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PubMed1993

Effect of humidity on hyperoxic toxicity.

Time to onset of hyperbaric oxygen-induced convulsions was measured in mice and rats exposed to hyperbaric oxygen (515-585 kPa) under conditions of low humidity (dry gas, < 10% relative humidity) or in a humidified environment (60% relative humidity). At all pressures tested, the duration of convulsive activity was markedly increased (P < 0.001), because of the earlier onset of severe generalized convulsions, in the groups of rodents exposed to the higher humidity. Pulmonary oxygen poisoning was determined by increases in lung wet and dry weights. Such pulmonary damage was also significantly (P < 0.001) increased in the humidified groups. Hyperoxic toxicity was also measured in rats and mice exposed to approximately 100% oxygen (normobaric hyperoxia) under conditions of 30 or 62% relative humidity. In contrast to the results obtained with hyperbaric oxygen exposure, there was slightly less toxicity in the rodents maintained at 62% compared with 30% humidity in normobaric hyperoxia.

Animals↗
PubMed2001

Humidity does not affect central nervous system oxygen toxicity.

Central nervous system (CNS) oxygen toxicity can occur as convulsions and loss of consciousness when hyperbaric oxygen is breathed in diving and hyperbaric medical therapy. Lin and Jamieson (J Appl Physiol 75: 1980-1983, 1993) reported that humidity in the inspired gas enhances CNS oxygen toxicity. Because alveolar gas is fully saturated with water vapor, we could not see a cause and effect and surmised that other factors, such as metabolic rate, might be involved. Rats were exposed to 507- and 608-kPa O(2) in dry (31 or 14%) or humid (99%) atmosphere until the appearance of the first electrical discharge preceding the clinical convulsions. Each rat served as its own control. A thermoneutral temperature (28 +/- 0.4 degrees C) yielded resting CO(2) production of 0.81 +/- 0.06 ml x g(-1) x h(-1). Latency to the first electrical discharge was not affected by humidity. At 507-kPa O(2), latency was 23 +/- 0.4 and 22 +/- 0.7 min in dry and humid conditions, respectively, and, at 608-kPa O(2), latency was 15 +/- 4 and 14 +/- 3 min in dry and humid conditions, respectively. When no effects of CO(2) and metabolic rate are present, humidity does not affect CNS oxygen toxicity. Relevance of the findings to diving and hyperbaric therapy is discussed.

Animals↗
PubMed2002

Seasonal difference in the occurrence of exercise-induced bronchospasm in asthmatics: dependence on humidity.

BACKGROUND: Most studies on the effects of temperature and humidity on exercise-induced bronchospasm (EIB) in asthmatics have been carried out under indoor conditions. However, any asthmatic patient is exposed to varying climatic conditions. OBJECTIVE: To investigate whether temperature or relative humidity plays a more important role in determining the degree of EIB in asthmatics under naturally exposed climate conditions. METHODS: To exclude the effects of pollen on EIB, we enrolled 69 subjects with perennial asthma (mean +/- SD: 20.1 +/- 1.5 years). The subjects performed outdoor free running tests. They were divided into winter (n = 25), spring/autumn (n = 22), and summer (n = 22) groups according to the season when they performed the tests. Initial spirometry and skin prick tests were performed. Methacholine bronchial challenge testing and, one day later, the free running tests were done. RESULTS: There were significant differences in temperature and relative humidity among the three groups: However, the relative humidity in winter did not differ from that in spring/autumn. There were no differences in pulmonary functions, airway responsiveness, and atopy score among the three groups. The percentage of cases of positive EIB --fall in forced expiratory volume in 1s FEV(1) of >15% from baseline --in winter (84%, p < 0.05) or spring/autumn (86.4%, p < 0.05) was higher than that in summer (50%). However, the percentage of subjects with a positive EIB in winter did not differ from that in spring/autumn. The maximal percent fall in FEV(1) after exercise in winter did not differ from that in spring/autumn. CONCLUSIONS: The occurrence of EIB is associated with environmental temperature and humidity. Under such climatic conditions as in Korea, relative humidity may be a more important factor than temperature in contributing to EIB in patients with perennial asthma.

Adult↗
PubMed2002

Effects of ventilation, humidity and temperature on airway responsiveness to methacholine in rats.

Exercise-induced bronchoconstriction is associated with heat and water loss from the airways. It is not known whether these conditions can influence the response to bronchoactive agonists. The effects of different degrees of alveolar ventilation on the pulmonary response to methacholine and the role of humidity and temperature in this response were evaluated. Wistar rats were anaesthetized, tracheostomized and mechanically ventilated. Increasing doses of methacholine were infused intravenously and respiratory system resistance (Rrs) and elastance (Ers) were measured. The rats were ventilated with dry air at 13 degrees C, dry air at 37 degrees C, humid air at 13 degrees C and humid air at 37 degrees C. These four groups were further divided into three subgroups with a respiratory frequency adjusted to reach a carbon dioxide tension in arterial blood of 30, 40 and 50 mmHg. Temperature, humidity and level of alveolar ventilation did not influence the position of the dose/response curve to methacholine. However, the maximal changes in Ers were significantly lower in the rats ventilated with humid air. In addition, maximal changes in Ers were significantly higher in the rats with lower alveolar ventilation. These differences were not observed for maximal values of Rrs. The pulmonary response to methacholine in normal rats is significantly affected by the humidity of inspired air and the level of alveolar ventilation. This influence is more intense in the small airways and/or distal airspaces. This suggests that exercise or hyperventilation can change the behaviour of airway smooth muscle.

Airway Resistance↗
PubMed1988

Responses of older and younger women to exercise in dry and humid heat without fluid replacement.

Eight older (52 to 62 yr old) post-menopausal and 8 younger (20 to 30 yr old) women were matched with respect to body size, fatness, and maximal oxygen consumption, heat-acclimated, and then exercised at 35 to 40% maximal oxygen consumption in a warm-humid (37 degrees C, 60% relative humidity) environment. Results were compared with similar data from a hot-dry (48 degrees C, 15% relative humidity) environment. No fluid replacement was provided during either of these sessions. In each environment, the older women stored more heat as evidenced by a higher rectal temperature response, but there were no inter-group differences in skin temperature or percent maximal heart rate. Four of the older women were unable to complete either the hot-dry or the warm-humid exposure, although they completed the full 2 h during acclimation sessions when water was provided ad libitum. In the hot-dry environment, the younger women's whole body and local sweat rates were significantly higher than those of the older women; in the warm-humid environment, there was no age-related difference in sweat rate. When local skin temperature and wettedness were artificially elevated, both groups exhibited the same pattern and rate of sweating. Percent decrease in plasma volume was greater for the older women in both conditions, but significantly so only in the warm-humid environment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

[Changes in temperature and humidity at different layers inside clothing during rest, exercise, and recovery].

This paper presents the results of experiments in which we measured humidity and temperature changes that took place in different layers inside and on clothing. The experiments were conducted during rest, exercise, and recovery. During each experiment, subjects wore one of three kinds of outerwear made of three different materials, respectively. These materials were nylon taffeta (N), nylon taffeta-Goretex-nylon tricot laminated fabric (G), and polyvinylchloride-coated plain cotton fabric (V). The subjects wore an undershirt and a T-shirt under the outerwear. The humidity and the temperature were measured in the following parts of each subjects' back: (1) the layer between the subject's skin and the undershirt (first layer), (2) the layer between the undershirt and the T-shirt (second layer), (3) the layer between the T-shirt and the outerwear (third layer), and (4) the surface of the outerwear (fourth layer). We also measured the sensation of comfort, the skin temperature, the oral temperature and the degree of sweating of the subjects. The experiments were conducted in a climatic chamber under conditions of 20.7 +/- 0.4 degrees C, 61.2 +/- 3.6% RH and 2.5 +/- 0.5 cm/sec. The results we obtained were as follows: 1) While the subjects kept still, little change of humidity was observed with time in all the four layers. When the subjects were in motion, humidity increased as they started sweating. After the exercise ended, the humidity reached its maximum and then gradually decreased. 2) When subjects kept still, there was no difference in humidity in all the four layers of the outerwear.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Influence of temperature and humidity on laser in situ keratomileusis outcomes.

PURPOSE: The influence of ambient factors on the results of refractive surgery is not well-known. This study evaluated the influence of temperature and humidity on laser in situ keratomileusis (LASIK) outcomes. METHODS: Two hundred thirty-seven patients who underwent LASIK at the Clivan Instituto de Oftalmologia in Salvador--Bahia--Brazil, between May 1999 and March 2000, were evaluated. A total of 156 (65.8%) patients were female. Mean age was 30.3 +/- 7.6 years. Refractive errors: 197 patients (83.12%) had compound myopic astigmatism, 17 patients (7.17%) had myopia, 11 patients (4.64%) had compound hyperopic astigmatism, and 12 patients (5.07%) had other. Results at 15 and 60 days after LASIK were compared according to different levels of temperature and humidity in the operating room during the procedure. RESULTS: Patients whose spherical equivalent refraction varied between -0.50 to +0.50 D at 15 days after LASIK had surgery performed when the temperature was 25.1 +/- 1.4 degrees C and humidity was 45.1 +/- 4.2%; for the others, temperature was 24.7 +/- 1.5 degrees C (P = .12) and humidity was 43.0 +/- 4.0% (P = .002). The linear regression coefficient showed that lower temperature levels were associated with lower spherical equivalent refractions at 60 days after LASIK (r2 = .14; P = .03) but not at 15 days after LASIK (P = .98). The evaluation of humidity indicated an influence at 15 days after LASIK (r2 = .44; P = .04), as well as at 60 days (r2 = .45; P = .0002). CONCLUSION: Operating room environment may influence LASIK outcomes; humidity may be more significant than temperature.

Adult↗
PubMed2000

Humidity and temperature profile in the nasal cavity.

OBJECTIVES/HYPOTHESIS: Adequate air conditioning in the nasal airways is mandatory for respiration and gas exchange in the lower respiratory tract. The aim of the present study was to measure relative humidity and temperature in the airstream at different sites within the nasal cavity for mapping of relative humidity and temperature in the upper airways. STUDY DESIGN: Intranasal relative humidity and temperature of 23 volunteers was measured during respiration at different locations in the nasal cavity. METHODS: The end-inspiratory temperature and humidity data, obtained with a miniaturized thermocouple and a capacitive humidity sensor, were determined. RESULTS: A high increase of humidity and temperature at the end of inspiration, in relation to the environmental conditions, was found in the anterior nasal segment. The further increase of both parameters between turbinate area and nasopharynx was less pronounced in spite of the longer distance. CONCLUSIONS: The anterior part of the nasal cavity contributes within a short nasal passage to air conditioning of inspired air.

Adult↗
PubMed2001

The influence of relative humidity on the effect of dentin bonding systems.

PURPOSE: The aim of the study was to measure the influence of relative humidity of the ambient air on bond strength to enamel and dentin of six different bonding systems. In this manner, the role of the primer solvent was assessed. MATERIALS AND METHODS: The bonding systems selected were Prime & Bond 2.1, One Step, Scotchbond MP, Syntac Single Component, Optibond Solo, and Perma Quick. The primers of these systems are based on either acetone, water or ethanol. Plane enamel and dentin surfaces were placed at relative humidities of 18%, 45%, 80% or 99% RH and then treated in accordance with the recommendations of the respective manufacturers. A resin composite was then bonded to the treated surfaces. After storage in water at 37 degrees C for 1 day, the bonded specimens were broken in shear. RESULTS: The bonds to enamel were either unaffected or in one case moderately increased by increasing ambient humidity. The bonds to dentin were either unaffected or in four cases strongly reduced by increasing humidity. CONCLUSIONS: The response of the bonding systems to differences in ambient humidity were not related to the solvent of the primer in a simple way. To exclude the damaging effect of high humidity on dentin bonding, the use of rubber-dam is recommended.

Acetone↗
PubMed1973

On the mechanism of adaptation of micro-organisms to conditions of extreme low humidity.

Low humidity is considered one of the main obstacles for life on Mars. Mechanisms of adaptation to extreme low humidity are investigated in asporogenic yeasts. Cryptococcus albidus var. diffluens inhabits the high mountain deserts of the Pamirs and the Tien Shan. The spin-echo nuclear magnetic resonance method shows that different ways of drying do not extract all liquid water from the cells. Residual humidity of the Cryptococcus cells may reach 30%. The polysaccharide capsule of Cryptococcus delays the drying process noticeably and also collects moisture at low relative humidity. The considerable quantity of conserved liquid water allows Cryptococcus to adapt to the great periodic oscillations of relative humidity resulting from the great diurnal temperature changes in the high mountain deserts. Data obtained indicate the presence of a humidity regulating mechanism on the cellular level in lower plants.

Adaptation, Physiological↗
PubMed2004

Rectal temperature changes of Wistar rats with second-degree scald burn in hot and humid environment following immediate cooling therapy.

OBJECTIVE: To observe the changes in rectal temperature (Tr) after immediate cooling therapy for Wistar rats with superficial second-degree scald burn in hot and humid environment, and evaluate the effect of the dressing material for cooling. METHODS: Twenty-four Wistar rats were randomly divided into 4 groups (n=6), namely normal temperature control (NTC), normal temperature cooling therapy (NTCT), hot and humid control (HHC), and hot and humid cooling therapy (HHCT) groups. Superficial second-degree scald burns were induced in the rats, followed by interventions with cooling therapy in the two therapy groups at dry bulb temperature (Tdb) of 35.33+/-0.35 degrees Celsius with relative humidity of 70.81%+/-1.38%, whereas the two control groups were treated at Tdb of 26.33+/-1.29 degrees Celsius with relative humidity of 71.05%+/-4.57% without dressing for cooling therapy. The exposure time of each group was 120 min, and the Tr was recorded every 20 min. RESULTS: On the basis of comparisons between the measurements taken at 7 different time points, we found that the Tr of the rats was elevated in hot and humid environment (P<0.001) and decreased when cooling therapy was applied (P<0.001). Interactions between the environmental temperature and cooling therapy were noted in their influence on Tr (P=0.003). As the exposure time was prolonged, Tr slowly decreased in NTC group, mildly fluctuated in NTCT group, but elevated in HHC and HHCT groups with gradual increase of the differences between the measurements taken at the same time point. CONCLUSION: Application of the dressing material on the abdomen for cooling therapy can efficiently lower the Tr, which may prevent the progression of the heat injury.

Animals↗
PubMed2004

[Skin temperature changes in Wistar rats with second-degree scald injury in hot and humid environment after cooling therapy].

OBJECTIVE: To observe the changes in skin temperature after cooling therapy immediate following superficial second-degree scald injury in Wistar rats in a hot and humid environment, and evaluate the effect of the dressing materials for the cooling therapy. METHODS: Twenty-four Wistar rats were randomly divided into normal temperature control (NTC), normal temperature cooling therapy (NCT), hot and humid control (HHC), and hot and humid cooling therapy (HCT) groups (n=6). Different interventions were applied to the scalded rats: dry bulb temperature (Tdb) of 26.33+/-1.29 degree with a relative humidity (rh) of 71.05%+/-4.57% for the two normal temperature groups, and Tdb 35.33+/-0.35 degree with rh of 70.81%+/-1.38% for the two hot and humid environment groups. The dressing materials for the cooling therapy were applied to the two cooling therapy groups but not for the two control groups. The exposure time for the therapy was 125 min, and the skin temperature was measured every 20 min, starting from 5 min after the scald. RESULTS: The skin temperature rose in hot and humid environment and decreased when cold therapy was applied (P<0.001). Interactions were found between the exposure time and environmental temperature (P<0.002), between the exposure time and cooling therapy (P<0.05), and between these 3 factors (P<0.05) to influence the skin temperature, which was 1.92+/-2.13 degrees Celsius lower in NCT group than in NTC group, and 2.36+/-1.03 degrees Celsius lower in HCT group than in HHC group. CONCLUSION: The dressing materials for cooling therapy effectively reduce the skin temperature at the site of the scald injury to prevent the progression of heat-induced injury and the unfavorable effects of the heat remaining on the scalded skin.

Animals↗
PubMedDate not supplied

Effect of humidity on the volumetric polymerization shrinkage of resin restorative materials.

This study measured the volumetric polymerization shrinkage of three resin restorative materials under ambient (that is, room) relative humidity conditions and compared it with shrinkage occurring under a higher humidity condition that simulated the oral cavity. Small, semi-spherical specimens of a compomer, microfill composite, and flowable microhybrid composite were formed and light-activated using a halogen photocuring unit. The volumetric polymerization shrinkage of 15 specimens of each product was measured using a drop shape analysis unit for the relative humidity level of the ambient room (58.6 +/- 5.9%) and a higher humidity level that simulated the oral cavity (98.0 +/- 2.9%). Mean volumetric shrinkage values were calculated for each resin composite and the data were analyzed using a two-way analysis of variance (alpha = 0.05) to determine if significant differences existed between the amount of volumetric polymerization shrinkage that occurred under ambient room humidity conditions and the amount that occurred under simulated intraoral humidity conditions. Statistical analysis indicated that there was no significant difference (p = 0.17).

Compomers↗
PubMed1979

Effect of temperature, relative humidity and medium on the aerosol stability of infectious bovine rhinotracheitis virus.

Aerosols of infectious bovine rhinotracheitis virus were generated with a Devilbiss 40 nebulizer from Eagle's minimum essential medium, nasal secretion from a noninfected calf and nasal secretion from a calf artificially infected with infectious bovine rhinotracheitis virus and aged in a rotating drum at temperatures of 6 degrees C or 32 degrees C and relative humidities of 30% or 90%. The aerosols were sampled at seven minutes after start of spraying, one hour, two hours and three hours with an all glass impinger (AGI-30) and titrated for infectivity in cell cultures. Physical decay was determined by a rhodamine B tracer technique. During spraying (seven minutes from start of spraying), the virus was usually more stable in aerosols of nasal secretion from a noninfected calf and at 90% relative humidity. In nasal secretion from a noninfected calf the virus survived best at 90% relative humidity when the temperature was 6 degrees C and best at 30% relative humidity when the temperature was 32 degrees C. During aging, biological decay was greater at the higher temperature, and at 6 degrees C, the highest decay rates occurred at 30% relative humidity in Eagle's minimum essential medium and at 90% relative humidity in nasal secretion from a noninfected calf. The stability of infectious bovine rhinotracheitis virus infected nasal secretion was not widely different from that in noninfected nasal secretion, although under certain conditions greater survival occurred in the noninfected secretion.

Aerosols↗
PubMed2002

Adsorption of a diverse set of organic vapors on quartz, CaCO3, and alpha-Al2O3 at different relative humidities.

Adsorption constants of a diverse set of 50 organic vapors have been measured on quartz (SiO(2)), CaCO(3), and alpha-Al(2)O(3) at different relative humidities at 15 degrees C. For nonpolar compounds we found an exponential decrease of the adsorption constants on a given mineral between 40 and 97% relative humidity. Extrapolated to 100% relative humidity, the adsorption constants of nonpolar compounds on the different minerals coincide and agree with those measured on a bulk water surface. The adsorption constants of polar compounds also decrease with increasing humidity up to 90%, but between 90% and 100% they increase again. We speculate that this effect is due to a change in the orientation of the water molecules that form the surface at which the organic vapors adsorb at this high humidity. The compound variability in the adsorption constants of all compounds on a given surface at a given relative humidity could be described rather well with a linear free energy relationship using Abraham's solvation parameters for the van der Waals and electron-donor/acceptor properties of the compounds. The remaining deviation between fitted and experimental data was found to be systematic, which indicated that an optimized parameter set for the used compounds could still considerably improve the fit.

Journal Article↗
PubMed1985

Low humidity and microtrauma.

Low-humidity dermatoses arise in the work place as a result of low water content of the air. At a relative humidity of 10% or less, the horny layer becomes rigid and brittle. The combination of low humidity, high temperature, and, frequently, rapid air movement dehydrates the outer stratum corneum. This leads to pruritus and, finally, to low-grade eczema. A roughened, scaly stratum corneum becomes more susceptible to mechanical trauma. Microtrauma from small particles can aggravate the dry scaly dermatosis. Low-humidity lesions resolve quickly with the simple expedients of routine use of moisturizers and/or raising the relative humidity.

Facial Dermatoses↗
PubMed1983

Humidity as a source of measurement error in osteometrics.

A simple experiment was conducted to test the hypothesis that variation in humidity causes expansion of bone and, thereby, affects measurements of dried, preserved skulls. The experiment consisted of subjecting ten macaque skulls to increased humidity for 24 hours. Measurements of nine skull dimensions taken immediately before and after humidification revealed a statistically significant treatment effect of increased skull size with increased humidity. The length of the molar tooth row increased by about 0.1 mm (0.50%) while the greatest length of the skull increased by about 0.9 mm (0.57%). The specimens returned to their original dimensions within 1-2 days after being removed from the humidity chamber. These results confirm the impression gained by the practical experience of measuring museum specimens in different locations and environments. It appears that bony changes associated with humidity differences represent a real, though minor, source of measurement error in osteometrics.

Animals↗
PubMed1998

Humidity control tool for neonatal incubator.

In the first days of life, the daily evaporative loss from premature neonates can reach up to 20% of body mass. Such loss can be reduced by increasing the air humidity inside the incubator. Neither passive humidification nor open loop systems allow high humidity rates to be maintained or easily controlled: at 34 degrees C, the maximum levels vary with the system from 40% to 77% of relative humidity. The skin evaporative exchanges between the neonate and the environment are directly proportional to the water vapour partial pressure difference between the neonate's skin and the air. An active closed loop system has been designed, which permits reliable and accurate control of humidity according to the water vapour partial pressure set, between 1 and 6 kPa, in an air temperature range of 28-39 degrees C. It is characterised by variations of about 0.05 kPa around the set value and a maximum humidification speed of 0.25 kPa min-1. The algorithm is based on optimal control and the dynamic programming principles. Test results place this active system above usual systems for its power, precision and adaptability. It is an exploitable tool in fundamental and clinical research, to precisely study the humidity effects on neonatal comfort and thermo-regulation evolution.

Algorithms↗