Serial assessment of peak expiratory flows

Jean-Luc Malo MD

Chest Physician

Université de Montréal and Hôpital du Sacré-Coeur

and Center for Asthma in the Workplace

Hôpital du Sacré-Cœurde Montréal

Université de Montréal

Axe de rechercheen santé respiratoire

Centre asthme et travailCenter 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

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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 1980. Action plans based on PEF.

In occupational asthma Burge PS et al. 1979 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) andelectronic (storage of data)

Predicted values(as a function of age, sex, heightand racial origin)

Normal valuesIn men: 500 to 700 L/minIn women: 350-500 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 asthmaAcute: essential in ER (FEV1 or PEF) and in

GP officeChronic: Poor perception of airflow limitation

Brittle asthma Discrepancy between symptoms and

need for medication: excludehyperventilation

To identify flare-upsIn occupational asthma

As a screening test : negative tracingand 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 PEFby 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; 56:758-764

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: 845-850Girard 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 historyand exposure to possible causal agents

Skin testing and/orspecific IgE assessment

(if possible)

Assessment of bronchial responsivenessto pharmacologic agents

Normal Increased

Subject stillat work

Subject no longerat work

Subject stillat work

Laboratory challengeswith the suspectedoccupational agent

Positive Negative

Consider return to work

Workplace or laboratory challengeswith the suspected occupational

agent, peak expiratory flowmonitoring, or both

Positive Negative

No asthma Occupational asthma

Nonocccupational asthma

Chan Yeung M, Malo JL. NEJM 1995; 333:107