incubation period, which can be divided into IgE-mediated type and non-IgE-mediated type, among which the former is often induced by high molecular weight allergens and a few low molecular weight allergens, and the latter is only seen in occupational asthma induced by low molecular weight allergens. Non-immunomediated type patients have no incubation period for asthma attacks, and the inflammation of their airways can be caused directly by the stimulating effect of asthma triggers, or indirectly caused by the pharmacological effects of asthma triggers on mast cells, smooth muscle cells, or nerve fibers, etc.

　　Currently, it has been found that occupational asthma patients engaged in industries related to high molecular weight allergens generally have atopy (atopy)体质, and studies have shown that it is related to the patient's genes. These groups are more prone to asthma after exposure to asthma triggers, allergens are easy to enter the body, B lymphocyte reactivity is abnormally increased, specific IgE is produced after exposure to allergens, forming a sensitized state, and it is easy to诱发 allergic reactions and asthma attacks when occupational allergens enter the body again.

　　The occurrence of occupational asthma symptoms is closely related to the working environment. Occupational asthma refers to asthma caused by exposure to asthma triggers in the occupational environment. This disease can complicate with pneumothorax, mediastinal emphysema, and mucous plug, which are the most common complications.

　　Typical occupational asthma symptoms include coughing, wheezing, chest tightness, or symptoms such as rhinitis and conjunctivitis during or after work, and the occurrence of symptoms is closely related to the working environment. Immediate asthma reactions induced by high molecular weight occupational asthma triggers manifest as asthma symptoms appearing upon entering the working environment, and symptoms quickly alleviate after leaving the scene, with characteristics of exposure to working environment-asthma onset-leaving working environment-asthma relief-re-exposure and recurrence. Occupational asthma induced by low molecular weight asthma triggers manifests as a delayed asthma reaction, with asthma symptoms appearing some time after work, and is therefore often overlooked or misdiagnosed.

　　The prevention of occupational asthma in patients lies in early detection and early diagnosis. Under normal lung function and clear pathogenic factors, timely departure from the original working environment can lead to complete recovery. There are many factors affecting the prognosis of patients with occupational asthma, including exposure time, age of onset, degree of atopy, severity of lung function damage, and airway reactivity. When patients have irreversible airway obstruction and develop chronic obstructive pulmonary disease or other complications, the prognosis is poor.

　　It is very important to evaluate the occupational etiology of asthma. To judge the cause, it is necessary to rely on the comprehensive analysis of various indicators, and the following indicators are currently recognized by countries around the world.

　　1. Disease history

　　Understanding the relationship between the occurrence and development of the disease and the occupation. The use of questionnaires is the most basic investigation tool and method, suitable for epidemiological and individual investigations, and is currently the most widely used method. A typical occupational asthma history is the worsening of asthma during work, improvement or alleviation of symptoms during weekends and holidays. However, not all cases have a typical history; many people can also have asthma attacks due to many factors outside of work, such as exposure to cigarette smoke, oil fumes, insecticides, and other irritants, or affected by cold air, exercise, etc., making the attacks irregular. Also, some people may frequently have asthma attacks at home or at night due to delayed-onset asthma.

　　2. Pulmonary function tests

　　Pulmonary function indicators show reversible airway obstruction, which can be proven by a salbutamol inhalation test. The decreased FEV1 value during asthma attacks can increase by more than 15% due to the inhalation of receptor agonists. Airway hyperreactivity can be confirmed by acetylcholine or histamine challenge tests. These indicators are all signs of asthma, not unique to occupational asthma. However, on the other hand, if a worker lacks airway hyperreactivity after shift change, it is difficult to determine the existence of occupational asthma even if there are subjective symptoms.

　　3. Monitoring of Maximum Expiratory Flow Rate (PEF)

　　Train workers to use a simple peak expiratory flow meter, and record it every day, conducting continuous observation for at least 3 weeks, including workdays and holidays, to discover the relationship between the occupational environment and pulmonary dysfunction, and determine suspected occupational allergens. Recent research has shown that PEF detection is useful for determining occupational asthma, with sensitivity and specificity reaching 81% to 89% and 74% to 89% respectively.

　　4. Immunological tests

　　This mainly refers to the abnormality of antigen-specific immune indicators, including antigen skin test (A-ST), specific IgE, IgG (S-IgE, S-IgG) antibody determination, antigen-induced histamine release test, and specific monocyte-derived histamine release factor (HRF) determination, which are mainly used to confirm allergy to occupational substances. This type of examination method is convenient to use and has high specificity and sensitivity. The positive rate of S-IgE for asthma caused by platinum complex salts, TDIPA, enzyme cleaner, grains, wood dust, etc., can reach 50% to 100%, and is consistent with other indicators such as S-IgG4, A-ST, etc. The positive rate of antigen-specific antibody examination not only depends on the immune status of the body, but also depends on factors such as the purity, titer of the antigen used, and the testing method.

　　5. Antigen-specific bronchial provocation test (A-BPT)

　　At present, A-BPT is widely considered to be the 'gold standard' in the diagnosis of the etiology of occupational asthma. The test can be conducted indoors or in the workplace, with the first hour set for 10-15 minutes, and then every 30 minutes in the second hour, followed by every hour, with at least 8 hours of observation. The typical forms of airway response to allergens are immediate reaction, delayed reaction, and bidirectional reaction.

　　6. Application of biomarkers

　　Detecting the content of eosinophils in the sputum of bronchial asthma patients and the content of NO in the exhaled air can be used as a non-invasive method to evaluate airway inflammation. For patients with occupational asthma suspected to be induced by juniper, a bronchial provocation test is performed, and the content of eosinophils in the sputum and the content of NO in the exhaled air are measured before and during the test. After 6 hours and 24 hours of BPT, the sputum eosinophils in asthma patients are significantly increased, which is related to the decrease in FEV1, but there is no correlation between the amount of NO in the exhaled air and lung function.

　　Occupational asthma patients should eat more vegetables and fruits rich in various vitamins, such as apples, green vegetables, cauliflower, and cabbage. Increasing vitamin intake can enhance the patient's resistance. Patients can often drink coffee, as caffeine in coffee has a certain inhibitory effect on asthma. To avoid allergens, one can change jobs, and it is also necessary to avoid spicy and stimulating foods, as well as sweet or salty foods. This includes candy, chocolate, and some puffed foods with high sugar content.

　　The treatment goal of occupational asthma is to quickly control symptoms, restore normal airway reactivity, and prevent irreversible changes in the airway. Once occupational asthma is diagnosed, the patient should be removed from an allergen-prone environment. Avoiding contact with allergens is the most important measure in the treatment of occupational asthma, as repeated exposure to allergen-prone environments will exacerbate airway inflammation. Inhaled corticosteroids can effectively prevent and treat airway inflammation, and can be used for up to half a year. The earlier airway inflammation is eliminated, the less likely irreversible changes will occur. Sometimes, hormones and bronchodilators are used in combination to relieve symptoms. Inhaled cromolyn can prevent allergic reactions induced by certain allergens.