SEARCH · PubMed Health

Results for “Humidity”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources

PubMedDate not supplied

Heated breathing tubes affect humidity output of circle absorber systems.

STUDY OBJECTIVE: To verify whether the airway climate in circle systems can be improved with heated breathing tubes. DESIGN: Randomized, controlled, prospective clinical study. SETTING: Operating theater of the Department of Maxillofacial Surgery. PATIENTS: 26 adult patients undergoing prolonged anesthesia. INTERVENTIONS: A total of 26 prolonged anesthetics were conducted in adult patients using a minimal fresh gas flow rate (0.6 L/min) and silicon breathing tubes (16 mm internal diameter) containing a heated coil. Group 1 (n = 10 patients) was the control group; breathing tubes were unheated. In Group 2 (n = 10 patients), breathing tubes were heated to 30 degrees C. In Group 3 (n = 6 patients), breathing tubes were heated to 36 degrees C. MEASUREMENTS AND MAIN RESULTS: Humidity and temperature were measured at the Y-piece. Inspiratory temperature on Group 2 was significantly higher than in Group 1. In Group 3, both inspiratory temperature and absolute humidity were significantly higher than in Group 1. After 5 minutes of ventilation, water content and temperature of inspiratory gases were significantly higher in Group 3 than in Group 1. CONCLUSION: Low-flow systems need at least 120 minutes to achieve a satisfactory airway climate. Heated breathing tubes effectively reduce this delay.

Absorption↗

PubMed2007

Atrazine sorption and fate in a Ultisol from humid tropical Brazil.

This study combined laboratory based microcosm systems as well as field experiments to evaluate the mobility of atrazine on a Ultisol under humid tropical conditions in Brazil. Results from sorption experiments fit to the Freundlich isotherm model [K(f) 0.99 mg kg(-1)/(mg l(-1))(1/n)], and indicate a low sorption capacity for atrazine in this soil and consequently large potential for movement by leaching and runoff. Microcosm systems using (14)C-atrazine to trace the fate of the applied herbicide, showed that 0.33% of the atrazine was volatilized, 0.25% mineralized and 6.89% was recorded in the leachate. After 60 d in the microcosms, 75% of the (14)C remained in the upper 5 cm soil layer indicating atrazine or its metabolites remained close to the soil surface. In field experiments, after 60 d, only 5% of the atrazine applied was recovered in the upper soil layers. In the field experiments atrazine was detected at a depth of 50 cm indicating leaching. Simulating tropical rain in field experiments resulted in 2.1% loss of atrazine in runoff of which 0.5% was adsorbed onto transported soil particles and 1.6% was in solution. Atrazine runoff was greatest two days after herbicide application and decreased 10 fold after 15 d. The use of atrazine on Ultisols, in the humid tropics, constitutes a threat to water quality, causing surface water and ground water pollution.

Adsorption↗

PubMed2005

Adsorption of water vapour from humid air by selected carbon adsorbents.

The water uptake by carbon molecular sieves (CMS) and graphitized carbons, all of which are used to determine volatile organic compounds in air, was investigated using a direct experimental approach. CMS, e.g. Carboxen 1002, Carboxen 1003 and Anasorb CMS adsorb substantial amounts of water, in the range 400 to 450 mg per gram of adsorbent. Graphitized carbons, e.g. Carbrogaph 5TD and Carbopack X show low water trapping, less than 30 mg g(-1) and Carbopack Y as little as 5 mg g(-1) or less. The water sorption capacity for graphitized carbons is strongly dependent on the relative humidity (RH). The change of RH from 95 to 90% decreases the amount of adsorbed water by more than a factor of 2. Two different water adsorption mechanisms are operative: adsorption on polar centers and micropore volume filling. For graphitized carbons and CMS at low RH, adsorption on polar centers is involved. For CMS, once the threshold value of relative humidity (RHth) is surpassed, micropore volume filling becomes predominant. RHth is 44 +/- 3 and 42 +/- 3% for Carboxen 1002 and 1003, respectively, and 32 +/- 3% for Anasorb CMS. The CMS mass in the trap was found not to affect the mass of retained water under condition of incomplete saturation of adsorbent bed with water. Thus, the restrictions commonly imposed on the CMS mass are not necessary. The dry purging technique is suggested to remove adsorbed water. Carbograph 5TD and Carbopack X require only a few hundred ml of dry air to remove adsorbed water entirely. Water can also be purged out from CMS; however, much larger volumes of dry air are needed.

Adsorption↗

PubMed2004

Determining the critical relative humidity for moisture-induced phase transitions.

A new method to determine the onset relative humidity for a glass transition and crystallization processes in amorphous or partially amorphous materials was developed using dynamic gravimetric vapor sorption (DVS). Water vapor can act as a plasticizing agent in amorphous materials, thus lowering the glass transition temperature below room temperatures. Additional water sorption can lead to a crystallization event below the glass transition temperature. On spray-dried lactose the glass transition RH and crystallization RH values were 30 and 58% at 25 degrees C, respectively. Glass transition and crystallization RH values were also measured at 5, 15, 25, 35, and 45 degrees C on a spray-dried salbutamol sulfate sample. The glass transition RH values for the salbutamol sulfate sample ranged from 64.5% RH (5 degrees C) to 32.8% RH (45 degrees C) while the crystallization RH values ranged from 81.0% RH (5 degrees C) to 50.4% RH (45 degrees C). The results clearly show that the glass transition and crystallization humidity values decrease as the sample temperature increases.

Albuterol↗

PubMed2004

Crystal forms of tolbutamide from acetonitrile and 1-octanol: effect of solvent, humidity and compression pressure.

The possibility of obtaining tolbutamide polymorphs was investigated using the solvents acetonitrile and 1-octanol. Tolbutamide is an oral hypoglycemic agent that exists in four polymorphic forms. Characterization of the various polymorphs was carried out by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), infrared spectroscopy (FTIR), optical microscopy and dissolution studies. Form A, crystallized from acetonitrile, resembled the form I polymorph, while form O, crystallized from 1-octanol, resembled the form III polymorph. Tablets of both form A and form O were produced at compression pressures of 2500 lbs and 5000 lbs using cornstarch and talc and were exposed to 40%, 75% and 95% RH conditions. DSC and PXRD studies did not show any significant drug-excipient interaction. Moreover, the change in the crystalline state of either form upon exposure to humidity was not evident. Dissolution studies showed a significantly lower drug release rate from form O tablets compressed at 5000 lbs pressure and exposed to 95% RH. Pressure and humidity had no significant effect on the dissolution profiles on the form A tablets. It was concluded that form A was the robust choice for further formulation development.

1-Octanol↗

PubMed2006

Dehydration of trehalose dihydrate at low relative humidity and ambient temperature.

The physico-chemical behaviour of trehalose dihydrate during storage at low relative humidity and ambient temperature was investigated, using a combination of techniques commonly employed in pharmaceutical research. Weight loss, water content determinations, differential scanning calorimetry and X-ray powder diffraction showed that at low relative humidity (0.1% RH) and ambient temperature (25 degrees C) trehalose dihydrate dehydrates forming the alpha-polymorph. Physical examination of trehalose particles by scanning electron microscopy and of the dominant growth faces of trehalose crystals by environmentally controlled atomic force microscopy revealed significant changes in surface morphology upon partial dehydration, in particular the formation of cracks. These changes were not fully reversible upon complete rehydration at 50% RH. These findings should be considered when trehalose dihydrate is used as a pharmaceutical excipient in situations where surface properties are key to behaviour, for example as a carrier in a dry powder inhalation formulations, as morphological changes under common processing or storage conditions may lead to variations in formulation performance.

Calorimetry, Differential Scanning↗

PubMed2005

Effects of partial humid heat exposure during different segments of sleep on human sleep stages and body temperature.

The effects of partial humid heat exposure applied at different segments of sleep on sleep stages and body temperature were examined. In the first experiment, eight male subjects slept under 26 degrees C 50% (26) and 26 degrees C for the first 3 h and 45 min followed by a 30-min transition to the conditions of 32 degrees C 80%, which was maintained for the final 3 h and 45 min (26-32). Wakefulness increased significantly over the last 4 h under 26-32 compared to 26. Mean skin temperature and clothing microclimate temperature (Tcm) were significantly higher during the last 3 h and 45 min, while rectal temperature (Tre) was higher during the last 3 h under 26-32 than in 26. In the second experiment, eight male subjects slept under 26 degrees C 50% (26) and 32 degrees C 80% for the first 3 h and 45 min followed by a 30-min transition to 26, which was then maintained for the last 3 h and 45 min (32-26). Wakefulness increased both in first and during the last 4 h, and slow wave sleep (SWS) decreased in the first 4 h under 32-26 compared to 26. Mean Tsk was significantly higher during the first 4:15 h. Tcm decreased in 32-26 compared to 26 just after the 30-min transition due to cooling effects. Tre was higher during the first 5 h under 32-26 compared to 26. These results suggest that humid heat exposure during the initial segment of sleep may be more disruptive to sleep stage distribution, Tre decline, and maintenance of Tcm than the same exposure during the later sleep segments.

Adult↗

PubMed2000

Column study of the influence of air humidity on the retention of hydrocarbons on soil.

Inverse gas chromatography (IGC) is used for the analysis of the influence of air relative humidity on the retention of hexane, benzene, toluene and p-xylene in a sandy soil under experimental conditions similar to those typical of soil vapor extraction (SVE). The advantages of IGC over other techniques, are (a) an efficient use of lab resources, (b) a high sensitivity to low partitioning coefficients and (c) a closer reproduction of field conditions. In our procedure, experiments with only two samples of different mass are necessary to establish if linear isotherms can be used to describe the retention of the contaminants. This approach gives information necessary for analyzing the feasibility and design of remediation technologies with a laboratory effort significantly smaller than the adsorption/desorption cycle for isotherm determination. The retention coefficients of the contaminants decrease as humidity increases in a similar fashion for all of them, probably because the reduction in the number of the adsorption sites available for the organic compounds due to the presence of water is quite similar for all the contaminants studied. These retention coefficients may be related to those obtained for dry air conditions for all the contaminants through (R - 1)RH% = A(R - 1)dry air(B), where the parameter B is found to remain approximately constant (0.90), while the parameter A decreases linearly with the relative moisture.

Adsorption↗

PubMed1998

High environmental temperature and humidity decrease oocyte quality in Bos taurus but not in Bos indicus cows.

Two experiments were conducted to assess the effects of environmental temperature and humidity on the quality and developmental capabilities of bovine oocytes. In Experiment 1, Bos taurus (Holstein and crossbred Angus) cows were subjected to 5 weekly sessions of ultrasound-guided follicle aspiration from February 16 through March 23 (cool season) and 5 sessions from May 22 through June 20 (hot season). In Experiment 2, Bos taurus (Holstein) and Bos indicus (Brahman) cows were superstimulated (Super-Ov) during the months of August (hot season) or January (cool season), and each cow was subjected to a single oocyte aspiration session. In each experiment, oocytes were classified as normal or abnormal based on ooplasm morphology and cumulus cell layers. In Experiment 1, oocytes classified as normal were in vitro matured and fertilized (IVM/IVF), and the resulting embryos cultured for 8 d. All oocytes recovered from superstimulated cows in Experiment 2 were matured and fertilized in vitro and the subsequent embryos cultured for 8 d, regardless of their morphological appearance. In Experiment 1, Bos taurus cows produced a higher (P = 0.02) percentage of normal oocytes during the cool season (75.9 +/- 8.0) than during the hot season (41.0 +/- 9.5). The percentage of fertilized oocytes developing to the 2-cell (82.4), 8-cell (65.4) and morula (46.6) stages were also greater (P < or = 0.06) during the cool season than the hot season (45.0, 21.2, 6.0 for 2-cell, 8-cell and morula stages, respectively). In Experiment 2, Bos taurus cows (Holstein) had a lower (P = 0.01) percentage of normal oocytes in the hot season (24.5 vs 80.0) and a lower (P < or = 0.003) percentage of fertilized oocytes developing to the 8-cell, morula and blastocyst stages. No difference (P > or = 0.57) in the percentage of normal oocytes or in embryo development was detected between seasons in Bos indicus (Brahman) cows. In conclusion, high environmental temperature and humidity resulted in a marked decline in the quality of oocytes retrieved from Bos taurus cows and markedly decreased their in vitro developmental capabilities. In contrast, a high percentage of oocytes retrieved from Bos indicus cows exhibited normal morphology and yielded a high proportion of blastocysts, regardless of season.

Animals↗

PubMed1996

Viability of the sporocysts of Sarcocystis cruzi after exposure to different temperatures and relative humidities.

The effect of temperature and relative humidity (RH) on the survival of sporocysts of S. cruzi were investigated in vitro. Under all experimental conditions (temperature of 4 degrees C, 37 degrees C, or room temperature; RH of 18%, 75%, or 100%) some sporozoites retained their viability to excyst for at least 90 days. The best conditions for survival were 4 degrees C at 100% RH (more than 240 days) and 37 degrees C at 18% RH (more than 180 days). Sporocysts maintained at room temperature at all humidities had the lowest level of survival. It is concluded that sporocysts of S. cruzi are able to survive in most environments for several months and that the fluctuation of the daily ambient temperature is likely to influence the viability of the sporocysts.

Animals↗

PubMed2000

Calorimetry a method to be used to characterise pyrolytically decarboxylated bicarbonate and assess its stability at elevated humidities.

Microcalorimetry was used to characterise bicarbonate after treatment at high temperatures. By measuring the heat flow from a sample of bicarbonate at 100% relative humidity, the net exothermic contribution could be used to estimate the fraction of pyrolytically formed Na(2)CO(3). The enthalpy value corresponding to the heat of solution of Na(2)CO(3) was also applicable to a physical mixture of NaHCO(3)/Na(2)CO(3). However, from the characteristic peaks of the heat flow versus time curve, pyrolytically formed Na(2)CO(3) could be distinguished from that present in the physical mixture. The different bicarbonate batches of varying degree of pyrolytic decarboxylation were also observed at an elevated relative humidity of 54%. From these measurements it could be inferred that a decarboxylation of up to 4.5% could be allowed without any significant effect on the stability of bicarbonate at 54%.

Calorimetry↗

PubMed2001

The use of inverse phase gas chromatography to study the change of surface energy of amorphous lactose as a function of relative humidity and the processes of collapse and crystallisation.

The purpose of this study was to assess the effect of relative humidity (RH) on the surface energy of amorphous lactose. Two samples of amorphous lactose were investigated; a spray dried 100% amorphous material and a ball milled sample of crystalline lactose. The milled sample had less than 1% amorphous content by mass, but on investigation at 0% RH, yielded surface energies comparable to those obtained from the 100% amorphous material, indicating that the surface was amorphous. The effect of increasing humidity was to reduce the dispersive surface energy of the two samples from 36.0 +/- 0.14 and 41.6 +/- 1.4 mJ m(-2) at 0% RH for the spray dried and milled samples respectively, to a value comparable to that obtained for the crystalline alpha-lactose monohydrate of 31.3 +/- 0.41 mJ m(-2). The change in surface energy due to water sorption was only reversible up to 20% RH; after exposure to higher RH values subsequent drying did not result in a return to the original surface energy of the amorphous form. This shows that the surface is reorganising as the glass transition temperature (Tg) is reduced, even though the sample has not collapsed or crystallised. It was possible to follow the collapse behaviour in the column with ease, using a number of different methods.

Absorption↗

PubMed2002

The influence of relative humidity on particulate interactions in carrier-based dry powder inhaler formulations.

An atomic force microscope (AFM) colloid probe technique has been used to investigate the effect of relative humidity (RH) on the adhesion properties of pharmaceutical powder surfaces. The adhesion between a model substrate, alpha-lactose monohydrate, and model particulate drugs, salbutamol sulphate and budesonide, was investigated between RHs of 15 and 75%. The surface topography of the model alpha-lactose monohydrate was produced by controlling the supersaturation conditions during crystal growth to produce sub-nanometre scale roughness. The adhesion interactions between lactose and drug probes of salbutamol sulphate and budesonide were shown to be significantly increased with each incremental rise in humidity. Capillary forces were significantly more dominant for the adhesion in the budesonide-lactose system up to 60% RH but were more dominant for salbutamol sulphate-lactose above 60% RH. These studies suggested that non-surface-specific capillary forces play a dominant role in the adhesion between drug and carrier, which may significantly reduce the deaggregation and dispersion properties of a dry powder formulation.

Administration, Inhalation↗

PubMed2000

Remote query measurement of pressure, fluid-flow velocity, and humidity using magnetoelastic thick-film sensors.

Free-standing magnetoelastic thick-film sensors have a characteristic resonant frequency that can be determined by monitoring the magnetic flux emitted from the sensor in response to a time varying magnetic field. This property allows the sensors to be monitored remotely without the use of direct physical connections, such as wires, enabling measurement of environmental parameters from within sealed, opaque containers. In this work, we report on application of magnetoelastic sensors to measurement of atmospheric pressure, fluid-flow velocity, temperature, and mass load. Mass loading effects are demonstrated by fabrication of a remote query humidity sensor, made by coating the magnetoelastic thick film with a thin layer of solgel deposited Al2O3 that reversibly changes mass in response to humidity.

Atmospheric Pressure↗

PubMed2001

The changes in surface energetics with relative humidity of carbamazepine and paracetamol as measured by inverse gas chromatography.

The surface energetic parameters of carbamazepine and paracetamol have been studied using inverse gas chromatography modified to produce dry and ambient conditions within the column. The values of the dispersive component of the surface free energy (gamma(S)D) do not change significantly at the increased relative humidity. In contrast the specific component of the free energy of adsorption (-DeltaG(A)SP) as measured by polar probes, can either remain constant or decrease by up to 10%, depending on the material and the probe. This indicates that an increase in the relative humidity causes a decrease in the surface energetics of the powder surface. It is proposed that where the water molecules are adsorbing to the same sites as the polar probes, the interaction of these probes with the surface is decreased. To identify these sites, the preferential interaction of each probe, including water, with the drug molecule has been modelled.

Acetaminophen↗

PubMed2003

An immersible manometric sensor for measurement of humidity and enzyme mediated changes in dissolved gas.

An immersible manometric sensor was made by covering the gaseous cavity of a pressure transducer with a 1 microm controlled pore membrane. Transfer of gas across the membrane allowed the pressure transducer to record changes in humidity or dissolved gas when immersed in solution. By immersing the sensor in distilled water, atmospheric humidity could be estimated by the deficit of atmospheric vapor pressure from saturation. In another application of the sensor, CO(2) was monitored continuously. This was not possible in previous closed-reactor type manometric sensors, and may allow the new technology to be used in applications requiring continuous monitoring of a process or stream. By coupling the sensor with enzymes liberating or consuming dissolved gas, different chemicals could be estimated. Urea was estimated by first hydrolyzing it with urease and then measuring the resulting CO(2) gas in solution. Glucose was measured through its enzymatic oxidation by glucose oxidase. The sensitivity to urea over the range 0-2.5 mM was about 1.02 kPa/mM, and the standard error was 0.086 mM. Due to the lower solubility of oxygen, the sensitivity to glucose in a range from 0 to 10 microM was over 100 kPa/mM, with a standard error of only 0.76 microM. This sensitivity was not possible in closed-reactor type manometric sensors due to constraints of dimensioning the head space gas volume for reproducibility and effective mass transfer. The 90% rise times for the sensor ranged from about 1-60 min for the different applications. The dynamic characteristics of the device may be improved by using a membrane with greater porosity, higher rigidity and lower thickness, and by reducing the dimensions of the cavity volume in the sensor through integrated microfabrication of the membrane onto the transducer.

Enzymes↗

PubMed1999

Do changing patterns of heat and humidity influence thermoregulation and endurance performance?

The purpose of this project was to determine whether changing patterns of temperature and humidity, as expected in the morning versus afternoon, had a differential effect on thermoregulation and endurance performance. Eight male distance runners each participated in two heat pattern tests consisting of two hours treadmill running at 70%-maximum oxygen consumption. The mean heat load for each test was identical (22.2 degrees C wet bulb temperature) but either dry bulb temperature increased (24 to 27.5 degrees C) or decreased (27.5 to 24 degrees C) over the course of the two hour heat stress test. Whole body sweat rate was 10.7% higher (p<0.05) and there was greater plasma volume loss (2.7 versus 1.6%, p<0.05) in the cooling versus warming pattern test. Mean skin and body temperature changed in a significantly different (p<0.05) manner between the two patterns and closely followed ambient dry bulb temperature change. The thermoregulatory variables of heart rate and rectal temperature were not affected and performance did not differ between pattern tests. Ratings of perceived exertion (RPE) and oxygen consumption were also not significantly different between cooling and warming test. In summary, although some minor differences were noted, thermal homeostasis was maintained equally well during either warming or cooling for wet bulb temperatures between 24 and 27 degrees C. The mean heat load is therefore more important than changing patterns of temperature and humidity in determining an individual's physiological response to exercise in a warm environment.

Adult↗

PubMed1995

Development of the free-living stages of Hyostrongylus rubidus and Oesophagostomum spp. at different temperatures and humidities.

Faeces containing a mixture of Hyostrongylus rubidus and Oesophagostomum spp. eggs were mixed with vermiculite and water and set up at combinations of different relative humidities (65.5%, 79.5% 90.0%, and 100%) and temperatures (5 degrees C, 10 degrees C, 15 degrees C, 20 degrees C, and 25 degrees C) in order to study the rate of egg hatching and larval development. The study established that the development from egg to infective larva showed similar patterns for the two parasites. Optimum development and survival was in the temperature range from 15 degrees C to 20 degrees C and at humidities from 79.5 to 95.5%.

Animals↗