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Biomedical subjects

R T McKay

Publications and source records attributed to R T McKay.

29 records · Page 2Linked to original sources
PubMed1986

Persistent airways disease caused by toluene diisocyanate.

The natural history of isocyanate-induced asthma is not well documented. We evaluated a patient who developed persistent shortness of breath, wheezing, and cough after a massive exposure to toluene diisocyanate (TDI). Despite no further occupational exposures to isocyanates, he continued to have symptoms of asthma and variable airway obstruction 12 yr later. A methacholine inhalation challenge test was markedly positive, and a bronchial challenge test to TDI produced a dual asthmatic response. This report demonstrates that sensitivity to TDI can persist for many years in the absence of further occupational exposure and suggests that some patients with TDI-induced asthma do not recover from their disease after being removed from isocyanate exposure.

Asthma↗
PubMed1986

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.

Adult↗
PubMed1985

Asthma and rhinitis due to ethylcyanoacrylate instant glue.

A 32-year-old man developed asthma due to a cyanoacrylate ester instant glue used in building remote control model airplanes. Typical asthma and rhinitis symptoms developed after 1 year using the adhesive. Delayed onset of symptoms was consistently related to the application of the glue to balsa wood. Bronchial provocation to the glue vapors in a manner simulating his home exposure resulted in a late asthmatic response with rhinorrhea and lacrimation. Increased bronchial hyperreactivity to methacholine occurred after bronchial challenge and persisted for several weeks. Complete resolution of the patient's asthma symptoms occurred with avoidance of the glue. Reversion to a negative methacholine challenge test occurred after 6 months of continued avoidance.

Adhesives↗
PubMed1984

Pulmonary changes after exposure to vermiculite contaminated with fibrous tremolite.

Workers exposed to vermiculite contaminated with fibrous tremolite were surveyed for the presence of respiratory symptoms by questionnaire, and for pneumoconiosis by chest radiograph. Pulmonary function was measured by spirometry and single-breath carbon monoxide diffusing capacity ( DLCOsb ). Fiber exposure indexes, expressed as fiber/ml-yr, were derived for each worker from available industrial hygiene data and work histories. The estimated cumulative exposure for the work force ranged from 0.01 to 39 fiber/ml-yr. Discriminant analysis demonstrated significant correlates with shortness of breath and pleuritic chest pain to cumulative fiber exposure. The radiographic changes were limited to pleural changes and involved 4.4% of the population. Parametric and discriminant analysis demonstrated a significant correlation with radiographic changes and cumulative fiber exposure. There were no correlations between spirometry or DLCOsb and fiber exposure. Exposure to vermiculite contaminated with fibrous tremolite can cause pleural changes in occupationally exposed workers. This is supported by the previously identified 12 cases of benign pleural effusions in this working population and the association of pleural radiographic changes and pleuritic chest symptoms with cumulative fiber exposure. The lack of significant parenchymal radiographic, spirometric, and DLCOsb changes most likely reflects the low cumulative fiber exposure.

Adult↗
PubMed1984

Hyperreactive airway smooth muscle responsiveness after inhalation of toluene diisocyanate vapors.

Guinea pigs were exposed to 29 parts per billion of toluene diisocyanate (TDI) vapors 5 h per day for 20 consecutive days. Control animal exposure was to filtered air, with similar length of exposure, air flow, heat load, humidity, and other factors. Animals were killed 20 h after the last exposure, and tracheal smooth muscle relaxation and contraction responses to agonists were determined. There was no difference in beta-adrenergic responsiveness between the 2 groups; the mean -log ED50 (concentration of agonist corresponding to 50% of maximal effect) for isoproterenol-induced responses was similar (9.73 +/- 0.06 SE for exposed animals and 9.56 +/- 0.13 for control animals, p = 0.29). Significant differences in carbachol-produced contractility were observed. The dose-effect curve from carbachol-stimulated strips was shifted upward and to the left for TDI-exposed animals. Beginning with the lowest dose of carbachol, significant differences were observed between exposure groups; these differences became even more pronounced as the concentration of carbachol was increased. The mean -log ED50 of carbachol-treated strips from TDI-exposed animals was 6.44 + 0.04 SE, which was significantly lower than that of the control strips, 6.23 + 0.04 (p = 0.01). The maximal smooth muscle tension was also greater in TDI-exposed animals. The observed increase in maximal tension and the shift of the dose-effect curve for TDI-exposed animals suggest a direct effect of TDI on tracheal smooth muscle.

Animals↗
PubMed1983

Effect of toluene diisocyanate on beta adrenergic receptor function. Biochemical and physiologic studies.

The effects of toluene diisocyanate (TDI) on beta adrenergic receptor function was investigated using 2 different experimental model systems: (1) a biochemical model measured beta adrenergic adenylate cyclase activity of frog erythrocytes and (2) guinea pig tracheal smooth muscle responsiveness after in vivo exposure was used to assess physiologic function. The TDI inhibited isoproterenol-stimulated erythrocyte adenylate cyclase activity in a dose-dependent manner. Similar results were obtained with fluoride-ion-stimulated activity, suggesting that TDI caused a nonspecific inhibition of adenylate cyclase activity. No difference in tracheal smooth muscle responsiveness, measured as the concentration of isoproterenol corresponding to 50% of maximal relaxation (ED50), was observed in TDI-exposed (9.36 +/- 0.11 SE) guinea pigs when compared with control (9.38 +/- 0.06 SE) animals, nor was there a difference in the degree of maximal relaxation induced by isoproterenol. The differences between the in vitro cell studies and the tracheal smooth muscle investigations suggest that mechanisms other than direct beta adrenergic blockade should be considered in TDI-induced asthma.

Adenylyl Cyclases↗
PubMedDate not supplied

Pulmonary function testing: guidelines for medical surveillance and epidemiological studies.

This chapter emphasizes spirometry guidelines for conducting medical surveillance and epidemiological studies beyond those addressed by the 1987 American Thoracic Society Spirometry Update. These guidelines include specific recommendations concerning testing equipment, test performance, quality control, and technician training. Use of these guidelines should help ensure that changes in lung function over time and/or from certain exposures can be correctly interpreted and analyzed without reservation regarding their accuracy and quality.

Education↗