Alterations in physiological and perceptual variables during exhaustive endurance work while wearing a pressure-demand respirator

The purpose of this investigation was to describe the time course of changes in physiological and perceptual variables during exhaustive endurance work with and without an air-supplied, full-facepiece, pressure-demand respirator. Thirty-eight healthy subjects (24 to 51 years of age) volunteered for this study. Treadmill speed was set at 5.5 kph (3.4 mph) and elevation was set at a level calculated to elicit 70% of a previously determined maximal aerobic capacity (VO2max). Subjects continued at this rate to exhaustion. Despite a constant work rate, VO2 and %VO2max increased during exercise and were significantly greater with the respirator (34.4 +/- 1.1 mL/kg.min; 84% VO2max) than without the respirator (31.9 +/- 1.1 mL/kg.min; 76% VO2max) at the "final" measurement point prior to termination of exercise by each subject. The final values for ventilation volume (VE) also were significantly greater with the respirator (89.2 +/- 3.4 L/min) than without (73.4 +/- 3.7 L/min). At the conclusion of the endurance walk, dyspnea index (VE/MMV.25) remained well below maximal values (with = 58.6 +/- 2%; without = 44.6 +/- 2%; p less than 0.001). Also, at the final period, no significant differences occurred in the subjects' perceptual ratings of work of breathing, yet work performance time was significantly reduced (p less than 0.0001) from 69.1 +/- 4.4 min (without) to 55.6 +/- 3.8 min (with). A significantly greater swing in peak pressure (maximum pressure measured within the facepiece of respirator), however, from inspired (PPi) to expired (PPe) occurred with the respirator (13.42 cmH2O) than without the respirator (9.25 cmH2O).(ABSTRACT TRUNCATED AT 250 WORDS)     

Respirator fit factor performance while sweating

The extent to which sweat accumulation inside respirators affects respirator fit has not been quantified. This study represents an attempt to measure facial sweating and to quantify its effects on fit factors of negative pressure, full-facepiece respirators. Respirator fit factor (FF) data were obtained while 14 subjects completed 30 minutes of treadmill walking at an intensity of 75% of age-predicted maximal heart rate in an aerosol test chamber under ambient environmental conditions. Subject facial and whole body sweat production were also measured. Statistical analysis of the treadmill FF results showed that respirator fit was significantly (p < 0.05) degraded after 14 minutes of exercise. Sweat accumulation inside the respirator facepiece averaged 30.9 +/- 15.5 g. However, no significant correlation of subject facial sweat production with overall FF values measured during exercise was found. The results of this study indicate that respirator FFs degrade significantly over time under moderate exercise and environmental conditions and suggest that facial sweat accumulation alone does not account for the reduced FF levels.     

The physiological cost of wearing a disposable respirator

In order to gain an understanding of the physiological stresses imposed by the wearing of a single-use disposable respirator, a series of experiments was done to measure the cardiopulmonary effects of wearing the respirator (heart rate, respiratory rate, and blood pressure); resistance to breathing while wearing a respirator; and heat stress imposed by the use of a respirator (changes in inspired and expired air temperature). Ten men, ages 24 to 35, of varying fitness levels, served as volunteers in the studies. All the men exercised on a treadmill both with and without 3M Model 8715 disposable respirators. Workloads corresponding to light, moderate, and heavy levels were calculated for each volunteer based on his maximal oxygen uptake. As work intensity increased, an increase in breathing resistance was found. Peak resistances were in the range of +/- 2 cm water. Work-intensity level increases in respiratory rates were found with and without the respirators, but the respirator use trial had a significantly increased respiratory rate. Heart rate also showed a dose-related increase as work intensity increased and was significantly greater in the respirator trials at heavy levels of work and during recovery. Systolic blood pressure showed a biphasic response to respirator use, being significantly lower at rest and higher at high levels of work. Diastolic blood pressure changes were less dramatic but were elevated in the respirator trials. Clinically important increases in blood pressure were found in two volunteers when respirators were worn. Air temperatures immediately anterior to the face were, on average, 7.5 degrees C higher in the respirator trials.(ABSTRACT TRUNCATED AT 250 WORDS)     

Powered air-purifying respirator use in healthcare: Effects on thermal sensations and comfort

Twelve subjects wore an N95 filtering facepiece respirator (N95 FFR), one tight-fitting full facepiece powered air-purifying respirator (PAPR), two loose-fitting PAPRs, and one elastomeric/PAPR hybrid for 1 hr each during treadmill walking at 5.6 km/hr while undergoing physiological and subjective response monitoring. No significant interaction (p ≥ .05) was noted between the five respirators in heart rate, respiratory rate, oxygen saturation, transcutaneous carbon dioxide, and perceptions of breathing effort or discomfort, exertion, facial heat, and overall body heat. Respirator deadspace heat/humidity were significantly greater for the N95 FFR, whereas tympanic forehead skin temperatures were significantly greater for the hybrid PAPR. Temperature of the facial skin covered by the respirator was equivalent for the N95 FFR and hybrid PAPR, and both were significantly higher than for the other three PAPRs. Perception of eye dryness was significantly greater for a tight-fitting full facepiece PAPR than the N95 FFR and hybrid PAPR. At a low-moderate work rate over 1 hr, effects on cardiopulmonary variables, breathing perceptions, and facial and overall body heat perceptions did not differ significantly between the four PAPRs and a N95 FFR, but the tight-fitting, full facepiece PAPR increased perceptions of eye dryness. The two loose-fitting PAPRs and the full facepiece tight-fitting PAPR ameliorated exercise-induced increases in facial temperature, but this did not translate to improved perception of facial heat and overall body heat.     

Parameters that bias the measurement of airborne concentration within a respirator

This paper describes the theoretical basis upon which a test system has been set up to evaluate the sampling error associated with in-facepiece sampling on half-mask respirators. The in-facepiece sampling technique evaluated in this study is the one currently used in the U.S. to conduct quantitative facepiece fit testing. An experimental design was developed to study the sampling bias associated with in-facepiece sampling when selected parameters of the man/respirator system were varied. The results indicated that significant errors can be made in estimating concentration within a respirator when the current in-facepiece sampling technique is employed. Sampling bias was determined when in-facepiece samples were collected only during the inhalation phase of the respiratory cycles. They were found to range from greater than -99% to greater than +98%. The mean sampling bias was -17 +/- 38%. When measured in-facepiece concentrations were used to calculate a fit factor the resulting range was 44 to 4728 even though the actual fit factor was only 87. Based upon the data presented, it was hypothesized that faceseal leakage was streamlining within the respirator cavity. As a result, quantitative facepiece fit data on half-mask respirators may be biased by the large measurement error.     

Effects of respirators under heat/work conditions

Physiological responses and perceived strain of five unacclimatized male subjects were studied. The subjects were exposed to heat during an exercise task and were evaluated while wearing half and full facepiece, cartridge-type, air-purifying respirators, and without a respirator. The exercise consisted of walking on a treadmill for a period of 1 hour in a controlled environmental chamber at each of two different energy expenditure levels (200 and 400 Kcal/hr) (approximately equal to 58 and 116 Watts) and two different heat exposures (air temperatures of 25 degrees C and 43.3 degrees C). The results indicated that wearing a full facepiece respirator imposed significant physiological strain added to that caused by the heat and workloads used in the study. Five of the six physiological measures show this increased physiological strain: heart rate; minute ventilation; oxygen consumption; energy expenditure; and oral temperature. There was no detectable effect on sweat rate. Although subjective ratings indicated more discomfort with increasing physiological strain, the observed correlations between such measures were low (Tb less than .60). The net consequence of the significant effects indicates that workers' tolerance to moderate or higher levels of work under hot conditions while wearing a respirator is reduced. The reduction is more pronounced when wearing a full mask than when wearing a half mask. Changes in respirator design which minimize respiratory dead space are suggested to alleviate this problem. Otherwise, prevention of excessive physiological strain from respirator use when working at moderate or higher levels at hot job sites could necessitate more rest breaks or limiting work time under such conditions.     

Physiological and subjective responses to working in disposable protective coveralls and respirators commonly used by the asbestos abatement industry

The physiological and subjective effects of working with different respirators while wearing lightweight disposable (Tyvek 1412 polyolefin) coveralls commonly used by the asbestos abatement industry were studied. Nine healthy men (mean age = 27.3 yr, weight = 76.9 kg) each performed a series of four exercise tests with four different respirator ensembles in counterbalanced order. Treadmill work was performed at a set walking speed of 4 kph (2.5 mph), 0 percent elevation (220 kcal/hr), a controlled environmental temperature of 33.9 degrees C, and 50% relative humidity. Each test continued up to 120 min, with repeated work/rest intervals of 26 min of work and 4 min of rest. Tyvek disposable coveralls and hoods were worn with each of these four different respirator ensembles: (1) control--a lightweight, low resistance mask; (2) HEPA--an air purifying, full facepiece respirator with dual high efficiency filters; (3) SAR--a supplied-air, pressure-demand respirator with escape filter; (4) SCBA--an open circuit, pressure-demand, self-contained breathing apparatus. Physiological measurements obtained every minute during each test included heart rate and skin and rectal temperatures. Subjective evaluations of clothing, respirator, and facepiece comfort, ease of breathing, temperature and perspiration in the mask and clothing, and respirator load also were measured at the end of the test. Data were analyzed using an analysis of variance. Results indicated that heart rate at the end of the test differed by less than 8 BPM between the control condition and the SCBA (heaviest) condition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of industrial respirator wear during exercise in subjects with restrictive lung disease

Few studies have examined the response of individuals with restrictive lung disease (RLD) to respirator wear. Such information should be of theoretical and practical interest when the need to determine fitness to wear respirators is considered. Seventeen females performed progressive submaximal treadmill exercise. Twelve control subjects with total lung capacity (TLC) = 5.71 +/- .19L (mean +/- SEM) and DLCO = 25.8 +/- 1.0 mL/min/mmHg were compared to five RLD subjects with TLC = 3.70 +/- 0.22 and DLCO = 14.5 +/- 0.7. Mean age, height and weight were similar. Separate exercise trials were performed with no added resistance (NAR), and with 5 cm H2O/L/sec inspiratory and 1.5 cm H2O/L/sec expiratory resistance (R2) to stimulate widely used respiratory masks. Comparisons of exercise data were made at an oxygen consumption of 0.8 L/min. With NAR, RLD subjects had significantly higher minute ventilation (VE) (29.0 vs. 21.2 L/min for controls), higher respiratory rate (RR), and lower tidal volume (VT). Heart rate, end-tidal PCO2 (PETCO2), and mouth pressure swing (Poral) were not different from control values. With R2 compared to NAR, the controls had reduced RR and VE; and increased VT, PETCO2, and Poral. While changes with R2 for the RLD subjects were in the same directions as controls, only the increase in Poral was statistically significant. Analysis of the differences showed that none of the changes with R2 in RLD subjects was different from control changes except for the greater increase in Poral and the smaller increase in VT. The former was explained by the RLD subjects' higher VE and flow rates, and the non-linear nature of R2 at higher flow rates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Filtration performance of NIOSH-approved N95 and P100 filtering facepiece respirators against 4 to 30 nanometer-size nanoparticles

This study investigated the filtration performance of NIOSH-approved N95 and P100 filtering facepiece respirators (FFR) against six different monodisperse silver aerosol particles in the range of 4-30 nm diameter. A particle test system was developed and standardized for measuring the penetration of monodisperse silver particles. For respirator testing, five models of N95 and two models of P100 filtering facepiece respirators were challenged with monodisperse silver aerosol particles of 4, 8, 12, 16, 20, and 30 nm at 85 L/min flow rate and percentage penetrations were measured. Consistent with single-fiber filtration theory, N95 and P100 respirators challenged with silver monodisperse particles showed a decrease in percentage penetration with a decrease in particle diameter down to 4 nm. Penetrations less than 1 particle/30 min for 4-8 nm particles for one P100 respirator model, and 4-12 nm particles for the other P100 model, were observed. Experiments were also carried out with larger than 20 nm monodisperse NaCl particles using a TSI 3160 Fractional Efficiency Tester. NaCl aerosol penetration levels of 20 nm and 30 nm (overlapping sizes) particles were compared with silver aerosols of the same sizes by a three-way ANOVA analysis. A significant (p < 0.001) difference between NaCl and silver aerosol penetration levels was obtained after adjusting for particle sizes and manufacturers. A significant (p = 0.001) interaction with manufacturers indicated the difference in NaCl, and silver aerosol penetrations were not the same across manufacturers. The two aerosols had the same effect across 20 nm and 30 nm sizes as shown by the absence of any significant (p = 0.163) interaction with particle sizes. In the case of P100 FFRs, a significant (p < 0.001) difference between NaCl and silver aerosol (20 nm and 30 nm) penetrations was observed for both respirator models tested. The filtration data for 4-30 nm monodisperse particles supports previous studies that indicate NIOSH-approved air-purifying respirators provide expected levels of filtration protection against nanoparticles.     

Effect of work load and respirator wear on postural stability, heart rate, and perceived exertion

The effects on postural stability (sway) were investigated for different work loads under conditions of wearing a full facepiece respirator and not wearing any respiratory protection device. Fifteen subjects accomplished light (40 W), moderate (85 W), and heavy (125 W) work loads under the two conditions. Measurements of postural sway were made immediately after each load by using a multicomponent, strain gage-type force platform. Changes in each subject's movement pattern of the center of pressure were quantitated and compared to their initial baseline sway tests. Each subject's heart rate and perceived exertion were also recorded during each condition. A statistically significant effect (p = 0.007) caused by work load was observed for total length of sway with or without a respirator. An interaction approaching statistical significance (p = 0.056) between work load and respirator use was found. This indicated that sway increased more quickly and in a more consistently linear fashion with increasing work load under the respirator condition (p = 0.02) compared to the nonrespirator condition. The results from the respirator condition showed linear increases in postural sway length across the entire range of work loads, but sway length in the nonrespirator condition showed an increase only at 125-W work loads. The greater increase in sway during the postural balance test could be attributable to the increasing work load-induced proprioceptive fatigue effect on the nervous system's ability to process signals from proprioception systems incongruent with body sway. The heart rate was significantly higher during respirator wear (an increase in heart rate averaging 5.62 beats/min).(ABSTRACT TRUNCATED AT 250 WORDS)     

Substrate utilization during exercise performed with and without glucose ingestion in female and male endurance trained athletes

Compared to males, females oxidize proportionately more fat and less carbohydrate during endurance exercise performed in the fasted state. This study was designed to test the hypothesis that there may also be gender differences in exogenous carbohydrate (CHOexo) oxidation during exercise. Healthy, young males (n = 7) and females (n = 7) each completed 2 exercise trials (90 min cycle ergometry at 60% VO2peak), 1 week apart. Females were eumenorrheic and were tested in the midfollicular phase of their menstrual cycle. Subjects drank intermittently either 8% CHOexo (1 g glucose x kg x h(-1)) enriched with U-13C glucose or an artificially sweetened placebo during the trial. Whole-body substrate oxidation was determined from RER, urinary urea excretion, and the ratio of 13C:12C in expired gas during the final 60 min of exercise. During the placebo trial, fat oxidation was higher in females then in males (0.42 +/- 0.07 vs 0.32 +/- 0.09 g.min(-1).kg LBM(-1) x 10(2)) at 30 min of exercise (p < .05). When averaged over the final 60 min of exercise, the relative proportions of fat, total carbohydrate, and protein were all similar between groups. During CHOexo ingestion, both the ratio of 13C:12C in expired gas (p < .05) and the proportion of energy derived from CHOexo relative to LBM (p < .05) were higher in females compared to males at 75- and 90-min exercise. When averaged over the final 60 min of exercise, the percentage of CHOexo to the total energy contribution tended to be higher in females (14.3 +/- 1.2%) than in males (11.2 +/- 1.2%; p = .05). Compared to males, females may oxidize a greater relative proportion of CHOexo during endurance exercise which, in turn, may spare more endogenous fuel. Based on these observations, ingested carbohydrate may be a particularly beneficial source of fuel during endurance exercise for females.     

Effects of a low carbohydrate isoenergetic diet on sleep behavior and pulmonary functions in healthy female adult humans

To study the effects of a low carbohydrate, isoenergetic diet on pulmonary physiology and sleep behavior, we measured pulmonary functions and respiratory gas exchange and carried out ambulatory electroencephalographic studies after a week's intake of isoenergetic diet containing only 50 g carbohydrate per day in 6 healthy female adult humans in a free-living condition. Compared with their normal intake, during the week of low carbohydrate intake there was a rise in the level of fasting plasma 3-hydroxybutyrate from 0.12 +/- 0.07 (mean +/- SD) to 1.01 +/- 0.40 mmol/L(P less than 0.01, paired t-test); a fall in serum bicarbonate from 26.2 +/- 0.75 to 25.0 +/- 1.41 mmol/L (P less than 0.05) and in serum chloride from 107 +/- 1.3 to 105 +/- 1.8 mmol/L (P less than 0.05). Serum urea rose from 4.3 +/- 0.71 to 5.7 +/- 0.70 mmol/L (P less than 0.01), and serum uric acid from 0.34 +/- 0.08 to 0.39 +/- 0.10 mmol/L (P less than 0.05). Functional residual capacity was increased from 2.07 +/- 0.35 to 2.26 +/- 0.34 L (P less than 0.01). Respiratory gas exchange ratio fell from 0.81 +/- 0.05 to 0.75 +/- 0.04 (P less than 0.05) and partial pressure of expired carbon dioxide reduced from 22 +/- 3.3 to 21 +/- 3.1 mmHg (P less than 0.05). There was a reduction in endogenous carbon dioxide production and arterial carbon dioxide tension. An analysis of ambulatory electroencephalogram showed that REM latency increased from 66 +/- 8 to 111 +/- 38 min (P less than 0.05), with no significant changes in sleep time and stages. These studies show that a low carbohydrate isoenergetic diet is tolerable, influences sleep behavior, reduces carbon dioxide production and respiratory gas exchange ratio, and may be therapeutically useful in patients with hypercapnic respiratory failure.     

Respiratory protection provided by N95 filtering facepiece respirators against airborne dust and microorganisms in agricultural farms

A new system was used to determine the workplace protection factors (WPF) for dust and bioaerosols in agricultural environments. The field study was performed with a subject wearing an N95 filtering facepiece respirator while performing animal feeding, grain harvesting and unloading, and routine investigation of facilities. As expected, the geometric means (GM) of the WPFs increased with increasing particle size ranging from 21 for 0.7-1 microm particles to 270 for 5-10 microm particles (p < 0.001). The WPF for total culturable fungi (GM = 35) was significantly greater than for total culturable bacteria (GM = 9) (p = 0.01). Among the different microorganism groups, the WPFs of Cladosporium, culturable fungi, and total fungi were significantly correlated with the WPFs of particles of the same sizes. As compared with the WPFs for dust particles, the WPFs for bioaerosols were found more frequently below 10, which is a recommended assigned protection factor (APF) for N95 filtering facepiece respirators. More than 50% of the WPFs for microorganisms (mean aerodynamic diameter < 5 microm) were less than the proposed APF of 10. Even lower WPFs were calculated after correcting for dead space and lung deposition. Thus, the APF of 10 for N95 filtering facepiece respirators seems inadequate against microorganisms (mean aerodynamic size < 5 microm). These results provide useful pilot data to establish guidelines for respiratory protection against airborne dust and microorganisms on agricultural farms. The method is a promising tool for further epidemiological and intervention studies in agricultural and other similar occupational and nonoccupational environments.     

酸奶中活菌对成年男性乳糖吸收不良者乳糖吸收的影响

目的　研究酸奶活性发酵菌对乳糖吸收的影响。方法　 4 5名健康、成年、男性志愿者填写知情同意书后 ,空腹服用 2 0g乳糖的水溶液 ,3h内每 30min收集一次肺末端的呼气样本 ,以任一点的呼气中氢气浓度高于空白基值 30 μmol mol者为乳糖吸收不良者。有 2 4名受试者成为观察对象 ,随机分为 3组 ,每组 8人。受试食品为含乳糖 2 0g的酸奶 (Y)、加热酸奶 (HY)和酸化牛奶 (M)。试验按照随机、双盲、拉丁方的设计原则 ,使三组受试者分别在三个清晨空腹服用三种不同的受试物 ,每 2次试验间隔为 7天。清晨服用受试物后 ,收集 8h内的呼气样本 ,并检测呼气中的氢气浓度。结果　服用酸奶后 ,呼气中的氢气浓度最大峰值显著低于加热酸奶和牛奶 (Y 113 2± 70 2 ,HY 186 5± 96 7,M174 7± 73 9) ,氢气峰值时间显著长于牛奶 (Y 390± 86 ,M 30 5± 10 5 ) ,氢气浓度曲线下面积显著低于加热酸奶和牛奶 (Y 14 90 0 1± 12 2 0 6 2 ,HY 2 7389 5±2 0 4 2 9 8,M 2 5 6 4 8 2± 14 0 6 4 0 )。结论　酸奶中的活性发酵菌可以增加乳糖吸收不良者对乳制品中乳糖的消化吸收     

Correlation between angiographic success and functional improvement assessed by exercise test following percutaneous transluminal coronary angioplasty.

Sixty-one consecutive patients with stable effort angina and single vessel disease underwent successful (reduction of coronary stenoses by greater than or equal to 20%) percutaneous transluminal coronary angioplasty (PTCA). Anatomical results were analysed on the basis of functional evaluation obtained by exercise test (ET) 1 week before (pre-PTCA) and within 1 month after (post-PTCA) PTCA. Total exercise duration and maximal double product significantly increased after PTCA (4.5 +/- 1 min vs 6.9 +/- 1.5 min, p less than 0.001 and 14.1 +/- 3.6 x 1000 mmHg x bpm vs 18 +/- 4.2 x 1000 mmHg x bpm, p less than 0.001). Pre-PTCA ET was positive in 43 patients (70%) and post-PTCA ET in 15 (24%). In patients with post-PTCA positive ET, mean stenosis diameter reduction was significantly lower than that obtained in patients with negative post-PTCA ET (29.6 +/- 8.9% vs 61.1 +/- 18.8%, p less than 0.001). In conclusion, PTCA improved exercise tolerance in the majority of patients with myocardial ischemia, however the definition of anatomical success used in this study appears to be poorly correlated with functional improvement as assessed by ET.     

Inhaled albuterol does not protect against ozone toxicity in nonasthmatic athletes

We evaluated the acute prophylactic efficacy of albuterol aerosol in protecting nonasthmatic athletes from the untoward effects of 0.21 ppm ozone (O3) on symptoms, pulmonary function, exercise performance, and post-exposure histamine bronchoprovocation. Fifteen trained competitive cyclists participated in a randomized crossover study consisting of double-blinded inhalations of albuterol (180 micrograms) and placebo approximately 30 min prior to heavy continuous exercise (minute ventilation, [VE] greater than or equal to 80 L/min) for 60 min, followed by a maximal sprint (peak VE greater than 140 L/min) until exhaustion. Each subject was exposed randomly to either 0.21 ppm O3 or filtered air (FA) during the four single-blinded exposure sessions. Albuterol pretreatment resulted in modest but significant bronchodilation as compared to placebo. However, albuterol did not prevent O3-induced respiratory symptoms, decrements in forced vital capacity (FVC), forced expired volume in one second (FEV1.0), and maximum midexpiratory flow rate (FEF25-75%), and positive histamine challenges as compared to that with placebo/O3. There were no statistically significant differences in the metabolic data or ride times across all drugs and exposures, although the peak VE was significantly lower with O3 than FA (142.3 vs. 150.7 L/min, respectively) regardless of drug. The results indicate that acute pretreatment with inhaled albuterol is unable to prevent or ameliorate O3-induced symptoms and alterations in pulmonary function and exercise performance. The contribution of beta-adrenergic mechanisms in the acute airway responses to O3 appears to be minimal.     

Effects of immersion and static lung loading on submerged exercise at depth

The effects of static lung loading in the range +20 cmH2O to -20 cmH2O was investigated in 3 male subjects breathing air during submerged exercise in the prone position at pressures ranging from 1.45 ATA to 6.76 ATA. Both maximal and submaximal exercise was performed and dry controls were done at 1.45 ATA. A low-resistance bag-in-a-box breathing apparatus (less than 1.25 cmH2O/liter/s at 8 g/liter density) was used. Static lung loading had little effect on maximal or submaximal VO2, VCO2, VE, heart rate, or end-tidal PCO2, while increased breathing gas density did affect these parameters to a larger extent. Imersion per se reduced the VE at a given level of VO2 and increased both the VT and VA at a given VE. Increasingly positive static lung load increased VC and ERV both during rest and exercise. Exercise-induced dyspnea was experienced and scored. At submaximal VO2 levels up to 2.5 liter/min this dyspnea did not limit exercise at any depth, but during maximal exertion at 6.76 ATA (VO2 from 3.45--3.77 liter/min), dyspnea became work limiting in several cases. Static load had a marked effect on dyspnea and a load of +10 cmH2O produced the least dyspnea, enabling all subjects to perform maximal exertions for 5 min at 6.76 ATA. The 15-s MVV was performed at all depths and static loads and neither it nor the VE/MVV ratio correlated with the degree of dyspnea.     

Ultrafine particle deposition in subjects with asthma

Ambient air particles in the ultrafine size range (diameter < 100 nm) may contribute to the health effects of particulate matter. However, there are few data on ultrafine particle deposition during spontaneous breathing, and none in people with asthma. Sixteen subjects with mild to moderate asthma were exposed for 2 hr, by mouthpiece, to ultrafine carbon particles with a count median diameter (CMD) of 23 nm and a geometric standard deviation of 1.6. Deposition was measured during spontaneous breathing at rest (minute ventilation, 13.3 +/- 2.0 L/min) and exercise (minute ventilation, 41.9 +/- 9.0 L/min). The mean +/- SD fractional deposition was 0.76 +/- 0.05 by particle number and 0.69 +/- 0.07 by particle mass concentration. The number deposition fraction increased as particle size decreased, reaching 0.84 +/- 0.03 for the smallest particles (midpoint CMD = 8.7 nm). No differences between sexes were observed. The deposition fraction increased during exercise to 0.86 +/- 0.04 and 0.79 +/- 0.05 by particle number and mass concentration, respectively, and reached 0.93 +/- 0.02 for the smallest particles. Experimental deposition data exceeded model predictions during exercise. The deposition at rest was greater in these subjects with asthma than in previously studied healthy subjects (0.76 +/- 0.05 vs. 0.65 +/- 0.10, p < 0.001). The efficient respiratory deposition of ultrafine particles increases further in subjects with asthma. Key words: air pollution, asthma, deposition, dosimetry, inhalation, ultrafine particles.     

Lack of a systematic sustained effect of prolonged exercise bouts on resting metabolic rate in fasting subjects

Resting metabolic rate (RMR) and respiratory quotient (RQ) were measured in nine young men of normal weight after an overnight fast on three occasions, twice with and once without exercise on the previous evening. Exercise was cycling for 90 min at 100 W or 175 W. A Latin-square experimental design was used to balance the order of treatment with the type of treatment. Energy expenditure was measured by indirect calorimetry using a ventilated hood system. No significant after-effect of exercise on RMR was found: on the 100 W treatment the RMR had decreased by 0.04 +/- 0.06 kJ/min from the control value (4.68 +/- 0.13 kJ/min), and after the 175 W treatment it had increased by 0.11 +/- 0.08 kJ/min. On the 175 W exercise treatment RQs decreased significantly from 0.85 +/- 0.01 (control) to 0.82 +/- 0.01 (P less than 0.05). This indicates that single bouts of prolonged exercise can have a persisting effect on the type of substrate oxidized in the fasting state.     

Technical and clinical testing of a computerized indirect calorimeter for use in mechanically ventilated neonates

Testing of a proprietary indirect calorimeter (MGM, Jr.) was performed by using nitrogen displacement and added carbon dioxide to simulate oxygen consumption (VO2), carbon dioxide production (VCO2), and the respiratory quotient (RQ; VCO2/VO2). Errors in measured VO2, VCO2, and RQ were less than or equal to 2.5% when VO2 and VCO2 were 4-43 mL/min and flow rate was 100-2000 mL/min. The relative error in predicted VO2 was increased as the inspired oxygen concentration (FiO2) was raised but the error was less than 4% when the value of FiO2 minus expired oxygen concentration (FeO2) was greater than or equal to 0.015 and the FiO2 was less than or equal to 0.6. Sixteen studies were performed on seven very-low-birth-weight (VLBW), mechanically ventilated infants aged less than or equal to 11 d. VO2 was 8.37 +/- 1.81 mL.kg-1.min-1, VCO2 was 8.15 +/- 2.03 mL.kg-1.min-1, and RQ was 0.969 +/- 0.061 (means +/- SD). The MGM, Jr. is accurate for studies of low-birth-weight infants on mechanical ventilators when VO2 and VCO2 are greater than or equal to 4 mL/min, flow rate is less than or equal to 3000 mL/min, and FiO2 is less than or equal to 0.6. Clinical testing resulted in values similar to previously published data but the variability was higher.