Measurement Variability of Peak Flow: A Laboratory Experiment Comparing Cough Testing Equipment
James C. Borders, James A. CurtisPurpose:
Cough peak flow is an important indicator of airway protection, and accurate measurement is essential for evaluating and treating individuals with hypotussic cough dysfunction. Although pneumotachographs are the gold standard for airflow measurement, their cost and complexity limit clinical feasibility. Handheld analog and digital peak flow meters (PFMs) offer practical, low-cost alternatives for measuring cough peak flow; however, measurement accuracy may vary with additional components such as bacterial filters, facemasks, and nebulizing chambers.
Method:
This laboratory-based study systematically evaluated the impact of equipment configuration on peak airflow measurement. A motorized air pump generated controlled airflow into cough testing equipment across a range of airflow resistance levels (80–420 L/min). Peak airflow was recorded for three devices (analog PFM, digital PFM, pneumotachograph) across eight unique configurations of facemasks, filters, and nebulizing chambers. Generalized additive multilevel models estimated nonlinear effects of equipment configuration and resistance level on airflow.
Results:
Facemasks alone introduced the greatest measurement error (up to 56%), while filters and nebulizing chambers had minimal effects. The pneumotachograph consistently measured airflow readings across all airflow resistance levels, whereas analog PFMs were unable to detect low airflow. Analog PFMs underestimated airflow by up to 50% compared to the pneumotachograph, whereas the digital PFMs closely approximated pneumotachograph readings.
Conclusions:
Analog PFMs and facemask attachments substantially reduced measurement accuracy, while digital PFMs without attachments provided reliable estimates comparable to pneumotachographs. Clinicians and researchers should standardize equipment configurations and recognize that analog PFMs with or without additional attachments may introduce considerable measurement error.
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