关节镜下可吸收空心界面螺钉固定、四股腘绳肌腱重建前交叉韧带

目的探讨关节镜下可吸收空心界面螺钉固定、四股自体腘绳肌肌腱重建前交叉韧带(anterior cruciate ligament,ACL)的方法及疗效. 方法关节镜下以四股自体腘绳肌肌腱作为ACL替代物,应用(96L-4D)SR-PLA聚丙交酯生物可降解界面螺钉进行移植物固定, 对42例ACL损伤行ACL重建术. 结果 42例术后随访3～22个月,平均11.4月,膝关节活动度均在正常范围.术后Lachman 试验:37例≤1 ,4例2 ,1 例3 .轴移试验:42 例均为阴性.术后Lysholm 评分(89.7 ±9.6)分较术前(49.4±9.1)分显著提高(t=2.12,P=0.038).术后Tegner 活动评分(5.3±1.1)分较术前(2.3±0.7)分显著提高(t=4.13,P=0.008).术后1年MRI示29例可吸收空心界面螺钉部分被吸收;27例重建的韧带位置良好、形态正常;2例韧带在股骨的止点偏前;3例胫骨止点偏前,有轻度顶撞击现象. 结论四股腘绳肌腱是ACL重建的理想替代材料,可吸收空心界面螺钉是ACL重建的理想内固定材料.     

单隧道双束腘绳肌腱双Intrafix固定重建前交叉韧带近期疗效观察

目的 探讨单隧道双束腘绳肌腱双Intrafix固定重建前交叉韧带(ACL)中应用的可行性及近期疗效.方法 对30例ACL损伤患者行关节镜下单隧道双束腘绳肌腱ACL重建术.采用膝关节镜前内侧入路(AM)建立股骨隧道,胫骨端用点对点ACL瞄准器建立隧道.隧道股骨端采用Femoral-Intrafix固定将腘绳肌腱分为前内侧束及后外侧束.通过旋转胫骨端移植物,将移植物调整为生理的双束位置,采用Bio-Intrafix固定胫骨端.结果 30例均获随访,时间6～8个月.根据Lysholm膝关节功能评分:术前为19～58(33.17±11.71)分;术后6个月为88～98(95.30±2.10)分(t=30.20,P<0.01).结论 单隧道双束腘绳肌腱双Intrafix固定重建ACL,手术操作简便,固定牢固,近期效果满意.     

膝关节镜下自体腘绳肌腱移植重建前十字韧带部分束损伤

目的探讨关节镜下自体腘绳肌腱单束移植重建前十字韧带（anterior cruciate ligament,ACL）部分束损伤的临床效果。方法2007年1月至2010年5月关节镜下行自体腘绳肌单束重建ACL部分束损伤16例。术前Ly．sholm评分平均为55．4±6．7分。结果全部获得随访,随访时间为12～23个月,平均18±4．3个月。术后Lysholm评分增至平均89．3±3．3分,有统计学差异（P〈0．05）。所有患者主观症状均消失,全部恢复正常工作与体育锻炼。结论应用自体腘绳肌腱重建ACL部分束损伤明显改善膝关节功能。     

关节镜下自体腘绳肌腱重建前交叉韧带

目的探讨关节镜下应用自体腘绳肌腱重建前交叉韧带(ACL)的临床疗效。方法在关节镜下采用4股自体腘绳肌腱、Endobutton钢板联合可吸收界面螺钉重建ACL治疗28例ACL损伤患者。结果 26例获得随访,时间4～20(12±2.3)个月。术后膝关节功能均在正常范围内,Lachman试验阴性23例,阳性3例(但终末点均"硬");Lysholm评分:术前为28～65(35.2±12.53)分,术后为90～98(93.12±5.10)分。结论关节镜下应用自体腘绳肌腱重建ACL创伤小,手术操作简便,效果可靠。     

关节镜下无植入物固定自体腘绳肌腱双束重建前交叉韧带

目的 总结关节镜下使用自体腘绳肌腱胫骨双隧道双束无植入物固定重建膝前交叉韧带(anterior oruciate ligament,ACL)的近期临床效果. 方法 2004年3月-2007年6月,收治12例ACL损伤患者,男8例,女4例:年龄23～56岁,平均32岁.车祸伤9例,运动伤3例.术前前抽屉试验(anterior drawer test,ADT):2度2例,3度10例:Lachrnan试验均为3度;轴移试验:1度2例,2度6例,3度4例.国际膝关节评分委员会(international knee doeumentation committee,IKDC)评分为(39.3±4.7)分,Lysholm评分为(44.4 ±4.9)分.均在关节镜下采用自体腘绳肌腱双束无植入物固定重建ACL. 结果 患者切口I期愈合,无术后并发症发生.术后患者均获随访,随访时间10～22个月,平均15个月.术后12周ADT试验1度9例,2度3例;Lachman试验1度8例,2度3例,3度1例;轴移试验:0度9例,1度3例.IKDC评分为(92.4±3.7)分,Lysholm评分为(91.6±2.7)分,均优于术前(P<0.01). 结论 关节 镜下应用自体腘绳肌腱胫骨双隧道双束无植入物固定,重建ACL符合其解剖重建和生理学功能,近期疗效好.     

腘绳肌腱移植单隧道双束保残重建前交叉韧带的疗效

目的:探讨腘绳肌腱单隧道双束保残重建前交叉韧带(ACL)的可行性及近期疗效。方法:自2011年8月至12月采用关节镜下腘绳肌腱单隧道双束保残重建ACL25例,其中男19例,女6例;年龄16～50岁,平均(26.26±9.53)岁;左侧15例,右侧10例;病程1～60d,平均9.6d;新鲜损伤20例,陈旧性损伤5例。新鲜损伤患者均有膝关节肿胀、疼痛,其中前抽屉试验阳性14例,Lachman试验阳性17例。5例陈旧性损伤膝关节疼痛,均有关节不稳,前抽屉试验及Lachman试验均阳性。采用膝关节镜髌腱入路保留ACL残端,前内侧入路(AM)建立股骨隧道,胫骨端用点对点ACL瞄准器建立隧道。隧道股骨端采用Femoral-Intrafix固定,将腘绳肌腱分为前内侧束及后外侧束。通过旋转胫骨端移植物,将移植物调整为生理的双束位置,采用Bio-Intrafix和staple固定胫骨端。所有患者术前及术后分别行前抽屉试验和Lachman试验,并采用Lysholm膝关节功能评分评价膝关节功能。结果:25例均获随访,时间12～18个月。根据Lysholm膝关节功能评分:术前25～49分,平均34.08±7.60;术后12个月89～98分,平均94.52±2.86(t=21.29,P<0.01)。术后评分高于术前。结论:腘绳肌腱单隧道双束保残重建ACL,手术操作简便,固定牢固,效果可靠。     

关节镜下半腱肌、股薄肌腱重建前交叉韧带

目的关节镜下以半腱肌、股薄肌腱重建膝前交叉韧带,分析影响疗效的因素。方法自2002年12月至2004年6月,关节镜下endobuttonl固定四股腘绳肌腱修复膝前交叉韧带损伤66例72膝。膝前小切口取半腱肌腱、股薄肌腱修整、对折后成四股,分别建立胫骨隧道及股骨隧道,用Endobutton和门形钉固定肌腱,重建ACL的解剖结构和生理功能。术后即行功能锻练。结果66例患者得到随访,随访时间13-30个月,平均22.25个月。术前Lachman征( ),术后Lachman征(-)。术前Lysholm评分从27分到71分,平均53.75分;术后Lysholm评分从70分到99分,平均90.83分,术前、术后评分有显著性差异(t=2.23,P<0.05)。结论腘绳肌腱具有良好的抗拉强度和刚度,在关节镜下用四股腘绳肌腱重建膝前交叉韧带是一种疗效可靠的治疗方式。     

关节镜下纽扣固定"人"字形肌腱移植物重建前交叉韧带的初步报告

目的 探讨关节镜下股骨端纽扣固定"人"字形肌腱移植物重建膝关节前交叉韧带(ACL)的手术方法和近期疗效.方法 2008年3月至2009年1月共收治12例ACL断裂患者,其中男8例,女4例;年龄17～36岁,平均25.2岁;左膝9例,右膝3例.致伤因为:运动伤11例.交通伤1例.急件损伤1例,陈旧件损伤11例.12例患者均取自体腘绳肌腱或异体肌腱编织形成6股"人"字形移植物,采用关节镜下胫骨舣隧道界面螺钉固定、股骨单隧道纽扣固定方法行ACL重建手术,观察术后近期疗效,以Lysholm评分、Larson评分及国际膝关节评分委员会(IKDC)评分评价比较手术前后膝关节功能,以X线片观察骨隧道变化情况.结果 12例患者术后获12～18个月(平均15个月)随访,末次随访时患膝关节活动度均正常.术后1年Lysholm评分由术前(61.25±3.77)分提高到(91.50±2.78)分(t=22.376,P=0.000);Larson评分由术前(58.08±2.58)分提高到(90.08±2.68)分(t=29.837,P=0.000):IKDC评分由术前(63.33±2.84)分提高到(91.75±2.38)分(t=26.576,P=0.000),差异均有统计学意义.所有患者术后X线片未见明显关节间隙改变.结论 关节镜下股骨端纽扣固定"人"字形移植物重建ACL能有效恢复膝火节的稳定性,近期疗效佳,中远期效果有待于进一步观察.     

关节镜下LARS韧带与自体腘绳肌腱重建前交叉韧带的早期临床疗效比较

目的回顾性研究LARS韧带和自体腘绳肌腱重建前交叉韧带(ACL)的早期临床疗效。方法自2008年7月～2011年2月对54例ACL损伤分别行关节镜下LARS韧带和自体腘绳肌腱重建ACL,腘绳肌腱组31例,LARS韧带组23例,分别对其术前术后行Lysholm、Tegner、IKDC评分,并选取最近一次随访结果进行统计分析。结果术后LARS韧带组的膝关节Lysholm、Tegner、IKDC评分略高于腘绳肌腱组,但两组差异无统计学意义(P>0.05)。结论 LARS韧带和自体腘绳肌腱重建ACL能明显改善患者的功能,LARS韧带组和自体韧带组有相似的早期疗效,且恢复时间明显缩短。     

关节镜下可吸收螺钉固定腘绳肌重建前交叉韧带疗效评价

目的评价关节镜下可吸收螺钉固定腘绳肌腱重建膝关节前交叉韧带(ACL)的效果。方法27例患者(27膝)经关节镜检查证实均为ACL断裂,采用关节镜下自体腘绳肌重建ACL,生物可吸收螺钉解剖位固定重建韧带。结果所有病例均得到随访,时间6~24个月,均无术中、术后并发症,切口均一期愈合。IKDC综合评定:术前异常10例、严重异常17例,术后正常9例、接近正常16例、异常2例。Lysholm膝关节功能评分:由术前33~60分(平均45.7分)提高至83~96分(平均90.3分),差异有显著性(P<0.05)。结论关节镜下可吸收螺钉固定自体腘绳肌腱重建ACL手术创伤小、固定确实、操作简捷,近期疗效满意。     

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.     

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.     

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.     

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.     

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.     

Systemic analgesia adapted to the children's condition

A concept of balanced analgesia using nonsteroidal anti-inflammatory drugs (NSAIDs), paracetamol (acetaminophen), opioids, and corticosteroids can also be used in patients with pre-existing illnesses. NSAIDs are the most effective treatment for acute pain of moderate intensity in children; however, these drugs should be avoided in patients at increased risk for serious side effects, e.g. patients with renal impairment, bleeding tendency, or extreme prematurity. NSAIDs can be given with minimal risks to the younger child with mild to moderate asthma, and, in these patients, the use of steroids can be encouraged; in addition to their antiemetic and analgesic action, a beneficial effect on asthma symptoms can be expected. In the non-intubated child with cerebral trauma, exaggerated sedation caused by opioids and increased bleeding tendency caused by NSAIDs must be avoided. In neonates and small infants, the oral administration of sucrose or glucose is helpful to minimize pain reaction during short uncomfortable interventions.     

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.