849
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849
L/min
0
%
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The Peak Expiratory Flow (PEF) Calculator estimates predicted peak flow based on age, sex, and height, and classifies measured PEF using the traffic light zone system for asthma management. PEF represents the maximum airflow velocity during a forced expiration, reflecting large airway caliber and respiratory muscle effort. It is the most widely used home monitoring tool for asthma self-management.
Predicted PEF values are derived from population-based regression equations. For males: PEF = (Height_cm x 5.48) + 1.58 - (Age x 3.18) L/min. For females: PEF = (Height_cm x 3.72) + 2.24 - (Age x 2.84) L/min. These equations are based on the EU Scale/EN 13826 standard and provide reference values for Caucasian adults. PEF increases with height (larger lungs) and decreases with age (reduced elastic recoil and respiratory muscle strength).
The traffic light zone system compares measured PEF to predicted (or personal best): Green Zone (80-100%) indicates good asthma control with normal airflow, continue current medications. Yellow Zone (50-80%) indicates caution with reduced airflow suggesting airway narrowing, increase reliever use and consider step-up therapy. Red Zone (below 50%) indicates a medical alert with significant airway obstruction requiring immediate bronchodilator use and possible emergency care.
Personal best PEF, established over a 2-3 week period of optimal control, is more accurate than predicted PEF for individual monitoring because of wide normal variation (up to 20-30% between individuals of similar demographics). Asthma action plans should ideally use personal best rather than predicted values for zone boundaries.
PEF monitoring is most valuable for detecting early deterioration before symptoms worsen, assessing response to treatment changes, identifying triggers through PEF diaries, guiding medication adjustments per written asthma action plans, and monitoring during acute exacerbations. Diurnal PEF variability greater than 20% suggests poorly controlled asthma or occupational exposure.
Technique matters: stand upright, take a deep breath, seal lips around mouthpiece, blow as hard and fast as possible. Take three measurements and record the highest. Common errors include inadequate effort, air leak around mouthpiece, coughing during maneuver, and incorrect device zero-point calibration.
Predicted PEF from regression equations based on age, sex, and height. Zone system: Green (80-100%), Yellow (50-80%), Red (<50%) of predicted or personal best.
Green: well controlled, continue therapy. Yellow: caution, airway narrowing, adjust medications. Red: emergency, significant obstruction, use bronchodilator and seek care. Track trends over time.
Inputs
Results
Measured 580 vs predicted 566 = 102%, green zone = well controlled.
Inputs
Results
67% of predicted = yellow zone, indicates airway narrowing.
Maximum airflow speed during forced expiration, measured in L/min. Reflects large airway caliber and is used for asthma monitoring.
Twice daily (morning and evening) when establishing baseline or during flares. Once daily or as-needed when well controlled.
Green (80-100%): good. Yellow (50-80%): caution, adjust treatment. Red (<50%): emergency, use rescue inhaler and seek medical help.
Personal best is more accurate for individual monitoring. Use predicted only when personal best has not been established.
PEF is typically lowest in early morning and highest in afternoon. Diurnal variation greater than 20% suggests poor asthma control.
No, PEF reflects only large airway function. Spirometry (FEV1, FVC) provides comprehensive assessment of airflow limitation.
COPD, vocal cord dysfunction, respiratory muscle weakness, effort, posture, altitude, and incorrect technique.
Record PEF twice daily for 2-3 weeks during optimal asthma control. The highest reliable reading is personal best.
Yes, equations vary by population. These use EU/EN 13826 standards. Separate equations exist for African American and Asian populations.
Red zone (PEF below 50%), no improvement after rescue inhaler, difficulty speaking, severe shortness of breath, cyanosis.
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