锁骨上神经营养血管皮瓣的应用解剖

目的为临床应用锁骨上神经营养血管皮瓣提供解剖学依据.方法在36侧经股动脉插管灌注红色乳胶溶液的成人尸体标本上,对锁骨上神经营养血管的横径、长度及穿深筋膜点的位置,进行了观测,并在标本上模拟手术设计.结果锁骨上神经营养血管包括颈升动脉肌皮支、颈横动脉颈段皮支、胸廓内动脉穿支、胸肩峰动脉胸肌支与肩峰支皮动脉,其穿深筋膜点外径分别为0.75、1.12、1.36、0.70、0.79!mm;且穿深筋膜点位置相对恒定,节段性地分布于锁骨上神经,为整段皮神经提供营养.结论以上述节段动脉为蒂,设计锁骨上神经营养血管皮瓣.     

带前臂外侧皮神经营养血管筋膜皮瓣的应用解剖

目的：为带前臂外侧皮神经及其营养血管筋膜皮瓣提供形态学基础。方法：在３２侧成人上肢标本上，观测前臂外侧皮神经营养血管及其周围皮肤的供血情况。结果：前臂外侧皮神经近侧的血供为肱动脉末端和桡动脉起始部的肌皮支，起始处外径分别为１．４ｍｍ、１．１ｍｍ，穿出深筋膜前长为１．９ｃｍ、１．４ｃｍ；远侧主要为桡动脉的粗大皮支，起始处外径为０．８ｍｍ，穿出深筋膜前长０．８ｃｍ；此外，桡动脉的茎突返支及掌浅支的皮支营养其远端。其神经支在神经束间或神经旁相互吻合构成纵向（链式）血管网，并借分支与筋膜皮支所形成的皮下筋膜血管网沟通。结论：可设计带前臂外侧皮神经及其营养血管的筋膜皮瓣，顺行或逆行转位修复邻近部位的软组织缺损。     

内踝前动脉穿支为蒂隐神经-大隐静脉营养血管远端蒂皮瓣的应用解剖

目的为内踝前动脉穿支隐神经-大隐静脉营养血管皮瓣设计提供解剖学依据.方法30侧经动脉内灌注红色乳胶成人下肢标本,解剖观察踝前内侧区的动脉来源、分支分布及其邻近动脉吻合.结果踝前内侧区动脉,前侧来自内踝前动脉和胫前动脉踝上支穿支,外径平均0.6～0.8mm;后侧来自胫后动脉肌间隙支和骨皮穿支,其中胫后动脉的肌间隙支2～3支,平均外径(0.9±1.2)(0.5～2.5)mm,骨皮穿支1～2支,外径(1.3±0.3)(0.7～2.0)mm.动脉穿支均发出骨膜支、深筋膜支、皮支、皮神经及浅静脉营养支,构成隐神经大隐静脉营养血管,以及深、浅筋膜血管网.结论踝前内侧区的隐神经、大隐静脉、筋膜及皮肤营养血管同源,呈明显的纵向性分布.设计以内踝前动脉筋膜穿支为蒂的隐神经-大隐静脉营养血管皮瓣,远端蒂的旋转点在内踝尖平面,可用于转位修复前足的软组织缺损.     

颈肩峰区跨区供血轴型皮瓣的应用解剖

目的 探讨颈肩峰区跨区供血轴型皮瓣的解剖学基础及临床应用可行性.方法 在北京协和医学院基础研究所解剖形态实验室提供的5具(10侧)新鲜成人尸体及10具(20侧)防腐成人标本上,应用医用红色乳胶灌注动脉,蓝色乳胶灌注静脉,在直视或手术显微镜下,解剖颈肩峰区动静脉、皮动脉以及真皮下血管网、深筋膜浅层血管网,对前界为锁骨、后界为肩胛冈、外侧界为肩峰、内侧为颈根部的颈肩峰区主要血供进行巨微解剖学观察.结果 ①皮动脉穿出点集中在斜方肌前缘及其延伸线的区域,宽度约4 cm的范围;②斜方肌前缘及其延伸线为轴心的中间部位,吻合支最为丰富,血管吻合多为网状,其次是肩胛冈上区.在众多的吻合支中可观察到每侧颈肩峰区均有2～3支明显的贯穿颈根至肩峰全长的吻合支,多位于中轴位置及后侧,在深筋膜浅层至真皮下血管网之间有丰富的交通支相连.结论 颈肩峰区皮动脉穿出点位置恒定,深筋膜浅层血管吻合支丰富,可形成颈肩峰区跨区供血轴型皮瓣.     

腘窝直接动脉穿支蒂股后皮神经营养血管皮瓣的解剖基础

目的探讨腘窝直接动脉穿支蒂股后皮神经营养血管皮瓣的解剖学基础。方法于30侧动脉内灌注红色乳胶的成人下肢标本上解剖观测:股后皮神经走行与分布;腘窝直接动脉穿支与股后皮神经营养血管间吻合关系。另在1侧新鲜成人下肢标本上进行摹拟手术设计。结果股后皮神经主干由臀大肌下缘中点穿出入股后部,主干沿股后正中线下行,终支伴小隐静脉下降,达小腿后面中部。其在穿臀大肌下缘和腘窝上角处横径分别为(3.0±0.6)mm和(2.0±0.7)mm。其营养血管为多节段、多源性,其中腘窝直接动脉穿支的位置相对恒定,于膝关节平面上7～11cm处,起于腘动脉上段后壁,起点外径(0.8±0.2)mm,伴行静脉1～2条。该动脉为股后皮神经下段主要血供来源,上行过程中发出5～8支皮支与股深动脉(第1～3穿动脉)皮穿支、闭孔动脉穿支和旋股外侧动脉皮穿支吻合,在股后形成顺沿中线和股后皮神经纵轴的血管丛。摹拟手术结果显示可形成腘窝直接穿支蒂股后皮神经营养血管皮瓣。结论腘窝直接动脉穿支蒂股后皮神经营养血管皮瓣血供相对恒定、手术操作简便,移位后可用于修复腘窝及膝周软组织缺损。     

前臂内侧皮神经--贵要静脉营养血管远端蒂复合皮瓣的应用解剖

目的为前臂内侧皮神经—贵要静脉营养血管远端蒂复合瓣设计提供解剖学基础。方法对30侧动脉灌注红色乳胶的成人上肢标本,解剖观测下1/3段前臂内侧皮神经-贵要静脉营养血管的来源、分支及其与尺骨膜血管的关系。结果下1/3段前臂内侧皮神经-贵要静脉营养血管来自:尺动脉皮支5～9支,外径(0.7±0.3)mm,尺动脉腕上皮支外径(0.7±0.2)mm。在尺骨茎突上(6.0～16.0)cm,骨间前动脉骨皮穿支2～3支,外径(0.7±0.2)mm;骨间后动脉骨皮穿支1～3支,外径(0.6±0.2)mm。二者分布尺骨中下段骨膜及相应区域的皮肤。上述穿支发皮支、筋膜支、骨膜支、皮神经—浅静脉营养血管,形成皮神经干血管链和贵要静脉旁营养血管链及深、浅筋膜和骨膜血管网。结论前臂内侧皮神经-贵要静脉营养血管与骨、皮营养血管同源,其远端蒂复合瓣的旋转轴点在腕关节平面,可用于转位修复手部远处组织缺损。     

带腓肠神经及其营养血管筋膜皮瓣的应用解剖

目的　为带腓肠神经及其营养血管筋膜皮瓣的应用提供解剖学基础。　方法　在３２ 侧成人下肢标本上进 行解剖， 对腓肠神经及其 营养血管进行详细观 测。　结果　 吻合型腓 肠神经占５３１ ％ ；非吻合型占４６９ ％ 。该神经的营养血管为腓肠浅动脉和穿动脉， 腓肠浅动脉于腓骨头上方（５０ ±１５）ｃ ｍ 由腘动脉发出，起始处外径为（０８ ±０３ ） ｍ ｍ ，伴腓肠内侧皮神经和腓肠神经下行， 与踝关节附近的皮动脉进行吻合；穿动脉则来源于胫后动脉肌皮支和腓动脉肌间隔皮支， 其外径分别为（０８ ±０４） ｍ ｍ 和（０８ ±０３） ｍ ｍ 。这些皮动脉除与腓肠浅动脉构成链式吻合外，并借分支与筋膜皮支形成广泛的筋膜皮血管网。　结论　可以腓肠神经及其营养动脉为蒂设计筋膜皮瓣，转位修复小腿中下部、踝关节周围等软组织缺损     

腓肠神经营养血管筋膜皮瓣的解剖及临床应用

目的分析腓肠神经及其营养血管筋膜皮瓣的解剖学特性，为临床应用提供依据。方法取32侧成人下肢标本进行解剖，对腓肠神经及其营养血管进行观测。临床应用皮瓣修复小腿和足部软组织缺损26例，皮瓣最大面积8cm×13cm。结果吻合型腓肠神经占53．1％；非吻合型占46．9％。神经的营养血管为腓肠浅动脉和穿动脉、腓肠浅动脉于腓骨头上方（5．0±1．5）cm的位置由胭动脉发出，起始处外径为（0．8±0．3）mm。伴腓肠内侧皮神经和腓肠神经下行，与踝关节附近的皮动脉进行吻合；穿动脉则来源于胫后动脉肌皮支和腓动脉肌间隔皮支，其外径分别为（0.8±0.4）mm和（0.8±0．3）mm。这些皮动脉除与腓肠浅动脉构成链式吻合外，并借分支与筋膜皮支形成广泛的筋膜皮血管网。临床应用26例，皮瓣全部成活。结论以腓肠神经及其营养动脉为蒂设计筋膜皮瓣，可转位修复小腿中下部、踝关节周围及足部等软组织缺损并获较好的临床效果。     

前臂外侧皮神经的血供特点与皮神经营养血管皮瓣的设计

目的：为临床设计带外侧皮神经营养血管筋膜皮瓣提供依据。方法：用显微解剖测量法、标本透明法研究前臂外侧皮神经外科解剖与头静脉的关系以及其神经血管皮肤穿支的位置、长度、对皮神经的营养形式等。结果：前臂外侧皮神经共有４支神经血管皮肤穿支,其全程由神经旁血管和主要动脉共同营养。前臂外侧皮神经前支与头静脉紧密伴行。结论：顺沿头静脉,可切取带外侧皮神经营养血管筋膜蒂或血管神经蒂岛状皮瓣,用于修复肘部、前臂远端１／３段和腕部等部位软组织缺损。     

以股后皮神经伴行血管为蒂的岛状皮瓣的应用解剖及临床意义

目的：为以股后皮神经伴行血管为蒂的岛状皮瓣的临床应用提供解剖依据。方法：在２７侧成人下肢标本上观察股后皮神经伴行血管的行程、外径及皮支分布情况。结果：（１）所有股后皮神经都有来源于知名血管的营养血管伴行。（２）股后皮神经的伴行血管既营养神经,同时沿途又发出多条分支营养皮肤,并与股后穿动脉皮支、动脉的升皮支广泛的吻合。（３）股后皮神经伴行血管穿出深筋膜有一定规律性。结论：股后皮神经伴行血管解剖恒定,口径较粗,具有形成岛状皮瓣顺行或逆行转移的解剖学条件。     

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.     

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.