Impact of correcting peak flow for nonlinear errors on air pollutant effect estimates from a panel study

[Impact of inaccuracy of peak flowmeters with Wright scale on asthma severity assessment in children]

INTRODUCTION

Measurement of daily variability of peak expiratory flow (PEF) is widely accepted as an objective method to assess asthma severity. Recent investigations have proved nonlinearity of original Wright scale of peak flowmeter. All country members of European Union have been obliged to implement a new scale according to standard EN 13826 since 2005. This study examined whether the correction of PEF values for the inaccuracy of the scale would affect asthma management based on their daily variability.

MATERIAL AND METHODS

We analyzed PEF values (2352) in 34 children, aged 5-16, during 3-5 weeks of monitoring in order to establish the diagnosis of asthma by using peak flowmeters with Write scale. The correction of measured values for inaccuracy was managed with original Dr. M. Miller's predictive equation. The daily variability of PEF (amplitude percent mean) up to 20% was considered as "normal", 20-29.9% as "raised", and 30% and above as "high ". The assessment of daily variability was performed before and after correction.

RESULTS

There was no significant change in the number of days with airway lability as regarding the assessed whole study group (p = 0.475). However, 22 (64.7%) of children had at least one false clinical message about daily variability during the monitoring. It was overestimated in 12 (7%) days in younger (6.6 +/- 0.8 years) or of shorter stature (122.6 +/- 3.6 cm) and underestimated in 13 (4%) days in older (11.1 +/- 2.7) or taller ones (150.9 +/- 12.5 cm) (p < 0.001).

CONCLUSION

Usage of peak flowmeters with Wright scale may lead to an error in asthma severity assessment based on daily variability of PEF. It may cause overtreatment or undertreatment of asthmatic children.

[Effects of nonlinear error correction of measurements obtained by peak flowmeter using the Wright Scale to assess asthma attack severity in children]

INTRODUCTION

Monitoring of peak expiratory flow (PEF) is recommended in numerous guidelines for management of asthma. Improvements in calibration methods have demonstrated the inaccuracy of original Wright scale of peak flowmeter. A new standard, EN 13826 that was applied to peak flowmeter was adopted on 1st September 2004 by some European countries. Correction of PEF readings obtained with old type devices for measurement is possible by Dr M. Miller's original predictive equation.

OBJECTIVE

Assessment of PEF correction effect on the interpretation of measurement results and management decisions.

METHOD

In children with intermittent (35) or stable persistent asthma (75) aged 6-16 years, there were performed 8393 measurements of PEF by Vitalograph normal-range peak flowmeter with traditional Wright scale. Readings were expressed as percentage of individual best values (PB) before and after correction. The effect of correction was analysed based on The British Thoracic Society guidelines for asthma attack treatment.

RESULTS

In general, correction reduced the values of PEF (p < 0.01). The highest mean percentage error (20.70%) in the measured values was found in the subgroup in which PB ranged between 250 and 350 l/min. Nevertheless, the interpretation of PEF after the correction in this subgroup changed in only 2.41% of measurements. The lowest mean percentage error (15.72%), and, at the same time, the highest effect of correction on measurement results interpretation (in 22.65% readings) were in children with PB above 450 l/min. In 73 (66.37%) subjects, the correction changed the clinical interpretation of some values of PEF after correction. In 13 (11.8%) patients, some corrected values indicated the absence or a milder degree of airflow obstruction. In 27 (24.54%) children, more than 10%, and in 12 (10.93%), more than 20% of the corrected readings indicated a severe degree of asthma exacerbation that needed more aggressive treatment.

CONCLUSION

Correction of PEF values obtained by peak flowmeters with traditional Wright scale shows a possibility of overtreatment in younger or short stature children and undertreatment in older or taller ones if we use old type of metres. The correction of peak flowmeter for non-linear error is a prerequisite in the application of asthma guidelines in PEF measurements.

Effects of daily variation in outdoor particulates and ambient acid species in normal and asthmatic children

BACKGROUND

Evidence suggests that the respiratory health of children may be adversely affected by daily variation in outdoor pollutants, particularly ozone and particulates. However, data from the UK are sparse and the contribution of different particulate fractions and acid species, together with the identification of those individuals most at risk, are not clear.

METHODS

One hundred and sixty two 9 year old children were enrolled from two inner city locations and recorded daily symptoms and twice daily peak expiratory flow (PEF) over 8 week periods in the winter and summer. Their results were analysed with daily pollutant levels at appropriate lags using regression models which corrected for trends, weather, pollen, and autocorrelation.

RESULTS

Pollutant levels were generally low, especially in the summer. Multiple statistically significant associations were noted between health outcomes and pollutant concentrations, but no consistent patterns in identified effects were apparent between pollutants, lags, direction of observed effect, or location. There was no evidence to suggest that subgroups with atopy or pre-existing wheeze are more sensitive to pollutant effects.

CONCLUSION

These data do not suggest that adverse health outcomes are associated with daily variations in pollutants [corrected]. No evidence was found to indicate that particulates or individual acid and anion species are more closely related to adverse health outcomes than other pollutants.