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At least 631 records · Page 35Linked to original sources
PubMed1977

Transepidermal water loss in newborn infants. I. Relation to ambient humidity and site of measurement and estimation of total transepidermal water loss.

Insensible water loss (IWL) is an important factor in the thermoregulation and water balance of the newborn infant. A method for direct measurement of the rate of evaporation from the skin surface has been developed. The method, which is based on determination of the vapour pressure gradient close to the skin surface, allows free evaporation. From measurements performed on 19 newborns placed in incubators, a linear relation was found between the evaporation rate (ER) and the humidity of the environment at a constant ambient temperature. A 40% lower ER was recorded at a high relative humidity (60%) than at a low one (20%) in the incubator. At measurements on different sites of the body, a high ER was observed on the face and peripheral parts of the extremities, while ER at other sites was relatively low. By determining ER from different parts of the body and calculating the areas of the corresponding surfaces, the total cutaneous insensible water loss for the infant in question could be obtained. The transepidermal water loss (TEWL) for the whole body surface area was calculated to be 8.1 g/m2h. On the basis of measurements performed it was found that the total cutaneous insensible water loss can be estimated with a reasonable degree of accuracy by recording ER from only three easily accessible measurement points.

Birth Weight↗
PubMed1995

Plasma volume and ions during exercise in cool, dry; hot, dry; and hot, humid conditions.

We studied the effects of heat and relative humidity (RH) on plasma volume (PV) and ion responses to submaximal exercise and 60 min recovery in Thoroughbreds. Five horses were exercised at 50% of peak VO2 in cool, dry (CD, T = 22 degrees C, RH = 45-55%), and hot, humid (HH, T = 30-34 degrees C, RH = 80-85%) conditions until a pulmonary artery temperature of 41.5 degrees C was reached. Blood was obtained from the carotid artery. Body mass was measured at rest and after 30 min of recovery. The thermal conditions had no effect on the PV and ion responses during exercise and initial 30 min of recovery. Exercise resulted in an 8.5% decrease in PV within the first 2 min and, in the absence of changes in plasma [Na+] and [Cl-], was responsible for a 150 to 185 mmol decrease in plasma Na+ and Cl- contents. The decrease in PV was responsible for about 50% of the increase in packed cell volume (37% at rest; 51% at 2 min of exercise). Plasma [K+] and K+ content increased rapidly during the first 2 min of exercise. With cessation of exercise, plasma [K+] declined with a half time of about 2 min; recovery of PV and plasma Na+ and Cl- contents occurred with a half time of 10-15 min, with nearly complete recovery by 30 min. In the HD trial, between 30 and 60 min of recovery there were further decreases in PV and ion contents. It is concluded that with this exercise protocol, thermal stress had minimal influence on the rate and magnitude of exercise-induced changes in PV and ion contents. However, thermal stress during recovery from exercise may impede the restoration of PV and ion contents.

Animals↗
PubMed1999

Ambient temperature and relative humidity influenced packed cell volume, total plasma protein and other variables in horses during an incremental submaximal field exercise test.

Thermoregulation may limit exercise performance under hot and humid conditions. This study compared heart rate (HR), respiratory rate (RR), rectal temperature (Tr), packed cell volume (PCV) and total plasma protein concentration (TPP) during a submaximal incremental field exercise test under high vs. low ambient temperature and relative humidity. Ten horses were tested 3 times in summer (July) and 3 times in autumn (September). Heart rate was measured continuously, the other variables at rest and immediately after 4 min at 3.5, 4.5 and 7.0 m/s, separated by 3 min rest intervals, and after 5 and 10 min recovery. Data for all variables were significantly greater during exercise and recovery in the hot vs. cool conditions, respectively: after 4 min at 7.0 m/s, HR was 135+/-1 and 123+/-1/min (P<0.0001), Tr was 39.0+/-0.06 and 38.0+/-0.05 degrees C (P<0.0001), RR was 99+/-3 and 50+/-3/min (P<0.0001), PCV was 48.8+/-0.06 and 42.1+/-0.3% (P<0.0001) and TPP was 7.7+/-0.14 and 7.6+/-0.12 g/l (P = 0.026). These data reflect the thermal burden during submaximal exercise under hot conditions in the field. The greater relative PCV increase in the heat probably conferred a thermoregulatory advantage and reflected a greater circulating red cell volume increase rather than a decrease of plasma volume. This study illustrates how differences in environmental conditions can affect assessment of exercise responses and how these factors must be considered in monitoring progress during fitness and acclimatisation regimes in the field.

Animals↗
PubMed1966

Activity of the human eccrine sweat gland during exercise in a hot humid environment before and after acclimatization.

1. Six unacclimatized African mine labourers were subjected to exercise for 4(1/2) hr in a hot humid environment (90 degrees - 93 degrees F wet-bulb/dry-bulb (W.B./D.B.); approximately 90% r.h.) 2. The patterns of glandular activity and the densities of active glands on the chest and back were assessed half-hourly from plastic impressions. Acclimatization increased and prolonged glandular activity. The increment in activity of the sweat glands on the back was greater than that on the chest. 4. There was no significant increase in the maximum number of active glands on either site after acclimatization. 5. Acclimatization greatly reduced the number of inactive glands, subsequent to the maximum count, on the back, but this was not observed on the chest. 6. The increased sweat rates with acclimatization were due mainly to increased glandular activity. 7. The decline in sweat rates and activity on prolonged exposure to hot humid environment was attributed to glandular fatigue. Other factors, such as increased body temperature, hydration of the skin and fatigue of the central nervous system, suggested by other investigators as possibly causing the decline in sweat rates, did not have support in this study.

Acclimatization↗
PubMed2000

Importance of temperature and humidity in the measurement of pulmonary oxygen uptake per breath during anesthesia.

Traditionally, measurement of pulmonary O2 uptake uses mass balance of N2 to correct for differences between inspired and expired volume (V) due to temperature (T) and relative humidity (RH). Often during anesthesia, N2 balance cannot be invoked due to high inspired O2 fraction (FIO2) or nonsteady state conditions. Then, O2 uptake per breath (VO2,br) must use assumed or measured T and RH differences between inspirate and expirate. This numerical analysis study examines how errors in inspired RH and T can affect VO2,br. Equations were developed to simulate a baseline metabolic and ventilatory condition. A unit error in inspired RH of 0.5 (during constant inspired T of 22 degrees C) caused percent errors in VO2,br of 5.6% during FIO2 = 0.2% and 28.8% during FIO2 of unity. Per(-57.6 x FIO2-0.115) VO2,br was given by (change in RH) (R2 > 0.999). Errors in inspired T (during constant inspired RH of 0.5) had similar effects on percent error in VO2,br( =-8.75 x FIO2-0.093) x (change in T) (R2 = 0.999). Because inspired VO2 is larger at higher FIO2 and because VO2,br is the difference between inspired and expired VO2, VO2,br is most affected by the inspired V error at the largest FIO2 . When tissue O2 consumption decreases relative to minute ventilation, T and RH errors have a greater effect on VO2 br because the error in inspired V affects a smaller VO2,br. At lower barometric pressure, RH errors affect VO2,br more because water vapor V occupies a larger fraction of inspired V. In summary, because inspired RH and T can vary significantly during anesthesia, a fast-response humidity and T sensor, combined with flow and FO2 measurements, are needed to allow accurate determination of VO2,br x VO2,br should become an important measure of metabolism and patient wellness during anesthesia.

Anesthesia↗
PubMedDate not supplied

Variations in response to radiation of a nylon-walled ionization chamber induced by humidity changes.

The volume of nylon-walled ionization chambers varies with relative air humidity due to the hygroscopic properties of nylon. A 6% increase in exposure calibration factor of a commonly employed 0.6 cm3 nylon-walled ionization chamber was observed when the relative air humidity decreased from 98% to 11%. The increase as well as the decrease in volume shows an initial fast change during the first day followed by an exponential change with half-lives of about 1.2 days and 2.4 days, for water uptake and water loss, respectively.

Cobalt Radioisotopes↗
PubMed1994

Effect of relative humidity on fungal colonization of fiberglass insulation.

Fiberglass duct liners and fiberglass duct boards from eight buildings whose occupants complained of unacceptable or moldy odors in the air were found to be heavily colonized by fungi, particularly by Aspergillus versicolor. Unused fiberglass was found to be susceptible to fungal colonization in environmental chambers dependent upon relative humidity. No colonization was observed at relative humidities below 50%.

Construction Materials↗
PubMed2003

Boundaries for biofilm formation: humidity and temperature.

Environmental conditions which define boundaries for biofilm production could provide useful ecological information for biofilm models. A practical use of defined conditions could be applied to the high-level nuclear waste repository at Yucca Mountain. Data for temperature and humidity conditions indicate that decreases in relative humidity or increased temperature severely affect biofilm formation on three candidate canister metals.

Biofilms↗
PubMed1966

Effect of diluent and relative humidity on apparent viability of airborne Pasteurella pestis.

Airborne Pasteurella pestis (A-1122) at low humidities [20 to 50% relative humidity (RH)] exhibited exponential decay when either 1% peptone or Heart Infusion Broth (HIB) was used as the diluent in the viable assay system. At higher RH values (65 and 87%), however, the 1% peptone diluent adversely affected the viability assay. In contrast, HIB as diluent was remarkably effective in demonstrating a higher number of viable cells in aerosols held at high RH values. Similarly, with HIB as diluent, aerosols were shown to contain viable cells during 90 min of observation; with 1% peptone, viability was not detectable after 20 min in the airborne state.

Aerosols↗
PubMed1971

Effect of relative humidity on formaldehyde decontamination.

Death rate studies were conducted to determine the effect of varying the concentration, humidity, and type of surface on the sporicidal activity of formaldehyde gas. Washed and unwashed spores were similarly exposed to detect the influence of residual nutrient growth medium upon the rate of kill. The results indicated that the sporicidal activity of formaldehyde gas varies directly with its concentration. Relative humidities (RH) over 50% proved essential for sterility. Spores on a porous surface (cotton cloth) were more readily killed at lower RH than those on a nonporous surface (glass). The reverse occurred at very high RH. At 75% RH, the unwashed spores on glass were killed faster than the washed spores.

Air Microbiology↗
PubMed1975

Effect of relative humidity on the survival of airborne unicellular algae.

A method is described which is suitable for assessing the effects of relative humidity (RH) on the viability of two unicellular algae in experimental aerosols. Viable cells of Nannochloris atomus collected from the airborne state were detected by plating onto agar surfaces of an appropriate growth medium, whereas viable airborne cells of Synechococcus sp., because of unreliable growth on solid media, were determined by a liquid assay system. The assays were performed at intervals during short-term and prolonged storage of algal aerosols in chambers preconditioned to a selected RH and temperature. Both species showed the greatest loss in viability during the first minute after atomization, and the extent of this inactivation, as a function of RH, reflected the subsequent long-term survival. The airborne eukaryotic alga was unable to survive at an RH below 91%, whereas the airborne prokaryotic alga was comparatively stable over a wide humidity range. Initial inactivation was least and long-term survival best, for both species, at 94% RH.

Aerosols↗
PubMed1961

Relative humidity and the killing of bacteria. The survival of damp Serratia marcescens in air.

The viability of washed moist cells of Serratia marcescens after storage has been measured in relation to variations in the prior treatment of the cells and in conditions of storage. The factors considered were: (i) water content during storage; (ii) method of arriving at water content (partial drying in vacuum or freeze-drying and addition of water); (iii) presence or absence of air during storage. Increasingly rapid decay occurs as the water content at which the cells are stored is diminished from above 90% to 20 or 30% ("critical" water content). It occurs in presence or absence of air and it occurs whether the final water content is approached by removal of water from wet cells or by addition of water to freeze-dried cells. The rate of decay during storage at 20 to 30% water is somewhat diminished by the presence of air ("protective" effect of air). As the water content is further reduced to less than 10%, the stability of cells stored in a vacuum approaches that of wet cells. In presence of air the reverse is true: the stability decreases until at less than 1% water, the decay rate is about as great as at the "critical" water content ("toxic" effect of air). Particularly rapid decay of S. marcescens at the "critical" water content has escaped attention in aerosol studies because accurate control of relative humidity (RH) in this region, RH 94 to 99%, is virtually impossible in such studies. On the other hand, values of decay rates referred to measured water contents are quite unreliable in the 20 to 80% RH zone because the corresponding variation of water content is too small to measure reliably. Thus data of the kind reported in this paper cannot be directly compared to the published results of studies of air-borne bacteria, although they are relevant to the practical question of air-borne infection in humid atmospheres.

Aerosols↗
PubMed1962

Survival of Serratia marcescens after freeze-drying or aerosolization at unfavorable humidity. I. Effects of sugars.

Zimmerman, Leonard (U.S. Army Biological Laboratories, Fort Detrick, Frederick, Md.). Survival of Serratia marcescens after freeze-drying or aerosolization at unfavorable humidity. I. Effects of sugars. J. Bacteriol. 84:1297-1302. 1962.-Suspensions of Serratia marcescens were subjected to freeze-drying or to aerosolization at unfavorable humidity levels. The survival of the cells during one or the other of these treatments was markedly improved in the presence of common sugars, but no one sugar stabilized the cells against both stresses. The protective effects of the sugars were correlated with their penetrability into cells; minimally penetrable sugars stabilized cells against aerosolization, and freely penetrable sugars stabilized cells during freeze-drying. These results were attributed to the modifications of intracellular water content induced by the presence of the sugars in the cell suspensions.

Carbohydrates↗
PubMed1977

Evaporation of sweat from sedentary man in humid environments.

UNLABELLED: Physiological and sensory responses were observed in four male subjects while they were seated on a balance. The chamber temperature always equaled mean skin (Tsk)(34-36 degrees C), thus eliminating all sensible heat transfer. Ambient water vapor pressure (Pa) was increased in steps from 10 to 40 Torr. Tests at air velocities from 0.1 to 2.4 m/s were conducted with subjects nude and clothed. Esophageal temperature (Tes) and Tsk, heat rate (HR) and weight loss (M) were measured throughout the 2.5-h tests. After each 25-min humidity step subjects recorded their warm discomfort, sensation of sweating, and thermal sensation. RESULTS: Tsk, HR, and M were unaffected by humidity until critical Pa (P a crit) was reached above which M decreased and Tsk and HR increased rapidly. P a crit decreased with clothing and decreasing velocity. Tes remainded relatively constant throughout the tests. Sweating, discomfort and temperature sensations increased gradually with increasing Pa. Above P a crit sweating and discomfort sensations accelerated markedly. Mass transfer coefficients and clothing vapor conductance factors were evaluated. Skin wettedness at Pa crit decreased from 74% at 0.1 m/s to 35% at 2.4 m/s.

Adolescent↗
PubMed1979

Effects of temperature, relative humidity, and mode of breathing on canine airway secretions.

Airway secretions were collected from the upper trachea of eight healthy nosebreathing mongrel dogs under general anesthesia, and the electrolytes and osmolality of these secretions were determined. Compared to plasma, secretions contained 15% higher Na+ and 33% higher Cl-, were 18% higher in osmolality, but had a lower Na+/Cl- throughout the 6-h experiments. When six nose-breathing dogs were exposed to air at 28.5 degrees C and 95% relative humidity, secretion osmolality became lower, but Na+/Cl- remained unchanged. In four other dogs, secretions approached the osmolality of plasma when inspired air was at 36.4 degrees C and 100% relative humidity. These secretions contained 22% higher Cl- and a lower Na+/Cl- than plasma. The differences between airway secretions and interstitial fluid suggest that secretions are formed by active Cl- transport. In another four dogs, secretion osmolality was higher with mouth breathing than breathing through the nose. Inasmuch as humidified and warmed air lowered and mouth breathing raised the osmolality of airway secretions, we postulate that the hyperosmolality of secretions results from water loss from the airway surface during conditioning of inspired air.

Animals↗
PubMedDate not supplied

Ocular Ferning test - effect of temperature and humidity on tear Ferning patterns.

BACKGROUND: The ocular ferning test is used as a diagnostic aid to evaluate patients with dry-eye disease. The ferning phenomenon is a dendritic growth form of dried tear fluid. The influence of temperature and relative humidity (rH) on the morphology of tear ferning patterns was investigated. METHODS: Two microliters of tear fluid of 5 volunteers with normal tear function were dropped onto a microscope slide with a pipette and were dried in a climatic chamber at four different temperatures (20, 22, 24 and 26 degrees C) and at four different grades of rH (30, 40, 50 and 60%) at each temperature. The dried droplet was divided according to distinct morphological features into a center, transition zone and margin. The center of the dried droplet was classified into four types according to the system of Rolando. RESULTS: In the temperature range between 20 and 26 degrees C, rH has a strong influence on the ferning patterns. At these temperatures, increasing rH resulted in a deterioration of type I ferning obtained at 30% rH to type II or type III at 60% rH in all subjects. Otherwise, at rH of 30, 40 and 50%, no definite influence of temperature between 20 and 26 degrees C was observed. At an rH of 60%, the ferning patterns changed with increasing temperature from 20 to 26 degrees C from type II to type III. CONCLUSION: High humidity can modify and deteriorate the ferning patterns of tear fluid from subjects with normal tear function. To obtain reproducible results using the ocular ferning test, stable conditions are necessary. An rH not higher than 50% at a temperature range between 20 and 26 degrees C produced ferning patterns without interstitial spaces which could be related to the best quality according to the system of Rolando.

Adult↗