Modeling the Pulmonary Effects of Respiratory Protective Masks During Physical Activity

Abstract

Current respirator design involves developing and testing a prototype, making modifications, and then re-testing until a suitable mask is obtained. If the physiological effects of the respirator could be modeled, design could proceed more rapidly. Such a model would be an important design tool that would provide valuable information on the potential physiological and psychological compatibility of a respirator with the wearer. The model would not eliminate the need for human testing, but would decrease the number of prototypes required, saving time and money. A successful model would be very complex because of the many factors to consider. And, because of the variability of human response to exercise, work, and respirator wear, the initial development of the model will include many assumptions that may limit the expected accuracy of the predictions. The goal of this research was to develop a model of the pulmonary effects of respirator wear during physical activity that would form the framework of a larger model that would include other factors as well. Empirical equations were developed that related oxygen consumption to physiological work rate, anaerobic threshold, minute ventilation and tidal volume to oxygen consumption, and exhalation time to respiratory period. Respirator resistance and dead volume effects were quantified. The model was implemented in Visual BASIC. The model predicted oxygen consumption, minute ventilation, and tidal volume well for a limited number of subjects exercising below 70% of maximal oxygen consumption. For three subjects wearing respirators and exercising at 80-85%, the errors in the model parameters were greater than those of the original equations. As model equations were based on average responses, predictions for any one individual may have large errors. Model simulations of a subject exercising at five different work rates with and without a respirator showed that the model made rational predictions of the effects of a respirator on respiratory parameters. More data is needed to completely validate the model. These results showed that the model structure was valid and that overall the model was capable of making rational predictions of the average effects of respirator wear on pulmonary system parameters during physical activity.