老年女性腰椎骨密度与年龄及椎旁体质成分相关性分析

目的探讨不同腰椎椎体骨密度(bone mineral density,BMD)与年龄及同层面椎旁腰大肌、竖脊肌、腹部脂肪、血管钙化情况的关系。方法收集体检中心行腰椎检查的老年女性90名,采用定量CT(quantitative CT,QCT)及后处理软件测量L2-L4椎体骨密度及三椎体同层面椎旁体质成分。统计学处理应用配对t检验、Pearson相关分析和多元逐步回归分析等。结果①3组椎体BMD均与年龄均呈负相关(P0.05),L2BMD、L3BMD均与双侧腰大肌、竖脊肌密度成正相关(r=0.233~0.301,P均0.05)。而L4BMD显示与双侧竖脊肌密度及腹部脂肪面积有良好的相关性,均呈正相关。②多元逐步回归分析显示除年龄外,肌肉是影响BMD的重要因素。年龄是唯一全部进入3组腰椎BMD回归方程,并呈负相关,是影响腰椎BMD的重要因素。结论老年女性的腰椎骨密度与椎旁腰大肌、竖脊肌密度,腹部脂肪面积及年龄密切相关,除年龄外椎旁肌肉密度对骨密度影响最大。QCT扫描更加直观、精确显示椎骨与椎旁体质成分情况,可作为测量诊断骨质疏松、体质成分的新手段。     

定量CT测量膝关节骨密度的重复性研究

目的探讨定量CT( QCT)测量膝关节骨密度（BMD )的重复性研究。方法选取北京积水潭 医院确诊为一侧膝关节前交叉韧带损伤（未经治疗）,另一侧膝关节健康的30名患者行双膝关节 QCT骨密度检测,2名观察者用定量CT的测量技术前后两次独立测量患者双膝关节股骨远端内外侧 髁及胫骨平台处骨密度。结果双因素方差分析,除双膝关节胫骨平台内上1/9处BMD值统计学有 差异（P <0.05 ,ICC >0.7 ),同一观察者不同时间测量同一部位的BMD值均值相近,无统计学差异（P >0.05,ICC >0. 9 )。不同观察者所测定的BMD值也无显著性差别（P >0.05,ICC >0.9 )。结论定 量CT能够测量膝关节松质骨的体积骨密度,并且重复性良好,可用于评价膝关节骨密度的状态及应 用于临床     

欧洲人胸腰椎尸体骨外周骨定量CT (pQCT)测定研究

目的　研究老年人 T3 至 L5椎体骨矿物含量 ,骨密度及面积。方法　用外周骨定量 CT(p QCT)仪测量 40具老年尸体 6 0 0个椎体骨矿物含量 ,骨密度 ,椎体横断面面积等。结果　 T3 至L5椎体总骨密度为 188.2 5 m g/ cm3～ 191.6 0 mg/ cm3 ,松质骨密度为 12 8.0 1mg/ cm3～130 .6 6 m g/ cm3 ,皮质下骨密度为 45 4.90 mg/ cm3～ 46 1.87mg/ cm3 ,皮质骨密度为 76 4.13mg/ cm3～76 9.5 5 m g/ cm3 。结论　为国内开展脊柱椎体 p QCT测量提供参考数据 ,为进行欧洲人与国人脊柱骨矿物含量、骨密度及椎体横断面面积对比提供依据。     

优化扫描参数宝石能谱CT测量腰椎骨密度临床效果评价

目的探讨优化扫描参数的宝石能谱CT测量人体L2、L3椎体骨密度的临床应用效果。方法研究组:本院同时接受腹部或腰椎宝石能谱CT检查和QCT检查的患者126例,男性60例,女性66例;年龄15~92岁。能谱CT采用优化后的扫描参数(管电流260 mA,球管转速0.8 s/r),重建的1.25 mm图像传至AW4.6工作站,并测量L2、L3椎体的HAP(脂)值;QCT图像传至Mindways工作站并测量L2、L3椎体的骨密度值。对照组:本院前期同时接受腹部或腰椎宝石能谱CT检查(采用机器默认参数,管电流375 mA,球管转速0.7 s/r)和QCT检查的57例患者。采用统计学软件SPSS 25.0对研究组及对照组L2、L3椎体的HAP(脂)值与QCT骨密度值行Pearson相关性分析,对其组间差异采用方差分析;采用统计学软件MedCalc对研究组与对照组的相关系数行相关系数对比检验。结果研究组及对照组L2、L3椎体HAP(脂)值与QCT骨密度值均具有显著相关性;研究组内各亚组HAP(脂)值与QCT骨密度值相关性较对照组更高;研究组CTDIvol(mGy)较对照组明显减低。结论优化扫描参数的宝石能谱CT对腰椎骨密度测量结果与QCT测量的一致性更好。     

应用双能CT与定量CT对椎体骨密度测量的对照研究

目的应用双能CT(DECT)及定量CT(QCT)测量腰椎骨密度,评价利用双能CT测量骨密度(BMD)的可行性。方法对56名志愿者采用DECT检查,获得钙值图,测量骨钙CT值及骨髓CT值,同时应用QCT测量骨密度(BMD),分析骨钙CT值及骨髓CT值与BMD值的相关性。结果腰椎椎体骨钙CT值与BMD值呈显著正相关(L1-5椎体Pearson相关系数分别为:r=0.715,0.692,0.739,0.673,0.686,P0.01);骨髓CT值与BMD值呈正相关(L1-5椎体Pearson相关系数分别为r=0.343、0.315、0.439、0.440、0.456,L5椎体P0.05,其余椎体P0.01)。结论 DECT所测量腰椎骨钙CT值及骨髓CT值与QCT所测BMD值密切相关,可定量反映腰椎BMD变化。     

定量CT研究成年女性腰部椎后肌群体质成分与腰椎骨密度的相关性

目的探讨成年女性腰部椎后肌群体质成分与腰椎骨密度的相关关系。方法将518名21~81岁的成年女性按年龄分为青中年组(≤50岁)和老年组(50岁),使用定量CT(QCT)测量L2~L4椎体骨密度(BMD)及L3椎体中部层面椎后肌群的脂肪面积、肌肉面积、脂肪肌肉比。使用独立样本T检验比较两组间差异,使用偏相关及多元线性回归分析研究BMD与年龄、BMI及椎后肌群体质成分的相关关系。结果青中年组BMI、椎后肌群脂肪面积及脂肪肌肉比低于老年组,而BMD及椎后肌群肌肉面积高于老年组,差异有统计学意义(P0.01)。控制年龄、BMI因素偏相关分析结果显示,青中年组及老年组BMD与椎后肌群脂肪面积呈负相关(r=-0.178、-0.200,P0.05),与脂肪肌肉比呈负相关(r=-0.138、-0.177,P0.05),而与肌肉面积无显著相关性(r=-0.050、0.066,P0.05)。回归分析显示,椎后肌群脂肪面积、年龄、BMI是BMD的主要影响因素。结论成年女性腰部椎后肌群脂肪浸润程度与腰椎骨密度存在相关性,且相关性随年龄而增加。     

定量CT与DXA测量近段股骨面积骨密度及T值的比较研究

目的 研究定量CT( QCT)测量近段股骨面积骨密度准确性和可重复性,并对QCT和DXA近段股骨测量结果及T值进行比较性研究。方法 来自前瞻性城乡流病研究（PURE)项目的103名女性和49名男性同一天进行髋关节QCT和DXA扫描。对观察者间及观察者内CTXA测量结果进行分析,为了减小QCT和DXA因体模不同造成的误差,用Mindways回归方程对QCT测量结果进行换算,并运用Bland-Altman分析及线性回归分析比较CTXA和DXA结果的差异和相关性。结果QCT 全髋关节(TH)与股骨颈(FN)的面积骨密度均低于DXA测量结果,分别为21. 0%和17. 8%。而QCT测量值用Mindways回归方程换算后,减小了与DXA测量结果的差异。FN及TH的观察者内及观察者间CTXA测量误差分别为0. 070和0. 024 g/ cm2及0. 030和0. 012 g/cm2,与DXA重复测量误差相近。经过Mindways校准方程换算后,Bland-Altman分析显示CTXA和 DXA的TH的偏倚为-0.002( SD =0.05) g/m2,而FN为-0.005 ( SD =0.06) g/m2。CTXA测量女性近段股骨的T值与DXA的T值相关性很好,FN的R2 =0. 809,TH的R2 =0. 883。结论CTXA测量的髋关节aBMD与DXA的测量的准确性相近,经过合适的调整,CTXA能够得出类似DXA的aBMD,对于老年女性其获得的全髋关节的T值与DXA结果相关性很好,从而能够用于诊断骨质疏松。     

腹部脂肪含量对低毫安定量CT测量腰椎体模骨密度的影响

目的 评估不同含量腹部脂肪对低毫安定量CT(quantitative computed tomography, QCT)测量腰椎体模骨密度(bone mineral density, BMD)准确性的影响。方法 选取不同面积的新鲜猪离体皮下脂肪包裹于欧洲腰椎体模(European spine phantom, ESP)周围,模拟人体腹部不同含量总脂肪组织(total adipose tissue, TAT),根据TAT面积分为四组：TAT=0、200、320、420 cm²。利用常规QCT及低毫安QCT对每组体模重复扫描10次,测定L_1～3椎体BMD值。采用单样本t检验分析低毫安QCT测量值与体模真实值之间的差异。利用单因素方差分析Tukey检验,比较不同TAT条件下低毫安QCT测量值组内差异。以配对样本t检验比较常规QCT与低毫安QCT之间各椎体BMD测量值的差异。计算并比较BMD测量值的均方根误差(RMSE);以Pearson相关分析观察RMSE与TAT的相关性。结果 TAT=0、200、320 cm²时,常规QCT...     

绝经妇女腰椎及髋关节定量cT骨密度测量诊断骨质疏松的初步研究

目的比较绝经后妇女L2-L4椎体及髋关节两个部位的定量CT骨密度（BMD )测量诊断骨 质疏松的效能。方法175例绝经妇女,年龄48-96岁,平均年龄为69 ±9岁。同时QCT测量L2-L4椎体的平均体积骨密度及髋关节类DXA的面积骨密度,右股骨颈和全髋二个感兴趣区（ROI )。 采用国际临床骨密度学会（ISCD )QCT骨质疏松诊断标准（<80 mg/cm3 )和WHO髋关节DXA骨密 度诊断标准即股骨颈或全髋感兴趣区的T值（-2.5 SD )进行骨质疏松诊断。比较二者诊断骨质疏 松的效能。结果175绝经后妇女中,QCT骨密度测量腰椎部位骨密度值骨质疏松的检出率是44%( 77/175 )。如果采用髋部检查股骨颈部位为11%.( 19/175 ),全髋部位为14%.( 24/175 ),或二者任一 部位为18%_( 31/175 )。如果只做腰椎,不做髋关节,有7人漏诊,而如果只做髋关节,不做腰椎会漏 诊44人。结论采用QCT骨密度测量,绝经妇女腰椎检查骨质疏松检出率为44%_,而髋部检查检出 率为18%_。采用QCT骨密度测量,测量腰椎一个部位就可以诊断骨质疏松。     

老年及不同老龄段脊柱椎体骨密度测定研究

目的 研究老年及各老龄段T3至L5椎体骨密度值。方法 用外周骨定量CT（pQCT)仪测量40具老年尸体600个椎体的总骨密度，松质骨密度，皮质下骨密度，皮质骨密度，椎体横断面总面积，松质骨面积，皮质下骨面积，皮质骨面积及皮质骨厚度，分别统计60-69岁（A组），70-79岁（B组），80-89岁（C组），90-98岁（D组）椎体骨密度值，结果 T3至L5椎体总骨密度为188.25-191.60mg/cm^3，松质骨密度为128.01-130.66mg/cm^3。皮质下骨密度为454.90-461.87mg/cm^3，皮质骨密度为764.13-769.55mg/cm^3,60-79岁椎体总骨密度值保持在相对稳定水平，80岁以后该值下降较明显。结论 为国内开展脊柱骨质疏松症研究及椎体pQCT测量提供参考数据，为进行欧洲人与国人脊体骨密度对比提供依据。     

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.