Development of a Small Portable Device for Measuring Respiratory System Resistance Based on Forced Oscillation Technique

Abstract

Spirometry and forced oscillation technique (FOT) are two different methods that are currently used for lung function test. However, the former requires patient’s effort to cooperate, thus is often unreliable for certain patients such as the young children and the latter is always related to bulky and expensive machines. In order to overcome the limitations of current device, we developed a portable prototype of FOT device for measuring respiratory resistance. The device consisted of a small advanced voice coil actuator to generate sinusoidal oscillatory airflow with amplitude of 2.5 cmH₂O and frequency of 5 Hz, which was then superimposed onto the normal breathing airflow of the patient via a mouth piece. The pressure and flow signals of the respiratory airflow after absorption and refraction by the airways and the lung tissues were detected and acquired using NI USB-6211 data acquisition card and synchronous sampling pressure and flow sensors. After the upper computer received the digital signals that the capture card converted, the signals were processed and analyzed in real-time by the proprietary LabVIEW-based software. The analysis included digital signal filtering and impedance calculation in frequency domain, resulting in respiratory system resistance (Rrs) and reactance (Xrs). The results of present experiments on healthy volunteers demonstrated that the device could measure the respiratory system resistance with good reliability and accuracy. Importantly, due to both the hardware and software design the weight and volume of this device was reduced down to 3.5kg and 2500 cm³, respectively, proving the prototype to be worth of further developing into an inexpensive and portable tool for testing or monitoring lung function at rural community clinics or homes.