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At least 181 records · Page 10Linked to original sources
PubMed1987

Circulatory and thermal responses of men with different training status to prolonged physical work in dry and humid heat.

Eight physically trained and eight untrained, unacclimated men walked on a treadmill at 30% of their maximum oxygen consumption up to 3.5 h in a thermoneutral [20 degrees C/40% relative humidity (RH)], a warm humid (30 degrees C/80% RH), and a hot dry (40 degrees C/20% RH) environment while wearing industrial work clothing. Their oxygen consumption, rectal and skin temperatures, sweating, cardiac output, heart rate, stroke volume, and peripheral blood pressure were measured during the tests. Thirteen of the 32 heat stress tests were prematurely stopped due to high rectal temperature, high heart rate, subjective fatigue, or heat syncope. The physiological strain, as indicated by the rectal temperature and heart rate, was not significantly different between the warm humid and hot dry environments (wet bulb globe temperature approximately 28 degrees C). The rectal temperature and heart rate responses of the physically trained and untrained subjects did not differ in any of the environments. In the heat, the heart rate was significantly higher than in the thermoneutral environment, but because of the markedly reduced stroke volume the average cardiac output was not different between the three environments. The impaired work performance in the heat seemed mainly to be related to the circulatory instability accompanying the increased cutaneous circulation.

Adult↗
PubMed2005

[Female responsibilities: midwives, nurses and mothers in the works of some antique and Renaissance physicians].

In his De morborum causis Galen presents the very moment of childbirth, in order to emphasise that the midwife's act of reception is instrumental in preventing malformations of the infant's "humid" limbs; nurses are also responsible for future malformations. The role of the midwife as the physician's assistant with female patients is stressed by Hippocrates and Soranos. The French Renaissance physicians Simon de Vallambert, Jacques and Charles Guillemeau refer to Galen in order to criticise the incompetence of midwives and nurses, as opposed to biological mothers, who have to breast-feed their babies because nurses lack moral integrity. Galen's commentator François Valleriole explains that nurses swaddle girls differently from boys because they aim at artificial (immoral) beauty. Leonhart Fuchs underlines that improper swaddling causes girls to lose their femininity. Thus, medical commentary changes into moralising remarks in order to maintain the moral and social status quo concerning women.

Europe↗
PubMed1993

Physiological strains in hot-humid conditions while wearing disposable protective clothing commonly used by the asbestos removal industry.

The purpose of this study is to investigate workers' responses to work in hot-humid conditions while wearing protective clothing commonly used by the asbestos removal industry, and to evaluate the effects of resting between work bouts in a cool environment on the physiological strain. Seven male students wearing impermeable protective clothing and air masks were exposed to the following conditions for 100 min on separate days: (1) hot conditions (35 degrees C/85%RH), (2) cool conditions (20 degrees C/85%RH), and (3) hot/cool conditions (working in hot conditions and resting in cool conditions). After 12 min rest, the subjects worked on an ergometer (70 Watts) for 18 min. This experimental schedule was repeated three times under each environmental condition. Rectal temperature (Tre), heart rate (HR), sweat rate (SR) and discomfort sensation were recorded. Two of the subjects were not able to complete the experiment in hot conditions. The increases in Tre and HR with time were not found in cool conditions. Although Tre increased in hot/cool conditions, it was almost half of that in hot conditions. Since HR did not return to the pre-work level during recovery in hot conditions, HR during work was accompanied by increases in HR at pre-work. HR during work in hot/cool conditions was higher than that in cool conditions, HR at pre-work, however, was almost the same as that in cool conditions because of rapid recovery. The means of SR in hot and hot/cool conditions were five and four times greater than that in cool conditions, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed2004

Adaptation and evaluation of a personal electronic nose for selective multivapor analysis.

The evaluation of a commercial, belt-mountable "electronic nose" modified for the rapid recognition and quantification of individual solvent vapors and simple vapor mixtures at low ppm concentrations is described. Marketed under the name VaporLab this direct-reading instrument was designed for qualitative determinations of the presence or absence of selected individual vapors and was adapted in this study for quantitative determinations of vapors and vapor-mixture components. Vapor samples are concentrated on a small adsorbent bed and then thermally desorbed for analysis by an array of four polymer-coated surface acoustic wave sensors. Tests were performed with 13 organic solvent vapors individually and in selected binary, ternary, and quaternary mixtures at concentrations ranging from 0.1 to 12 times the respective American Conference of Governmental Industrial Hygienists' (ACGIH) threshold limit value (TLV). Pattern recognition analyses yielded a library of response patterns to which subsequent actual and virtual (i.e., Monte-Carlo simulated) samples were compared to assess performance. Limits of detection >0.025 x TLV are achieved (based on the most sensitive sensors) for 0.25 L of preconcentrated air samples collected over a 2-min period. Individual vapors from different functional group classes can be recognized, quantified, and discriminated from other vapors with little error, and discrimination of the components of binary mixtures is possible where the component vapor response patterns are sufficiently different. Within-class individual vapor and binary-mixture discriminations are more difficult and most ternary and higher-order mixtures could not be analyzed with acceptable accuracy. Changes in ambient humidity have no effect on responses and changes in temperature lead to well-behaved and compensable changes in responses. Tests of fluctuating concentrations demonstrate the capability for accurately tracking short-term variations in exposure. Overall, results suggest that this instrument could serve effectively as a personal exposure monitor in previously characterized occupational environments with proper revisions in design.

Air Pollution, Indoor↗
PubMed2006

Heart rate, thermoregulatory and humoral responses during a 9-day cycle race in a hot and humid climate.

Seven acclimated elite road cyclists were recruited from among the participants in the Tour de Guadeloupe, a 9-day cycle race (D1-D9) held in hot/humid climate (approximately 31 degrees C dry temperature and 76 % relative humidity). Each day of the competition, heart rate (HR) was recorded every 15 s, tympanic temperature (Ttym) was recorded before exercise and immediately at the end of each stage, and body mass loss (BML) was measured by changes in nude body mass at rest and after each stage. Blood lactate concentration [La] was measured at rest and 5 min after each stage. Venous blood samples were collected before the competition and on the 4 th and 8 th days (D4, D8) for hematological and serum determinations and biochemical analyses. No significant differences were found in cardiac, thermoregulatory, or [La] parameters at rest over the 9 days. The subjects spent 31 +/- 6 % of their time below the lactate threshold (LT), 52 +/- 8 % between LT and the onset of blood lactate accumulation (OBLA), and 18 +/- 6 % above OBLA. The increase in Ttym at D3 (0.48 +/- 0.3 degrees C) was significantly lower (p < 0.05) than at D1, D4, D5, and D6. No difference was found for BML between the different stages. Significant increases (p < 0.05) were observed in monocytes at D8 vs. D4 and pre-race values (D0) and in serum Cl-concentration at D4 vs. D0 and D8 (p < 0.05). A significant reduction was observed in mean corpuscular hemoglobin concentration (MCHC) at D8 and D4 vs. D0 (p < 0.01). No difference was found in other blood parameters at D0, D4, or D8. Taken together, these results suggest that a consecutive 9-day cycle competition in hot/humid climate did not alter homeostasis at rest in acclimated well-trained cyclists. No major effect of repeated cycling stages on thermoregulatory and blood parameters was observed during the Tour de Guadeloupe. Further research is needed to compare the cardiac adaptations of natives to tropical climate and un-acclimated subjects during long-duration exercise.

Adult↗
PubMed2003

Enhancement of transpiration by ethylene is responsible for absence of internodal elongation in floating rice at low humidity.

Internodal elongation in floating rice (Oryza sativa) is known to be enhanced by treatment with ethylene or gibberellic acid (GA3) at high relative humidity (RH). However, ethylene-induced internodal elongation is inhibited at low RH, while GA3-induced internodal elongation is hardly affected by humidity. We examined the effects of ethylene and GA3 on the rate of transpiration in stem segments incubated at 30% or 100% RH. Ethylene promoted the transpiration of stem segments at 30% RH, but not at 100% RH, while GA3 had little effect on transpiration at either 30% or 100% RH. We propose that the absence of ethylene-induced internodal elongation at low RH is due, at least in part, to ethylene-induced transpiration.

Abscisic Acid↗
PubMed2006

Dynamics of spatial heterogeneity of stomatal closure in Tradescantia virginiana altered by growth at high relative air humidity.

The spatial heterogeneity of stomatal closure in response to rapid desiccation of excised well-watered Tradescantia virginiana leaves grown at moderate (55%) or high (90%) relative air humidity (RH) was studied using a chlorophyll fluorescence imaging system under non-photorespiratory conditions. Following rapid desiccation, excised leaves grown at high RH had both a greater heterogeneity and a higher average value of PSII efficiency (Phi(PSII)) compared with leaves grown at moderate RH. Larger decreases in relative water content resulted in smaller decreases in water potential and Phi(PSII) of high RH-grown leaves compared with moderate RH-grown leaves. Moreover, the Phi(PSII) of excised high RH-grown leaves decreased less with decreasing water potential, implying that the stomata of high RH-grown leaves are less sensitive to decreases in leaf water potential compared with moderate RH-grown leaves. After desiccation, some non-closing stomata were distributed around the main vein in high RH-grown leaves. Direct measurements of stomatal aperture showed 77% stomatal closure in the margins after 2 h desiccation compared with 40% closure of stomata in the main-vein areas in high RH-grown leaves. Faster closure of stomata in leaf margins compared with main-vein areas of leaves grown at high RH was related to substantially lower relative water content in these areas of the leaves.

Desiccation↗
PubMed1966

Stimulation of the salt receptor of the blowfly. II. Temperature.

The response of the salt receptor of the blowfly increased with increasing ambient temperature. At constant ambient temperature, the response increased as the relative humidity was raised. At low relative humidity, the temperature of the stimulating solution near its air interface was markedly below ambient temperature, due to evaporation. Warming and cooling the tip of the sensillum while recording from its side respectively raised and lowered the frequency of "spontaneous" action potentials of the receptor. The results indicate that the response of the salt receptor is dependent on the temperature of the stimulus. The Q10 is probably several times greater than one.

Action Potentials↗
PubMed2007

Thin films composed of multiwalled carbon nanotubes, gold nanoparticles and myoglobin for humidity detection at room temperature.

Optically transparent and electrically conductive nanocomposite thin films consisting of multiwalled carbon nanotubes (MWCNTs), gold nanoparticles (GNPs) and myoglobin molecules that glue GNPs and MWCNTs together are fabricated for the first time on glass substrates from aqueous solution. The nanocomposite thin film is capable of varying its resistance, impedance or optical transmittance at room temperature in response to changes in ambient humidity. The conductometric sensitivity to relative humidity (RH) of the nanocomposite thin film is compared with those of the pure and Mb-functionalized MWCNT layers. The pure MWCNT layer shows a small increase in its resistance with increasing RH due to the effect of p-type semiconducting nanotubes present in the film. In contrast, a four times higher sensitivity to RH is observed for both the nanocomposite and Mb-functionalized MWCNT thin films. The sensitivity enhancement is attributable to swelling of the thin films induced by water absorption in the presence of Mb molecules, which increases the inter-nanotube spacing and thereby causes a further increase of the film resistance. A humidity change as low as DeltaRH=0.3 % has been readily detected by conductometry using the nanocomposite thin film.

Gold↗
PubMed1986

Stomatal and nonstomatal limitations to net photosynthesis in Pinus taeda L. under different environmental conditions.

Net photosynthesis, transpiration and stomatal conductance of two-year-old Pinus taeda L. seedlings were compared under various environmental conditions. Responses to air temperature, irradiance, ambient CO(2) concentration, absolute humidity deficit and xylem pressure potential were examined. The seedlings exhibited little response to a wide range of absolute humidity deficits (7 to 16 g m(-3)) and temperatures (20 to 35 degrees C), but were sensitive to changes in water deficit, irradiance and CO(2) concentration. Net photosynthesis and stomatal conductance were linearly related under all of the environmental conditions measured. However, the gas phase limitation to photosynthesis was generally small (20 to 30%). It was concluded that although the stomatal response was closely coupled to changes in photosynthesis, internal limitations, rather than the rate of gaseous diffusion of CO(2), were primarily responsible for limiting photosynthesis.

Journal Article↗
PubMed1976

The effect of moisture supply upon the development and hatching the eggs of Nematodirus battus.

Experiments were carried out to investigate the effect of variations in humidity and osmotic pressure upon the development and hatching of the eggs of Nematodirus battus. It was found that no development or hatching took place unless there was free water available, though humidity effects could enhance the subsequent response of the eggs in water. Larvae were found to be very resistant to prolonged exposure to low humidity. The concentration of the hatching medium showed little effect upon development of eggs, though the rate of larval emergence was reduced as the concentration of the culture medium increased. The relevance of this information is discussed in the context of other requirements of the egg stages during their hatching phase and how this may affect the behaviour of this nematode under field conditions.

Animals↗
PubMed2003

Carbon dioxide effects on stomatal responses to the environment and water use by crops under field conditions.

Reductions in leaf stomatal conductance with rising atmospheric carbon dioxide concentration ([CO2]) could reduce water use by vegetation and potentially alter climate. Crop plants have among the largest reductions in stomatal conductance at elevated [CO2]. The relative reduction in stomatal conductance caused by a given increase in [CO2] is often not constant within a day nor between days, but may vary considerably with light, temperature and humidity. Species also differ in response, with a doubling of [CO2] reducing mean midday conductances by <15% in some crop species to >50% in others. Elevated [CO2] increases leaf area index throughout the growing season in some species. Simulations, and measurements in free air carbon dioxide enrichment systems both indicate that the relatively large reductions in stomatal conductance in crops would translate into reductions of <10% in evapotranspiration, partly because of increases in temperature and decreases in humidity in the air around crop leaves. The reduction in evapotranspiration in crops is similar to that in other types of vegetation which have smaller relative reductions in stomatal conductance, because of the poorer aerodynamic coupling of the canopy to the atmosphere in crops. The small decreases in evapotranspiration at elevated [CO2] may themselves be important to crop production in dry environments, but changes in climate and microclimate caused by reduced stomatal conductance could also be important to crop production.

Air↗
PubMed2003

Evidence that enforced sunlight exposure can cause hyperthermia in cattle ingesting low levels of ergot of rye (Claviceps purpurea), when air temperature and humidity conditions are only moderate.

OBJECTIVE: To determine the rectal temperature response of cattle, following the oral administration of ergot of rye (Claviceps purpurea), under pen conditions of enforced sunlight compared with those of enforced shade. DESIGN AND PROCEDURE: Hereford cross steers were divided into two groups of 18. One group was dosed once, on a Monday morning, with finely ground rye grass ergots at a rate of 180 mg/kg body weight and held in the sun for 7 h each day until Friday afternoon. The other group was not dosed but was similarly held in the sun during the same period. Their rectal temperatures were measured early morning and mid afternoon, from Monday to Friday inclusive. The process was repeated for each group, but this time they were held in the shade. The four treatment options were run concurrently by conducting the experiments over 6 weeks and using 3 animals in each treatment group, each week. RESULTS: The thermic response over all weeks, of the ergot treated, sunlight exposed cattle, was deemed greater than for the other groups, based on the following four parameters. The increase in rectal temperature between early morning and mid afternoon, the size of the mid afternoon rectal temperature rise, the difference between the maximum mid afternoon rectal temperature recorded by an animal in the sun compared with that recorded by the same animal in the shade, and finally the number of animals in a treatment group that recorded rectal temperatures > 40.00 degrees C. The difference in the daily increase in body temperature between the ergot treated, sun exposed cattle and the ergot treated, shaded cattle, was greater than that observed between the sun exposed and shade restricted control cattle. Nine of 18 ergot treated and sun exposed cattle developed hyperthermia; no cattle in the other three groups did. CONCLUSIONS: Some sunlight exposed cattle, dosed with a low amount of ergot of rye, can experience a body temperature elevation above the normal range, even under mild ambient temperature and humidity conditions. Sunlight exposure causes an increase in body temperature in normal cattle that is probably attributable to solar radiant heat. Ergot ingestion causes an increase in body temperature in shaded cattle that is probably attributable to ambient temperature and humidity effects. This response can be increased by sun exposure and this increase is attributable to solar radiant heat effects and possibly also solar radiation. A response to radiant heat is consistent with the known physiological effects of ingested ergot alkaloids, but a response to solar radiation is not.

Animal Feed↗
PubMed1991

Effect of humidity on the deswelling function of the human cornea.

The present study determined the effect of the full range of humidities on the deswelling function of the human cornea. The closed-eye deswelling function and the open-eye deswelling responses for five different levels of humidity (0%, 25%, 60%, 85%, and 100%) were assessed for 8 normal, young-adult subjects. Open-eye corneal deswelling for the 8 subjects was unaffected by relative humidities from 0 to 100%. Therefore, osmotically-driven corneal thinning effect of tear evaporation does not significantly contribute to the deswelling function of the human cornea. We conclude, contrary to recent reports, that the endothelial pump is the primary mechanism that maintains normal corneal thickness and provides recovery from stromal edema.

Adult↗
PubMed1977

Responses to the thermal environment.

Human responses to the thermal environment and to internal heat production serve to maintain a narrow range of internal body temperatures of 36-38 C. There are two categories of responses: voluntary or behavioral responses, and involuntary or physiological autonomic responses. Voluntary or behavioral responses consist generally of avoidance or reduction of thermal stress by modification of the body's immediate environment by modification of clothing insulation or by comfort conditioning of his microenvironment. Physiological responses consist of peripheral vasoconstriction to reduce the body's thermal conductance and increased heat production by involuntary shivering in the cold, and peripheral vasodilation to increase thermal conductance and secretion of sweat for evaporative cooling in hot environments. Autonomic responses are proportional to changes in internal and mean skin temperatures. Repeated exposures to heat, humidity, and exercise will modify the physiological response mechanisms by acclimation to produce more effective responses. Physiological responses also depend on the point in a diurnal cycle, on physical fitness, and on the sex of the individual. Behavioral responses rely on thermal sensations and thermal discomfort. Thermal discomfort appears to be closely related to the level of autonomic responses so that warm discomfort is closely correlated with skin wettedness, and cold discomfort similarly relates to cold extremities and shivering activity.

Acclimatization↗
PubMed1990

Responses of young and older men during prolonged exercise in dry and humid heat.

Eight young, sedentary men (aged 34 years, SD 3) and six older moderately active, unacclimated men (aged 57 years, SD 2) walked on a treadmill at 30% of their maximum oxygen consumption up to 3.5 h in a thermoneutral [dry bulb temperature (Td) 21 degrees C, relative humidity (r.h.) 43%)], a warm humid (Tdb 30 degrees C, r.h. 80%) and a hot dry (Tdb 40 degrees C, r.h. 20%) environment while wearing ordinary working clothes (0.7 clo). Their oxygen consumption, heart rate (fc), rectal (Tre) and mean skin temperature (Tsk), sweat rate (SR), and evaporative rate (ER) were measured during the tests. The ratings of thermal sensation (TS) and perceived exertion (RPE) were assessed using standard scales. In the heat stress tests, the number of experiments discontinued did not significantly differ between the two groups. The mean levels and end-exercise values of Tre, Tsk, fc, TS and RPE were not significantly different between the young and older subjects in any of the environments. In the warm humid environment, however, the Tre and RPE of the older subjects increased continuously (P less than 0.05) during the test compared to the young subjects. No significant difference between the groups was observed in SR or in ER. In the hot dry environment, however, the ER of older men increased more slowly compared to the young men. In spite of some time-related differences observed in Tre, RPE, and ER, the older subjects did not exhibit higher fc during exercise in the heat, they were not more hyperthermic and their performance times were similar to the young subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗