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PubMed1989

Damp housing and childhood asthma; respiratory effects of indoor air temperature and relative humidity.

In a questionnaire survey of a random sample of 1000 children aged 7 years, a significantly greater proportion of those living in homes reported as damp were affected by wheeze (22% v 11%), day cough, night cough, and chesty colds. Simultaneous estimation of relative humidity in the bedrooms of 778 children and continuous 7 day recordings of ambient temperature and humidity in a stratified sample of 317 bedrooms showed no association with the same respiratory symptoms. No correlation was found between bedroom conditions and baseline ventilatory function or exercise induced reduction in FEV1. These results run counter to the widely held belief that indoor temperature and humidity are important determinants of respiratory ill health, although they do not directly exclude effects due to mites or moulds, whose survival is determined by the humidity of their respective microenvironments.

Asthma↗

PubMed1990

Upper respiratory tract infection in children, domestic temperatures, and humidity.

STUDY OBJECTIVE: The aim of the study was to seek for a possible association between the incidence of upper respiratory tract infections and air temperature and humidity in the home. DESIGN: Recordings of temperature and relative humidity were made in living rooms and children's bedrooms over a six month period and related to incidence of upper respiratory tract infection. SETTING: The study was carried out in one general practice of 10,000 patients. PATIENTS: 297 children aged 24-59 months were studied, selected in random order from the practice age-sex register. MEASUREMENTS AND MAIN RESULTS: Temperature and humidity recordings were made with thermohygrograph recorders over six days. Upper respiratory tract infections were recorded (a) retrospectively over the previous 12 months, and (b) during the study period. Past history of acute otitis media and recent family history of respiratory infection were also obtained. No significant association was found between the variables, although the bedrooms of children with reported upper respiratory tract infections were cooler overnight than those of non-infected children (mean difference 0.8 degrees C, 95% confidence limits 0.7 degrees C). No association was found between reported or recorded upper respiratory tract infections and age or type of home, family size, level of occupancy, social class, or smoking habits. Only 15 children (5%) were identified by their parents as having had asthma, but 58 (19.5%) had had a "wheezy chest". A greater proportion of children who wheezed slept in cooler bedrooms, had gas fires rather than central heating, and had more smokers in the house. CONCLUSIONS: No association between upper respiratory tract infection and domestic temperature or humidity levels could be shown in this study. Since dampness is repeatedly presented as a health risk, further study is required.

Child, Preschool↗

PubMed1987

Survival of human rhinovirus type 14 dried onto nonporous inanimate surfaces: effect of relative humidity and suspending medium.

To study the survival of human rhinovirus 14 on environmental surfaces, each stainless steel disk (1 cm in diameter) was contaminated with 10 microL (about 10(5) plaque-forming units) of the virus suspended in either 1 chi tryptose phosphate broth (TPB), 5 mg/mL of bovine mucin in normal saline, or undiluted human nasal discharge. The inoculum was dried in a laminar flow cabinet for 1 h under ambient conditions. The disks were then placed in a glass chamber (20 +/- 1 degree C) with the relative humidity at either low (20 +/- 5%), medium (50 +/- 5%), or high (80 +/- 5%) level. At appropriate intervals, the disk to be tested was placed in 1 mL of tryptose phosphate broth and the eluate titrated in A-5 HeLa cells. When the virus was suspended in either tryptose phosphate broth, mucin, or the nasal discharge and subjected to initial drying, there was a 3.0 +/- 1.0, 82.0 +/- 6.7, and 89.0 +/- 3.0% loss in virus infectivity, respectively. The half-life of the TPB-suspended virus was about 14 h at the high relative humidity as compared with less than 2 h at the other two relative humidity levels. The half-lives for the mucin-suspended virus at the high, medium, and low relative humidity were 1.42, 0.55, and 0.24 h, respectively; the corresponding values for the nasal discharge suspended virus being 0.17, 0.25, and 0.09 h.

Culture Media↗

PubMed1998

Acclimation to humid heat lowers resting core temperature.

The purpose of this study was to test the hypothesis that a reduction in resting rectal temperature (Tre) is partially responsible for the attenuation in the rise of core temperature during the heat exposure following acclimation to humid heat. Nine male volunteers completed 7 days of acclimation, performing 2 h of exercise per day in a hot, humid environment (35 degrees C, 75% relative humidity). Mean (+/- SD) ending Tre significantly (P < 0.05) decreased from 38.9 +/- 0.5 degrees C on day 1 to 38.3 +/- 0.4 degrees C on day 7. Likewise, mean (+/- SD) resting Tre significantly (P < 0.05) decreased from 37 +/- 0.3 to 36.7 +/- 0.4 degrees C. In fact, all nine men showed a decrease in resting Tre from day 1 to day 7, ranging from -0.1 to -0.5 degrees C. In addition, resting Tre and ending Tre were significantly correlated (r = 0.68). However, the mean increases in Tre (ending Tre minus resting Tre) and heat storage that occurred on each of the 7 acclimation days were not significantly different. These results support the hypothesis that a reduction in resting Tre is partially responsible for the attenuation in ending Tre during heat exposure following short-term acclimation to humid heat.

Acclimatization↗

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↗

PubMed1998

Measuring temperature and humidity in the breathing circuit.

Accurate measurement of temperature and humidity in the breathing circuit can be a difficult task. This article introduces basic humidity concepts, outlines the problems that are unique to the breathing circuit, and describes the various methods that are available to measure temperature and humidity. Recommendations are made on how to measure temperature and humidity in four commonly encountered situations.

Humans↗

PubMed1998

The effect of temperature and humidity on dengue virus propagation in Aedes aegypti mosquitos.

The effect of temperature and relative humidity on dengue virus propagation in the mosquito as one of the possible contributing factors to dengue hemorrhagic fever (DHF) outbreaks was studied. Ae. aegypti mosquitos were reared under standard conditions and inoculated intrathoracically with dengue virus. Virus propagation in the mosquitos was determined at the temperature and relative humidity of all 3 seasons of Yangon and for the simulated temperature and relative humidity of Singapore. The virus propagation was detected by direct fluorescent antibody technique (DFAT) with mosquito head squash and the virus titer was determined by plaque forming unit test (PFUT) in baby hamster kidney-21 cells. The results show that the infected mosquitos kept under the conditions of the rainy season and under the simulated conditions of Singapore had a significantly higher virus titer (p=<0.05) when compared with the other 2 seasons of Yangon. So it is thought that the temperature and relative humidity of the rainy season of Yangon and that of Singapore favors dengue virus propagation in the mosquito and is one of the contributing factors to the occurence of DHF outbreaks.

Aedes↗