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1.
Sex difference in initial thermoregulatory response to dehydrated exercise in the heat.
Giersch, GEW, Morrissey, MC, Butler, CR, Colburn, AT, Demarais, ZS, Kavouras, SA, Jay, O, Charkoudian, N, Casa, DJ
Physiological reports. 2021;(14):e14947
Abstract
Although it is well established that dehydration has a negative impact on thermoregulation during exercise in the heat, it is unclear whether this effect of dehydration is different between men and women, or across the phases of the menstrual cycle (MC). Twelve men and seven women (men: 20 ± 2 years, 70.13 ± 10.5 kg, 173.4 ± 6.0 cm, 54.2 ± 8.6 ml kg-1 min-1 ; women: 20 ± 2 years, 57.21 ± 7.58 kg, 161 ± 5 cm, 40.39 ± 3.26 ml kg-1 min-1 ) completed trials either euhydrated (urine specific gravity, USG ≤ 1.020, Euhy) or dehydrated (USG > 1.020, Dehy). Trial order was randomized and counterbalanced; men completed two trials (MEuhy and MDehy) and women completed four over two MC phases (late follicular: days 10-13, FDehy, FEuhy; midluteal: days 18-22, LDehy, LEuhy). Each trial consisted of 1.5 h, split into two 30 min blocks of exercise (B1 and B2, 15 min at 11 W/kg & 15 min at 7 W/kg) separated by 15 min rest in between and after. Rectal temperature (Tre ) was measured continuously and estimated sweat loss was calculated from the body mass measured before and after each block of exercise. When dehydrated, the rate of rise in Tre was greater in women in the first block of exercise compared to men, independently of the MC phase (MDehy: 0.03 ± 0.03°C/min, FDehy: 0.06 ± 0.02, LDehy: 0.06 ± 0.02, p = 0.03). Estimated sweat loss was lower in all groups in B1 compared to B2 when dehydrated (p < 0.05), with no difference between sexes for either hydration condition. These data suggest that women may be more sensitive to the negative thermoregulatory effects of dehydration during the early stages of exercise in the heat.
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2.
Skipping Breakfast for 6 Days Delayed the Circadian Rhythm of the Body Temperature without Altering Clock Gene Expression in Human Leukocytes.
Ogata, H, Horie, M, Kayaba, M, Tanaka, Y, Ando, A, Park, I, Zhang, S, Yajima, K, Shoda, JI, Omi, N, et al
Nutrients. 2020;(9)
Abstract
Breakfast is often described as "the most important meal of the day" and human studies have revealed that post-prandial responses are dependent on meal timing, but little is known of the effects of meal timing per se on human circadian rhythms. We evaluated the effects of skipping breakfast for 6 days on core body temperature, dim light melatonin onset, heart rate variability, and clock gene expression in 10 healthy young men, with a repeated-measures design. Subjects were provided an isocaloric diet three times daily (3M) or two times daily (2M, i.e., breakfast skipping condition) over 6 days. Compared with the 3M condition, the diurnal rhythm of the core body temperature in the 2M condition was delayed by 42.0 ± 16.2 min (p = 0.038). On the other hand, dim light melatonin onset, heart rate variability, and clock gene expression were not affected in the 2M condition. Skipping breakfast for 6 days caused a phase delay in the core body temperature in healthy young men, even though the sleep-wake cycle remained unchanged. Chronic effects of skipping breakfast on circadian rhythms remain to be studied.
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3.
Heat exhaustion.
Kenny, GP, Wilson, TE, Flouris, AD, Fujii, N
Handbook of clinical neurology. 2018;:505-529
Abstract
Heat exhaustion is part of a spectrum of heat-related illnesses that can affect all individuals, although children, older adults, and those with chronic disease are particularly vulnerable due to their impaired ability to dissipate heat. If left uninterrupted, there can be progression of symptoms to heatstroke, a life-threatening emergency. Signs and symptoms of heat exhaustion may develop suddenly or over time. Exposure to a hot environment for a prolonged period and performing exercise or work in the heat can overwhelm the body's ability to cool itself, causing heat exhaustion. Heat exhaustion can be worsened by dehydration due to inadequate access to water or insufficient fluid replacement. Heat exhaustion can be managed by the immediate reduction of heat gain by discontinuing exercise and reducing radiative heat source exposure. The individual should be encouraged to drink cool fluids and remove or loosen clothing to facilitate heat loss. In more extreme situations, more aggressive cooling strategies (e.g., cold shower, application of wet towels) to lower core temperature should be employed. Heat-related illnesses such as heat exhaustion can be prevented by increasing public awareness of the risks associated with exposure to high temperatures and prolonged exercise.
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4.
Effect of branched chain amino acids on perioperative temperature, glucose level and fat metabolism in patients with gastrointestinal tumors.
Wen, LY, Zhang, YS, Zhou, X, Li, G, Hu, CY, Li, Y, Jin, LJ
Journal of biological regulators and homeostatic agents. 2018;(2):357-363
Abstract
This study aimed to investigate the effect of branched chain amino acids (BCCAs) on perioperative temperature, glucose and fat metabolism in patients with gastrointestinal tumors. Fifty-six patients undergoing gastrointestinal tumor surgery were included in the study and randomly divided into two groups of 28 patients each: an experimental and a control group. During surgery, the experimental group received 5.64mL·Kg-1·h-1(4KJ·Kg-1·h-1) of BCCAs intravenously, through an infusion pump, and the control group received an equal volume of NaCl 0.9%. Vital signs were continuously monitored during the operation. Nasopharynx temperature levels of glucose, insulin, free fatty acid and ketone bodies in the blood were determined 30 min before anesthesia (t 0), after anesthesia and before surgery (t 1), 30 min after the start of surgery (t 2), 2 h after start of surgery (t 3) and 1 h after the end of surgery (T4). Patients shivering intensity (Wrench grading) and pain degree [Visual analogue scale (VAS)]) were estimated 1 h after the endotracheal tube was removed. Nasopharynx temperature was decreased (p less than 0.05) in both groups after anesthesia induction, while 1 h after the tube was removed it was higher in the experimental group than the control group (p less than 0.05); compared with pre-surgery values, blood glucose levels were increased during surgery in both groups, but the experimental group had a lower increasing trend compared to the control group, though without statistical significance (p>0.05). Insulin levels were significantly different between the two groups at all time-points during surgery (p less than 0.05). However, the rising trend of the experimental group was more dramatic during the period from t 0 to t 3. One hour after surgery (t 4), the insulin levels varied, but still at higher levels than pre-surgery, with a significant difference (p less than 0.05); levels of free fatty acids had a downward trend in both groups, and levels in the experimental group continued to decline until 1 h after surgery. Patients who received branched chain amino acids had less temperature decrease during surgery. Moreover, blood glucose levels were not increased, which limits fat mobilization and leads to production of ketone bodies, reduces the shivering and its intensity after surgery.
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5.
Conjunctival Tear Layer Temperature, Evaporation, Hyperosmolarity, Inflammation, Hyperemia, Tissue Damage, and Symptoms: A Review of an Amplifying Cascade.
McMonnies, CW
Current eye research. 2017;(12):1574-1584
Abstract
PURPOSE This review examines the evidence for and significance of pre-conjunctival tear temperature being higher than central pre-corneal temperature with associated more rapid evaporation of warmer pre-conjunctival tears in normal eyes but especially in hyperemic dry eye disease. METHODS PubMed searches using the terms "evaporative dry eye," "conjunctival tear evaporation," "tear evaporation," and "dry eye conjunctival hyperemia" indicated 157, 49, 309, and 96 potentially relevant papers, respectively. Selections from these lists were the basis for examining the significance of the evidence relevant to pre-conjunctival tear layer temperature and evaporation. RESULTS There is evidence supporting an amplifying inflammatory and para-inflammatory hyperemia dry eye cascade, which increases pre-conjunctival tear temperature and the risk of accelerated pre-conjunctival tear evaporation with exacerbated osmolarity elevation and inflammation. Dry eye cascade amplification is consistent with increases in symptoms and inflammatory as well as para-inflammatory hyperemia toward the end of the waking day. Apart from age-related conjunctivochalasis, dry eye-related conjunctival epithelial cell pathology including reduced goblet cell numbers and associated mucin deficiency, squamous metaplasia, and increased separation of cell layers could help to destabilize tears and facilitate evaporation as part of an amplifying cascade. CONCLUSIONS Greater difficulty in assessing conjunctival tear break up may contribute to an underestimation of a role for faster evaporation of pre-conjunctival tears in dry eye disease and help explain any non-correspondence between symptoms and corneal signs of dry eye disease. Success with anti-inflammatory therapies for dry eye disease may be at least partly due to reductions in conjunctival hyperemia and deamplification of evaporative cascades. Conjunctival inflammatory hyperemia in other diseases may contribute to accelerated pre-conjunctival tear evaporation and the risk of tear-deficiency- associated exacerbation of those diseases including impaired responses to therapeutic approaches to them. Similarly, postsurgical conjunctival inflammation and associated acceleration of tear evaporation could contribute to delayed wound healing.
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6.
A Comparison of Mixed-Method Cooling Interventions on Preloaded Running Performance in the Heat.
Stevens, CJ, Bennett, KJ, Sculley, DV, Callister, R, Taylor, L, Dascombe, BJ
Journal of strength and conditioning research. 2017;(3):620-629
Abstract
Stevens, CJ, Bennett, KJM, Sculley, DV, Callister, R, Taylor, L, and Dascombe, BJ. A comparison of mixed-method cooling interventions on preloaded running performance in the heat. J Strength Cond Res 31(3): 620-629, 2017-The purpose of this investigation was to assess the effect of combining practical methods to cool the body on endurance running performance and physiology in the heat. Eleven trained male runners completed 4 randomized, preloaded running time trials (20 minutes at 70% V[Combining Dot Above]O2max and a 3 km time trial) on a nonmotorized treadmill in the heat (33° C). Trials consisted of precooling by combined cold-water immersion and ice slurry ingestion (PRE), midcooling by combined facial water spray and menthol mouth rinse (MID), a combination of all methods (ALL), and control (CON). Performance time was significantly faster in MID (13.7 ± 1.2 minutes; p < 0.01) and ALL (13.7 ± 1.4 minutes; p = 0.04) but not PRE (13.9 ± 1.4 minutes; p = 0.24) when compared with CON (14.2 ± 1.2 minutes). Precooling significantly reduced rectal temperature (initially by 0.5 ± 0.2° C), mean skin temperature, heart rate and sweat rate, and increased iEMG activity, whereas midcooling significantly increased expired air volume and respiratory exchange ratio compared with control. Significant decreases in forehead temperature, thermal sensation, and postexercise blood prolactin concentration were observed in all conditions compared with control. Performance was improved with midcooling, whereas precooling had little or no influence. Midcooling may have improved performance through an attenuated inhibitory psychophysiological and endocrine response to the heat.
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7.
The impact of morning light intensity and environmental temperature on body temperatures and alertness.
Te Kulve, M, Schlangen, LJM, Schellen, L, Frijns, AJH, van Marken Lichtenbelt, WD
Physiology & behavior. 2017;:72-81
Abstract
Indoor temperature and light exposure are known to affect body temperature, productivity and alertness of building occupants. However, not much is known about the interaction between light and temperature exposure and the relationship between morning light induced alertness and its effect on body temperature. Light intensity and room temperature during morning office hours were investigated under strictly controlled conditions. In a randomized crossover study, two white light conditions (4000K, either bright 1200lx or dim 5lx) under three different room temperatures (26, 29 and 32°C) were investigated. A lower room temperature increased the core body temperature (CBT) and lowered skin temperature and the distal-proximal temperature gradient (DPG). Moreover, a lower room temperature reduced the subjective sleepiness and reaction time on an auditory psychomotor vigilance task (PVT), irrespective of the light condition. Interestingly, the morning bright light exposure did affect thermophysiological parameters, i.e. it decreased plasma cortisol, CBT and proximal skin temperature and increased the DPG, irrespective of the room temperature. During the bright light session, subjective sleepiness decreased irrespective of the room temperature. However, the change in sleepiness due to the light exposure was not related to these physiological changes.
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8.
Ice ingestion with a long rest interval increases the endurance exercise capacity and reduces the core temperature in the heat.
Naito, T, Iribe, Y, Ogaki, T
Journal of physiological anthropology. 2017;(1):9
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Abstract
BACKGROUND The timing in which ice before exercise should be ingested plays an important role in optimizing its success. However, the effects of differences in the timing of ice ingestion before exercise on cycling capacity, and thermoregulation has not been studied. The aim of the present study was to assess the effect of length of time after ice ingestion on endurance exercise capacity in the heat. METHODS Seven males ingested 1.25 g kg body mass-1 of ice (0.5 °C) or cold water (4 °C) every 5 min, six times. Under three separate conditions after ice or water ingestion ([1] taking 20 min rest after ice ingestion, [2] taking 5 min rest after ice ingestion, and [3] taking 5 min rest after cold water ingestion), seven physically active male cyclists exercised at 65% of their maximal oxygen uptake to exhaustion in the heat (35 °C, 30% relative humidity). RESULTS Participants cycled significantly longer following both ice ingestion with a long rest interval (46.0 ± 7.7 min) and that with a short rest interval (38.7 ± 5.7 min) than cold water ingestion (32.3 ± 3.2 min; both p < 0.05), and the time to exhaustion was 16% (p < 0.05) longer for ice ingestion with a long rest interval than that with a short rest interval. Ice ingestion with a long rest interval (-0.55 ± 0.07 °C; both p < 0.05) allowed for a greater drop in the core temperature than both ice ingestion with a short rest interval (-0.36 ± 0.16 °C) and cold water ingestion (-0.11 ± 0.14 °C). Heat storage under condition of ice ingestion with a long rest interval during the pre-exercise period was significantly lower than that observed with a short rest interval (-4.98 ± 2.50 W m-2; p < 0.05) and cold water ingestion (2.86 ± 4.44 W m-2). CONCLUSIONS Therefore, internal pre-cooling by ice ingestion with a long rest interval had the greatest benefit on exercise capacity in the heat, which is suggested to be driven by a reduced rectal temperature and heat storage before the start of exercise.
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9.
Environmental and Physiological Factors Affect Football Head Impact Biomechanics.
Mihalik, JP, Sumrall, AZ, Yeargin, SW, Guskiewicz, KM, King, KB, Trulock, SC, Shields, EW
Medicine and science in sports and exercise. 2017;(10):2093-2101
Abstract
PURPOSE Recent anecdotal trends suggest a disproportionate number of head injuries in collegiate football players occur during preseason football camp. In warmer climates, this season also represents the highest risk for heat-related illness among collegiate football players. Because concussion and heat illnesses share many common symptoms, we need 1) to understand if environmental conditions, body temperature, and hydration status affect head impact biomechanics; and 2) to determine if an in-helmet thermistor could provide a valid measure of gastrointestinal temperature. METHODS A prospective cohort of 18 Division I college football players (age, 21.1 ± 1.4 yr; height, 187.7 ± 6.6 cm; mass, 114.5 ± 23.4 kg). Data were collected during one control and three experimental sessions. During each session, the Head Impact Telemetry System recorded head impact biomechanics (linear acceleration, rotational acceleration, and severity profile) and in-helmet temperature. A wet bulb globe device recorded environmental conditions, and CorTemp™ Ingestible Core Body Temperature Sensors recorded gastrointestinal temperature. RESULTS Our findings suggest that linear acceleration (P = 0.57), rotational acceleration (P = 0.16), and Head Impact Technology severity profile (P = 0.33) are not influenced by environmental or physiological conditions. CONCLUSIONS We did not find any single or combination of predictors for impact severity. Rotational acceleration was approaching significance between our early experimental sessions when compared with our control session. More research should be conducted to better understand if rotational accelerations are a component of impact magnitudes that are affected due to changes in environmental conditions, body temperature, and hydration status.
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10.
Assessment of Antishivering Medication Requirements During Therapeutic Normothermia: Effect of Cooling Methods.
Kirk, A, McDaniel, C, Szarlej, D, Rincon, F
Therapeutic hypothermia and temperature management. 2016;(3):135-9
Abstract
Shivering during targeted temperature management (TTM) should be minimized because it can cause cerebral and metabolic stress. It has been proposed that surface cooling (SC) may result in more shivering than endovascular cooling (EC) methods. The purpose of this study was to compare antishivering medication requirements and degree of shivering in these groups during TTM to Normothermia (NT). This was a retrospective single-center cohort study of patients treated with protocolized TTM through SC and EC methods to achieve NT (37.0-37.5°C). The number of interventions and daily dose of antishivering medications, per institutional protocol, were compared between the two groups. The intensity of shivering was assessed with the Bedside Shivering Assessment Scale. Patients in the EC group (n = 23) had more antishivering interventions per patient day than those in the SC group (n = 43) (3.28 vs. 2.67, p = 0.002). Acetaminophen (81% vs. 59%, p < 0.001), buspirone (75% vs. 53%, p < 0.001), and magnesium infusions (52% vs. 36%, p = 0.012) were used on more patient days in the EC group. Patients treated with SC required more patient days of propofol (35% vs. 19%, p = 0.006) and higher average dexmedetomidine dosing per patient-day (0.70 vs. 0.56 μg/[kg·h], p = 0.03). Dosing of other medications was similar. There were no observed differences in degree or intensity of shivering. In our cohort, patients in EC group required more antishivering interventions, but less sedation, during TTM than patients in SC group. Optimizing nonsedating medications, such as acetaminophen, buspirone, and magnesium infusions, may decrease the requirement for sedatives to control shivering in both SC and EC.