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PubMed1989

Design and development of a micro-thermocouple sensor for determining temperature and relative humidity patterns within an airstream.

This paper describes the production and calibration of a miniature psychrometer treated with a specially developed porous coating. The investigation was conducted to determine localized patterns of rapidly changing temperature and relative humidity in dynamic flowing gas environments (e.g., with particular attention to future applications to the human respiratory system). The technique involved the use of dry miniature thermocouples and wetted miniature thermocouples coated with boron nitride to act as a wicking material. A precision humidity generator was developed for calibrating the psychrometer. It was found that, in most cases, the measured and expected (i.e., theoretically predicted) relative humidity agreed to within 0.5 to 1.0 percent relative humidity. Procedures that would decrease this discrepancy even further were pinpointed, and advantages of using the miniature psychrometer were assessed.

Air↗
PubMed1971

Effect of relative humidity and temperature on airborne Venezuelan equine encephalitis virus.

Inactivation of airborne Venezuelan equine encephalitis (VEE) virus disseminated from liquid suspensions or from lyophilized preparations as 1- to 5-mum particles was investigated under various conditions of relative humidity and temperature in a 2,500-liter static aerosol chamber. Relative humidity ranging from 18 to 90% at 24 C and temperature ranging from -40 to 24 C had no marked effect on the biological decay rate or the recovery of viable airborne VEE virus disseminated from liquid suspensions. However, at 49 C a significant increase in the biological decay rate and decrease in aerosol recovery of the VEE virus were observed. Airborne lyophilized VEE virus was significantly affected by relative humidity. An increase in relative humidity from 20 to 90% resulted in progressive decrease in aerosol recovery of viable VEE virus. A twofold reduction in aerosol recovery of the lyophilized virus was observed at and above 29 C as compared to the lower temperatures studied. However, the differences among biological decay rates of lycphilized VEE virus were not significant within temperature range of -40 to 38 C.

Air Microbiology↗
PubMed1973

Influence of temperature and humidity on microbial, enzymatic, and physical changes of stored, pickling cucumbers.

Pickling cucumbers stored at five temperatures and four relative humidities were examined for growth of eight microbial groups, the activities of two enzyme systems (pectinolytic and cellulolytic), and weight loss. Twenty-four storage tests for 6 days each were conducted during the 2-year study. In general, microbial populations of the eight groups increased rapidly at the higher temperature (>21 C) and humidity (>70%) treatments. Moisture loss of the cucumbers was rapid with combinations of high temperatures and low humidities. The results suggest that the best environmental conditions for storage or transport of cucumbers would be a combination of low temperature (10 C) with high relative humidity (about 95%). These conditions minimized undesirable microbial, enzymatic, and physical changes of stored, pickling cucumbers.

Bacteria↗
PubMed1982

Influence of humidity on rotavirus prevalence among Nigerian infants and young children with gastroenteritis.

Rotaviruses were detected by counterimmunoelectro-osmophoresis in the feces of 16 (13.8%) of 116 infants and young children with gastroenteritis during a 5-month period (September 1979 through January 1980) in Ife, Nigeria. The rate of rotavirus detection varied inversely with relative humidity and was highest in December (38.5% positive) when the humidity was lower. There was not such a distinct relationship with temperature or vapor pressure; and although the rate of rotavirus detection was higher in the drier months (November to January; 19.3% positive) than in the rainy season months (September and October; 8.5% positive), the average humidity was lower in the drier months than in the rainy months. Low relative humidity (49 to 78%) is apparently the most important environmental factor for rotavirus survival and spread in this area.

Child, Preschool↗
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↗
PubMed1999

Effect of high versus low ambient humidity on the severity of obstructive sleep apnoea.

BACKGROUND: Surface tension forces appear to make a significant contribution to upper airway closure in patients with obstructive sleep apnoea (OSA). It is possible that drying of the upper airway mucosa at night might contribute to these surface tension forces and the severity of OSA might therefore change with alteration of the ambient humidity. METHODS: A randomised single blind crossover study of high ambient relative humidity (HRH) versus low ambient relative humidity (LRH) was performed in 12 men of mean (SD) age 49 (9) years with mild OSA (apnoea/hypopnoea index (AHI) 14 (5.2)). On one night patients slept in continuous HRH (85 (4)%, range 80-93%) and on the other in LRH (16 (4)%, range 11-22%). RESULTS: The AHI was similar on the HRH and LRH nights (mean difference 3; 95% CI -2 to 9, p = 0.20 and no statistically significant differences in AHI were observed on the two nights after standardising for body position and sleep stage. Sleep stage distribution and the proportion of time spent in the supine position were similar on the HRH and LRH nights. The number of non-respiratory arousals was also similar on the two nights. CONCLUSION: Altering ambient humidity alone has no significant impact on the severity of OSA.

Humans↗
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↗
PubMed2000

Heat storage in horses during submaximal exercise before and after humid heat acclimation.

The effect of humid heat acclimation on thermoregulatory responses to humid and dry exercise-heat stress was studied in six exercise-trained Thoroughbred horses. Horses were heat acclimated by performing moderate-intensity exercise for 21 days in heat and humidity (HH) [34.2-35.7 degrees C; 84-86% relative humidity (RH); wet bulb globe temperature (WBGT) index approximately 32 degrees C]. Horses completed exercise tests at 50% of peak O(2) uptake until a pulmonary arterial temperature (T(pa)) of 41.5 degrees C was attained in cool dry (CD) (20-21.5 degrees C; 45-50% RH; WBGT approximately 16 degrees C), hot dry (HD 0) [32-34 degrees C room temperature (RT); 45-55% RH; WBGT approximately 25 degrees C], and HH conditions (HH 0), and during the second hour of HH on days 3, 7, 14, and 21, and in HD on the 18th day (HD 18) of heat acclimation. The ratios of required evaporative capacity to maximal evaporative capacity of the environment (E(req)/E(max)) for CD, HD, and HH were approximately 1.2, 1.6, and 2.5, respectively. Preexercise T(pa) and rectal temperature were approximately 0.5 degrees C lower (P < 0. 05) on days 7, 14, and 21 compared with day 0. With exercise in HH, there was no effect of heat acclimation on the rate of rise in T(pa) (and therefore exercise duration) nor the rate of heat storage. In contrast, exercise duration was longer, rate of rise in T(pa) was significantly slower, and rate of heat storage was decreased on HD 18 compared with HD 0. It was concluded that, during uncompensable heat stress in horses, heat acclimation provided modest heat strain advantages when E(req)/E(max) was approximately 1.6, but at higher E(req)/E(max) no advantages were observed.

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↗
PubMed2002

Vertical movement and posture of blacklegged tick (Acari: Ixodidae) nymphs as a function of temperature and relative humidity in laboratory experiments.

We measured three components of the behavioral activity of blacklegged tick (Ixodes scapularis Say) nymphs under controlled conditions of daylength, temperature, and relative humidity in the laboratory. Temperature and relative humidity were experimentally manipulated among replicated treatment groups in two experiments. Humidity treatment had a significant effect on mean questing height, which was greater at 100% RH than at any lower humidity (P < 0.01), but it had no effect on mean distance moved between observations or the mean percentage of time in questing posture. Temperature had no effect on mean questing height, but significantly affected mean distance moved (P < 0.01) and the percentage of time in questing posture (P < 0.001). Mean distance moved and percentage of time in questing posture were both greater at 25 degrees C than at higher or lower temperatures. A mechanistic understanding of the factors affecting tick behavior is likely to be useful for interpreting field data, designing field studies, and predicting risk of exposure to tick-borne pathogens.

Animals↗
PubMed2005

Hematological change in venous blood of the lower leg during prolonged sitting in a low humidity and hypobaric environment.

The present study examined the effects of low humidity and hypobaric conditions on hematological change in venous blood of the lower leg during quiet prolonged sitting. Ten healthy male students participated as the subjects after singing a consent form to participate in this study. Their diet and water intake were controlled from 19:00 on the day before the experiments. The subjects sat for 130 min in a climatic chamber. Four experimental conditions in the chamber were designed from a combination of relative humidity (20% or 60%) and air pressure (sea level or equivalent to an altitude of 2,000 m). Ambient temperature was maintained at 24 degrees C in every condition. Venous blood was sampled from the lower leg before and after exposure to the experimental conditions, and was analyzed for blood viscosity and hematological indices. Also, body weight and leg circumference were measured as indices of total water loss and edema, respectively. Regarding the results of ANOVA, significant interactions between humidity and time were observed in blood viscosity, red blood cell count and hematocrit (each p<0.05). However, there were no significant differences in these indices among the conditions. Significant increases were observed in leg circumference (p<0.01), platelet count (p<0.05) and total protein (p<0.05) after the exposure compared with those before the exposure. There were no noticeable effects of hypobaric conditions in every measurement. In conclusion, prolonged sitting seems to be a more hazardous factor for thrombogenesis low humidity and hypobaric conditions during a long-distance flight.

Adult↗
PubMed2006

Physiological responses of Bos taurus and Bos indicus cattle to prolonged, continuous heat and humidity.

Two experiments were conducted to investigate the physiological responses of Bos taurus (Angus cross, n = 6) and Bos indicus (Brahman, n = 6) cattle to prolonged heat and humidity, as can occur during live export by sea. Each experiment was carried out in climate-controlled rooms, where heifers were exposed to 15 d of sustained heat and humidity. The treatment was designed to be representative of a long-haul, live-export voyage leaving a southern Australian winter and traveling to a Middle Eastern summer. Wet bulb temperature (WBT) was used to give a combined measure of dry bulb temperature and relative humidity and was increased over several days, culminating in 5 d at 32 degrees C WBT between d 7 and 11. By d 11, the respiratory rate and core body temperature increased (P < 0.001) compared with values at lower ambient temperature on d 1 and 2 when climate-controlled rooms were not operating. Feed intake of Bos taurus was reduced (P < 0.001) by d 11, whereas that of Bos indicus did not change (P = 0.14). Despite no diurnal variation in climatic conditions, core body temperature of both Bos taurus and Bos indicus continued to show a circadian amplitude of approximately 1 degrees C throughout the hottest period. This amplitude increased during the recovery period after heat was removed (up to 1.8 degrees C for Bos indicus and 1.6 degrees C for Bos taurus). Water intake for both Bos taurus and Bos indicus increased when WBT increased (P < 0.01 on d 11). Significant acid-base and blood electrolyte imbalances occurred in both Bos taurus and Bos indicus, with changes in Bos taurus being more substantial and prolonged. The increase in respiratory rate coincided with a decrease in the partial pressures of carbon dioxide and bicarbonate in venous blood. However, during the hottest period, average daily venous blood pH remained unchanged. When the heat load was reduced after d 11, the blood pH decreased, indicating metabolic acidosis. Blood pH declined from 7.44 to 7.36 for Bos taurus (P < 0.001) and from 7.44 to 7.38 for Bos indicus (P < 0.001). Other parameters measured include heart rate; packed cell volume; plasma and urine Na, K, and Cl; urine pH; and specific gravity. Our results suggest that Bos taurus cattle experience significant physiological changes during exposure to prolonged and continuous high heat and humidity, with alterations persisting for some days after the heat-stress conditions subside. Bos indicus experience similar but less pronounced physiological changes.

Acclimatization↗
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↗
PubMed2003

[Effects of temperature, humidity, minor injury and washing on penetration of dermatophytes into human stratum corneum].

We evaluated the minimum time for penetration of Trichophyton mentagrophytes into human stratum corneum using an experimental model of tinea pedis. After fungal elements were applied on the surface of stratum corneum obtained from a healthy human heel, samples were incubated under designated conditions of temperature and humidity. The penetration of fungal elements was much faster at 35 degrees C than 27 degrees C despite the fact that the latter is an optimal temperature for fungal growth. At 35 degrees C and 100% humidity the minimum time required for penetration was one day. When we applied fungal elements on an abraded surface of stratum corneum, fungi penetrated within a half day under the same conditions. This suggests that minor injury of stratum corneum is a significant factor for infection. The development of tinea pedis does not occur frequently in daily life. We examined the effect of washing the surface of stratum corneum to which T. mentagrophytes had been applied. The samples were incubated under conditions simulating daily life: i.e. with 80% humidity for 8 hours, and 100% humidity for 16 hours. After washing, nearly all the fungal elements had been removed from the surface of stratum corneum within one day. The data suggests that to prevent tinea pedis, daily washing of soles and interdigital regions is effective.

Arthrodermataceae↗