Drowsiness is considered a potential risk for traffic accidents. Exposure to high carbon dioxide (CO2) levels in vehicles may result in unpleasant feeling, fatigue, drowsiness or lethargy among drivers and passengers. However, little is known about whether reducing CO2 levels in vehicles by air filtration can relieve adverse effects among human subjects during driving. We recruited a panel of 84 healthy participants to drive a vehicle equipped with a CO2 filtration system for 1 h on a coastal road in a Northern Taiwan rural area. The operation modes of the CO2 filtration system, including fresh air from open windows without a CO2 filtration system (Control-mode), fresh air from an air conditioning (AC) system with closed windows and a false CO2 filtration system in operation (Off-mode) or a true CO2 filtration system in operation (On-mode), were examined. The repeated measurements of heart rate (HR), blood pressure (BP), CO2, total volatile organic compounds (TVOCs), particulate matter ≤2.5 μm in aerodynamic diameter (PM2.5) and a simple question about drowsiness were obtained for each participant in three different modes. We found that decreased HR, systolic BP (SBP) and diastolic BP (DBP) and increased drowsiness were associated with increased levels of in-vehicle CO2. The effects of in-vehicle CO2 on adverse effects were highest in the Off-mode during driving. In the On-mode, the participants showed slight decreases in HR, SBP and DBP and slight increases in drowsiness. We concluded that the utilization of a CO2 filtration system can reduce in-vehicle CO2 levels and modify the effect of in-vehicle CO2 on HR, BP and drowsiness among human subjects during driving.
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