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At least 127 records · Page 7Linked to original sources
PubMed1976

Influence of relative humidity on functional effects of an inhaled SO2-aerosol mixture.

Lightly anesthetized guinea pigs were exposed to 1 ppm of sulfur dioxide (SO2) and 1 mg per m3 of sodium chloride aerosol, individually and in combination, at low and high relative humidities. At low relative humidity (less than 40 per cent) the aerosol was a crystal, at high relative humidity (greater than 80 per cent) a droplet. Exposures lasted one hour. Changes in pulmonary mechanical function characterized by an increase in flow resistance and decrease in compliance were seen only when the mixture was administered at high relative humidity. The effect is ascribed to absorption of the highly soluble SO2 into the droplet before inhalation.

Aerosols↗
PubMed1980

Aerodynamic size distribution of cromolyn sodium at ambient and airway humidity.

The aerodynamic size distribution of cromolyn sodium was determined at ambient and high (98%) humidity using the single particle aerodynamic relaxation time analyzer. This instrument measures the aerodynamic size single, suspended solid particles and liquid droplets in the respirable size range. The measurement accommodates all properties such as density, shape and surface characteristics that affect aerodynamic behavior. Particle morphology under ambient humidity conditions was studied using scanning electron microscopy. Count median aerodynamic diameter increased from 1.40 to 1.52 micron (p < 0.05), and the mass median aerodynamic diameter increased from 2.31 to 3.02 micron (p < 0.005) when measured at ambient and high humidities. The total mass of 0.99 mg of active ingredient aerosolized at ambient humidity in the size range compatible with pulmonary deposition was approximately 5% of the total mass of active ingredient packaged in the capsule. The low mass of particle aerosolized in the size range appropriate for pulmonary deposition may explain the low estimated deposition of cromolyn reported by other investigators.

Aerosols↗
PubMed1991

Aerosol, humidity and oxygenation.

Patients with artificial airways frequently need aerosol or humidity therapy. For this study, we used aerosols generated from a heated Puritan all-purpose nebulizer and humidity generated from a heated Bennett cascade humidifier to determine the effects of these therapies in spontaneously breathing neurosurgical patients with nasal endotracheal tubes and normal lungs. Crossover comparison of oxygenation status before and after aerosol or humidity therapy was done by analyzing P(A-a)O2 in these patients. We found that aerosols have a detrimental effect on the patient's oxygenation status, suggesting that humidity is preferable in maintaining adequate oxygenation in a patient with a normal lung plus artificial airway. The arterial pH and PaCO2 were not affected by aerosol therapy. Care should be exercised with regard to the adverse hypoxemic effect of bland aerosols when a large-reservoir jet nebulizer is used in an intubated patient who already has impaired cardiopulmonary function or borderline PaO2.

Aerosols↗
PubMed1976

Relationship of temperature and humidity to conception rate of Holstein cows in Hawaii.

Weather data and breeding records for a Holstein herd of 1300 cows in Hawaii were evaluated to determine effects of climate on reproductive performance. The dairy is in a coastal climate near latitude 21 degrees N. Average maximum temperature, relative humidity, and resulting temperature-humidity index for the warmest month of the year were 31 C, 44%, and 79. Average minimum temperature and attending values for the same period were 20 C, 96%, and 68. From late April to November, conception rates were correlated negatively with the average temperature-humidity index of each day of the estrous cycle beginning 11 days prior to breeding. Slopes of regression lines differed, suggesting varying sensitivity of conception rate to heat stress on different days of the cycle. The temperature-humidity index of the 2nd day prior to breeding was most closely correlated with conception rate. Conception rates declined from 66% to 35% as the index increased from 68 to 78. Only the temperature-humdity index of the 2nd day prior to breeding had a significant partial correlation coefficient when the index of the 2nd and 1st day prior to breeding, the day of breeding, and the day following breeding were each evaluated with the index of the others held constant.

Animals↗
PubMed1989

Humidity of the Bain and circle systems reassessed.

The humidity outputs of the Bain circuit, a traditional non-coaxial Mapleson D system, and a circle system with and without a soda lime absorber were evaluated in a laboratory model simulating a 70-kg subject. The breathing systems were tested with tidal volumes of 0.35 and 0.70 L and frequencies of 10-20 breaths/min to maintain an end-expiratory CO2 of 4.5%. There were small differences in inspiratory gas humidity between the Bain and the non-coaxial Mapleson D system. With a fresh gas flow of 5 L/min in the Bain circuit, the humidity was 9.8-16.5 mg H2O/L depending on tidal volume and respiratory frequency. The humidity output of the circle absorber system with fresh gas flows of 0.5 or 2 L/min was 21.6-25.2 mg H2O/L at 60 min. Therefore, this study does not support previous studies, which propose that the Bain circuit has superior humidifying properties compared with those of the circle absorber system.

Anesthesiology↗
PubMed1987

Acute modest changes in relative humidity do not affect energy expenditure at rest in human subjects.

Energy expenditure at rest was determined twice in 10 healthy subjects with a 2-d interval at a relative humidity of 32 and 66 per cent respectively. The relative humidity over the 2 d preceding each observation was estimated to be about 32 per cent. The average (+/- s.e.m.) difference between the RMR at a relative humidity of 32 and 66 per cent respectively was found to be 0.3 +/- 1.2 watt. The results presented here justify the commonly used practice of neglecting variations in humidity when reporting on results of observations of resting metabolic rates in apparently healthy subjects.

Body Weight↗
PubMed1986

Film-coated zinc sulphate tablets and the effect of humidity on tablet properties.

Preparation of film-coated zinc sulphate tablets and the effect of relative humidity and aging on the physical properties of these coated tablets were investigated in this study. Shellac; Eudragit E and L, hydroxypropyl methylcellulose (HPMC) and HPMC-Eudragit E mixture were used as film-forming materials. As zinc sulphate has efflorescent properties, the effect of humidity on the coated tablets was studied and physical stability tests were carried out. Coated tablets were kept in bottles and in open petri-dishes at different relative humidities (30, 55 and 85%) at room temperature over 12 weeks, and the weight loss, hardness, and disintegration times of these tablets were followed. Findings indicated that film-coated zinc sulphate tablets having good tablet quality can be prepared using the formulations (F-VI) HPMC-Eudragit E mixture and (F-III) Eudragit E as coating materials. Thus, the effect of relative humidity on tablet properties can be reduced.

Drug Stability↗
PubMed1978

[Changes in the biochemical and morphological indices of broiler chickens depending on the temperature and humidity conditions].

A varying temperature and humidity regime was tested on a total of 200 hybrid birds (White Plymouth Rock x Cornish crosses). Investigated were some indices of the carbohydrate metabolism and the deposition of vitamins in the organism as well as the effect of the temperature and humidity regime on the growth and development of broilers. It was established that the content of glycogen in the liver and the muscles in birds raised first at 32 degree C and relative air humidity of 65--70 per cent was higher than in birds raised at 36 degree C and relative air humidity of 45--50 per cent. Besides, these observations were coupled with some changes in the content of blood sugar and the amount of A and E vitamins in the liver. The body weight of the test broilers by the end of the experiment was 30 grams higher than that of the control group broilers.

Age Factors↗
PubMedDate not supplied

[Effect of air temperature and relative humidity on the preimaginal development of Ctenophthalmus teres fleas (Siphonaptera)].

The duration of the development and survival of preimaginal stages of fleas at a temperature of 5 to 30 degrees and relative humidity of 60 to 90% was studied. Minimal average duration of the development an the highest survival rate at all stages were registered at a temperature of 20 to 25 degrees and humidity of 85 to 90%. Under these conditions the whole cycle from egg to image lasts on an average 23 days. The threshold of the development for different stages falls within the limits of 3 to 6 degrees. The duration of the development of all stages was distinctly affected by temperature while the duration of larval development was affected as well by humidity. The survival of larvae was found to be affected by humidity while the survival of individuals in cocoons was considerably affected by temperature.

Animals↗
PubMed1994

Humidity regulation in the management of asthma patients sensitized to house dust mites.

Substances in the faeces of house dust mites are well-recognized as common allergens in the pathogenesis of asthma. There have been many trials of interventions aimed at reducing mite populations in the home, but most have been uncontrolled, too small, or too short to determine with confidence any beneficial effects. Of those which succeeded, very few used methods which reduced mite populations on a permanent basis. House dust mites are sensitive to humidity. Their geographical distribution is closely correlated to the availability of moisture. Very little work has been done on the effects of reducing humidity in the home environment in the long term, with a view to controlling dust mite populations. Two different methods which might reduce humidities to levels which could successfully reduce dust mite numbers are dehumidifiers, and mechanical ventilation with heat recovery (MVHR). To date there has been no work assessing the effectiveness of dehumidifiers and very little (although promising) work on MVHR. We discuss the potential of humidity control as an adjunct to the clinical treatment of asthma.

Animals↗
PubMed1993

Humidity effects on atomic force microscopy of gold-labeled DNA on mica.

Recent work in atomic force microscopy (AFM) of deoxyribonucleic acid (DNA) has relied on immobilizing DNA molecules by drying a small volume of buffered DNA solution onto cleaved mica. When imaging in air, relative humidity has been known to affect both the resolution and measured height of the DNA strands. We present data of measured height versus humidity for DNA and attached gold labels, and we propose a model for this data based on swelling of coadsorbed buffer salts upon exposure to moisture. In this model, small particles (e.g., DNA) stay near the top of the swelling salt layer, whereas larger particles (e.g., gold spheres) tend to be anchored down to the substrate until a moderate humidity is reached. At high humidity (around 65%), the salt layer becomes fluid-like and susceptible to tip-induced motion; the salts are either removed from the scan area or aggregate into island structures, depending on initial salt concentration on the surface.

Aluminum Silicates↗
PubMed1995

Effect of temperature and humidity on longevity of unfed adults and on oviposition of engorged females of Dermacentor reticulatus (Ixodidae).

The effect of ambient temperature and relative humidity on longevity of unfed adult ticks and on oviposition of engorged female ticks of Dermacentor reticulatus was examined. The 50% mortality time of unfed adult ticks, incubated at 5 degrees C, 10 degrees C, 20 degrees C and 27 degrees C and humidities of 15%, 50% and 100%, increased irrespective of their sex with rising relative humidity and decreasing temperature. It was longest at 5 degrees C and 100% r.h. being 617.8 days and shortest at 27 degrees C and 15% r.h. amounting only to 33.6 days. All unfed ticks survived an incubation of 150 days at -10 degrees C and 15%, 50% and 100% r.h. as well as an exposure of 180 days at 0 degrees C and 100% r.h. At 0 degrees C the percent survival was 75% for the males and 40% for the females at 50% r.h. but 100% for males and 95% for the females at 15% r.h. after exposure of 180 days. Oviposition of engorged females occurred at a temperature range of 10-27 degrees C, at 10 degrees C merely at 50% and 100% r.h. The percentage of ovipositioning females amounted to at least 80% apart from 10 degrees C and 50% r.h. being only 10%. The egg index and the egg conversion index as well as the larvae index and the larvae conversion index generally increased with rising temperature and relative humidity. The indices were lowest at 10 degrees C and 50% r.h. and were highest at 20 degrees C and 27 degrees C at 100% r.h. The reproduction capability of engorged female ticks, held at -10 degrees C, 0 degrees C and 5 degrees C and 15%, 50% and 100% r.h. and transferred to 20 degrees C and 95% r.h., persisted for 10 weeks at -10 degrees C and for 2 weeks at 0 degrees C at the most, but for at least 20 weeks at 5 degrees C. There were no significant differences of the preoviposition periods, egg indices and larvae indices as well as of the minimum embryonic developmental times and hatching rates with regard to the preceding incubation conditions and the length of the ticks' exposure.

Animals↗
PubMed1996

The Effect of Humidity on the Physical and Chemical Stability of Spray-Dried Aluminum Hydroxycarbonate

The moisture sorption isotherm of amorphous spray-dried aluminum hydroxycarbonate (SDAHC) at 25&deg;C revealed that moisture sorption increased sharply when the relative humidity exceeded 80%. The physical and chemical stability of SDAHC was studied for 1 year at 25&deg;C and 0, 11, 54, 84, or 100% RH. The results were interpreted to reveal that two mechanisms affect the properties of SDAHC at 25&deg;C. The sample stored at 0% RH did not exhibit any significant changes during the 1-year study period. The surface area and rate of acid neutralization decreased when samples were stored at 11 or 54% RH, but the material remained amorphous. This change is believed to be due to aggregation and cementation of particles. Much larger changes in surface area and the rate of acid neutralization occurred in the samples aged at 84 or 100% RH. Under these humidity conditions, polymorphic transformations occurred in addition to aggregation and cementation. X-ray diffraction indicated that microcrystalline boehmite was an intermediate phase. The stable polymorph was bayerite, which is believed to form due to the high surface pH produced by water sorption at 84 or 100% RH. The moisture sorption isotherm was useful in identifying the humidity conditions which resulted in high moisture sorption. Polymorphic transformations were only detected when the SDAHC was aged under these humidity conditions.

Journal Article↗
PubMed1990

Crystal structure of low humidity tetragonal lysozyme at 2.1-A resolution. Variability in hydration shell and its structural consequences.

Tetragonal crystals of hen egg white lysozyme undergo a reversible transformation, accompanied by loss of water, when the relative humidity of the environment is reduced to about 90%. The structure of the low humidity form has been analyzed, using x-ray data collected at 88% relative humidity, in order to explore the variability in protein hydration caused by a change in the amount of water surrounding the protein molecule and the consequent conformational perturbations in the molecule. The structure has been refined by the restrained least-squares method to an R value of 0.162 for 6269 observed reflections in the 10-2.1-A resolution shell. The refined structure provides interesting examples for the variability in helical parameters, the role of interactions involving side chains and water in the stabilization of secondary structural features, and favorable specific hydration sites. The protein molecule as a whole moves slightly in the low humidity form from its position in the native crystals. The hydration shell tends to move along with the protein. Significant changes, however, occur in the hydration shell. These changes cause structural perturbations in the enzyme molecule, which are most pronounced in regions involved in substrate binding.

Animals↗
PubMed1983

Multiple observers, humidity, and choice of precision statistics: factors influencing craniometric data quality.

This study investigates three topics: (1) interobserver measurement error in craniometry, (2) the effects of humidity on craniometric measurements, and (3) the current status of estimators of measurement precision in craniometry and anthropometry. The results of the three-observer error analysis based on 24 linear measurements taken on 47 crania indicate that minor idiosyncratic variations in measurement technique can lead to high levels of statistical discrimination among the data produced by the different observers. The results of the humidity experiment substantiate the contention that increasing levels of relative humidity are associated with cranial expansion. The results of the comparison of 11 univariate precision estimators suggest that the combination of percentage agreement, the mean absolute difference, and Fisher's nonparametric sign test can give an instructive picture of the frequency, magnitude, and directionality of measurement imprecision. Information on the comparability of technique and measurement precision can then be used in the variable selection process prior to the application of multivariate statistical procedures to strengthen the substantive interpretation of craniometric data.

Analysis of Variance↗
PubMed1986

Effect of mesomorphy on hyperthermia during exercise in a warm, humid environment.

The hyperthermic response to exercise in a warm (30 degrees C), humid (80% relative humidity) environment was obtained for 27 men who exhibited a wide range of body physique in terms of the mesomorphy component of somatotype. Increase in tympanic temperature (Yty) was significantly dependent on mesomorphy rating (X) according to the regression equation Yty = -0.390 + 0.088X. Increase in rectal temperature (Yre) was also significantly dependent on mesomorphy rating according to the equation Yre = -0.100 + 0.066X. The hyperthermic response was significantly correlated with other measures of physique, including ectomorphy, surface area/weight ratio, and body weight, but was not correlated with fatness or fitness. The results support the generalization that during exercise in a warm, humid environment individual differences in heat strain can be highly dependent on physique, especially if fitness and fatness are similar. In this context, mesomorphy appears to provide the optimum description of physique variation. Individuals with a mesomorphy rating greater than 7 warrant designation as being at high risk for heat intolerance during exercise in environments that significantly impair the rate of body heat loss.

Adolescent↗
PubMed1986

Physique and thermoregulation in prepubertal males during exercise in a warm, humid environment.

The hyperthermic response to exercise in a warm (30 degrees C), humid (80% relative humidity) environment was obtained for 23 prepubertal males. After the initial increase of core temperatures (tympanic and rectal) to elevated set points, further hyperthermia was minimal and was unrelated to any physique variable except for the case of endomorphy, which was weakly correlated with hyperthermia at the rectal site. This result for boys is attributed to the combination of small body size (relative to adults) and absence of pronounced, age-dependent muscular development as evidenced by low rating and small variation of the mesomorphy component of somatotype. Both of these factors were associated with a high surface area to weight ratio compared to adults, which facilitated heat loss. It is concluded that prepubertal males thermoregulate efficiently during moderate exercise in a warm, humid environment. Other than cases of obesity, variation in physique is not an important consideration for assessing the risk of heat strain.

Adolescent↗