Design method of a bidirectional flow meter for a metered dose inhaler

Area of Science:

• Biomedical Engineering
• Respiratory Device Technology
• Fluid Dynamics

Background:

• Accurate airflow measurement in metered-dose inhalers (MDIs) is crucial for drug deposition and efficacy.
• Existing devices struggle to capture both low inhalation and high exhalation flow rates.
• Understanding patient-specific respiratory waveforms requires precise bidirectional flow measurement.

Purpose of the Study:

• To design and validate a bidirectional flow meter for MDIs.
• To accurately measure airflow across a wide dynamic range (0-150 L/min inhalation, up to 700 L/min exhalation).
• To enable quantification of patient-specific respiratory waveforms.

Main Methods:

• Utilized numerical simulations to analyze complex flow physics.
• Conducted physical measurements to assess geometric parameter influence (width, height).
• Developed a flow element with minimal added resistance.

Main Results:

• Established a predictable quadratic relationship between pressure drop and flow rate.
• Exhalation measurement sensitivity to flow element height was identified.
• Inhalation measurement demonstrated robustness against minor geometric variations.
• Validated flow meter with minimal resistance.

Conclusions:

• The designed bidirectional flow meter accurately quantifies inhalation and exhalation airflow.
• This technology supports improved drug deposition studies and efficacy assessment for MDIs.
• Patient-specific respiratory waveform analysis is now feasible with this device.