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At least 613 records · Page 34Linked to original sources

PubMed2006

Influence of relative humidity on transmission of Campylobacter jejuni in broiler chickens.

Horizontal transmission of Campylobacter jejuni among broiler chickens has been documented; however, the influence of RH on transmission rates is an important factor that has not been extensively studied. The purpose of our experiments was to determine the rate of C. jejuni colonization among groups of broilers raised in microbiological isolation under high (approximately 80%) and low (approximately 30%) RH conditions. Day-of-hatch chicks (n = 100 per group) were placed on wood shavings in high and low humidity-controlled pens and challenged with C. jejuni by introducing 2 seeder birds orally inoculated with C. jejuni into each group. The rate of colonization was monitored by analyzing ceca from 10 chicks from each group at d 1, 2, 3, 4, and 7. After 3 wk, the remaining chickens were removed, and 100 newly hatched chicks were placed on the contaminated litter. A second trial was conducted with the litter as the only inoculum source. Trials were repeated in this manner with the time between removing birds and placing newly hatched chicks on the litter extended to 6 h, 24 h, and 1 wk. Significant differences in Campylobacter colonization rates were observed between chickens raised under the high and low RH conditions. A delay in colonization was observed in birds raised under the low RH conditions, which increased with the increased time between removal of birds and placement of newly hatched chicks. These experiments demonstrate the importance of humidity in the transmission of Campylobacter from litter, and they could lead to practical applications to help reduce Campylobacter colonization in broilers.

Animals↗

PubMed1994

The effect of aging, humidity, and fly-ash additive on the radon exhalation from concrete.

Radon exhalation rates of concrete samples have been periodically determined for 6-8 y after pouring the concrete. From the results, it can be concluded that the radon exhalation rate changes with the age of the concrete. The exhalation rate varies considerably in the first 6-12 mo after pouring with a factor of 1.5. After this period, the variation in exhalation rates is much less. Starting 1 y after pouring, the radon exhalation rate was decreased with increasing age of concrete to 0.3-0.6 of the maximum at the end of the observed period. Low humidity conditions dramatically reduce the radon exhalation rate of concrete. If 25% by volume of the cement is replaced by fly ash, the 226Ra concentration is elevated by a factor of 1.5. The radon exhalation rate of concrete made with Portland cement and fly ash was increased only slightly or even decreased, despite the higher 226Ra content. The results indicate that measurements of radon exhalation from samples of concrete have to be standardized on a certain humidity and age of the sample. Under certain conditions, the addition of fly ash to the concrete can reduce the radon exhalation.

Air Pollutants, Radioactive↗

PubMed2002

Humidity devices in vitreoretinal surgery.

PURPOSE: To assess a humidity device used in vitreoretinal surgery. METHODS: Infrared absorption spectroscopy analysis of absolute water content (absolute humidity) was determined for a typical vitreoretinal air infusion line with and without the humidifying device. A variety of experimental laboratory conditions were utilized and designed to mimic those found in the operating room. The effect on physical parameters, such as flow rates and resistance to flow, were also determined. RESULTS: While large bore infusion (LBI) lines had a negligible effect on flow rate and resistance to flow (reduction in infusion pressure), the standard 20 G infusion line (SI) reduced flow rate and infusion pressure by approximately 25%. When used together, the humidifying device and SI reduced flow rate and infusion pressure by one third. The humidifying device was found to add 6.5 mg/L water content to the air infusion line system. Typical operating room (OR) air contains 9.5 mg/L water content, and 43.876 mg/L water content is required to saturate air at body temperature. CONCLUSION: To eliminate dehydration as a cause of intraocular morbidity, one must first saturate the infused air. If the visual field defects and other complications are eliminated, this would be good evidence for saturating infused air. As infusion pressure (flow rate) influences dehydration rate, unless saturated air is used, infusion pressure cannot be considered an independent variable in the analysis of field defects.

Body Temperature↗

PubMed2002

Thiol diffusion and the role of humidity in "Dip Pen Nanolithography".

The radii of octadecanethiol spots deposited by an atomic force microscope tip onto a gold surface were studied as a function of contact time and humidity. The deposition is well described by two-dimensional diffusion from an annular source of constant concentration, with a surface diffusion coefficient of 8400 nm(2) s(-1), independent of humidity. Facile transfer is observed even after near continuous deposition for more than 24 h in a dry N2 environment, indicating that a water meniscus is not required.

Biosensing Techniques↗

PubMed2000

Hydration, mobility and accessibility of lysozyme: structures of a pH 6.5 orthorhombic form and its low-humidity variant and a comparative study involving 20 crystallographically independent molecules.

The structure analyses of orthorhombic lysozyme grown at pH 6.5 and its low-humidity variant are reported. The structures of the same form grown at pH 9.5 and 4.5 and that of the low-humidity variant of the pH 9.5 form are available. A comparison between them shows that the changes in molecular geometry and hydration caused by changes in the amount of solvent surrounding protein molecules are more pronounced than those caused by variation in pH. In particular, the conformation and the mutual orientation of the catalytic residues Glu35 and Asp52 remain unaffected by change in pH. A comparative study involving 20 crystallographically independent lysozyme molecules, including five in the orthorhombic form, leads to the delineation of the relatively rigid, moderately flexible and highly flexible regions of the molecule. Half the binding cleft (subsites D, E and F) belong to the rigid region but the other half (subsites A, B and C) belong to a flexible region. There is no marked correlation between relative rigidity and conservation of side-chain conformation except at the binding site. The study permits the identification of seven invariant water molecules associated with the protein. Most of them are involved in important tertiary interactions, while one occurs in the active-site cleft. The study demonstrates a weak correlation between non-accessibility and rigidity. On average, the level of hydration of polar atoms increases rapidly with accessible atomic surface area, but levels off at about 15 A(2) at a little over one ordered water molecule per polar protein atom. Only 15 N and O atoms are hydrated in all 20 molecules. 13 of these are hydrated by the seven invariant water molecules. Of the seven, only one water molecule is totally buried within the protein.

Animals↗

PubMed2002

Interdigitated humidity sensors for a portable clinical microsystem.

This paper presents and compares two capacitive humidity sensors with interdigitated electrodes for a portable clinical application. A polyimide-sensitive layer covers the first structures and the optimized ones include a benzocyclobutene-sensitive layer and a heating resistor. Humidity measurements results are presented, in particular sensors response time in absorption, which are very small (inferior to 500 ms). Next, mechanisms of absorption and adsorption in a polymer layer are described and the two structures are compared. Suitability of optimized sensors for our application is discussed: new structures allow us to increase sensitivity and decrease response time. When the structure is maintained at 40 degrees C by its heater, the response time is 200 ms and the total desorption time is 11 s.

Adsorption↗

PubMed2003

Rapid laboratory evolution of adult wing area in Drosophila melanogaster in response to humidity.

We examined the evolutionary response of wing area (a trait highly correlated with other measures of body size) to relative humidity (RH), temperature, and their interaction in Drosophila melanogaster, using replicated lines that had been allowed to evolve at low or high humidity at 18 degrees C or at 25 degrees C. We found that after 20 weeks of selection (5-10 generations), low RH lines had significantly greater wing areas than high RH lines in both sexes. This evolutionary response may have resulted from selection of larger flies with a smaller surface area for water loss relative to their weight, or as a correlated response to selection on some other unidentified trait. There were no evolutionary effects of temperature on wing area or cell density. This may have been due to the short duration of the selection experiment, and/or counteracting selection pressures on body size at warm temperature.

Analysis of Variance↗

PubMed2005

The effects of different air velocities on heat storage and body temperature in humans cycling in a hot, humid environment.

AIM: The purposes of this study were to determine (i) the effects of different facing air velocities on body temperature and heat storage during exercise in hot environmental conditions and (ii) the effects of ingesting fluids at two different rates on thermoregulation during exercise in hot conditions with higher air velocities. METHODS: On five occasions nine subjects cycled for 2 h at 33.0 +/- 0.4 degrees C with a relative humidity of 59 +/- 3%. Air velocity was maintained at 0.2 km h(-1) (0 WS), 9.9 +/- 0.3 km h(-1) (10 WS), 33.3 +/-2.2 km h(-1) (100 WS) and 50.1 +/- 3.2 km h(-1) (150 WS) while subjects replaced 58.8 +/- 6.8% of sweat losses. In the fifth condition, air velocity was maintained at 33.7 +/- 2.2 km h(-1) and subjects replaced 80.0 +/- 6.8% of sweat losses (100.80 WS). RESULTS: Heat storage, body temperature and rating of perceived exertion were higher in 0 and 10 WS compared with all other conditions. There were no differences in any measured variable between 100 and 150 WS, or between 100 and 100.80 WS. Thus, the evaporative capacity of the environment is increased with higher air velocities, reducing heat storage and body temperature. At higher air velocities, a higher rate of fluid ingestion did not influence heat storage, body temperature or sweat rate. CONCLUSION: The finding of previous laboratory studies showing a beneficial effect of high rates of fluid ingestion on thermoregulation during exercise in hot, humid, windstill conditions cannot be extrapolated to out-of-doors exercise in which facing air velocities are seldom lower than the athlete's rate of forward progression.

Adult↗

PubMed1997

The effect of a heat and moisture exchanger on humidity in a low-flow anaesthesia system.

The heat and humidity in a low-flow breathing system was measured in order to study the inherent humidifying properties of the system at low fresh gas flows (< 1 and 21.min-1) and whether a heat and moisture exchanger could compensate for the loss of heat and humidification occurring at higher fresh gas flows (51.min-1) in these systems. Sixty patients were randomly divided into three groups (< 1, 2 and 51.min-1 fresh gas flows) with a heat and moisture exchanger and three groups without a heat and moisture exchanger in the breathing system. Thirty minutes after the start of anaesthesia a control measurement was performed, after which a heat and moisture exchanger was inserted into the breathing system of the three groups randomly allocated to have one. Three more measurements were performed at 10, 30 and 60 min after control. At low fresh gas flows the humidifying properties of the low-flow breathing system are adequate (i.e. provide an absolute humidity > 20 mg.l-1) but at a fresh gas flow of 51.min-1 there is a need for a heat and moisture exchanger for adequate humidification of the inspired gas.

Abdomen↗

PubMed2005

Windy weather and low humidity are associated with an increased number of hospital admissions for acute pain and sickle cell disease in an urban environment with a maritime temperate climate.

Sickle cell disease (SCD) is characterised by intermittent episodes of acute severe pain, related to vaso-occlusion. Environmental factors are thought to play an important role, and studies in tropical countries have suggested that cold and rainy seasons are associated with increased episodes of acute pain. We have studied retrospectively the number of admissions with acute pain and SCD to King's College Hospital, London, together with daily meteorological records collected locally. Data from 1400 d and 1047 separate admissions were analysed. Increased admissions were significantly associated with increased wind speed and low humidity, but showed no relationship to temperature, rainfall or barometric pressure. The strongest effect was for (maximum wind speed)/humidity, with 464 admissions on days in the lowest two quartiles of this parameter and 582 in the highest quartiles. The effect of high wind and low humidity is likely to be related to skin cooling.

Acute Disease↗

PubMed2004

The effect of temperature, humidity and peak inspiratory nasal flow on olfactory thresholds.

Temperature, humidity and nasal peak inspiratory flow rate (PIFR) are potential variables in the quantitative measurement of olfactory thresholds in the clinic. To date, these variables have not been properly evaluated with respect to olfactory perception, and therefore the aim of this study was to determine their effect on the thresholds. These variables were measured on 10 occasions in 10 subjects over a 10-week period. The results obtained were then subjected to statistical analysis using a linear mixed-effect model. This demonstrated that olfactory thresholds are sufficiently independent of room temperature, peak humidity and nasal PIFR in a routine outpatient clinic environment in normal subjects, with no evidence of any statistically significant influence by these variables.

Adult↗

PubMed1992

Fungal and actinomycete spore aerosols measured at different humidities with an aerodynamic particle sizer.

An aerodynamic particle sizer (APS) that uses laser Doppler velocimetry was used to determine aerodynamic diameters of spores of fungal and thermophilic actinomycete species common in mouldy hay, aerosolized at different humidities and temperatures. Results were compared with those obtained from inertial impaction in a cascade impactor. The APS gave slightly smaller measurements than the cascade impactor. Both methods gave aerodynamic diameters generally slightly smaller than the average spore dimensions observed on cascade impactor slides with a microscope. The latter measurements were less than axial dimensions given in the literature. Brief passage of spores through air at 95% relative humidity (RH) and 38 degrees C, compared with 40% RH and 20 degrees C, caused an immediate increase in their aerodynamic diameter and the breaking of chains of spores. Cultures maintained at 75% RH and aerosolized at 98% RH similarly produced larger spore particles than those passed through dry air. These findings have implications for mould-induced asthma and allergic alveolitis since they relate to physical behaviour of airborne spores and particle deposition sites in the lung.

Aerosols↗

PubMed2004

High humidity suppresses ssi4-mediated cell death and disease resistance upstream of MAP kinase activation, H2O2 production and defense gene expression.

The Arabidopsis ssi4 mutant, which exhibits spontaneous lesion formation, constitutive expression of pathogenesis-related (PR) genes and enhanced resistance to virulent bacterial and oomycete pathogens, contains a gain-of-function mutation in a TIR-NBS-LRR type R gene. Epistatic analyses revealed that both PR gene expression and disease resistance are activated via a salicylic acid (SA)- and EDS1-dependent, but NPR1- and NDR1-independent signaling pathway. In this study, we demonstrate that in moderate relative humidity (RH; 60%), the ssi4 mutant accumulates H(2)O(2) and SA prior to lesion formation and displays constitutive activation of the MAP kinases AtMPK6 and AtMPK3. It also constitutively expresses a variety of defense-associated genes, including those encoding the WRKY transcription factors AtWRKY29 and AtWRKY6, the MAP kinases AtMPK6 and AtMPK3, the powdery mildew R proteins RPW8.1 and RPW8.2, EDS1 and PR proteins. All of these ssi4-induced responses, as well as the chlorotic, stunted morphology and enhanced disease resistance phenotype, are suppressed by high RH (95%) growth conditions. Thus, a humidity sensitive factor (HSF) appears to function at an early point in the ssi4 signaling pathway. All ssi4 phenotypes, except for MAP kinase activation, also were suppressed by the eds1-1 mutation. Thus, ssi4-induced MAP kinase activation occurs downstream of the HSF but either upstream of EDS1 or on a separate branch of the ssi4 signaling pathway. SA is a critical signaling component in ssi4-mediated defense responses. However, exogenously supplied SA failed to restore lesion formation in high RH-grown ssi4 plants, although it induced defense gene expression. Thus, additional signals also are involved.

Arabidopsis↗

PubMed1981

Influence of relative humidity and repeated exercise on exercise-induced bronchoconstriction.

The relationship between previous exercise-induced bronchoconstriction (EIB) of different magnitude and the pulmonary response to exercise 1 h later was examined in asthmatic children. After acclimatization they performed repeated, paired exercise tests in a clean-air climatic chamber at 23 degree C. The first test of each pair was carried out in 15%, 50% and 85% relative humidity (RH), respectively, to produce different degrees of EIB. All second tests were performed in 50% RH. Changes in pulmonary function were assessed by measuring PEF and FEV1. Bronchodilatation during exercise was not influenced by RH, whereas dry air increased and humid air decreased the bronchoconstrictive response to exercise. When both tests were performed in 50% RH, the second test caused significantly less EIB than did the first test. However, no differences were found between the three second test responses. This suggests that the relative refractoriness after an episode of EIB is not related to the severity of previous bronchoconstriction, but could be associated with exercise as such or other mechanisms in EIB.

Adolescent↗

PubMed1981

Humidity and temperature changes during low flow and closed system anaesthesia.

Water humidity and temperature were measured in the proximal end of the inspiratory limb in anaesthetic circuits used to anaesthetize three groups of adult patietnts using various fresh gas flows (FGF). Humidity increased as FGF's were lowered, with 98% water humidification achieved when FGF's of less than 0.51/min were administered. Temperature at the same site changed about 1-2.5 degrees C in inverse proportion to the volume of FGF. This advantage of closed system and low flow anaesthesia is a further reason for their wide-spread utilization.

Adult↗

PubMed1994

Geomagnetic activity, humidity, temperature and headache: is there any correlation?

Meterological factors influence several biological functions. Geomagnetic activity (GMA) can be considered a trigger factor of migraine attacks. We studied the possible relationship between 40 migraine patients and some meteorological factors: humidity, temperature and geomagnetic activity in particular. All frequency changes of geomagnetic activity, temperature and humidity values are recorded daily. The study was performed from March to June 1988 over a geographically small area in order to avoid climatic and environmental influences. Our results indicate a significant correlation between geomagnetic activity and migraine attack frequency. Controversial opinions concerning the modalities of data collection and the possible relationships between environment and headache raise the need of further studies.

Adult↗

PubMed1995

Soft lens movement: effects of humidity and hypertonic saline on lens settling.

Hydrogel contact lenses require a settling period before lens fit stabilizes, but the process underlying the initial reduction in lens mobility is poorly understood. Explanations for this phenomenon include base curve steeping with dehydration, expulsion of postlens tear fluid, and osmotic flow of hypotonic tears into the cornea. We conducted two randomized, single-masked interocular comparisons for ten subjects wearing HEMA lenses for 1 h. We investigated potential mechanisms of dehydration-dependent lens tightening, by limiting dehydration in one eye using a high humidity environment (experiment 1), and of a hypotonic lacrimation-dependent decrease in lens movement, by presoaking lenses in isotonic (0.9%) or hypertonic (1.5%) saline (experiment 2). Lens mobility profiles were not significantly affected by modification of environment; lenses in both normal and high humidity environments displayed a significant reduction in lens movement during the first 15 min of wear (ANOVA, p = 0.0001), and no change in lens mobility thereafter. Lens mobility profiles were identical for lenses presoaked in isotonic and hypertonic saline, with initial lens movement being significantly greater than for subsequent measurements (ANOVA, p < 0.05). These studies find no evidence to support dehydration-dependent steepening of base curve, or osmotic-dependent binding from hypotonic lacrimation as mechanisms for the initial postinsertion decrease in lens movement.

Adult↗

PubMed2004

Wall relative humidity: a simple and reliable index for predicting Stachybotrys chartarum infestation in dwellings.

UNLABELLED: Because the indoor mold Stachybotrys chartarum has been considered as potentially responsible for serious health effects, its identification in dwellings with water damages is of utmost importance. As such dwellings are many, it would be of great value to have a simple and reliable index for predicting its presence. The aim of the study was to compare measurements of wall relative humidity (RH) to mold identification in 458 samples from 100 dwellings. Mold identification was performed by direct microscopic examination of a sample collected on the wall by the gummed paper technique. Mean (+/- s.d.) wall RH (%) was much higher (97.0 +/- 6.1) on the 30 samples where S. chartarum was identified compared with the 291 samples where other molds were identified (41.8 +/- 36.9) and to the 137 samples where no molds were identified (38.9 +/- 34.8). There was no straightforward relationship between wall and room RH. In conclusion, this study clearly demonstrate that the simple measurement of wall RH can be used as a reliable index for discarding and suspecting S. chartarum infestation in dwellings. PRACTICAL IMPLICATIONS: This paper suggests that very high relative humidity (RH) within walls is a strong risk factor for their infestation with the 'toxic mold' Stachybotrys chartarum. Besides, data from the literature demonstrate that other molds are able to produce mycotoxins when RH is very high. Thus, measurement of wall RH, which is easy to perform and very cheap, could be used as a screening tool to select those dwellings where mold identification should be performed and remediation should be promptly carried out.

Air Pollution, Indoor↗