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At least 397 records · Page 22Linked to original sources

PubMed1999

Whole-body pre-cooling and heat storage during self-paced cycling performance in warm humid conditions.

The aim of this study was to establish the effect that pre-cooling the skin without a concomitant reduction in core temperature has on subsequent self-paced cycling performance under warm humid (31 degrees C and 60% relative humidity) conditions. Seven moderately trained males performed a 30 min self-paced cycling trial on two separate occasions. The conditions were counterbalanced as control or whole-body pre-cooling by water immersion so that resting skin temperature was reduced by approximately 5-6 degrees C. After pre-cooling, mean skin temperature was lower throughout exercise and rectal temperature was lower (P < 0.05) between 15 and 25 min of exercise. Consequently, heat storage increased (P < 0.003) from 84.0+/-8.8 W x m(-2) to 153+/-13.1 W x m(-2) (mean +/- s(mean)) after pre-cooling, while total body sweat fell from 1.7+/-0.1 l x h(-1) to 1.2+/-0.1 l h(-1) (P < 0.05). The distance cycled increased from 14.9+/-0.8 to 15.8+/-0.7 km (P < 0.05) after pre-cooling. The results indicate that skin pre-cooling in the absence of a reduced rectal temperature is effective in reducing thermal strain and increasing the distance cycled in 30 min under warm humid conditions.

Adolescent↗

PubMed2000

Aerosol light scattering measurements as a function of relative humidity.

The hygroscopic nature of atmospheric fine aerosol was investigated at a rural site in the Great Smoky Mountains National Park during July and August 1995. Passing the sample aerosol through an inlet, which housed an array of Perma Pure diffusion dryers, controlled the sample aerosol's relative humidity (RH). After conditioning the aerosol sample in the inlet, the light scattering coefficient and the aerosol size distribution were simultaneously measured. During this study, the conditioned aerosol's humidity ranged between 5% < RH < 95%. Aerosol response curves were produced using the ratio bspw/bspd; where bspw is the scattering coefficient measured at some RH greater than 20% and bspd is the scattering coefficient of the "dry" aerosol. For this work, any sample RH values below 15% were considered dry. Results of this investigation showed that the light scattering ratio increased continuously and smoothly over the entire range of relative humidity. The magnitude of the ratio at a particular RH value, however, varied considerably in time, particularly for RH values greater than approximately 60%. Curves of the scattering coefficient ratios as a function of RH were generated for each day and compared to the average 12-hour chemical composition of the aerosol. This comparison showed that for any particular RH value the ratio was highest during time periods of high sulfate concentrations and lowest during time periods of high soil or high organic carbon concentrations.

Aerosols↗

PubMed1980

A comparison of heat stress indices in a hot-humid environment.

The results of a study of nine physically fit young men performing moderate exercise under various levels of hot-humid conditions are reported. Environmental stress and physiological strain data from the total of 72 test sessions were collected and computed in terms of heat stress and heat strain indices. Single and multiple factor correlation coefficients were calculated on the basis of 11 stress indices versus 4 strain indices. Most of the empirical heat stress indices correlated best with the mean skin temperature, whereas the rational indices correlated best with heart rate and sweat loss. Because of its ease of use, the WGT or the CET index may be the best choice for preliminary industrial surveys in hot-humid environments. A simple and convenient nomogram was developed on the basis of the test data relating increase in heart rate to temperature, humidity, and air velocity.

Adult↗

PubMed1989

"Worst case" aerosol testing parameters: II. Efficiency dependence of commercial respirator filters on humidity pretreatment.

Previous studies have shown that relative humidity has a degrading effect on the performance of commercially available particulate air-purifying respirator filters. That degradation results from a reduction of charge within the filter. This study was done to evaluate the time-dependent effects of relative humidity pretreatment and the reduction of charge on filter penetration against a most penetrating, "worst case" aerosol challenge. Filters of the dust and mist; dust, fume, and mist; paint, lacquer, and enamel mist; and high efficiency types were tested after being pretreated in an environment of 38 degrees C and 85% relative humidity for periods up to 42 days. After various intervals of pretreatment (1, 7, 14, 28, and 42 days), the filters were tested against neutralized worst-case sodium chloride (NaCl) and dioctyl phthalate (DOP) aerosols for percent penetration. The results showed a drop in filter efficiency of approximately 2%-6% depending on preconditioning time, except for the high efficiency filters tested which showed no detectable change.

Aerosols↗

PubMed2005

Indoor air quality in two urban elementary schools--measurements of airborne fungi, carpet allergens, CO2, temperature, and relative humidity.

This article presents measurements of biological contaminants in two elementary schools that serve inner city minority populations. One of the schools is an older building; the other is newer and was designed to minimize indoor air quality problems. Measurements were obtained for airborne fungi, carpet loadings of dust mite allergens, cockroach allergens, cat allergens, and carpet fungi. Carbon dioxide concentrations, temperature, and relative humidity were also measured. Each of these measurements was made in five classrooms in each school over three seasons--fall, winter, and spring. We compared the indoor environments at the two schools and examined the variability in measured parameters between and within schools and across seasons. A fixed-effects, nested analysis was performed to determine the effect of school, season, and room-within-school, as well as CO2, temperature and relative humidity. The levels of all measured parameters were comparable for the two schools. Carpet culturable fungal concentrations and cat allergen levels in the newer school started and remained higher than in the older school over the study period. Cockroach allergen levels in some areas were very high in the newer school and declined over the study period to levels lower than the older school. Dust mite allergen and culturable fungal concentrations in both schools were relatively low compared with benchmark values. The daily averages for temperature and relative humidity frequently did not meet ASHRAE guidelines in either school, which suggests that proper HVAC and general building operation and maintenance procedures are at least as important as proper design and construction for adequate indoor air quality. The results show that for fungi and cat allergens, the school environment can be an important exposure source for children.

Air Microbiology↗

PubMed2001

Effect of relative humidity on mixed aerosols in atmosphere.

In this study, the effects of relative humidity on the deliquescent point and size of internally mixed aerosols diameter, NH4NO3 and (NH4)2SO4 were investigated using a Tandem Differential Mobility Analyzer (TDMA) with a relative humidity conditioner. The growth of mixed aerosols appears to have two deliquescent steps. The first one was at about 61.2-61.3%, but the second one was at around 77-78%. At the first deliquescence point, growth ratio at phase change was 7.5%, which agrees with the growth ratio of ammonium nitrate aerosol. Growth ratio of phase change at the second deliquescence point was about 20%, lower than the growth ratio of ammonium sulfate aerosol. In the relative humidity range of 80-85%, the growth ratio of the mixed aerosols reached 60%. In other words, it appears that growth ratio increases with the size of aerosol. Furthermore, a theoretical growth model of mixed aerosols was developed and applied to estimate the amount of composition of the mixed aerosols dissolved at each deliquescence point. The results also show that some of ammonium sulfate already dissolved at the first deliquescence point according to the theoretical growth model.

Aerosols↗

PubMed1996

The influence of air humidity on an unsealed ionization chamber in a linear accelerator.

The safe and accurate delivery of the prescribed absorbed dose is the central function of the dose monitoring and beam stabilization system in a medical linear accelerator. The absorbed dose delivered to the patient during radiotherapy is often monitored by a transmission ionization chamber. Therefore it is of utmost importance that the chamber behaves correctly. We have noticed that the sensitivity of an unsealed chamber in a Philips SL linear accelerator changes significantly, especially during and after the summer season. The reason for this is probably a corrosion effect of the conductive plates in the chamber due to the increased relative humidity during hot periods. We have found that the responses of the different ion chamber plates change with variations in air humidity and that they do not return to their original values when the air humidity is returned to ambient conditions.

Air↗

PubMed1997

The importance of humidity in the in vitro study of the cranium with regard to initial bone displacement after force application.

The aim of this pilot study was to find a suitable model for simulating in vivo initial displacements of the maxilla after force application. Force was exerted on the maxillae of four dogs by means of a dental splint. To register the bone displacement, speckle interferometry was used as the measurement technique. The initial orthopaedic effect as a result of force application in vivo was registered by the construction of rotation centres around which the maxilla rotated. The orthopaedic effect after force application in vivo was compared with different in vitro situations of the laboratory animal. After the animal had been killed and its maxilla macerated, the cranium was placed in a sealed conditioned box. Only three skulls were found to be suitable for this experiment. The environment thus created can be influenced by changes in relative humidity. Various forces were applied in various directions on the maxilla of three Alsatians. By changing the relative humidity, an attempt was made to create a situation in which the initial bone displacements after force application were comparable to the in vivo situation. None of the laboratory animals used showed a comparable condition for the in vivo situation through manipulation of relative humidity. As only three dogs were experimented on, these findings are tentative. This experiment will be extended to three more dogs from the same litter.

Animals↗

PubMed1984

Body temperature responses of aged mice to ambient temperature and humidity stress.

Male C57BL/6 mice aged 6 to 7 months, 13 to 14 months, and 19 to 20 months were acutely exposed to four ambient temperature (15 degrees C, 20 degrees C, 30 degrees C, 35 degrees C) and two relative humidity (50% rh, 80% rh) conditions. Three-hour average rectal temperatures were compared across age groups and environmental conditions. At the two temperature extremes of 15 degrees C and 35 degrees C, there was a very marked age-associated hypothermia and hyperthermia, respectively. This hypothermic response was maintained by the 19 to 20-month-old mice during exposure to 20 degrees C and thermoneutrality (30 degrees C). At any given ambient temperature, relative humidity had no effect on thermoregulatory function in the oldest mice, whereas the 6 to 7-month- and 13 to 14-month-old mice were sensitive to the effects of humidity at 15 degrees C and 20 degrees C.

Aging↗

PubMed1982

Childhood respiratory illness and the home environment. I. Relations between nitrogen dioxide, temperature and relative humidity.

The relation between the use of gas for cooking, nitrogen dioxide (NO2), temperature and relative humidity was investigated in an urban area of northern England. In a pilot study conducted in a random sample of 40 homes measurements of temperature and relative humidity were not significantly different between homes with a gas cooker and homes with an electric cooker but weekly average levels of NO2 were higher in bedrooms (p less than 0.005) and living rooms (P less than 0.01) of gas homes. In the main study conducted in gas cooking homes only, access was gained to 183 (54.3%) of 337 randomly selected homes. No correlation was found in children's bedrooms between with weekly average level of NO2 (range 4.7 to 160.8 ppb) and weekly average temperature (ranged 7.7 to 22.0 degree C; r = 0.05, p greater than 0.10) or relative humidity (range 37.0 to 98.1%; r = 0.07, p greater than 0.10). Levels of NO2 in the bedroom were positively correlated with those in the living room (range 9.0 to 292.2 ppb; r = 0.39, p less than 0.01). Factors which tended to be associated with high levels of NO2 in the home included gas fires, paraffin heaters and use of the cooker for heating and drying clothes.

Air Pollutants↗

PubMedDate not supplied

Impact of hot and humid tropical conditions on Toxi-Lab thin-layer chromatographic systems for the screening of basic and neutral drugs.

Because thin-layer chromatography can be affected by climatic conditions, we investigated the impact of high temperatures (33-38 degrees C) and high relative humidities (80-100%) on the applicability of Toxi-Lab thin-layer chromatographic systems for the screening of basic and neutral drugs during a 6-month climatological cycle in Jakarta, Indonesia that can be characterized as hot and humid. In general, the Rf values as observed on the plate showed substantial deviations from those in the literature obtained in moderate climates. Most substances gave higher Rf values, and the deviations (sometimes amounting to 20 Rf units) increased with increasing humidities. However, when the observed Rf values were corrected by means of a reference mixture of standard drugs that was run on each plate, much better accuracy and reproducibility were obtained. Thus, these corrected Rcf values were compatible with the existing databases developed in temperate climates. These results are in line with earlier studies carried out under hot and dry conditions. In the earlier studies, the observed Rf values tended to be lower than those present in other databases, but here too, the Rf correction procedure corrected this phenomenon.

Chromatography, Thin Layer↗

PubMed1992

Effects of temperature and humidity on ovipositional biology and egg development of the tropical horse tick, Dermacentor (Anocentor) nitens.

The ovipositional biology and egg development of the tropical horse tick, Dermacentor (Anocentor) nitens (Neumann), was observed at four temperatures (20, 25, 30, and 35 degrees C) and relative humidities (40, 61, 75, and 91% RH). Relative humidity had little effect on length of preoviposition and oviposition periods. With increased rearing temperatures, there was a decrease in both preoviposition and oviposition periods. Oviposition rate increased with temperature and was not affected by relative humidity. Instantaneous rates of oviposition were calculated for each temperature by fitting the data to the logistic growth function. High percentage egg hatch was observed in low saturation deficit environments, and decreased when saturation deficit was increased.

Animals↗

PubMed1998

Population dynamics of the house dust mites Dermatophagoides farinae, D. pteronyssinus, and Euroglyphus maynei (Acari: Pyroglyphidae) at specific relative humidities.

Experiments were conducted to determine the effects of relative humidity on the population dynamics of single and mixed species of Dermatophagoides farinae Hughes, D. pteronyssinus (Trouessart), and Euroglyphus maynei (Cooreman) at specific relative humidities maintained at 20 degrees C, with unlimited food. The population density of single and mixed species (D. farinae and D. pteronyssinus) increased exponentially when cultured at 65, 70, and 75% RH. The mean population growth rates were 17.3 +/- 4.4 SD and 32.5% +/- 4.7/wk for D. farinae and D. pteronyssinus, respectively. Mean population doubling times were 2.2 +/- 0.3 and 4.2 +/- 1.3 wk for D. pteronyssinus and D. farinae, respectively. Mixed species cultures, started with equal numbers of D. farinae and D. pteronyssinus, resulted in higher percentages of D. farinae than D. pteronyssinus. In cultures started with 75% of one species and 25% of the other, the more numerous species remained dominant and in similar ratios throughout the experiment. Both D. farinae and D. pteronyssinus population densities maintained at 85% RH declined over a 12-wk culture period because of mold growth. E. maynei were unable to survive at 65, 70, 75, and 85% RH, which indicated that their climatic requirements were different from those of D. farinae and D. pteronyssinus. Population densities of D. farinae and D. pteronyssinus cultures declined when held at 21-22 degrees C and relative humidities of < or = 50%; however, at 50% RH, significant proportions of the populations survived for 10 wk. Half-life for desiccation of D. farinae and D. pteronyssinus at 45% RH was 11.5 and 1.2 wk, respectively, but at 50% RH was 86.3 and 4.0 wk, respectively. The data indicated that a < or = 50% RH would have to be maintained for long periods to reduce both D. farinae and D. pteronyssinus by desiccation procedures. The results of this study show that D. farinae and D. pteronyssinus have high reproductive potentials and population growth rates, which indicate that mite reduction procedures must be thorough or mite densities will return to high levels quickly following remediation if adequate food and suitable microclimatic conditions exist.

Animals↗

PubMed1998

Air temperature and relative humidity effects on behavioral activity of blacklegged tick (Acari: Ixodidae) nymphs in New Jersey.

Air-temperature and relative humidity data were used to explain variation in behavioral activity of Ixodes scapularis Say nymphs. We estimated behavioral activity as the residual variation in drag-sample data after seasonal changes in population density were removed by regression. The seasonal decline in drag samples between June and August 1995 on field plots at Morristown National Historical Park, NJ, can be described by a simple negative exponential function. Residuals around a fitted exponential were significantly correlated with temperature and with relative humidity measured at the leaf-litter surface, and explained 34 and 44% of the variance, respectively. Multiple regression on temperature and relative humidity explained 51% of the variance. These regressions estimated the explanatory power of microclimate, independent of seasonal correlations, and might provide a basis for day-to-day prediction of human exposure to Lyme disease.

Animals↗

PubMed1999

Effects of temperature and humidity on oviposition, molting, and longevity of Dermanyssus gallinae (Acari: Dermanyssidae).

The juvenile development and survival of Dermanyssus gallinae (De Geer) kept in vitro at different temperatures and humidity were investigated to obtain biological baseline data for a Swedish population. Individual females, eggs, larvae, and protonymphs were observed with regard to egg production, duration of various stages, and longevity when kept at different temperatures and relative humidities. Female mites laid eggs at temperatures between 5 and 45 degrees C with the highest numbers laid at 20 degrees C and 70% RH, but development to larvae and protonymphs was only observed at temperatures ranging from 20 to 25 degrees C. The average duration of oviposition varied from 1.0 to 3.2 d within the temperature range 20-45 degrees C but was gradually increased to 28 d at 5 degrees C. Specimens survived for up to 9 mo without access to food when kept in the temperature range of 5-25 degrees C. Temperatures > 45 degrees C and at -20 degrees C were found to be lethal. Longevity was similar for females and protonymphs kept at 30 and 45% RH, but it was enhanced at 70 and 90% RH for protonymphs. This study showed that D. gallinae can survive for a long time without feeding if the microclimate is suitable, but it does not thrive at low relative humidities and at temperature extremes. This indicates that changing of the abiotic conditions in infested poultry houses could be a possible measure to reduce mite populations.

Animals↗

PubMed1997

Improved running performance in hot humid conditions following whole body precooling.

On two separate occasions, eight subjects controlled speed to run the greatest distance possible in 30 min in a hot, humid environment (ambient temperature 32 degrees C, relative humidity 60%). For the experimental test (precooling), exercise was preceeded by cold-water immersion. Precooling increased the distance run by 304 +/- 166 m (P < 0.05). Precooling decreased the pre-exercise rectal and mean skin temperature by 0.7 degrees C and 5.9 degrees C, respectively (P < 0.05). Rectal and mean skin temperature were decreased up to 20 and 25 min during exercise, respectively (P < 0.05). Mean body temperature decreased from 36.5 +/- 0.1 degrees C to 33.8 +/- 0.2 degrees C following precooling (P < 0.05) and remained lower throughout exercise (P < 0.01) and at the end of exercise (by 0.8 degrees C; P < 0.05). The rate of heat storage at the end of exercise increased from 113 +/- 45 to 249 +/- 55 W.m-2 (P < 0.005). Precooling lowered the heart rate at rest (13%), 5 (9%), and 10 min (10%) exercise (P < 0.05) and increased the end of exercise blood lactate from 4.9 +/- 0.5 to 7.4 +/- 0.9 mmol.L-1 (P < 0.01). The VO2 at 10 and 20 min of exercise and total body sweating are not different between tests. In conclusion, water immersion precooling increased exercise endurance in hot, humid conditions with an enhanced rate of heat storage and decreased thermoregulatory strain.

Adult↗

PubMed1993

Humidity-conditioned gravimetric method to measure the water content of hydrogel contact lens materials.

A method to determine the humidity-conditioned gravimetric water content of hydrogel contact lens materials has been developed, in which errors due to blotting have been eliminated by conditioning the lens in a series of relative humidity (RH) environments before measuring the water content gravimetrically, and then extrapolating the water content to 100% RH. This method has been used to determine the water contents of representative materials from each of the four FDA lens groups, which were compared with their labeled values, as well as with values obtained from refractive index measurements. The deviation of the water content of soft contact lenses as measured by refractive index from that obtained gravimetrically increased as the water content decreased. The humidity-conditioned gravimetric method to determine water content of hydrophilic contact lenses is being proposed as an International Organization for Standardization (ISO) standard, as an improvement over the gravimetric and refractive index methods.

Caprolactam↗

PubMed2004

Hospital admissions for heart disease: the effects of temperature and humidity.

BACKGROUND: We estimated the effects of temperature and humidity on hospital admissions for heart disease (International Classification of Diseases, 9th revision [ICD-9] codes 390-429) and myocardial infarction (ICD-9 code 410) of persons age 65 and older in 12 U.S. cities with a wide range of climates. To account for possible delayed effects and harvesting, we examined the impact of weather up to 20 days before each admission. METHODS: Poisson regression models were fitted in each city, with regression splines used to control for season and barometric pressure. We also controlled day of the week. We estimated the effect and the lag structure of both temperature and humidity based on a distributed lag model. FINDINGS: For cities in both hot and cold climates, we found that hospital admissions for all heart disease increased monotonically with average temperature on the same day as and the day before admission. The effect of very high temperatures had a temporal pattern consistent with harvesting: several days after an episode of high temperature, there were fewer admissions. In contrast, a protective effect of cold temperature persisted without rebound. The effects of either hot or cold temperature disappeared within 10 days of exposure. There was no evidence for a humidity effect. Similar but smaller effects of temperature were seen for admissions for myocardial infarction specifically. CONCLUSIONS: The effects of temperature on hospital admissions predominantly occur within a few days after exposure, and much of the effect of hot temperatures is short-term displacement of events.

Algorithms↗