Absence of airway hyperreactivity to methacholine in a worker sensitized to toluene diisocyanate (TDI)

Evaluation of a 4-steps-1-day whole body challenge protocol for the diagnosis of occupational asthma due to diisocyanates

Inhalative challenges are important in the diagnosis of occupational asthma due to diisocyanates. As existing protocols are time-consuming and costly, it was the aim of this study to develop a short duration whole body exposure protocol. Ninety three subjects with suspected occupational diisocyanate-induced asthma and verified current or previous occupational exposure to diisocyanates and ten control subjects without diisocyanate exposure but with bronchial hyperresponsiveness were investigated. After baseline examination on the first day, subjects underwent a standardized whole body multiple-steps-1-day challenge with exposures of up to four times 30 min to concentrations of 5, 10, 20, and 30 ppb of the dominant diisocyanate used at work on the second day. Common spirometric and body plethysmographic parameters were used as positivity criteria. Overall, 14 subjects demonstrated a positive diisocyanate challenge, 19 were considered doubtful, and 60 were negative. All controls had negative challenges. Positive reactions occurred during the challenge (n = 10) or during follow-up (n = 4). Eight subjects showed >40 % fall of FEV1. These severe reactions occurred after 5 ppb (n = 2) or 10 ppb (n = 3), while isolated late reactions after 2 h of follow-up were not observed. Multivariate analysis showed an association between a positive challenge and both the degree of previous occupational exposure and the presence of baseline bronchial hyperresponsiveness. In summary, the proposed 4-steps-1-day diisocyanate challenge protocol induced pronounced bronchial reactions in a small number of subjects. As these reactions were more likely to occur after low concentrations, it is recommended to shift the initial concentration/dose step to lower exposures.

The spectrum of building-related airway disorders: difficulty in retrospectively diagnosing building-related asthma

INTRODUCTION

The specific causes and mechanism(s) for asthma occurring among occupants of non-residential buildings with poor indoor air quality are not known, but allergic and nonallergic processes are possible explanations

METHODS

Repeated indoor air quality measurements were made while employees were working in a building where cigarette smoking was allowed. Seven of 19 employees who sought medical care from their private physicians because of respiratory complaints received a diagnosis of asthma. Subsequently, 19 symptomatic employees were examined at the University of South Florida (USF) 2 +/- 0.8 months (mean +/- SD) after removal from the building.

RESULTS

The first floor of the building, where employee complaints were prevalent, was characterized by markedly reduced outdoor fresh air supply, diminished air circulation to the occupant spaces, and elevated airborne concentrations of formaldehyde. Nineteen workers examined at the USF 2 +/- 0.8 months after leaving the building reported ear, nose, and throat irritation and asthma-like symptoms while working in the building. There was resolution of symptoms in most of the seven employees (37%) with asthma previously diagnosed by their private physician. In fact, 16 of 19 subjects (84%) reported resolution or significant improvement of symptoms. Among 11 persons with symptoms suggesting asthma while working in the building, 4 persons (21%) showed a negative provocative concentration of methacholine producing a 20% fall in FEV1, including two subjects with doctor-diagnosed asthma.

CONCLUSIONS

Confirmation of building-related asthma is influenced by time factors and the clinical criteria used for diagnosis. A nonallergic mechanism seems operative in our cases. While considered an example of occupational asthma, building-related asthma is a challenge for the practicing physician to confirm retrospectively.

Provocation studies in the diagnosis of occupational asthma

Specific and nonspecific provocation studies, although not always essential for diagnosing OA, help confirm the diagnosis and identify the offending agent. Nonspecific bronchial challenge testing is used to detect airway hyperresponsiveness and to clarify the nature of the patient's symptoms. Pharmacologic bronchoconstrictor agents (eg, methacholine, histamine) most commonly are used for the challenge, but nonisotonic aerosols, exercise and hyperventilation also can show airway hyperresponsiveness. Nonspecific challenges usually are done in the laboratory, but can be done at the workplace if emergency equipment is available. A comparison of results obtained at and away from the workplace (at least 1 week apart) may be helpful in diagnosing OA. Specific bronchial challenge testing is considered the gold standard for OA diagnosis. It can be crucial in helping physicians, employers, and employees make decisions about continued employment, compensation, career changes, and treatment. Testing can pinpoint new industrial agents that cause OA, enabling dissemination of information on its hazards to the public and within the industry. The nature of the agent determines the type of protocol that is used for testing. Agents can be in the form of dusts, powders, aerosols, vapors gases, and animal dander. Exposure can be as simple as having patients simulate their work activities, or as complicated as using special challenge chambers with controlled environments and precise delivery of agents. Performing control challenges with a component that is separate from the test agent is essential to avoid false-positive results. The timing, duration, and dosing of exposure depend on the type of reaction that has been experienced previously, the nature of the agent, and the patient's baseline airway hyperresponsiveness. Serial spirometry and observation often are done for up to 8 hours to monitor early and late reactions. SBC testing should be performed in the proper medical setting in which emergency equipment available and should be administered only by healthcare personnel who are trained and experienced in the procedures. Safety of the patient is the primary consideration.

Diagnostic testing in occupational asthma

BACKGROUND

Occupational asthma may often be a challenge to diagnose as the relationship between work and symptoms may not be immediately clear. The potential consequences for the worker's career make an accurate diagnosis essential. A history of work-associated asthma symptoms that recede when the patient is not at work is the first clue.

METHODS

A nonspecific bronchial challenge, most commonly with methacholine, can help confirm the diagnosis of asthma. Specific IgE to suspected agents can be tested for, preferably with skin testing. Serial monitoring of peak expiratory flow rate (PEFR) or forced expiratory volume in 1 second (FEV1) at work and outside of work can determine if the asthma is occupational in nature.

CONCLUSION

Specific bronchial challenge to suspected occupational agents is the gold standard for diagnosis of occupational asthma.

Occupational asthma and extrinsic alveolitis due to isocyanates: current status and perspectives

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Peak expiratory flow rates in possible occupational asthma

Objective criteria for interpretation of peak expiratory flow rate readings were assessed in 50 patients evaluated for suspected occupational asthma who had at least two weeks of PEFR readings and an objective diagnosis based on other investigations. The prevalence of OA was 36 percent. Peak flows were interpreted by two observers blinded to other results. Criteria for a PEFR interpretation of OA were as follow: diurnal variation greater than or equal to 20 percent relatively more frequently or with greater variation on working days than days off work. With the objective diagnoses as the gold standard, the sensitivity of the PEFR interpretations was 72 percent for OA; specificity for no asthma was 53 percent. Excluding those with greater than or equal to 20 percent variation on only one day sensitivity improved to 93 percent for OA, and specificity to 77 percent. There was an acceptable level of interobserver variation (kappa 62 to 83 percent). We conclude that simple objective criteria for PEFR interpretation can be developed with acceptable interobserver variation.

Persistent asthma due to isocyanates. A follow-up study of subjects with occupational asthma due to toluene diisocyanate (TDI)

Thirty-five subjects with occupational asthma due to toluene diisocyanate (TDI) exposure were examined. All the subjects were studied with inhalation challenges with TDI and with methacholine. TDI asthma was documented by a positive inhalation challenge to low levels of TDI. Airway responsiveness to methacholine was in the range of asthmatic patients at the time of diagnosis. After an average follow-up interval of 10 months, all the subjects were re-examined. Of the 35 subjects examined, 30 subjects (85.7%) left the workplace, and 5 remained in the same job. Twenty-seven subjects (77.1%) continued to have asthmatic attacks requiring medication for relief of symptoms. At follow-up examination, TDI asthma was documented by a positive inhalation challenge to TDI in 27 subjects. Of these 27 TDI reactors, 22 subjects were removed from occupational exposure to TDI. The TDI reactors had persistent respiratory symptoms and airway hyperresponsiveness to methacholine. At follow-up visit, 8 subjects (22.9%) lost sensitization to TDI; 5 subjects (62.5%) in this group had also normal airway responsiveness to methacholine after removal from exposure. Only 1 subject among the TDI nonreactors complained of mild respiratory symptoms. At diagnosis, there were no significant differences between subjects who recovered and those who did not with regard to age, smoking habits, atopy, duration of exposure to isocyanates, duration of symptoms, baseline FEV1 (% pred), and baseline airway responsiveness to methacholine.(ABSTRACT TRUNCATED AT 250 WORDS)

Isocyanates and respiratory disease: current status

This paper reviews the known respiratory effects of isocyanates. There is good evidence to indicate that isocyanates: cause chemical bronchitis/pneumonitis; are potent pulmonary sensitizers capable of causing "isocyanate asthma"; cause nonspecific airways disease, including chronic bronchitis; can induce a general asthmatic state; and can cause hypersensitivity pneumonitis. Similar dose-response relationships are seen for both acute and chronic effects. There are plants operating in which exposures are well controlled and in which no respiratory effects can be detected. Suggestions are provided for preplacement assessment and periodic surveillance for workers exposed to these compounds.

Chronic asthma due to toluene diisocyanate

Twelve subjects were studied with inhalation challenge testing to toluene diisocyanate (TDI) because of suspected TDI asthma based on a consistent clinical and occupational history. In seven cases, TDI asthma was documented by a positive inhalation challenge to low levels of TDI. Six of the seven TDI reactors had persistent respiratory symptoms and required daily treatment even though they had been removed from isocyanate exposure for intervals as long as 12 years (mean 4.5 years). These six TDI reactors had either dual (four cases) or late bronchospasm (two cases) to less than 20 ppb TDI, and all had a positive methacholine or cold air challenge prior to study. The one TDI reactor with a negative methacholine challenge had a positive (immediate) bronchospastic response to a TDI challenge performed one week after removal from isocyanate exposure. Five workers had a negative TDI challenge, two of whom had persistent respiratory symptoms and positive methacholine challenges at the time of TDI inhalation testing. We conclude that respiratory symptoms may persist following long-term removal from occupational exposure to TDI and are associated with nonspecific bronchial hyperreactivity. The TDI sensitivity may also persist for a long time even in the absence of any additional occupational exposure. Long-term prospective studies of symptomatic isocyanate workers are needed to fully define the extent of this problem.

Absence of hyperresponsiveness to methacholine in a worker with methylene diphenyl diisocyanate (MDI)-induced asthma

A 29-year-old man had a persuasive history of respiratory illness following exposures to methylene diphenyl diisocyanate (MDI). He was evaluated by measuring bronchial reactivity to methacholine, both before and after controlled laboratory exposures to MDI. Despite evidence of progressive declines in FEV1 with increasing (but subirritant) doses of MDI on three consecutive days, there was no bronchial hyperresponsiveness to methacholine, before or after MDI challenge. We conclude that the absence of nonspecific bronchial hyperresponsiveness does not exclude the possibility of isocyanate asthma. In the face of a compelling history, a negative result of methacholine challenge should not deter observation or laboratory testing for specific respiratory allergy to these chemicals.

Respiratory effects of inhaled isocyanates

Numerous industrial chemicals are known to cause allergic reactions in the lung. Prominent among such chemicals are isocyanates, the starting material in the production of polyurethanes. In view of the extensive worldwide production of isocyanates (1.5 million metric tons per year), and the diversity of products manufactured from isocyanates (i.e., cars, airplanes, furniture, bedding, etc.) there is considerable potential for adverse health effects associated with exposure to isocyanates. Syndromes of immediate respiratory reactivity, delayed-onset sensitivity, and hypersensitivity pneumonitis have all been associated with isocyanate exposure. However, little is known concerning how sensitivity develops, which individuals are most likely to become sensitized, or how to best detect early sensitivity. Answers to such questions are beginning to emerge from the recent development of animal models of lung sensitivity. These models will be discussed together with their application to clinical situations.

Respiratory disease in a photographer

Reversible airways obstruction occurred in a photographer after long-term exposure (over many years) to sulfuric and acetic acid fixers. Air-exchange recommendations for darkrooms by the Building Officials Code Administration [1981] differ markedly from those recommended by the American Society of Heating, Refrigerating, and Airconditioning Engineers [1977] and the fixer manufacturer (Eastman Kodak). Use of fume hoods or rates of air-exchange higher than are required by law may be necessary to prevent symptoms and disease in certain workers.

Accelerated loss of FEV- in polyurethane production workers: a four-year prospective study

A four-year longitudinal study of ventilatory function in polyurethane-foam production workers exposed to toluene diisocyanate (TDI) revealed a dose-response relationship between average exposure to TDI and change in forced expiratory volume per second (FEV-1). Workers with mean exposure in excess of 0.0035 ppm showed a greater rate of decline of FEV-1 over the four-year period than that expected from aging. Factors other than TDI exposure (sex, smoking history, history of atopy) do not account for the loss. The current threshold limit value (TLV) for exposure to TDI in industry (0.02 ppm) does not protect workers from accelerated impairment of ventilatory capacity.