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PubMed1967

Influence of platen temperatures and relative humidity during storage on the survival of freeze-dried Salmonella typhimurium.

Salmonella typhimurium survived freeze-drying at a platen temperature of 120 F (48.9 C) and also, though to a much lesser degree, at 160 F (82.6 C). The extent of the survival at these temperatures was dependent on the composition of the model system employed. The incidence of damage immediately after freeze-drying was greater for cells dried at the higher platen temperature and was influenced by the composition of the menstruum in which the cells were dried. In model systems having protein-dominant isotherms, survival during subsequent storage depended greatly on relative humidity, with recovery highest at relative humidities below those corresponding to moisture contents at which a monomolecular layer is formed. In menstrua having a higher sugar content, survival was best at low relative humidities corresponding to a very low equilibrium moisture content in the model system used. Damage during storage tended to be a function of the composition of the gels in which the organisms were freeze-dried, and also depended greatly on the presence of air and on the relative humidity. The maximal percentage of damage usually occurred at the low relative humidities as storage time increased.

Freeze Drying↗
PubMed1970

Microbiological aspects of ethylene oxide sterilization. 3. Effects of humidity and water activity on the sporicidal activity of ethylene oxide.

An investigation determined the effects of environmental moisture content or water activity (Aw), exposure humidity, and sterilant concentration on the resistance of microbial spores. Decimal reduction values [expressed as D values at 54.4 C-specified concentration (milligrams per liter) of ethylene oxide] were determined from spore destruction curves of Bacillus subtilis var. niger dried on hygroscopic and nonhygroscopic surfaces. Four groups of spore preparations were preconditioned in one of four Aw environments (<0.1, 0.1, 0.5, 0.95) for 2 weeks or longer and were exposed to 500 mg of ethylene oxide per liter at 54.4 +/- 3 C and 10, 50, and 95% relative humidity in a specially designed thermochemical death rate apparatus. A fifth group did not receive any preconditioning treatment and was exposed immediately after preparation, in the same apparatus at the same temperature, to ethylene oxide concentrations of 200, 400, 600, 800, and 1,200 mg/liter and relative humidities of 15, 30, 50, 60, and 90%. The resistance of the spores on both types of surfaces to ethylene oxide increased proportionately with the Aw of the conditioning environment. The study also showed that moisture in the exposure system was not as critical a variable as the ethylene oxide concentration. The spore destruction rates, irrespective of the carrier types at all concentrations and at different humidities, varied little from one another. The decimal reduction values were reduced as the ethylene oxide concentration increased, and no optimal exposure humidity concentration was observed.

Bacillus subtilis↗
PubMed1970

Dry-heat destruction of Bacillus subtilis spores on surfaces: effect of humidity in an open system.

Bacillus subtilis var. niger spores were tested for dry-heat resistance on stainless-steel strips hung in an oven. Heat resistance was dependent on the relative humidity before and during treatment, which in turn affected the water content of the spores. Higher humidities increased the heat resistance of the spores. D-values ranged from 16.1 min for spores conditioned at <2% relative humidity (RH) and treated at 0.34% RH to 37.6 min for spores conditioned at 89% RH and treated at 1.1% RH. The y-intercept of the regression line ranged from 6.94 x 10(4) for spores conditioned and treated at the low humidities to 2.00 x 10(5) for spores conditioned at 89% RH and treated at 0.34% RH. For a constant value of N(0), the y-intercept appears to be lowered by low-humidity conditions. The statistic log y(0)/log N(0) is used to measure the downward displacement of the regression line. Values obtained in this experiment range from 0.90 for spores conditioned at <2% RH and treated at 0.34% RH to 1.04 for spores conditioned at <2% RH and treated at 1.1% RH. A combination of linear regression and analysis of variance methods was used for data analysis. The former estimates D-values and y-intercepts, whereas the latter is sensitive to differences between treatments.

Analysis of Variance↗
PubMed1968

Role of relative humidity in the survival of airborne Mycoplasma pneumoniae.

Aerosols of Mycoplasma pneumoniae were studied at several relative humidities at a controlled temperature of 27 C. Production of an experimentally reproducible aerosol required preatomization of the organism in its suspending fluid and was dependent on the type of fluid used in atomization as well as on the procedures used to produce an aerosol. The airborne particles studied were within the range of epidemiological significance, with most being 2 mum or less in diameter. Survival of the airborne mycoplasma in these particles was found to be best at very low and at very high humidities. The most lethal relative humidity levels were at 60 and 80%, at which levels fewer than 1% of the organisms survived over a 4-hr observation period. However, survival of the organism at most relative humidity levels was such that long-term infectivity could be expected from aerosols of M. pneumoniae. Because of the extreme sensitivity of M. pneumoniae at critical humidity levels, control of the airborne transmission of these organisms may be possible in selected spaces.

Aerosols↗
PubMed1996

Influence of relative humidity and suspending menstrua on survival of Acinetobacter spp. on dry surfaces.

Acinetobacter spp. are being reported with increasing frequency as a cause of nosocomial infection and have been isolated from the skin of healthy individuals, patients, hospital staff, dry nonbiotic objects, and different pieces of medical equipment. Factors affecting the survival of Acinetobacter spp. under conditions closely similar to those found in the hospital environment were investigated in the present study to help us understand the epidemiology of nosocomial Acinetobacter infection. Bacterial cells were suspended in distilled water or bovine serum albumin and were dried onto glass coverslips and kept at different relative humidities. Cells washed from coverslips were used to determined viable counts. Freshly isolated strains of Acinetobacter spp. belonging to the clinically important Acinetobacter calcoaceticus-Acinetobacter baumannii complex were found to be more resistant to drying conditions (e.g., 30 days for A. baumannii 16/49) than American Type Culture Collection strains (e.g., 2 days for A. baumannii ATCC 9955). The majority of strains belonging to the Acb complex had survival times similar to those observed for the gram-positive organism Staphylococcus aureus tested in the experiment. Survival times were prolonged for almost all the strains tested when they were suspended in bovine serum albumin (e.g., 60 days for A. baumannii R 447) compared with those for strains suspended in distilled water (11 days for R 447). The survival times for strains at higher relative humidity (31 or 93%) were longer than those for strains of Acinetobacter kept at a relative humidity of 10% (11 days at 31% relative humidity and 4 days at 10% relative humidity for R447). These findings are consistent with the observed tendency of Acinetobacter spp. to survive on dry surfaces, and they can be transferred not only by moist vectors but also under dry conditions in a hospital environment during nosocomial infection outbreaks. The results obtained in the experiment support the previously suggested airborne spread of Acinetobacter spp. in hospital wards and repeated outbreaks after incomplete disinfection of contaminated dry surfaces.

Acinetobacter↗
PubMed1988

Effect of environmental temperature and relative humidity on breathing pattern and heart rate in ponies during and after standardised exercise.

A preliminary study attempted to assess the influence of atmospheric conditions on the breathing pattern of ponies. The respiratory airflow, tidal volume, breathing frequency, minute volume, total pulmonary resistance and heart rate of five ponies (257 +/- 9 kg and three to five years old) were measured by a standardised procedure. Data were collected at rest, during a nine minute period of treadmill exercise and during a five minute recovery period. The ambient temperature (degrees C) and relative humidity (%) were recorded at the time of each investigation and the respiratory parameters were divided into two groups according to whether the sum of these measurements was less than 85, ie, the conditions were cold and dry or greater than 85, ie, the conditions were relatively hot and humid. Data for each pony in both conditions were compared. The ambient temperature and relative humidity did not significantly modify the breathing pattern of the ponies either at rest or during exercise. On the other hand the frequency of breathing was significantly higher and the tidal volume and total pulmonary resistance were significantly lower during recovery in hot and humid conditions than in cold and dry conditions, while the minute volume remained unchanged. It was concluded that, during recovery, environmental conditions may modify the breathing pattern of horses. This suggests that in hot and humid weather conditions the respiratory rate may be an unreliable measure of the fitness of a horse and, consequently, that a more complete pulmonary investigation should be undertaken for an assessment of fitness.

Animals↗
PubMed1985

Effect of relative humidity, atmospheric temperature, and suspending medium on the airborne survival of human rotavirus.

The Wa strain of human rotavirus, grown in MA-104 cells, was suspended either in tryptose phosphate broth or feces from a case of rotaviral diarrhea. It was then aerosolized into a rotating drum using a Collison nebulizer. The drum air was sampled using an all-glass impinger containing tryptose phosphate broth as collecting fluid. At 20 +/- 1 degree C, the virus aerosolized from tryptose phosphate broth was found to survive best at 50 +/- 5% relative humidity, where its half-life was 44.2 +/- 6.3 h. At 30 +/- 5% and 80 +/- 5% relative humidity, the half-life of the virus was 24.5 +/- 3.5 and 3.8 +/- 1.0 h, respectively. At 6 +/- 1 degree C, the airborne survival of the virus at the mid and low relative humidity levels was further enhanced, but at the high relative humidity it remained very similar to that seen at 20 +/- 1 degree C. When aerosols of fecally suspended human rotavirus were held at 20 +/- 1 degree C with 50 +/- 5% relative humidity, nearly 80% of the airborne virus particles remained infectious even at the aerosol age of 24 h. These findings may help in our understanding of the epidemiology of rotaviral infections.

Aerosols↗
PubMed2005

Measurement of tracheal humidity and temperature.

BACKGROUND: After tracheostomy, patients often present with chest complaints. Measurement of objective parameters of the tracheal climate is important to evaluate 'artificial noses' or humidifying devices. OBJECTIVES: The purpose of this study was to present an experimental setup for measurement of tracheal temperature and humidity for possible use in clinical studies in tracheotomized patients. METHODS: The study design was a prospective study. Patients with tracheal stoma were chosen as study participants. Tracheal temperature and humidity during the respiratory cycle were measured using a miniaturized thermocouple and a humidity sensor connected to a suction system. RESULTS: Accurate measurement of tracheal temperature and humidity was feasible in patients with tracheal stoma. Tracheal humidity and temperature values measured in this study were similar to values reported earlier by other working groups. CONCLUSIONS: The experimental setup presented may reliably be used in the evaluation of 'artificial noses' or other passive humidifiers in tracheotomized patients.

Body Temperature↗
PubMed1994

Humidity of anaesthetic gases with respect to low flow anaesthesia.

It has been demonstrated in an experimental study in swine using the scanning electron microscope that a rebreathing technique utilising minimal fresh gas flowrates significantly improves climatization of anaesthetic gases. Consequently, effects of various anaesthetic techniques on airway climate must be assessed, which covers the need for suitable measuring devices. Basic principles and methods of humidity measurement in flowing anaesthetic gases include gravimetric hygrometry, dew point hygrometry, wet-dry bulb psychrometry, mass spectrometry, spectroscopic hygrometry and electrical hygrometry. A custom-made apparatus for continuous measurement of humidity and temperature in the inspired and expired gas mixtures of a breathing circuit (separated by a valve system, integrated between the endotracheal tube and the Y-piece) is described. Comparative evaluation of this apparatus and the psychrometer was carried out. It could be demonstrated that the apparatus, measuring with capacitive humidity sensors, is more suitable for prolonged use under clinical conditions than the psychrometer. In the second part of the study, climatization of anaesthetic gases under clinical conditions was investigated using fresh gas flowrates of 0.6, 1.5, 3.0 and 6.0 l/min. In the inspiratory limb of the circuit an absolute humidity of 21.3 mg H2O/l and a temperature of 31.5 degrees C were obtained after 120 minutes of minimal flow. Humidity and temperature of inspired air obtained with fresh gas flowrates of 6.0 and 3.0 l/min were found to be inadequate for prolonged anaesthesia. Reducing the fresh gas flow to 1.5 l/min increases heat and moisture content in the respired gases, but conditions are still inadequate for prolonged anaesthesia. Sufficient moisture (> or 20 mg H2O/l) and temperature are obtained under minimal flow conditions after one hour.

Absorption↗
PubMed2005

Respiratory and acid-base responses during migration and to exercise by the terrestrial crab Discoplax (Cardisoma) hirtipes, with regard to season, humidity and behaviour.

The terrestrial crab Discoplax hirtipes (formerly Cardisoma hirtipes) exhibits a seasonally dichotomous activity pattern governed by the seasonal rainfall on Christmas Island, with a breeding migration in the wet season. Greater activity in the wet season reflects a release of constraints on ion and water balance independent of changes in exercise physiology. The respiratory responses to walking exercise by D. hirtipes were assessed with regard to humidity and season. In the laboratory, crabs walked 38% faster when humidity was high, while the O(2) uptake across the lung became diffusion limited despite a Ca(2+)-induced increase in O(2) affinity of the haemocyanin. Crabs walking in 90% relative humidity exhibited a larger metabolic acidosis while re-oxidation of l-lactate was only 0.49 mmol l(-1) h(-1). The wet-season crabs were more active and exhibited a respiratory acidosis compared with the quiescent dry-season crabs. The migration was close to the limit of the aerobic scope of the crabs, and the pulmonary oxygen partial pressure (P(O(2))) was depressed, the O(2) uptake diffusion limited and the arterial-venous P(O(2)) difference diminished. Additional, enforced exercise induced a metabolic acidosis. The optimum strategy for migration would be walking continuously but at a speed within the aerobic scope. D. hirtipes is influenced by seasonal rain and responds to lower ambient humidity by limiting exercise. The behavioural response is paramount since the changes in respiratory status were determined primarily by the differences in commitment to, and investment in, walking and not by direct effects of humidity on respiratory physiology.

Analysis of Variance↗
PubMed1981

[Distribution of environmental temperature and relative humidity according to the number of conditioned air changes in laboratory animals rooms].

The relation of the rate of circulating air change to room temperature and relative humidity in animal quarters with a central air-conditioning system during heating and cooling seasons was investigated, with the results as follows: During the period of heating, the ambient temperature generally rose with a fall of relative humidity as the number of conditioned air changes per hour was increased. Vertical differences in temperature and humidity between levels of 0.5 and 1.5 m above the floor also diminished with increasing air change rate. This tendency was more conspicuous in small animals rooms with outer walls facing north and west. With increasing rate of air changes, the room temperature was prone to decline and the relative humidity to rise during the period of cooling. There were less vertical differences in temperature and humidity during this period. The velocity of air circulation within the animal quarters and its variations tended to increase progressively with increasing rate of ventilation, though the changes were modest.

Air Conditioning↗
PubMed1996

Change of skin roughness due to lowering air humidity in climate chamber.

Rough skin ("dry skin") is characteristic of atopy and thought to be a pre-stage of atopic eczema. Atopic eczema frequently deteriorates in winter, which may be related to low air humidity during the heating period. We have assessed skin roughness before and after decreasing air humidity to 30% in a climatic chamber. Replicas of clinically non-inflamed and not scaling skin from 10 patients with atopic eczema and 10 controls were taken before and after lowering air humidity for 3 h and were analyzed for the roughness parameters Ra, RZ(DIN) and RZ(ISO). After exposure to low air humidity there was a significant increase of RZ(DIN) from 61.5 microns to 66.9 microns (p < 0.05) and of RZ(ISO) from 63.8 microns to 66.4 microns (p < 0.05) in patients with atopic eczema, whereas no significant change occurred in controls. Development of skin roughness over 3 h under natural indoor environmental conditions did not indicate spontaneous variations. These quantitative data show that a short period of exposure to low air humidity increases skin roughness and may particularly influence the condition of patients with atopic eczema.

Adult↗
PubMed2000

Effects of side cooling on temperature, humidity and water recycling efficiency in a culture vessel for a space experiment--results of ground experiment.

Seed-to-seed experiments using dwarf plants will be conducted in Cell Biology Experiment Facility (CBEF) set up in the International Space Station (ISS). Development of a simple system to recycle water transpired by plants is necessary to save space and electrical power. A cooling system using a cooling plate that cools one side of the ventilated culture vessel to enhance water vapor condensation was developed. Effects of side cooling on air temperature, relative humidity and water recycling efficiency in the culture vessel were investigated on the ground. Decreasing the cooling plate temperature lowered temperatures of cooled side and inside air. Cooling treatment also decreased relative humidity inside the vessel less than 90% and lowered the amount of water vapor lost from the vessel through ventilation filters. This seemed to be due to the increased water vapor condensation onto the cooled side. To investigate the effect of increases in outside humidity on water recycling efficiency in the culture vessel, a water vapor transfer model was established. The calculation results indicate that an increase in relative humidity around the vessel can decrease water vapor loss from the vessel, increase water condensation onto the cooled side, and therefore, enhance water recycling efficiency in the vessel. The side cooling system seems to be useful for the CBEF in ISS because relative humidity in the CBEF is controllable.

Air Conditioning↗
PubMed1998

Relationship between the electrical resistivity of enamel and the relative humidity.

The present study was carried out to investigate the relationship between the relative humidity and the electrical resistivity of enamel in vitro. The electrical resistivity of enamel samples was measured in a thermo-hygrostat where the relative humidity varied between 60% and 90%, with the measurements carried out first in a descending direction and then in an ascending direction. When the electrical resistivity was measured from a low to high relative humidity in an ascending direction, a higher value of electrical resistivity was always obtained in comparison to that when measured in the reverse descending direction. The difference between the mean electrical resistivity in an ascending and a descending direction increased in proportion to the relative humidity. These findings suggest that the diffusion of electrolytes and water in enamel is sensitive to changes in the relative humidity.

Adult↗
PubMed1998

Thermal and mechanical characterization of cellulose acetate phthalate films for pharmaceutical tablet coating: effect of humidity during measurements.

Films from a polymer used in pharmaceutical coating (cellulose acetate phthalate) were analyzed by thermomechanical techniques including dynamic mechanical thermal analysis (DMTA) and tensile tests. Emphasis was placed on relative humidity (RH) at the measurement site (as opposed to storage or conditioning RH). The films were plasticized with either triethyl citrate or diethyl phthalate. The results show that the films respond rapidly to changes in the environmental humidity. This in turn influences the data obtained from DMTA and tensile testing; thus, good control of the humidity is essential. Absorption isotherms have been obtained for the two types of films, and the results were interpreted in terms of the equilibrium moisture content which is determined by the polar nature of the plasticizer. This factor must be considered when formulating a film composition because moisture can, apart from its influence on mechanical properties, also speed the chemical degradation processes. When the stability of a film composition during storage is studied, the actual measurements on the films should preferably be done at 0% RH, irrespective of the storage RH. At 0% RH, the mechanical testing results will reflect the chemical stability correctly, without interference from plasticizing effect of absorbed water. A functionality test for films has been suggested: DMTA under isothermal conditions using either step or continuous humidity scans. Isothermal dynamic humidity scans on the DMTA were performed for the first time, and the utility of these measurements is discussed.

Cellulose↗
PubMed2005

Humidity as an aversive stimulus in learning in Drosophila melanogaster.

The learned suppression of photopositive tendencies was studied at the individual level in young flies of both sexes. In a T-maze, flies had to choose between an arm leading to a lighted vial associated with an aversive stimulus (i.e., a solution of quinine chlorhydrate deposited on a filter paper in the vial) and another arm leading to a darkened vial free of quinine. The present experiments were carried out to determine the roles of quinine and relative humidity in the maze. The flies avoided the lighted vial containing quinine even if they had no tarsal contact with quinine, and this result was not due to any odor of quinine. Subsequent experiments showed that relative humidity in the lighted vial, and probably in the arm leading to it, was an aversive stimulus, which partly explains why the flies avoided the lighted vial. However, in conditions in which the flies had tarsal contact with water or quinine it was confirmed that flies trained with quinine have higher avoidance scores than those trained with water only. Moreover, individual aversion to humidity was not correlated with the individual avoidance score: At similar levels of motivation (i.e., similar levels of aversion to humidity), some flies learn to avoid the lighted vial containing quinine whereas others do not. All these results show that, in addition to quinine, humidity is an unconditioned aversive stimulus in our paradigm and thus needs to be tightly controlled in experiments of conditioned avoidance.

Animals↗
PubMedDate not supplied

Exploiting the igloo principle and greenhouse effect to regulate humidity and temperature.

BACKGROUND: Toxic epidermal necrolysis can be fatal and nursing care with careful monitoring of temperature and humidity can improve survival rate. We adapted the greenhouse and igloo principle using a common hood to monitor the temperature and humidity. METHODS: A small heater with a regulator was placed in a mini hood and temperature was recorded inside the uncovered hood and hood covered with green cloth and aluminium foil separately. The regular hood was placed over a volunteer and the temperature was measured inside the open hood and hood covered with green cloth and aluminium foil separately. The relative humidity was also monitored using Zeal mercury dry--wet bulb hygrometer. RESULTS: Temperature increase was most marked in the foil-covered hood followed by cloth-covered hood, both with the heater and the volunteer. Similarly, in the volunteer study, the humidity was best maintained inside the aluminium foil-covered hood. CONCLUSION: We recommend the use of regular hood with suitable cover to monitor the humidity and temperature of patients with toxic epidermal necrolysis.

Body Temperature↗
PubMed2003

Effect of inoculum size, relative humidity, storage temperature, and ripening stage on the attachment of Salmonella Montevideo to tomatoes and tomatillos.

The influence of inoculum populations and environmental factors on attachment of Salmonella Montevideo to the surface of tomatoes and tomatillos was evaluated. To study the effect of inoculum size, red, ripe tomatoes were spot-inoculated with bacterial suspensions (10(5) and 10(8) CFU/fruit) and stored at 22 degrees C under 100% relative humidity. The effects of temperature (12, 22, and 30 degrees C) and relative humidity (75, 85, and 97%) on attachment of the pathogen (10(7) CFU/fruit) to tomatoes (red and green) and ripe tomatillos were also evaluated. Inoculated fruits were stored for 90 min at all combinations of temperature and relative humidity, and after rinsing with water, the number of cells attached to the surface was determined. Salmonella Montevideo attached to the surface of tomatoes within 90 min. A direct correlation between the number of attached cells and the population in the inoculum was observed. The percentage of cells that attached immediately after inoculation was approximately 0.3% for the three test products. After storage for 90 min at various temperature and relative humidity conditions, the number of adhering cells ranged from 4.0 to 5.4 log CFU/fruit (1.2% of inoculum). Both the type of product and the temperature/relative humidity combination had a significant (P < 0.05) effect on attachment of Salmonella Montevideo to the surfaces of tomatoes and tomatillos. Scanning electron micrographs of the cuticles of inoculated washed tomatoes and tomatillos revealed typical skin cell patterns, and only a few randomly dispersed Salmonella Montevideo were observed. Deposition of Salmonella Montevideo on the surface of tomatoes and tomatillos could result in attachment and subsequent colonization under suitable conditions.

Bacterial Adhesion↗