Usefulness of monitoring lung function in asthma

Abstract

There is no firm evidence from randomised controlled trials that routine monitoring of lung function improves asthma control in children. Guidelines for management of asthma consistently recommend routine home monitoring of peak expiratory flow (PEF) in each patient. However, changes in PEF poorly reflect changes in asthma activity, PEF diaries are kept very unreliably, and self management programmes including PEF monitoring are no more effective than programmes solely based on education and symptom monitoring. PEF diaries may still be useful in isolated cases of diagnostic uncertainty, in the identification of exacerbating factors, and in the rare case of children perceiving airways obstruction poorly and exacerbating frequently and severely. If a reliable assessment of airways obstruction in asthma is needed, forced expiratory flow-volume curves are the preferred method. Monitoring of hyperresponsiveness and nitric oxide cannot be recommended for routine use at present. Clinical judgement and expiratory flow-volume loops remain the cornerstone of monitoring asthma in secondary care.

Figure 1

Design of the clinical trial needed to test the hypothesis that monitoring of lung function in childhood asthma is useful. Such studies are rare in children, and no such studies have been published showing usefulness of routine lung function monitoring.

Figure 2

Flow-volume curve of a child with asthma, showing the characteristic concave expiratory pattern with markedly reduced mid-expiratory flow rates. The reference values for peak expiratory flow (PEF), mid-expiratory flows at 25%, 50%, and 75% (MEF_25–75) of forced vital capacity (FVC), and the FVC itself are represented by squares, and are connected by a dashed line representing a hypothetical "normal" expiratory flow-volume curve. The FEV₁ can not be read directly from a flow-volume curve because there is no time axis, but the spirometer software will provide it. In this case, the FEV₁ was 71% of the predicted value. Note that despite considerable airways obstruction, PEF is normal.

Figure 3

Asthma severity scores in three groups of asthmatic children, one monitoring symptoms only (dashed line), one monitoring peak expiratory flow (PEF) at home on a daily basis (thin solid line), and one monitoring PEF at home only when symptomatic for one year. Although there was a trend towards a difference in asthma severity between symptom only monitoring and PEF monitoring after three months (p = 0.07) this difference disappeared during further follow up (after Yoos et al²⁴).

Figure 4

Nitric oxide levels in exhaled air (eNO) in asthmatic children, treated for one year with a constant dose of fluticasone (thin line, open squares) or a stepdown schedule with a high starting dose tapering off to a low maintenance dose (thick line, solid circles). Run-in: six week period during which all patients inhaled 200 µg/day fluticasone by dry powder inhaler. No ICS: wash-out period of 2–4 weeks during which no inhaled corticosteroids were used. The results show no effect of the dose of fluticasone on eNO levels. After Visser et al.⁵⁰