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CMAJ • August 5, 2003; 169 (3)
© 2003 Canadian Medical Association or its licensors

Letters
Correspondance

An Oasys for occupational asthma

Susan M. Tarlo and Gary Liss

Gage Occupational and Environmental Health Unit, St. Michael's Hospital and University of Toronto, Toronto, Ont.

We agree that the Oasys method of interpreting serial peak expiratory flow readings is an objective scoring system. This and other methods1 are alternatives to visual inspection of graphed results, especially if an "experienced reader" is not available to interpret the graphs. Among experienced readers, visual inspection has a reported sensitivity of 87% and specificity of 84% compared with specific challenge tests.2 Even if a computerized or other objective method of interpretation is used, it may be helpful to inspect visual records and review records of symptoms (e.g., of upper respiratory infection), medications and other relevant factors, such as unusual workplace exposure, all of which may be relevant to the interpretation of changes in peak flow.

Compliance with serial recordings is often suboptimal.1,3 Although we agree that 2-hourly recordings of peak expiratory flow rate provide greater sensitivity than 4-hourly measurements (73% v. 61%),4 many workers may find it difficult to adhere to this schedule. Such difficulties with compliance may be particularly important when monitoring is required for prolonged periods both at work and away from work. Four-hourly recordings (before work, midshift, after shift and at bedtime) are less likely to interfere with the patient's work schedule and are usually more practical, especially for industrial workers.

Regardless of the method used, a significant minority of records are typically incomplete or inconclusive.5 Therefore, several investigations should be performed, if possible, to improve the accuracy of diagnosis of work- related asthma.

Susan M. Tarlo Gary Liss Gage Occupational and Environmental Health Unit St. Michael's Hospital and University of Toronto Toronto, Ont.

Footnotes

Competing interests: None declared.


References

  1. Liss GM, Tarlo SM. Peak expiratory flow rates in possible occupational asthma. Chest 1991; 100: 63-9.[Abstract/Free Full Text]
  2. Perrin B, Lagier F, L'Archeveque J, Cartier A, Boulet LP, Cote J, et al. Occupational asthma: validity of monitoring of peak expiratory flow rates and non-allergic bronchial responsiveness as compared to specific inhalation challenge. Eur Resp J 1992;5;40-8.[Abstract]
  3. Malo JL, Trudeau C, Ghezzo H, L'Archeveque J, Cartier A. Do subjects investigated for occupational asthma through serial peak expiratory flow measurements falsify their results? J Allergy Clin Immunol 1995;96:601-7.[Medline]
  4. Malo JL, Cote J, Cartier A, Boulet LP, L'Archeveque J, Chan-Yeung M. How many times per day should peak expiratory flow rates be assessed when investigating occupational asthma? Thorax 1993;48:1211-7.[Abstract/Free Full Text]
  5. Tarlo SM, Liss GM. Occupational asthma: an approach to diagnosis and management. CMAJ 2003; 168(7):867-71.[Free Full Text]




This Article
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