Respirator inspiratory resistance can affect performance times, especially when the experiment is optimized to elicit respiratory stress. Twelve subjects performed on a treadmill at constant speeds and grades chosen to result in performance times of 5-15 min. Six levels of inspiratory resistance were used, ranging from 0.78 to 7.64 cm H2O.sec/L. The results showed that performance times decrease linearly with resistance level, and no threshold resistance value is apparent. Inspiratory resistance also induces hypoventilation, with lower minute volumes and lower oxygen consumption values at higher resistances. These trends are also linear. From these results, there is no value for inspiratory resistance that can be given as a design goal. Other parameters such as weight and space may dictate filter resistance values, and these, in turn, will lead to determined performance degradations.
Respirator inspiratory and expiratory breathing resistances impact ventilation and performance when studied independently. However, it is less clear as to how various combinations of inhalation and exhalation resistance affect user performance. The present study investigated the performance of 11 individuals during constant load, demanding work to exhaustion while wearing respirators with eight different combinations of inhalation and exhalation resistance. Exercise performance time, performance rating, minute volume, and peak inspiratory and expiratory airflow were recorded at the end of each test trial, and independent correlations with inhalation resistance and exhalation resistance were assessed. The combined impacts of respirator inhalation and exhalation resistances were quantified as the total external work of breathing (WOB(tot)) and correlations between the test variables and WOB(tot) were also examined. Significantly linear decreases in performance were found with increased inhalation resistances independent of exhalation resistance (R(2) = 0.99; p < 0.001) and with increased WOB(tot) (R(2) = 0.92; p < 0.001). Performance also decreased with increased exhalation resistance but no significant relationships were found. Minute volume decreased linearly with increased inhalation resistance independent of exhalation resistance (R(2) = 0.99; p < 0.001), but the linear decrease observed between minute volume and WOB(tot) was weak (R(2) = 0.36; p < 0.05). These findings suggest that WOB(tot) serves as a reliable estimate of the combined impacts of respirator inhalation and exhalation resistances on user performance during hard work, but that inhalation resistance alone serves as a better predictor of ventilation during respirator wear.
This study evaluated performance of individuals exercising at a fixed workload and wearing full-facepiece respirators modified to provide expiratory resistances of 0.27, 0.47, 1.81, 4.43, and 12.27 cmH20 x s x L(-1). On five separate occasions, 15 volunteers exercised to voluntary endpoint on a treadmill at fixed speeds and grades chosen to elicit 85% of maximal aerobic capacity for an unencumbered condition. Exercise performance time was recorded at the cessation of each test. Results showed that performance time decreased linearly (R2 = 0.79; p<0.001) with increased resistances, and no threshold value below which expiratory resistance has no impact on performance was found. Average oxygen consumption rates and minute ventilation also decreased linearly with increased expiratory resistances, indicating that increases in expiratory resistance result in a considerable level of hypoventilation. From the perspective of respirator design, the results of this study suggest that the only practical expiratory resistance level limitation is the reduction in performance that will be acceptable to the end users.
Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204. Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information N it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)2 SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION I AVAILABILITY STATEMENTApproved for public release; distribution is unlimited. SUPPLEMENTARY NOTES ABSTRACTTest methods currently used by the National Institute for Occupational Safety and Health (NIOSH) are designed to assure that respirators meet a minimum level of efficacy when tested under standard laboratory protocols. For air-purifying respirators (APRs), the primary performance tests most affected by airflow rate are filter gas-life capacity, particulate filter efficiency, and respirator breathing resistances. Presently, NIOSH measures all three parameters using constant-rate airflow conditions. An analysis of the measured and estimated minute volumes contained in the literature indicated a range from about 8 to 162 L'min' for unencumbered ventilation and work activities that spanned from mild to exhaustive. The mean minute volume of the distribution was 38.5 ± 16.6 L'min-1, and the median was 33.6 L-minin. Based on an empirical relationship between minute volume and peak inspiratory flow (PIF), peak flows between 72 L'min-' and 183 L'min-1 would be expected for the mean minute volume for 38.5 L'min'. The anticipated range of PIF rates for the 9 5 dh percentile minute volume is between 182 L-min-' and 295 L-min-'. The results of this literature review suggest an increase in cyclic flow rates used for respirator certification testing should be considered to better represent ventilation rates found in the workplace. Blank EXECUTIVE SUMMARY Test methods currently used by the National Institute for Occupational Safety and Health (NIOSH) are designed to assure that all respirators of a given type will meet a minimum level of efficacy when tested under standard laboratory protocols. The relevance and adequacy of airflow rates used in respirator certification testing has been a longstanding debate. The concern is that the current test flow rates substantially underestimate real world values, implying that filters certified under existing standards may not provide adequate protection. For qualifying airpurifying respirators (APRs), the primar...
Background: Maximum pressures developed by the respiratory muscles can indicate the health of the respiratory system, help to determine maximum respiratory flow rates, and contribute to respiratory power development. Past measurements of maximum pressures have been found to be inadequate for inclusion in some exercise models involving respiration.
There has been a long-standing debate regarding the adequacy of airflow rates used in respirator certification testing and whether these test flow rates underestimate actual values. This study investigated breath by breath inspiratory peak flow rate, minute ventilation, and instantaneous flow rates of eight young, healthy volunteers walking on a treadmill at 80-85% of maximal aerobic capacity until exhaustion while wearing an air-purifying respirator with one of eight combinations of inhalation and exhalation resistance. An analysis of variance was performed to identify differences among the eight conditions. Scheffe's post hoc analysis indicated which means differed. The group of conditions with the highest average value for each parameter was identified and considered to represent a worst-case scenario. Data was reported for these conditions. A Gaussian distribution was fit to the data and the 99.9% probability levels determined. The 99.9% probability level for the peak and instantaneous flow rates were 374 L/min and 336 L/min, respectively. The minute ventilation distribution was not Gaussian. Less than 1% of the recorded minute ventilations exceeded 135 L/min. Instantaneous flow rates exceeded the National Institute for Occupational Safety and Health's respirator test standards of 64, 85, and 100 L/min constant flow 91%, 87%, and 82% of the time, respectively. The recorded minute ventilations exceeded the 40 L/min minute ventilation test standard (for tests with a sinusoidal flow pattern) 100% of the time. This study showed that young, healthy respirator wearers generated peak flow rates, minute ventilations, and instantaneous flow rates that consistently exceeded current test standards. Their flow rates should be higher than those of a respirator wearer performing occupational work and could be considered upper limits. Testing respirators and respirator cartridges using a sinusoidal breathing pattern with a minute ventilation of 135 L/min (peak flow rate approximately 424 L/min) would encompass 99% of the recorded minute ventilations and 99.9% of the predicted peak and instantaneous flow rates from this study and would more accurately reflect human respiration during strenuous exercise.
The accumulation of sweat inside a full-facepiece respirator mask and the rise in facial skin temperature can be important factors for acceptability of respirators worn in the heat. This study questioned how much sweat would have to be removed from a respirator (if a design to remove accumulated sweat were possible). Results from 20 subjects sitting in a warm, humid environment (35 degrees C and 90% relative humidity) for 90 minutes indicated that the average value was about 0.203 g sweat/min from the face, head, and neck, with most of that coming from the neck region. Men were found to have higher sweating rates than women. The results indicate that a large amount of sweat could accumulate inside the mask over a typical 8-hour day. Average facial skin temperature was found to rise about 2 degrees C over the 90-minutes test, and this rise could likely be the cause of the very uncomfortable rating given to the respirator.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.