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Leaves of Piper hispidum, a shrub native to the lowland tropics of Mexico, have a strong stomatal response to humidity that results in similar rates of water loss under a wide range of leaf-to-air water-vapor concentration gradients. Stomatal conductance of these leaves is insensitive to CO(2) concentration and increases in response to high humidity even in the dark.
In order to investigate the influence of low relative humidity, we measured saccharin clearance time (SCT), frequency of blinking, heart rate (HR), blood pressure, hydration state of skin, transepidermal water loss (TEWL), recovery sebum level and skin temperature as physiological responses. We asked subjects to judge thermal, dryness and comfort sensations as subjective responses using a rating scale. Sixteen non-smoking healthy male students were selected. The pre-room conditions were maintained at an air temperature (Ta) of 25 degrees C and a relative humidity (RH) of 50%. The test room conditions were adjusted to provide a Ta of 25 degrees C and RH levels of 10%, 30% and 50%.RH had no effect on the activity of the sebaceous gland and on cardiovascular reactions like blood pressure and HR. However, it was obvious that low RH affects SCT, the dryness of the ocular mucosa and the stratum corneum of the skin and causes a decrease in mean skin temperature. Under 30% RH, the eyes and skin become dry, and under 10% RH the nasal mucous membrane becomes dry as well as the eyes and skin, and the mean skin temperature decreases. These findings suggested that to avoid dryness of the eyes and skin, it is necessary to maintain an RH greater than 30%, and to avoid dryness of the nasal mucous membrane, it is necessary to maintain an RH greater than 10%. Subjects felt cold immediately after a change in RH while they had only a slight perception of dryness at the change of humidity.
Three trials were conducted to investigate the effect of RH (35, 60, and 85%) on thermoregulation of 1-wk-old broiler chickens at different temperatures (35, 30, and 25 degrees C). The response to humidity in rectal temperature and plumage temperature at the back and breast within 24 h after exposure were recorded at 5 time points (1,4,8,16, and 24 h). Humidity affected the thermoregulation of 1-wk-old broiler chickens by redistributing heat within the body at high, low, and thermoneutral temperatures. The redistribution of heat resulted in decreased rectal temperature and increased peripheral temperature, which were, respectively, beneficial and unfavorable at high and low temperatures. These results suggested that feedback effects of surface temperature on core temperature also exist in poultry, as already observed in mammals, and could be induced not only by changed ambient temperature but also by the changes in humidity at high temperature. The disturbance of thermal equilibrium could not be established solely by changes in RT, but rather core and surface temperatures had to be considered. The daily rhythms in rectal and surface temperatures were affected by humidity.
Using an automated scanning microscope, we report the surprising result that individual dormant spores of Bacillus thuringiensis grow and shrink in response to increasing and decreasing relative humidity. We simultaneously monitored the size of inorganic calibration particles. We found that the spores consistently swell in response to increased relative humidity, and shrink to near their original size on reexposure to dry air. Although the dispersion of swelling amplitudes within an ensemble of spores is wide (approximately 30% of the average amplitude), amplitudes for individual spores are highly correlated between different swelling episodes, suggesting that individual spores respond consistently to changes in humidity. We find evidence for two distinct time scales for swelling: one with a time scale of no more than approximately 50 s, and another with a time scale of approximately 8 min. We speculate that these two mechanisms may be due to rapid diffusion of water into the spore coat + cortex, followed by slower diffusion of water into the spore core, respectively. Humidity-dependent swelling may account for the greater kill effectiveness of spores by gas-phase chlorine dioxide, formaldehyde, and ethylene oxide at very high relative humidity.
To determine the effects of exercise, high heat and humidity and acclimation on plasma adrenaline, noradrenaline, beta-endorphin and cortisol concentrations, five horses performed a competition exercise test (CET; designed to simulate the speed and endurance test of a three-day event) in cool dry (CD) (20 degrees C/40% RH) and hot humid (30 degrees C/80% RH) conditions before (pre-acclimation) and after (post-acclimation) a 15 day period of humid heat acclimation. Plasma adrenaline and noradrenaline concentrations pre-acclimation were significantly increased compared with exercise in the CD trial at the end of Phases C (P<0.05) and D (P<0.05 and P<0.01, respectively) and at 2 min recovery (P<0.01), with adrenaline concentrations still elevated after 5 min of recovery (P<0.001). Plasma beta-endorphin concentrations were increased at the end of Phases C (P<0.05) and X (P<0.01) and at 5 and 30 min recovery (P<0.05) in the pre-acclimation session. Plasma cortisol concentrations were elevated after the initial warm up period pre-acclimation (P<0.01) and at the end of Phase C (P<0.05), compared with the CD trial. A 15 day period of acclimation significantly increased plasma adrenaline concentrations at 2 min recovery (P<0.001) and plasma cortisol concentration at the end of Phase B (P<0.01) compared with pre-acclimation. Acclimation did not significantly influence noradrenaline or beta-endorphin responses to exercise, although there was a trend for plasma beta-endorphin to be lower at the end of Phases C and X and after 30 min recovery compared with pre-acclimation. Plasma adrenaline, noradrenaline, beta-endorphin and cortisol concentrations were increased by exercise in cool dry conditions and were further increased by the same exercise in hot humid conditions. Exercise responses post-acclimation suggest that adrenaline and noradrenaline may play a role in the adaptation of horses to thermal stress and that changes in plasma beta-endorphin concentrations could be used as a sensitive indicator of thermal tolerance before and after acclimation. The use of plasma cortisol as a specific indicator of heat stress and thermal tolerance before or after acclimation in exercising horses appears limited.
Water-use efficiency (WUE) is critical in determining the adaptation and productivity of plants in water-limited areas, either under the present climate or future global change. Data on WUE are often highly variable and a unifying and quantitative approach is needed to analyse and predict WUE for different environments. Hsiao has already proposed a set of paradigm equations based on leaf gas exchange for this purpose, calculating WUE (ratio of assimilation to transpiration) relative to the WUE for a chosen reference situation. This study tests the validity and applicability of these equations to cotton and sweet corn stands with full canopies in the open field. Measured were evapotranspiration and downward flux of atmospheric CO2 into the canopy, soil CO2 efflux, canopy temperature, and CO2 and vapour pressure of the air surrounding the canopy. With the measured mean WUE and conditions at midday serving as the reference, WUE for other times was predicted from the air CO2 and water vapour data, intercellular water vapour pressure calculated from canopy temperature, and an assumed ratio of Ci/Ca based on leaf gas-exchange data. Provided that the stomatal response to humidity as it affected the Ci/Ca ratio was accounted for, the equations predicted the moment-by-moment changes in canopy WUE of cotton over daily cycles reasonably well, and also the variation in midday WUE from day-to-day over a 47 d period. The prediction for sweet corn was fairly good for most parts of the day except the early morning. Measurement uncertainties and possible causes of the differences between predicted and measured WUE are discussed. Overall, the results indicate that the equations may be suitable to simulate changes in WUE without upscaling, and also demonstrate clearly the importance of stomatal response to humidity in determining stand WUE in the field.
We determined the effect of breathing cold dry air (-39 degrees C, 0.1% relative humidity, RH) and warm humid air (43 degrees C, 100% RH) on airway mucosal blood flow (Qaw) in normal human subjects (n = 8, age 25-53 years) at rest. Qaw was measured with a dimethylether uptake technique which reflects blood flow in the mucosa of large airways corresponding to a 50 ml anatomical dead-space segment extending distally from the trachea. Mean Qaw was 10.1 +/- 1.9 ml min-1 (mean +/- S.D.) during room air breathing (25 degrees C, 70% RH) and decreased to 4.7 +/- 2.1 ml min-1 during cold dry air breathing (p < 0.05). Within 20 min of resuming room air breathing, mean Qaw had returned to baseline. Breathing warm humid air had no significant effect on mean Qaw (8.2 +/- 1.4 ml min-1). These results indicate that quiet breathing of frigid air causes vasoconstriction in central airways.
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Twenty-five dogs were anesthetized, paralyzed, and artificially ventilated. Their cranial tracheal arteries were perfused bilaterally with blood at constant flow, and the perfusion pressures (Patr) were measured. Tracheal smooth muscle function was assessed by recording changes in external diameter (delta Dtr). The perfused segment of the trachea was exposed to air at a constant unidirectional airflow of 25 l/min. Group 1 (n = 6) was exposed to cold dry air, ambient room air, and hot dry and hot humid air, each for 10 min with exposures starting from zero flow. The tracheal vascular responses to all four conditions were small vasodilations (delta Patr from -2 to -6%) followed by recovery or small vasoconstrictions. In group 2 (n = 19), exposures to cold dry and hot humid air were preceded and followed by body-temperature fully humidified air. Cold dry air caused a sustained vasodilation (delta Patr -9.0 +/- 1.1%), and hot humid air usually caused a biphasic response: a vasoconstriction (delta Patr 4.4 +/- 1.0%) followed by a vasodilation (delta Patr -5.7 +/- 1.9%). The warm humid air after cold dry air or hot humid air caused a further vasodilation, which lasted a short time after cold dry air (delta Patr -3.7 +/- 0.4%) but greater than 10 min after hot humid air (delta Patr -13.8 +/- 1.4%). In both groups, all exposures that cooled the trachea (cold dry air, ambient room air, and hot dry air) caused smooth muscle contraction, and hot humid air that warmed the trachea caused relaxation.
An amperometric sensor consisting of a film of silica gel over an interdigitated microsensor electrode provided a humidity-independent response to CO over the range of 9%-76% humidity. The residual solvent contents were in the 20%-50% range, depending on the age of the gels and the humidity. Variations in this range did not change the sensitivity. Gaseous CO was quantified in the absence of a contacting liquid phase using either linear scan voltammetry (LSV) or flow injection amperometry (FIamp) at constant applied potential. With LSV after a 2-min exposure to the sample, sensors with gels aged for 28-40 days yielded sensitivities of 0.38, 0.41, and 0.38 nA/ppmv for measurements at 9%, 33%, and 76% humidity, respectively; the corresponding correlation coefficients were 0.992, 0.995, and 0.999. The detection limit with FIamp was 5 ppmv.
Studies have been conducted on 6 young healthy Indians in simulated comfortable, hot humid and very hot humid conditions to evaluate the physiological reactions during work. Physiological responses like exercise oxygen consumption (VO2), pulmonary ventilation (VE) and heart rate (HR) were noted during sub-maximal fixed work rates of 400, 500 and 600 kgM/min. In addition, duration of continuous work at these three rates of work, in the three simulated environments was also noted. Physiological responses i.e. VO2, VE and HR were noted every 15 minutes of work. Besides these responses, rectal temperature (Tr), mean skin temperature (Ts) and mean sweat rate were also noted during the continuous work. Results indicated a significantly higher oxygen cost (VO2) during 400 kgM/min of work in hot and very hot humid environments whereas, in the higher rates of work, the changes were not significant. The cardiac frequency showed a significantly higher rise during different grades of activities in hot and very hot environments except in the highest work rate in hotter environments, possibly due to attainment of maximum heart rate. The duration of continuous physical efforts in various grades of activities decreased significantly (P less than 0.001) in hot humid environments than in the comfortable temperature. During the progression of the work, the mean skin temperature decreased in comfortable temperature but increased in hot humid environments. The mean rectal temperature, increased during work in hot humid environment, and the rate of rise was much faster in higher work rates attaining the target temperature much earlier. The rate of sweating increased significantly as the heat load of the body increased. In hot humid environments, work performance decreased due to early attainment of maximum heart rate, reduction in VO2 max, disproportionate rise in rectal temperature, narrowing of the difference between the core and the skin temperature and attainment of maximum sweating rate.
In this study we characterized the sensitive to low humidity 1 (slh1) mutant of Arabidopsis ecotype No-0 which exhibits normal growth on agar plate medium but which on transfer to soil shows growth arrest and development of necrotic lesions. cDNA microarray hybridization and RNA gel blot analysis revealed that genes associated with activation of disease resistance were upregulated in the slh1 mutants in response to conditions of low humidity. Furthermore, the slh1 mutants accumulate callose, autofluorescent compounds and salicylic acid (SA). We demonstrate that SA is required for the slh1 phenotype but not PAD4 or NPR1. SLH1 was isolated by map-based cloning and it encodes a resistance (R)-like protein consisting of a domain with Toll and interleukin-1 receptor homology (TIR), a nucleotide-binding domain (NB), leucine-rich repeats (LRR) and a carboxy-terminal WRKY domain. SLH1 is identical to the R gene RRS1-R of the Arabidopsis ecotype Nd-1, a gene which confers resistance to the bacterial pathogen Ralstonia solanacearum GMI1000 and also functions as an R gene to this pathogen in No-0. We identified a 3 bp insertion mutation in slh1 that results in the addition of a single amino acid in the WRKY domain; thereby impairing its DNA-binding activity. Our data suggest that SLH1 disease resistance signaling may be negatively regulated by its WRKY domain in the R protein and that the constitutive defense activation conferred by the slh1 mutation is inhibited by conditions of high humidity.
Ozone injury to Bel W3 tobacco and pinto bean plants increases with increasing humidity. The degree of plant injury sustained correlates well with porometer measurements; this indicates that the size of stomatal apertures increases with increasing humidity. Humidity may therefore influence plant response to all pollutants and may account in part for the greater sensitivity of plants to ozone-type injury in the eastern United States compared with the same species of plants grown in the Southwest. with those grown in the Southwest.
Ten subjects with asymptomatic seasonal allergy, outside of their allergy season, underwent allergen provocation following 1 hour of exposure to air at either 20 degrees C and 30% relative humidity (RH) or air at 37 degrees C and 90% RH. The ipsilateral changes following antigen challenge were compared under the two conditions. Conditioning of the nose to 37 degrees C, 90% RH reduced total histamine release (7.9 +/- 1.8 ng vs 4.2 +/- 1.3 ng; p < or = 0.05), sneezes (6 +/- 2 vs 3 +/- 1; p < or = 0.05), pruritus (score of 17.4 +/- 6.0 vs score of 2.0 +/- 1.8 out of a total score of 100, p < or = 0.01), nasal airway resistance (1.4 +/- 0.8 kPa/L/sec vs 0.2 +/- 0.1 kPa/L/sec; p < or = 0.05), human serum albumin levels (389.6 +/- 53.4 micrograms vs 242.2 +/- 37.9 micrograms; p < or = 0.05), and congestion (score of 23.8 +/- 4.8 vs score of 10.6 +/- 5.4 out of a total score of 100, p < or = 0.01). It had no effect on the volume of secretions (p = 0.8), lactoferrin levels (p = 0.3), or rhinorrhea (p = 1.0). Thus air at 37 degrees C and 90% RH partially reduces the early response to antigen. Its effects are greatest on histamine release, the vascular response, and neural responses, with no effect on the glandular response. The mechanisms underlying these effects are unknown.
Six different brands of passive card monitors representing three different types of card monitor were evaluated for their effectiveness in testing for hydrogen sulfide in workplace atmospheres. The cards were evaluated both in the laboratory and in a kraft pulp mill according to a protocol that closely follows that recommended by the National Institute for Occupational Safety and Health and other researchers for passive samplers. The performances of the Envirometrics Air-Chem Technologies and the Gilian ChemAir quantitative cards, the Gilian ChromAir and VICI Metronics Colortec semiquantitative cards, and the American Gas & Chemical Co. Leak-Tec and Gilian SafeAir indicator cards were evaluated. The detection limits of the cards were determined, and the cards were exposed to a range of hydrogen sulfide concentrations (1, 5, 10, 20 ppm), face velocities (0, 50 ft/min), and temperature/humidity combinations (95 degrees F/90% humidity, 77 degrees F/50% humidity, 40 degrees F/20% humidity). The cards' responses to short-term and variable concentration exposures as well as to the potential interferents methyl mercaptan, dimethyl sulfide, dimethyl disulfide, sulfur dioxide, and carbon monoxide were assessed. Each of the cards tested demonstrated a usefulness for the detection and/or quantification of hydrogen sulfide at concentrations and under conditions relevant to kraft pulp mill workplace atmospheres. Which card is best depends on the application, sampling conditions, and level of confidence necessary in the results. The Gilian ChemAir quantitative card performed well under most conditions with acceptable accuracy (13% lab, 26% field), and no response to potential interferents or to changes in face velocity, temperature, and humidity. The Envirometrics ACT quantitative cards did not perform as well, with an accuracy level of only 46% in the lab. They also seemed to be more affected by changes in face velocity, temperature, and humidity. Both semiquantitative cards (Gillian ChromAir, VICI Metronics Colortec) provided reasonable approximations of hydrogen sulfide levels in the range of the hydrogen sulfide occupational exposure levels although the VICI card had a much lower detection limit. Neither performed well at high temperature and humidity. The response of VICI card was more affected by changes in face velocity, whereas the Gilian ChromAir showed some response to reduced sulfur gas interferents. Both indicator cards (Leak-Tec, Gilian SafeAir) performed well, responding to 20 ppm hydrogen sulfide within 1 min and to 5 ppm within 5 min. Neither was significantly affected by extremes of temperature and humidity.
We report that long-range proton diffusion (>0.3 mm) is generated in monolithic ultraporous manganese oxide nanoarchitectures upon exposure to gas-phase water. The sol-gel-derived ambigel nanoarchitectures, with bicontinuous networks of covalently bonded nanoscale solid and through-connected mesopores, exhibit conductometric sensitivity to humidity as established by impedance spectroscopy. The spectra contain a Warburg feature from which the concentration and diffusion length of the protonic charge carriers are determined. Water adsorbs conformally onto the architecture's continuous solid network in equilibrium with atmospheric humidity to create a continuous water sheath that acts as a 3-D proton wire. As a result, monolithic manganese oxide ambigels exhibit an equilibrium conductometric response to humidity that is 14 times greater than that of previous reports for electrolytic manganese oxide. A packed bed of 1-10-microm ambigel particulates in physical contact with one another, each with the same nanoscale morphology as the monolithic nanoarchitecture, also support long-range proton diffusion; however, the sensitivity to humidity is four times lower than the monolithic form due to restricted proton transport between adjacent particulates. Films composed of 0.3-12-microm ambigel particulates supported on interdigitated array electrodes with 20-microm electrode spacing express finite-diffusion behavior due to the short distance between the contact electrodes and have a conductometric sensitivity to humidity comparable to electrolytic MnO2 and 17 times lower than the monolithic ambigel. These results suggest that controlling the nature of the porous and solid phases in a nanoarchitecture provides a mechanism to limit interference from condensed water in conductometric gas-phase sensors. In addition, continuous monolithic architectures should improve electrochemical performance in devices where efficient long-range transport of protons or other ions is critical.
BACKGROUND: We have previously reported that preconditioning allergic subjects with hot, humid air (HHA) (temperature, 37 degrees C; relative humidity >95%) in an environmental chamber resulted in partial inhibition of the early response to nasal allergen challenge. OBJECTIVE: To investigate whether this inhibitory effect could be achieved by inhalation of HHA via a face mask. DESIGN: Randomized, 4-way crossover study. SUBJECTS: Eighteen subjects with seasonal allergic rhinitis participated in the study outside of their allergy season. INTERVENTIONS: Subjects underwent preconditioning with room air (RA) (temperature, 25 degrees C; relative humidity <20%) or HHA either in a chamber or delivered via a face mask for 1 hour prior to and during nasal challenge with diluent for the allergen extract followed by 2 increasing doses of allergen. RESULTS: Net changes from diluent challenge for all parameters were compared between HHA and RA in each delivery method. Hot, humid air delivered by mask significantly inhibited the mean+/-SEM number of allergen-induced sneezes (HHA, 2.7+/-0.6; RA, 6.6+/-2.1; P=.03), congestion score (HHA, 2.3+/-0.5; RA, 3.4+/-0.5; P=.01), and secretion weights (HHA, 26.9+/-4.4 mg; RA, 38.6+/-5.0 mg; P=.048). However, HHA inhaled in a chamber significantly inhibited only the mean+/-SEM allergen-induced congestion (HHA, 1.2+/-0.4; RA, 3.6+/-0.6; P=.002) and pruritus (HHA, 0.7+/-0.3; RA, 2.3+/-0.5; P=.002) scores. CONCLUSIONS: Preconditioning the nasal mucosa with HHA partially decreases the early response to nasal challenge with antigen irrespective of the administration technique. The secretory response, however, is only inhibited by localized delivery of HHA to the nose. The inhibitory effects of HHA are therefore probably related to local changes in the nasal mucosa and are not dependent on total body exposure to HHA.