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At least 127 records · Page 7Linked to original sources
PubMed1994

Intermittent microclimate cooling during rest increases work capacity and reduces heat stress.

Requirements for special protective equipment while working in hazardous environments can present a significantly increased thermal burden and early onset of physical fatigue. Ambulatory (backpack) or tethered personal cooling can accelerate metabolic heat removal, but is often not practical from an ergonomic standpoint. The efficacy of incorporating personal cooling during non-ambulatory rest periods was evaluated in subjects (n = 8) with varying levels of fitness. Treadmill work (approximately 475 W, 40% VO2 max) was alternately performed for 30 min followed by 30 min of rest. Subjects walked and rested under three separate experimental conditions: (1) control (C), in which light clothing was worn; (2) CPE, in which a chemical protective ensemble (CPE) was worn, and (3) CPE plus intermittent microclimate cooling (COOL). The WBGT condition for all trials was 31 degrees C. During the COOL trial the subjects additionally wore a personal cooling vest which allowed for the circulation of chilled liquid over the torso during rest. Under C conditions, relatively modest changes in rectal temperature (Tre) were observed, which stabilized over time. CPE wear resulted in a progressive rise in Tre and early fatigue. The addition of intermittent cooling during each rest cycle (COOL trial) significantly attenuated heat storage such that an oscillating, but equilibrated Tre was established and work capacity was at least doubled. Moreover, the perceived cooling effect was appreciable for all subjects. Therefore, intermittent personal cooling provided a useful means of enhancing work productivity and may have application for certain military and industrial personnel performing heavy work in hot environments. This approach should provide a practical alternative for reducing stress/fatigue when work/rest cycles are employed.

Body Temperature Regulation↗
PubMed2005

Modeling tree water deficit from microclimate: an approach to quantifying drought stress.

Tree water deficit estimated by measuring water-related changes in stem radius (DeltaW) was compared with tree water deficit estimated from the output of a simple, physiologically reasonable model (DeltaWE), with soil water potential (Psisoil) and atmospheric vapor pressure deficit (VPD) as inputs. Values of DeltaW were determined by monitoring stem radius changes with dendrometers and detrending the results for growth. We followed changes in DeltaW and DeltaWE in Pinus sylvestris L. and Quercus pubescens Willd. over 2 years at a dry site (2001-2002; Salgesch, Wallis) and in Picea abies (L.) Karst. for 1 year at a wet site (1998; Davos, Graubuenden) in the Swiss Alps. The seasonal courses of DeltaW in deciduous species and in conifers at the same site were similar and could be largely explained by variation in DeltaWE. This finding strongly suggests that DeltaW, despite the known species-specific differences in stomatal response to microclimate, is mainly explained by a combination of atmospheric and soil conditions. Consequently, we concluded that trees are unable to maintain any particular DeltaW. Either Psisoil or VPD alone provided poorer estimates of DeltaW than a model incorporating both factors. As a first approximation of DeltaWE, Psisoil can be weighted so that the negative mean Psisoil reaches 65 to 75% of the positive mean daytime VPD over a season (Q. pubescens: approximately 65%, P. abies: approximately 70%, P. sylvestris: approximately 75%). The differences in DeltaW among species can be partially explained by a different weighting of Psisoil against VPD. The DeltaW of P. sylvestris was more dependent on Psisoil than that of Q. pubescens, but less than that of P. abies, and was less dependent on VPD than that of P. abies and Q. pubescens. The model worked well for P. abies at the wet site and for Q. pubescens and P. sylvestris at the dry site, and may be useful for estimating water deficit in other tree species.

Climate↗
PubMed2006

Effect of chloride on pH microclimate and electrogenic Na+ absorption across the rumen epithelium of goat and sheep.

Active Na+ absorption across rumen epithelium comprises Na+/H+ exchange and a nonselective cation conductance (NSCC). Luminal chloride is able to stimulate Na+ absorption, which has been attributed to an interaction between Cl-/HCO3- and Na+/H+ exchangers. However, isolated rumen epithelial cells also express a Cl- conductance. We investigated whether Cl- has an additional effect on electrogenic Na+ absorption via NSCC. NSCC was estimated from short-circuit current (Isc) across epithelia of goat and sheep rumen in Ussing chambers. Epithelial surface pH (pHs) was measured with 5-N-hexadecanoyl-aminofluorescence. Membrane potentials were measured with microelelectrodes. Luminal, but not serosal, Cl- stimulated the Ca2+ and Mg2+ sensitive Isc. This effect was independent of the replacing anion (gluconate or acetate) and of the presence of bicarbonate. The mean pHs of rumen epithelium amounted to 7.47 +/- 0.03 in a low-Cl- solution. It was increased by 0.21 pH units when luminal Cl- was increased from 10 to 68 mM. Increasing mucosal pH from 7.5 to 8.0 also increased the Ca2+ and Mg2+ sensitive Isc and transepithelial conductance and reduced the fractional resistance of the apical membrane. Luminal Cl- depolarized the apical membrane of rumen epithelium. 5-Nitro-2-(3-phenylpropylamino)-benzoate reduced the divalent cation sensitive Isc, but only in low-Cl- solutions. The results show that luminal Cl- can increase the microclimate pH via apical Cl-/HCO3- or Cl-/OH- exchangers. Electrogenic Na+ absorption via NSCC increases with pH, explaining part of the Cl- effects on Na+ absorption. The data further show that the Cl- conductance of rumen epithelium must be located at the basolateral membrane.

Absorption↗
PubMed1985

Localization of acid microclimate along intestinal villi of rat jejunum.

Considering the significance that pH value could have for digestive and absorptive processes, these investigations were aimed at precisely localizing the position of the acid microclimate, i.e., of proton accumulation along the surface of intestinal villi. The determinations were carried out under microscopic control on jejunal segments of rats incubated at 25 degrees C in O2-saturated phosphate buffer (pH 7.4). Specially manufactured antimony microelectrodes (tip diam 50 microns) and calomel reference electrodes were used for pH registration. Highest proton concentration (214-224 nmol/l not equal to pH 6.67-6.65) was found 10-100 microns below the tip of the villus in the zone of digestive and absorptive epithelial cells. Toward the crypt, a steep decrease of proton concentration was registered with alkaline values 200 microns below the villus tip. Toward the bulk phase, the decrease of the proton concentration was moderate due to the existence of the unstirred water layer as an effective diffusion barrier. The pH value of the bulk phase was reached 440 microns over the villus tip, a distance possibly identical to the thickness of the unstirred water layer.

Acid-Base Equilibrium↗
PubMed1987

Effect of small bowel resection on the intestinal surface acid microclimate in the rat.

The effect of extensive (65%) proximal and middle small bowel resection on the intestinal surface acid microclimate (ISAM) of the remaining ileum in the rat was examined and the results were compared to those of sham-operated rats. ISAM pH measurements were performed in vivo using a pH microelectrode; incubation was performed in Krebs-Ringer phosphate buffer (pH 7.40 +/- 0.02). In the resected rats, ISAM pH of 6.03 +/- 0.07 and 7.22 +/- 0.03 were recorded in the proximal and distal part of the remaining ileum, respectively. In the sham-operated rats, ISAM pH of 6.04 +/- 0.07, 6.98 +/- 0.03 and 7.28 +/- 0.02 were recorded in the proximal jejunum and in the proximal and distal part of the corresponding ileal segment. ISAM pH was significantly lower (p less than 0.01) in the proximal part of the remaining ileum of the resected rats as compared to the corresponding part in the sham-operated rats but was similar in distal ileum. In fact, the ISAM pH of the proximal part of the remaining ileum of resected rats was as acidic as that of the jejunum of the sham-operated rats. These results clearly demonstrate that adaptation in the ISAM occurs in the remaining ileum following extensive resection of proximal and middle small intestine.

Animals↗
PubMed1987

Studies on the intestinal surface acid microclimate: developmental aspects.

The existence and general characteristics of the intestinal surface acid microclimate (ISAM) in the developing intestine of suckling and weanling rats were examined. ISAM pH measurements were performed in vitro using a sensitive glass pH-microelectrode. The results showed that the ISAM does exist in both suckling and weanling rat intestine. In both suckling and weanling rats, ISAM pH was significantly (p less than 0.01) lower in the jejunum than in the ileum, an observation similar to that previously reported in the small intestine of adult rats. In the colon, however, ISAM pH of suckling rats was significantly (p less than 0.01) lower than that of weanling and adult rats. Studies on the relationship between jejunal ISAM pH of weanling rats and incubation buffer pH showed that the two are not in equilibrium. Jejunal ISAM pH of weanling rats was significantly inhibited by: 1) the mucolytic agent N-acetyl-L-cysteine, 2) stirring of the incubation medium, 3) Na+ removal, 4) glucose removal (or substitution by the unmetabolizable galactose), and 5) metabolic inhibitors (iodoacetate and dinitrophenol). These results demonstrate the existence of the ISAM in the developing intestine of suckling and weanling rats and shows the dependence of the ISAM on Na+, metabolizable substrate(s) and normal intracellular metabolism. Furthermore, surface mucus appears to play a role in maintaining the ISAM, most probably through retaining the H+ at the intestinal surface.

Acid-Base Equilibrium↗
PubMed2006

Marine reserve design: optimal size, habitats, species affinities, diversity, and ocean microclimate.

The design of marine reserves is complex and fraught with uncertainty. However, protection of critical habitat is of paramount importance for reserve design. We present a case study as an example of a reserve design based on fine-scale habitats, the affinities of exploited species to these habitats, adult mobility, and the physical forcing affecting the dynamics of the habitats. These factors and their interaction are integrated in an algorithm that determines the optimal size and location of a marine reserve for a set of 20 exploited species within five different habitats inside a large kelp forest in southern California. The result is a reserve that encompasses approximately 42% of the kelp forest. Our approach differs fundamentally from many other marine reserve siting methods in which goals of area, diversity, or biomass are targeted a priori. Rather, our method was developed to determine how large a reserve must be within a specific area to protect a self-sustaining assemblage of exploited species. The algorithm is applicable across different ecosystems, spatial scales, and for any number of species. The result is a reserve in which habitat value is optimized for a predetermined set of exploited species against the area left open to exploitation. The importance of fine-scale habitat definitions for the exploited species off La Jolla is exemplified by the spatial pattern of habitats and the stability of these habitats within the kelp forest, both of which appear to be determined by ocean microclimate.

California↗
PubMed2003

[Integral evaluation of optimal microclimate and human thermoregulation].

The article presents integral parameters of heat comfort determined numerically through parameters of microclimate and human heat state. The authors defined human heat state classes that necessitate differentiated evaluation of heat comfort depending on energy expenditure. The materials also cover regression equations to calculate criterial parameters for optimal heat state.

Body Temperature Regulation↗
PubMed1992

Heat strain during at-sea helicopter operations and the effect of passive microclimate cooling.

Twelve Navy H-3 helicopter aircrew members were monitored (heart rate, skin and rectal temperatures) in both microclimate cooling (ice) vest and non-vest conditions during at-sea operations in the high heat environment of the Persian Gulf. During all flights and flight phases, ambient dry bulb temperatures ranged from 31.0 degrees C (in-flight) to 48.6 degrees C (hover). Heart rate was greatest during hover and on-deck (range: 89.9 to 145.0 beats/min) without an ice vest, yet was significantly reduced with ice (range: 79.7 to 86.0 beats/min) (p less than 0.05). Rectal temperature was not found to be different between vest and non-vest conditions; however, change across flight phases in both conditions was significant (p less than 0.05). Analysis of variance demonstrated significantly lower mean weighted skin temperatures (p less than 0.05) when wearing the ice vest. These data suggest that wearing a protective cooling vest can reduce the heat strain associated with helicopter flight in high heat environments.

Adult↗
PubMed1990

Evaluation of three commercial microclimate cooling systems.

Three commercially available microclimate cooling systems were evaluated for their ability to reduce heat stress in men exercising in a hot environment while wearing high insulative, low permeability clothing. Five male volunteers performed three 180-min experiments (three repeats of 10 min rest, 50 min walking at 440 watts) in an environment of 38 degrees C dry bulb (Tdb), 12 degrees C dew point (Tdp). The cooling systems were: 1) ILC Dover Model 19 Coolvest (ILC), mean inlet temperature 5.0 degrees C; 2) LSSI Coolhead (LSSI), mean inlet temperature 14.5 degrees C; and 3) Thermacor Cooling Vest (THERM), mean inlet temperature 28.3 degrees C. Endurance time (ET), heart rate (HR), rectal temperature (Tre), mean skin temperature (Tsk), sweating rate (SR), rated perceived exertion (RPE), and thermal sensation (TS) were measured. A computer model prediction of ET with no cooling was 101 min. ET was greater (p less than 0.01) with ILC (178 min) than THERM (131 min) which was greater (p less than 0.01) than LSSI (83 min). The subjects self terminated on all LSSI tests because of headaches. Statistical analyses were performed on data collected at 60 min to have values on all subjects. There were no differences in HR, Tre, SR, or TS values among the cooling vests. The subjects' Tsk was lower (p less than 0.05) for the LSSI than THERM; and RPE values were higher (p less than 0.05) for LSSI than the other two vests. These data suggest an improved physiological response to exercise heat stress with all three commercial systems with the greatest benefit in performance time provided by the ILC cooling system.

Air Conditioning↗
PubMed1988

Portable, ambient air microclimate cooling in simulated desert and tropic conditions.

We examined the feasibility of providing ambient air during exercise and conditioned (cooled) air during rest on reducing physiological strain and optimizing tolerance time. Six male soldiers attempted 250-min exposures in hot/dry and hot/wet environments. Subjects wore chemical protective clothing over the combat vehicle crewman uniform and an air-cooled vest. They alternated between 50 min of treadmill walking (420 W) and 50 min of rest (105 W). During the walks, a backpack mounted blower provided a total of 10 or 18 cfm of air to the vest and face; while subjects received 18 cfm of conditioned air from an umbilical during rest. A control test with conditioned air during rest, but only a ventilated facepiece during work was also conducted in the hot/dry environment. In the hot/dry environment the ambient air backpack extended (p less than 0.05) tolerance time and significantly reduced rectal temperatures, heart rates and sweating rates compared to control; no differences were found between 10 and 18 cfm. In the hot/wet environment, tolerance time was extended compared to a predicted tolerance time assuming no microclimate cooling. We conclude that the ambient air backpack reduced physiological strain and improved tolerance time of combat vehicle crewmen during exercise in the heat.

Adult↗
PubMed1987

Nest microclimate and incubation water loss of eggs of the African ostrich (Struthio camelus var. domesticus).

The microclimate of the nest and the rates of egg water loss were studied at weekly intervals throughout the 41-day incubation period in six ostrich nests. Overall mean values were a central egg temperature of 34.9 degrees C associated with saturation vapor pressure of 42 torr, a mean nest vapor pressure of 11 torr, and an ambient vapor pressure of 8.4 torr. The egg water loss increased from 4,000 to 4,800 mg X day-1 over the incubation period, and the total water loss was equal to 13.2% of the initial egg mass of 1,368 gm. The mean rate of water loss (4,403 mg X day-1) divided by the water vapor conductance of the shell (147 mg X day-1 X torr-1) equals 30 torr. When this value is added to the nest vapor pressure of 11 torr, it predicts an egg saturation vapor pressure of 41 torr, similar to that derived from the central egg temperature.

Animals↗
PubMed1995

Continuous and intermittent personal microclimate cooling strategies.

A comparison was made between two personal auxiliary cooling approaches for the relief of thermal stress while wearing the standard USAF Chemical Defense Ensemble (CDE). Subjects exercised at approximately 40% VO2max in either warm (28/24/34 degrees C) or hot (38/26/43 degrees C) environmental conditions, (Tdb/Twb/Tbg degrees C, respectively). During each of three trials, four hours of intermittent work (four work/rest cycles) were attempted. Microclimate air cooling was applied in two different fashions and compared with a control trial during which no cooling was received (NC). In one trial, conditioned air cooling (Tin approximately 20 degrees Cdb) was delivered during rest periods only (intermittent cooling, IC), while during the second trial, ambient air cooling was also applied during the work period in addition to the conditioned air delivered during rest periods (continuous cooling, CC). During the warm condition, exposure cycle time was 45 min work and 15 min rest, while under the hot conditions, exposure cycle time was 30 min work and 30 min rest. Both CC and IC trials resulted in significantly extended work times, lower final rectal temperatures, heart rates, and sweat production (SP) than in the NC trial. Additionally, CC results in significantly lower SP, higher % sweat evaporation, and lower ratings of perceived exertion (RPE) and thermal comfort (TC) than IC at both warm and hot temperatures. Moreover, subjects were better able to maintain thermal equilibrium (i.e., cumulative heat balance) over time using CC compared to IC in the warm environment. The physiological significance of these findings, in some cases, was secondary to the improvement in subjective measures of TC and RPE.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Formaldehyde activity on historical glass objects in museum microclimate.

Degradation of some cultural heritage monuments has been caused by interaction with the closest environment (micro-climate). Amount of separate compounds is very small and because of it, this fact becomes neglected. Time and temperature can induce their activity finally causing deterioration. In this category organic compounds can be interpreted as one of museum show - case element. This statement has been improved by testing glass objects and their suitable sensors (model glasses). Destructive activity of formaldehyde on historical glasses belonging to the XVIII-th c. objects with totally different compositions has been confirmed by carried out experiments. For historical material which is very limited, sensor glass method has been applied. Sensors are prepared on the base of results of chemical analyses of original glass chemical analyses and melted on laboratory scale (according to historical data). Induced corrosion for sensor supports knowledge about deterioration process in real micro-environmental conditions. The following testing methods were used: scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), optical interferometer (OI), inductively couple plasma (ICP).

Formaldehyde↗
PubMed2002

Rainforest air-conditioning: the moderating influence of epiphytes on the microclimate in tropical tree crowns.

Epiphytes are often assumed to influence the microclimatic conditions of the tree crowns that they inhabit. In order to quantify this notion, we measured the parameters "temperature" (of the substrate surface and the boundary layer of air above it), "evaporative drying rate" and "evapotranspiration" at various locations within tree crowns with differing epiphyte assemblages. The host tree species was Annona glabra, which was either populated by one of three epiphyte species (Dimerandra emarginata, Tillandsia fasciculata, or Vriesea sanguinolenta) or was epiphyte-free. We found that during the hottest and driest time of day, microsites in the immediate proximity of epiphytes had significantly lower temperatures than epiphyte-bare locations within the same tree crown, even though the latter were also shaded by host tree foliage or branches. Moreover, water loss through evaporative drying at microsites adjacent to epiphytes was almost 20% lower than at exposed microsites. We also found that, over the course of several weeks, the evapotranspiration in tree crowns bearing epiphytes was significantly lower than in trees without epiphytes. Although the influence of epiphytes on temperature extremes and evaporation rates is relatively subtle, their mitigating effect could be of importance for small animals like arthropods inhabiting an environment as harsh and extreme as the tropical forest canopy.

Animals↗
PubMed1987

Thermal interaction between animal and microclimate: a comprehensive model.

An equation based on heat transfer theory is developed to predict the rate of heat loss from a homeothermic vertebrate to the environment, specified by the air temperature, humidity, windspeed and radiation receipt. The analysis incorporates the animal's thermoregulatory responses--sweating ability, vasomotor action, and regulation of body-core temperature, metabolic and respiratory rate. The loss of heat and water vapour from cattle is used as an illustration, and particular attention is given to their heat balance in hot environments. The predicted rates of heat loss from cattle indoors at various air temperatures and humidities are consistent with experiments. Outdoors, intercepted solar radiation can reduce substantially heat loss through the body tissue when the air temperature is low. In contrast, at high air temperatures the heat dissipation may not be sensitive to the radiation load, although body-core temperature is. Increased rates of air movement can aggravate strain at low air temperatures, but mitigate strain in a hot environment.

Air↗