![]() ![]() ![]() ![]() This paper discusses the latest evolution of this approach. The US Environmental Protection Agency's air pollution exposure models have used different methodologies over the years to estimate breathing rates associated with human activities so that reasonable intake dose rate metrics can be obtained as exposed individuals go through their daily life ( Johnson, 1995 McCurdy, 1995). These modifications result in improved modeling of ventilation patterns, and should improve intake dose estimates associated with exposure to airborne environmental contaminants. The relationships between the oxygen deficit and METS limits are nonlinear and are derived from published data on work capacity and oxygen consumption. The method simulates a cumulative oxygen deficit for each individual and uses it to impose appropriate time-dependent reductions in the METS time series and additions for EPOC. A unified method for simultaneously performing these adjustments is developed. In addition, since an individual's capacity for work decreases during extended activity, methods are also required to adjust downward those METS estimates that exceed physiologically realistic limits over time. This effect, which is termed excess post-exercise oxygen consumption (EPOC), requires upward adjustment of the METS estimates that follow high-energy expenditure events, to model subsequent increased ventilation and intake dose rates. However, oxygen consumption remains elevated after a moderate- or high-intensity activity is completed. Activity level is quantified via standardized values of metabolic equivalents of work (METS) for the activity being performed and converted into activity-specific oxygen consumption estimates. Oxygen consumption is dependent on the modeled individual's physical activity level as described in an activity diary. Human exposure and dose models often require a quantification of oxygen consumption for a simulated individual. ![]()
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