| Summary: | 碩士 === 國立臺灣大學 === 職業醫學與工業衛生研究所 === 98 === Coughing and sneezing, as shown in previous studies, are important ways of generating aerosols, and therefore, common route to spread respiratory diseases. Both coughing and sneezing are audible and visible to alert people nearby. In this work, the mechanisms and characteristics of aerosol emission from “silent” breathing were experimentally investigated and validated.
An Exhaled Breath Aerosol Monitoring System, composed of a pneumotachograph, a condensation particle counter (or an optical counter with sizing capability) and an aerosol-free chamber with flow rate over 200 L/min, was the backbone of the experimental system set-up. The subject(s) were asked to respire through a mouth piece and the home-made pneumotachograph connected the aerosol-free chamber. In order to monitor the aerosol concentration during inhalation and exhalation , a condensation particle counter (and/or an aerosol size spectrometer) with sampling rate at least 10 Hz was connected to the T-shape adaptor between the mouth piece and the pneumotachograph. A nose clip was used to force the respiration through mouth only. Subjects were asked to perform a variety of breathing patterns generated by a cylinder-piston type breathing simulator, in order to study the breathing pattern dependency.
Among the aerosol instrument tested, Welas 2000H and TSI CPC 3025 had the shortest response time. The Welas has the advantage of providing sizing information of the exhaled breath aerosols. Condensation particle counter needs to be used when the aerosol size is smaller than the lower detection limit of Welas. From monitoring data of exhaled breath of a voluntary male subject, we found that under sedentary condition (low tidal volume, low breathing frequency), the aerosol concentration of the exhaled breath decreased from near room air down to zero after several breaths. Therefore, the subject was hooded with humidified (RH 70%) aerosol-free air to speed up the test process. The aerosol generation rate increased with increasing tidal volume but decrease with increasing frequency. For the same tidal volume, exhaled breath aerosol concentration decreased with increasing breathing frequency, indicating that portion of the exhaled breath aerosols were deposited due to inertial impaction.
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