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At least 109 records · Page 6Linked to original sources

PubMed1980

The influences of temperature and humidity upon the isolated surfactant film of the dog.

A model of the gas-liquid barrier (surfactant film) of the lung was used to investigate the influence of temperature and of humidification of the gas upon the behaviour of films during rhythmic compression and expansion of their surface. Film behaviour was studied at room temperature or 37 degrees C, and at ambient humidity or high relative humidity. Changes of minimal surface tension (gamma min) and maximal surface tension (gamma max) were followed up to 1000 cycles. At 37 degrees C we measured higher values for gamma min and lower values for gamma max. At room temperature complete humidification does not influence surface tension, but at 37 degrees C gamma min increases. Thus both high temperature and high relative humidity result in sharp rise of gamma min, whereas high temperature alone is responsible for the temporary drop of gamma max. Considering these effects, investigations to study influences of foreign gases and of air pollution upon the surfactant film should be performed under conditions which approach those of the lung as close as possible. The possible influence of CO2 is discussed.

Animals↗

PubMed1984

The effect of humidity on the transmission of Brugia pahangi infective larvae to mammalian hosts by Aedes aegypti.

The transmission of Brugia pahangi by Aedes aegypti to the mammalian host was compared at low and high humidity. There was no statistical difference between the number of infected mosquitoes feeding or the egress of infective larvae from these mosquitoes at high or low humidity. The penetration of the host by the infective larvae was however significantly greater (p less than 0.05) at high than at a low humidity.

Aedes↗

PubMed1986

The survival of Escherichia coli in an aerosol at air temperatures of 15 and 30 degrees C and a range of humidities.

The survival of Escherichia coli in an aerosol was studied at several temperatures and over a range of relative humidities using a Henderson apparatus. Death occurred in two phases, the first lasting approximately 1 min; in the second the number of viable microorganisms declined exponentially. E. coli was robust and remained viable for many hours. Death was most rapid at low humidities (less than 50% r.h.) at 15 and 30 degrees C, with half-lives of 14 and 3 min respectively. In humid conditions the half-lives were much longer, approximately 83 and 14 min respectively. Based on this work, preliminary recommendations for the climate of livestock buildings can now be given to control the airborne spread of E. coli.

Air Microbiology↗

PubMed1987

Water vapor sorption of water-soluble substances: studies of crystalline solids below their critical relative humidities.

Water vapor sorption on unground and ground samples of sodium chloride and sodium salicylate at relative humidities below RHo, that at which deliquescence is initiated, has been measured. Sorption isotherms, expressed as the amount sorbed per unit area of solid surface, were different for unground and ground samples. Measurement of specific surface area for samples previously exposed to various relative humidities revealed no change with unground samples but a significant reduction with ground samples beyond about 20% relative humidity. Correcting isotherms for this change in area brings the results with ground and unground samples into closer agreement. These studies reveal that relatively low levels of water vapor sorption on crystalline water-soluble solids, below RHo, can give rise to some form of "surface dissolution" when the solid had been subjected to various forms of mechanical disturbance.

Absorption↗

PubMed1989

"Worst case" aerosol testing parameters: II. Efficiency dependence of commercial respirator filters on humidity pretreatment.

Previous studies have shown that relative humidity has a degrading effect on the performance of commercially available particulate air-purifying respirator filters. That degradation results from a reduction of charge within the filter. This study was done to evaluate the time-dependent effects of relative humidity pretreatment and the reduction of charge on filter penetration against a most penetrating, "worst case" aerosol challenge. Filters of the dust and mist; dust, fume, and mist; paint, lacquer, and enamel mist; and high efficiency types were tested after being pretreated in an environment of 38 degrees C and 85% relative humidity for periods up to 42 days. After various intervals of pretreatment (1, 7, 14, 28, and 42 days), the filters were tested against neutralized worst-case sodium chloride (NaCl) and dioctyl phthalate (DOP) aerosols for percent penetration. The results showed a drop in filter efficiency of approximately 2%-6% depending on preconditioning time, except for the high efficiency filters tested which showed no detectable change.

Aerosols↗

PubMed1984

Body temperature responses of aged mice to ambient temperature and humidity stress.

Male C57BL/6 mice aged 6 to 7 months, 13 to 14 months, and 19 to 20 months were acutely exposed to four ambient temperature (15 degrees C, 20 degrees C, 30 degrees C, 35 degrees C) and two relative humidity (50% rh, 80% rh) conditions. Three-hour average rectal temperatures were compared across age groups and environmental conditions. At the two temperature extremes of 15 degrees C and 35 degrees C, there was a very marked age-associated hypothermia and hyperthermia, respectively. This hypothermic response was maintained by the 19 to 20-month-old mice during exposure to 20 degrees C and thermoneutrality (30 degrees C). At any given ambient temperature, relative humidity had no effect on thermoregulatory function in the oldest mice, whereas the 6 to 7-month- and 13 to 14-month-old mice were sensitive to the effects of humidity at 15 degrees C and 20 degrees C.

Aging↗

PubMed1992

Effects of temperature and humidity on ovipositional biology and egg development of the tropical horse tick, Dermacentor (Anocentor) nitens.

The ovipositional biology and egg development of the tropical horse tick, Dermacentor (Anocentor) nitens (Neumann), was observed at four temperatures (20, 25, 30, and 35 degrees C) and relative humidities (40, 61, 75, and 91% RH). Relative humidity had little effect on length of preoviposition and oviposition periods. With increased rearing temperatures, there was a decrease in both preoviposition and oviposition periods. Oviposition rate increased with temperature and was not affected by relative humidity. Instantaneous rates of oviposition were calculated for each temperature by fitting the data to the logistic growth function. High percentage egg hatch was observed in low saturation deficit environments, and decreased when saturation deficit was increased.

Animals↗

PubMed1987

Preservation of humidity and heat of respiratory gases during anaesthesia--a laboratory investigation.

Humidification and heating of anaesthetic gases are desirable to prevent respiratory tract damage and a fall in body temperature during operative procedures. Numerous studies on the humidity and temperature of inspiratory gases in different breathing systems for anaesthesia have been carried out, but comparisons are difficult since different methods have been used. In this laboratory set-up we studied a non-rebreathing system with and without humidifiers and a circle absorber system with low (0.5 l/min) or medium (5 l/min) fresh gas flows regarding their ability to heat and humidify anaesthetic gases. The humidity of inspired gases was acceptable in the non-rebreathing system using either a Bennett Cascade humidifier or disposable humidifiers and in the circle absorber system using a fresh gas flow of 5 l/min or less. The temperature of the inspired gases was highest with the Bennett Cascade humidifier, followed by the low-flow circle system. The circle absorber system used with low fresh gas flow gave higher inspiratory gas temperature and humidity than the non-rebreathing system with a good disposable humidifier.

Anesthesia, Inhalation↗

PubMed1969

Plant injury by air pollutants: influence of humidity on stomatal apertures and plant response to ozone.

Ozone injury to Bel W3 tobacco and pinto bean plants increases with increasing humidity. The degree of plant injury sustained correlates well with porometer measurements; this indicates that the size of stomatal apertures increases with increasing humidity. Humidity may therefore influence plant response to all pollutants and may account in part for the greater sensitivity of plants to ozone-type injury in the eastern United States compared with the same species of plants grown in the Southwest. with those grown in the Southwest.

Air Pollution↗

PubMed1968

Infectivity-destroying effect of humidity for dried coliphage T1.

Infectivity of dried coliphage T1 has been measured as a function of humidity, temperature, and atmospheric pressure. Loss of infectivity by a factor of 10(4) was caused by water vapor of approximately 40 to 85% saturation when the microorganisms were kept for 3 days at 34 C in evacuated containers. At humidities below 40% and above 90% saturation, no loss of infectivity occurred. At a temperature of 24 C, the infectivity loss was 20-fold. When the virus preparation was kept at 34 C and atmospheric pressure, some loss of infectivity was also found at humidities below 40% and above 90% saturation. Damage to tail proteins or to the phage chromosome is considered as a possible explanation for the inactivation.

Coliphages↗

PubMed1971

Effect of relative humidity on dynamic aerosols of adenovirus 12.

Dynamic aerosols of adenovirus 12 were generated in the same Henderson apparatus under conditions of high, medium, and low relative humidity. High relative humidities resulted in more recovery of adenovirus 12 from aerosols and lungs of newborn Syrian hamsters. At 89, 51, and 32% relative humidity, the total infectious virus recovered from a 20-min aerosol was 10(6.7), 10(6.0), and 10(4.3) TCD(50), respectively. Hamsters exposed to these 20-min aerosols retained measured lung doses of 10(3.0), 10(2.4), and 10(1.0) TCD(50), respectively. The measured retained lung doses were compared to calculated inhaled lung doses based on both total virus aerosolized and total virus recovery from the aerosols.

Adenoviridae↗

PubMed1972

Effect of relative humidity on the inactivation of airborne Serratia marcescens by ultraviolet radiation.

Apparatus was designed and constructed in which a bacterial aerosol of known age, particle size, and relative humidity (RH) could be exposed to ultraviolet (UV) radiation of measured intensity for a given period of time and then be sampled quantitatively. Aerosols of Serratia marcescens were exposed to UV dosages between 96.0 and 0.75 (muw-sec)/cm(2) at humidities ranging from 25 to 90%. A sharp decline in the fraction of organisms killed was found at RH values above 60 to 70%. Above 80% RH, there was evidence for reactivation induced by UV. The plot of "log fraction organisms remaining" versus UV dose was curvilinear, suggesting noncompliance with the monomolecular law of reaction velocity, but the Bunsen-Roscoe law of reciprocity between time and intensity of UV exposure was demonstrated to hold. These results could be accounted for by postulating the presence in the aerosol of two populations of organisms with different sensitivities to UV, each individually obeying the monomolecular law of reaction velocity. The data amplify existing information on the relationship between UV disinfection of airborne organisms and RH. In the middle range of humidities, the sensitivity of the organisms to UV was greater than would be expected from published reports.

Aerosols↗

PubMed1986

Testicular torsion and low relative humidity in a tropical country.

One hundred and thirty one patients with testicular torsion were reviewed retrospectively to investigate the association of testicular torsion with air temperature and low relative humidity in Zaria, Nigeria. The incidence of testicular torsion was significantly increased during the harmattan season (November to February), when relative humidity is low and temperature decreased. Relative humidity was more closely correlated with the incidence of testicular torsion than was air temperature. Testicular torsion is a major contributor to male infertility in Zaria, and further study of its causes is required.

Adolescent↗

PubMed1985

Effect of relative humidity on the airborne survival of rhinovirus-14.

Rhinovirus-14, suspended in tryptose phosphate broth supplemented with uranine (physical tracer) and an antifoam, was aerosolized by use of a Collison nebulizer. The aerosols were held in a rotating drum with the relative humidity at either the low (30 +/- 5%), medium (50 +/- 5%), or high (80 +/- 5%) level at 20 +/- 1 degrees C. An all-glass impinger was used to recover the virus from the air in the drum, with the first air sample being collected after a 15-min period of aerosol stabilization. Subsequent air samples were withdrawn at 2, 4, 8, and 14 h after stabilization of the aerosol. At the low and medium relative humidity levels, the infectivity of the airborne virus was rapidly lost and less than 0.25% could be detected in the first air sample. At the high RH level, however, the airborne virus had a half-life of 13.7 +/- 1.91 h and nearly 30% of the input infectious virus could be detected in the drum air even after 24 h of aerosolization. These findings suggest that under certain environmental conditions, notably high relative humidity, air may act as a vehicle for the spread of rhinovirus infections.

Air Microbiology↗

PubMed1976

Effects of hypoxia, heat, and humidity on physical performance.

The effects of hot, humid environment were compared with the effects of high altitude on the physical performance capacity of Ne-palese residents by measuring oxygen uptakes and heart rates at various work rates. The following groups of men were selected: 66 residents of a hot and humid environment in the Terai at sea level; 24 residents and 16 sojourners at 3,8000 m. The maximal oxygen uptake of the sea-level residents was, on the average, 2.55 1.min-1, at which a maximal heart rate of about 200 beats/min was reached. The sojourners at 3,800 m showed a higher maximal oxygen uptake (2.94 1. min-1) at their maximal heart rate of about 175 beats/min. The residents of 3,800 m achieved a similiar oxygen uptake as the sojourners, but did not show a similar maximal heart rate limitation, suggesting that they were capable of achieving a higher maximal oxygen uptake. This study shows that hot, humid environment at sea level is as much incapacitating as is hypoxia at high altitude.

Adult↗

PubMed1976

A new method of measuring skin humidity.

A device suitable for the long-time measurement of relative skin humidity is described. This is a simple circuit with a resistance bridge for lithium chloride sensors connected to a digitally steered logic circuit, which causes dried air to stream intermittently through a measuring chamber placed on the skin in such a way that the relative humidity over the skin is maintained at a constant level. The number of switching time periods is proportional to the relative humidity (secretion performance) of the skin and can be counted, recorded, or directly fed into a digital calculator. The apparatus, including a two-channel version with skin temperature recording, has proved useful in sleep investigations under extreme climatic conditions.

Electronics↗

PubMed1975

Effects of low humidity on small premature infants in servocontrol incubators. I. Decrease in rectal temperature.

19 small premature infants in servocontrol incubators, whose abdominal skin temperature was 36.0 +/- 0.3 degrees C, were subjected to alternate high- and low-humidity environments. With low humidity, rectal temperature dropped significantly below abdominal skin temperature. Skin was the predominant site of evaporative heat loss. The temperature was lower on naked skin than on an area covered by adhesive tape. Thus, servocontrol with low humidity increases evaporative heat loss and engenders a cycle of events that results in paradoxical body temperature decrease as the incubator temperature increases.

Abdomen↗

PubMed1975

Effects of low humidity on small premature infants in servocontrol incubators. II. Increased severity of apnea.

Apneic spells were recorded in 8 of 19 premature infants nursed in high and low humidity alternately in servocontrol incubators. A significantly greater proportion of severe apnea occurred in low than in high humidity. It is postulated that this frequency and severity was due to the increased (as well as widely fluctuating) ambient temperature during low humidity.

Abdomen↗