三种液冷装备致冷效果的医学研究

本文研究了在环境温度为45℃、露点温度为28℃,受试者处于运动和安静两种状态下,液冷帽、液冷背心和简易液冷服的致冷效果。结果表明,几种液冷装备均具有明显的致冷效果和显著的隔热作用。致冷效能以简易液冷服最大,其次为液冷背心和液冷帽。相反,致冷效率液冷帽最高,其次为液冷背心和简易液冷服。由于被致冷部位的解剖和生理机能的不同,致冷时生理反应并不一样。致冷躯干时,皮肤温度达稳定状态的时间比致冷头、颈部时间约长1小时,并且前者皮肤温度也较后者低4℃。     

液冷服装备设计的生理基础及医学要求

论述了身体各部位组织的基础代谢、基础血流及基础热容量等热生理特征，改变气温和风速对身体各部位体表温度的影响，各部位致冷效能和效率的比较，及活动强度和致冷介质对各部位致冷效能的影响等。从而提出了两种全身液冷服（ＬＣＧ）的流量分配比例。即Ⅰ型为头颈部２０％、躯干３５％、上肢１５％、下肢３０％；Ⅱ型为头颈部２０％、躯干２５％、上肢１５％、下肢４０％。     

舱外航天液冷服传热分析

简单介绍了舱外航天液冷服的结构、功能，分析了通风气体与液冷服基础服装间的对流换热、液冷服的传热传质过程，给出了液冷服传热传质数学模型。通过舱外航天服液冷通风系统与人体的联合热生理实验，该模型得到了验证，并为舱外航天服液冷通风系统的设计提供了依据。     

液冷服散热原理模型及其分析

目的 建立舱外航天液冷服散热的原理模型,提出其在工程设计中应遵循的基本原则。并以该原理模型为基础找到液冷服设计参数与散热量和散热效率的模化关系。方法 根据工程实际,对舱外航天液冷服散热过程进行分析。结果 液冷服各参数（管长、管径、流率和进口液温）对散热量和散热效率的影响是相互制约,相互作用的,因此各参数的合理取值是设计液冷服的关键。结论 该分析和研究对今后舱外航天液冷服的设计研制具有一定的指导意义     

基于径向基网络的液冷服人体实验非线性模型辨识

目的建立液冷服人体实验的非线性数学模型,研究人体状态参数与液冷服入口水温的关系.方法根据人体热学特性和以前的实验数据,运用径向基（RBF）神经网络辨识建模,考察了网络对该实验系统建模的适应性.结果 RBF液冷服人体网络对人体状态和液冷服相关数据有很好的辨识能力,逼近速度快.结论 RBF网络适合本文仿真实验,有利于今后实时的自适应控制.     

应用潜热型功能热流体的液冷服散热性能分析

目的 研究潜热型功能热流体作为液冷服(LCG)冷却液的散热性能及其影响因素.方法 基于Pennes生物热方程建立人体躯干穿着液冷服的传热模型,通过对比各种条件下的液冷服散热量、液冷服效率、冷却液温度和人体皮肤温度等参数,分析液冷服的散热性能以及人体热舒适性.结果 相比以水为冷却液,潜热型功能热流体可以显著提高液冷服散热...     

利用暖体假人对液冷服散热特性的实验研究分析

目的：利用暖体假人对液冷服的各设计参数间的内在关系进行分析,同时对液冷服的散热特性进行评价分析。方法：温度舱内暖体假人着液冷服和隔热服,在不同的温度环境和不同的暖体假人体谢率条件下,改变服装设计参数,以获得液冷服在不同实验条件下进口液温、液体流率和液冷服散热量及温度比效率间的关系。并测量冷却液进出口温度,计算液冷服的实际散热量。结果：得到了液冷服在不同实验条件下进口液温、液体流率与液冷服散热量及温度比效率间的关系和液冷服的实际散热量,为服装设计了参数的合理性提供了评价依据。结论：验证了该舱外航天服的液冷服结构参数选取较为合理,揭示了液体流率受管道结构等条件的限制,合理调节流较窄,服装国度比效率不会很高,应主要靠调节进口液温来改变服装的散热量。     

皮肤温度反馈模式对微气候条件下制冷方式的优化

用一种新颖的、与皮肤平均温度反馈相结合的脉冲制冷方法和普通制冷法、依赖时间变化的脉冲制冷法作了比较。在每次测试中，8名身着个人防护装备的男性在温暖、干燥的环境（干球温度：30℃；露点温度：11℃中做运动。用80min完成跑步机运动（约为225w／mz），身体表面区域的72％被液冷服覆盖。在运动过程中需要测量的指标有：核心温度、局部皮肤温度、心率、液冷服的进121和出121处灌注液的温度、流量、液冷服的功率、新陈代谢率。     

航空航天个人降温服的生物医学应用

航天员在飞行器舱外活动期间,为清除闷热宇航员的代谢热,需要使用个人温度调节系统。在过去的25年中,美国国家航空航天局(NASA)的Ames研究中心航天飞行器舱外活动防护系统研究科,研制过多种先进液冷服的方案,以供工业和生物医学方面的应用。具体实例如下:供直升机飞行员和赛车驾驶员用的液冷     

体温过高时的头部致冷问题

体温过高时可采用个体调温装置进行全身或局部致冷。头部是有效的致冷区，有极高的致冷效率，但由于体表面积不大，对其致冷重要性的认识尚不一致。本文以实验事实为依据，系统论述了头部具有极好的致冷效果，应作为局部致冷的首选部位。尤其在航空活动中，头部致冷有着特殊重要的意义。文章还讨论了应注意的若干医学－工程学问题，以供工程设计参考。     

The effect of temperature on the mechanical aspects of rigor mortis in a liquid paraffin model

Rigor mortis is an important phenomenon to estimate the postmortem interval in forensic medicine. Rigor mortis is affected by temperature. We measured stiffness of rat muscles using a liquid paraffin model to monitor the mechanical aspects of rigor mortis at five temperatures (37, 25, 10, 5 and 0 °C). At 37, 25 and 10 °C, the progression of stiffness was slower in cooler conditions. At 5 and 0 °C, the muscle stiffness increased immediately after the muscles were soaked in cooled liquid paraffin and then muscles gradually became rigid without going through a relaxed state. This phenomenon suggests that it is important to be careful when estimating the postmortem interval in cold seasons.     

On the variation of the 210Po half-life at low temperature

Experiments were performed to verify the possible influence of the temperature and source matrix on the half-life of ²¹⁰Po. Since the precise measurement of the activity of an α-emitting source at cryogenic temperature is far from trivial, a simpler approach was used: the activity of a ²¹⁰Po source was measured at ambient temperature, but in between the measurements, the source was cooled down during a few weeks in a liquid helium Dewar. A ²¹⁰Po solid source was prepared by electro-deposition on a silver plate. The activity of this source was first measured at room temperature, using the defined solid angle α measurement method. The source was then placed in a specific gastight container inside a liquid helium bath at 4 K during 28 days. Then the source was heated up and measured again using the same instrument in the same geometric conditions. The same experiment was repeated with the source coated with a thin layer of silver, in order to be sure that the radioactive material was fully embedded inside the metallic matrix. Our experiments showed no evidence of ²¹⁰Po half-life change at low temperature. A reduction of the half-life of ²¹⁰Po by 6.3% at low temperature, as claimed by Raiola et al. (2007), would have lead to a decay-corrected activity reduction of about 1% after 29 days, which would have been easily detectable.The paper describes the steps of this experiment and gives a detailed uncertainty budget for the measurements. The half-life of ²¹⁰Po obtained in each measurement is compared with the evaluated value of (138.3763±0.0017) d.     

Estimated ventilation requirements for personal air-cooling systems

BACKGROUND: Individuals wearing encapsulating garments require auxiliary cooling systems to sustain physical and cognitive performance when exposed to high temperatures or workloads. Heat transfer in such cooling systems is typically based on either air or liquid as the heat exchange medium. Designing air-cooled systems requires knowledge of the quantity of heat to be extracted and cooling system design criteria, inlet air temperature and humidity and ventilation rates. METHODS: This paper addresses this issue by viewing the human as a simple time averaged heat source whose temperature must be maintained within a specified range. Integrating heat production over time permits heat extraction to be separated from physiological thermoregulation. RESULTS AND CONCLUSIONS: Framing physical workload and ambient conditions in terms of military relevant scenarios for rear cabin helicopter aircrew (25 yr old male working at 45% VO2max), families of curves were identified that define air conditioning system design criteria for given conditions.     

Laboratory comparison of technique for rewarming hypothermic casualties

The efficacy of inhalation, hot bath, piped suit and spontaneous rewarming have been directly compared under controlled conditions. Hot bath rewarming was significantly more effective at raising deep body temperature than the piped suit technique and both were more effective than the other two methods. The effect of inhalation rewarming was not significantly different from that of spontaneous rewarming. All techniques gave rise to afterdrops of core temperature of widely varying degrees and durations. It is concluded that inhalation rewarming should not be employed if it entails a delay in transporting a patient to a facility for rapid external rewarming. Piped suit rewarming is a convenient field alternative to the use of a hot bath and a simple apparatus for carrying this out is described. The sluggish response of rectal temperature to cooling and rewarming in this study suggests that it should not be relied upon as the sole indicator of a patient's thermal state during treatment. Auditory canal temperature is a more valid substitute.     

Automatic control of thermal neutrality for space suit applications using a liquid cooling garment

BACKGROUND: Thermal control in the EVA spacesuit requires attention from the astronaut which is not always desirable or feasible. Improvements in thermal control involve implementation of an automatic thermal control system operating independently of the knowledge of the working astronaut. METHODS: A control system was designed, developed, and tested to automatically maintain a subject's thermal neutrality while wearing a liquid cooling garment (LCG). Measurement of CO2 production as an indication of metabolic rate was used as a signal to initiate the control response. Mean body temperature, computed as a function of ear canal temperature and mean skin temperature, provided feedback to account for the thermal state of subjects as they were being cooled by the LCG. The control algorithm was tested on nine subjects, six males and three females, who performed a varying 90-min metabolic profile using an arm cranking ergometer. A total of 27 tests, three for each subject, were conducted in a thermal chamber at three different environmental temperatures: 10 degrees C, 18.3 degrees C and 26.7 degrees C. RESULTS AND CONCLUSIONS: Evaluation of subjective comfort rating and quantitative energy storage indicates good performance of the controller in maintaining thermal neutrality for the subject over a wide range of environmental and transient metabolic states. Measurements of metabolic rate effectively initiated controller response, and feedback of mean body temperature to the controller proved very capable of accounting for various steady-state environmental conditions and inter-subject variability.     

Thermoregulation and heat exchange in a nonuniform thermal environment during simulated extended EVA. Extravehicular activities

BACKGROUND: Nonuniform heating and cooling of the body, a possibility during extended duration extravehicular activities (EVA), was studied by means of a specially designed water circulating garment that independently heated or cooled the right and left sides of the body. The purpose was to assess whether there was a generalized reaction on the finger in extreme contradictory temperatures on the body surface, as a potential heat status controller. METHOD: Eight subjects, six men and two women, were studied while wearing a sagittally divided experimental garment with hands exposed in the following conditions: Stage 1 baseline--total body garment inlet water temperature at 33 degrees C; Stage 2--left side inlet water temperature heated to 45 degrees C; right side cooled to 8 degrees C; Stage 3--left side inlet water temperature cooled to 8 degrees C, right side heated to 45 degrees C. RESULTS: Temperatures on each side of the body surface as well as ear canal temperature (Tec) showed statistically significant Stage x Side interactions, demonstrating responsiveness to the thermal manipulations. Right and left finger temperatures (Tfing) were not significantly different across stages; their dynamic across time was similar. Rectal temperature (Tre) was not reactive to prevailing cold on the body surface, and therefore not informative. Subjective perception of heat and cold on the left and right sides of the body was consistent with actual temperature manipulations. CONCLUSIONS: Tec and Tre estimates of internal temperature do not provide accurate data for evaluating overall thermal status in nonuniform thermal conditions on the body surface. The use of Tfing has significant potential in providing more accurate information on thermal status and as a feedback method for more precise thermal regulation of the astronaut within the EVA space suit.     

Efficacy of wrist/palm warming as an EVA countermeasure to maintain finger comfort in cold conditions

INTRODUCTION: This study explored the effectiveness of local wrist/palm warming as a potential countermeasure for providing finger comfort during extended duration EVA. METHODS: There were six subjects (five males and one female) who were evaluated in a liquid cooling/warming garment (LCWG) wearing modified liquid cooling/warming (LCW) gloves in three different experimental conditions: Condition 1: Stage 1--no LCWG, LCW glove inlet water temperature 33 degrees C; Stage 2--no LCWG, LCW glove inlet water temperature cooled to 8 degrees C; Stage 3--no LCWG, LCW glove inlet water temperature warmed to 45 degrees C; Condition 2: Stage 1--LCWG and LCW glove inlet water temperature 33 degrees C; Stage 2--LCWG inlet temperature cooled to 31 degrees C, LCW gloves, 8 degrees C; Stage 3--LCWG inlet water temperature remains at 31 degrees C, LCW glove inlet water temperature warmed to 45 degrees C; Condition 3: Stage 1--LCWG and LCW gloves 33 degrees C; Stage 2--LCWG inlet water temperature cooled to 28 degrees C, LCW gloves, 8 degrees C; Stage 3--LCWG remains at 28 degrees C, LCW glove water temperature warmed to 45 degrees C. RESULTS: Wrist/palm area warming showed a statistically significant increase in finger temperature (Tfing) in Stage 3 compared with Stage 2. Blood perfusion showed a trend toward a significantly greater value in Stage 3 compared with Stage 2. The LCW gloves were significantly more effective in increasing Stage 3 Tfing in Condition 1 (33 degrees C) compared with Condition 3 (28 degrees C). Across conditions, subjective perception of heat in the hands was significantly greater at Stage 3 than Stage 2; perception of overall body heat showed a trend for higher heat ratings in Stage 3 than Stage 2. CONCLUSIONS: Local wrist/palm warming was effective in increasing blood circulation to the distal upper extremities, suggesting the potential usefulness of this technique for enhancing astronaut comfort during EVA while decreasing power requirements.     

Soft tissue thermodynamics before, during, and after cold pack therapy.

BACKGROUND: Cold packs are commonly used by clinicians, trainers, and others, often as an interim treatment for many acute conditions, but the extent of temperature change associated with this form of treatment remains poorly understood. METHODS: In 16 healthy male and female volunteers aged 25.4 +/- 3.6 yr, we monitored skin temperature, and recorded the temperature of the quadriceps muscle at 1, 2, and 3 cm depths below the skin, before, during, and after 20 min of cold pack treatment. RESULTS: The results revealed a slight rise in temperature at all four levels during the 5 min pretreatment period, but significant temperature falls at the skin and 1 cm levels beginning from 8 min of treatment (P < 0.001). There was no significant change in tissue temperature at the 2.0 cm or 3.0 cm depths throughout treatment. However, after treatment, cutaneous temperature and the temperature at 1.0 cm depth rose rapidly, returning to baseline levels at variable intersubject times. As these superficial temperatures rose, there were concurrent falls in the temperatures at the 2.0 cm and 3.0 cm levels. Thus, the deeper tissues lost heat (cooled) simultaneously as the superficial tissues rewarmed; to the extent that 40 min after treatment, the deeper levels were cooler than the cutaneous and 1.0 cm levels. CONCLUSION: 1) Cold pack therapy produces significant temperature falls in cutaneous and subcutaneous superficial tissues without directly changing the temperature of tissues at or more than 2.0 cm below the skin; and 2) the temperature gradients of both layers of tissue reverses after treatment, indicating that the deep tissue beneath is at least one of the sources of heat used to rewarm the cooled superficial tissue. The latter finding underscores the importance of the hemodynamic interchange between superficial and deep tissues, and offers an explanation for the reduction of pain, muscle spasm, and edema observed with cold therapy in several clinical situations.     

Moderate exercise increases the post exercise resting warm thermoregulatory response thresholds

BACKGROUND: The purpose of this study was to evaluate the effect of exercise on the subsequent post-exercise core temperature thresholds for vasodilation and sweating. METHODS: On two separate days, with 6 subjects (3 males and 3 females), a whole-body water-perfused suit decreased mean skin temperature until the threshold for vasoconstriction was demonstrated. Mean skin temperature was then slowly increased (approximately 5.0 degrees C x h(-1)) until thresholds for vasodilation and sweating were clearly established. Subjects were cooled by decreasing water temperature until both esophageal and mean skin temperatures returned to near baseline values. Subjects then either performed 15 min of cycle ergometry (60% V(O2max)) followed by 30 min of recovery (Exercise), or remained seated with no exercise for 45 min (Control). Subjects were then cooled again until the onset of cutaneous vasoconstriction followed by a second warming period. The core temperature thresholds for vasodilation and sweating increased significantly by 0.49 degrees C and 0.19 degrees C post-exercise, respectively (p < 0.05). In order to compare thresholds between conditions in which both esophageal and mean skin temperatures were changing, we mathematically compensated for changes in skin temperatures using the established linear cutaneous contribution of skin to the control of vasodilation and sweating (10%). RESULTS: The calculated core temperature threshold (at a designated skin temperature of 36.0 degrees C) for vasodilation increased significantly from 36.56 +/- 0.12 degrees C to 37.11 +/- 0.21 degrees C post-exercise (p < 0.01). Likewise, the sweating threshold increased from 36.79 +/- 0.18 degrees C to 37.05 +/- 0.23 degrees C postexercise (p < 0.01). In contrast, sequential measurements, without exercise, demonstrate a time-dependent decrease (0.18 degrees C) in the sweating threshold, with no difference in the vasodilation threshold. CONCLUSION: These data indicate that exercise has a prolonged effect by increasing the post-exercise thresholds for both warm thermoregulatory responses.