Untersuchungen zum zentralen chemosensiblen Mechanismus der Atmung

Summary The extracellular hydrogen ion concentration of the brain cannot be determined by direct measurement. For experiments, in which the composition of the cerebrospinal fluid is varied independently of the composition of the blood, a mathematical model is proposed which allows approximate calculation of the extracellular pH from acid-base parameters of the blood and the cerebrospinal fluid. The model is based on former investigations regarding the diffusion of CO₂ and bicarbonate in brain tissue. Cerebral blood flow is considered as a function of the arterial CO₂ tension. For simplification homogenous perfusion has been assumed. The theoretical model is valid for stationary conditions only. Solutions of the model indicate that under the conditions specified above the extracellular pH is a function of the distance from the brain surface. The cerebrospinal fluid composition influences the extracellular hydrogen ion concentration not farther than 400–500 m below the surface. It has been concluded that structures reacting to variations of the hydrogen ion concentration in the cerebrospinal fluid must be located within this distance from the surface. The central chemoreceptors of the respiratory system which in the cat respond to changes in cerebrospinal fluid pH locally limited to the ventral surface of the medulla, are thus very probably not identical with the medullary respiratory centres which have to be assumed as being located at a greater depth.

     

严重烧伤回吸收期液体治疗的探讨

烧伤回吸收期的补液如何进行,尚未有一个为广大临床工程师所接受的方案.为此,本文作者对本院救治的103例严重烧伤病人进行了回顾性研究,认为对严重烧伤病人在此阶段的补液.除生理需要量外,至少应保持在53ml/1%BSA/d,方能补充其失水量.从而提出本作者的观点,以探讨此阶段的补液问题.     

Wall Shear Stress Modulation of ATP/ADP Concentration at the Endothelium

A mathematical model of ATP/ADP reaction at the surface of the endothelium for any two-dimensional or axisymmetric nonsingular functional form of the wall shear stress has been presented. Excellent agreement is obtained with the numerical solution for the parallel plate case. For spatially varying wall shear stress, such as the stagnation point flow and a backward facing step the ATP concentrations are shown to have a maximum at the stagnation point streamline and the reattachment point respectively. Increasing the Reynolds number increases both the ATP and ADP concentrations. For the backward facing step significant spatial variations occur in the concentration. Hence, a strong controlling factor for physiological kinetic values is the geometry of the arterial vessel since this determines the wall shear stress and thence the transport to the reactive surface. The area of high concentration also occurs where the wall shear stress is low (limiting case is zero shear stress). Atherosclerotic plaques are known to occur in areas of low wall shear stress and at vessel bifurcations where the wall shear stress is spatially varying. The ATP/ADP concentrations at these particular points may very well contribute to the formation of plaques. © 2003 Biomedical Engineering Society. PAC2003: 8719Tt, 8710+e, 8380Lz     

Intraoperative fluid management in open gastrointestinal surgery: goal-directed versus restrictive

OBJECTIVE:

The optimal strategy for fluid management during gastrointestinal surgery remains unclear. Minimizing the variation in arterial pulse pressure, which is induced by mechanical ventilation, is a potential strategy to improve postoperative outcomes. We tested this hypothesis in a prospective, randomized study with lactated Ringer''s solution and 6% hydroxyethyl starch solution.

METHOD:

A total of 60 patients who were undergoing gastrointestinal surgery were randomized into a restrictive lactated Ringer''s group (n = 20), a goal-directed lactated Ringer''s group (n = 20) and a goal-directed hydroxyethyl starch group (n = 20). The goal-directed fluid treatment was guided by pulse pressure variation, which was recorded during surgery using a simple manual method with a Datex Ohmeda S/5 Monitor and minimized to 11% or less by volume loading with either lactated Ringer''s solution or 6% hydroxyethyl starch solution (130/0.4). The postoperative flatus time, the length of hospital stay and the incidence of complications were recorded as endpoints.

RESULTS:

The goal-directed lactated Ringer''s group received the greatest amount of total operative fluid compared with the two other groups. The flatus time and the length of hospital stay in the goal-directed hydroxyethyl starch group were shorter than those in the goal-directed lactated Ringer''s group and the restrictive lactated Ringer''s group. No significant differences were found in the postoperative complications among the three groups.

CONCLUSION:

Monitoring and minimizing pulse pressure variation by 6% hydroxyethyl starch solution (130/0.4) loading during gastrointestinal surgery improves postoperative outcomes and decreases the discharge time of patients who are graded American Society of Anesthesiologists physical status I/II.     

不同初始补液速率对内毒素休克猪肺损伤的影响

目的:观察不同初始补液速率对内毒素休克猪肺损伤的影响。方法:健康巴马香猪24头,采用静脉注射内毒素(LPS,20μg/kg)建立内毒素休克模型后,随机分为4组:内毒素休克组、慢速补液组(10ml/kg/h)、中速补液组(30ml/kg/h)和快速补液组(120ml/kg/h),每组各6头。观察注射LPS前、液体复苏即刻、复苏3h、复苏6h、复苏9h和复苏12h血乳酸水平变化。复苏12h后处死动物,取肺组织,HE染色观察肺组织病理变化,免疫荧光法观察肺组织髓过氧化物酶(MPO)、白细胞介素-6(IL-6)、白细胞介素-1β(IL-1β)水平,Tunnel染色观察肺细胞凋亡情况。结果:与内毒素休克组相比,各补液组乳酸值、肺组织MPO、IL-6、IL-1β及细胞凋亡指数均显著降低(P<0.05);在各补液组中,中速补液组和快速补液组血乳酸值显著低于慢速补液组(P<0.05),乳酸清除率显著高于慢速补液组(P<0.05);中速补液组肺组织MPO、IL-6、IL-1β及细胞凋亡指数较其余两补液组明显降低(P<0.05)。结论:初始进行液体复苏能够降低内毒素休克时肺损伤程度,但不同复苏策略减轻肺损伤的程度不同,中速补液减轻肺损伤效果最佳。     

Sodium 'need' and sodium appetite during the estrous cycle of sheep

Fluid and electrolyte balance, together with plasma and salivary electrolytes were observed during 34 estrous cycles in housed sheep, in order to evaluate the appropriateness of the pattern of sodium appetite in relation to tangible criteria of sodium requirement. Sodium balance definitely changes during the cycle, but not as expected: peak loss is at estrus, precisely when sodium appetite is minimal. Recovery of sodium appetite occurs during a period of progressive potassium retention and incomplete recovery from the water deficit established at estrous. Neither intake nor excretion pattern would be predicted from data in other species, emphasising the dangers of such extrapolation in this field. Whether the pattern of sodium appetite is dictated by hormones, potassium balance or water balance is under investigation but these data rule out one other factor. The changes in salt appetite are certainly not an appropriate response to sodium balance or extracellular sodium.     

The role of fluid hydrostatic pressure in bone-implant interface load transfer

Permeability of the soft tissue-bone system surrounding artificial joints fixed in cancellous bone was measured in four adult dogs after implants had been in place 2 months. Fluid was forced through a cavity formed by removal of the implant, the cavity was capped with a stopper to allow for pressure generation. Surface permeability of the 2-month-old implant cavity was 45 times less than the permeability of freshly drilled holes in cancellous bone. A mathematical model of a rigid implant resting on a biphasic solid-fluid layer showed the fluid carried 90% of the load when the implant cavity permeability was assumed, but only 27% when the freshly drilled permeability was used. The results suggest caution in interpreting finite-element models with bonded interfaces and suggest a possible role of the fluid in biological response at the interface.     

MEMS微针阵列及其在生物医学上的应用

利用微机械技术制作的 MEMS微针阵列是 MEMS技术在生物医学上一个重要应用 ,它为生物医学领域提供了新的医疗手段。微针技术在精确药物注射、临床监测、生化检测等领域有着广泛的发展前景。本文介绍了MEMS微针阵列在生物医学领域的三个方面的重要应用 :生物医学微针电极、经皮药物传输及流体采样 ,对他们的应用原理和当前的最新技术进展进行了概述 ,说明了 MEMS微针应用的特点 ,它为患者提供了无痛、高效、安全的医疗手段 ,更符合医学研究人性化的特点。另外 ,讨论了微针阵列制作的一系列工艺方法。     

Effects of fluid,electrolyte and substrate ingestion on endurance capacity

Summary The availability of carbohydrate (CHO) as a substrate for the exercising muscles is known to be a limiting factor in the performance of prolonged cycle exercise, and provision of exogenous CHO in the form of glucose can increase endurance capacity. The present study examined the effects of ingestion of fluids and of CHO in different forms on exercise performance. Six male volunteers exercised to exhaustion on a cycle ergometer at a workload which required approximately 70% of . After one preliminary trial, subjects performed this exercise test on six occasions, one week apart. Immediately before exercise, and at 10-min intervals throughout, subjects ingested 100 ml of one of the following: control (no drink), water, glucose syrup, fructose syrup, glucose-fructose syrup or a dilute glucose-electrolyte solution. Each of the syrup solutions contained approximately 36 g CHO per 100 ml; the isotonic glucose-electrolyte solution contained 4 g glucose per 100 ml. A randomised Latin square order of administration of trials was employed. Expired air samples for determination of , respiratory exchange ratio and rate of CHO oxidation were collected at 15-min intervals. Venous blood samples were obtained before and after exercise. Subjects drinking the isotonic glucose-electrolyte solution exercised longer (90.8 (12.4) min, mean (SEM)) than on the control test (70.2 (8.3) min; p<0.05). Endurance capacity was not affected by any of the other drinks. Blood glucose concentration at exhaustion was higher when concentrated sugar solutions were given, but no instance of hyperglycaemia or hypoglycaemia was observed in any trial. Neither the rate of CHO oxidation nor the total amount of CHO oxidised was influenced by the ingestion of large quantities of glucose or fructose.     

Cardiovascular disease management: the need for better diagnostics

Current diagnostic testing for cardiovascular pathology usually rests on either physiological or anatomic measurement. Multiple tests must then be combined to arrive at a conclusion regarding treatment of a specific pathology. Much of the diagnostic decisions currently made are based on rough estimates of outcomes, often derived from gross anatomic observations or extrapolation of physical laws. Thus, intervention for carotid and coronary disease is based on estimates of diameter stenosis, despite data to suggest that plaque character and lesion anatomy are important determinants of outcome. Similarly, abdominal aortic aneurysm (AAA) intervention is based on maximal aneurysm diameter without regard for arterial wall composition or individual aneurysm geometry. In other words, our current diagnostic tests do not reflect the sophistication of our current knowledge of vascular disease. Using a multimodal approach, computer modeling has the potential to predict clinical outcomes based on a variety of factors including arterial wall composition, surface anatomy and hemodynamic forces. We term this more sophisticated approach “patient specific diagnostics”, in which the computer models are reconstructed from patient specific clinical visualizing modalities, and material properties are extracted from experimental measurements of specimens and incorporated into the modeling using advanced material models (including nonlinear anisotropic models) and performed as dynamic simulations using the FSI (fluid structure interaction) approach. Such an approach is sorely needed to improve the effectiveness of interventions. This article will review ongoing work in “patient specific diagnostics” in the areas of carotid, coronary and aneurismal disease. We will also suggest how this approach may be applicable to management of aortic dissection. New diagnostic methods should allow better patient selection, targeted intervention and modeling of the results of different therapies.     

A nonlinear model for myogenic regulation of blood flow to bone: Equilibrium states and stability characteristics

A simple compartmental model for myogenic regulation of interstitial pressure in bone is developed, and the interaction between changes in interstitial pressure and changes in arterial and venous resistances is studied. The arterial resistance is modeled by a myogenic model that depends on transmural pressure, and the venous resistance is modeled by using a vascular waterfall. Two series capacitances model blood storage in the vascular system and interstitial fluid storage in the extravascular space. The static results mimic the observed effect that vasodilators work less well in bone than do vasoconstrictors. The static results also show that the model gives constant flow rates over a limited range of arterial pressure. The dynamic model shows unstable behavior at small values of bony capacitance and at high enough myogenic gain. At low myogenic gain, only a single equilibrium state is present, but at high enough myogenic gain, two new equilibrium states appear. At additional increases in gain, one of the two new states merges with and then separates from the original state, and the original state becomes a saddle point. The appearance of the new states and the transition of the original state to a saddle point do not depend on the bony capacitance, and these results are relevant to general fluid compartments. Numerical integration of the rate equations confirms the stability calculations and shows limit cycling behavior in several situations. The relevance of this model to circulation in bone and to other compartments is discussed.     

肝内胆管分叉部流体力学体外模拟测试的临床意义

临床发现肝内管结石和狭窄，多发于各级胆管的分叉部，其原因与该部胆管的解剖组织的结构和流体力学参数有关。因此研究肝内胆管分叉部的流体力学，对肝内胆管结石和狭窄成因的研究及其防治，均将具有重要意义。本文叙述了我们所进行的体外模拟肝内管分叉部流体力学参数的测试，和对该部位生物力学与特点的探讨。     

青海高原地区96例大面积烧伤患者休克期补液分析

目的对比传统公式计算量与实际补液量,总结青海高原地区96例大面积烧伤患者休克期补液复苏经验。方法收集96例大面积烧伤患者休克期补液临床资料,分为两组,A组:1990～2000年55例,按照传统烧伤公式计算量补液;B组:2000～2008年41例,在传统烧伤公式计算量的基础上,根据患者实际需要进行补液。通过观察两组休克期补液量及尿量,分析总结休克期补液疗效。结果第一个24h,B组患者液体总入量[(12590±1450)mL]明显多于A组[(9530±1305)mL],差异有统计学意义,P0.01。两组患者每小时尿量比较,A组[(53±15)mL]少于B组[(78±11)mL],差异有统计学意义,P0.05。第二个24h,B组患者液体总入量[(9895±993)mL]多于A组[(6880±910)mL],差异有统计学意义,P0.05。两组患者每小时尿量比较,差异无统计学意义,P0.05。两组患者在伤后第一个24h内的第三个8h和第二个24h内的第一个8h尿量明显减少,各时间段内两组尿量比较差异无统计学意义,P0.05。结论青海地处青藏高原,气候干燥,烧伤患者不论面积大小其不显性失水均增多,气管切开插管患者丢失量更大,抗休克治疗应增加液体的补充才能平稳度过休克期。     

Melanoma with signet-ring cells in a peritoneal effusion

Melanoma may occasionally give rise to a malignant effusion and when this occurs it can present a challenging differential diagnosis. We present such a patient who developed a peritoneal effusion. Cytologic examination of the peritoneal fluid revealed individual malignant cells with prominent cytoplasmic vacuoles raising the possibility of a signet-ring cell adenocarcinoma. Immunohistochemical studies were indicative of a malignant melanoma. in this case we believe that the cytoplasmic vacuoles may be a degenerative phenomenon and as such may represent another mechanism for the development of a signet-ring morphology in malignant melanoma. © Wiley-Liss, Inc.     

Numerical Solution of Ocular Fluid Dynamics in a Rabbit Eye: Parametric Effects

Numerical calculations of the aqueous humor dynamics in the anterior chamber of a rabbit's eye are presented to delineate the basic flow mechanisms. The calculations are based on a geometrical model of the eye, which represents the Trabecular meshwork (TM) as a multilayered porous zone of specified pore sizes and void fraction. The outer surface of the cornea is assumed to be at a fixed temperature (corresponding to the ambient temperature), while the iris surface is assumed to be at the core body temperature. Results are obtained for both the horizontal upward-facing orientation of the eye, and the vertical orientation of the eye. Parameters varied include: the temperature difference between the iris and the cornea to underscore the important role of buoyancy in driving the aqueous humor flow; and, the pupil size reflecting different levels of ambient light. Buoyancy is observed to be the dominant driving mechanism for the convective motion in both orientations of the eye. Variations in the pupil size appear to have little influence on the IOP or flow distribution in view of the dominant role of buoyancy in controlling the flow motion. The study provides distributions of the shear stress and flow patterns and delineates the important role of the eye-orientation on these results.     

Equipment using an impedance technique for automatic recording of fluid-volume changes during haemodialysis

An instrument for continuous monitoring of fluid-volume changes has been developed. A tetrapolar whole-body impedance technique is employed with a constant current of 100 μA at 1·5 kHz and 150 kHz. A microprocessor automatically calculates changes in fluid volume from changes in whole-body impedance. Body-surface area is used as a normalising factor together with an empirically determined constant to obtain readings expressed in litres. Estimates of fluid-volume changes obtained by the method were compared with concomitant changes in the body weight of ten patients undergoing haemodialysis, and a correlation coefficient of 0·89 was found.     

Angiotensin II and fluid ingestion in old rats

Fluid ingestion was studied in Fischer 344/Brown Norway F1 rats aged 3, 12, 20, and 24 months of age. There was an age-related decrease in fluid ingestion when fluid intake was measured over 24 h. After water deprivation, 24- and 20-month-old rats drank less than 3- and 12-month-old rats. Twelve, 20-, and 24-month-old rats had less fluid intake associated with food deprivation than did 3-month-old rats. Three month old rats drank more fluid after angiotensin II than did 12-, 20-, and 24-month-old rats when expressed as fluid intake per kg body weight. These studies confirm that the rat is a reasonable model to study age-related hypodipsia.     

Extracellular free calcium and fluid secretion by the rabbit lacrimal gland in vivo

A possible role of extracellular free Ca²⁺ in methacholine-induced fluid secretion in the in vivo rabbit lacrimal gland has been investigated. Lowering the extracellular Ca²⁺ concentration by either intra-arterial injection or infusion of EGTA at doses which caused no systemic effects produced a dose related and reversible inhibition of methacholine-induced secretion. The inhibitory effect of EGTA was diminished when EGTA chelated with CaCl₂ in varying concentration ratios was administered. On the other hand, intra-arterial injection of CaCl₂ potentiated fluid secretion stimulated by submaximal doses of methacholine. These results suggest that fluid secretion from the rabbit lacrimal gland is dependent on the extracellular free Ca²⁺ concentration.     

Estimation of parameters in transcapillary fluid movement by digital simulation

A modified computer model of the terminal vascular bed is presented. The capillary model consists of two parts; the arterial and venous capillary segments in series with the corresponding resistances. A third segment, in parallel with the capillary, represents the varying volume interstitial space. In addition to equations describing the fluid flow between the various segments, the dynamics of protein-mass flow are described. In contrast to models described by earlier investigators, the plasma osmotic pressure π_PL is also a variable. Thus, small changes in π_PL due to variations in venous pressure could be detected. The percentage increase in π_PL per mm Hg increase in venous pressure has an average value of 0·255% per mm Hg. Finally, a hysteresis phenomenon was demonstrated while increaseing and decreasing extravascular tissue volume; the total simulated energy expenditure was EH=1·542 mm Hgx ml for a venous pressure change from 5 to 20 mm Hg. An abbreviated report was presented at the 3rd Annual Meeting of the Biomedical Engineering Society, 7th April, Baltimore, Md., USA