Serial assessment of peak expiratory flows Jean-Luc Malo MD Chest Physician Université de Montréal and Hôpital du Sacr é -Coeur and Center for Asthma in the Workplace Hôpital du Sacré-Cœur de Montréal Université de Montréal Axe de recherche en santé respiratoire Centre asthme et travail Center for Asthma in the Workplace

Chronic Obstructive Pulmonary Diseases Definition (functional) Diseases characterized by a reduction in expiratory flow rates caused by either bronchial obstruction (bronchial involvement per se) or a loss in the elastic support of the bronchi by emphysema (destruction of the lung parenchyma) (peribronchial involvement).

Manifestations: reduction of expiratory flow rates Functional indices: 1. Forced expiratory volume-one second (FEV1) 2. FEV1/forced vital capacity (“Tiffeneau Index”, 1947) 3. Peak Expiratory Flows (Rates): Wright and McKerrow 1959 Chronic Obstructive Pulmonary Diseases

flow (volume / time) peak expiratory flow one second time maximum inspiratory capacity (vital capacity) FEV1 forced vital capacity

Origin of the assessment of peak expiratory flows (PEF) in Asthma and Occupational Asthma In asthma  Daily peak flow measurements in the assessment of steroid therapy for airway obstruction.Epstein SW, Fletcher CM, Oppenheimer EA. BMJ 1969  On observing patterns of airflow obstruction in chronic asthma.Turner-Warwick M. Br J Dis Chest 1977 Identification of three patterns: 1. Brittle asthmatic; 2. Morning dipper; 3. Pseudo irreversible asthmatic.  Comparison of normal and asthmatic circadian rhythms in peak expiratory flow rate. Hetzel MR, Clark TJH. Thorax  Action plans based on PEF. In occupational asthma  Burge PS et al onwards

Interest, advantages  assessment with portable, cheap instruments  provides serial assessment of airway caliber (relevant for asthma diagnosis and management) Disadvantages  effort-dependent manoeuver  reflects large airway caliber (discredit from lung physiologists who focused on «small airways»)

To assess peak expiratory flows : Portable peak flow meters : standard (cheap) and electronic (storage of data) Predicted values (as a function of age, sex, height and racial origin) Normal values In men: 500 to 700 L/min In women: L/min

Number of recordings/day: In asthma: morning value (before medication) In occupational asthma: at least four times a day How many values at each time ? 3 times, 2 best values within 20 L/min Significant changes ? 50 L/min In occupational asthma, for how long ? Two weeks at work, two weeks off-work

Indications In asthma Acute: essential in ER (FEV1 or PEF) and in GP office Chronic: Poor perception of airflow limitation Brittle asthma Discrepancy between symptoms and need for medication: exclude hyperventilation To identify flare-ups In occupational asthma As a screening test : negative tracing and absence of airway hyper- responsiveness at work Diagnostic ? In rhinitis Nasal peak flows can be assessed.

Examples of tracings

Development of an expert system for interpretation of PEF by Burge PS and coworkers * Two methods for assessing PEF: 1.Visual examination by experts: satisfactory within- and between- observers’ reproducibility 2. Interpretation by discriminant analysis (OASYS) * Burge PS et al. Occup Environ Med 1999; 56:

Pitfalls  Compliance: poor (50%) in asthma and in occupational asthma (Quirce & Chan-Yeung 1995)  Falsification of data : 20% of values are invented  Interpretation of data: visual vs computed- assisted method (OASYS) ?  contamination of results in field studies  variable figures for sensitivity and specificity by comparison with specific inhalation challenges (gold standard)

Girard D et al. Am J Respir Crit Care Med 2004; 170: Girard F et al. Am J Respir Crit Care Med 2004

Conclusion Advantages  assess subjects in a natural setting  simplicity: inexpensive and handy devices  readily available  as a screening test, more to exclude than to confirm the diagnosis Limitations  subject’s motivation and honesty  long monitoring may be necessary  return to work without supervision  interpretation of results

Compatible clinical history and exposure to possible causal agents Skin testing and/or specific IgE assessment (if possible) Assessment of bronchial responsiveness to pharmacologic agents NormalIncreased Subject still at work Subject no longer at work Subject still at work Laboratory challenges with the suspected occupational agent PositiveNegative Consider return to work Workplace or laboratory challenges with the suspected occupational agent, peak expiratory flow monitoring, or both PositiveNegative No asthma Occupational asthma Nonocccupational asthma Chan Yeung M, Malo JL. NEJM 1995; 333:107