Human thermoregulation and the cardiovascular system

A key but little understood function of the cardiovascular system is to exchange heat between the internal body tissues, organs and the skin to maintain internal temperature within a narrow range in a variety of conditions that produce vast changes in external (exogenous) and/or internal (endogenous) thermal loads. Heat transfer via the flowing blood (i.e. vascular convective heat transfer) is the most important heat-exchange pathway inside the body. This pathway is particularly important when metabolic heat production increases many-fold during exercise. During exercise typical of many recreational and Olympic events, heat is transferred from the heat-producing contracting muscles to the skin surrounding the exercising limbs and to the normally less mobile body trunk and head via the circulating blood. Strikingly, a significant amount of heat produced by the contracting muscles is liberated from the skin of the exercising limbs. The local and central mechanisms regulating tissue temperature in the exercising limbs, body trunk and head are essential to avoid the deleterious consequences on human performance of either hyperthermia or hypothermia. This brief review focuses on recent literature addressing the following topics: (i) the dynamics of heat production in contracting skeletal muscle; (ii) the influence of exercise and environmental heat and cold stress on limb and systemic haemodynamics; and (iii) the impact of changes in muscle blood flow on heat exchange in human limbs. The paper highlights the need to investigate the responses and mechanisms of vascular convective heat exchange in exercising limbs to advance our understanding of local tissue temperature regulation during exercise and environmental stress.     

A microcomputer-based, R-wave triggered system for hemodynamic measurements in the forearm

A microcomputer (with 8088 or 80286 processor)-based, R-wave triggered system for on-line, semi-continuous measurement of blood flow of one or two limbs, simultaneous with heart rate and eventually intra-arterial blood pressure, is described. The minimal interval between measurements is approximately 4 s, allowing the accurate measurement of maximal flow after ischemia. When compared to hand-operated plethysmography, the use of this system improves the precision of the measurements, minimizes perturbations of the limb circulation and eliminates the possible bias of analysis by hand.     

Analysis of flow and wall shear stress in the peroneal veins under external compression based on real-time MR images

As a widely accepted prophylaxis for deep vein thrombosis, the underlying mechanism of compression stocking still remains unclear. In this study, computational fluid dynamics was applied to in vivo data to provide quantitative insight into the hemodynamic response of the deep venous system to static external compression. The geometry and flow information of deep veins before and after compression was acquired from ten healthy volunteers using magnetic resonance imaging.Our results indicated that application of the compression stocking led to a small reduction in blood flow rate but a significant reduction in cross-sectional area of the peroneal veins in the calf, resulting in an increase in wall shear stress (WSS), but the individual effects were highly variable. The mean volume reduction of the deep veins was 58%, while the time-averaged WSS showed an average increase of 398% after compression (median 98%). The analysis also showed a strong linear correlation between the time-averaged WSS and mean blood velocity, suggesting that flow in the deep veins under the level of compression examined here can be approximated by Poiseuille's law despite local geometric variations. It is hoped that quantitative analysis of WSS in the deep venous system will aid in the future design and optimisation of the compression stocking.     

超声二进制编码激励血流测量的实验研究

编码激励技术在医用超声成像中已得到了广泛的应用，但对编码激励的彩色血流成像还缺乏深入系统的研究。在以往理论研究的基础上，通过超声二进制编码激励血流测量实验，进一步研究编码激励彩色血流成像系统的可行性和成像效果。利用搭建的模拟血流循环装置和射频血流数据采集平台，首先通过单反射面回波实验研究了直接对射频回波解码和对解调后I、Q信号分别解码两种解码方法之间的关系；然后分别利用多普勒体模和乳胶管进行实验，研究了编码激励在改善穿透深度和纵向分辨率方面的优势。实验结果表明，在本实验所采用的硬件条件下，达到相同的纵向分辨率时，采用5位Barker码激励获得的穿透深度比传统方法至少增加了10mm；达到相同的穿透深度时，采用5位Barker码激励所能分辨的最小距离约相当于传统方法的1／4。     

Interstitial heating: experiments in artificially perfused bovine tongues

Isolated perfused bovine tongues were heated with a 2 x 2 hot water tube interstitial hyperthermia system (tube outer diameter 2.0 mm, spacing 16 mm). Tongue blood flow ranged between 0 and 17 ml min-1/100 g. The temperature distribution was mapped with 5 to 8 single thermocouples (diameter 50 microns). Model predictions using both the conventional bioheat transfer equation and the effective conductivity model were compared to the experimental results, with emphasis on the role of blood flow. Results indicate a better qualitative agreement with the k-effective model than with the heat sink model. In this set up a 16 mm spacing proved sufficient for adequate heating between the needles at normal blood flow rates, in the absence of large vessels.     

Thigh and calf blood flows after isometric contraction in untrained and trained subjects

The present study was undertaken to examine whether or not there were any differences between untrained and trained subjects in the changes of blood flow in the ipsilateral and contralateral lower limbs after isometric exercise. Blood flow of the thigh and calf in both right and left legs were measured simultaneously before and after isometric contraction with mercury-in-silastic strain gauge venous occlusion plethysmography. In the present study, the main pattern of blood flow responses in the active and non-active limbs was strikingly similar in all subjects: a significant fall in blood flow immediately after isometric contraction at a force of about 50% of maximal muscle strength for 15 sec was observed in the non-active lower limbs. Peak blood flow of the exercised thigh in the trained group was significantly higher than that in the untrained ones. From these results, it was suggested that higher blood flow after isometric exercise in the trained subjects may be due to the improvement of degree of vasodilation in the lower limb as a result of physical training.     

老年人上、下肢多部位皮肤的微区血流

应用激光多普勒血流仪对２０例正常老年人（平均年龄６６．５岁）上、下肢多部位皮肤微区血流进行了动态观察。结果表明：（１）在老年人组中，无论上肢或下肢、肢体末端（如指腹、手背、趾腹、足背）微区血流灌注波形半数受检者呈现为高波幅波动或低波幅波动，而正常青年人则上肢、下肢各个部位均表现为高、低灌流相交替出现的波形。（２）无论老年人或青年人上、下肢皮肤微区血流都存在着离心端小于近心端的趋势，即：趾腹＜足背＜小腿＜膝部，指腹＜手背＜前臂＜肘部。（３）老年人上肢、下肢各个部位的微区血流均明显低于正常青年人（Ｐ＜０．０５）。（４）无论老年人或青年人，上、下肢左右二侧，内、外二侧血流波形及最高平均血流值相比无明显差异（Ｐ＞０．０５）。结果提示：随着年龄的增加．肢体皮肤微区微循环亦随之发生障碍，血流量降低，血管弹性差，舒张、收缩功能的调节能力下降。无论青年人或老年人肢体皮肤微循环血流，其离心端明显低于近心端。同组同一水平左右二侧、内外二侧肢体微区血流具有对称性量效关系。     

五种叶轮血泵体外溶血试验的研究

血泵的标准溶血指数反映了它对血液的破坏程度，是衡量血泵性能的一个重要指标，选用I型离心，II型轴流，磁耦合，I型和II型螺旋混流5种叶轮血泵，用新鲜抗凝羊血500ml，平均压力100mmHg，流量5L／min,在转泵0，0．5，1．0…4．0h后，测量血浆游离血红蛋白含量和血泵出口处的表面温度，计算标准溶血指数。结果表明，5种血泵的转速，温度变化与溶血指数是没有直接关系的，由结构形成的运动流场是对血液造成破坏的主要原因。本文对5种血泵的温度变化，转速和溶血之间的关系做一探讨。     

下肢静脉血栓的彩色多普勒超声诊断

目的 探讨下肢静脉血栓的彩色多普勒超声声像图特点。方法 回顾性分析71例下肢静脉血栓形成患者的彩色多普勒声像图特点。结果 左下肢的发病率明显高于右下肢，常累及股静脉、股浅静脉、股深静脉、月国静脉等。声像图特点为管腔内探及实性高或低回声团块CDFI血流信号变细或无血流信号；脉冲多普勒血流速度减慢且不受呼吸影响。结论 彩色多普勒超声诊断下肢静脉血栓具有直观性、可靠性。     

糖尿病患者足部皮肤反应性充血在三种血流阻断压力下的变化

目的:探讨2型糖尿病患者足部皮肤微血管反应性充血在3种血流阻断压力下的变化。方法:对28例2型糖尿病患者右足相关部位施以三种持续压力阻断血流,分别为收缩压以上20mmHg/2min,30mmHg/3min,40mmHg/4min,减压后造成反应性充血(PORH)。用激光多普勒血流仪(LDF)连续检测内踝及足背皮肤微血流值,比较三种压力下皮肤微血流基值(PU0),最小血流值(PUmin),反应性充血最大值(PUmax)及最大储备量(PUmax-PUmin)、最大变化程度(PUmax-PU0)。结果:三种压力条件下的内踝和足背皮肤PU0、PUmin差异无统计学意义(P>0.05),PUmax、PUmax-PUmin、PUmax-PU0等指标在40mmHg/4min时明显大于20mmHg/2min,差异有非常显著性统计学意义(P<0.01)。结论:LDF检测PORH可用于糖尿病患者内皮依赖性舒张功能的判断,对足部施加收缩压以上40mmHg压力持续4min能获得较满意的临床检测结果。     

Influence of static pressure and shear rate on hemolysis of red blood cells

The purpose of this study was to investigate the effect of multiple mechanical forces in hemolysis. Specific attention is focused on the effects of shear and pressure. An experimental apparatus consisting of a rotational viscometer, compression chamber, and heat exchanger was prepared to apply multiple mechanical forces to a blood sample. The rotational viscometer, in which bovine blood was subjected to shear rates of 0, 500, 1,000, and 1,500 s(-1), was set in the compression chamber and pressurized with an air compressor at 0, 200, 400, and 600 mm Hg. The blood temperature was maintained at 21 degrees C and 28 degrees C. Free hemoglobin at 600 mm Hg was observed to be approximately four times higher than at 0 mm Hg for a shear rate of 1,500 s(-1) (p < 0.05). The results suggest that the increase in hemolysis is strongly related to pressure when high shear rates are applied to the erythrocytes. The data acquired in this study will be helpful in the development of artificial organs, where it will facilitate the prediction of hemolysis in flow dynamics analysis, flow visualization, and computational fluid dynamics.     

面部皮肤温度与面部血流量关系的对照观察

使用红外热像方法和超声多普勒技术,对３０ 例周围性面神经麻痹患者面部表浅的颞浅动脉和面动脉的血流量与其分布区的皮肤温度进行了对照观察。结果显示：（１）面部动脉血流量较大者,其分布区的皮肤温度也较高,反之则较低;（２）在面部的穴位针刺治疗后,面部血流量增加,皮肤温度随之上升;（３）在面部所分析的四个区域之间和针刺的前后,温度与血流的对应关系趋向基本一致,两者比值相差的范围较小,在０９５３８～１２８３５∶１ 之间。说明面部动脉与相应供血区的皮肤温度有一定的定量关系。     

面部皮肤温度与面部血流关系的对照观察

使用红外热像方法和超声多普勒技术,对３０例周围性面神经麻痹患者面部表浅的颞浅动脉和面动脉的血流量与其分布区的皮肤温度进行了对照观察。     

A biocompatible flow chamber to study the hemodynamic performance of prosthetic heart valves

The goal of this study was to design, fabricate, and characterize a biocompatible flow chamber to study the performance of artificial heart valves. The system consists of a testing fluid chamber and a water chamber (separated by a latex diaphragm), following the design of a left ventricular assist device. Two St. Jude bileaflet mechanical heart valves were placed oppositely in the testing fluid chamber to control flow direction. The flow rate of the testing fluid chamber was set at 5.6 L/min, with a stroke volume of 80 ml. The performance of the system was examined through three-dimensional numerical simulation and in vitro experiments with whole blood and washed platelets. Hemolysis was measured with whole blood using a spectrophotometer. Platelet activation was measured by platelet surface P-selectin expression using flow cytometry. The three-dimensional computational fluid dynamics model demonstrated that the flow field in the chamber was laminar and physiological. Results from in vitro experiments indicated that the flow conditions in the chamber did not induce hemolysis or platelet activation with the presence of St. Jude heart valves. Overall, the flow chamber can provide a feasible environment to study the hemodynamic performance of artificial heart valves.     

Local regulation of subcutaneous blood flow and capillary filtration in limbs with occlusive arterial disease. Studies before and after arterial reconstruction

The aim of the study was to examine the local blood flow regulation and the capillary filtration rate in patients with occlusive arterial disease before and after arterial reconstructive surgery. Fourty-seven normal subjects and 99 patients were studied. Subcutaneous blood flow was measured on the forefoot by the local 133Xenon method. Forefoot arterial blood pressure was measured indirectly by cuff and strain-gauge technique. Capillary filtration rate was measured by strain-gauge plethysmography on the forefoot. The arterial and venous pressures of the forefoot were changed by elevating or lowering the foot in relation to heart level. In normal limbs autoregulation was demonstrated during elevation of the limb when blood flow remained almost constant despite the reduction in arterial and perfusion pressures. The local vasoconstrictor response to increased venous transmural pressure was demonstrated when the limb was lowered and blood flow decreased about 30% despite a constant perfusion pressure. In limbs with occlusive arterial disease both local blood flow regulation mechanisms became progressively more abnormal the severe the symptoms and the lower the distal blood pressure. Estimations of the changes in local vascular resistance suggested that the abnormalities in blood flow regulation in all but the severest cases are the result of changes in local perfusion pressure rather than the result of inability of the arteriolar smooth muscle to dilate and constrict in response to changes in arterial and venous pressures. After arterial reconstruction the two mechanisms generally normalized within about a week. However, disturbances occurred in some cases in the early postoperative period, possibly as the result of postoperative pain and stress. Postreconstructive hyperaemia developed in most limbs despite the early normalization of local blood flow regulation. Compared with normal limbs, the forefoot capillary filtration rate was reduced in limbs with occlusive arterial disease. In the early postoperative period the filtration rate remained reduced, but it increased to normal values within three months. Postreconstructive oedema developed independently of the normalization of blood flow regulation, and almost exclusively after femoro-distal by-pass surgery. The study supports the hypothesis that the postreconstructive oedema is a lymphoedema due to surgical trauma, rather than the result of microvascular derangement.     

Post-exercise leg and forearm flexor muscle cooling in humans attenuates endurance and resistance training effects on muscle performance and on circulatory adaptation

The influence of regular post-exercise cold application to exercised muscles trained by ergometer cycling (leg muscles) or handgrip exercise using a weight-loaded handgrip ergometer (forearm flexor muscles) was studied in human volunteers. Muscle loads were applied during exercise programs three to four times a week for 4–6 weeks. Besides measuring parameters characterizing muscle performance, femoral and brachial artery diameters were determined ultrasonographically. Training effects were identified by comparing pre- and post-training parameters in matched groups separately for the trained limbs cooled after exercise by cold-water immersion and the corresponding trained limbs kept at room temperature. Significant training effects were three times more frequent in the control than in the cold group, including increases in artery diameters in the control but not in the cold group. It is concluded that training-induced molecular and humoral adjustments, including muscle hyperthermia, are physiological, transient and essential for training effects (myofiber regeneration, muscle hypertrophy and improved blood supply). Cooling generally attenuates these temperature-dependent processes and, in particular, hyperthermia-induced HSP formation. This seems disadvantageous for training, in contrast to the beneficial combination of rest, ice, compression and elevation in the treatment of macroscopic musculo-tendinous damage. Part of the results were presented at the Congress on Physiology and Pharmacology of Temperature Regulation held in Rhodes (Greece) in October 14, 2004 [Ohnishi N, Yamane M, Uchiyama N, Shirasawa S, Kosaka M, Shiono H, Okada T (2004) Adaptive changes in muscular performance and circulation by resistance training with regular cold adaptation. J Therm Biol 29: 839–843].     

Effect of chronic sympathetic denervation upon the transcapillary filtration rate induced by venous stasis

The effect of venous pressure elevation upon capillary filtration rate in the limb was studied in 6 chronically sympathectomized patients. Five healthy subjects served as controls. Volume changes of the forearm or calf were recorded by a strain-gauge plethysmograph. Relative blod flow in subcutaneous and muscle tissue during venous stasis was measured by the local ¹³³Xe washout technique. In the denervated limbs there was a linear relationship between net capillary filtration rate and venous pressure elevation. In the controls a non-linear relationship was seen as venous pressure elevation of 40 mmHg only caused an increase in net filtration rate of about 66% of that expected from a linear relationship. In the denervated limbs blood flow in muscle and subcutaneous tissue remained constant during venous pressure elevation of more than 30 mmHg whereas in the non-denervated limbs blood flow decreased by about 50% in both tissues. The results suggest that a local sympathetic veno-arteriolar (axon) reflex plays a dominant role for the reduced increase in net capillary filtration rate during large increases in venous pressure. The local axon reflex may therefore act as an edema protecting factor.     

^99Tc^m-亚甲基二膦酸盐在肢体高压电损伤中的诊断价值

目的研究应用^99Tc^m-亚甲基二膦酸盐（MDP）评估高压电烧伤患者肢体受损稗度。方法选取46例肢体高压电烧伤患者,分别于术前进行^99Tc^m-MDP显影、多普勒检测、术中观察组织大体改变,出现血管栓塞或组织坏死者予以切除并进行组织病理学检查。结果轻度损伤肢体血池相及血流相均显示局部放射性浓聚,重度损伤肢体远端影像暗淡,近端影像明显增强,毁损性电击伤肢体血流灌注中断,各种组织均不显影,与未受损影像界限清晰,与彩色多普勒超声检测、临床表现和组织病理学检查相符。结论^99Tc^m-MDP三相动态显像可较直观地显示深度电烧伤后局部血供的改变及组织受损情况,它可以作为诊断电烧伤患者组织损伤程度的一种检测手段。     

The role of the liver in non-shivering thermogenesis in the rat

1. The temperatures of the liver and afferent aortic and portal blood were measured in 20 degrees C acclimated rats at different environmental temperatures (T(a)) between 20 and 37 degrees C. The heated-thermocouple technique was used to measure the metabolic heat production of the liver, its blood flow, and to correct the temperature difference between it and the reference junction for blood flow.2. The temperature of the liver was higher than that of the afferent blood. On raising T(a) from 20 to 30 degrees C the liver temperature fell and the temperature difference between the liver and the aortic blood was reduced despite the decrease in the thermal gradient between the liver and the exterior and a small reduction in hepatic blood flow. A further rise in T(a) to 37 degrees C led to an increase in the liver and blood temperatures. The same pattern was seen when the temperature differences were corrected for blood flow.3. Metabolic heat production in the liver decreased when T(a) was raised from 20 to 30 degrees C.4. In a 20 degrees C environment inhibition of non-shivering thermogenesis with propranolol HCl (10 mg/kg body wt. I.V.) led to a fall in the temperature of the liver and its metabolic heat production towards levels found in untreated rats at T(a) = 30 degrees C. Consequently, in treated rats the change in metabolic heat production on raising T(a) to 30 degrees C was less than in untreated ones.5. These results are interpreted as evidence for the participation of the liver in thermoregulatory non-shivering thermogenesis.     

Possible role of red cell deformability and microvasculature in microcirculation.

The roles of the deformability of red blood cells (RBC) and the microvasculature in the maintenance of blood flow were investigated in terms of the pressure (P)-flow rate (Q) relationships in human RBC suspension perfusions of bullfrog hind limb. Although isotonicity for the bullfrog is approximately 215 mOsm/kgH2O, perfusions in intact hind limbs showed no change in the P-Q relationship at test solution osmolalities ranging from approximately 150 to approximately 300 mOsm/kgH2O. The deformability of RBC was examined in glutaraldehyde-fixed hind limbs. Perfusion of fixed limbs with RBC suspension revealed minimum resistance to flow at osmolalities of approximately 250 to approximately 420 mOsm/kgH2O, whereas the same experiment in intact limbs revealed minimum flow resistance at osmolalities of approximately 200 to approximately 300 mOsm/kgH2O. It was noteworthy that the reduction of RBC deformability was not observed in intact limbs at osmolalities of approximately 250 to approximately 200 mOsm/kgH2O. Heinz body-forming RBC from a patient with unstable hemoglobin (Hb) disease (Hb Yokohama) exhibited a marked reduction in deformability as compared with normal RBC in fixed limbs, while there was no discernible difference between the two types of RBC in intact limbs, thereby suggesting that the microvascular bed can compensate, to an appreciable extent, for the impaired deformability of RBC, probably via its distensibility and/or a wall effect. The present study has considerable implications concerning the link between in vitro experiments and the in vivo situation, including the hemodynamic characteristics of RBC suspensions such as the effective viscosity.