关节软骨源性微载体生物相容性及异位成软骨特性观察

目的 观察改良后软骨源性微载体的微观结构及主要成分,其对软骨细胞增殖的影响及体内异位成软骨特性.方法 将新鲜猪软骨片粉碎后,梯度筛滤后得到直径大200～400 μm的软骨源性微载体,经1%十二烷基硫酸钠（SDS）脱细胞处理后,Hoechst 33258荧光染色观察其DNA残留,采用扫描电镜对其微结构进行观察,通过甲苯胺蓝、番红花O组织学染色和Ⅱ型胶原免疫荧光染色观察微载体的主要成分;体外复合软骨细胞后,通过MTT观察软骨源性微载体对软骨细胞增殖的影响;将复合有软骨细胞的软骨源性微载体包埋于裸鼠皮下观察其异位成软骨能力.结果 改良后的微载体形态近似椭圆形,直径200～400 μm,微丝覆盖其表面,微丝长度40～90 nm;脱细胞处理后Hoechst 33258荧光染色阴性;甲苯胺蓝和番红花O组织学染色及Ⅱ型胶原免疫组化染色阳性;在MTT检测细胞增殖中,第1天以后软骨源性微载体组及条件培养基组的OD值均高于完全培养基组（P〈0.05）;复合有软骨细胞的软骨源性微载体具有异位成软骨能力.结论 本实验成功制备的软骨源性微载体,可作为天然微载体高效扩增软骨细胞,可为组织工程提供优质种子细胞;其具有异位成软骨能力,有望成为软骨组织工程的新型支架.     

关节软骨源性微载体生物相容性及异位成软骨特性观察

目的 观察改良后软骨源性微载体的微观结构及主要成分,其对软骨细胞增殖的影响及体内异位成软骨特性.方法 将新鲜猪软骨片粉碎后,梯度筛滤后得到直径大200～400 μm的软骨源性微载体,经1%十二烷基硫酸钠（SDS）脱细胞处理后,Hoechst 33258荧光染色观察其DNA残留,采用扫描电镜对其微结构进行观察,通过甲苯胺蓝、番红花O组织学染色和Ⅱ型胶原免疫荧光染色观察微载体的主要成分;体外复合软骨细胞后,通过MTT观察软骨源性微载体对软骨细胞增殖的影响;将复合有软骨细胞的软骨源性微载体包埋于裸鼠皮下观察其异位成软骨能力.结果 改良后的微载体形态近似椭圆形,直径200～400 μm,微丝覆盖其表面,微丝长度40～90 nm;脱细胞处理后Hoechst 33258荧光染色阴性;甲苯胺蓝和番红花O组织学染色及Ⅱ型胶原免疫组化染色阳性;在MTT检测细胞增殖中,第1天以后软骨源性微载体组及条件培养基组的OD值均高于完全培养基组（P〈0.05）;复合有软骨细胞的软骨源性微载体具有异位成软骨能力.结论 本实验成功制备的软骨源性微载体,可作为天然微载体高效扩增软骨细胞,可为组织工程提供优质种子细胞;其具有异位成软骨能力,有望成为软骨组织工程的新型支架.     

关节软骨源性微载体与软骨细胞的体外相容性

目的评估人关节软骨源性微载体与人软骨细胞的体外粘附性。方法切取人关节软骨,对之冷冻干燥后,经粉碎机粉碎,筛取150～200μm大小的软骨粒,经0.25%的胰酶在37℃消化24h,再经1%的化学去污剂TritonX-100震荡72h,蒸馏水清洗48h后,在冻干机内再次冻干12h,经钴60灭菌后,与第6代人软骨细胞共同培养,分别在倒置显微镜下和电镜下观察即刻、2h、8h、30h的粘附情况。结果倒置显微镜下见软骨粒变为绒球状或毛刷状,将此微载体加入培养基后,即见有呈圆球形的软骨细胞与微载体相粘附,2h见微载体上粘附了大量软骨细胞,仍呈圆球形,8h见微载体上粘附的大量软骨细胞仍呈圆球形,而瓶底贴附的软骨细胞已呈现为成纤维细胞样形状,30h见软骨细胞-微载体复合体已沉降贴附于培养瓶底部,软骨细胞增殖明显并向周围伸展,而电镜下观察见粘附于微载体上的软骨细胞仍维持了软骨细胞的形状。整个观察期间均见软骨细胞增殖良好,提示制备的关节软骨源性微载体对软骨细胞无毒害作用。结论关节软骨源性微载体与软骨细胞的体外相容性良好。     

可注射性组织工程软骨源性微载体的微观结构及其生物相容性观察

[目的]改进软骨源性微载体的制备方法.对其微观结构特征及其与骨髓间充质细胞的生物相容性进行观察,探索新的可注射性组织工程软骨的制备方法.[方法]将新鲜的猪关节软骨在液体中粉碎,梯度离心后制备成150～300 μm的颗粒,去细胞处理后采用常规组织学方法观察软骨微粒的空间结构及化学组成,采用扫描电镜观察软骨源性微载体的形态特征,随后体外获取扩增骨髓间充质细胞,与软骨微粒复合,然后采用旋转式生物反应器扩增,构建可注射性组织工程软骨细胞.[结果]本研究制备的软骨微粒呈圆形或椭圆形,表面呈毛刷状结构,主要成分是Ⅱ型胶原和GAG,而毛刷的主要成份Ⅱ型胶原、骨髓间充质干细胞不仅与微载体结合良好,还能够在其表面大量扩增.[结论]与传统的微载体不同,软骨源性微载体与细胞复合后,不需要再将细胞消化,避免了软骨细胞外基质的损失,可以作为可注射性组织工程软骨的理想材料和方法.     

骨关节炎软骨中Ⅰ型和Ⅱ型胶原的分布

目的：研究骨关节炎软骨中Ⅰ型和Ⅱ型胶原的分布。方法：从正常关节软骨和骨关节炎软骨上取样本做切片，所有样本行HE、蕃红0染色及Ⅰ型和Ⅱ型胶原免疫组化。结果：骨关节炎软骨中Ⅱ型胶原免疫组化染色不均匀。Ⅰ型胶原染色，在表层和中层的部分区域有不规则着色，纤维样组织中，Ⅰ型胶原免疫组化呈阳性，Ⅱ型胶原免疫组化不着色，结论：骨关节软骨基质中Ⅱ型胶原和蛋白聚糖的破坏增强与软骨细胞对其合成增强同时存在，软骨修复的过程中，部分软骨细胞发生去分化，而表达Ⅰ型胶原。     

人关节软骨脱细胞基质的制备

目的制备人关节软骨脱细胞基质。方法切取人关节软骨,对之冷冻干燥后,采取化学去污剂TritonX100及DNA酶和RNA酶等试剂制备脱细胞的人关节软骨。做HE、番红0及软骨蛋白聚糖(aggrecan)免疫组化染色等方法进行检测。结果HE染色、番红0染色均显示细胞陷窝内己无细胞结构番红花0染色阳性;软骨蛋白聚糖免疫组化染色阳性。结论人关节软骨冻干后,经去污剂酶等处理方法可脱去软骨的细胞成分,并且保留了软骨细胞外基质,成功制备了人关节软骨脱细胞基质。     

大鼠不同部位软骨细胞的形态及表型特征比较研究

目的:比较研究大鼠椎间盘软骨终板和膝关节软骨的细胞表型特征的相关性.方法:大鼠的软骨终板和关节软骨细胞分别予以消化培养.进行光镜、电镜观察其形态.使用免疫组化技术分别检测不同部位细胞的Ⅱ型胶原表达.结果:大鼠椎间盘软骨终板和关节软骨细胞形状相似,并且均表达Ⅱ型胶原.结论:本研究提示软骨终板表达软骨细胞的特征性胶原,与关节软骨细胞相似.     

羊软骨细胞在生物反应器中的培养和扩增

[目的]探索在旋转生物反应器内，应用微载体技术快速扩增分化良好的羊软骨细胞的方法。[方法]将培养的羊软骨细胞应用Cytodex-3微载体在旋转生物反应器（RCSS）内，进行动态培养，应用倒置显微镜对微载体表面的软骨细胞进行动态观察，并对收获的软骨细胞进行Ⅰ、Ⅱ型胶原的细胞免疫化学染色分析。[结果]关节软骨细胞于1d内贴附于Cytodex-3微载体表面，细胞初期为圆球形、半球形凸起，逐渐向周围伸展，随时间的延长，贴附于微载体的细胞逐渐增多，到培养后期，细胞密度可达最初接种的15～17倍，在微载体上收获的软骨细胞经Ⅰ型胶原的免疫细胞化学染色呈阴性，Ⅱ型胶原染色则呈强阳性。[结论]利用微载体细胞培养技术可简便快速地在体外扩增羊软骨细胞，可为构建组织工程化人工软骨提供大量活性、分化良好的软骨细胞。     

重组腺病毒介导外源性SOX9在正常关节软骨细胞中诱导软骨基质合成的体外表达

背景：关节软骨损害是临床一种常见的损伤,软骨形成转录因子SOX9是一种调控Ⅱ型胶原合成的关键因子。 目的：观察以表达外源性SOX9的腺病毒体外成功感染关节软骨细胞后对Ⅱ型胶原和蛋白聚糖（Aggrecan）合成的影响,探讨软骨损伤后修复软骨缺损的基因治疗方法。 方法：体外构建腺病毒载体AdSOX9和AdGFP,成功感染培养的人关节软骨细胞,分别以逆转录聚合酶链式反应（RT-PCR）技术检测了病毒感染前后SOX9、II型胶原和蛋白聚糖基因mRNA的表达,同时以免疫组化技术检测了病毒感染前后关节软骨细胞中Ⅱ型胶原的表达。 结果：应用AdEasy腺病毒构建专利技术体外成功构建了能高效表达外源性SOX9的腺病毒AdSOX9和只表达绿色荧光蛋白GFP的腺病毒AdGFP;以腺病毒AdSOX9和AdGFP体外成功感染人关节软骨细胞后48h,未感染对照组和AdGFP感染组,均检测到了Ⅱ型胶原和蛋白聚糖的表达;而AdSOX9感染组的细胞中,检测到了SOX9基因mRNA的表达明显增高,与未感染对照组和AdGFP感染组相比有显著性差异（P〈0．05）,同时,Ⅱ型胶原和蛋白聚糖的表达也较未感染对照组和AdGFP感染组明显增高,差异显著（P〈0．05）。 结论：以外源性SOX9为目的基因的腺病毒介导基因治疗方法,在促进关节软骨细胞Ⅱ型胶原和蛋白聚糖合成方面得出了初步满意的结果,SOX9可能是关节软骨缺损基因治疗研究领域一个新的理想靶点,值得继续深入研究。     

兔半月板纤维软骨细胞的培养及生物学特性研究

目的 :通过半月板纤维软骨细胞的分离、培养、鉴定 ,观察其生长特点 ,研究半月板生物学特性及其损伤修复的细胞学基础。方法 :机械分离兔半月板软骨 ,胰蛋白酶、胶原酶联合消化 ,10 ?S的DMEM中原代和传代培养 ,倒置显微镜动态观察细胞形态及生长情况 ,GAG、Ⅱ型胶原免疫组化染色 ,电镜观察细胞超微结构。结果 :培养细胞呈多角形 ,有突起 ,富含分泌颗粒 ,GAG、Ⅱ型胶原染色阳性 ,细胞线粒体和内质网发达。结论 :培养的细胞保持了体内纤维软骨细胞的基本特性。     

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 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.     

Influence of dopexamine hydrochloride on haemodynamics and regulators of circulation in patients undergoing major abdominal surgery

Background: Catecholaminergic support is often used to improve haemodynamics in patients undergoing major abdominal surgery. Dopexamine is a synthetic vasoactive catecholamine with beneficial microcirculatory properties. Methods: The influence of perioperative administration of dopexamine on cardiorespiratory data and important regulators of macro- and microcirculation were studied in 30 patients undergoing Whipple pancreaticduodenectomy. The patients received randomized and blinded either 2 μg · kg^?1 · min^?1 of dopexamine (n=15) or placebo (n=15, control group). The infusion was started after induction of anaesthesia and continued until the morning of the first postoperative day. Endothelin-1 (ET-1), vasopressin, atrial natriuretic peptide (ANP), and catecholamine plasma levels were measured from arterial blood samples. Measurements were carried out after induction of anaesthesia, 2 h after onset of surgery, at the end of surgery, 2 h after surgery, and on the morning of the first postoperative day. Results: Cardiac index (CI) increased significantly in the dopexamine group (from 2.61±0.41 to 4.57±0.78 1 · min^?1 · m^?2) and remained elevated until the morning of the first postoperative day. Oxygen delivery index (DO₂I) and oxygen consumption index (VO₂I) were also significantly increased in the dopexamine group (DO₂I: from 416±91 to 717±110 ml/m² · m²; VO₂I: from 98±25 to 157±22 ml/m² · m²), being significantly higher than in the control group. pHi remained stable only in the dopexamine patients, indicating adequate splanchnic perfusion. Vasopressive regulators of circulation increased significantly only in the untreated control patients (vasopressin: from 4.37±1.1 to 35.9±12.1 pg/ml; ET-1: from 2.88±0.91 to 6.91±1.20 pg/ml). Conclusion: Patients undergoing major abdominal surgery may profit from prophylactic perioperative administration of dopexamine hydrochloride in the form of improved haemodynamics and oxygenation as well as beneficial influence on important regulators of organ blood flow.     

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.