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PubMed1989

[Factors affecting the setting time of zinc oxide-eugenol impression materials--the influence of humidity and temperature to the reaction velocity].

Zinc oxide-eugenol paste are widely used in clinical dentistry, principally for impression of non-undercut edentulous ridges, or bite taking materials. However it has been realized by those who use these paste that different products, direction for mixing, or different conditions for mixing, have different characteristics. An experiment have been made to observe the influence of different conditions for mixing to the setting time. Zinc oxide-eugenol impression pastes were mixed in accordance with the manufacturer's instruction when supplied. The condition for mixing was at temperature of 15 +/- 1, 20 +/- 1, 25 +/- 1, 30 +/- 1 degrees C and at humidity of 40 +/- 5, 70 +/- 5, 90 +/- 5%. The setting time (a initial setting time, a final setting time) was defined in the A.D.A. specification No. 16. The following results were obtained. 1. A higher temperature and humidity shortened the initial setting time of all paste. 2. A higher temperature and humidity shortened slightly the time interval between a initial and a final setting time of all paste. 3. In clinical use, sample C is better than other ones, so that a setting time of the sample is property for impression making.

Dental Impression Materials↗

PubMed1991

Effect of humidity on the deswelling function of the human cornea.

The present study determined the effect of the full range of humidities on the deswelling function of the human cornea. The closed-eye deswelling function and the open-eye deswelling responses for five different levels of humidity (0%, 25%, 60%, 85%, and 100%) were assessed for 8 normal, young-adult subjects. Open-eye corneal deswelling for the 8 subjects was unaffected by relative humidities from 0 to 100%. Therefore, osmotically-driven corneal thinning effect of tear evaporation does not significantly contribute to the deswelling function of the human cornea. We conclude, contrary to recent reports, that the endothelial pump is the primary mechanism that maintains normal corneal thickness and provides recovery from stromal edema.

Adult↗

PubMed1992

Study of lipid changes in freeze-dried fish during storage. I. The interaction of relative humidity and tissue lipids.

Several studies on lipid stability of freeze-dried fish pointed out the relationship between relative humidity (RH) and autoxidation of highly unsaturated fatty acids. The present study shows the changes of tissue lipids in two different fish, freeze-dried and stored under various RH conditions. Fillets of Scomber scomber L and Sardina pilchardus sardina were freeze-dried and stored for 1, 3, 6 and 9 months. periodically, the sample of both fish were analyzed to evaluate the autoxidation of lipids. The results show that the autoxidation of lipids is quicker during 1st-3rd month of storage, while in a high humidity environment the tissue lipids change slower. According to these results both time of storage and relative humidity must be controlled to maintain the nutritive value of freeze-dried fish.

Animals↗

PubMed1992

Heat stress in protective clothing: validation of a computer model and the heat-humidity index (HHI).

Ability to work while wearing protective clothing is often limited by rising body temperature. Peterson analyzed the combined effects of heat, humidity and workload using the Texas Model of Thermoregulation and suggested that environmental heat load imposed on a person wearing heavy, semipermeable clothing could be predicted using the Heat-Humidity Index (HHI = 0.5 Tdb + 0.5 Twb), where Tdb = dry bulb temperature and Twb = wet bulb temperature. Our study was designed to: 1) test the validity of this computer model; and 2) evaluate the applicability of the HHI to heavily clothed subjects working in a variety of thermal environments. Nine men wearing chemical defense clothing were each studied under eight conditions over the range Tdb = 20 - 40 degrees C, Tbg = Tdb + 5 degrees C, relative humidity = 9-75%, and oxygen uptake = 14-27 ml.kg-1 x min-1. Variables analyzed included tolerance time (TT), rectal temperature (Tre), skin temperature, heart rate (HR), weight loss, sweat rate, evaporation rate, and evaporative efficiency. Experiments were designed to last 30-180 min, and continued until Tre = 39 degrees C except when subjective tolerance limits occurred first (12 of 72 experiments). The observed time to reach Tre = 39 degrees C bracketed the predicted time in the more severe conditions, but the model seriously underestimated heat storage in the milder conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed1992

Impact of tropical conditions on thin layer chromatography in analytical toxicology: high temperatures and moderate humidities.

The impact of high temperatures (24 to 39 degrees C) and low to moderately high humidities (20 to 70%) on the applicability of TLC systems for drug identification was studied during a 6 month climatologic cycle in Burkina Faso (West Africa). In general, the Rf values as observed on the plates were found to be substantially affected as compared with values obtained at temperate climates. Some TLC systems were more affected than others and the largest deviations of up to 30 Rf units were at low humidities. Tropical conditions also had a negative effect on the reproducibility of Rf values. However, when an Rf-correction procedure was applied, using reference mixtures of known drugs on each plate, accuracy as well as reproducibility of the resulting Rfc values were drastically improved and data thus corrected were found to be compatible with existing TLC data bases developed under moderate climatological conditions. The impact of high to extremely high humidities (70 to 100%) remains to be investigated.

Burkina Faso↗

PubMed1991

[Disturbances in the process of hatching of larvae Argas (A) reflexus (Fabr.) (Acari: Ixodida: Argasidae) exposed to various thermal and humidity conditions].

The most cases of abnormal hatch larvae (40.2%) of A. reflexus were in relative humidity 90% and temperature 25 degrees C; the least (0-2.8%)--at the low relative humidity levels (10 and 30%) in all examined temperatures of experiments. The rise of relative humidity caused the greater number of the disturbances of hatch larvae. The most often +non-separation of integument eggs from body of larvae was observed, what made impossible normal formation of legs and made difficult locomotive faculty.

Animals↗

PubMed1976

Effect of temperature and relative humidity on variola virus in crusts.

The viability of variola virus in crusts under different conditions of temperature and relative humidity was studied for 16 weeks. At the ambient temperature of 25.8-26.4 degrees C and 85-90% relative humidity, the virus survived only 8 weeks but at lower temperatures and relative humidities the survival time was considerably prolonged.

Humans↗

PubMed1990

[Characteristics of the relative humidity and temperature in the inspiratory part of the Dräger circle system and their influence on the function of the ciliary epithelium].

Changes in relative humidity and temperature of the anaesthetic gases were measured in the inspiratory limb of the Dräger circle system next to the carbon dioxide absorber in 29 patients requiring ENT surgery under general anaesthesia. Immediately following intubation and prior to extubation, nasal and tracheal cytologic samples were taken with a brush technique and ciliary beat frequency was determined. At a fresh gas flow of 6 l/min, relative humidity increased from 57.6 +/- 1.5 to 62.5 +/- 1.8% (p less than 0.05) after 110 minutes. Temperature increased continuously from 21.96 +/- 0.97 degrees C to 23.83 +/- 0.48 degrees C after 200 minutes. The number of vital ciliated cells in the tracheal samples decreased from 24.4% following induction of anaesthesia to 6% at the end of anaesthesia (p less than 0.05), and from 35.7% to 26.8% (p less than 0.05) in the nasal samples. Ciliary beat frequency remained unchanged at the end of anaesthesia as compared to control in tracheal as well as in nasal samples. It is concluded that the output of relative humidity and temperature in the circle system is not sufficient to prevent broncho-epithelial damage. Ciliary beat automaticity appears to behave according to an all or nothing principle.

Adult↗

PubMed1989

[Drug interactions during storage of mixtures of the antacid group. III. Effect of relative humidity on structural changes in mixtures aluminum hydroxide gel and magnesium hydroxide in the solid phase].

Mixtures of A1(OH)3 gel and Mg(OH)2 were stored for 14 months in the solid phase in chambers with relative air humidity of 35%, 55%, 76% and 92%. IR spectra of the stored mixtures were measured. In mixtures stored at relative air humidity of 35% there were found no changes in IR spectra, while the mixtures stored at relative air humidity of 92% proved to exhibit IR spectra characteristic for hydrotalcite.

Aluminum Hydroxide↗

PubMed1988

Humid air increases airway resistance in asthmatic subjects.

Eight persons with asthma were exposed to seven air conditions varying in temperature (37 degrees C to 49 degrees C [98.6 degrees F to 120.2 degrees F]) and water content (44 mg H2O per liter to 79 mg H2Oper liter) . Normocapnic hyperventilation for three minutes at 40% maximal voluntary ventilation was carried out for each condition. A constant-volume body plethysmograph measured the functional residual capacity and specific airway conductance (SGaw), followed by two forced expiratory manuevers. Measurements were taken before and 1, 5, 10, and 20 minutes after each challenge. Air conditions with 100% relative humidity caused a fall in the SGaw that was maximal in 1 minute. Air conditions at 100% relative humidity caused a greater fall in both the forced expiratory volume in 1 second (FEV1) (P<.05) and the SGaw (P<.005) than did conditions of the same temperature but less water content. At 44 degrees C and 100% relative humidity, the mean percent change in FEV1 and SGaw was -2% and -40%, respectively, at 1 minute after challenge. Of the conditions examined, the optimal temperature was 44 degrees C, and we speculate that the optimal water content is less than 44 mg H2O per liter. Inhaled water concentrations exceeding 44 mg H2O per liter should probably not be used in patients with asthma.

Adult↗

PubMed1977

Studies on water vapor pressure gradient from external air through clothing to the skin in relation to external humidity and clothing conditions.

Using a hygrometric capsule method developed by the authors, water vapor pressure was measured at each layer of clothing as well as at the skin surface on a human subject under actual wearing conditions. The pattern of vapor pressure gradient from the skin surface through clothing to the external air was examined in relation to the ambient vapor pressure and ths sort of textiles worn. The following findings were obtained. 1) Water vapor pressure gradient was greater between coat and external air than that between coat and underwear. The gradient became steeper again between underwear and the skin. 2) Under given clothing conditions, vapor pressure at each layer of clothing as well as at the skin varied according to the ambient humidity. However, the pattern of vapor pressure gradient from the skin through clothing to the external air was not greatly influenced by the external humidity. 3) The pattern of vapor pressure gradient from the skin through clothing to the external air was not greatly influenced by the external humidity. 3) The pattern of vapor pressure gradient through the clothing as a whole differed according to the kinds of textiles used for coat and underwear.

Adult↗

PubMed1977

[Effect of the temperature-humidity regime during broiler raising on serum proteins and amino acids].

The study on the effect of the temperature and moisture regime on the serum proteins and amino acids in broiler chickens has revealed that under the conditions of relatively lower temperatures and higher relative moisture levels the total protein, the albumin, and the gamma-globulin fraction show higher contents. Noticeable are also some changes in the content of the bound amino acids (tyrosin, alfa- and beta-alanine, aspartic acid, and glycin) in the blood sera that are likewise depending on the temperature and moisture regime. The total amount of amino acids and the free forms of arginine and lysine are at higher levels in the broilers raised prior to the experiment at 32 degrees C and relative air humidity 70--75 per cent. With the remaining free and bound amino acids in the blood serum there are no differences in broilers raised at various temperature and moisture regimes. The body weight of broilers raised prior to the experiment at 32 degrees C and relative air humidity 70--75 per cent is higher, while the consumption of forage for kilogram weight gain is lower as compared to that with birds raised at higher temperature and lower relative humidity (35--45 and 50 per cent).

Amino Acids↗

PubMed1978

Influence of heat, wind, and humidity on ultraviolet radiation injury.

We investigated the influence of heat, wind, and humidity on UVR-induced acute and chronic skin damage of experimental animals housed in environmental chambers and irradiated under controlled conditions. Hairless mice (strain HRS/J) irradiated after an increase of 10 degrees F in skin temperature had more skin damage than irradiated controls. Significantly more Swiss albino mice irradiated for 400 days while maintained at 90 degrees F developed tumors than did those receiving the same amount of UVR but maintained at room temperature. Mice exposed to UVR daily for 4 weeks while kept in wind of 7 mph had greater damage and slower recovery than animals irradiated but protected from wind. Wind also accelerated tumorigenesis in mice than received chronic UVR. Mice kept at 80% relative humidity and given a single dose of UVR had greater skin injury than animals irradiated while at 5% relative humidity. High midity also appears to accelerate skin cancer formation in animals that were exposed to chronic UVR.

Air Movements↗

PubMed1978

Heat stress upon undressed man due to different combinations of elevated environmental temperature, air humidity, and metabolic heat production: a critical comparison of heat stress indices.

In several 100 climatic chamber experiments young healthy acclimatized men were exposed successively to combinations of ambient temperature and air humidity that were varied systematically from day to day within the range of 15 to 57 degrees C and 8 to 97% relative humidity, with air speed kept constant at 0.3 m/s. The subjects who were nearly nude were exposed at rest and at different treadmill work levels (metabolic rates up to about 1350 kJ/h). Each exposure lasted between two and six h. It was found that body temperatures and heart rate, but not loss of sweat, were suitable criteria for indicating equal stress conditions. Equations were derived describing those climatic combinations which were equivalent at the various activity levels of each subject. The slope of the respective equivalence curves plotted in psychrometric charts varied systematically with work level. The curves obtained for various subjects at any given activity level showed similarities, so that the calculation of an equivalence system common to all subjects seemed to be justified. A detailed comparison of these results with previous indices is presented. The combinations of ambient temperatures and humidities that were found to be equivalent under the given conditions of physical activity corresponded particularly well with the Index of Physiological Effect (ROBINSON et al.). There was also good agreement with the P4SR Index (MCARDLE et al.). The combinations corresponded with other indices (Heat Stress Index of BELDING and HATCH, Index of Thermal Stress of GIVONI) and with Basic Effective Temperature and Wet-bulb Globe Temperature only within limited ranges of climate depending upon work level. A procedure is presented which allows one to evaluate in terms of physiological responses how far various indices describe equivalent stress conditions correctly.

Adult↗

PubMedDate not supplied

Air humidity and mucociliary activity.

The relationship between varying humidity levels in the surrounding air and the mucociliary activity in rabbit trachea has been investigated. At a relative humidity (R.H.) above 70% the risk for ciliestasis is very small in the temperature range between 34 C and 40 C. At 37 C ciliestasis is not obtained until a relative humidity (R.H.) of 50% has been reached. The critical border is reached already at 60% R.H. if the temperature is 40 C. At 37 C and a decrement from 90% to 60% R.H. the mucociliary wave frequency was reduced by 30%, but at 40 C the corresponding reduction was 60%.

Animals↗

PubMed1975

[The problem of the measurement of relative humidity in the disinfecting dryceaning process (author's transl)].

One of the most important conditions for obtaining reproducible microbiological results by disinfecting drycleaning is a control of the relative humidity of the drycleaning bath. An apparatus called "Wasserkontroller" (see Fig. 1) had been recommended as a device for the determination of the relative humidity. It consists of a special cylindrical casing into which the sensor of a hair hygrometer has been introduced. In contrast to electric instruments, this apparatus has the advantages of rigidity, simple adjustment, and above all of a low cost price. In practice, however, the "Wasserkontroller" proved to be a failure, since it indicated false values at times. In the studies published and discussed in the present paper, the causes for the malfunction of the hair hygrometer, in the device mentioned were determined. It could be observed that a malfunction of the hair hygrometer mainly occurred when the hairs fixed in the sensor were moistened by the drycleaning bath or by the drycleaning solvent (perchloroethylene), respectively. Then the hair hygrometer is no longer capable of reacting sufficiently to the fluctuation of the relative humidity of the bath. On the basis of the experimental results obtained instructions are given for the employment of hair hygrometers in drycleaning and for the design of the device casing: 1. The hair hygrometer has to be protected inside the device casing against a contamination by the bath or the condensing drycleaning solvent. 2. The inlet pipes to the device casing and the casing itself have to be protected against loss of heat as well as against the influence of heat sources. Temperatures of drycleaning bath and device should be balanced. 3. The inlet pipes to the device should be provided with a flowmeter or a flow detector, respectively. 4. The outlets of the device should be connected directly with the drum filled with the drycleaning bath. 5. The device has to be constructed in such a way that no infiltrated air may be sucked in. 6. The hair hygrometer has to be cleaned and to be adjusted at suitable time intervals. Provided that the technical requirements are met, hair hygrometers may also be considered as reliable measuring instruments in the practice of drycleaning.

Clothing↗

PubMed1977

Effect of temperature and relative humidity on nitrazepam stability in solid state.

The decomposition of a 1% dilution of nitrazepam in microcrystalline cellulose was established by quantitative determination of the two main breakdown products, 2-amino-5-nitrobenzophenone and 3-amino-6-nitro-4-phenyl-2(1H)-quinolone, using in situ diffuse reflectance measurements on thin-layer chromatograms. The decomposition and formation rate constant of nitrazepam and of the breakdown products, respectively, were determined at four temperatures and six relative humidities. By means of a three-parameter regression equation, it was possible to correlate quantitatively the decomposition constant of nitrazepam to both temperature and relative humidity.

Chromatography, Thin Layer↗

PubMed1990

Effect of hydrophobic coating on the behavior of a hygroscopic aerosol powder in an environment of controlled temperature and relative humidity.

Powders of uncoated disodium fluorescein (DF) and DF coated with various amounts of lauric or capric acids were generated as aerosols in an environment of controlled temperature and relative humidity. The particle size and distribution of these powders were characterized using a cascade impactor and a computerized data inversion method of analysis. Disodium fluorescein exhibited a hygroscopic growth ratio of 1.5 at a relative humidity of 97%. This growth was reduced to 1.3 by coating with 0.15 g of lauric acid or 0.8 g of capric acid per gram of DF, and was eliminated with 0.2 g of lauric acid or 0.18 g of capric acid per gram of DF. The reduction in hygroscopic growth probably reflects an inhibition of the growth rate. In the time following generation and prior to deposition in the collection device, approximately 40 s, the coated aerosol powders do not seem to reach their equilibrium droplet diameter. These studies indicate that these combinations of DF and fatty acid would result in larger equilibrium droplet diameters than that of the dye alone.

Aerosols↗