Mechanism of S. aureus ATCC 25923 in response to heat stress under different water activity and heating rates

This study was designed to characterize the regional and systemic hemodynamic and sympathoadrenal responses to heating after 24 and 48 h of water deprivation in chloralose-anesthetized, male Sprague-Dawley rats (n = 7 per group). Water deprivation produced significant decreases in body weight of 8.1 and 13.7% in the 24- and 48-h groups (P < 0.05), respectively. After water deprivation, rats were exposed to an ambient temperature of 43 degrees C. After correction for body weight differences, heating rates were faster in the 48-h group compared with both euhydrated and 24-h groups. Mean arterial blood pressure (MAP), heart rate, and colonic (Tco) and tail (Ttail) temperatures increased above baseline in all groups during heating. Renal and mesenteric artery blood flow velocities decreased, and vascular resistances increased in response to heating. Compared with euhydrated controls, 48-h water-deprived rats exhibited attenuated pressor (delta MAP = 36 +/- 3 vs. 18 +/- 3 mmHg) and visceral vasoconstrictor (% delta in mesenteric resistance = 122.6 +/- 27.3 vs. 54.9 +/- 6.9%) responses during heating. Tail-skin blood flow estimated from Ttail was also lower at baseline and the onset of heating in water-deprived rats. However, peak Ttail and Tco values were similar across groups. Plasma catecholamines measured in separate groups of rats (n = 6 per group) were significantly higher at baseline and the end of heating in the 48-h group compared with euhydrated and 24-h groups. Despite this exaggerated sympathoadrenal response, the 48-h group exhibited attenuated hemodynamic responses to nonexertional heating compared with euhydrated and 24-h water-deprived rats. These data suggest that cardiovascular and thermoregulatory adjustments can compensate for small changes in hydration state (i.e., 24 h), but more severe levels of hypohydration significantly alter blood pressure and body temperature regulation during heat stress.

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Differential effects of exercise and heat stress on liver HSP70 accumulation with aging

Journal of Applied Physiology ◽

10.1152/jappl.1996.80.2.547 ◽

1996 ◽

Vol 80 (2) ◽

pp. 547-551 ◽

Cited By ~ 60

Author(s):

K. C. Kregel ◽

P. L. Moseley

Keyword(s):

Heat Stress ◽

Heat Shock ◽

Heat Shock Protein ◽

Age Groups ◽

Exercise Group ◽

Moderate Intensity ◽

Control Group ◽

Passive Heating ◽

Heating Rates ◽

Colonic Temperature

Previous reports have suggested that the heat shock response to passive heating may be blunted by aging. However, during exertional heating, factors in addition to elevated temperature may amplify the degree of stress compared with hyperthermia alone. The purpose of this study was to compare the pattern of accumulation of the highly inducible 72-kDa heat shock protein (HSP72) in liver tissue of mature (12-mo-old) and senescent (24-mo-old) male Fischer 344 rats after either passive or exertional heat stress. A euthermic control group was exposed to an ambient temperature (Ta) of 25 degrees C for 4.5 h. A passive heating (heat) group was exposed to an Ta of 42 degrees C until colonic temperature (Tco) reached 41 degrees C. An exertional heating (exercise) group performed intermittent moderate-intensity treadmill exercise (similar absolute intensities for the two age groups) at an Ta of 32 degrees C until Tco reached 41 degrees C. Heating rates were similar in the heat and exercise groups (approximately 0.08 degrees C/min). Rats in both the heat and exercise groups were maintained at a Tco of 41 degrees C for an additional 30 min and subsequently returned to an Ta of 25 degrees C for 3 h. Liver HSP72 accumulation was increased in mature rats after both the heat (+192% vs. control) and exercise (+292%) protocols. In contrast, the senescent rats demonstrated no significant increase in inducible HSP70 with heating but a large increase with exercise (+232%; P < 0.01 compared with control and heat groups). These data suggest that the blunted heat shock protein response to heating observed with aging is not a result of the inability to produce inducible HSP72 because older rats had an robust response to exertional hyperthermia.

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Lengthening of Warm Periods Increased the Intensity of Warm-season Marine Heatwaves Over the Past Four Decades

10.21203/rs.3.rs-700862/v1 ◽

2021 ◽

Author(s):

Xinru Li ◽

Simon Donner

Keyword(s):

Heat Stress ◽

Coral Reefs ◽

Thermal Structure ◽

Warm Season ◽

Marine Ecosystems ◽

Marine Conservation ◽

Heating Rates ◽

Thermal Thresholds ◽

The Past ◽

Peak Intensity

Abstract Marine heatwaves (MHWs), periods of anomalously warm sea surface temperature (SST) which can have significant impacts on marine ecosystems, have increased in frequency and severity over recent decades. Many coastal systems (e.g. coral reefs) are particularly vulnerable to warm-season heat stress when temperature can exceed organisms’ thermal thresholds and lead to mass mortality. While many studies have examined the change of the warm-season heat stress occurrence over time, e.g., for coral reefs, there has been less analysis of the thermal structure of heat stress events. Here we examined the trend in the characteristics of warm-season heat stress (referred to as warm-season MHWs) at the global-scale from 1985 to 2019, using multiple metrics for each of duration, peak intensity, accumulated heat stress, heating rates and level of intensity. The results showed that warm-season MHWs have become more frequent, longer-lasting, featured higher peak intensity and accumulated heat stress across most of the ocean over the past four decades. Furthermore, decomposition of the trends in warm-season MHWs structure showed that the increased accumulated heat stress was predominantly driven by the increased duration rather than the increased intensity, especially in the western and central equatorial Pacific. The results contribute to improving the understanding of warm-season MHWs, which may help inform the prediction of their impacts on marine ecosystems as well as marine conservation and management under climate change.

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Measuring performance changes in highly transient extreme heat stress: Rationale, problem, and experimental procedures.

PsycEXTRA Dataset ◽

10.1037/e420282004-001 ◽

1963 ◽

Author(s):

Hilde Groth ◽

John Lyman

Keyword(s):

Heat Stress ◽

Extreme Heat ◽

Extreme Heat Stress

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Comparing fast inductive tempering and conventional tempering: Effects on microstructure and mechanical properties

Metallurgical Research & Technology ◽

10.1051/metal/2018015 ◽

2018 ◽

Vol 115 (4) ◽

pp. 407 ◽

Cited By ~ 4

Author(s):

Annika Eggbauer Vieweg ◽

Gerald Ressel ◽

Peter Raninger ◽

Petri Prevedel ◽

Stefan Marsoner ◽

...

Keyword(s):

Mechanical Properties ◽

Impact Energy ◽

Charpy Impact ◽

Heat Treating ◽

Processing Route ◽

High Heating Rate ◽

Heating Rates ◽

High Heating ◽

Tempering Treatment ◽

Carbide Distribution

Induction heating processes are of rising interest within the heat treating industry. Using inductive tempering, a lot of production time can be saved compared to a conventional tempering treatment. However, it is not completely understood how fast inductive processes influence the quenched and tempered microstructure and the corresponding mechanical properties. The aim of this work is to highlight differences between inductive and conventional tempering processes and to suggest a possible processing route which results in optimized microstructures, as well as desirable mechanical properties. Therefore, the present work evaluates the influencing factors of high heating rates to tempering temperatures on the microstructure as well as hardness and Charpy impact energy. To this end, after quenching a 50CrMo4 steel three different induction tempering processes are carried out and the resulting properties are subsequently compared to a conventional tempering process. The results indicate that notch impact energy raises with increasing heating rates to tempering when realizing the same hardness of the samples. The positive effect of high heating rate on toughness is traced back to smaller carbide sizes, as well as smaller carbide spacing and more uniform carbide distribution over the sample.

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