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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↗
PubMed1990

Responses of young and older men during prolonged exercise in dry and humid heat.

Eight young, sedentary men (aged 34 years, SD 3) and six older moderately active, unacclimated men (aged 57 years, SD 2) walked on a treadmill at 30% of their maximum oxygen consumption up to 3.5 h in a thermoneutral [dry bulb temperature (Td) 21 degrees C, relative humidity (r.h.) 43%)], a warm humid (Tdb 30 degrees C, r.h. 80%) and a hot dry (Tdb 40 degrees C, r.h. 20%) environment while wearing ordinary working clothes (0.7 clo). Their oxygen consumption, heart rate (fc), rectal (Tre) and mean skin temperature (Tsk), sweat rate (SR), and evaporative rate (ER) were measured during the tests. The ratings of thermal sensation (TS) and perceived exertion (RPE) were assessed using standard scales. In the heat stress tests, the number of experiments discontinued did not significantly differ between the two groups. The mean levels and end-exercise values of Tre, Tsk, fc, TS and RPE were not significantly different between the young and older subjects in any of the environments. In the warm humid environment, however, the Tre and RPE of the older subjects increased continuously (P less than 0.05) during the test compared to the young subjects. No significant difference between the groups was observed in SR or in ER. In the hot dry environment, however, the ER of older men increased more slowly compared to the young men. In spite of some time-related differences observed in Tre, RPE, and ER, the older subjects did not exhibit higher fc during exercise in the heat, they were not more hyperthermic and their performance times were similar to the young subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

The effects of elevated temperature and humidity on rectal temperature and respiration rate in the New Zealand white rabbit.

In 2 replicated factorial experiments, 7-h climate chamber exposures were used to study the responses of adult NZW rabbits to a range of elevated temperatures and humidities. At 18 mm Hg water vapour pressure, 23.8 degrees C was well tolerated, rectal temperature (RT) and respiration rate (RR) averaging 38.6 +/- 0.3 degrees C and 82.9 +/- 15.5 breaths/min, respectively. Both parameters were elevated (P less than 0.001) at 32.2 degrees, 37.8 degrees and 43.3 degrees C. RT and RR reached plateau levels of 39.5-40.1 degrees C and 410-460/min at 32.2 degrees C, which was tolerated for the full 7-h test period. Test temperatures of 37.8 degrees and 43.3 degrees C, on the other hand, could be tolerated for only 80 and 40 min respectively, before RT reached the safe upper limit of 41.7 degrees C. Final RR values at 37.8 degrees and 43.3 degrees C were 701.6 +/- 42.7 and 812 +/- 55.1/min, respectively. In a 34.5 degrees C atmosphere a humidity of 21 mm Hg water vapour pressure was classified as "dry", and was tolerated for 323 +/- 123 min. RT and RR increased by 0.6 degrees C and 316/min during the first 20 min of exposure (P less than 0.05). Thereafter both parameters increased progressively, but with no significant differences between successive recording periods, until RR reached 550.3 +/- 88.8/min at 41.7 degrees C RT. Humidities of 25, 29 and 33 mm Hg water vapour pressure were, on the other hand, classified as "wet" and were tolerated for only 92 +/- 22, 81 +/- 16 and 119 +/- 50 min, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Population increase and damage by three species of mites on wheat at 20 degrees C and two humidities.

Twenty bisected grains of wheat infested with five pairs of the three commonest British grain-storage mites, Acarus siro L., Glycyphagus destructor (Shrank) and Tyrophagus longior (Gervais), were examined every week for 20 weeks. Mite populations, the resulting damage to germ and endosperm, and visible fungal growth were observed at 20 degrees C and relative humidities (r.h.) of 90% and 75%. At 90% r.h., A. siro populations reached nearly 14,000 per test-tube before slowly dropping to 5000. The mites ate the germ before the endosperm, leaving an impenetrable layer of crushed endosperm cells between these regions. The G. destructor population reached only 800 before declining to 300; these mites ate over 75% of the germ and small amounts of endosperm. Tyrophagus longior populations rose to 2200 mites before crashing at week 12 to the initial population level; these mites ate over 75% of the germ and small amounts of endosperm. At 75% r.h., both A. siro and T. longior populations were lower than at the higher r.h., peaking at 3000 and 1000 respectively and decreasing to 500 and 600 mites respectively. Glycyphagus destructor did markedly better than at 90% r.h., reaching 1500 before falling to 400. The damage at this humidity was slower to occur but was similar to that at 90% r.h. at the end of 20 weeks. At both humidities visible fungus was always less abundant on infested grain that uninfested grain.

Animals↗
PubMed1988

Effects of environmental temperature, relative humidity and vaccination on Pasteurella haemolytica in lungs of mice.

Groups of mice were kept in four combinations of environmental temperature (8 and 20 degrees C) and humidity [50 per cent and 90 per cent relative humidity (RH)]. The mice were anaesthetized and inoculated intranasally with Pasteurella haemolytica growing logarithmically. Groups of 11 mice were killed at 0.5 h intervals for 6 h after inoculation and the number of colony-forming-units (CFU) of Pasteurella haemolytica in the lungs was determined. The CFU in the lungs of mice were affected by a significant interaction of temperature, relative humidity and time after inoculation (P less than 0.01). From 0.05 to 5.0 h after inoculation, fewer CFU were found in the lungs of mice kept in 8 degrees C 50 per cent RH than in mice kept in 8 degrees C 90 per cent RH, 20 degrees C 50 per cent RH and 20 degrees C 90 per cent RH. In each environment, CFU in the lungs of mice increased from inoculation to approximately 3.5 h after inoculation and then decreased (P less than 0.01). In a similar experiment in an environment of approximately 20 degrees C and 50 per cent RH, there were significantly fewer CFU in the lungs of mice vaccinated intranasally 21 days earlier with live P. haemolytica than in the lungs of mice either vaccinated intranasally with formalized P. haemolytica or not vaccinated with P. haemolytica (P less than 0.01).

Animals↗
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↗
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↗