Frequency response of variable orifice type peak flow meters: requirements and testing

Area of Science:

• Respiratory Mechanics
• Medical Device Engineering

Background:

• Variable orifice peak flow meters are widely used for monitoring respiratory conditions.
• Their performance under high-frequency flow input, crucial for accurate peak expiratory flow (PEF) measurement, is not well understood.

Purpose of the Study:

• To define and evaluate the dynamic requirements for variable orifice peak flow meters.
• To assess the frequency response of commonly used peak flow meters under simulated physiological conditions.

Main Methods:

• Peak expiratory flow (PEF), rise time (tr), and flow durations above 97.5%, 95%, and 90% PEF were measured in a population sample using a calibrated Fleisch pneumotachograph.
• Three peak flow meters (Mini Wright, Vitalograph, Ferraris) were tested using an explosive decompression calibrator, simulating diverse PEF and tr values across male and female percentiles.

Main Results:

• The 95th percentile PEF values were 597 L/min for females and 894 L/min for males.
• The 5th percentile rise times (tr) were 55 ms for females and 45 ms for males.
• All tested meters showed less than 5% deviation at a peak duration of 10 ms, indicating satisfactory frequency response.

Conclusions:

• Peak expiratory flow (PEF), rise time (tr), and peak duration are suitable metrics for characterizing the dynamic properties of variable orifice meters.
• The Mini Wright, Vitalograph, and Ferraris peak flow meters exhibit adequate frequency response for clinical use in predominantly normal subjects.