腰椎前路可调式一体化钢板融合器的研制及生物力学测试

目的:研制腰椎前路可调式一体化钢板融合器(ALCP),并对其进行生物力学测试。方法:根据国人腰椎结构特点设计,应用医用钛合金材料制成ALCP。取15具6月龄猪腰椎标本,随机分成3组,每组5具,一组不行任何处理(对照组);两组行L3/4、L4/5椎间盘切除,并在L4椎体上开槽,一组用ALCP固定(ALCP组),另一组用前路钢板人工椎体固定(AVB组),测量每组标本在受到轴向压缩、前屈、后伸、侧屈及扭转状态下的载荷-位移、载荷-应变关系及强度和刚度的变化。结果:三组在轴向压缩、前屈、后伸和侧屈时腰椎的应变随载荷增大而增大,相同载荷下三组间应变无显著性差异(P0.05);在500N以内载荷作用下,腰椎纵向压缩位移随载荷的增加而增加,三组间位移无显著性差异(P0.05)。500N载荷轴向压缩时,ALCP组的应力强度最大(P0.05),而在前屈、后伸及侧屈时三组间应力强度无统计学差异(P0.05);三组间轴向刚度和弯曲刚度均无显著性差异(P0.05)。ALCP组的最大扭矩为4.12N·m,AVB组为3.87N·m,对照组为4.18N·m,三组间无显著性差异(P0.05)。ALCP组的扭转刚度与AVB组和对照组比较亦无显著性显差异(P0.05)。结论:腰椎经ALCP固定后的生物力学性能接近人工椎体加前路钢板固定和正常腰椎。     

Wallis棘突间动态稳定装置的生物力学研究

目的 观察Wallis棘突间动态稳定装置对腰椎力学载荷传导及活动度的影响.方法 采用6具新鲜成人脊柱标本(L1～S1),采用自身前后对照,分为正常组、损伤组、椎弓根螺钉固定组、置入Wallis装置组,分别测量中立位、前屈后伸、左右侧弯、旋转运动加载下节段腰椎的力学载荷及活动范围.结果 W组固定节段椎间盘、关节突应力载荷明显小于Ⅰ组(P＜0.05),明显大于PS组(P＞0.05),但与N组比较差异无统计学意义(P＞0.05);临近节段椎间盘、关节突应力载荷与Ⅰ组、N组比较差异无统计学意义(P＞0.05),但明显小于PS组(P＜0.05).W组固定节段的屈伸活动范围(ROM)小于Ⅰ组及N组(P＜0.05),但明显大于PS组(P＜0.05);侧弯及旋转运动范围,W组与Ⅰ组比较差异无统计学意义(P＞0.05),但与N组及PS组比较差异有统计学意义(P＜0.05).结论 Wallis棘突间动态稳定装置限制固定节段的异常活动,降低固定及临近节段椎间盘及关节突关节应力载荷,减小邻近节段应力集中.     

四种不同内固定治疗胫骨平台后外侧剪应力骨折的生物力学研究

目的 比较4种不同内固定方式治疗胫骨平台后外侧剪应力骨折的生物力学性能.方法 将40具人工合成右侧胫骨模型根据胫骨平台后外侧剪应力骨折的形态学特征建立胫骨平台后外侧剪应力骨折模型,随机分成4组(n=10):A组采用前外侧2枚拉力螺钉固定,B组采用前内侧有限接触动力加压钢板(LC-DCP)固定,C组采用外侧解剖锁定钢板固定,D组采用后外侧支撑钢板固定.测量4组在轴向载荷500、1000及1500 N下的垂直位移和最大失效载荷.结果 A、B、C、D组在500 N载荷下骨折块的相对位移分别为(0.459±0.045)、(0.365±0.035)、(0.264±0.025)、(0.128±0.018)mm,在1000 N载荷下骨折块相对位移分别为(1.058±0.091)、(0.882±0.053)、(0.551±0.053)、(0.440±0.068)mm,在1500 N载荷下骨折块的相对位移分别为(1.559±0.097)、(1.466±0.079)、(1.291±0.077)、(0.832±0.130)mm,同一载荷下D组与其他3组比较差异均有统计学意义(P＜0.05).A、B、C、D组失效载荷分别为(1870±156)、(2520±186)、(2816±190)、(3465±210)N,D组与其他3组比较差异均有统计学意义(P＜0.05).结论 后外侧支撑钢板固定组抗载荷力学性能最佳,对固定胫骨平台后外侧剪应力骨折有明显的生物力学优势.     

锁定钢板外置与外固定支架固定骨折的生物力学研究

目的 通过对锁定钢板(LCP)外置与外固定支架固定骨折进行生物力学分析,为应用锁定钢板外置固定治疗提供理论依据。方法 选择不同长度的牛小腿骨,制备成骨折标本,分别采用锁定钢板外置固定和外固定支架固定,观察标本在不同载荷下承受的轴向压缩、扭转和弯曲位移。结果 两组在100、200、300、400、500、600和700 N载荷下轴向压缩值比较,均有显著差异(P<0.05),且随着载荷越大轴向压缩值差距越大。两组在4、6、8、10、12和14 N.cm载荷下扭转角度比较,差异均有统计学意义(P<0.05),且随着载荷越大则扭转角度值差距越大。两组在50、100、150、200、250和300 N载荷下弯曲位移值比较,差异均有统计学意义(P<0.05),且随着载荷越大弯曲位移值差距越大。结论 锁定钢板外置固定骨折在生物力学性能上优于外固定支架,可在临床应用,为治疗开放性骨折提供了一种新的方法。     

小牛胸腰椎解剖、生物力学研究及其临床意义

目的　测量小牛胸腰椎相关解剖数据并测试其生物力学性能 ,探讨其作为胸腰椎前路内固定模型的可行性。方法　采集 1周以内的新鲜小牛胸腰椎脊柱标本 2 0具 ,测量椎体及椎间盘的最大横径、矢状径和前部高度。测试屈曲、伸展、侧屈及扭转状态下的载荷 -应变、载荷 -位移关系以及最大载荷时的应力强度及轴向刚度 ,并进行极限力学性能测试。结果　小牛胸腰椎椎体及椎间盘矢径、横径、高度自T10 至L5逐渐递增 ,椎体横径与矢径之比约为 1∶1,其T10 ～L5段椎间盘高度之和与椎体高度比值为 1∶0 .9。小牛胸腰椎载荷 -应变及载荷 -位移关系呈线性变化 ,生理载荷下屈曲、伸展及侧屈状态下的应力强度分别为 (2 .86± 0 .2 4 )N/mm2 ,(2 .17± 0 .2 0 )N/mm2 ,(5 .2 9± 0 .5 0 )N/mm2 。屈曲、伸展、侧屈及扭转状态下的轴向刚度分别为 (37.13± 4 .30 )N/mm ,(35 .38± 4 .2 0 )N/mm ,(34.5 6± 4 .2 0 )N/mm ,(5 1.6 9± 1.6 2 )N/mm。结论　小牛胸腰椎形态及大小可满足前路内固定模型的需要 ,以小牛标本作为体外非破坏性生物力学实验模型具有可行性。     

跨骨折椎体固定联合单侧伤椎植钉治疗胸腰椎爆裂骨折的生物力学研究

目的探讨经后路跨骨折椎体固定联合单侧伤椎椎弓根钉固定胸腰椎爆裂骨折的稳定性。方法取18具新鲜小牛脊柱胸腰段(T_(11)~L_(3))标本,根据不同内固定方式随机分为A、B、C 3组(n=6);各组标本采用Panjabi落锤实验制作L_(1)椎体爆裂骨折模型后,采用脊柱通用椎弓根钉固定系统分别行跨骨折椎体固定(A组)、跨骨折椎体固定基础上联合单侧伤椎固定(B组)、跨骨折椎体固定基础上联合双侧伤椎固定(C组)。于各组标本正常、骨折及固定状态下,运用三维激光扫描仪测定前屈、后伸、左右侧弯及左右轴向旋转方向伤椎上、下相邻节段的椎间活动度;采用MTS-858型生物材料试验机测定300 N载荷下标本抵抗轴向变形能力,计算轴向刚度。结果A、B、C组标本在正常状态和骨折状态下各方向椎间活动度及轴向刚度比较,差异均无统计学意义(P0.05),提示各组标本具有可比性。固定状态下,B、C组各方向椎间活动度均小于A组(P0.05),但B、C组间比较差异无统计学意义(P0.05);B、C组轴向刚度显著大于A组(P0.05),B组小于C组,但差异无统计学意义(P0.05)。结论对于胸腰椎爆裂骨折,经伤椎椎弓根植钉能提高脊柱稳定性,且单侧与双侧植钉稳定性无明显差异。     

可调式中空钛合金人工椎体的生物力学评价

目的 测试并评价可调式中空肽合金人工椎体的生物力学性能。方法 27具小牛胸腰椎标本随机分为对照组(IS)、髂骨植骨组(IBG)及人工椎体组(AVB)3组，测试屈曲、伸展、侧屈及扭转状态下的载荷—应变、载荷—位移关系变化以及最大载荷时的应力强度及刚度。IBG组、AVB组分别附加前路钢板及后路椎弓根螺钉进行第2次、第3次测试，各组间进行比较，并进行统计学处理。结果 髂骨植骨组不同状态下应变及位移均大于原始标本，人工椎体组小于原始标本，且差异具显著性(P＜0．05)；附加内固定后应变及位移均较不附加内固定者减小(P＜0．05)，且人工椎体组附加内固定后分别小于髂骨植骨组(P＜0．05)。人工椎体附加或不附加内固定时的应力强度及轴向刚度均大于或接近原始标本，而单纯髂骨植骨组伸展及侧屈状态下，以及附加前路或后路固定后的侧屈状态下的应力强度低于原始标本；轴向压缩刚度亦小于原始标本，附加前路钢板后有所提高，但只有附加后路椎弓根螺钉后才与原始标本相当。人工椎体组的扭转强度大于髂骨组，扭转刚度与原始标本接近。而髂骨植骨组即使附加内固定后的扭转刚度亦远小于原始标本。结论 单纯人工椎体替代基本可满足生物力学性能要求，附加前路或后路固定后，可满足包括扭转性能在内的生物力学要求；单纯髂骨植骨后不满提供足够的生物力学稳定性、必须辅加内固定，同时应注意术后保护。     

前路单节段融合内固定治疗伴椎弓根断裂的Denis B型胸腰椎爆裂骨折生物力学研究

目的探讨前路单节段融合内固定治疗伴椎弓根断裂的Denis B型胸腰椎爆裂骨折后的脊椎生物力学稳定性。方法取6具新鲜成人尸体胸腰椎标本(T11~L3)作为正常组(A组),采用椎体切除法依次建立L1Denis B型爆裂骨折模型并行前路单节段融合内固定,分别为椎弓根完整组(B组)、单侧椎弓根切断组(C组)和双侧椎弓根切断组(D组)。通过脊柱三维运动机依次测定各组在8.0 N·m纯力偶矩下屈伸、左右侧弯及左右旋转活动度(range of motion,ROM)。结果 B、C、D组T12、L1脊柱运动单元前屈、后伸、左右侧弯ROM均显著低于A组(P0.05),D组显著高于B、C组(P0.05),B、C组间差异无统计学意义(P0.05);B、C组左右旋转ROM均显著低于A、D组(P0.05),B、C组间及A、D组间比较差异无统计学意义(P0.05)。各组间L1、L2脊柱运动单元前屈、后伸、左右侧弯、左右旋转ROM比较,差异均无统计学意义(P0.05)。结论前路单节段融合内固定治疗Denis B型胸腰椎爆裂骨折伴一侧椎弓根断裂时,在屈伸、侧弯及旋转方向能提供足够初始生物力学稳定性,而伴双侧椎弓根断裂时生物力学稳定性差。     

经皮激光椎间盘减压术对山羊腰椎稳定性影响的生物力学测试

目的:观察经皮激光椎间盘减压术对正常山羊腰椎问盘髓核汽化后腰椎稳定性的影响.方法:选取正常新鲜山羊腰椎标本40具,截取L1～L6节段,剔除肌肉组织.两端用牙托粉固定.随机分为A、B、C、D、E共5组,每组8个标本.A组为空白对照组,不对椎间盘进行处理;B组L3/4(单节段组),C组L3/4和L4/5(相邻双节段组),D组L2/3和LA/5(间隔双节段组),E组L2/3、L3/4和L4/5(3节段组)椎间盘分别行激光汽化,每个椎间盘总能量为500J.所有标本处理后在生物力学测定仪上测定轴向拉伸、轴向加压、前方加压、后方加压、左侧加压及右侧加压试验,分别记录负荷加载力为20N、40N、60N、80N和100N时标本的位移.结果:在不同负荷下,各组标本在相同加载方式的位移量均随负荷增大而增加;在相同负荷相同加载方式时,A组与B、C、D、E组标本位移量比较均无统计学意义(P>0.05),B、C、D、E组标本位移量相互比较均无统计学意义(P>0.05).结论:经皮激光椎间盘减压术汽化3个节段及3个节段以内的椎间盘组织对山羊腰椎的稳定性没有明显影响.     

齿轮撑开式脊柱复位固定板装置的研制及生物力学评价

[目的] 研制一种新型的齿轮撑开式脊柱复位固定板装置(GDP),进行生物力学测试并评价其生物力学性能.[方法] 采用医用钛合金制成GDP植入物,用不锈钢制成专用工具.18具新鲜小牛腰椎标本随机分为3组,对GDP组内固定进行载荷-应变、载荷-位移、强度、刚度、扭转强度及极限承载能力测试,并与对照组(CD、Steffee)对比分析.[结果] 齿轮撑开式脊柱复位固定板(GDP)组在载荷-应变、载荷-位移、强度、刚度、扭转强度及极限承载能力方面均优于对照组,统计学分析有显著性差异(P<0.05).[结论] GDP具有良好的生物力学稳定性,对促进骨折愈合、防止后突畸形复发和椎体高度丢失具有重要意义.     

Vasopressor hormone response following mesenteric traction during major abdominal surgery

Background : We investigated the vasopressor hormone response following mesenteric traction (MT) with hypotension due to prostacyclin (PGI₂) release in patients undergoing abdominal surgery with a combined general and epidural anesthesia. Methods : In a prospective, randomized, placebo-controlled study we administered 400 mg ibuprofen (i.v.) in 42 patients scheduled for abdominal surgery. General anesthesia was combined with epidural anesthesia (T4-L1). Before as well as 5, 15, 30, 45, and 90 min after MT we recorded plasma osmolality, hemodynamics and measured 6-keto-PGFlα (stabile metabolite of PGI₂), TXB₂ (stabile metabolite of thromboxane A₂) active renin, and arginine vasopressin (AVP) plasma concentrations by radioimmunoassay. Catecholamine levels were assessed by high-pressure liquid chromatography (HPLC) with electrochemical detection. Results : Following MT, arterial hypotension occurred along with a substantial PGI₂ release. This was completely abolished by ibuprofen administration. Although plasma levels of 6-keto-PGF_1α (1133 (708) vs. 60 (3) ng/L, median (median absolute deviation), P=0.0001, placebo vs. ibuprofen) remained significantly elevated, blood pressure was restored within 30 min after MT in the placebo group. At the same point in time plasma concentrations of TXB² (164 (87) vs. 58 (1) ng/L, P=0.0001), epinephrine (46 (33) vs. 14 (6) ng/L, P=0.001), AVP (41 ± (18) vs. 12 (7) ng/L, P=0.0004), and active renin (27 (12) vs. 12 (4) ng/L, P = 0.001) were significantly higher in placebo-treated patients. Conclusion : Under combined general and epidural anesthesia arterial hypotension following MT due to endogenous PGI₂ release is associated with enhanced release of AVP, active renin, epinephrine and thromboxane A₂, presumably contributing to hemodynamic stability within 30 min after MT.     

A comparison of the inhibitory effects of four volatile anaesthetics on the metabolism of chlorzoxazone, a substrate for CYP2E1, in rabbits

Background: Halothane inhibits in vitro and in vivo activity of cytochrome P-450 (CYP) 2E1. There are several fluorinated volatile anaesthetics besides halothane, and most of them are defluorinated by CYP2E1. It is unclear whether other fluorinated anaesthetics inhibit the in vivo activity of CYP2E1.
Methods: We compared the inhibitory effects of therapeutic concentrations of four inhalational anaesthetics, halothane, enflurane, isoflurane, and sevoflurane, on chlorzoxazone metabolism in rabbits receiving artificial ventilation.
Results: All four inhalational anaesthetics decreased arterial blood pressure and increased plasma chlorzoxazone concentration. However, no significant differences in the plasma chlorzoxazone concentration were found between the four anaesthetics. The estimated chlorzoxazone clearance increased after beginning inhalation with all four agents, but no significant difference in clearance was noted between agents.
Conclusions: At therapeutic concentrations, the in vivo inhibitory effect on chlorzoxazone metabolism was similar for all four inhalational anaesthetics examined, even though their chemical characteristics and extent of hepatic metabolism differ considerably.     

A Teaspoon Pump for Pumping Blood with High Hydraulic Efficiency and Low Hemolysis Potential

Abstract: Virtually all blood pumps contain some kind of rubbing, sliding, closely moving machinery surfaces that are exposed to the blood being pumped. These valves, internal bearings, magnetic bearing position sensors, and shaft seals cause most of the problems with blood pumps. The original teaspoon pump design prevented the rubbing, sliding machinery surfaces from contacting the blood. However, the hydraulic efficiency was low because the blood was able to "slip around" the rotating impeller so that the blood itself never rotated fast enough to develop adequate pressure. An improved teaspoon blood pump has been designed and tested and has shown acceptable hydraulic performance and low hemolysis potential. The new pump uses a nonrotating "swinging" hose as the pump impeller. The fluid enters the pump through the center of the swinging hose; therefore, there can be no fluid slip between the revolving blood and the revolving impeller. The new pump uses an impeller that is comparable to a flexible garden hose. If the free end of the hose were swung around in a circle like half of a jump rope, the fluid inside the hose would rotate and develop pressure even though the hose impeller itself did not "rotate"; therefore, no rotating shaft seal or internal bearings are required.     

Microspheres Based Detoxification System: A New Method in Convective Blood Purification

Abstract: A variety of protein-bound or hydrophobic substances, accumulating as a result of pathologic conditions such as exogenous or endogenous intoxications, are removed poorly by conventional detoxification methods because of low accessibility (hemodialysis), insufficient adsorption capabilities (hemosorption), low efficiency (peritoneal dialysis), or economic limitations (high-volume plasmapheresis). Combining advantages of existing methods with microspheric technology, a module-based system was designed. Major operating parameters of the latter can be modified to allow for adjustment to individual clinical situations. An extracorporeal blood circuit including a plasmafilter is combined with a secondary high-velocity plasma circuit driven by a centrifugal pump. Different microspheric adsorbers can be combined in one circuit or applied in sequence. Thus, a prolonged treatment can be tailored using specially designed selective adsorber materials. Comparing this system with existing methods (high-flux hemodialysis, molecular adsorbent recycling system), results from our in vitro studies and animal experiments demonstrate the superior efficiency of substance removal.     

Tissue perfusion in relation to cardiac output during continuous positive-pressure ventilation and administration of propranolol or verapamil

Background : Our objective was to determine whether administration of propranolol or verapamil modifies the hemodynamic adaptation to continuous positive-pressure ventilation (CPPV), in particular the regional distribution of cardiac output (CO).
Methods : General hemodynamics and regional blood flows assessed by microsphere technique (15 (μm) were recorded in 16 anesthetized pigs during spontaneous breathing (SB) and CPPV with 8 cm H₂O end-expiratory pressure (CPPV8) before and after intravenous administration of propranolol (0.3 mg · kg⁻¹ followed by 0.15 mg · kg⁻¹ · h⁻¹, n=8) or verapamil (0.1 mg · kg⁻¹ followed by 0.3 mg · kg⁻¹ · h⁻¹, n=8).
Results : CPPV8 depressed CO by 25% without shifts in its relative distribution with the exception of a noteworthy increase in adrenal perfusion. Propranolol increased arterial blood pressure, and due to a fall in heart rate, CO dropped by 25%. The kidneys and, to a lesser extent, the splanchic region and central nervous system received increased fractions of the remaining CO at the expense of skeletal muscle flow. Similar patterns were seen during SB and CPPV8 such that the combination of propranolol and CPPV8 depressed CO by 50%. The circulatory effects of verapamil were less evident but myocardial perfusion tended to increase.
Conclusions : The combination of propranolol or verapamil with CPPV does not result in any specific hemodynamic interaction in anesthetized pigs, except that the combined effect of propranolol and CPPV may severely reduce CO.     

Volatile anaesthetics reduce adhesion of blood platelets under low-flow conditions in the coronary system of isolated guinea pig hearts

Background : Inhibitory effects of volatile anaesthetics on platelet aggregation have been demonstrated in several studies. However, the influence of volatile anaesthetics on intracoronary platelet adhesion has not been elucidated so far.
Methods : Isolated hearts of guinea pigs were perfused with buffer in the absence or presence of volatile anaesthetics (0.5 and 1 MAC) at constant coronary flow rates of 5 ml/min for 25 min, then 1 ml/min for 30 min and again 5 ml/min for 10 min. Before, during and after low-flow perfusion, a bolus of human platelets was applied into the coronary system. To simulate thrombogenic conditions, 0.3 U/ml human thrombin was infused during low-flow perfusion and reperfusion. The number of platelets sequestered to the endothelium was calculated from the difference between coronary in- and output of platelets. The myocardial production of lactate and consumption of pyruvate and coronary perfusion pressure were also determined.
Results : At a flow rate of 5 ml/min only about 3% of the applied platelets did not emerge from the coronary system, in any group. In contrast, 13.1±1.2% (mean±SEM) of infused platelets became adherent in low-flow perfusion in the control group without anaesthetic. The adherence was reduced with each 1 MAC isoflurane (to 6.2±1.2%), sevoflurane (to 4.4±0.9%) or halothane (to 3.2±1.5%) (each P <0.05 vs. control). Volatile anaesthetic, 0.5 MAC, did not inhibit platelet adhesion to a statistically significant extent in any case. Perfusion pressure and metabolic parameters were not statistically different between the control and the hearts exposed to anaesthetics.
Conclusion : Volatile anaesthetics in a concentration of 1 MAC can reduce the adhesion of platelets in the coronary system under reduced flow conditions. This action does not arise from vasodilation or inhibition of ischaemic stress.     

Bariatric Surgery in Some "Central and East-European (former Eastern bloc)"Countries - Current Status and Prediction for the Next Millennium

Background: Obesity is increasing globallly, including in the formerly "Eastern Bloc" countries. Methods: A survey was made of obesity and bariatric surgery. Results: In the 8 East and Central European countries studied, with total population 300 million, roughly 43% of the population was overweight (BMI 25-30), 23% obese (BMI > 30), with about 15 million people morbidly obese (BMI > 40). From 0-10 morbidly obese individuals/100,000/year undergo bariatric surgery. Conclusion: Most countries were found to provide inadequate treatment for obesity.The majority of the morbidly obese are not treated effectively. However, health-care awareness of obesity and bariatric surgeons are slowly increasing.     

Is the recovery profile of mivacurium independent of the rate of decay of its plasma concentration in patients with normal plasma cholinesterase activity?

Background: The duration of action of muscle relaxants is poorly correlated to the rate of decay of their plasma concentration. The plasma concentration of mivacurium may rapidly decrease below its active concentration because of the extensive hydrolysis of mivacurium. By inflating a tourniquet on one upper limb for 3 min after the administration of atracurium, mivacurium or vecuronium, we studied the influence of the initial decline of their plasma concentration on their effect. Methods: In 50 patients anaesthetised with thiopental, isoflurane and fentanyl, the effect of bolus doses of 0.15 or 0.25 mg . kg^?1 mivacurium (MIV 15, MIV 25), 0.3 or 0.5 mg . kg^?1 atracurium (ATR 30, ATR 50) and 0.06 or 0.1 mg . kg^?1 vecuronium (VEC 06, VEC 10) were measured on both arms (evoked response of the adductor pollicis to train-of-four stimulation every 12 s), a tourniquet being applied on one arm just before and during 3 min after the muscle relaxant bolus. Results: Tourniquet inflation of 3 min almost abolished the neuromuscular effect of mivacurium. In the vecuronium groups and in the ATR 50 group, tourniquet inflation did not modify the maximum degree of depression of the twitch response. Also, the duration of action of vecuronium was unaffected by the tourniquet. In the ATR 30 group, times to return of the twitch response to 25% (duration 25%) and 75% (duration 75%) of control response were significantly shorter in the cuffed arm, 23 min vs 27 min, and 41 min vs 45 min, respectively. In the ATR 50 group, only duration 25% was significantly shorter in the cuffed arm (41 min vs 45 min). Conclusion: The results suggest that the rate of decline of the plasma concentration of mivacurium is so rapid, that a very low and almost clinically ineffective concentration is present as soon as 3 min after its administration. The results also indicate that the recovery from a mivacurium-induced neuromuscular blockade is not influenced by the rate of decay of its plasma concentration in patients with genotypically normal plasma cholinesterase.     

Membranes in Artificial Organs

Abstract: Membrane processes play a pivotal and enabling role in modern replacement therapy for acute and chronic organ failure and in the management of immunologic diseases. In fact, virtually all contemporary extracorporeal blood purification methods employ membrane devices, and the next generation of artificial organs and tissue engineering therapies are almost certain to be similarly grounded in membrane technology. In this short essay, we comment on the similarities and differences among synthetic membranes and their natural counterparts and also provide a critical overview of the demographics and technology of hemodialysis, hemofiltration, apheresis, oxygenation, and emerging membrane technologies and applications.     

Synergistic interaction between the effects of propofol and midazolam with fentanyl on phrenic nerve activity in rabbits

Background: It has been shown that the depressive effects of both propofol and midazolam on consciousness are synergistic with opioids, but the nature of their interactions on other physiological systems, e. g. respiration, has not been fully investigated. The present study examined the effect of propofol and midazolam alone and in combination with fentanyl on phrenic nerve activity (PNA) and whether such interactions are additive or synergistic. Methods: PNA was recorded in 27 anaesthetised and artificially ventilated rabbits. In three groups, propofol, fentanyl and midazolam were administered intravenously in incremental doses to construct dose-response curves for the depressant effects of each one on PNA. In another two groups, the effect of pretreatment with either fentanyl 1 μg · kg^?1 i. v. or midazolam 0.05 mg · kg^?1 i. v. on the effects of propofol and fentanyl respectively on PNA were studied. Results: Propofol and fentanyl caused a dose-dependent depression of PNA with complete abolition at the highest total doses of 16 mg · kg^?1 i. v. and 32 μg · kg^?1 i. v., respectively. In contrast, midazolam in incremental doses to a total of 0.8 mg · kg^?1 reduced mean PNA by 63%, but approximately 12% of PNA remained at a total dose as high as 6.4 mg · kg^?1. The mean ED₅₀s, calculated from dose-response curves, were 5.4 mg · kg^?1, 3.9 μg · kg^?1 and 0.4 mg · kg^?1 for propofol, fentanyl and midazolam, respectively. Initial doses of either fentanyl 1 μg · kg^?1 i. v. or midazolam 0.05 mg · kg^?1 i. v. acted synergistically with subsequent doses of either propofol or fentanyl to abolish PNA at total doses of 8 mg · kg^?1 and 8 μg · kg^?1, respectively. Conclusion: Fentanyl has a synergistic interaction with both propofol and midazolam on PNA and hence potentially on respiration.