Responses in acral and non-acral skin vasomotion and temperature during lowering of ambient temperature

Arteriovenous anastomoses (AVA) in acral skin (palms and soles) have a huge capacity to shunt blood directly from the arteries to the superficial venous plexus of the extremities. We hypothesized that acral skin, which supplies blood to the superficial venous plexus, has a stronger influence on blood flow adjustments during cooling in thermoneutral subjects than does non-acral skin. Thirteen healthy subjects were exposed to stepwise cooling from 32 °C to 25 °C and 17 °C in a climate chamber. Laser Doppler flux and skin temperature were measured simultaneously from the left and right third finger pulp and bilateral upper arm skin. Coherence and correlation analyses were performed of short-term fluctuations at each temperature interval. The flux from finger pulps showed the synchronous spontaneous fluctuations characteristic of skin areas containing AVAs. Fluctuation frequency, amplitude and synchronicity were all higher at 25 °C than at 32 °C and 17 °C (p<0.02). Bilateral flux from the upper arm skin showed an irregular, asynchronous vasomotor pattern with small amplitudes which were independent of ambient temperature. At 32 °C, ipsilateral median flux values from the right arm (95% confidence intervals) were 492 arbitrary units (au) (417, 537) in finger pulp and 43 au (35, 60) in upper arm skin. Flux values gradually decreased in finger pulp to 246 au (109, 363) at 25 °C, before an abrupt fall occurred at a median room temperature of 24 °C, resulting in a flux value of 79 au (31, 116) at 17 °C. In the upper arm skin a gradual fall throughout the cooling period to 21 au (13, 27) at 17 °C was observed. The fact that the response of blood flow to ambient cooling is stronger in acral skin than in non-acral skin suggests that AVAs have a greater capacity to adjust blood flow in thermoneutral zone than arterioles in non-acral skin.     

Estimating the cortex and autonomic nervous activity during a mental arithmetic task

The cerebral cortex has massive connections with autonomic nervous system and then arouses cardiovascular events, but the coupling mechanism between brain and heart is not clear. In this study the heart rate variability (HRV) and directed transfer function (DTF) methods are used to investigate the cortico-cortical functional coupling and direction of information flow between brain and heart during a mental arithmetic (MA) task. Electroencephalogram (EEG) and ECG were used for measuring neural/cardiac activity. Forty-three healthy male subjects were voluntarily participated in the study. Our results showed compared with control, LF/HF and LFn significantly increased while HF, HFn and total power significantly decreased (P < 0.05) during MA task. HR (79 ± 1.7 beats/min) was also significantly higher compared with the control (71 ± 1.4 beats/min). Moreover, MA task trigger the neurons of pre-central and central areas and then information transmit from front to back, and finished information integration at parietal and occipital locations. Our findings suggested that MA task caused an increase of the coupling of brain regions and quickened heart rate by virtue of increasing sympathetic activity and decreasing parasympathetic activity. The regulation from post-central areas to heart as well as feedback regulation from heart to central areas exists in the MA task.     

A 10-day confinement to normobaric hypoxia impairs toe,but not finger temperature response during local cold stress

The study examined the effects of a 10-day normobaric hypoxic confinement on the finger and toe temperature responses to local cooling. Eight male lowlanders underwent a normoxic (NC) and, in a separate occasion, a normobaric hypoxic confinement (HC; FO₂: 0.154; simulated altitude ~3400 m). Before and after each confinement, subjects immersed for 30 min their right hand and, in a different session, their right foot in 8 °C water, while breathing either room air (AIR) or a hypoxic gas mixture (HYPO). Throughout the cold-water immersion tests, thermal responses were monitored with thermocouples on fingers and toes. Neither confinement influenced thermal responses in the fingers during the AIR or HYPO test. In the foot, by contrast, HC, but not NC, reduced the average toe temperature by ~1.5 °C (p=0.03), both during the AIR and HYPO test. We therefore conclude that a 10-day confinement to normobaric hypoxia per se augments cold-induced vasoconstriction in the toes, but not in the fingers. The mechanism underlying this dissimilarity remains to be established.     

Hybrid cooling vest for cooling between exercise bouts in the heat: Effects and practical considerations

While continuous cooling strategies may induce some ergonomic problems to occupational workers, cooling between work bouts may be an alternative for cooling them down in hot environments. The purpose of this study was to assess the effects of wearing a newly designed hybrid cooling vest (HCV) between two bouts of exercise. Inside a climatic chamber set at an air temperature of 37 °C and a relative humidity of 60%, twelve male participants underwent two bouts of intermittent exercise interspersed with a 30 min between-bout recovery session, during which HCV or a passive rest without any cooling (PAS) was administered. The results indicated that thermoregulatory, physiological, and perceptual strains were significantly lower in HCV than those in PAS during the recovery session (p≤0.022), which were accompanied with a large effect of cooling (Cohen's d=0.84–2.11). For the second exercise bout, the exercise time following HCV (22.13±12.27 min) was significantly longer than that following PAS (11.04±3.40 min, p=0.005, d=1.23) During this period, core temperature T_c was significantly lower by 0.14±0.0.15 °C in HCV than that in PAS. The heart rate drift over time was declined by 2±2 bpm min⁻¹ (p=0.001, d=1.00) and the rise in physiological strain index was reduced by 0.11±0.12 unit min⁻¹ (p=0.010, d=0.96) following the use of HCV. These findings suggested that using HCV could accelerate between-bout recovery and improve subsequent exercise performance by the enlarged body core temperature margin and blunted cardiovascular drift.     

Sinoaortic denervation attenuates vasopressin-induced hypothermia and reduction of sympathetic nerve activity innervating brown adipose tissue in rats

It is well known that sympathetic nerve activity innervating brown adipose tissue (BAT sympathetic nerve activity) plays an important role in BAT thermogenesis. We have found that peripheral administration of arginine vasopressin (AVP) induced hypothermia by reduced thermogenesis in BAT. However, little is known about AVP-induced hypothermic response and its relationship with BAT sympathetic nerve activity. Because increases in baroreceptor inputs inhibit peripheral sympathetic nervous activity, we hypothesized that AVP-induced hypothermia is related to baroreceptor reflex suppression of BAT sympathetic nerve activity. To test this hypothesis, Male Sprague-Dawley rats were subjected to sinoaortic denervation or sham denervation, and implanted with radiotelemetry transmitters to assess the effects of peripheral administration of AVP on BAT sympathetic nerve activity, core and BAT temperatures. In sham-operated rats, an intraperitoneal (i.p.) injection of 10 µg/kg AVP led to a significant decrease in core and BAT temperatures. However, sinoaortic denervation significantly reduced the fall of core and BAT temperatures induced by AVP, compared with levels in sham-operated rats. AVP (10 µg/kg i.p.) rapidly decreased BAT sympathetic nerve activity in control and sham-operated rats, with the greatest levels of suppression occurring at 35 min and these lowest levels attained were with 30.6% and 29.24%, respectively. Furthermore, we found that sinoaortic denervation attenuated the suppressive effects of AVP (10 µg/kg i.p.) on BAT sympathetic nerve activity. The greatest level of suppression was only 20.8% occurring at 35 min after AVP. Therefore, these results indicate that the hypothermic effects of peripheral administration of AVP are partially mediated by the arterial baroreceptor reflex suppression of BAT sympathetic nerve activity and BAT thermogenesis.     

Individualising the exposure of −110 °C whole body cryotherapy: The effects of sex and body composition

The purpose of this study was to investigate the effects of whole body cryotherapy (WBC) on a range of thermoregulatory measures. We also sought to examine the influence of sex and body composition. A convenience sample of 18 healthy participants (10 males and 8 females) (27±6 yr) volunteered for this study. Temperature (core, tympanic, skin and mean body), heart rate, blood pressure, and thermal comfort and sensation were recorded pre- and post- (immediately and every 5 min until 35 min post) exposure to a single bout of WBC (30 s at −60 °C, 150 s at 110 °C). Anthropometric data (height, weight, body surface area, body mass index, fat mass and fat free mass) were also recorded. No significant differences in temperature (core, tympanic, skin and mean body), heart rate, blood pressure, or thermal comfort / sensation were observed between male and females at baseline. Immediately post WBC mean body (male:31.9±0.8 °C; female:31.0±0.9 °C; ∆ mean body temperature:0.9±0.1 °C; P≤0.05, d=0.64) and mean skin (male:22.1±2.2 °C; female:19.6±2.8 °C; ∆ mean skin temperature:−2.5±0.6 °C; d=0.99, P≤0.05) temperature was significantly different between sexes. Sex differences were also observed in regional skin temperature (male thigh, 20.8±1.1 °C; female thigh, 16.7±1.1 °C, ∆ mean thigh skin temperature:−4.1 °C; d=3.72; male calf, 20.5±1.1 °C; female calf, 18.2±1 °C, ∆ mean calf skin temperature:−2.3±0.1 °C; d=3.61; male arm, 21.7±1 °C; female arm, 19±0.4 °C, ∆ mean arm skin temperature: −2.7±0.3 °C; d=3.54; P≤0.05). Mean arterial pressure was significantly different over time (P≤0.001) and between sexes (male 0 mins:94±10 mmHg; female 0 mins:85±7 mmHg; male 35 mins:88±7 mmHg; female 35 mins:80±6 mmHg; P≤0.05). Combined data set indicated a strong negative relationship between skin temperature and body fat percentage 35 min’ post WBC (r=−0.749, P≤0.001) and for core temperature and body mass index in males only (r=0.726, P≤0.05) immediately after WBC. There were no significant differences between sexes in any other variables (heart rate, tympanic and perceptual variables). We observed sex differences in mean skin and mean body temperature following exposure to whole body cryotherapy. In an attempt to optimise treatment, these differences should be taken into account if whole body cryotherapy is prescribed.     

Association of body fat percentage and heart rate variability measures of sympathovagal balance

AimsWe tested the hypothesis that body fat percentage determines cardiac sympathovagal balance in healthy subjects.Main methodsHeart rate variability (HRV) measurements were made of the standard deviation of the normal–normal RR intervals (SDNN) and the low frequency/high frequency (LF/HF) ratio, from time domain and fast Fourier transform spectral analysis of electrocardiogram RR intervals during trials of uncontrolled and controlled (paced) breathing at 0.2 Hz. Body fat percentage was measured by dual energy x-ray absorptiometric (DEXA) scanning. Significance of differences between uncontrolled and controlled (paced) breathing was determined by analysis of variance and correlations between body fat percentage and HRV measurements by Pearson's coefficient at P < 0.05.Key findingsPercent body fat was negatively correlated with LF/HF during the uncontrolled breathing (r = ? 0.56, two-tailed P < 0.05, one-tailed P < 0.01) but not during the paced breathing trial (r = ? 0.34, (P > 0.1).SignificanceWe conclude that sympathetic activity produced by paced breathing at 0.2 Hz can obscure the relationship between body fat percentage and sympathovagal balance and that high body fat percentage may be associated with low sympathetic modulation of the heart rate in healthy adolescent/young adult males.     

Cutaneous application of an accessory-gland secretion after sperm exchange in a terrestrial slug (Mollusca: Pulmonata)

Competition for fertilisation in hermaphroditic animals seems to have led to many odd behaviours and complex morphologies involved in the transfer of accessory-gland products to the partner. Terrestrial slugs of the genus Deroceras show remarkably elaborate and interspecifically diverse penis morphologies and mating behaviours. Most species have an appending penial gland, which in Deroceras panormitanum consists of a few long fingers that are everted after sperm exchange and laid onto the partner’s back. To investigate whether this gland transfers a secretion onto the partner’s skin, we killed slugs at different mating stages and studied their penial glands and skin histologically. Two types of secretion granules appeared at a very early stage of courtship, and the penial gland was already filled 15 min into the courtship. At copulation, the gland everted this secretion onto the partner’s body, where it remained for at least 50 min. No lysis of skin tissue or other effects on the skin were observed. The slugs tried to lick the received secretion off their own body, and some droplets were observed to be shed with the body mucus. Our results indicate the external application of a glandular substance that could function as either a pheromone or allohormone. The behaviours of the recipients suggest sexual conflict, although mutual interest cannot be ruled out.     

Indirect hand and forearm vasomotion: Regional variations in cutaneous thermosensitivity during normothermia and mild hyperthermia

In this experiment, hand and forearm vasomotor activity was investigated during localised, but stable heating and cooling of the face, hand and thigh, under open-loop (clamped) conditions. It was hypothesised that facial stimulation would provoke the most potent vascular changes. Nine individuals participated in two normothermic trials (mean body temperature clamp: 36.6 °C; water-perfused suit and climate chamber) and two mildly hyperthermic trials (37.9 °C). Localised heating (+5 °C) and cooling (−5 °C) stimuli were applied to equal surface areas of the face, hand and thigh (perfusion patches: 15 min), while contralateral forearm or hand blood flows (venous-occlusion plethysmography) were measured (separate trials). Thermal sensation and discomfort votes were recorded before and during each thermal stimulation. When hyperthermic, local heating induced more sensitive vascular responses, with the combined thermosensitivity of both limb segments averaging 0.011 mL·100 mL⁻¹·min⁻¹·mmHg⁻¹·°C⁻¹, and 0.005 mL·100 mL⁻¹·min⁻¹·mmHg⁻¹·°C⁻¹ during localised cooling (P<0.05). Inter-site comparisons among the stimulated sites yielded minimal evidence of variations in local thermal sensation, and no differences were observed for vascular conductance (P>0.05). Therefore, regional differences in vasomotor and sensory sensitivity appeared not to exist. When combined with previous observations of sudomotor sensitivity, it seems that, during mild heating and cooling, regional representations within the somatosensory cortex may not translate into meaningful differences in thermal sensation or the central integration of thermoafferent signals. It was concluded that inter-site variations in the cutaneous thermosensitivity of these thermolytic effectors have minimal physiological significance over the ranges investigated thus far.     

Effect of the timing of ice slurry ingestion for precooling on endurance exercise capacity in a warm environment

It has been demonstrated that precooling with ice slurry ingestion enhances endurance exercise capacity in the heat. However, no studies have yet evaluated the optimal timing of ice slurry ingestion for precooling. This study aimed to investigate the effects of varying the timing of ice slurry ingestion for precooling on endurance exercise capacity in a warm environment. Ten active male participants completed 3 experimental cycling trials to exhaustion at 55% peak power output (PPO) after 15 min of warm-up at 30% PPO at 30 °C and 80% relative humidity. Three experimental conditions were set: no ice slurry ingestion (CON), pre-warm-up ice slurry ingestion (−1 °C; 7.5 g kg⁻¹) (PRE), and post-warm-up ice slurry ingestion (POST). Rectal and mean skin temperatures at the beginning of exercise in the POST condition (37.1±0.2 °C, 33.8±0.9 °C, respectively) were lower than those in the CON (37.5±0.3 °C; P<0.001, 34.8±0.8 °C; P<0.01, respectively) and PRE (37.4±0.2 °C; P<0.01, 34.6±0.7 °C; P<0.01, respectively) conditions. These reductions increased heat storage capacity and resulted in improved exercise capacity in the POST condition (60.2±8.7 min) compared to that in the CON (52.0±11.9 min; effect size [ES]=0.78) and PRE (56.9±10.4 min; ES=0.34) conditions. Ice slurry ingestion after warm-up effectively reduced both rectal and skin temperatures and increased cycling time to exhaustion in a warm environment. Timing ice slurry ingestion to occur after warm-up may be effective for precooling in a warm environment.     

Effects of rapid temperature fluctuations prior to breeding on reproductive efficiency in replacement gilts

Rapidly cooling pigs after heat stress (HS) results in a pathophysiological condition, and because rapid temperature fluctuations may be associated with reduced reproductive success in sows, it lends itself to the hypothesis that these conditions may be linked. Objectives were to determine the effects of rapid cooling on thermal response and future reproductive success in pigs. Thirty-six replacement gilts (137.8±0.9 kg BW) were estrus synchronized and then 14.1±0.4 d after estrus confirmation, pigs were exposed to thermoneutral conditions (TN; n=12; 19.7±0.9°C) for 6 h, or HS (36.3±0.5°C) for 3 h, followed by 3 h of rapid cooling (HSRC; n=12; immediate TN exposure and water dousing) or gradual cooling (HSGC; n=12; gradual decrease to TN conditions) repeated over 2 d. Vaginal (T_V) and gastrointestinal tract temperatures (T_GI) were obtained every 15 min, and blood was collected on d 1 and d 2 during the HS and recovery periods at 180 and 60 min, respectively. Pigs were bred 8.3±0.8 d after thermal treatments over 2 d. Reproductive tracts were collected and total fetus number and viability were recorded 28.0±0.8 d after insemination. HS increased T_V and T_GI (P=0.01; 0.98 °C) in HSRC and HSGC compared to TN pigs. During recovery, T_V was reduced from 15 to 105 min (P=0.01; 0.33 °C) in HSRC compared to HSGC pigs, but no overall differences in T_GI were detected (P<0.05; 39.67 °C). Rapid cooling increased (P<0.05) TNFα compared to HSGC and TN pigs during recovery-d 1 (55.2%), HS-d 2 (35.1%), and recovery-d 2 (64.9%). Viable fetuses tended to be reduced (P=0.08; 10.5%) and moribund fetuses tended to be increased (P=0.09; 159.3%) in HSRC compared to HSGC and TN pigs. In summary, rapid cooling prior to breeding may contribute to reduced fetal viability and reproductive success in pigs.     

Local muscle cooling does not impact expression of mitochondrial-related genes

Recovery that takes place in a cold environment after endurance exercise elevates PGC-1α mRNA whereas ERRα and NRF2 mRNA expression are inhibited. However, the effect of local skeletal muscle cooling on mitochondrial-related gene expression is unknown.PurposeTo determine the impact of local skeletal muscle cooling during recovery from an acute bout of exercise on mitochondrial-related gene expression.MethodsRecreationally-trained male cyclists (n=8, age 25±3 y, height 181±6 cm, weight 79±8 kg, 12.8±3.6% body fat, VO_2peak 4.52±0.88 L·min⁻¹ protocol) completed a 90-min variable intensity cycling protocol followed by 4 h of recovery. During recovery, ice was applied intermittently to one leg (ICE) while the other leg served as a control (CON). Intramuscular temperature was recorded continuously. Muscle biopsies were taken from each vastus lateralis at 4 h post-exercise for the analysis of mitochondrial-related gene expression.ResultsIntramuscular temperature was colder in ICE (26.7±1.1 °C) than CON (35.5±0.1 °C) throughout the 4 h recovery period (p<0.001). There were no differences in expression of PGC-1α, TFAM, NRF1, NRF2, or ERRα mRNA between ICE and CON after the 4 h recovery period.ConclusionLocal muscle cooling after exercise does not impact the expression of mitochondrial biogenesis-related genes compared to recovery from exercise in control conditions. When these data are considered with previous research, the stimuli for cold-induced gene expression alterations may be related to factors other than local muscle temperature. Additionally, different intramuscular temperatures should be examined to determine dose-response of mitochondrial-related gene expression.     

Chronic central ghrelin infusion reduces blood pressure and heart rate despite increasing appetite and promoting weight gain in normotensive and hypertensive rats

Acute studies showed that ghrelin acts on the central nervous system (CNS) to reduce blood pressure (BP), heart rate (HR) and sympathetic activity. However, the long-term CNS cardiovascular actions of ghrelin are still unclear. We tested whether chronic intracerebroventricular (ICV) infusion of ghrelin causes sustained reductions in BP, HR and whether it alters baroreceptor sensitivity (BRS) and autonomic input to the heart. A cannula was placed in the lateral ventricle of male Sprague–Dawley (SD) rats for ICV infusions via osmotic minipump (0.5 μl/h). BP and HR were measured 24-h/day by telemetry. After 5 days of control measurements, ghrelin (0.21 nmol/h) or saline vehicle were infused ICV for 10 days followed by a 5-day post-treatment period. Chronic ICV ghrelin infusion increased food intake (22 ± 3 to 26 ± 1 g/day) leading to ∼50 g body weight gain. BP fell slightly during ghrelin infusion while HR decreased by ∼26 bpm. In control animals BP and HR increased modestly. ICV Ghrelin infusion caused a 50% reduction in sympathetic tone to the heart but did not alter BRS. We also tested if the depressor responses to ICV ghrelin infusion were enhanced in spontaneously hypertensive rats (SHR) due to their high basal sympathetic tone. However, we observed similar BP and HR responses compared to normotensive rats. These results indicate that ghrelin, acting via direct actions on the CNS, has a sustained effect to lower HR and a modest impact to reduce BP in normotensive and hypertensive animals despite increasing appetite and body weight.     

Exercise time to fatigue and the critical limiting temperature: effect of hydration

The purpose of this study was to investigate the effect of active pre-warming combined with three regimens of fluid ingestion: (1) fluid replacement equal to sweat rate (FF), (2) fluid replacement equal to half the sweat rate (HF), and (3) no fluid replacement (NF). Eight males cycled to voluntary fatigue at 70% of peak power output (PPO) in 31.3±0.4°C, 63.3±1.2% relative humidity in a randomised fashion in either of FF, HF or NF conditions. For each trial the time to fatigue test was preceded by 2×20 min active pre-warming periods where subjects also cycled at 70% PPO. Subjects commenced each exercise period with identical rectal temperatures (T_re). The rate of increase in T_re for each condition during the first 20 min of active pre-warming was not different. However, the rate of increase in T_re was significantly reduced in the second active pre-warming period for all fluid conditions but no differences between conditions were noted. During the fatigue test, the rate of increase in T_re for FF was 0.29°C h⁻¹ and 0.58°C h⁻¹ for HF but were not significantly different. The rate of increase in T_re for the NF trial was 0.92°C h⁻¹ and was significantly higher compared to the FF trial. Overall mean skin temperatures and mean body temperatures were higher for NF compared to FF and HF. The rate of heat storage during the fatigue test was similar for FF (80.1±11.7 W m⁻²) and HF (73.0±13.7 W m⁻²) conditions but increased to 155.8±31.2 W m⁻² (P<0.05) in the NF trial. The results indicate that fluid ingestion equal to sweat rate has no added benefit over fluid ingestion equal to half the sweat rate in determining time to fatigue over 40 min of sub-maximal exercise in warm humid conditions. Fluid restriction accelerates the rate of increase in T_re after 40 min of exercise, thereby reducing the time to fatigue. The data support the model that anticipation of impending thermal limits reduces efferent command to working skeletal muscle ensuring cellular preservation.     

Body temperatures of Tropidurus torquatus (Squamata,Tropiduridae) from coastal populations: Do body temperatures vary along their geographic range?

We studied the geographic variation in body temperatures of the lizard Tropidurus torquatus in 10 restinga populations along approximately 1500 km of Brazilian coast. The mean activity body temperatures (30.8–36.2 °C) seems to remain constant along the populations and the differences recorded among them result from the adjustment of each lizard population to the local thermal environment (i.e. may express in part the local microhabitat temperatures occurring in each of the localities in that particular moment). Forested and open habitat tropidurine species have different mean activity body temperatures, probably as a consequence of the different thermal environments in these habitats.     

A reduced core to skin temperature gradient,not a critical core temperature,affects aerobic capacity in the heat

The purpose of this study was to determine the impact of the core to skin temperature gradient during incremental running to volitional fatigue across varying environmental conditions. A secondary aim was to determine if a “critical” core temperature would dictate volitional fatigue during running in the heat. 60 participants (n=49 male, n=11 female; 24±5 yrs, 177±11 cm, 75±13 kg) completed the study. Participants were uniformly stratified into a specific exercise temperature group (18 °C, 26 °C, 34 °C, or 42 °C) based on a 3-mile run performance. Participants were equipped with core and chest skin temperature sensors and a heart rate monitor, entered an environmental chamber (18 °C, 26 °C, 34 °C, or 42 °C), and rested in the seated position for 10 min before performing a walk/run to volitional exhaustion. Initial treadmill speed was 3.2 km h⁻¹ with a 0% grade. Every 3 min, starting with speed, speed and grade increased in an alternating pattern (speed increased by 0.805 km h⁻¹, grade increased by 0.5%). Time to volitional fatigue was longer for the 18 °C and 26 °C group compared to the 42 °C group, (58.1±9.3 and 62.6±6.5 min vs. 51.3±8.3 min, respectively, p<0.05). At the half-way point and finish, the core to skin gradient for the 18 °C and 26 °C groups was larger compared to 42 °C group (halfway: 2.6±0.7 and 2.0±0.6 vs. 1.3±0.5 for the 18 °C, 26 °C and 42 °C groups, respectively; finish: 3.3±0.7 and 3.5±1.1 vs. 2.1±0.9 for the 26 °C, 34 °C, and 42 °C groups, respectively, p<0.05). Sweat rate was lower in the 18 °C group compared to the 26 °C, 34 °C, and 42 °C groups, 3.6±1.3 vs. 7.2±3.0, 7.1±2.0, and 7.6±1.7 g m⁻² min⁻¹, respectively, p<0.05. There were no group differences in core temperature and heart rate response during the exercise trials. The current data demonstrate a 13% and 22% longer run time to exhaustion for the 18 °C and 26 °C group, respectively, compared to the 42 °C group despite no differences in beginning and ending core temperatures or baseline 3-mile run time. This capacity difference appears to result from a magnified core to skin gradient via an environmental temperature advantageous to convective heat loss, and in part from an increased sweat rate.     

Injury due to extravasation of thiopental and propofol: Risks/effects of local cooling/warming in rats

Inadvertent leakage of medications with vesicant properties can cause severe necrosis in tissue, which can have devastating long-term consequences. The aim of this study was to evaluate the extent of extravasation injury induced by thiopental and propofol, and the effects of cooling or warming of local tissue on extravasation injury at macroscopic and histopathologic levels. Rats were administered intradermally thiopental (2.5 mg/100 µL) or propofol (1.0 mg/100 µL). Rats were assigned randomly to three groups: control (no treatment), cooling and warming. Local cooling (18–20 °C) or warming (40–42 °C) was applied for 3 h immediately after agent injection. Lesion sizes (erythema, induration, ulceration, necrosis) were monitored after agent injection. Histopathology was evaluated in skin biopsies taken 24 h after agent injection. Thiopental injection induced severe skin injury with necrosis. Peak lesions developed within 24 h and healed gradually 18–27 days after extravasation. Propofol induced inflammation but no ulceration, and lesions healed within 1–2 days. Local cooling reduced thiopental- and propofol-induced extravasation injuries but warming strongly exacerbated the skin lesions (e.g., degeneration, necrosis) induced by extravasation of thiopental and propofol. Thiopental can be classified as a “vesicant” that causes tissue necrosis and propofol can be classified as an “irritant”. Local cooling protects (at least in part) against skin disorders induced by thiopental and propofol, whereas warming is harmful.     

Cool gleaners: Thermoregulation in sympatric bat species

Thermoregulatory behavior in temperate bats is influenced by gender, food availability, ambient temperature and reproduction. Ecologically and morphologically similar bat species (Myotis bechsteinii, M. nattereri, and Plecotus auritus; Vespertilionidae) facing similar diurnal conditions should therefore not differ in their thermoregulatory behavior. Identified day roosts (n = 23) of radio-tagged bats (n = 30) were spread over an area of 33.1 ha, but ambient temperature did not differ between roosting sites. Furthermore, there was no significant difference in cardinal direction, roost height, canopy coverage, and breast height diameter between day roosts used by the three species. Minimum roost temperatures and isolation values, however, differed significantly between our species with lowest values in P. auritus. The range of skin temperatures (min–max) recorded by temperature-sensitive transmitters was not species-specific with the lowest ranges in late pregnancy (mean ± SD: 7.1 ± 1.1 °C) and highest in post-lactation (mean ± SD: 13.1 ± 1.1 °C). The minimum skin temperature, however, was species-specific with the lowest values in P. auritus (mean ± SD: 20.2 ± 1.1 °C), intermediate in M. nattereri (mean ± SD: 23.4 ± 1.0 °C), and the highest in M. bechsteinii (mean ± SD: 26.8 ± 1.0 °C). Species-specific usage of energy-saving mechanisms might represent an important niche differentiation of species. Different mechanisms might allow, e.g. one species to occupy colder roosts with higher temperature variations or to shorten foraging times due to distinct thermoregulatory behavior.     

Synthesis and bioevaluation of [18F]4-fluoro-m-hydroxyphenethylguanidine ([18F]4F-MHPG): A novel radiotracer for quantitative PET studies of cardiac sympathetic innervation

A new cardiac sympathetic nerve imaging agent, [¹⁸F]4-fluoro-m-hydroxyphenethylguanidine ([¹⁸F]4F-MHPG), was synthesized and evaluated. The radiosynthetic intermediate [¹⁸F]4-fluoro-m-tyramine ([¹⁸F]4F-MTA) was prepared and then sequentially reacted with cyanogen bromide and NH₄Br/NH₄OH to afford [¹⁸F]4F-MHPG. Initial bioevaluations of [¹⁸F]4F-MHPG (biodistribution studies in rats and kinetic studies in the isolated rat heart) were similar to results previously reported for the carbon-11 labeled analog [¹¹C]4F-MHPG. The neuronal uptake rate of [¹⁸F]4F-MHPG into the isolated rat heart was 0.68 ml/min/g wet and its retention time in sympathetic neurons was very long (T_1/2 >13 h). A PET imaging study in a nonhuman primate with [¹⁸F]4F-MHPG provided high quality images of the heart, with heart-to-blood ratios at 80–90 min after injection of 5-to-1. These initial kinetic and imaging studies of [¹⁸F]4F-MHPG suggest that this radiotracer may allow for more accurate quantification of regional cardiac sympathetic nerve density than is currently possible with existing neuronal imaging agents.     

Validation of a new whole-body cryotherapy chamber based on forced convection

Whole-body cryotherapy (WBC) and partial-body cryotherapy (PBC) are two methods of cold exposure (from −110 to −195 °C according to the manufacturers). However, temperature measurement in the cold chamber during a PBC exposure revealed temperatures ranging from −25 to −50 °C next to the skin of the subjects (using isolating layer placed between the sensor and the skin). This discrepancy is due to the human body heat transfer. Moreover, on the surface of the body, an air layer called the boundary layer is created during the exposure and limits heat transfer from the body to the cabin air. Incorporating forced convection in a chamber with a participant inside could reduce this boundary layer. The aim of this study was to explore the use of a new WBC technology based on forced convection (frontal unilateral wind) through the measurement of skin temperature. Fifteen individuals performed a 3-min WBC exposure at −40 °C with an average wind speed of 2.3 m s⁻¹. The subjects wore a headband, a surgical mask, underwear, gloves and slippers. The skin temperature of the participants was measured with a thermal camera just before exposure, just after exposure and at 1, 3, 5, 10, 15 and 20 min after exposure. Mean skin temperature significantly dropped by 11 °C just after exposure (p<0.001) and then significantly increased during the 20-min post exposure period (p<0.001). No critically low skin temperature was observed at the end of the cold exposure. This decrease was greater than the mean decreases in all the cryosauna devices with reported exposures between −140 °C and −160 °C and those in two other WBC devices with reported exposures between −60 °C and −110 °C. The use of this new technology provides the ability to reach decreases in skin temperature similar to other technologies. The new chamber is suitable and relevant for use as a WBC device.