(PEFR) the maximum rate at which a person can forcibly expel air from the lungs at any time, expressed usually in litres per minute (occasionally in litres per second). A low value can help diagnose asthma in the correct clinical context, and differences between the morning and evening values can also be a feature of poor control of asthma. There is a place for PEFR in the monitoring of acute exacerbations of chronic pulmonary obstructive disease (COPD) but not in the diagnosis of COPD.... peak expiratory flow rate
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