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At least 271 records · Page 15Linked to original sources
PubMed2006

Influence of ambient humidity on the current delivered by air-vented ionization chambers revisited.

The influence of ambient humidity on the current delivered by a vented ionization chamber has been re-investigated. A Nucletron 077.091 well-type chamber together with a (192)Ir HDR brachytherapy source was enclosed in a climatic test chamber and the current was recorded for various humidity values. Great care has been taken for the design of the experimental setup in order to obtain reliable measurements of currents and humidity values inside the chamber active volume. A +/-0.35% linear variation of the measured currents has been observed over a common range of humidities. This result is larger than the expected variation. No formal explanation of such a discrepancy has been found yet, however the present results could lead to a set of recommendations.

Air↗
PubMed1998

Improved control of gas humidity in neonatal intensive care ventilators.

Difficulties experienced by nursing staff in controlling humidity in neonatal intensive care ventilators are shown to originate in the use of a single control, namely a heater, to condition two parameters, namely temperature and humidity, at the inlet to the inspiratory tube. It is shown that better control can be achieved by separating the gas flow through the humidifier into two streams, only one of which is humidified. It is proposed that the temperature along most of the inspiratory tube should be maintained about 3-5 degrees C higher than the target delivery temperature. This eliminates the risk of condensation in the tube, a second commonly occurring problem in existing systems. It is shown why the control of ventilator systems should be based on absolute humidity, not relative humidity, even though the latter may be preferred for monitoring purposes.

Humans↗
PubMed1982

Childhood respiratory illness and the home environment. II. Association between respiratory illness and nitrogen dioxide, temperature and relative humidity.

The relation of respiratory illness to nitrogen dioxide (NO2), temperature and relative humidity in homes with a gas cooker was investigated in five and six year old children living in an urban area of the northern England. NO2 was measured for one week in the child's bedroom and living room of each home, and temperature and relative humidity were measured in the bedroom only. Information on respiratory conditions experienced by the child and characteristics of the home was collected in a self-administered questionnaire completed by the child's mother. Access was gained to 183 homes (54.3% of 337) where only gas was used for cooking. Complete information was obtained for 179 (93.7%) of 191 children who lived in the 183 homes. After allowing for the effects of age, sex, social class, and number of cigarette smokers in the home and temperature or relative humidity, no statistically significant relation was found between the prevalence of having one or more respiratory conditions and weekly average levels of NO2 in the bedroom (range 4.7 to 160.8 ppb) or living room (range 9.0 to 292.2 ppb). However, the prevalence of having one or more respiratory conditions tended to be highest in homes with high levels of NO2 and lowest in homes with low levels, consistent with earlier findings. A significant positive association was found between the prevalence of respiratory conditions and relative humidity (p less than .05). A harmful effect on health from NO2 cannot be totally dismissed but if it exists it is weak and difficult to detect in small samples of children.

Air Pollutants↗
PubMed1991

Influence of humidity and temperature on the diel periodicity of oviposition of Toxorhynchites moctezuma (Diptera: Culicidae) in the field.

The diurnal pattern of oviposition by Toxorhynchites moctezuma (Dyar & Knab), ambient relative humidity, and ambient air temperature were monitored hourly between 0600 and 1800 hours for 46 consecutive d in a tropical rainforest in Trinidad, West Indies. The mean number of eggs per ovitrap per hour was correlated negatively with mean ambient relative humidity and positively with air temperature. Partial correlation coefficients among these variables and contingency table analysis indicated a stronger relationship between the oviposition rate and relative humidity than between oviposition rate and temperature. We suggest that this relationship is further evidence of the ability of female Tx. moctezuma to detect suitable oviposition sites using humidity gradients.

Animals↗
PubMed1993

Temperature- and humidity-dependent longevity of unfed adult Hyalomma truncatum (Acari: Ixodidae).

The survival of unfed adult Hyalomma truncatum Koch held under different regimes of constant temperature (5, 17, 24, and 30 degrees C) and relative humidity (10, 50, and 80%) was monitored during > 1 yr. Longevity of this medically important African tick was shortest at the highest temperature and lowest relative humidity (100% dead at week 25). Conversely, H. truncatum lived longest at lower temperatures and higher relative humidity (< 100% dead at week 64). The combined effects of temperature and humidity, measured as vapor pressure deficit, were strongly related to survival of these ticks. The survival of males and females was similar and was independent of the weight of ticks. These findings have implications for the maintenance and study of laboratory colonies of H. truncatum and for the development of tick control strategies to reduce vectorial capacity.

Animals↗
PubMed2005

Thermoregulation responses of broiler chickens to humidity at different ambient temperatures. I. One week of age.

Three trials were conducted to investigate the effect of RH (35, 60, and 85%) on thermoregulation of 1-wk-old broiler chickens at different temperatures (35, 30, and 25 degrees C). The response to humidity in rectal temperature and plumage temperature at the back and breast within 24 h after exposure were recorded at 5 time points (1,4,8,16, and 24 h). Humidity affected the thermoregulation of 1-wk-old broiler chickens by redistributing heat within the body at high, low, and thermoneutral temperatures. The redistribution of heat resulted in decreased rectal temperature and increased peripheral temperature, which were, respectively, beneficial and unfavorable at high and low temperatures. These results suggested that feedback effects of surface temperature on core temperature also exist in poultry, as already observed in mammals, and could be induced not only by changed ambient temperature but also by the changes in humidity at high temperature. The disturbance of thermal equilibrium could not be established solely by changes in RT, but rather core and surface temperatures had to be considered. The daily rhythms in rectal and surface temperatures were affected by humidity.

Aging↗
PubMed1994

Adsorption of 222Rn by open-faced and diffusion-barrier canisters at different conditions of temperature and humidity.

Open-faced and diffusion-barrier charcoal canisters were individually exposed to a fixed temperature, humidity, and radon concentration in a chamber for a period of 7 d. The radon progeny activity in the canister under study was measured every 3 h. A total of 15 runs were made for the open-faced canisters and nine runs for the barrier canisters with temperatures and absolute humidities ranging from 15-30 degrees C and 0-15 g m-3, respectively. In addition, several runs were made with the radon, temperature, and humidity changing during the 7 d. Results show that open-faced canisters adsorb radon up to 60% more efficiently at 15 degrees C than at 30 degrees C while the barrier canisters show little temperature dependence. The barrier canisters are much less sensitive to humidity effects than the open-faced canister. When used to measure the radon concentration in air, the open-faced canister integrates over a period of only approximately 48 h while the barrier canister integrates over a period of approximately 96 h. The short integration time and the interference of water adsorption by open-faced canisters indicate that the open-faced canisters should be used for exposure times of 48 h and no longer.

Adsorption↗
PubMed1996

High 222Rn levels, enhanced surface deposition, increased diffusion coefficient, humidity, and air change effects.

Measurements have been made of surface deposition rates for 218Po radon decay products in a small (0.283m3) aluminum test chamber for 222Rn levels from 1 to 1,600 kBq m-3. an increase in macroscopic surface deposition rate has been found to be induced by the high 222Rn concentrations. A distinct 222Rn level threshold has been found below which plateout is constant at the normal rate for ambient residential conditions. Above the threshold, an increase in plateout is observed and the transition quickly reaches a constant, higher plateout. With all environmental conditions remaining constant and varying humidity, the threshold 222Rn level decreases with increasing relative humidity. The rate of rise to the new plateau is found to increase with increasing humidity. For the constant air change rate of ACH = 0.2 h-1, the fraction of airborne 218Po lost by the enhanced plateout was consistently 0.4 +or- 0.25 for seven values of humidity from 8 to 54% RH. For a fixed RH = 40 +or- 2%, it was found that the threshold increases from 5 to 58 kBq m-3 for a change in ACH from 0 1.06 h-1. In converting the deposition data to values of diffusion coefficient D, using Crump and Seinfeld's theory, a very high D of 0.18 cm2s-1 is assumed for ambient air conditions. Results indicate an ambient D = 0.027 cm2s-1. The results may impact on research utilizing high levels in test chambers and diffusion coefficients and attached and unattached fractions, and also for cancer studies using animals with 222Rn levels as much as 10(4) times greater than ambient residential levels.

Air Pollutants, Radioactive↗
PubMed1999

Structures of orthorhombic lysozyme grown at basic pH and its low-humidity variant.

The structures of orthorhombic lysozyme grown at basic pH and its low-humidity variant have been solved and refined at 1.9 and 2.0 A resolution, respectively. A comparison of the native structure with those of crystals grown at acidic pH does not show any systematic pH-dependent difference in the molecular geometry. The conformations, mutual orientation and interactions of the catalytic residues Glu35 and Asp52 also remain unchanged. However, comparison between the native and low-humidity forms in the orthorhombic form show that the changes in molecular geometry which accompany the water-mediated transformation to the low-humidity form are more pronounced in the C-terminal residues than in the other regions of the molecule. During the transformation from the native to the low-humidity form, the locations of only about half the water molecules in the hydration shell remain unchanged, but the hydration shell as a whole moves along with the protein molecule.

Animals↗
PubMed1981

Influence of environmental temperature and humidity on bronchial responses during assessment of selectivity of beta-adrenoceptor antagonists in man.

1 The effects of beta-adrenoceptor antagonists given intravenously in single doses were examined in a double-blind, placebo controlled study performed in six healthy volunteers. Heart rate and peak expiratory flow rate (PEFR) were measured at rest and during standardised exercise. 2 Atenolol 0.2 mg/kg, betaxolol 0.15 mg/kg, practolol 1 mg/kg and propranolol 0.2 mg/kg all reduced heart rate to a similar extent during exercise at 2 and 4 h after administration; betaxolol 0.6 mg/kg had a significantly greater effect than the other treatments at all times. Only betaxolol 0.15 and 0.6 mg/kg significantly inhibited exercise tachycardia at 24 h. 3 None of the treatments studied had any effect on PEFR at rest or during exercise. 4 A second study was performed to determine whether this lack of effect of propranolol on exercise PEFR could have been due to the warm and humid conditions prevailing during the experiment. Eight healthy men underwent a standardised exercise test under alternately 'warm and humid' and 'cool and dry' conditions before and after propranolol 0.2 mg/kg or saline placebo intravenously. 5 Propranolol treatment did not influence resting or exercise PEFR in either environment, but did reduce FEV1 immediately after exercise under the cool and dry conditions but not under the warm and humid conditions. 6 Comparison of the effects of beta-adrenoceptor antagonists on exercise heart rate and PEFR is not a reliable or sensitive method of measuring the cardioselectivity of these drugs. 7 Environmental temperature and humidity should ideally be controlled when the action of any drug on airflow resistance is being studied.

Adrenergic beta-Antagonists↗
PubMed1998

Preservation of humidity and heat of respiratory gases in spontaneously breathing, tracheostomized patients.

BACKGROUND: Ventilation with endotracheal intubation bypasses the upper airway and the normal heat and moisture exchanging process of inspired gases. A continuous loss of moisture and heat occurs and predisposes patients to serious airway damage. We therefore prospectively studied one heated humidifier system, one cold humidifier system and one heat and moisture exchanger in spontaneously breathing, tracheostomized intensive care unit patients to determine the ability to preserve patients' heat and water. METHODS: Following a randomized order, 10 patients were spontaneously ventilated for 24-h periods with the Nam 35 humidifier (Europe Medical, France, a cold water humidifier), the heat and moisture exchange Trach-Vent (Gibeck, Sweden), and the Aerodyne humidifier (Kendall USA). In each patient, during the inspiration phase, the following measurements were performed: mean values of temperature and relative humidity of inspired gases. The absolute humidity was calculated. Values were obtained in each patients after 40 min and 24 h. RESULTS: The Trach-Vent filter and the Aerodyne humidifier had better humidification and thermic capacities than the Nam 35 humidifier (P < 0.001). With the Nam 35 humidifier, no patient had temperature of inspired gas > 29 degrees C. Concerning absolute humidity of inspired gases, the Nam 35 humidifier achieved a lower performance than the other two tested systems (P < 0.001). CONCLUSION: In spontaneously breathing, tracheostomized intensive care unit patients, the Trach-Vent heat and moisture exchanger and the Aerodyne heated system achieved satisfactorily preservation of heat and humidity of inspired gases.

Body Temperature↗
PubMed1990

Do ambient temperature and humidity influence the breast-milk intake of babies?

This study explored the possible effect of ambient temperature and humidity on the breast-milk intakes of Australian infants (n = 35) aged 6-12 weeks. Over a 24 h period, each baby was fed only on milk from the breast; milk intakes, temperature and humidity were monitored. Milk intakes--determined by test-weighing the baby, with a correction for evaporative losses during feeds--showed a mean of 830 g/24 h, with median 818 and s.d. 152. The mean correction for evaporative losses was 46 g/24 h; omission of this correction would have led to an average underestimate of 5.5% in 24 h intakes. Ambient conditions varied substantially between subjects: 24 h mean temperatures ranged from 14 to 28 degrees C, and humidities from 48 to 97%. Over these ranges, breast-milk intakes did not appear to be significantly influenced by ambient temperature or ambient humidity; however, the rate of evaporative losses increased by 0.008 g/min for each 1 degree C rise in ambient temperature.

Australia↗
PubMed2006

Volatile organic compound (VOC) adsorption on material: influence of gas phase concentration, relative humidity and VOC type.

UNLABELLED: This paper presents the results of a factorial experiment design analysis to investigate volatile organic compounds (VOC) adsorption on a ceiling tile. The impacts of three factors, VOC gas phase concentration, relative humidity, and VOC type, as single parameters and as a combination, on adsorption have been investigated. Cyclohexane, toluene, ethyl acetate, isopropyl alcohol and methanol were the five VOCs used in this study. A factor significant level was determined through evaluating its F value and comparing it with the critical value of F distribution at 95% confidence level. It was found that: (i) neither the relative humidity and gas phase concentration nor any interaction effect between them had significant impacts on toluene adsorption on the ceiling tile; (ii) the adsorption isotherm appeared to be linear for the non-polar compounds and non-linear for the semi-polar and polar compounds; (iii) no significant impact of relative humidity on adsorption was observed for most VOC compounds except for methanol; and (iv) the ceiling tile had the highest adsorption capacity toward the polar compounds, followed by the aromatic compounds and aliphatic compounds. In addition, the statistical analysis regarding the experimental results of toluene as a single compound or as a part of a mixture showed that toluene adsorption capacity on the ceiling tile as a single compound was higher than as a part of a mixture. PRACTICAL IMPLICATIONS: Building materials and furnishings may act as source and sink of VOCs in the indoor environment. In this study, a factorial experiment design analysis technique was used to show the impact of three factors, VOC gas phase concentration, relative humidity, and VOC type, as single parameters and as a combination, on the adsorption process (sink effect). The aim was to better understand the interaction between these parameters and to verify the common assumptions made in the model development and measurement of indoor air quality.

Adsorption↗
PubMed1986

24-h evaporative and sensible heat losses in relation to ambient humidity at 24 degrees C in clothed human subjects.

The effect of ambient humidity on the energy expenditure of clothed subjects was investigated. Fifty-six healthy men and women, weighing about 65 kg, spent 24 h in a large human calorimeter at 24 degrees C and performed either of two fixed activity programmes. The ambient humidity varied between experiments from 3 to 11 g m-3. The sensible heat output did not vary significantly with humidity but the evaporative heat loss decreased by about 1.5 W for each g m-3 increase in humidity.

Adolescent↗
PubMed1980

The effect of low- and high-humidity ageing on the hardness, disintegration time and dissolution rate of dibasic calcium phosphate-based tablets.

The effect of low- and high-humidity ageing on hardness, disintegration time and dissolution rate of dibasic calcium phosphate dihydrate-based tablets prepared at different initial moisture concentrations was studied. Hardness increased while distintegration and dissolution rate decreased on ageing in low humidity. The dissolution rate of tablets containing higher initial moisture was slower than the tablets containing lower initial moisture. On ageing in high humidity, hardness, disintegration and dissolution rates decreased at all initial moistures. The results suggest that the effects of moisture and humidity should be thoroughly investigated for dibasic calcium phosphate dihydrate-based tablets in order to ensure stability and bioavailability of the drug.

Calcium Phosphates↗
PubMed1988

Influence of relative humidity on the adhesive properties of a model interactive system.

The influence of relative humidity on the adhesive properties of model drug-carrier interactive systems was investigated using the centrifuge method. The degree of adhesion was quantified by determining the S50 from the adhesion profile. High ambient humidity (greater than 40% r.h.) decreased the degree of interaction of three sulphonamide powders with model hydroxypropyl methylcellulose phthalate-coated glass bead carriers during blending. All drug-carrier interactive systems displayed decreases in the degree of adhesion during storage. The extent and rate of the decreases increased with relative humidity and was interactive system-dependent. Preconditioning the powders to varying moisture contents produced contrasting results during blending, with one system showing a decrease in adhesion as the relative humidity increased, while the other's interactive capability increased. This increase was attributed to the enhancement of charging sites on the drug's powders surface by the adsorbed moisture.

Adsorption↗
PubMed1993

Effect of environmental humidity on the transformation pathway of nitrofurantoin modifications during grinding and the physicochemical properties of ground products.

The effect of humidity on the physicochemical properties of nitrofurantoin anhydrate and monohydrate during grinding in a humidity-controlled system was investigated using X-ray diffraction analysis, IR spectroscopy, thermal analysis and scanning electron microscopy. Anhydrate and monohydrate were transformed into a noncrystalline solid and a stable monohydrate, respectively, during grinding in a closed system. During grinding in an open system, in which the humidity level of the air was controlled (5, 50 and 75% r.h.), the anhydrate absorbed moisture from the supplied air and water content was increased at 75% r.h.; thereafter the compound was transformed into monohydrate II. The anhydrate did not absorb at 5 or 50% r.h. and was transformed into a noncrystalline solid. Monohydrate I desorbed crystal water during grinding at 5% r.h. and was transformed into a noncrystalline solid. However, monohydrate I was transformed into monohydrate II at 50 and 75% r.h. without desorption of crystal water. These results suggest that the solid-state transformation of nitrofurantoin during grinding depends upon the environmental humidity.

Anhydrides↗
PubMed1979

Air humidity and carotid rete function in thermoregulation of the goat.

1. The effects of air humidity on respiratory rate have been studied in conscious goats exposed to an air temperature of + 33 degrees C. Before the experiments the animals had been chronically implanted with hypothalamic thermodes and intravascular heat exchangers to manipulate hypothalamic and general body core temperatures.2. Raising air humidity from 37 to 96% at constant air temperature resulted in a rise of respiratory rate, an immediate increase in hypothalamic temperature and a delayed smaller increase in general body core temperature.3. The rise of respiratory rate was smaller when general body core temperature was clamped at its control level and was absent when hypothalamic and general body core temperatures were clamped at their control levels during the humid air phase.4. It is concluded that the effect of high air humidity on respiratory rate in goats is predominantly the result of a rise in hypothalamic temperature acting on local thermosensitive structures. The carotid rete heat exchanger is thought to provide the thermal link between the evaporating surfaces of the upper respiratory tract and the hypothalamus.5. This function of the carotid rete heat exchanger is restricted to heat stressed animals. In animals subject to central cooling no local effects on hypothalamic temperature could be observed when the temperature of the inspired air was altered from + 33 to - 17 degrees C.

Animals↗