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PubMed2006

Molecular complexes in close and far away.

In this review, gas-phase chemistry of interstellar media and some planetary atmospheres is extended to include molecular complexes. Although the composition, density, and temperature of the environments discussed are very different, molecular complexes have recently been considered as potential contributors to chemistry. The complexes reviewed include strongly bound aggregates of molecules with ions, intermediate-strength hydrogen bonded complexes (primarily hydrates), and weakly bonded van der Waals molecules. In low-density, low-temperature environments characteristic of giant molecular clouds, molecular synthesis, known to involve gas-phase ion-molecule reactions and chemistry at the surface of dust and ice grains is extended here to involve molecular ionic clusters. At the high density and high temperatures found on planetary atmospheres, molecular complexes contribute to both atmospheric chemistry and climate. Using the observational, laboratory, and theoretical database, the role of molecular complexes in close and far away is discussed.

Journal Article↗
PubMedDate not supplied

Ecophysiological adaptations to dry thermal environments measured in two unrestrained Namibian scorpions, Parabuthus villosus (Buthidae) and Opisthophthalmus flavescens (Scorpionidae).

The daily changes in body temperature experienced by Parabuthus villosus (Buthidae), a scorpion found on the gravel plains around Gobabeb, Namibia, and by Opisthophthalmus flavescens (Scorpionidae), a dune-dwelling species from the same area, were measured under similar field conditions. Thermocouples implanted under the segments of the mesosoma measured maximum temperatures as high as 43 degrees C in the shade. Air temperatures reached a maximum of 33 degrees C during the daytime and a minimum of 12 degrees C at night. Very low metabolic rates compared with those of other nonsedentary invertebrates were recorded in both species; oxygen consumption ranged from 8 microL g-1 h-1 at 16 degrees C to 115 microL g-1 h-1 at 40 degrees C. A pulsed Doppler system was used to measure heart rate in situ in free-moving scorpions. At night, heart rate declined to about 4 beats min-1 in resting undisturbed scorpions. During daylight excursions and while scorpions hunted for food, heart rates as high as 180 beats min-1 were observed. Heart rate was linearly correlated with temperature in P. villosus, with a slope of 2.37 (Q10 = 2.18), but in O. flavescens only a limited correlation was observed, with a slope of 1.18 (Q10 = 1.69). In O. flavescens, heart rate showed hysteresis as body temperature rose during daylight and then decreased during the late afternoon and evening; the reverse was observed in P. villosus. In both species, haemocyanin-oxygen affinity was independent of temperature, with a higher oxygen affinity and a larger pH sensitivity in O. flavescens. The Q10's of oxygen consumption and heart rate are quite different in O. flavescens but not as different in P. villosus. Although changes in the cardiovascular system, such as stroke volume, may also play a role in meeting increased oxygen demand, the features of the haemocyanin oxygen transport system, such as the absence of temperature sensitivity and a marked pH sensitivity, can also influence the maintenance of VO2 under temperature stress. The differences in the normal thermal habitats of the two species may be used to explain the distinctions between the evolved physiological responses to temperature increase shown by the two species.

Acclimatization↗
PubMed1984

Influence of skin temperature distribution on thermal sensation in a cool environment.

Thermal sensation and distribution of skin temperatures in persons exercising at 36.5 W on a bicycle ergometer and resting in a cool environment (10 degrees C) in two different clothings, one with the insulation mainly over the trunk (1.22 clo), and one with well insulated limbs (1.67 clo), were studied. Their general thermal sensations varied from slightly warm to slightly cool. The placing of the insulation had a decisive influence on skin temperature distribution, so that skin temperature was always high in well-insulated areas. When the insulation was placed over the limbs, a greater amount of heat was lost than if a similar insulation was placed on the trunk. Neither Tsk nor skin temperature distribution correlated with general thermal sensation. Instead, mean body temperature seemed to be the determinant of general thermal sensation in these conditions. The best prediction of general thermal sensation was obtained by adding Tre with a weighting factor of 0.8-0.9 and Tsk with a weighting factor of 0.1-0.2.

Adolescent↗
PubMed1983

The effect of growth temperature on the membrane lipid environment of the psychrophilic bacterium Micrococcus cryophilus.

The relationship between the delta 9-desaturase activity of the psychrophilic bacterium Micrococcus cryophilus grown at different temperatures and the physical state of its membrane lipids as measured by ESR spectroscopy has been studied. Arrhenius plots of desaturase activity were biphasic with a discontinuity at a temperature which depended upon the bacterial growth temperature. Changes in the desaturase activation energy, which increased as the growth temperature was lowered, are discussed in the context of membrane lipid fluidity adaptation to changing environmental temperature. The fluidity of membranes and isolated lipids was measured using nitroxide-labeled fatty acids. The spectra of 2-(10-carboxydecyl)-2-hexyl-4,4-dimethyl-3-oxazolidinoxyl in membranes indicated that there were two lipid environments within the membrane whose relative proportions were dependent both on temperature of measurement and on bacterial growth temperature. In contrast, 2-(3-carboxypropyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinoxyl spectra showed a single lipid environment and plots of log order parameter (S3) vs 1/T were biphasic with inflexion temperatures which were closely related to the bacterial growth temperature. As with membranes, plots of log S3 vs 1/T for total lipids, phosphatidylglycerol and cardiolipin, but not phosphatidylethanolamine, were biphasic and showed inflexions which correlated well with bacterial growth temperature. These results are interpreted as being consistent with a location for the desaturase within the bulk lipid of the membrane rather than in association with specific lipid types.

Electron Spin Resonance Spectroscopy↗
PubMed2000

Investigation of the effects of the pre-cooling on the physiological responses to soccer-specific intermittent exercise.

Whole-body cooling prior to activity has the potential to reduce thermal strain and fatigue during subsequent endurance exercise. Intermittent activity is associated with greater increases in rectal temperature compared with continuous exercise. Thus, the effect of pre-cooling on thermoregulatory responses was examined during an intermittent test under "normal" environmental conditions. Six male university soccer players [mean (SD) age 27 (2) years; height 1.77 (0.3) m; mass 72.2 (1.5) kg; maximal oxygen consumption 58.9 (3.5) ml x kg(-1) x min(-1)] completed a 90-minute soccer-specific intermittent exercise protocol on a non-motorized treadmill. The run was completed with and without pre-cooling under normal laboratory conditions (20 degrees C) and without pre-cooling in a heated laboratory (26 degrees C). The pre-cooling strategy involved exposure to a cold shower (26 degrees C) for 60 min. The pre-cooling manipulation lowered rectal temperature prior to exercise [-0.6 (0.6) degrees C, range -1.5 degrees C; P < 0.05]. The rectal temperature response to exercise was significantly lower following pre-cooling than in the heated condition [pre-cooled 38.1 (0.6) degrees C, heated 38.6 (0.3) degrees C]. The increase in rectal temperature during the second half of the protocol following pre-cooling was significantly greater than the increase observed under normal or heated conditions (P < 0.05). No significant differences were observed between the three conditions for oxygen consumption, heart rate, minute ventilation, rating of perceived exertion and plasma lactate, glucose or free fatty acid concentrations. Based on the current investigation, it can be concluded that there is no evidence for the beneficial effects of pre-cooling on the physiological responses to soccer-specific intermittent exercise under normal environmental conditions.

Adult↗
PubMedDate not supplied

Dynamic thermal responses of five commercially available infant radiant warmer systems.

Five commercially available infant radiant warmer systems were characterized through radiant-energy measurements at the mattress surface under identical environmental conditions. Average irradiance levels for each warmer were then calculated. In addition, all systems were thermally evaluated for warm-up time using the International IEC standard black anodized aluminum disk simulator. Warm-up time and radiant-energy bed mapping tests were conducted in manual mode. To assess thermal performance under dynamic conditions, skin and core temperatures were measured using a patient simulator test-load device. Dynamic patient simulator response-time data and side-wall temperature data are provided. The radiative heat contribution from the warmer side walls on patient simulator core and skin temperatures was demonstrated. Extreme differences in warmer performances and energy to the mattress surface are documented. Differences in infant radiant warmer performances are principally due to heater-element composition, reflector design, and heater-to-mattress distance.

Analog-Digital Conversion↗
PubMed1975

Respiration during heat stress.

In human subjects at rest changes in heart rate pulmonary ventilation, tidal volume, respiratory rate, and end-tidal carbon dioxide tension were examined at increases in deep body temperature of 1 degrees C and 2 degrees C. Each of these latter target temperatures was achieved at two different rates of temperature increase. The increase in deep body temperature was associated with a rise in heart rate and tidal volume and a reduction in respiratory rate. An increase in pulmonary ventilation associated with a reduction in end-tidal carbon dioxide tension occurred only when deep body temperature increase reached 1.5 degrees C. The apparently greater change in both pulmonary ventilation and end-tidal carbon dioxide tension during the more rapid increase in deep body temperature by 2 degrees C was not significant.

Adult↗
PubMed1993

The physiological consequences of simulated helicopter flight in NBC protective equipment.

The physiological effects of wearing U.S. Army aviator nuclear-biological-chemical (NBC) individual protective equipment (IPE) were evaluated in the USAARL UH-60 research flight simulator. There were 16 male aviators who flew the simulator in 4 test conditions: standard flight suit and cool cockpit, standard flight suit and hot cockpit, NBC IPE and cool cockpit, NBC IPE and hot cockpit. The cool condition was a WBGT of 17.9 degrees C, the hot 30.6 degrees C. Rectal temperature, mean skin temperature, and heart rate were monitored and showed significant increases for the NBC hot condition compared with the other three. Seven subjects failed to complete the sortie in the NBC hot condition, with a mean survival time of 298 min. All subjects flew for the target 6 h in the other conditions.

Adult↗
PubMed1977

Histological features of respiratory epithelium of calves held at differing temperature and humidity.

The effect of ambient temperature and humidity on the structure of respiratory epithelium of calves was studied. Four calves of each of three experiments were acclimatized to a nonoperational environmental chamber for six days and then exposed to constant extremes of temperatures and relative humidity of one of 30 degrees C --35%, or 27 degrees C--92%, or 5 degrees C--92% respectively in this chamber for eight days each. Five calves (3 and 2) were similarly acclimatized then exposed to 1 degrees C--40%. Nasal swabs were taken from all animals at regular intervals. Swabs of three animals yielded Mycoplasma spp. and one swab yielded the virus of infectious bovine rhinotracheitis. Detailed histological studies of respiratory epithelium of nose, trachea, major bronchus and terminal bronchioli were conducted at four sites. Goblet cells were least in calves held in hot and dry air; calves held in dry air had the least polymorphonuclear cells and the greatest prevalence of hypochromatic cell layers and vacuolation of epithelial cells. Differences between experiments were evident most for sites of trachea and major bronchus.

Animals↗
PubMed1986

[The hand and environment--physiological changes of digital functions in adult men by vibratory stimulations, water immersions and climatic conditions].

Skin temperature, 125 Hz vibratory sensibility and pinch strength of the hand were recorded continuously in adult men through water immersion tests ((1) 40 degrees C (2) 15 degrees C (3) 10 degrees C) and vibratory stress tests ((1) 32 Hz-2 g (2) 32 Hz-3g (3) 125 Hz-2 g) in climatic chambers ((1) 20 degrees C-50% humidity (2) 20 degrees C-50% (3) 30 degrees C-40% and 80%). As a stressor to the hand, the cold water immersion was the most effective. The warm water immersion was effective to slightly decrease the skin temperature and the vibratory sensibility. The younger group showed higher sensitivities of the digital functions than the older group.

Adult↗
PubMed1972

Influence of the carotid rete on brain temperature in cats exposed to hot environments.

1. Thermocouples were chronically implanted in various intracranial and extracranial structures in adult cats. Temperature of arterial blood on the proximal and distal sides of the carotid rete was determined by measuring temperature in the aortic arch and at the anterior cerebral arteries. Temperatures of brain stem regions supplied by the carotid rete and by the vertebral-basilar system were determined by measuring temperature in the anterior hypothalamus and the caudal medulla. Nasal mucosal temperature was measured with a thermocouple implanted in the nasal cavity.2. In a cool environment (25 degrees C), the temperature of anterior cerebral arterial blood was lower than aortic arterial temperature. Anterior cerebral temperature showed shifts which were not present in central (aortic) arterial blood and which were clearly associated with changes in heat loss from the nasal mucosa and with the behaviour of the animal. When the cats were relaxed or in e.e.g. slow-wave sleep, the nasal mucosal temperature was high and the temperature at the anterior cerebral arteries was as much as 0.30 degrees C less than aortic temperature. During behavioural arousal and paradoxical sleep, the nasal mucosal temperature fell and the anterior cerebral arterial temperature rose toward central arterial temperature. Shifts in hypothalamic temperature followed the changes in anterior cerebral arterial temperature. Medullary temperature was higher than aortic temperature and showed shifts which suggested that blood from the rostral circle of Willis mixed with vertebral blood in the basilar artery.3. When the ambient temperature was raised to 40-45 degrees C the cooling of cerebral arterial blood and brain increased as the rate of thermal panting increased. Respiratory rate increased tenfold and aortic temperature rose by 2.0-2.5 degrees C. Anterior cerebral arterial temperature fell below aortic temperature by as much as 1 degrees C, hypothalamic temperature dropping in parallel with cerebral arterial temperature. Medullary temperature cooled below aortic temperature during heat exposure, but the temperature drop in the medulla was not as high as in the rostral brain stem.4. Blowing air into the nasal cavity of anaesthetized cats produced a large, rapid temperature drop at the anterior cerebral arteries and in the hypothalamus, with little effect on central arterial temperature. The same experiments in a dead animal cooled the brain after a longer period of time, suggesting that an active process is involved in the brain cooling observed in living animals.5. It is concluded that the cooling of the rostral cerebral arterial blood and brain which occurs in cats in a cool environment and is accelerated during thermal panting, is a result of countercurrent heat exchange between arterial blood in the carotid rete and venous blood draining the evaporative surfaces of the upper respiratory passages. Such direct brain cooling during thermal panting has now been demonstrated in the cat, the sheep and the gazelle, and probably explains the high heat tolerance of the carnivores and hoofed mammals in which a rete is present.

Animals↗