Correction for nonlinearity of body flow plethysmograph

Area of Science:

• Pulmonary Function Testing
• Biomedical Engineering
• Respiratory Physiology

Background:

• Conventional flow plethysmography exhibits nonlinearity at high flow rates, particularly during forced expiration.
• Woven screens used as flow elements exhibit nonlinear pressure drop-flow relationships due to viscous and inertial resistance.
• This nonlinearity can lead to inaccuracies in pulmonary function measurements.

Purpose of the Study:

• To propose a modified signal processing technique for pressure-compensated flow plethysmography.
• To correct for the nonlinearity of the flow element at high flow rates.
• To improve the accuracy of thoracic flow measurements during forced expiration.

Main Methods:

• Developed a modified signal processing approach for pressure-compensated flow plethysmography.
• Characterized the nonlinear pressure drop-flow relationship using a second-degree equation.
• Validated the correction method using flow step inputs simulating forced expiration.

Main Results:

• The pressure drop-flow relationship was accurately described by a second-degree equation.
• The proposed correction method was integrated into the computation of the thoracic signal.
• Testing with simulated forced expiration flow demonstrated the necessity of the correction.

Conclusions:

• The modified signal processing effectively corrects for flow element nonlinearity in plethysmography.
• This correction prevents overestimation of thoracic forced vital capacity by up to 0.5 liters.
• The findings enhance the reliability of pulmonary function testing, especially during forced expiration maneuvers.