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1.
This study investigated the impact of ice vests and hand/forearm immersion on accelerating the physiological recovery between
two bouts of strenuous exercise in the heat [mean (SD), 49.1(1.3)°C, RH 12 (1)]. On four occasions, eight firefighters completed
two 20-min bouts of treadmill walking (5 km h, 7.5% gradient) while wearing standard firefighter protective clothing. Each
bout was separated by a 15-min recovery period, during which one of four conditions were administered: ice vest (VEST), hand/forearm
immersion (W), ice vest combined with hand/forearm immersion (VEST + W) and control (CON). Core temperature was significantly
lower at the end of the recovery period in the VEST + W (37.97 ± 0.23°C) and W (37.96 ± 0.19°C) compared with the VEST (38.21 ± 0.12°C)
and CON (38.29 ± 0.25°C) conditions and remained consistently lower throughout the second bout of exercise. Heart rate responses
during the recovery period and bout 2 were similar between the VEST + W and W conditions which were significantly lower compared
with the VEST and CON which did not differ from each other. Mean skin temperature was significantly lower at the start of
bout 2 in the cooling conditions compared with CON; these differences reduced as exercise progressed. These findings demonstrate
that hand/forearm immersion (~19°C) is more effective than ice vests in reducing the physiological strain when firefighters
re-enter structural fires after short rest periods. Combining ice vests with hand/forearm immersion provides no additional
benefit. 相似文献
2.
James R. House Heather C. Lunt Rowan Taylor Gemma Milligan Jason A. Lyons Carol M. House 《European journal of applied physiology》2013,113(5):1223-1231
Cooling vests (CV) are often used to reduce heat strain. CVs have traditionally used ice as the coolant, although other phase-change materials (PCM) that melt at warmer temperatures have been used in an attempt to enhance cooling by avoiding vasoconstriction, which supposedly occurs when ice CVs are used. This study assessed the effectiveness of four CVs that melted at 0, 10, 20 and 30 °C (CV0, CV10, CV20, and CV30) when worn by 10 male volunteers exercising and then recovering in 40 °C air whilst wearing fire-fighting clothing. When compared with a non-cooling control condition (CON), only the CV0 and CV10 vests provided cooling during exercise (40 and 29 W, respectively), whereas all CVs provided cooling during resting recovery (CV0 69 W, CV10 66 W, CV20 55 W and CV30 29 W) (P < 0.05). In all conditions, skin blood flow increased when exercising and reduced during recovery, but was lower in the CV0 and CV10 conditions compared with control during exercise (observed power 0.709) (P < 0.05), but not during resting recovery (observed power only 0.55). The participants preferred the CV10 to the CV0, which caused temporary erythema to underlying skin, although this resolved overnight after each occurrence. Consequently, a cooling vest melting at 10 °C would seem to be the most appropriate choice for cooling during combined work and rest periods, although possibly an ice-vest (CV0) may also be appropriate if more insulation was worn between the cooling packs and the skin than used in this study. 相似文献
3.
Temperature of the skin (TSk) and core (TC) play key roles in sleep–wake regulation. The diurnal combination of low TSk and high TC facilitates alertness, whereas the transition to high TSk and low TC correlates with sleepiness. Sleepiness and deteriorating vigilance are induced with peripheral warming, whereas peripheral cooling appears to transiently improve vigilance in narcolepsy. This study aimed to test the hypothesis that foot cooling would maintain vigilance during extended wakefulness in healthy adults. Nine healthy young adult participants with habitually normal sleep completed three constant‐routine trials in randomized crossover order. Trials began at 22:30 hours, and involved continuous mild foot cooling (30°C), moderate foot cooling (25°C) or no foot cooling, while undertaking six × 10‐min Psychomotor Vigilance Tasks and seven × 7‐min Karolinska Drowsiness Tasks, interspersed with questionnaires of sleepiness and thermal perceptions. Foot temperatures in control, mild and moderate cooling averaged 34.5 ± 0.5°C, 30.8 ± 0.2°C and 26.4 ± 0.1°C (all p < .01), while upper‐limb temperatures remained stable (34–35°C) and TC declined (approximately ?0.12°C per hr) regardless of trial (p = .84). Foot cooling did not improve vigilance (repeated‐measures‐ANOVA interaction for response speed: p = .45), but transiently reduced subjective sleepiness (?0.8 ± 0.8; p = .004). Participants felt cooler throughout cooling trials, but thermal comfort was unaffected (p = .43), as were almost all Karolinska Drowsiness Tasks’ encephalographic parameters. In conclusion, mild or moderate cooling of the feet did not attenuate declines in vigilance or core temperature of healthy young adults during the period of normal sleep onset and early sleep, and any effect on sleepiness was small and transient. 相似文献
4.
Matthew R. Kuennen Trevor L. Gillum Fabiano T. Amorim Young Sub Kwon Suzanne M. Schneider 《European journal of applied physiology》2010,108(6):1217-1223
This study examined whether palm cooling (PC) could reduce heat strain, measured through changes in core, mean skin, mean
body temperatures, and thermal sensation in resting hyperthermic subjects wearing chemical protective garments. Ten male subjects
performed three exercise bouts (6.1 km h−1, 2–4% grade) in a hot, dry environment [mean (SD) air temperature 42.2 (0.5°C), relative humidity 36.5 (1%)] until core temperature
reached 38.8°C. Subjects then simulated transport in an armoured vehicle by resting in a seated position for 50 min with either
no cooling (NC), (PC at 10°C) or palm cooling with vacuum application around the hand (PCVAC, 10°C, 7.47 kPa negative pressure).
Core, skin, and mean body temperatures with PC and PCVAC were lower (P < 0.05) than NC from 15 to 50 min of cooling, and thermal sensation was lower (P < 0.05) from 30 to 50 min, with no differences in any variables between PC and PCVAC. Maximal heat extraction averaged 42
(12 W), and core temperature was reduced by 0.38 (0.21°C) after 50 min of PC. Heat extraction with PC was modest compared
to other cooling approaches in the literature. 相似文献
5.
Astrid van der Heide Claire E. H. M. Donjacour Hanno Pijl Robert H. A. M. Reijntjes Sebastiaan Overeem Gert J. Lammers Eus J. W. Van Someren Rolf Fronczek 《Journal of sleep research》2015,24(5):566-575
Patients suffering from narcolepsy type 1 show altered skin temperatures, resembling the profile that is related to sleep onset in healthy controls. The aim of the present study is to investigate the effects of sodium oxybate, a widely used drug to treat narcolepsy, on the 24‐h profiles of temperature and sleep‐wakefulness in patients with narcolepsy and controls. Eight hypocretin‐deficient male narcolepsy type 1 patients and eight healthy matched controls underwent temperature measurement of core body and proximal and distal skin twice, and the sleep–wake state for 24 h. After the baseline assessment, 2 × 3 g of sodium oxybate was administered for 5 nights, immediately followed by the second assessment. At baseline, daytime core body temperature and proximal skin temperature were significantly lower in patients with narcolepsy (core: 36.8 ± 0.05 °C versus 37.0 ± 0.05 °C, F = 8.31, P = 0.01; proximal: 33.4 ± 0.26 °C versus 34.3 ± 0.26 °C, F = 5.66, P = 0.03). In patients, sodium oxybate administration increased proximal skin temperature during the day (F = 6.46, P = 0.04) to a level similar as in controls, but did not affect core body temperature, distal temperature or distal–proximal temperature gradient. Sodium oxybate administration normalised the predictive value of distal skin temperature and distal–proximal temperature gradient for the onset of daytime naps (P < 0.01). In conclusion, sodium oxybate administration resulted in a partial normalisation of the skin temperature profile, by increasing daytime proximal skin temperature, and by strengthening the known relationship between skin temperature and daytime sleep propensity. These changes seem to be related to the clinical improvement induced by sodium oxybate treatment. A causal relationship is not proven. 相似文献
6.
The aim of the present study was to examine the effectiveness of ice-packs (ICE) and phase change material (PCM) cooling devices in reducing physiological load based on subjects' physiological and subjective responses while the subjects exercised on a bicycle ergometer while wearing firefighting protective clothing in a relatively high temperature environment (30 degrees C, 50%RH). Subjects were eight graduate students, aged 25.9 years (SD 3.2). Each subject participated in four 50-min exposures: control (CON), ICE, PCM of 5 degrees C [PCM(5)] and 20 degrees C [PCM(20)]. Each subject rested in a pre-test room for 10 min before entering the test-room where they rested for another 10 min, followed by 30 min-exercise and a 10 min-recovery period. The exercise intensity was set at 55%VO(2max). Cooling effects were evaluated by measuring rectal temperature (Tre), mean skin temperature (Tsk), body weight loss and subjective responses. An increase in Tre for PCM(5) and PCM(20) which was less than that for CON and ICE was observed. The increases in Tsk were depressed using cooling devices, but the cooling effects of PCMs were greater than ICE. The subjects with CON felt hotter and wetter than those in the other conditions. The larger surface cooling area, higher melting temperature and softer material of PCMs which reduces absorption capacity caused a decrease in Tre and Tsk for PCM(5) and PCM(20) which was more than that for CON and ICE. Furthermore, PCM(20) does not require refrigeration. These results suggest that PCM(20) is more effective than other cooling devices in reducing the physiological load while wearing firefighting protective clothing. 相似文献
7.
Tourula M Fukazawa T Isola A Hassi J Tochihara Y Rintamäki H 《European journal of applied physiology》2011,111(4):633-640
It is a common practice in Northern countries that children aged about 2 weeks to 2 years take their daytime sleep outdoors
in prams in winter. The aim was to evaluate the thermal insulation of clothing of infants sleeping outdoors in winter. Clothing
data of infants aged 3.5 months was collected, and sleep duration, skin and microclimate temperatures, humidity inside middle
wear, air temperature and velocity of the outdoor environment were recorded during sleep taken outdoors (n = 34) and indoors (n = 33) in families’ homes. The insulation of clothing ensembles was measured by using a baby-size thermal manikin, and the
values were used for defining clothing insulation of the observed infants. Required clothing insulation for each condition
was estimated according to ISO 11079. Clothing insulation did not correlate with ambient air temperature. The observed and
required insulation of the study group was equal at about −5°C, but overdressing existed in warmer and deficiency in thermal
insulation in colder temperatures (r
s 0.739, p < 0.001). However, even at −5°C a slow cooling (ca. 0.012°C/min) of mean skin temperature (T
sk) was observed. When the difference between observed and required insulation increased, the cooling rate of T
sk increased linearly (r
s 0.605, p < 0.001) and the infants slept for a shorter period (r
s 0.524, p = 0.001). The results of this study show the difficulty of adjusting systematically the optimal thermal insulation for outdoor
sleeping infants during northern winter. Therefore, the necessity for guidelines is obvious. The study provides information
for adequate cold protection of infants sleeping in cold conditions. 相似文献
8.
Cheuvront SN Goodman DA Kenefick RW Montain SJ Sawka MN 《European journal of applied physiology》2008,102(5):577-583
Protective vests worn by global security personnel, and weighted vests worn by athletes, may increase physiological strain
due to added load, increased clothing insulation and vapor resistance. The impact of protective vest clothing properties on
physiological strain, and the potential of a spacer garment to reduce physiological strain, was examined. Eleven men performed
3 trials of intermittent treadmill walking over 4 h in a hot, dry environment (35°C, 30% rh). Volunteers wore the US Army
battledress uniform (trial B), B + protective vest (trial P), and B + P + spacer garment (trial S). Biophysical clothing properties
were determined and found similar to many law enforcement, industry, and sports ensembles. Physiological measurements included
core (T
c), mean skin (T
sk) and chest (T
chest) temperatures, heart rate (HR), and sweating rate (SR). The independent impact of clothing was determined by equating metabolic
rate in all trials. In trial P, HR was +7 b/min higher after 1 h of exercise and +19 b/min by the fourth hour compared to
B (P < 0.05). T
c (+0.30°C), T
sk (+1.0°C) and Physiological Strain Index were all higher in P than B (P < 0.05). S did not abate these effects except to reduce T
sk (P > S) via a lower T
chest (−0.40°C) (P < 0.05). SR was higher (P < 0.05) in P and S versus B, but the magnitude of differences was small. A protective vest increases physiological strain
independent of added load, while a spacer garment does not alter this outcome. 相似文献
9.
We evaluated the cooling rate of hyperthermic subjects, as measured by three estimates of deep core temperatures (esophageal,
rectal and aural canal temperatures), during immersion in a range of water temperatures. The objective of the study was to
compare the three indices of core temperature and define safe cooling limits when using rectal temperature to avoid the development
of hypothermia. On 4 separate days, seven subjects (four males, three females) exercised for 45.4±4.1 min at 65%
at an ambient temperature of 39°C, RH: 36.5%, until rectal temperature (T
re) increased to 40.0°C (39.5°C for two subjects). Following exercise, the subjects were immersed in a circulated water bath
controlled at 2, 8, 14 and 20°C until T
re returned to 37.5°C. When T
re reached normothermia during the cooling period (37.5±0.05°C), both esophageal (T
es) (35.6±1.3°C) and aural canal (T
ac) (35.9±0.9°C) temperatures were approaching or reaching hypothermia, particularly during immersion in 2°C water (T
es=34.5±1.2°C). On the basis of the heat loss data, the heat gained during the exercise was fully eliminated after 5.4±1.5,
7.9±2.9, 10.4±3.8 and 13.1±2.8 min of immersion in 2, 8, 14 and 20°C water, respectively, with the coldest water showing a
significantly faster cooling rate. During the immersion in 2°C water, a decrease of only 1.5°C in T
re resulted in the elimination of 100% of the heat gained during exercise without causing hypothermia. This study would therefore
support cooling the core temperature of hyperthermic subjects to a rectal temperature between 37.8°C (during immersion in
water >10°C) and 38.6°C (during immersion in water <10°C) to eliminate the heat gained during exercise without causing hypothermia. 相似文献
10.
11.
Rebekah A. I. Lucas Philip N. Ainslie Jui-Lin Fan Luke C. Wilson Kate N. Thomas James D. Cotter 《European journal of applied physiology》2010,109(1):101-108
Skin surface cooling has been shown to improve orthostatic tolerance; however, the influence of severe heat stress on cardiovascular
and cerebrovascular responses to skin cooling remains unknown. Nine healthy males, resting supine in a water-perfusion suit,
were heated to +1.0 and +2.0°C elevation in body core temperature (T
c). Blood flow velocity in the middle cerebral artery (transcranial Doppler ultrasound), mean arterial pressure (MAP; photoplethysmography),
stroke volume (SV; Modelflow), total peripheral resistance (TPR; Modelflow), heart rate (HR; ECG) and the partial pressure
of end-tidal carbon dioxide (PETCO2) were measured continuously during 1-min baseline and 3-min lower body negative pressure (LBNP, −15 mm Hg) when heated without
and again with skin surface cooling. Nine participants tolerated +1°C and six participants reached +2°C. Skin cooling elevated
(P = 0.004) MAP ~4% during baseline and LBNP at +1°C T
c. During LBNP, skin cooling increased SV (9%; P = 0.010) and TPR (0.9 mm Hg L−1 min, P = 0.013) and lowered HR (13 b min−1, P = 0.012) at +1°C T
c and +2°C T
c collectively. At +2°C T
c, skin cooling elevated PETCO2 ~4.3 mm Hg (P = 0.011) and therefore reduced cerebral vascular resistance ~0.1 mm Hg cm−1 s at baseline and LBNP (P = 0.012). In conclusion, skin cooling under severe heating and mild orthostatic stress maintained cerebral blood flow more
effectively than it did under moderate heating, in conjunction with elevated carbon dioxide pressure, SV and arterial resistance. 相似文献
12.
Thermal manikin experiments were carried out to investigate the effect of manikin surface temperature on the performance of a personal cooling system (PCS), more specifically, a liquid circulating garment (LCG). Three manikin temperatures were tested using a dry thermal manikin torso: 38, 34, and 30°C. Mean environmental temperature during experiments was 23.5±1°C. Results show that more heat was extracted from the thermal manikin by the PCS as the manikin surface temperature was increased. This is due to the larger difference in temperature between the manikin and the chilled fluid flowing in the PCS when the manikin temperature is high. Finally, it was demonstrated that if insulating garments that reduce heat losses to the environment were worn over the PCS, the PCS efficiency increased. 相似文献
13.
The influence of temperature on the development and survival of Toxocara canis larvae was investigated under laboratory conditions, in water at 15, 20, 25, 30 and 35°C and at room temperature 22°C ± 1°C.
T. canis eggs were able to develop to the larvated stage at all the tested temperatures. Development rate increased with temperature.
Linear regression of development rate against temperature predicted a lower development threshold of 11.8°C. Eggs survived
cooling to 1 and −2°C for 6 weeks, and could develop to the infective, larvated stage when transferred to higher temperatures,
but their development rates were then retarded compared with non-chilled eggs. Larvated eggs remained viable after 7 weeks
of incubation across the tested temperature range, with the highest percentage viability (47%) obtained at 25°C. Development
of eggs to the infective larval stage required, on average, 121 degree days between 20°C and 30°C. Results provide a basis
for predicting variation in the infectivity of eggs in the environment over time in different climates. 相似文献
14.
B. L. Bennett R. D. Hagan K. A. Huey C. Minson D. Cain 《European journal of applied physiology》1995,70(4):322-328
This study evaluated the effectiveness of a six-pack versus a four-pack cool vest in reducing heat strain in men dressed in firefighting ensemble, while resting and exercising in a warm/humid environment [34.4°C (day bulb), 28.9°C (wet bulb)]. Male volunteers (n = 12) were monitored for rectal temperature (T
re), mean skin temperature (T
sk), heart rate, and energy expenditure during three test trials: control (no cool vest), four-pack vest, and six-pack vest. The cool vests were worn under the firefighting ensemble and over Navy dungarees. The protocol consisted of two cycles of 30 min seated rest and 30 min walking on a motorized treadmill (1.12 m · s–1, 0% grade). Tolerance time for the control trial (93 min) was significantly less than both vest trials (120 min). Throughout heat exposure, energy expenditure varied during rest and exercise, but no differences existed among all trials (P > 0.05). During the first 60 min of heat exposure, physiological responses were similar for the four-pack and six-pack vests. However, during the second 60 min of heat exposure the six-pack vest had a greater impact on reducing heat strain than the four-pack vest. PeakT
e andT
sk at the end of heat exposure for 6-pack vest [mean (SD) 38.0(0.3)°C and 36.8(0.7)°C] were significantly lower compared to four-pack [38.6 (0.4)°C and 38.1(0.5)°C] and controls [38.9(0.5)°C and 38.4(0.5)°C]. Our findings suggest that the six-pack vest is more effective than the four-pack vest at reducing heat strain and improves performance of personnel wearing a firefighting ensemble. 相似文献
15.
Susan Dewhurst Andrea Macaluso Leonardo Gizzi Francesco Felici Dario Farina Giuseppe De Vito 《European journal of applied physiology》2010,108(3):451-458
Muscle temperature has a profound effect on the neuromuscular system of young individuals, however, little is known about
the effects of altered temperature on the muscles of older individuals. The purpose of this study was to investigate the effect
of altered local temperature on maximal torque and electromyography signal characteristics in 15 young (21.5 ± 2.2 years;
mean ± SD) and 12 older (73.6 ± 3.2 years) women. Subjects completed maximal voluntary isometric knee extension and flexion,
together with isokinetic knee extensions (30, 60, 90, 120 and 240°/s) at three muscle temperatures: control (~34°C), cold
(~30°C) and warm (~38°C). The torque was lower in the older compared to young subjects at all temperatures (range of difference
for 240°/s, 25–40%; P < 0.001). Warming had no effect on torque in either group, whereas cooling decreased the torque during the isokinetic contractions
in the young group only (range of decrease 6–10%; P < 0.05). In both groups, muscle fibre conduction velocity was slower with cooling compared to the warm condition (−15% in
the young and −17% in the older subjects; P < 0.05).Temperature, however, had no effect on the agonist–antagonist coactivation level or the rate of force development
in either group. The results suggest that, in particular, cooling the muscles has a greater effect on motor performance in
young than older adults, which may indicate reduced adaptation of the neuromuscular system of older adults to altered temperature. 相似文献
16.
Amorim FT Yamada PM Robergs RA Schneider SM Moseley PL 《European journal of applied physiology》2008,104(6):965-972
Hsp72 concentration has been shown to be higher in the serum (eHsp72) of runners with symptoms of heat illness than in non-ill
runners. Recently, it has been suggested that the rate of heat storage during exercise in the heat may be an important factor
in the development of heat stroke. Therefore, we compared the effect of two rates of heat storage on eHsp72 concentration
during exercise in which subjects reached the same final core temperature. We hypothesized that with a lower rate of heat
storage the increase in eHsp72 would be attenuated compared to a higher rate of heat storage. Nine heat acclimated subjects
performed two exercise trials in a counterbalanced order in the heat (42°C, 30% relative humidity). The trials consisted of
walking on a treadmill (~50% VO 2 peak) dressed in military summer fatigues until rectal temperature reached 38.5°C. A high rate of heat storage (HS, 1.04 ± 0.10 W m−2 min−1, mean ± SE) occurred when subjects walked without cooling. To produce a lower rate of heat storage (LS, 0.54 ± 0.09 W m−2 min−1) subjects walked while wearing a water-perfused cooling vest underneath clothing. eHsp72 increased pre- to post-exercise
(P < 0.05) but there was no difference (P > 0.05) in eHSP between the two rates of heat storage (LS 1.25 ± 0.73 to 2.23 ± 0.70 ng ml−1, HS 1.04 ± 0.57 to 2.02 ± 0.60 ng ml−1). This result suggests that eHsp72 is a function of the core temperature attained rather than the rate of heat storage. 相似文献
17.
The Pennes bioheat equation and finite element method (FEM) are used to solve for the temperature distributions in the spinal
cord and cerebrospinal fluid (CSF) during 30 min of cooling for spinal cord injury (SCI) patients. The average CSF and spinal
cord temperatures are reduced by 3.48 and 2.72°C, respectively. The 100-mm wide pad provides the desired cooling and uses
the least amount of material. The presence of zero-average CSF oscillation under normal conditions decreases the cooling extent
in the spinal cord due to the introduction of warm CSF surrounding the spinal cord. The temperature decrease in the spinal
cord is more than doubled when the temperature at the back of the torso is lowered from 20 to 0°C. Spinal cord ischemia, often
observed after traumatic spinal cord injury, promotes cooling penetration. The proposed technique can reduce the spinal cord
temperature by 2°C within 30 min and may be a feasible treatment for traumatic SCI. 相似文献
18.
Davis JK Bishop PA Zhang Y Matt Green J Casaru C Orrick KD Curtner-Smith M Richardson MT Schumacker RE 《European journal of applied physiology》2012,112(2):725-734
This study examined heat stress, heart rate (HR), fluid balance, micro-environment temperature and humidity with Islamic athletic
clothing (IC) compared to traditional soccer uniform (SC). Ratings of perceived exertion (RPE), session RPE (S-RPE), comfort,
and cooling response were also examined. Female volunteers (N = 8) completed a treadmill
[(V)\dot]\textO2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}} test and then, in a randomized, counter-balanced order, two intermittent running bouts (45 min total) in a hot environment
(30.0°C WBGT) in IC and SC. Thereafter, participants sat for 40 min in the hot ambient environment. Repeated measures ANOVA
revealed significantly greater micro-environment temperature (p = 0.02) (IC 33.3 ± 3.2°C, SC 32.0 ± 2.8°C) and humidity (p = 0.04) (IC 48.4 ± 8.1%, SC 42.9 ± 7.9%) in IC during the exercise trial but no difference in the 40-min recovery period
for micro-environment temperature (p = 0.25) or humidity (p = 0.18). No significant difference (p > 0.05) was shown for core temperature (T
rec) (IC 38.3 ± 0.4°C, SC 38.2 ± 0.4°C), HR (IC l54 ± 28 beats min−1, SC 151 ± 26 beats min−1) or RPE (IC 4.7 ± 2.1, SC 3.8 ± 1.7) during the exercise trial or recovery period. Results from a paired t test revealed a significantly greater (p < 0.05) S-RPE (IC 5.8 ± 1.2, SC 4.3 ± 1.9), sweat loss (IC 1.4 ± 0.4 L h−1, SC 1.2 ± 0.4 L h−1) and greater discomfort during the exercise and recovery period for the IC. IC clothing appears to have no detrimental effects
on heat storage or heat strain during exercise or recovery. 相似文献
19.
Selective brain cooling (SBC) of varying strengths has been demonstrated in a number of mammals and appears to play a role in systemic thermoregulation. Although primates lack obvious specialization for SBC, the possibility of brain cooling in humans has been debated for many years. This paper reports on the use of mathematical modeling to explore whether surface cooling can control effectively the temperature of the human cerebrum. The brain was modeled as a hemisphere with a volume of 1.33?1 and overlying layers of cerebrospinal fluid, skull, and scalp. Each component was assigned appropriate dimensions, physical properties and physiological characteristics that were determined from the literature. The effects of blood flow and of thermal conduction were modeled using the steady-state form of the bio-heat equation. Input parameters included core (arterial) temperature: normal (37°C) or hyperthermic (40°C), air temperature: warm (30°C) or hot (40°C), and sweat evaporation rate: 0, 0.25, or 0.50 l?·?m?2?·?h?1. The resulting skin temperatures of the model ranged from 31.8°C to 40.2°C, values which are consistent with data obtained from the literature. Cerebral temperatures were generally insensitive to surface conditions (air temperature and evaporation rate), which affected only the most superficial level of the cerebrum (≤1.5?mm) The remaining parenchymal temperatures were 0.2–0.3°C above arterial temperatures, regardless of surface conditions. This held true even for the worst-case conditions combining core hyperthermia in a hot environment with zero evaporative cooling. Modeling showed that the low surface-to-volume ratio, low tissue conductivity, and high rate of cerebral perfusion combine to minimize the potential impact of surface cooling, whether by transcranial venous flow or by conduction through intervening layers to the skin or mucosal surfaces. The dense capillary network in the brain assures that its temperature closely follows arterial temperature and is controlled through systemic thermoregulation independent of head surface temperature. A review of the literature reveals several independent lines of evidence which support these findings and indicate the absence of functionally significant transcranial venous flow in either direction. Given the fact that humans sometimes work under conditions which produce face and scalp temperatures that are above core temperature, a transcranial thermal link would not necessarily protect the brain, but might instead increase its vulnerability to environmentally induced thermal injury. 相似文献
20.
To evaluate the effect of temperature on the activity and mortality of the L3 of Angiostrongylus vasorum, 1,500 L3 were isolated from experimentally infected snails and distributed into five equal groups. Three groups were incubated
at 37°C, 27°C, and 5°C. The remaining two groups were incubated at 27°C and 5°C for 10 days, at which time the temperature
for the 27°C group was reduced to 5°C and the 5°C group increased to 27°C. Larva activity was observed daily and inactive
larvae were removed. At 37°C, larvae survived up to 8 days. At 27°C, larvae were active until day 6. When subjected to a reduction
in temperature from 27°C to 5°C beginning on day 10, the number of active larvae increased until day 13. Only on day 17 did
the number of active larvae decline to zero. At 5°C, larvae remained active until day 15, surviving to 24 days. When temperature
was increased from 5°C to 27°C beginning on day 10, larvae were found active until day 12 and maintained an intermediate level
of activity to day 21. Survival of larvae was greater at lower temperatures, while high temperatures were associated with
higher mortality. 相似文献