Wood smoke pollution is a common problem across the world, including in the US. This wood smoke comes from people using wood to heat and cook, as well as from wildfires. Woodsmoke (WS) derived from wildland fires account for a significant fraction of ambient air pollution, including particulate matter (PM) and volatile organic compounds (VOCs) in the gaseous phase. It remains unclear whether the gaseous fraction of woodsmoke contributes to acute or chronic health effects. The present study is designed to test whether the gaseous fraction of woodsmoke, volatile organic compounds, produce acute cardiac, respiratory, and systemic inflammatory health effects after controlled exposure to woodsmoke in health, young volunteers. Results from this study will also increase understanding of how wood smoke exposure adversely affects the functioning of the human cardiovascular and respiratory systems. This understanding may be especially important for patients with cardiopulmonary diseases.
Study design Volunteers will participate in two exposure sessions. Each exposure session will be 2 hours in duration and will take place in a specialized exposure chamber. Woodsmoke (WS) will be generated by smoldering untreated oak and diluting the resulting WS emissions with clean air to achieve a target concentration of WS in the exposure chamber at an average of approximately 500 μg/m3 for the 2-hour exposure period. During the exposure, participants will exercise intermittently using a stationary bicycle with rest periods (i.e., 4 x 15 minutes on, 4 x 15 minutes off). The workload on the bicycle will be pre-determined on the training day to produce a minute ventilation rate of approximately 25 L/min/m2, which is considered a moderate level of exercise. During the exposure, fluctuations in the WS concentration will be corrected by controlling the flow of dilution air. The concentrations of carbon monoxide and nitrogen oxides will be monitored continuously to maintain the safety of the atmosphere.
During each exposure session, participants will wear a modified MaxAIR controlled air pressure respirator (CAPR) manufactured by Syntech International (BMD), Irvine, CA, USA, that will deliver filtered woodsmoke directly to the participant. The MaxAIR CAPR is a NIOSH approved (TC 21C-1050) powered air purifying respirator used for infectious disease control in laboratory and medical settings. The CAPR is a commercially available, integrated helmet system that delivers filtered air directly to the participant's breathing zone. A flexible lens (shield) with a thin film cuff is attached to the front of the helmet. The thin filament is pulled under the participant's chin to ensure that breathing space is enclosed but not sealed. This allows air to "leak" around the cuffs margin using positive pressure generated by the internal air pump.
In the modified MAXAIR CAPR used during this study's exposure sessions, an external pump and different filtering media will be added to remove volatile organic compounds and/or particulate matter from the woodsmoke being delivered to the breathing space. The flow rate generated will be significantly higher than the participant's maximum peak inspiratory flow to ensure a positive pressure is maintained during the entire two-hour exposure session. Additional safety monitoring enhancements, notably a pressure sensor at the interface of the tubing bundle and pump heads, have been added to ensure that the pump maintains a constant flow and pressure as it delivers filtered woodsmoke to the volunteer's breathing zone.
During one of the exposures, virtually all particulate matter (PM) and volatile organic compounds (VOC's) will be removed using commercially available P100/VOC respirator filters. During the other exposure, only the PM will be removed from the woodsmoke. The participant will be blinded as to what filters are used during each exposure. The flow rate of filtered woodsmoke into the CAPR will be monitored to ensure that it exceeds the respiratory rate and peak inspiration flow of the subject (\>180 lpm). The PM filtering medium used with this respirator will be P100 filters (3M, cat. #: 2097) or equivalent. The PM/VOC filter will consist of 3M cartridge (60925 or equivalent). A follow-up visit will be scheduled approximately 24 hr after each exposure during which bronchoalveolar lavage and NELF procedures will be performed (as described below).
