The prevalence of reversible airways obstruction has been assessed in children in three areas in Zimbabwe-northern Harare (high socioeconomic class urban children), southern Harare (low socioeconomic class urban children), and Wedza Communal Land (rural children from peasant families). Peak expiratory flow (PEF) was measured before and after six minutes' free running in 2055 Zimbabwean primary school children aged 7-9 years. Height and weight were measured and nutritional state expressed as a percentage of the 50th centile for age (Tanner-Whitehouse standards). Reversible airways obstruction was deemed to be present when peak expiratory flow was below the 2-5th centile for height before exercise and rose by more than 15% after inhalation of salbutamol and when it fell by 15% or more after exercise and rose again after salbutamol. The prevalence of reversible airways obstruction was 5-8% (95% confidence interval 4-1-7-5%) in northern Harare (n = 726); 3-1% (1P8-45%) in southern Harare (n = 642), and 0-1% (0-0-0-4%) in Wedza (n = 687). In northern Harare, the only study area in which white children were found, the prevalence of reversible airways obstruction was similar in white (5-3%, 10/188) and black (5 9%, 32/538) children. Indicators of nutritional state also showed no significant differences between white and black children in northern Harare but were lower in southern Harare and lower still in Wedza. Urban living and higher material standards of living appear to be associated with a higher prevalence of reversible airways obstruction in children in Zimbabwe.Childhood asthma is an extremely common problem in industrialised countries and there is evidence that the prevalence may have increased in the last 20 years.`15 Studies from the developing world have shown large variations in asthma prevalence in genetically similar populations living in different environments.' Both lines of evidence suggest that the major determinants of asthma prevalence in any particular population are environmental. Knowledge of different prevalence rates in differing environments should help to guide the design of further studies in an attempt to identify which factors in the environment are relevant to the development of asthma in genetically predisposed individuals.The epidemiological study of asthma is beset by problems of definition,9 and comparison of the results of the various studies is made difficult by differences between the methods of data collection. The measurement of change in peak expiratory flow (PEF) in a free running exercise challenge test, however, is a sensitive method of screening for bronchial hyperreactivity in children'0 and can easily be used to screen large numbers of children.7"' Careful adherence to method within a particular study allows confidence in the significance of differences between groups-The study of Van Niekerk and others7 in South Africa showed the prevalence of exercise induced bronchoconstriction in Xhosa children to be 20 times higher in an urban setting than in a rural setting....

During resting tidal breathing the shape of the expiratory airflow waveform differs with age and respiratory disease. While most studies quantifying these changes report time or volume specific metrics, few have concentrated on waveform shape or area parameters. The aim of this study was to derive and compare the centroid co-ordinates (the geometric centre) of inspiratory and expiratory flow-time and flow-volume waveforms collected from participants with or without COPD. The study does not aim to test the diagnostic potential of these metrics as an age matched control group would be required. Twenty-four participants with COPD and thirteen healthy participants who underwent spirometry had their resting tidal breathing recorded. The flow-time data was analysed using a Monte Carlo simulation to derive the inspiratory and expiratory flow-time and flow-volume centroid for each breath. A comparison of airflow waveforms show that in COPD, the breathing rate is faster (17 ± 4 vs 14 ± 3 min(-1)) and the time to reach peak expiratory flow shorter (0.6 ± 0.2 and 1.0 ± 0.4 s). The expiratory flow-time and flow-volume centroid is left-shifted with the increasing asymmetry of the expired airflow pattern induced by airway obstruction. This study shows that the degree of skew in expiratory airflow waveforms can be quantified using centroids.

Breath analysis in respiratory disease is a non-invasive technique which has the potential to complement or replace current screening and diagnostic techniques without inconvenience or harm to the patient. Recent advances in ion mobility spectrometry (IMS) have allowed exhaled breath to be analysed rapidly, reliably and robustly thereby facilitating larger studies of exhaled breath profiles in clinical environments. Preliminary studies have demonstrated that volatile organic compound (VOC) breath profiles of people with respiratory disease can be distinguished from healthy control groups but there is a need to validate, standardise and ensure comparability between laboratories before real-time breath analysis becomes a clinical reality. It is also important that breath sampling procedures and methodologies are developed in conjunction with clinicians and the practicalities of working within the clinical setting are considered to allow the full diagnostic potential of these techniques to be realised. A protocol is presented, which has been developed over three years and successfully deployed for quickly and accurately collecting breath samples from 323 respiratory patients recruited from 10 different secondary health care clinics.

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