Design and Analysis of Breath Collection System for Rapid Analysis of Breath Condensate

Abstract

Introduction Breath analysis has attracted a lot of interest as a less-invasive method for health diagnostics and the detection of biomarker for various illnesses. A number of research studies have examined miniaturization of the sensing devices to achieve portability and lower the cost so that point of care application can be considered [1]. However, one major issue in breath analysis is that the breath sample needs some preconditioning before sensing can be carried out. Specifically, the water droplets and water vapor fraction should be separated from the volatile organic compounds. [2]. For that reason, a miniaturized water vapor and suspended droplet extraction device would be useful for a portable breath analysis system. The device must be able to provide a dry breath sample gas at the outlet as well as collecting the extracted condensate which contains biomarkers for diseases [3]. In this paper, a serpentine-type mini channel [4] is proposed as miniaturized water vapor extraction device. An analytical model is developed to obtain the height, width, and length values of the channel that is sufficient to remove moisture content in exhaled breath as it is cooled by using thermoelectric element. Method An analytical mathematical model is developed to calculate the optimized channel dimensions with design objectives of maximum condensing water vapor, minimum overall space, and minimum pressure drop. Based on calculation, the geometrical dimensions of 3 x 0.5 x 30 mm (width x height x length) are selected. The mini channel is made of serpentine-patterned aluminum sheet and a lid made of PMMA (Figure 1a). The aluminum sheet and PMMA are hermetically bonded by using cyanoacrylate adhesive. To verify the calculated outlet temperature and water vapor concentration of breath flow as well as liquid collection rate of the device, an experiment using artificial breath flow is conducted with the setup as shown schematically in figure 1a. An artificial breath flow is generated by pumping ambient air at 0.06 L/s using a mini diaphragm pump (SparkFun Electronics RP 10398) through a water bubbler heated with a strip heater (HT640). It generates a humid air with RH 100% and temperature varied from 27-38oC in the mini channel inlet. The mini channel is cooled by a thermoelectric (Peltier) element (CP85438 40x40 mm) to a cold side temperature of 16oC. At the inlet and outlet side of the mini channel, a DHT22 sensor is attached to measure temperature and humidity value at both ends. Results and Conclusions Figure 1b and 1c shows the plot of temperature and water molecule concentration at the inlet and outlet side of the channel. Based on the result, the calculated temperature and water vapor concentration values have a good agreement with the measured values with margin of error ±10%. With the thermoelectric element cooled up to 16 oC, a moisture removal efficiency of 69.5% is achieved. In this case, the steady state liquid collection rate is 2 x 10-3 ml/s. It produces gas phase breath sample with RH 58% at room temperature (25 oC). Using the same model, calculation is further carried to obtain that theoretical removal efficiency of 90% can be achieved by cooling down the Peltier element to 0oC. In this case, the steady state liquid collection rate is 2.4 x 10-3 ml/s, and the device will produce gas phase breath sample with RH 18% at room temperature.