the following formula: The reverse calculation is: Where is the value in the Wright scale. These formulas have also been trended over time in both rural and metropolitan areas both as air quality studies and as studies on asthma due to the Peak Flow measurement's accuracy as a predictor of mortality and poor prognosis. Measurement Measurements may be based on 1 second or less but are usually reported as a volume per minute. Electronic devices will sample the flow and multiply the sample volume(Litres) by 60, divided by the sample time(seconds) for a result measured in L/minute : The highest of three readings is used as the recorded value of the Peak Expiratory Flow Rate. It may be plotted out on graph paper charts together with a record of symptoms or using peak flow charting software. This allows patients to self-monitor and pass information back to their doctor or nurse. Peak flow readings are often classified into 3 zones of measurement according to the American Lung Association; green, yellow, and red. Doctors and health practitioners can develop an asthma management plan based on the green-yellow-red zones. History The measurement of peak expiratory flow was pioneered by Martin Wright, who produced the first meter specifically designed to measure this index of lung function. Since the original design of instrument was introduced in the late 1950s, and the subsequent development of a more portable, lower cost version (the "Mini-Wright" peak flow meter), other designs and copies have become available across the world. See also Asthma Chronic obstructive pulmonary disease (COPD) Metered-dose inhaler Respiratory monitoring Salbutamol Spirometry References External links National Asthma Council of Australia Estimated Peak Expiratory Flow Calculator American inventions Flow meters Medical equipment Respiratory therapy Asthma