Environmental Chamber Research Articles

The Collapse Mechanism of Slope Rill Sidewall under Composite Erosion of Freeze-Thaw Cycles and Water

The composite erosion of freeze-thaw and water flow on slope rills is characterized by periodicity and spatial superposition. When revealing the collapse mechanism of slope rill sidewalls under the composite erosion of freeze-thaw and water flow, it is necessary to fully consider the effect of water migration and its impact on the stability of the rill sidewall. In this paper, we placed the self-developed collapse test system in an environmental chamber to carry out model tests on rill sidewall collapse on slopes under the composite erosion of freeze-thaw and water flow. We utilized three-dimensional reconstruction technology and the fixed grid coordinate method to reproduce the collapse process of the rill sidewall and precisely locate the top crack. We obtained the relationship between the water content of the specimen and mechanical indexes through the straight shear test. The main conclusions are as follows: The soil structure of the rill sidewall is significantly affected by the freeze-thaw cycle, which benefits capillary action in the soil. One freeze-thaw cycle has the most serious effect on the soil structure of the rill sidewall, and the change in the moisture field is more intense after the soil temperature drops below zero. The friction angle of the soil increases with the number of freeze-thaw cycles and tends to stabilize gradually. The effect of the freeze-thaw cycle on the rate of change of the water content of the soil at each position of the wall can be accurately described by a logarithmic function. The expression of the two-factor interaction effect on the rate of change of water content of soil at each position of the rill sidewall can be accurately fitted. We propose a calculation system for locating cracks at the top of the rill sidewall and determining the critical state of instability and collapse of the rill sidewall during the process of freeze-thaw and water flow composite erosion. The results of this research can help improve the accuracy of combined freeze-thaw and water flow erosion test equipment and the development of a prediction model for the collapse of the rill sidewall under compound erosion. This is of great significance for soil and water conservation and sustainability.

High freezing sensitivity of legumes relative to other herbaceous species in northern temperate plant communities.

Reduced snow cover and increased air temperature variability are predicted to expose overwintering herbaceous plants to more severe freezing in some northern temperate regions. Legumes are a key functional group that may exhibit lower freezing tolerance than other species in these regions, but this trend has been observed only for non-native legumes. Our aim was to confirm if this trend is restricted to non-native legumes or whether native legumes in these regions also exhibit low freezing tolerance. First, we transplanted legumes (five non-native species and four native species) into either an old field (non-native) or a prairie (native) and used snow removal to expose the plots to increased soil freezing. Second, we grew plants in mesocosms (old field) and pots (prairie species) and exposed them in controlled environment chambers to a range of freezing treatments (control, 0, -5 or -10 °C) in winter or spring. We assessed freezing responses by comparing differences in biomass, cover and nodulation between freezing (or snow removal) treatments and controls. Among legume species, lower freezing tolerance was positively correlated with a lower proportion of nodulated plants and active nodules, and under controlled conditions, freezing-induced reductions in above-ground biomass were lower on average in native legumes than in non-native legumes. Nevertheless, both non-native and native legumes (except Desmodium canadense) exhibited greater reductions in biomass in response to increased freezing than their non-leguminous neighbours, both in controlled environments and in the field. These results demonstrate that both native and non-native legumes exhibit low freezing tolerance relative to other herbaceous species in northern temperate plant communities. By reducing legume biomass and nodulation, increased soil freezing could reduce nitrogen inputs into these systems.

An experimental investigation on the effect of lighting colour of localized radiant panel thermal comfort system

This study investigated the effect of different correlated colour temperature (CCT) lighting on perceived thermal comfort in a simulated domestic environment with radiant heating. A prototype with adjustable CCT lighting (4000K neutral, 1800K warm, 6500K cold) alongside electric radiant panels was installed in an environmental chamber set to 18 °C. The investigation involved sixty participants who each underwent 30-min exposure sessions to one of the lighting scenarios in a blinded setup, during which they filled out thermal comfort questionnaires at predetermined intervals. Overall, the findings revealed satisfactory comfort levels, with average global comfort votes of “good” and 82.32 % thermal acceptability, across scenarios. The radiant heating prototype successfully maintained thermal comfort in the less-conditioned space. Looking at the different lighting scenarios, the “warm” lighting initially provided the highest thermal comfort, aligning with the hue-heat hypothesis, with global comfort votes of 1.13, compared to 0.96 for “neutral” and 0.78 for “cold” after the first 10 min. However, differences became less pronounced over time. Contrary to hypotheses, the “cold” lighting scenario did not reduce comfort compared to “neutral”. Moreover, Participants indicated greater thermal satisfaction under “warm” lighting. Although changes in lighting CCT did not drastically alter thermal perceptions, they did have a subtle influence on comfort, particularly during the initial stages of the experiment. This finding suggests the need for further research into how visual and thermal comfort interactions can be optimized.

4D printing of lattice structures to test their behavior by repetitive shape processing cycles

This study thoroughly investigated the shape memory effects of 4D printed lattice structures influenced by repetitive shape processing cycles and materials variability. The structures were fabricated by an amorphous and semicrystalline type shape memory material (SMP) and subjected to time-temperature-based thermomechanical memory cycles. Shape programming and recovery characteristics for 4D printing were done inside an environmental chamber at a loading rate of 2 mm. min−1. The shape memory effects driven by SMP’s viscoelastic behavior and performance factors were studied by stress-free strain recovery experiments upon the interaction of thermal stimuli. The stress-free strain recovery analysis expressed, that the influence of repetitive cycles was exceptional and significant for both materials. Extensive investigation on shape memory reactive strain components (i.e., programming strain, residual strain, and thermal strain) reflected, with the increasing number of cycles, the shape recovery ratios of the first to fourth cycles increased from 82 → 100% of amorphous and 79 → 95% of semicrystalline SMP and then tend to stable thereafter. Contrarily, the shape fixity ratios of semicrystalline structures have shown a decreased tendency during the consecutive cycles from 100 → 80%. The successful execution of data-oriented shape processing cycles enhanced the potential of SMP-based lattice structures for their monotonous applications as intelligent devices. The time and temperature-dependent shape memory characteristics of repetitive cycles presented in this study are advantageous to model the viscoelastic behavior of such artful structures.

Experimental approach for characterizing the nonlinear, time and temperature‐dependent constitutive response of open‐cell polyurethane foams

AbstractElastomeric foams are composite materials comprising of a polymeric elastomer and interconnected gas‐filled pores, endowing them with exceptional compliance and the ability to undergo large, reversible deformations along with substantial volume change. These foams find extensive utility in contexts demanding compliance and compressibility, such as impact protection and cushioning, spanning a diverse range of applications. Changing temperature can dramatically alter foam stiffness, strength and deformation characteristics specifically around the material's glassy‐rubbery transition temperature (). With the aim of informing new constitutive model developments for elastomeric foams, we conducted a comprehensive series of large deformation, homogeneous compression and tension tests across strain rates from 10−2 s−1 to 100 s−1 and ambient temperatures ranging from −10°C to 50°C covering an even range around the material's of 20°C. To achieve precise control of ambient temperatures during mechanical testing, we constructed a custom‐designed environmental chamber for controlling the ambient temperature from −10°C to 50°C with a variation of less than 1°C. The obtained digital image correlation based stress‐strain data shows significant tension‐compression asymmetry as well as significant dependence on strain rate and ambient temperature, especially above and below the glass transition temperature. We provide full access to these data sets for the future development of rate‐ and temperature‐dependent constitutive models.

Formulation and Evaluation of Multipurpose Herbal Cream

The remedies used to improve a person's look are called herbal cosmetics. The current study set out to create a herbal cream with antifungal, antibacterial, anti-acne properties, as well as moisturizing, nourishing, lightening, and treating a range of skin conditions. Various unrefined medications were consumed, including Curcuma longa (turmeric rhizomes), Nirgundi (Vitex negundo Linn), Azadirachta Indica (neem leaves). The cream is prepared by slab Technique. Final samples underwent accelerated stability testing in an environmental chamber with a temperature of 25 ± 100C and a humidity of 60 ± 10% RH. It was discovered that every product was stable, showing no evidence of phase separation or color change. Additionally, a patch test was performed for sensitivity testing, and there was no indication of any allergic reactions or skin irritation. This work primarily it focuses on evaluating the microbiological quality of prepared cosmetics. To everyone's amazement, both formulations passed the microbiological limit tests according to international standards. It has been established that the formulation of herbal cosmetics is safe for use and can be applied as a barrier to protect skin.

Influence of progressive skin heating upon arterial blood pressure and tolerance to a simulated hemorrhage challenge following exercise in a cold environment

Purpose: Our aim was to examine the role of graded skin heating on blood pressure and tolerance to a simulated hemorrhage (lower body negative pressure, LBNP) in individuals who have exercised in a cold environment. We hypothesized that arterial blood pressure and tolerance would be lower during LBNP at higher skin temperatures. Methods: Following completion of a maximal exercise test, 7 participants (181±7 cm, 88.7±14 kg and 25±6 yrs) four exercise cold stress trials, comprising high intensity interval exercise on a cycle ergometer: 5 min at 60% VO2 max (1.9±0.4 L.O2.min) followed by 15 intervals of 60 sec at 88% peak power output (Wmax) (239±51 W) and 60 sec at 10% Wmax (27±6 W) in an environmental chamber (0°C 70% RH, Can-Trol International). Upon completion participants remained in the environmental chamber and underwent LBNP to pre syncope. Rectal (Tcore; °C) and mean skin (8 site average, Tskin; °C) temperatures, arterial blood pressure (Brachial Artery Auscultation, Suntech Tango; MAP; mmHg) and cutaneous vascular conductance (Laser Doppler Flowmetry, Perimed, CVC; AU/mmHg) were measured throughout. After the onset of LBNP, skin temperature was either kept cold (Cold), increased back to baseline (Normothermic), mildly heated (Warm) or severely heated (Hot) using a water perfused suit. LBNP tolerance was calculated via cumulative strain index (CSI). MAP, CVC, Tcore and Tskin were analyzed using a two-way ANOVA with repeated measures. CSI was compared between trials using a one-way ANOVA with repeated measures. Results: After exercise and immediately prior to LBNP, Tcore had increased from baseline 1.0±0.2°C and was not different between trials (P = 0.67), while Tskin was reduced from 33.2±0.5°C to 28.3±1.9°C (P = 0.001). MAP was elevated following exercise and immediately prior to LBNP in all trials relative to baseline, from 82±6 to 89±8mmHg. During LBNP, Tskin remained low in the Cold trial (27.6±1.2 °C) but was increased in all other trials (Normothermic: 32.3±0.8°C, Warm: 34.8±0.5°C and Hot: 36.4±0.7°C, all P < 0.05). MAP was different between trials (Trial Effect P = 0.022). MAP was lowest in the Hot trial whether expressed 3 min after the onset of LBNP or at 60% CSI (81±9mmHg and 78±7 mmHg, respectively) relative to the Cold (89±10 and 84±9 mmHg) Normothermic (86±8 and 82±6 mmHg) and Warm trials (86±7 and 80±6 mmHg), respectively. MAP was reduced at pre syncope in all trials (59±9mmHg). CVC was different between trials (Trial Effect, P < 0.0001). At 60% CSI, CVC was lowest in the Cold trial (0.17±0.11 AU/mmHg) but increased in the Normothermic (0.27±0.08 AU/mmHg) Warm (0.43±0.40 AU/mmHg) and Hot trials (0.60±0.43 AU/mmHg). LBNP tolerance was different between trials (Main Effect: P < 0.01). LBNP tolerance was lowest in the Cold trial (700 ± 346 mmHg*min) and was increased in Normothermic (856±399 mmHg*min) Warm (821±345 mmHg*min) and Hot trials (990±328mmHg*min). Conclusion: These preliminary findings suggest that skin warming >32°C increases tolerance to a simulated hemorrhagic challenge while further heating to ~36°C lowers arterial blood pressure without compromising LBNP tolerance in exercise cold stressed individuals. Supported by a RMACSM Grant. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Terahertz Nondestructive Evaluation of Corroding Multilayer Paint Stacks

This paper showcases terahertz nondestructive detection of corrosion buried underneath a multilayer paint stack. Periodically, during the accelerated corrosion protocol, samples are removed from the environmental chambers and characterized using terahertz pulse imaging. Analysis of the reflected waveforms indicates that corrosion leads to a decrease in the amplitude of the deconvoluted pulse, which reflects from the metallic layer. The decrease in amplitude results from a roughening of the metallic surface with corrosion. Surface roughness increases with corrosion, eventually leading to detachment of the multilayer paint stack from the substrate.

Age-Related Differences in the Onset of Cardiovascular Drift during Progressive Heat Stress (PSU HEAT Project)

As a result of the increasing duration, frequency, and severity of heat waves, older men and women are at greater risk for heat-related morbidity and mortality, with the majority of excess heat-related deaths attributed to increased cardiovascular strain associated with heat stress. PURPOSE: To (1) identify the environmental conditions (ambient temperature (Tdb) and humidity (rh)) at which heart rate (HR) begins to increase from equilibrium (i.e., the onset of cardiovascular drift), and (2) compare the environments in which cardiovascular drift begins relative to those at which a continuous rise in core temperature (Tc) is observed in young (Y), middle (MA), and older (O) adults. Methods: 26 Y (10 F; 19-29 yrs), 27 MA (21F; 40-64 yrs), and 19 O (7 F; 65-76 yrs) subjects were exposed to progressive heat stress in an environmental chamber at a low metabolic rate reflecting activities of daily living (159 ± 34 W) in a warm-humid (WH, 34-36°C, 50-80% rh) and a hot-dry (HD, 38°C-52°C, <30% rh) environment. The environmental thresholds above which HR and Tc equilibrium could no longer be maintained were identified. Results: In WH environments, sustained increases in HR preceded the Tc inflection point in Y (73±5% rh vs. 81±5% rh; p<0.001), MA (67±11% rh vs. 73±12% rh; p<0.001), and O adults (53±11% rh vs. 57±12% rh; p=0.041). Similarly, in HD (15-20% rh) environments, the onset of cardiovascular drift preceded the Tc inflection point in Y (47±3°C vs. 49±3°C; p=0.004), MA (44±4°C vs. 46±4°C; p<0.001), and O adults (42±5°C vs. 44±4°C; p=0.007). Additionally, in WH environments, cardiovascular drift began at lower combinations of Tdb and rh in O vs. Y subjects (34°C, 53±11% rh vs. 34°C, 73±5% rh; p<0.001) and O vs. MA adults (34°C, 53±11% rh vs. 34°C, 67±11% rh; p=0.008). In HD environments, cardiovascular drift began at lower environments in MA vs. Y (44±4°C, 18% rh vs. 47±3°C, 15% rh; p=0.044) and O vs. Y (42±5°C, 20% rh vs. 47±3°C, 15% rh; p=0.006) CONCLUSION: These data suggest that cardiovascular drift, indicating increases in cardiovascular strain, occurs during compensable heat stress at metabolic rates reflecting activities of daily living in Y, MA, and O adults. Further, there is an age-associated shift in the onset of cardiovascular drift toward lower combinations of Tdb and rh. SIGNIFICANCE/NOVELTY: These results are the first to identify the specific environmental conditions at which increases in cardiovascular strain occur across the adult age spectrum. These findings provide concrete data for the development of safety guidelines and policy decisions to mitigate cardiovascular-related morbidity and mortality during impending heat events. Supported by NIA Grant T32 AG049676 (to R.M.C.) and NIH Grant R01 AG067471 (to W.L.K.). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effects of gestational intermittent hypoxia on the autoresuscitation response following anoxia-induced apneas in neonatal mice

Introduction: Sudden infant death syndrome (SIDS) is the leading cause of death in infants from one month to one year of age. Smoking is a significant risk factor in SIDS, and smoking probably causes intermittent hypoxia in the fetus. Therefore, we modeled the effects of intermittent hypoxia during gestation in mice to determine if gestational intermittent hypoxia would adversely affect the capacity of neonatal mice to autoresuscitate effectively after exposure to anoxic stimuli. A degraded capacity to autoresuscitate could explain, in part, why infants born to mothers who smoke have an increased risk of dying from of SIDS. The primary objective of this study was to investigate the effects of intermittent gestational hypoxia on the autoresuscitation responses to anoxia-induced apneas in neonatal mice. Our hypothesis was that pups born to intermittently hypoxic dams would struggle more to recover from anoxic apneas — would have impaired cardiorespiratory responses to anoxic stress compared to the control mice born to dams exposed to room air during gestation. Methods: We studied C57Bl/6 dams who previously had one litter to prove their capability to breed and rear pups. Dams were placed in either an hypoxic or room air chamber at approximately embryonic day 5 (E5; fifth day of pregnancy). The fractional inspired oxygen concentration (FIO2) was reduced to 11% for 10 minutes, three times per hour, with 10 minute periods of 21% oxygen between them. Each hour of intermittent hypoxia was followed by an hour breathing 21% FiO2. The room air control chamber was maintained at a constant FIO2 of 21% with inflows of compressed air that mimicked the noise and flow of nitrogen in the hypoxic chamber. The dams spent the entirety of their pregnancies in the environmental chambers. Once the pups were delivered, the cages were placed in room air, housing environments. The pups were allowed to stay with their mothers until approximately post-natal day 8 (P8). On P8, each pup was fitted into a head out plethysmograph to measure respiratory flow using a pneumotachograph. We recorded respiratory activity, ECG activity, and body movements (using a piezo sensitive film). The pups were maintained at ~34 degrees C in the pneumotachographic chamber. We measured the highest respiratory rate, highest heart rate, longest apnea, gasp latency, mean heart rate recovery, and mean respiratory rate recovery. Results: The mean heart rate recovery and mean longest apnea (in seconds) doubled in the mice exposed to gestational intermittent hypoxia compared to pups born to dams exposed to room air during gestation. The mean heart rate recovery and mean longest apnea in gestationally hypoxic pups was 41.0 +/- 13.7 seconds and 22.05 +/- 12.0 seconds, respectively. The mean heart rate recovery and mean longest apnea in normal, room air-exposed pups was 22.4 +/- 11.1 seconds and 10.3 +/- 7.0 seconds, respectively. The longest apnea in gestational intermittent hypoxic pups was significantly longer than in control pups (53.0 +/- 13.7 seconds and 19.1 +/- 15.0 seconds). Pups exposed to gestational intermittent hypoxia also had increased mean respiratory rate recovery times and gasp latency times (start of apnea until the first gasp). The average body weight of hypoxic pups was 4.3 grams while the average body weight for the normal pups was 4.9 grams. Conclusion: Gestational intermittent hypoxia was associated with delayed and prolonged the autoresuscitation responses in neonatal mice following acute anoxic exposure. We hypothesize that this is due to changes in the brain’s serotonin system. We are investigating how intrauterine hypoxia may decrease serotonin and serotonergic signaling pathways as changes in serotonergic function may degrade the capacity of mice to autoresuscitate following anoxic gas exposure. NIH/NICHD. HD100823 and NIH/NICHD. HD 107060. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Impact of anaerobic fitness on performance and physiology during simulated firefighting tasks

BACKGROUND: Firefighting requires high levels of physical fitness and due to abnormal work schedules, on-duty training is necessary to meet occupational demands. However, firefighters are concerned with possible impairments in occupational readiness from various types of on-shift exercise. It has yet to be determined if higher levels of strength prove protective against potential decrements in readiness following on-shift exercise. Therefore, this study sought to determine if maximal strength influences occupational performance and physiological responses during simulated firefighting tasks (SFT) following different types of acute exercise. METHODS: 32 participants (17M/15F; 25.2 ± 4.1 yrs; 173.8 ± 9.8 cm; 75.6 ± 13.2 kg) completed 3-repetition max bench press (MBP), squat (MBS), deadlift (MDL), and vertical jump (VJ), and 3 experimental trials: resistance exercise (RE), aerobic exercise (AE), and rested control (CON) followed by the SFT (4 rounds of 10 deadlifts (using 85 or 135lbs) and a 0.15-mile carry with a 40lb-sandbag) in an environmental chamber (35°C; 50% humidity). Time to complete (TTC), rating of perceived exertion (RPE), and blood lactate concentrations (BLC) were analyzed. Participants were split into tertiles based on low, moderate, and high strength and power. Two-way ANOVAs were used to compare fitness level by exercise condition. RESULTS: There was a main effect of MDL on TTC (Low MDL: 1395 ± 248; Moderate MDL: 1135 ± 179; High MDL: 1007 ± 176; p < 0.01). Low DL participants had higher TTC compared to Moderate DL regardless of exercise type (ps < 0.02). Additionally, Moderate MDL participants had higher TTC compared to High MDL regardless of exercise type (ps < 0.01). There was a main effect of MBP on RPE (Low MBP: 14.7 ± 1.6; Moderate MBP: 13.7 ± 1.9; High MBP: 13.1 ± 1.6; p < 0.01). Participants with a High MBP had a lower RPE compared to Low MBP regardless of exercise type (ps < 0.01). There was a main effect of MBS on RPE (Low MBS: 14.7 ± 1.7; Moderate MBS: 13.5 ± 2.0; High MBS: 13.3 ± 1.5; p < 0.01). Participants with a Low MBS had higher RPE compared to Moderate and High MBS regardless of exercise type (ps < 0.02). There was a main effect of MDL on RPE (Low MDL: 14.3 ± 1.9; Moderate MDL: 14.2 ± 2.0; High MDL: 13.3 ± 1.6; p = 0.03). Participants with a High MDL had a lower RPE compared to Low MDL regardless of exercise type (ps = 0.03). There was an effect of MDL on BLC (Low MDL: 6.2 ± 3.2; Moderate MDL: 8.6 ± 3.0; High MDL: 8.8 ± 3.7; p < 0.01). Participants with a Low MDL had lower BLC compared to Moderate and High MDL participants regardless of exercise type (ps < 0.02). There was a main effect of VJ on BLC (Low VJ: 5.9 ± 2.7; Moderate VJ: 8.8 ± 2.9; High VJ: 8.9 ± 3.9; p < 0.01). Low VJ participants had lower BLC compared to Moderate and High VJ regardless of exercise type (ps < 0.02). All other interaction and main effects of TTC or physiological variables were not different based on fitness (ps > 0.15). CONCLUSIONS: These findings suggest performance and physiological responses during SFT differ based on anaerobic fitness (strength and power). Specifically, those with greater strength and power completed SFT faster, with lower perceived exertion and lactate accumulation. However, these differences in strength did not influence how participants responded after each type of exercise (RE, AE, CON). These findings emphasize the importance of strength training and provide support for using strength assessments to ensure occupational readiness. This project has no funding sources to disclose. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The impact of training status on firefighter task performance after acute exercise

Background: Though on-shift exercise provides firefighters structured time to maintain fitness levels needs for their job; many are concerned on-shift exercise may impair their readiness. It also remains unclear if their current fitness level is protective of potential exercise-induced decrements. Therefore, we aimed to determine if aerobic fitness and body composition impact occupational performance and physiological stress after acute exercise. Methods: 32 participants (17M/15F; 25.2 ± 4.1 yrs; 173.8 ± 9.8 cm; 75.6 ± 13.2 kg; 23.3 ± 7.4% body fat) completed 2 visits assessing fitness (VO2peak and %body fat (%BF)), and 3 experimental trials: resistance exercise (RE), aerobic exercise (AE), and rested control (CON). Each trial was followed by an occupational task assessment (OTA; 4 rounds of 10 deadlifts (set to 85 or 135lbs) and a 0.15-mile 40lb-sandbag carry) in an environmental chamber (35°C; 50% humidity). Time to complete (TTC), blood lactate concentrations (BLC), and core temperature (CT) were assessed. Participants were split into tertiles based on high, moderate, and low VO2peak and %BF. Two-way ANOVAs were used to compare fitness level by exercise condition. RESULTS: There was a main effect of VO2peak on TTC (High VO2: 1094 ± 235; Moderate VO2: 1120 ± 200; Low VO2: 1365 ± 263 sec; p < 0.01). High VO2peak participants had a shorter TTC compared to moderate or low VO2max regardless of exercise prior (ps < 0.01). There was a main effect of VO2peak on CT (High VO2: 38.1 ± 0.6; Moderate VO2: 38.2 ± 0.6; Low VO2: 38.4 ± 0.5°C; p < 0.01). High VO2peak participants had a lower CT during the OTA compared to low VO2peak regardless of exercise prior (p < 0.01). There was a main effect of %BF on TTC (High %BF: 1029 ± 150; Moderate %BF: 1098 ± 210; Low %BF: 1399 ± 259 sec; p < 0.001). High %BF participants had a longer TTC compared to average or low %BF regardless of exercise prior (ps < 0.01). There was a significant main effect of %BF on BLC (High %BF: 6.6 ± 2.8; Moderate %BF: 7.6 ± 3.0; Low %BF: 9.9 ± 3.8 mMol/L; p < 0.01). Low %BF participants had lower BLC after the OTA compared to high %BF regardless of exercise prior (p < 0.01). CT were significantly higher following AE compared to RE and CON (AE: 38.7 ± 0.3; RE: 38.5 ± 0.5; CON: 37.6 ± 0.4°C; p < 0.01). All other interaction and main effects of TTC or physiological stress variables were not significantly different based on fitness (VO2peak and %BF; ps > 0.18). CONCLUSIONS: Our findings suggest fitness (VO2peak and %BF) impacts time to complete and physiological stress during occupational tasks. However, fitness did not influence the response to occupational tasks differently based on if acute exercise (aerobic or resistance) was performed beforehand. These findings contribute to our understanding of the impact of acute on-shift exercise methods and provide relevant metrics of fitness related to firefighter occupational performance. FUNDING DISCLOSURE: There are no funding sources to disclose. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Metabolic dysfunction in the myocardium three months after exertional heat stroke in mice

In humans, exposure to heat stroke has proven to be a risk factor for development of cardiovascular disease later in life. We hypothesized that exposure to exertional heat stroke (EHS) would result in the development of similar long-term cardiac disease in mice. In this study we followed mice for three months after EHS, using ultrasound imaging of the heart, metabolomics and histological analysis of ventricular tissue and biomarker analysis after 4 weeks of recovery. Methods: Mice were instrumented with temperature telemetry devices and were trained to run on forced running wheels using an incremental exercise protocol. EHS mice ran in an temperature elevated environmental chamber; females 37.5°C; males 34°C; whereas, matched exercise control mice (EXC) ran in 22-23°C. Running stopped when EHS mice reached symptom limitation (unconsciousness). The mice were followed for 12 wks post EHS, with two ultrasound measures at 2 and 10 wks of recovery. At the end of the study, mice were anesthetized, a blood sample drawn, and ventricular tissue collected for metabolomics. RESULTS: Male but not female EHS mice gained ~10% greater body mass compared to EXC over the course of recovery ( P<0.01). Hearts from male but not female EHS mice exhibited elevations in heart mass per tibia length ( P<0.01). At three months, metabolomics in male EHS hearts revealed significant elevations in glucose and glucose metabolites and significant decreases in acylcarnitines consistent with a metabolic shift toward glucose and away from lipid metabolism. In contrast, female hearts exhibited fewer abnormalities but with significant elevations in lipid and arachidonate metabolites. At two weeks post, there were no differences in male ultrasound measures between EHS and EXC mice but in females there was a reduced posterior wall velocity ( P=0.012) and a trend towards narrower posterior wall thickness ( P= 0.06) . Between 2 and 12 wks post EHS, there were significant elevations in fractional shortening in males ( P<0.05) and elevations in posterior wall velocity ( P<0.01). In contrast, females exhibited significant reductions posterior wall velocity. From blood samples, male EHS mice had increased HDL and females exhibited decreased HDL (p<0.01 in both). LDL increased only in males P<0.05. Vascular adhesion molecules sICAM ( P<0.01) and Pecam1 ( P<0.01) were significantly decreased in EHS males and females and e-Selectin was decreased in EHS males only ( P<0.001). Total serum protein was significantly reduced in both male and females ( P<0.01). Male EHS mice also exhibited significant elevations in white blood cell count and total lymphocytes ( P=0.01) suggesting ongoing activation of the immune system . CONCLUSIONS: In this controlled preclinical model of EHS, both male and female mice exhibited long-lasting cardiovascular and systemic disorders that could account for the lingering incidence of cardiovascular disease and poor overall health in heat stroke victims. Supported by US Army Med. Research and Devel. Command BA180078 and the BK and Betty Stevens Endowment. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Critical Environmental Limits for Middle-Aged Adults (PSU HEAT Project)

Critical environmental limits are the combinations of temperature and humidity above which heat balance cannot be maintained for a given metabolic heat production. Our lab has previously established critical environmental limits for young and older adults; however, these limits have yet to be established for middle-aged adults. The purpose of the present study was to (1) identify critical environmental limits for middle-aged adults, and (2) investigate age-related differences in critical environmental limits at a low metabolic rate reflecting activities of daily living across the adult age spectrum. Twenty-six older (71±5 yrs, 14F/12M), 36 middle aged (51±9 yrs, 26F/10M), and 27 young adults (23±3 yrs, 13F/14M) were exposed to progressive heat stress in a controlled environmental chamber during minimal activity. Progressive heat stress for the determination of critical environmental limits comprised either (1) constant dry-bulb (Tdb) temperature at 34°C with progressively increasing water vapor pressure (Pa) by 1 mmHg every 5 minutes (Pcrit trial), or (2) constant Pa at 12 mmHg with progressively increasing Tdb by 1°C every 5 minutes (Tcrit trial). Critical environmental limits in hot-dry environments were higher in young compared to middle aged (49.3±2.3 °C vs. 45.4±4.0 °C; p = 0.002) and older adults (49.3±2.3°C vs. 43.2±4.0°C; p < 0.001), but were not different between middle aged and older adults (45.4±4.0 °C vs. 43.2±4.0°C; p = 0.125). Critical environmental limits in warm-humid conditions were lower in older adults compared to young (23.1±6.1 mmHg vs 31.7±1.5 mmHg, p < 0.001) and middle aged (23.1±6.1 mmHg vs 29.0±5.1 mmHg, p = 0.004), but were not different between the young and middle aged (31.7±1.5 mmHg vs 29.0±5.1 mmHg, p = 0.220). Age was correlated with critical environmental limits in Tcrit (R2 = 0.34; p < 0.001) and Pcrit (R2 = 0.51; p < 0.001) trials based on linear and curvilinear regression, respectively. Critical environmental limits for middle aged adults performing minimal activity in warm-humid and hot-dry environments are intermediate to young and older adults. These data demonstrate an age-related decline in critical environmental limits that can be characterized by linear decline in hot-dry environments and by curvilinear decline in warm-humid environments. Supported by NIH Grant R01 AG067471. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Influence of thermal fatigue cycles on concrete cold joints

Mass concrete structures in northern climates experience extreme oscillations in temperature each year. These fluctuating conditions incur large thermal stresses, which are of particular concern at cold joint locations. To better understand the behaviour of cold joints subjected to these thermal fatigue cycles, an experimental program was conducted at the University of Manitoba, focusing on the performance of concrete cylinders with concrete-to-concrete interfaces. Specimens were prepared with joints oriented either horizontally to evaluate direct tensile performance or at a 35°, 40°, or 45° angle for slant shear. These cylinders were then installed in specially designed vertical translation-restricting frames and placed in an environmental chamber, where they were subjected to temperatures cycling between −25 °C and 40 °C. Static testing after 50, 150, and 250 cycles was performed to ascertain remaining bond strength. An increase in performance of approximately 20 % was observed in direct tension after 50 cycles, followed by a subsequent decrease. In general, the thermal fatigue cycles did not appear to detrimentally impact bond strength after 250 cycles in both direct tension and slant shear. Additionally, interface friction demonstrated no meaningful trend between specimens that had experienced zero to 250 cycles, remaining relatively consistent with their corresponding roughness level defined in the Canadian Design of Concrete Structures code, and bond cohesion appeared to follow a similar trend to mean direct tensile bond strength results.

Rhinoconjunctivitis severity induced by cat exposure influences early and late asthmatic responses: Evidence from an environmental exposure chamber.

The impact of allergic rhinoconjunctivitis on the early (EAR) and late asthmatic response (LAR) has yet to be assessed during optimal allergen exposure conditions. We aimed to assess predictive factors of the EAR and LAR and to evaluate the relation between rhinitis, conjunctivitis and asthma induced by cat allergen exposure in an environmental exposure chamber (EEC). Data from two cohort studies involving asthmatic patients with cat allergy who performed a cat allergen exposure challenge in ALYATEC EEC were analysed. Spirometry, visual analogue scale (VAS) for asthma, VAS for rhinitis, Total Nasal Symptoms Score, Total Ocular Symptoms Score (TOSS), Rhinoconjunctivitis Total Symptoms Score and Abelson score were used to assess asthma, rhinitis and conjunctivitis during and after exposure. An EAR occurred in 65.1% of patients, 32.1% of whom had a LAR. The diameter of the prick test to cat allergens and non-specific bronchial hypersensitivity level were independent risk factors for EAR (p < .05). No independent risk factors for LAR were identified. Rhinoconjunctivitis severity during exposure correlated with the asthma VAS during EAR and LAR (p < .05). Allergen exposure time needed to trigger an EAR correlated with the Abelson score during exposure (p < .05). The asthma VAS and TOSS during exposure correlated with faster LAR occurrence (p < .05). Prick test size and non-specific bronchial hypersensitivity level were confirmed as independent predictive factors of EAR during allergen exposure in an EEC. This study demonstrated the relation between the severity of rhinitis, conjunctivitis and asthma induced by allergen exposure for both EAR and LAR.

Mixed-Method Heat Acclimation Induces Heat Adaptations in International Triathletes Without Training Modification

PurposeHeat acclimation (HA) kinetics often necessitates that the intervention is conducted in the weeks immediately preceding athletic competitions, potentially interfering with a training taper. Therefore, we investigated the efficacy of a mixed-method HA protocol, superimposed over planned external training loads, during the 3-weeks prior to the 2022 U23 World Triathlon Championships.MethodsSix international triathletes completed 8 pre-competition HA sessions (5 active: running/cycling, 3 passive: hot water immersion [HWI]), across 2-weeks. Outdoor high-intensity training sessions were followed by 30–60 min HWI, whilst low-intensity cycling/running sessions were completed in a hot, humid environmental chamber. To assess heat adaptations, participants completed three 25 min heat stress tests (HST) involving iso-speed treadmill running (session 1 = HST1, session 5 = HST2, and session 8 = HST3). Physiological, haematological and wellbeing monitoring were conducted throughout HA.ResultsReduced heart rate (~ − 6 beats/min) was observed within HST3 (P = 0.01, ηp2 = 0.64), versus HST1 and HST2. No changes in core temperature were observed across HSTs (P = 0.055,ηp2 = 0.44). Sweat sodium concentration was lower by HST2 at the arm (− 23 ± 16 mmol/L, P = 0.02) and back (− 27 ± 17 mmol/L, P = 0.01). White blood cell count reduced from baseline to the end of HA (P = 0.02, ηp2 = 0.27), but no changes were found in any other haematological markers (all P > 0.05). Perceptual wellbeing measures did not change across HA (all P > 0.05).ConclusionBy HST3, seven prior mixed-method HA sessions improved markers of heat adaptation (exercising HR and sweat concentration) within international triathletes. Mixed-method HA may be implemented without modifying training load, with no apparent detrimental effects on athlete health or training stress markers.

Efficacy ofhydroxypropyl-guar dropsin improving tear film index and ocular surface dynamicsusing two treatment methods under a controlled desiccating environment.

This study aimed to assess the efficacy of hp-guar eye drops on tear film index and ocular surface dynamics under desiccating conditions using protection and relief treatment modalities. The 12 normal, non-dry eye participants were subjected to adverse environmental conditions using a Controlled Environment Chamber (CEC) where the relative humidity (RH) was 5% and the ambient temperature was 21°C. The participants were screened for ocular symptoms, tear osmolarity, ocular surface temperature (OST), tear production using the Ocular Surface Disease Index questionnaire (OSDI), OcuSense TearLab Osmometer, FLIR System ThermaCAM P620, and Schirmer strips. Tear production was calculated by the Tear Function Index test (TFI). The mean tear film osmolarity decreased significantly from 296mOsm/L at 40% RH to 285mOsm/L at 5% RH (p = 0.01). Conflicting responses were seen for osmolarity in protection and relief. Mean tear osmolarity was significantly higher in the protection method in comparison to the relief method (p = 0.005). The mean TFI increased from 557 at 40% to 854 at 5% (p = 0.02). A significant increase in TFI was observed in the relief method in comparison with both 40% (p = 0.001) and 5% (p = 0.04). In the relief method, the mean TFI score went up to 1139 when hp-guar was installed. A significant improvement in ocular comfort was experienced in both the protection (p = 0.041) and relief (p = 0.010) methods at 5% RH. The instillation of hp-guar drops in the relief method resulted in a significant reduction in OST. The mean OST dropped to 33.01 ºC, significantly lower than the recorded OST for both normal (p = 0.040) and dry (p = 0.014) environmental conditions. Hp-guar drops significantly improve tear film parameters under a desiccating environment, however, tear film parameters respond differently to the management modalities. In the protection method, tear film osmolarity was protected against a dry environment, while in the relief mode, an improvement in tear production and a decrease in ocular surface temperature were seen. Hp-guar performance could be maximized for the management of exposure to adverse environments by using a treatment protocol that targets the most affected parameters in each group of patients. Using CEC has the potential to provide researchers with a readily available method to evaluate the efficiency of tear supplementation.

Environmental Chamber Characterization of an Ice Detection Sensor for Aviation Using Graphene and PEDOT:PSS.

In the context of improving aircraft safety, this work focuses on creating and testing a graphene-based ice detection system in an environmental chamber. This research is driven by the need for more accurate and efficient ice detection methods, which are crucial in mitigating in-flight icing hazards. The methodology employed involves testing flat graphene-based sensors in a controlled environment, simulating a variety of climatic conditions that could be experienced in an aircraft during its entire flight. The environmental chamber enabled precise manipulation of temperature and humidity levels, thereby providing a realistic and comprehensive test bed for sensor performance evaluation. The results were significant, revealing the graphene sensors' heightened sensitivity and rapid response to the subtle changes in environmental conditions, especially the critical phase transition from water to ice. This sensitivity is the key to detecting ice formation at its onset, a critical requirement for aviation safety. The study concludes that graphene-based sensors tested under varied and controlled atmospheric conditions exhibit a remarkable potential to enhance ice detection systems for aircraft. Their lightweight, efficient, and highly responsive nature makes them a superior alternative to traditional ice detection technologies, paving the way for more advanced and reliable aircraft safety solutions.

Fractal Characteristics of Natural Fiber-Reinforced Soil in Arid Climate Due to Cracking

Fractal geometry is a geometry that focuses on irregular geometric forms and can quantitatively describe rough and uneven surfaces and interfaces. As the main material for making natural fiber geotextile, rice straw fiber can reduce the direct impact of rainfall on soil and reduce the intensity of hydraulic erosion. This study investigates whether the use of rice straw fiber as an additive to reinforce arid soil can inhibit moisture evaporation and prevent cracking. Samples with different fiber contents added (0%, 1%, 2%, and 4%) are placed in an environmental chamber to simulate the effects of an arid climatic condition and control the temperature and humidity levels. The cracking process of the samples is recorded by using a digital camera, and the parameters of the evaporation and cracking processes are quantitatively examined through digital image processing. The results show that all of the samples with fiber have a higher residual water content and can retain 31.4%, 58.5%, and 101.9% more water than without the fibers, respectively. Furthermore, both the primary and secondary cracks as well as crack networks are inhibited in samples with a higher fiber content, that is, 2% or 4% fiber contents. The samples reinforced with fiber also have a smaller crack ratio. Compared with the samples without straw fiber, the final crack ratio of the samples with 1%, 2%, and 4% fiber is reduced by 8.05%, 24.09%, and 35.01% respectively. Finally, the final fractal dimensions of the cracks in samples with fiber contents are also reduced by 0.54%, 5.50%, and 6.40% for the samples with 1%, 2%, and 4% fiber, respectively. The addition of natural fiber as an additive to reduce evaporative cracking in soil can: (1) reduce the soil porosity; (2) enhance the binding force between the soil particles; and (3) block the hydrophobic channels. Therefore, the addition of rice straw fiber to soil can effectively reduce soil evaporation and inhibit soil cracking.