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.

This study was designed to determine the reliability of measurements of respiratory volumes obtained with a respiratory inductive plethysmograph (RIP) during exercise. Tidal volumes (VT) from the RIP were compared with simultaneous flowmeter volumes in 8 healthy subjects at 5 incremental work rates of 60, 90, 120, 150, and 180 W during cycling and treadmill exercise. During cycling, average RIP and flowmeter values did not differ significantly at work rates below 180 W for 63% of the subjects. Average RIP and flowmeter VT were similar at work rates below 180 W for 50% of the subjects, and for 83% of the subjects at intensities below 150 W. The variability in these results may be attributed to several factors including RIP calibration errors and slippage of the RIP elastic bands containing the inductive coils. Correlations of breath-by-breath flowmeter and RIP VT were significant for subjects during cycling (R = 0.73, P < 0.05) and treadmill exercise (R = 0.78, P < 0.05). These findings suggest that the RIP should be considered a semi-quantitative method for measurements of tidal volume during exercise with and without respirator wear.

The purpose of this study was to determine the effects of different inspiratory resistances on exercise performance and to describe physiological and subjective responses during constant load work of an intensity that elicits the maximum sensitivity to respiratory factors of respirator wear. Nine subjects (mean age 25.8 +/- 4.8 years) performed exhaustive treadmill exercise during constant load work of 80% of maximal aerobic capacity while inspiring against one of five randomly assigned inspiratory resistance conditions. For inspiratory resistances of 0.20 kPa (R1), 0.29 kPa (R2), 0.39 kPa (R3), and 0.49 kPa (R4), measured at a steady air flow rate of 85 L min-1, average performance times were 84, 75, 54, and 30% of the control condition. Performance time reductions were significant for R3 and R4 trials. Results also indicated a significantly reduced mean respiration rate, minute ventilation, and oxygen ventilatory equivalent (VE/VO2) for the R4 condition at exercise breakpoint compared to control. For resistances R1-R4, mean VE/VO2 were significantly reduced from control by approximately 12, 17, 19, and 31%. At breakpoint, mean ratings of perceived exertion were similar for control, R1, R2, and R3 conditions but were significantly lower for R4 versus control. Breathing comfort did not differ significantly between resistances below the R3 level, but discomfort was significantly greater for conditions R3 and R4. These findings suggest that the impact of the respiratory limitations of respirators can be diminished by employing respirators with inspiratory resistances below the R3 level.

Severe lactic acidosis usually accompanies intense endurance exercise. It has been postulated that glycogen depletion working in concert with elevated muscle and plasma lactate levels lead to a concomitant reduction in pH. Their cumulative effect during prolonged physical exertion now leads to muscular fatigue and eventually limit endurance capacity. Therefore in the present study, dichloroacetate (DCA), a compound which enhances the rate of pyruvate oxidation thus reducing lactate formation, has been evaluated in a validated rat model of sub-maximal exercise performance. Male rats (350 g) were divided into two groups (control-saline, i.v. and DCA 5 mg/kg, i.v.) and were exercised to exhaustion in a chamber (26 degrees C) on a treadmill (11 m/min, 6 degrees incline). When compared to controls, the DCA-treated rats had longer run times (169 vs 101 min) and a decreased heating rate (0.020 vs 0.029 degrees C/min). In addition, DCA attenuated the increase in plasma lactate (28 vs 40 mg/dl) and significantly reduced both the rate and absolute amount of depletion of muscle glycogen stores. These results suggest that the activation of pyruvate dehydrogenase activity by DCA resulted in a reduction in the rate of glycogenolysis in addition to decreasing lactate accumulation by presumably limiting the availability of pyruvate for conversion to lactate, therefore increasing muscle carbohydrate oxidation via the TCA cycle. Thus DCA effected a significant delay in muscle fatigue.

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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.

A study was performed to determine average inhaled carbon dioxide (F(I)CO2) concentrations of multiple respirators using unmanned test methods, and to compare results among test procedures to determine whether they could be used interchangeably. Respirator experiments were performed according to the National Institute for Occupational Safety and Health (NIOSH) (NF(I)CO2), standard European (ENF(I)CO2), and a modified method of the European test (BF(I)CO2) using full-facepiece air-purifying respirators and one air-purifying escape respirator. Bland-Altman statistics for determination of limits of agreement were applied to assess agreement among the various test methods. A considerable lack of agreement was found between NF(I)CO2 and ENF(I)CO2 methods and between BF(I)CO2 and NF(I)CO2 methods for average F(I)CO2. The modified EN136 method produced F(I)CO2 averages about 0.13% to 0.23% above unmodified EN136 values, but the agreement between methods was generally acceptable. These results demonstrate that NIOSH and European unmanned test methods for determining respirator average F(I)CO2 concentrations produce different results for like respirators. However, the findings suggest that the ENF(I)CO2 and BF(I)CO2 unmanned methods could be used interchangeably for quantifying respirator F(I)CO2 concentrations.