Cross-Circulation for Extracorporeal Liver Support in a Swine Model

Although machine perfusion has gained momentum as an organ preservation technique in liver transplantation, persistent organ shortages and high waitlist mortality highlight unmet needs for improved organ salvage strategies. Beyond preservation, extracorporeal organ support platforms can also aid the development and evaluation of novel therapeutics. Here, we report the use of veno-arterial-venous (V-AV) cross-circulation (XC) with a swine host to provide normothermic support to extracorporeal livers. Functional, biochemical, and morphological analyses of the extracorporeal livers and swine hosts were performed over 12 hours of support. Extracorporeal livers maintained synthetic function through alkaline bile production and metabolic activity through lactate clearance and oxygen consumption. Beyond initial reperfusion, no biochemical evidence of hepatocellular injury was observed. Histopathologic injury scoring showed improvements in sinusoidal dilatation and composite acute injury scores after 12 hours. Swine hosts remained hemodynamically stable throughout XC support. Altogether, these outcomes demonstrate the feasibility of using a novel V-AV XC technique to provide support for extracorporeal livers in a swine model. V-AV XC has potential applications as a translational research platform and clinical biotechnology for donor organ salvage.

Left ventricular mechanoenergetics in excised, cross-circulated rat hearts under hypo-, normo-, and hyperthermic conditions

We investigated the effects of altering cardiac temperature on left ventricular (LV) myocardial mechanical work and energetics using the excised, cross-circulated rat heart model. We analyzed the LV end-systolic pressure-volume relationship (ESPVR) and linear relationship between myocardial oxygen consumption per beat (VO2) and systolic pressure-volume area (PVA; total mechanical energy per beat) in isovolumically contracting rat hearts during hypo- (32 °C), normo- (37 °C), and hyperthermia (42 °C) under a 300-beats per minute pacing. LV ESPVR shifted downward with increasing cardiac temperature. The VO2-PVA relationship was superimposable in these different thermal conditions; however, each data point of VO2-PVA shifted left-downward during increasing cardiac temperature on the superimposable VO2-PVA relationship line. VO2 for Ca2+ handling in excitation-contraction coupling decreased, which was associated with increasing cardiac temperature, during which sarcoplasmic reticulum Ca2+-ATPase (SERCA) activity was suppressed, due to phospholamban phosphorylation inhibition, and instead, O2 consumption for basal metabolism was increased. The O2 cost of LV contractility for Ca2+ also increased with increasing cardiac temperature. Logistic time constants evaluating LV relaxation time were significantly shortened with increasing cardiac temperature related to the acceleration of the detachment in cross-bridge (CB) cycling, indicating increased myosin ATPase activity. The results suggested that increasing cardiac temperature induced a negative inotropic action related to SERCA activity suppression in Ca2+ handling and increased myosin ATPase activity in CB cycling. We concluded that thermal intervention could modulate cardiac inotropism by changing CB cycling, Ca2+ handling, and basal metabolism in rat hearts.

A unique case of craniopagus twins: considerations and challenges for dental rehabilitation

The purpose of this case report was to describe oral findings and outline challenges and considerations for general anesthetic (GA) and dental management of 4-year-old female craniopagus (cranially conjoined) twins, at high risk for medical comorbidity, who presented for treatment of severe early childhood caries. This hospital-based procedure required good interdisciplinary communication, cooperation, and presurgical planning to address unique challenges and ensure positive postoperative outcomes. Two separate anesthesia teams delivered GA simultaneously to each twin. To minimize anesthetic exposure, two pediatric dental teams completed dental care concurrently. Extensive plaque accumulation and unusual "mirror-image" caries distribution were attributed to frequency and postural pooling during feeding. The rehabilitation objective was to provide definitive dental management, minimizing future need for dental retreatment under GA. Two-month follow-up revealed intact dental restorations, good oral hygiene, and weight gain. For these unique twins however, the challenge of long-term oral health maintenance remains.

HYPOVOLEMIA DOES NOT AFFECT SPEED OF ISOVOLUMIC LEFT VENTRICULAR CONTRACTION AND RELAXATION IN EXCISED CANINE HEART

Hypovolemia results in hypotension due to a decrease in left ventricular (LV) stroke volume. We have showed a logistic relaxation time constant (tauL) that is a superior lusitropic index during the LV pressure (LVP) falling phase independent of LV preload compared with the conventional monoexponential relaxation time constant (tauE). In the present study, we investigated the effect of decreasing LV preload on tauL and tauE during the LV contraction and other relaxation phases. The isovolumic LVP curve was analyzed at LV Volumes (LVVs) of 18, 14, and 10 mL during 2-Hz pacing in seven excised, cross-circulated canine hearts. TauL and tauE were evaluated using logistic and monoexponential analyses of the four phases of the cardiac cycle: the period from the onset to the maximum time derivative of LVP (LV dP/dtmax), from LV dP/dtmax to peak LVP, from peak LVP to the minimum time derivative of LVP (LV dP/dtmin), and from LV dP/dtmin to LV end-diastolic pressure. TauL and tauE during the four phases did not change significantly with the decrease in LVV. During the change in LVV, the logistic function always fit significantly better compared with the monoexponential function. In conclusion, hypovolemia does not affect the speed of isovolumic LV contraction and relaxation. Each phase of the LVP curve is of a logistic nature. TauL is as a useful index for estimation of the speed of alteration during each phase of cardiac systole and diastole.

Anaesthetic management of thoracopagus twins with complex cyanotic heart disease for cardiac assessment: special considerations related to ventilation and cross-circulation

We describe the anaesthetic management of a pair of thoracopagus twins of 14 months of age undergoing complex cardiac evaluation. Synchronous ventilation of the twins, needed for the ECG-gated magnetic resonance imaging-angiography, was achieved through a Carlens (Y) adaptor during procedures and transport. The complex logistical implications are obvious. We also describe the first use of bispectral index monitor for detection of cross-circulation in conjoint twins.

Detrimental effects after dobutamine infusion on rat left ventricular function: mechanical work and energetics

We have previously reported that continuous infusion of dobutamine into the coronary artery induces positive inotropic effects but induces no detrimental effects in cross-circulated, excised normal rat hearts and even in Ca2+ overload-induced contractile failing rat hearts. However, we hypothesized that some detrimental effects on left ventricular (LV) function are induced after continuous dobutamine infusion and the following clearance of blood dobutamine, as is the case after beta-adrenergic receptor stimulation. To test this hypothesis, we investigated LV mechanical work and energetics in the same type of preparations that underwent continuous dobutamine infusion and clearance of blood dobutamine. We found that both mean end-systolic pressure and systolic pressure-volume area (PVA; a measure of total mechanical energy per beat) at midrange LV volume were significantly (P < 0.01) decreased. The mean myocardial oxygen consumption per beat intercept, which is composed of for the total Ca2+ handling in excitation-contraction coupling and basal metabolism, of the and PVA linear relation was also significantly (P < 0.05) decreased (n=8). The mean slope of the linear relation was unchanged in such hearts. Post-dobutamine basal metabolism was unchanged (n = 5 of the 8 hearts). The moderate proteolysis of a cytoskeleton protein, alpha-fodrin was identified (n = 7 of the 8 hearts with the decreased intercept), after clearance of blood dobutamine. In agreement with our hypothesis, the detrimental effect of the post-beta-adrenergic receptor stimulation was induced by a moderate concentration of dobutamine; we found systolic dysfunction due to the impairment of Ca2+ handling in excitation-contraction coupling in the rat LV and proteolysis of a cytoskeleton protein, alpha-fodrin.

Congenital Heart Disease: A Surgical-Historical Perspective

Pediatric cardiac surgery began with Dr Gross's first successful ligation of a patent ductus arteriosus on August 8, 1938, at the Children's Hospital in Boston. The beginnings of open-heart surgery for repair of congenital malformations, aside from Gibbon's first successful closure in Philadelphia of an atrial septal defect using an artificial heart-lung machine, can be traced to members of the Department of Surgery at the University of Minnesota during the fifties and sixties of the 20th century. This story will be told, and other advances will be discussed, some of which also carry the imprint of the Minnesota surgical training program, with its heavy emphasis on research.

Lillehei, Lewis, and Wangensteen: The Right Mix for Giant Achievements in Cardiac Surgery

The dawn of open-heart surgery occurred at the University of Minnesota on September 2, 1952, when Dr John Lewis and his surgical team closed an atrial septal defect using total-body hypothermia and inflow stasis. Eighteen months later on March 26, 1954, Dr C. Walton Lillehei and his surgical team used a parent as a biologic oxygenator to repair a ventricular septal defect in a 1-year-old boy. This technique of cross circulation was then used in a total of 45 children during the next 16 months to successfully repair tetralogy of Fallot, atrioventricular canal, and ventricular septal defect. Remarkably, two thirds of these children were discharged from the hospital. Thirty years later, Dr Lillehei reported that 17 of his 27 patients with repair of a ventricular septal defect had survived and were all New York Heart Association class I. These landmark operations in the open heart could not have been achieved by Drs Lewis and Lillehei without the remarkable support that they received from their surgical chief, Dr Owen Wangensteen. Doctor Wangensteen would later state in his book, The Rise of Surgery, that: "The outstanding contribution to the advancement of surgery in the 20th century has been the development of open-heart surgery."

Myocardial microvascular perfusion after transfusion of liposome-encapsulated hemoglobin evaluated in cross-circulated rat hearts using tracer digital radiography

The effect of hemodilution with Neo Red Cell (NRC, liposome-encapsulated hemoglobin) on myocardial perfusion was evaluated in cross-circulated rat hearts under 300-bpm pacing and 100-mmHg perfusion pressure. In NRC-transfused hearts (n = 5), NRC volume fraction and hematocrit were 9% +/- 3% and 22% +/- 4%, respectively; the latter decreased from 43% +/- 3% before NRC transfusion. Coronary perfusion rate and left ventricular isovolemic developed pressure increased after NRC transfusion to 4.6 +/- 1.0 ml/min/g and 127 +/- 32 mmHg from basal values of 2.5 +/- 0.3 ml/min/g and 115 +/- 28 mmHg, respectively. In contrast, the flow increase during reperfusion following 30-s flow cessation decreased from 74% +/- 24% to 64% +/- 24%. The arteriovenous difference in O2 saturation was slightly higher after NRC transfusion. Within-layer regional flow distributions from subepicardium to subendocardium assessed by tracer digital radiography (100-microm resolution) showed that coefficients of variation of flows in 400 x 400-microm regions were 0.41 +/- 0.10 in NRC-transfused hearts and 0.54 +/- 0.11 in nontransfused hearts (n = 5); i.e., the myocardial flow distribution was more uniform in NRC-transfused hearts. These results suggest that NRC is superior to erythrocytes in terms of the homogenization of O2 delivery, indicating its potential therapeutic value in myocardial microcirculatory failure.

[Fifty years of the heart-lung machine. Report on the pioneers and heroes and about the circumstances that led to the great invention, which allowed the treatment, and in many cases, the cure of heart illnesses]

In 1953 DNA was discovered and the Everest was conquered but also a great invention was developed: the heart-lung machine, which allowed the treatment, and in many cases, the cure of most cardiovascular illnesses. In fact, on May 6, 1953 John Gibbon crowned with success the work of his entire life closing for the first time an atrial septal defect in a young woman using a heart-lung machine of his own invention. Before that, surgeons had explored other roads like hypothermia, cooling the patient in a cold water tub and then rapidly performing the surgical correction of a heart malformation. After his first success, the following 4 patients of Gibbon died, which led him to abandon heart surgery and produced a generalized pessimism about extracorporeal circulation. However, a year later Walton Lillehei reverted this situation with the introduction of controlled cross-circulation in which a patient, usually a child, was connected to a "donor", usually his father or mother, whose heart and lung served as a pump and oxigenator, allowing the performance of open heart surgery. Finally, it was Lillehei again who a year later introduced the bubble oxigenator, simple and inexpensive, opening the doors of open heart surgery to all surgeons around the world. For this, and many other reasons, Walton Lillebei is considered by most surgeons as the "Father of Open Heart Surgery". Lillehei visited Chile in 1963 and operated on a patient in the surgical theaters of the Hospital Clínico de la Universidad Católica and was named an Honorary Member of the School of Medicine of this University. Before that, in 1957 Helmut Jaeger at the Hospital Luis Calvo Mackenna performed the first successful surgical closure of an atrial septal defect with extracorporeal circulation in Chile using a De Wall-Lillebei bubble oxigenator.

Cardiac effects of clinically available Kampo medicine assessed with canine isolated, blood-perfused heart preparations

Cardiac effects of 10 kinds of clinically available Kampo medicines were investigated: Kakkon-to (TJ-1), Dai-saiko-to (TJ-8), Boi-ogi-to (TJ-20), Chorei-to (TJ-40), Rokumi-gan (TJ-87), Tsu-do-san (TJ-105), Gosha-jinki-gan (TJ-107), San'o-shashin-to (TJ-113), Sairei-to (TJ-114) and Inchin-gorei-san (TJ-117). Chronotropic and inotropic effects were studied using canine isolated, blood-perfused heart preparations, while subcellular mechanisms were analyzed by measuring the drug-induced changes of the adenylate cyclase activity in the canine ventricular membrane preparation. Intracoronary injections of TJ-1, TJ-20, TJ-105 and TJ-113 increased the sinoatrial rate and developed tension of papillary muscle in a dose-related manner, which was significantly attenuated by the pretreatment of the preparations with beta-blocker propranolol. Meanwhile, the other extracts hardly affected these parameters. TJ-1, TJ-20 and TJ-113 increased the adenylate cyclase activity in a dose-related manner, but their potency was significantly less compared with that by an equivalent concentration of isoproterenol. Moreover, TJ-105 did not increase the adenylate cyclase activity. These results suggest that the positive chronotropic and inotropic effects of TJ-1, TJ-20, TJ- 105 and TJ-113 may be exerted through the direct stimulation of the beta-adrenoceptor and/or the norepinephrine release from the postganglionic nerve terminals in the heart.

Cardiac effects of a selective rho-associated kinase inhibitor, Y-27632, assessed in canine isolated, blood-perfused heart preparations

Chronotropic, inotropic and coronary effects of Y-27632 ((+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride, monohydrate), a specific inhibitor of Rho-associated coiled-coil forming protein serine/threonine kinase (ROCK), were assessed using canine isolated, blood-perfused heart preparations. Y-27632 slightly enhanced sinoatrial automaticity and significantly increased coronary blood flow, while it decreased ventricular contraction. The concentrations of Y-27632 needed to cause the currently observed changes were similar to those inhibiting ROCK in a previous in vitro study. These results suggest that the constitutional ROCK in the heart mainly regulates the ventricular contractility and coronary vascular tone rather than the sinoatrial automaticity.

Influence of extracorporeal porcine liver perfusion on nonhuman primates: minimizing hemolysis improves subsequent survival

The aim of this study is to detect and analyze risk factors of direct cross-circulation between porcine liver and nonhuman primates before a clinical application of extracorporeal liver perfusion (ECLP) as a liver-assist method. Porcine livers were perfused with baboon blood in an ECLP system. Six healthy baboons were directly connected to the ECLP system with continuous prostaglandin E(1) administration. Cross-circulation was terminated in the following circumstances: (1) hepatic arterial or portal perfusion pressures elevated to 200 or 60 mm Hg, respectively; (2) massive exudative bleeding from the graft surface; or (3) bile output decreased to less than 5 microL/h/g of liver weight. In case 1, cross-circulation was continued for 10 hours. Severe macroscopic hemolysis occurred, and serum hemoglobin (s-Hb) concentration reached a peak of 47 mg/dL. The baboon died of acute renal failure 2 days later. Histological study of the perfused porcine liver showed marked microthrombi formation. In 3 of the later 5 cases, cross-circulation was discontinued when mild macroscopic hemolysis was observed. The duration of the 5 cross-circulations was maximally 6 hours (mean, 4.4 +/- 1.2 [SD] hours). Mean s-Hb concentration in the 5 cases was elevated to 14.8 +/- 5.8 mg/dL at the end of cross-circulation and decreased to the baseline level within 24 hours. These 5 baboons survived without organ dysfunction or immunologic disturbance. When severe hemolysis is avoided, direct cross-circulation using the ECLP system can be achieved without serious complications in nonhuman primates.

Pulmonary vasoconstriction during regional nitric oxide inhalation: evidence of a blood-borne regulator of nitric oxide synthase activity

BACKGROUND

Inhaled nitric oxide (INO) is thought to cause selective pulmonary vasodilation of ventilated areas. The authors previously showed that INO to a hyperoxic lung increases the perfusion to this lung by redistribution of blood flow, but only if the opposite lung is hypoxic, indicating a more complex mechanism of action for NO. The authors hypothesized that regional hypoxia increases NO production and that INO to hyperoxic lung regions (HL) can inhibit this production by distant effect.

METHODS

Nitric oxide concentration was measured in exhaled air (NO(E)), NO synthase (NOS) activity in lung tissue, and regional pulmonary blood flow in anesthetized pigs with regional left lower lobar (LLL) hypoxia (fraction of inspired oxygen [FIO2] = 0.05), with and without INO to HL (FIO2 = 0.8), and during cross-circulation of blood from pigs with and without INO.

RESULTS

Left lower lobar hypoxia increased exhaled NO from the LLL (NO(E)LLL) from a mean (SD) of 1.3 (0.6) to 2.2 (0.9) parts per billion (ppb) (P < 0.001), and Ca2+-dependent NOS activity was higher in hypoxic than in hyperoxic lung tissue (197 [86] vs. 162 [96] pmol x g(-1) x min(-1), P < 0.05). INO to HL decreased the Ca2+-dependent NOS activity in hypoxic tissue to 49 [56] pmol x g(-1) x min(-1) (P < 0.01), and NO(E)LLL to 2.0 [0.8] ppb (P < 0.05). When open-chest pigs with LLL hypoxia received blood from closed-chest pigs with INO, NO(E)LLL decreased from 2.0 (0.6) to 1.5 (0.4) ppb (P < 0.001), and the Ca2+-dependent NOS activity in hypoxic tissue decreased from 152 (55) to 98 (34) pmol x g(-1) x min(-1) (P = 0.07). Pulmonary vascular resistance increased by 32 (21)% (P < 0.05), but more so in hypoxic (P < 0.01) than in hyperoxic (P < 0.05) lung regions, resulting in a further redistribution (P < 0.05) of pulmonary blood flow away from hypoxic to hyperoxic lung regions.

CONCLUSIONS

Inhaled nitric oxide downregulates endogenous NO production in other, predominantly hypoxic, lung regions. This distant effect is blood-mediated and causes vasoconstriction in lung regions that do not receive INO.

Establishment of a parabiotic rat model by anastomosis of common carotid artery

A cross circulation model was established by replacing mutual blood between two rats by anastomoses of each common carotid artery. In this model, parabiotic rats were shown to replace their mutual blood completely without any artificial materials or instruments, such as silicon tubes or pumps. The rate of blood exchange was measured by intravenous injection of Evans blue dye without the use of the radioactive materials that were so far commonly used. The partial alteration of blood circulation through microvascular surgery may reveal the mechanisms of organ tropism of bacteria, protozoa, and parasites. Microvascular surgery is available for reconstruction and analysis of organ functions as well as for clinical use in organplasty.

Lazaroid U74500A is superior to U74006F in preserving rabbit heart for 24 hours

BACKGROUND

Lazaroid, a series of 21-aminosteroids, has been shown to reduce free-radical-mediated injury after ischemia and reperfusion. Recent in vitro studies have demonstrated that, among the various compounds studied, the most efficient agent was U74500A. The question is whether these findings apply to the whole heart experiencing ischemia-reperfusion injury. In this study we compared the myocardial protective effects of U74006F, the only clinical candidate, and U74500A.

METHODS

An isolated rabbit heart preparation perfused with the blood from a support rabbit was used. All hearts were divided into three groups according to the administration of U74500A (4 mg/kg, group A; n = 7), U74006F (4 mg/kg, group F; n = 7), or solvent (group S; n = 7) to the donor rabbit before preservation. After 24 hours of preservation with University of Wisconsin solution at 0 degrees C, all hearts were perfused with cross-circulated blood for 60 minutes with the Langendorff mode followed by 40 minutes in the working mode.

RESULTS

After 10 minutes of reperfusion the serum lipid peroxide levels were significantly (p < 0.05) lower in group A (0.62+/-0.31 nmol/mL) than those in group S (2.1+/-1.3 nmol/mL) and group F (1.0+/-0.6 nmol/mL). The aortic flow rate at 10 mm Hg of left atrial pressure was significantly higher in group A (164+/-37 mL/min) than that of other groups (71+/-28 mL/min in group S and 97+/-28 mL/min in group F). There were no significant differences in high-energy phosphate levels after reperfusion among the three groups.

CONCLUSION

These data imply that U74500A inhibits lipid peroxidation and prevents ischemia-reperfusion injury more efficiently than U74006F.

The central action of lignocaine and its effect on cardiac output

Fifty-nine tests were performed on twenty-four anaesthetized dogs in a study of the effects of lignocaine on circulatory and respiratory functions. In single-dog experiments, it was shown that lignocaine (1 to 2 mg./kg. body weight) increased ventilation somewhat, but had no effect on O(2) consumption. Cardiac output was increased due to a rise in both heart rate and stroke volume. There was an elevation of arterial blood pressure. The central blood volume was increased, but central venous pressure, total peripheral resistance and the ventilationperfusion ratio were decreased. The increase in cardiac output after lignocaine was abolished both in decerebrate and in vagotomized dogs. In cross-circulation experiments with dogs, it was demonstrated that the primary site of action of lignocaine on cardiac output was central. The effect of lignocaine on cardiac output could be blocked by intravenous procaine.

Homohemodialysis: a technique of dialysis for the uremic animal

As an alternative to kidney transplantation in conditions of renal failure, an in situ kidney of a healthy individual may be used. The present study utilizes the kidney of a healthy rabbit as a hemoperfusion unit for another, uremic, animal. The study comprised 17 experimental models, each of which consisted of 2 adult New Zealand rabbits. One animal of each model was rendered uremic by means of bilateral nephrectomy. The blood chemistry (urea, creatinine, sodium, potassium, pH and base deficit) was examined pre- and 4-hourly post-operatively. When after 48 hours post-nephrectomy, the blood chemistry had reached a level sufficient to endanger the animal's life, homohemodialysis was performed. The anticoagulated blood was circulated from the uremic animal to the normal one and then back to the uremic animal through the femoral vessels using a tube system. The blood chemistry was determined every 10 minutes and pH and base deficit every 30 minutes. All animals died or were sacrificed within 21 hours after shunting was started, and autopsy was done. Serum sodium was the first to normalize within the first 10 minutes post-shunting, followed by serum potassium and pH in 30 minutes. Blood urea and creatinine reached normal levels in 40 minutes and base deficit in 60 minutes post-shunting. The pathologic examination of specimens from the vital organs of both the normal and uremic animals showed different degrees of cellular damage probably due to hypotension or acute effects of the unbalanced animal homeostasis. The cellular damage was much less in the normal than in the uremic animals. In conclusion, homohemodialysis proved to be effective in normalizing the concentrations of the different substances retained in the blood of uremic animals within only 60 minutes of dialysis.

Cardiovascular and antiarrhythmic effects of the azulene-1-carboxamidine derivative N1,N1-dimethyl-N2-(2-pyridylmethyl)-5-isopropyl-3, 8-dimethylazulene-1-carboxamidine

The azulene-1-carboxamidine derivative N1,N1-Dimethyl-N2-(2- pyridylmethyl)-5-isopropyl-3,8-dimethyl-azulene-1-carboxamidine (CAS 186086-10-2, HNS-32) is a newly synthesized compound. In the present study, direct cardiovascular effects of HNS-32 were assessed using the canine isolated, blood-perfused sinoatrial node, papillary muscle and atrioventricular node preparations, while the antiarrhythmic action was examined using the canine two-stage coronary ligation-induced arrhythmia model. Intracoronary administration of HNS-32 (1-300 micrograms) suppressed the sinus nodal automaticity and ventricular contractile force, while it increased the atrio-His and His-ventricular conduction time as well as the coronary blood flow. Intravenous administration of HNS-32 (5 mg/kg) suppressed the ventricular arrhythmia for approximately 30 min. Since HNS-32 possesses multiple cardiac direct effects which are unique compared with well-established antiarrhythmic drugs, it may become a leading compound in the search for novel antiarrhythmic agents.

Effects of intracoronary fentanyl on left ventricular mechanoenergetics in the excised cross-circulated canine heart

BACKGROUND

It is still unclear whether fentanyl directly alters left ventricular (LV) contractility and oxygen consumption. This is because of the difficulty in defining and evaluating contractility and energy use independently of ventricular loading conditions and heart rate in beating whole hearts.

METHODS

This study was conducted to clarify the mechanoenergetic effects of intracoronary fentanyl in six excised cross-circulated canine hearts. The authors used the framework of the E(max) (a contractility index)-PVA (systolic pressure-volume area, a measure of total mechanical energy)-VO2 (myocardial oxygen consumption per beat) relationship practically independent of ventricular loading conditions. The authors measured LV pressure, volume, coronary flow, and arteriovenous oxygen content difference to calculate E(max), PVA, and VO2. They first obtained the VO2-PVA relationship for varied LV volumes at control E(max). The authors then obtained the VO2-PVA relationship at a constant LV volume, whereas coronary blood fentanyl concentration was increased in steps up to 240 ng/ml. Finally, they obtained the VO2-PVA relationship for varied LV volumes at the final dose of fentanyl.

RESULTS

Fentanyl at any concentrations did not significantly change E(max), PVA, and VO2 from the control. The linear end-systolic pressure-volume relations and their slopes were virtually the same between the control and fentanyl volume loading in each heart. Further, either the slope (oxygen cost of PVA) or the VO2 intercept (unloaded VO2) of the linear VO2-PVA relationship remained unchanged by fentanyl.

CONCLUSIONS

These results indicate that intracoronary fentanyl produces virtually no effects on LV mechanoenergetics for a wide range of its blood concentration.

Selective hypoglycemia in the liver induces adrenomedullary counterregulatory response

The present study was designed to investigate adrenal medullary responses to a selective regional hypoglycemia in the liver of dogs with hepatic cross-perfusion. The liver of recipient dogs (Rc) was perfused with vena caval and aortic blood of donor dogs (Dn) through the portal vein and hepatic artery, respectively. Total hepatic venous blood of Rc was returned to Dn through the left jugular vein. Upon the cross-perfusion, glucose (Glc, 5%) was infused at an average rate of 3.5 +/- 0.2 mg.kg-1.min-1 (n = 12) in Rc to compensate the loss of hepatic Glc delivery into the systemic circulation. Insulin (5.0 IU/kg i.v.) was administered to Dn followed by infusion with an average rate of 0.95 +/- 0.17 IU kg-1.min-1 (n = 6), and this served as the hepatic hypoglycemic group. Saline was similarly administered to Dn, which served as the normoglycemic control group. In the hepatic hypoglycemic group, aortic and vena caval Glc levels in Dn, which represent Glc concentrations entering the liver of Rc, decreased from 129.9 +/- 7.1 and 122.5 +/- 7.8 to 44.6 +/- 6.1 and 38.0 +/- 5.9 mg/dl (P < 0.05) 45 min after insulin administration, respectively. During this regional hepatic hypoglycemia in Rc, the systemic glycemia being kept within a normal range, adrenal epinephrine and norepinephrine output increased from 245.5 +/- 55.8 and 39.1 +/- 9.9 to 618.9 +/- 180.4 and 134.3 +/- 52.7 ng/min (P < 0.05), respectively. By contrast, aortic Glc and insulin levels in Dn of the normoglycemic control group remained unchanged, as did adrenal epinephrine and norepinephrine output in Rc. The results indicate that the regional hepatic hypoglycemia can significantly increase adrenal catecholamine secretion even during systemic (central) normoglycemia. The study suggests that the hepatoadrenal Glc counter-regulatory reflex may be functionally implicated in insulin-induced hypoglycemia.

Efferent renal nerve stimulation inhibits the antihypertensive function of the rat renal medulla when studied in a cross-circulation model

The aim of this study was to investigate the effects of renal nerve stimulation on the humoral renal antihypertensive system. An isolated kidney (IK) was perfused at normal or high arterial pressures from a normotensive assay rat by means of a perfusion pump. Perfusion pressure (PP) to the IK was 90 mmHg for a control period of 30 min. In three of five experimental groups PP was then increased to 175 mmHg. In two of the groups the renal nerves were stimulated at 2 (P-175(2Hz)) or 5 Hz (P-175(5Hz)) for 60 min. The remaining group served as a control (P-175C). In two groups IK pressure was maintained at 90 mmHg with 5 Hz nerve stimulation (P-90(5Hz) or without nerve stimulation (P-90C). MAP of the assay rat decreased by 22 and 27% (P < 0.001) in the P-175C and P-175(2Hz) groups, respectively during the 60 min period of nerve stimulation, but remained stable in P-175(5Hz). Renal blood flow increased in the IK when PP was increased in P-175C, but did not change significantly in P-175(2Hz) or P-175(5Hz). Blood pressure remained constant in the assay rat when the IK was perfused at 90 mmHg. The renal excretory functions of the IK decreased in a frequency dependent manner by 2 and 5 Hz renal nerve stimulation compared with P-175C. We conclude that 5 Hz renal nerve stimulation inhibits the pressure dependent release of humoral depressor substances from an IK perfused at 175 mmHg, whereas this is not seen when stimulating at 2 Hz. It is suggested that hte release of antihypertensive substances from the renal medulla requires an increased renomedullary blood flow.

Ca(2+)-free, high-Ca2+ coronary perfusion suppresses contractility and excitation-contraction coupling energy

We studied the mechanoenergetic effects of a short-term Ca(2+)-free, high-Ca2+ Tyrode solution coronary perfusion in eight excised, cross-circulated canine hearts. The perfusion protocol consisted of coronary perfusion with Ca(2+)-free Tyrode solution for 10 min followed by high-Ca2+ (16 mM) Tyrode solution for 5 min. This new protocol successfully induced acute contractile failure in seven hearts, without myocardial ultrastructural changes. We studied the end-systolic pressure-volume relation (slope = Emax, a contractility index) and the relation between oxygen consumption per beat (VO2) and systolic pressure-volume area (PVA) in these failing hearts. These hearts had no increase in end-diastolic pressure at a given volume, a 40% decrease in Emax and a proportional decrease in the PVA-independent VO2 for 1-4 h, but no decrease in the oxygen cost of PVA, defined as the slope of the VO2-PVA relation. The oxygen cost of Emax for Ca2+ handling, defined as the slope of the relation between PVA-independent VO2 and Emax, was unchanged in the failing hearts. We conclude that the present protocol induced left ventricular contractile failure, primarily involving the suppression of Ca2+ handling energy for excitation-contraction coupling.

Left ventricular mechanoenergetics under altered coronary perfusion in guinea pig hearts

Coronary perfusion pressure (CPP) is well known to affect left ventricular (LV) mechanoenergetics (Gregg's phenomenon). The garden hose effect via the Frank-Starling mechanism caused by coronary distension has long been considered to be the underlying mechanism of this phenomenon. However, recent studies have revealed a close correlation between CPP and the excitation-contraction coupling in myocytes. The aim of this study was to investigate the mechanoenergetic aspects of Gregg's phenomenon by the ventricular contractility (Emax) dependency of the myocardial oxygen consumption (VO2)-total mechanical energy (PVA, systolic pressure-volume area) relationship. Experiments were performed in the excised, cross-circulated guinea pig heart preparation. The protocol consisted of LV volume loading (VOL run), changing coronary perfusion pressure at a fixed LV volume (CPP run) and intracoronary calcium (Ca) infusion also at the same LV volume (Ca run). In all seven hearts, we obtained a linear VO2-PVA relation in VOL run. The VO2-PVA relations in CPP and Ca runs, which equally enhanced Emax, were highly linear and had no significant difference in their slopes, both significantly steeper than in VOL run. These findings suggest no significant difference in the oxygen cost of Emax between CPP and Ca runs. The enhanced LV mechanoenergetics under increasing CPP is characterized by increases in the VO2 component primarily for the excitation-contraction coupling to a greater degree than expected from the mechanical (garden hose) effect.

Utilization of an isolated, blood-perfused canine papillary muscle preparation as a model to assess efficacy and adversity of class I antiarrhythmic drugs

To develop a model to predict the efficacy and adversity of class I antiarrhythmic drugs, intraventricular conduction time (IVCT), coronary blood flow (CBF), developed tension of papillary muscle (DT) and idioventricular automaticity rate (VR) were measured following drug administration in an isolated canine papillary muscle preparation cross-circulated with the heparinized blood of a donor dog. Tetrodotoxin, the prototypic fast Na+ channel blocker, and class I drugs increased IVCT and CBF, but decreased DT and VR, in a dose-dependent manner. The profiles of known class I drugs, procainamide, disopyramide, lidocaine, mexiletine and flecainide were similar, but the potencies of each drug were different. Two new class I drugs, ME3202 and AN-132, were also tested and found to have effects that were similar to that of tetrodotoxin. There was a good correlation between the doses of drugs prolonging IVCT by 50% and the canine antiarrhythmic plasma concentrations in our previous study. This model can also be used to estimate the use-dependency and the kinetics of use-dependent sodium channel block; however, it is not suitable for extensive investigation of cellular and molecular mechanisms. Thus, the use of this model facilitates the comparison of multiple cardiac effects of class I drugs and may be an effective way to better assess new antiarrhythmic drugs.

Effects of capsaicin on mechanoenergetics of excised cross-circulated canine left ventricle and coronary artery

Capsaicin selectively acts on sensory nerve endings in cardiac muscles and coronary arterial smooth muscles. Capsaicin at high doses has cell-nonselective effects including both inhibition of cardiac muscle exciteability and enhancement of vascular smooth muscle tone. We studied whether and how intracoronary infusion of capsaicin affects mechanoenergetics of the excised blood-perfused canine heart and coronary vascular resistance. We found that capsaicin at low concentrations increased Emax (a contracility index) and oxygen consumption (VO2) possibly due to a specific action on capsaicin-sensitive sensory nerves in left ventricular muscles, though in a small number of hearts (3/10). This result coincides with the reported histochemical observations that the distribution of capsaicin-sensitive sensory nerves in the canine left ventricle is not dense. Capsaicin at high doses dose-dependently decreased Emax and proportionally decreased coronary flow. It also lowered the linear VO2-PVA (pressure-volume area; total mechanical energy) relationship without a change in the slope, decreasing unloaded VO2 (VO2 intercept of the VO2-PVA relation). These effects of high-dose capsaicin seem to be direct negative inotropic action on cardiac muscles associated with enhancement of coronary arterial smooth muscle tone, since these effects were not desensitized. No morphological changes of myocardial cells or mitochondria were detected. Therefore, the negative inotropic action is not due to the toxic effect of capsaicin.

Postextrasystolic transient contractile alternans in canine hearts

We found that postextrasystolic potentiated contractility after a spontaneous extrasystole most frequently decayed as a transient alternans over several beats in excised, cross-circulated, atrially paced canine hearts. This type of heart preparation; which we have been using consistently in mechanoenergetic studies, had normal coronary blood perfusion pressure as well as flow and mechanoenergetic performance. Spontaneous atrial and ventricular extrasystoles occurred occasionally in every heart. Arrhythmic changes in left ventricular (LV) pressure at a fixed volume reflected corresponding changes in contractility. We analyzed nearly 3,600 cases of postextrasystolic potentiation in 68 hearts; 84% decayed as transient alternans, 6% decayed exponentially, and 10% belonged to neither type. We found that a postextrasystolic compensatory pause always preceded the transient alternans after either an atrial or ventricular extrasystole at any constant atrial pacing rate (85-188 beats/min). The decay was either exponential or nonalternating when the pause did not exist after an atrial extrasystole during occasional pacing failure. Therefore, the compensatory pause after either an atrial or ventricular extrasystole seems essential for the postextrasystolic transient alternans of LV contractility in the type of canine heart preparation we have been using.

[The central mechanism of pressor response induced by infusing 7.5% sodium chloride solution in hemorrhagic hypotension dog]

Nine pairs of dogs were operated with head cross circulation and four pairs of dogs with brain cross circulation. Bleeding of formoral artery decreased the mean arterial pressure to 5.33 kPa and maintained for 30 min. In each pair of A dog 10% of total blood lose was infused intravenously by 7.5% NaCl solution (as test) or normal saline (as control), but B dog was not treated. The results showed that in the test group the arterial blood pressure recovered immediately in both A and B dogs and lasted for more than 60 min after infusion. The recovery value of systolic pressure was higher than diastolic pressure and pulse pressure increased. In the control group the blood pressure recovered slightly but of no statistical significance. There was no remarkable difference in heart rate between the two groups. A marked decrease in hematocrit appeared after bleeding and infusion, but there was no significant difference between the two groups (P > 0.05). Plasma sodium increased significantly after infusion in A dogs of the test group (P < 0.01), but the change in B dogs was the same in the control group. These results mentioned above indicate that the central nervous system plays important role on the mechanism of pressor response induced by infusing 7.5% NaCl solution in the hemorrhagic hypotension dog.

PEEP ventilation does not cause humorally mediated cardiac output depression in pigs

OBJECTIVE

This study was designed to see if humorally mediated negative inotropism contributes to the cardiac output (CO) depression seen during positive end-expiratory pressure (PEEP) ventilation.

DESIGN

8 pairs of piglets were used and a combined blood circulation was established between the two animals in each pair. One animal was ventilated with a PEEP of 15 cmH20 (donor) and the other was ventilated without PEEP (recipient).

MEASUREMENT AND RESULTS

CO and stroke volume deteriorated in the donors by 32% and 44%, respectively, while no change was seen in the recipients.

CONCLUSION

As humorally mediated negative inotropism during PEEP ventilation has earlier been demonstrated in dogs, the results suggest that this mechanism might be species-dependent.

Adrenal medullary counterregulatory response to hypoglycemia in dogs with hepatic cross perfusion

The present study was conducted to investigate adrenal medullary response to cross perfusion of the liver in postabsorptive anesthetized dogs. The liver of the first dog (recipient) was perfused with vena caval and aortic blood of the second dog (donor) through the portal vein and hepatic artery, respectively. Hepatic venous blood was returned to the donor through an intracaval double-lumen hepatic catheter placed in the vena cava of the recipient. A portacaval shunt was made through the right femoral vein in the recipient. Upon the cross perfusion, normoglycemic clamp in the recipient was started to compensate the loss of hepatic glucose input into the systemic circulation. When the glucose infusion was discontinued, aortic glucose level rapidly declined, within 45 min, from 125.2 +/- 10.2 to 30.3 +/- 4.6 mg% (p < 0.05, n = 6) along with a similarly rapid decline of aortic insulin level. Inversely, both adrenal venous epinephrine and norepinephrine increased significantly (163.2 +/- 88.0 vs. 794.9 +/- 55.7 ng/mL (p < 0.05) and 36.6 +/- 22.4 vs. 119.7 +/- 15.3 ng/mL (p < 0.05), respectively; n = 6) during this hypoglycemic period. However, in the donor, glucose level did not change either in aortic or vena caval blood, indicating that the recipient's liver was perfused with normal blood glucose levels. In the control group in which the normoglycemic clamp in the recipient was continued during the cross perfusion, both aortic glucose and adrenal venous catecholamines remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of dynamic cardiac compression on ventricular mechanics and energetics. Role of ventricular size and contractility

The purpose of this study was to determine the role of ventricular size or contractility in the effectiveness of dynamic cardiac compression in terms of the pressure-volume relationship and myocardial oxygen consumption. In 10 isolated cross-circulated dog hearts, the ventricle was directly compressed during systole. For the volume run, measurements for slope of the end-systolic pressure-volume relation, pressure-volume area, external work, coronary blood flow, and myocardial oxygen consumption were achieved before and during a fixed amount of dynamic cardiac compression. Left ventricular volume was then increased while stroke volume was kept constant, and measurements were repeated. For the contractility run, after the control measurements were taken, left ventricular contractility was significantly increased or decreased by infusion of either dobutamine or propranolol into the coronary circulation. Measurements were repeated before and during dynamic cardiac compression at the control level of end-diastolic and stroke volumes. Dynamic cardiac compression significantly increased slope of the end-systolic pressure-volume relation, pressure-volume area, and external work (p < 0.01), whereas coronary blood flow and myocardial oxygen consumption were not affected. The increase in pressure-volume area caused by dynamic cardiac compression was greater with the larger volume. Despite the significant differences in the native left ventricular contractility, the increases in slope of the end-systolic pressure-volume relation, pressure-volume area, and external work did not differ among the three groups. We conclude that dynamic cardiac compression enhances left ventricular systolic function independent of ventricular contractility and without affecting coronary blood flow or myocardial oxygen consumption. Mechanical enhancement is more effective in the dilated heart.

Central hypoxic depression of respiration determined by perfusing a recipient cat's carotid bodies with blood from a donor cat

The respiratory response to sustained hypoxia reflects the net effect of the peripheral chemoreceptor excitation and the central depression. To obtain a pure depressant effect of central hypoxia (alv. PO2, 35-75 mmHg) on respiration, the recipient cat's carotid bodies were vascularly isolated and bilaterally perfused with blood from a donor cat. Cats were anesthetized, vagotomized, paralyzed, and artificially ventilated. Alv. PCO2 was kept at a normal value (iso- and normocapnia) throughout the experiment. The minute integrated phrenic nerve activity (Min. PNA) was used as an indication of inspiratory activity. The Min. PNA at which the recipient and donor cats were both breathing room air (central normoxia and peripheral chemoreceptor normoxia) was taken as 100% (control), and Min. PNA expressed as a percentage of the control was measured in a series of three experiments (A, B, and C): experiment A (normoxia-hypoxia; central normoxia and peripheral chemoreceptor hypoxia), experiment B (hypoxia-hypoxia; central hypoxia and peripheral chemoreceptor hypoxia), and experiment C (hypoxia-normoxia; central hypoxia and peripheral chemoreceptor normoxia). At alv. PO2 of about 50 mmHg, Min. PNA was 169.7 +/- 23.6% (mean +/- SD) in experiment A, 127.3 +/- 22.0% in experiment B, and 71.6 +/- 17.3% in experiment C. Thus, a pure depressant effect of normocapnic hypoxia (alv. PO2 of 50 mmHg) was 42.4% (= 169.7-127.3) or 28.4% (= 100-71.6). At alv. PO2 of about 40 mmHg, Min. PNA was 185.2 +/- 16.8% in experiment A, 146.2 +/- 19.0% in experiment B, and 54.8 +/- 15.2% in experiment C. Thus, a pure depressant effect of normocapnic hypoxia (alv. PO2 of 40 mmHg) was 39.0% (= 185.2-146.2) or 45.2% (= 100-54.8). From these results, we concluded that a pure depressant effect of normocapnic central hypoxia (alv. PO2, 40-50 mmHg) was 28-45% and this was affected by a stimulating drive from the peripheral chemoreceptors.

[Evaluation of cross circulation in conjoined twins]

This report describes the evaluation of cross circulation in conjoined twins. Female thoracoomphalopagus conjoined twins were delivered by cesarean section after 37 week's gestation. CT, MRI and echography were performed. A partial communication of pericardium and sternum, and a union of the liver were found. For the preoperative evaluation of cross circulation, a bolus of indigo carmine was injected, and the pigment appeared in the urine of the other twin. RI angiography showed that radionuclides in one twin were similar to those in the other after 5-10 minutes. During the operation, an injected bolus of SCC to one twin was not effective for the other twin. Inhaled isoflurane in one twin did not appear in the expired gas of the other twin. After the intentional hemorrhage for 3 minutes from one twin, the hemoglobin concentration of one of the twin was the same as that of the other. This demonstrates that acute hemorrhage from one twin seems to result in a significant and rapid decrease of hemoglobin in both babies equally. However, intravenous infusion of drugs to one of the twins requires a relatively long time to take effect in the other baby. We must be careful in anesthetic management of the surgical separation of conjoined twins.

The shivering response during cross-circulation in the common eider duck (Somateria mollissima)

The possible role of humoral factors in the control of shivering in the common eider duck (Somateria mollissima) was investigated using a cross-circulation technique. Pairs of animals were coupled so that the arterial system of one animal was connected to the venous system of the other. The rate of blood transferral was 12.8 ml min-1. By adequate heparinization of the extracorporeal blood supply, cross-circulation could be maintained for periods of up to 12 h. The temperature of blood entering each animal Tinlet) was controlled by heat exchangers. During control experiments Tinlet was maintained at a temperature close to normal body temperature. During cooling experiments Tinlet was maintained at c. 20 degrees C. Changes in metabolic heat production and oesophageal temperature in response to blood cooling were measured in cross-circulated pairs of animals cooled simultaneously or individually. Based on analysis of the metabolic responses under the different experimental situations, no evidence was found to indicate that blood-borne substances are involved in the shivering response in these animals.

A natriuretic factor is released by saline infusion into rat renal artery

Saline (154 mM NaCl) infused into one renal artery of anesthetized rats produced a prompt and substantial increase in sodium excretion without significant alteration of arterial pressure, renal blood flow, or glomerular filtration rate. A 1-h infusion at rates of 0.0375, 0.05, or 0.1 ml/min increased sodium excretion by the infused kidney from 0.15 +/- 0.04 to 0.70 +/- 0.12, from 0.45 +/- 0.10 to 2.17 +/- 0.40, and from 0.27 +/- 0.06 to 4.29 +/- 0.80 mumol/min, respectively. Natriuresis also occurred in the contralateral kidney. No comparable responses resulted from infusions at 0.0375 ml/min into the jugular vein, inferior vena cava, or carotid artery. Cross-circulation of blood from infused rats increased sodium excretion in uninfused recipients from 0.36 +/- 0.11 to 1.43 +/- 0.43 mumol.min-1.kidney-1. Isovolemic exchange-transfusion of blood from infused donor rats increased sodium excretion in uninfused recipients from 0.30 +/- 0.05 to 0.51 +/- 0.09 mumol.min-1.kidney-1. In both experiments, aortic infusions below the renal artery produced no comparable effect in recipient rats. Infusion of 300 mM glucose was not natriuretic. Infusion of two NaCl loads, 5.8 and 15.4 mumol/min, each at two different rates, increased sodium excretion in proportion to the load of NaCl and not to the rate of infusion. Infusions of a protein-free artificial rat plasma or of 140 mM NaCl, both with the sodium concentration of rat plasma, produced very little increase in sodium excretion. Infusion of 154 mM sodium lactate produced an increase in sodium excretion comparable to that produced by 154 mM NaCl. Reducing the infusion rate of 154 mM NaCl from 0.05 to 0.01 ml/min produced a rapid decline in the rate of sodium excretion. We conclude that renal arterial saline infusion activates a mechanism that increases sodium excretion by the infused kidney and concurrently causes the release of a natriuretic factor. Increased sodium concentration in renal arterial blood was the only stimulus found to produce the effect.

Left ventricular ORS widening decreases Emax without lowering VO2-PVA relation in dog hearts

We observed a few rare spontaneous cases of a suddenly widened QRS wave of left ventricular ECG associated with a simultaneous decrease in left ventricular (LV) contractility (Emax, end-systolic pressure-volume ratio) in excised cross-circulated dog heart experiments. The decreased Emax was not associated with a descent of the relation between cardiac oxygen consumption (VO2) and LV systolic pressure-volume area (PVA, a measure of total ventricular mechanical energy). This result is intriguing because ventricular VO2-PVA relation generally changes its elevation in proportion to Emax under various inotropic interventions. We suspected the unusual observation to reflect no change in myocardial contractility despite ventricular asynchrony augmented by an intraventricular conduction defect.

Oxygen consumption for constant work is minimal at lowest working contractility in normal dog hearts

We tested whether minimal myocardial oxygen consumption (MVO2) for a given external work would exist in the middle of a normal contractility range as previously predicted theoretically. The left ventricle of the excised cross-circulated dog heart preparation was connected to a volume servo pump. Myocardial contractility in terms of ventricular end-systolic elastance (Emax) was gradually increased from control 8.9 +/- 3.4 (mean +/- SD) to 30.0 mmHg/(ml/100 g) by epinephrine and decreased to 1.8 mmHg/(ml/100 g) by propranolol while heart rate, end-systolic pressure and stroke work were kept constant. MVO2 was determined as the product of total coronary flow and coronary arteriovenous oxygen content difference in each contractile state. We plotted MVO2 values against E(max) values in each heart. The MVO2-E(max) relation for a constant cardiac work showed that MVO2 was minimal at the low end of the covered E(max) range. We conclude that minimal MVO2 for a given cardiac work is generally obtained at the lowest working contractility in normal dog hearts. This conclusion might pose some problems in the previous theoretical prediction as to the contractility that achieves the minimal MVO2 in a given external work.