Controlled Human Inhalation-Exposure Studies at EPA (2017) / Chapter Skim
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The committee also was asked to assess health risks to study subjects who had participated in recent EPA CHIE studies. And the committee was asked, if it supported the continued conduct of such studies, to provide further guidance on methods for estimating risks posed to study subjects and on characterizing reasonably foreseeable risks when seeking consent from people to participate in CHIE studies.2 1 In this context, controlled refers to the aspect of experimental design intended to minimize the effects of factors other than the exposure conditions (that is, the type of pollutant, concentration, and duration)
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VALUE OF CONTROLLED HUMAN INHALATION-EXPOSURE STUDIES The committee assessed the value of past CHIE studies by considering their scientific contributions and the societal benefit of providing a basis for NAAQS decisions. The Clean Air Act requires that EPA periodically review each of the NAAQS by evaluating the most recent evidence and uncertainties and then deciding whether the existing NAAQS are adequate to protect public health with an adequate margin of safety and whether they should be retained or revised in the light of new information.
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Although the EPA CHIE study design generally precludes inclusion of subjects who have serious health conditions, the studies have helped to define an adequate margin of safety, as required in the Clean Air Act, and have begun to define the groups that have substantial risk factors associated with air-pollution exposures, including people who have heart or pulmonary disease and people of low socioeconomic status. CHIE studies of O3 have been of critical importance for the NAAQS by providing a number of advances, including A basis for EPA's decision to move from a 1-hour to an 8-hour averaging time for the O3 NAAQS level (concentration)
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Risks of adverse events temporally associated with a subject's participation in a CHIE study might be affected by one or more of the following: Air-pollutant exposures occurring independently of the study several days before or during the multiday experiment, Intended pollutant exposures during the experiments, Subjects' preexisting medical conditions or sensitivities to study pollutants, Other experimental procedures during the study (such as blood sampling or bronchoscopy) , and Pathophysiologic events (such as a serious adverse cardiac or pulmonary event)
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To examine biologic responses to exposure to concentrated ambient ultrafine particles exposure in patients who have metabolic syndrome, a collection of risk factors (such as high blood pressure) that increase the likelihood of developing cardiovascular disease or type-2 diabetes mellitus.
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Selection of Study Subjects In using CHIE studies to assess biologic plausibility of a pollutant-related effect or sensitivity to pollutant exposures, involvement of study subjects from groups with stable chronic conditions hypothesized to exhibit increased biomarker responses or physiologic effects of pollution (but not adverse events) might be more informative than involvement of healthy young adults.
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EPA should convene an external scientific advisory committee of experts on a regular basis to review the agency's progress and provide advice on the creation of a portfolio of CHIE studies with the objectives of breaking new scientific ground relevant to Clean Air Act mandates and ensuring protection of human subjects. CHARACTERIZING RISKS TO SUBJECTS IN FUTURE STUDIES Health risks to participants cannot be assumed to be the same for each CHIE study.
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In considering chronic effects, 2–4 hours of participation in a CHIE study would add only incrementally to the cumulative ambient background exposure over the life of a person, and calculating a risk estimate would involve so much uncertainty that the estimate would have little meaning. Therefore, the committee strongly prefers the use of an ESC approach for the characterization of risks related to participation in a CHIE study.
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EPA should Provide accumulated information on the occurrence of serious adverse events associated with previous CHIE studies and on the resolution of the events to illustrate that a study in volves risks of serious adverse events that can be anticipated and those that cannot be antic ipated; Describe uniformly the risks from experimental procedures that are used often (such as bronchoscopy) and indicate how the risk profile of study subjects (such as mild asthmatic)
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only when a CHIE study is expected to provide additional knowledge that informs policy decisions and regulation of pollutants that cannot be obtained by other means and (2) when it is reasonably foreseeable that the risks for study participants will not exceed transient and reversible biomarker or physiologic responses.
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