Pressure-flow analysis of portal vein and hepatic artery interactions in porcine liver

Hepatic Hemodynamics and Elevation of Liver Stiffness as Possible Predictive Markers of Late-onset Hepatic Failure

A 52-year-old Japanese woman admitted to our hospital for the treatment of liver dysfunction due to an undetermined cause developed disorientation on the 58th hospital day and was diagnosed with late-onset liver failure. Abdominal ultrasound examinations were performed several times from the admission. Before the disorientation appeared, the results of the examinations revealed that the portal flow decreased, after which the hepatic arterial flow increased and the degree of liver stiffness became elevated. Although the pathophysiology of these changes remains unclear, hemodynamic changes and elevation of liver stiffness might be predictive markers of severe liver tissue damage.

Organ perfusion during voluntary pulmonary hyperinflation; a magnetic resonance imaging study

Pulmonary hyperinflation is used by competitive breath-hold divers and is accomplished by glossopharyngeal insufflation (GPI), which is known to compress the heart and pulmonary vessels, increasing sympathetic activity and lowering cardiac output (CO) without known consequence for organ perfusion. Myocardial, pulmonary, skeletal muscle, kidney, and liver perfusion were evaluated by magnetic resonance imaging in 10 elite breath-hold divers at rest and during moderate GPI. Cardiac chamber volumes, stroke volume, and thus CO were determined from cardiac short-axis cine images. Organ volumes were assessed from gradient echo sequences, and organ perfusion was evaluated from first-pass images after gadolinium injection. During GPI, lung volume increased by 5.2 ± 1.5 liters (mean ± SD; P < 0.001), while spleen and liver volume decreased by 46 ± 39 and 210 ± 160 ml, respectively (P < 0.05), and inferior caval vein diameter by 4 ± 3 mm (P < 0.05). Heart rate tended to increase (67 ± 10 to 86 ± 20 beats/min; P = 0.052) as right and left ventricular volumes were reduced (P < 0.05). Stroke volume (107 ± 21 to 53 ± 15 ml) and CO (7.2 ± 1.6 to 4.2 ± 0.8 l/min) decreased as assessed after 1 min of GPI (P < 0.01). Left ventricular myocardial perfusion maximum upslope and its perfusion index decreased by 1.52 ± 0.15 s(-1) (P < 0.001) and 0.02 ± 0.01 s(-1) (P < 0.05), respectively, without transmural differences. Pulmonary tissue, spleen, kidney, and pectoral-muscle perfusion also decreased (P < 0.05), and yet liver perfusion was maintained. Thus, during pulmonary hyperinflation by GPI, CO and organ perfusion, including the myocardium, as well as perfusion of skeletal muscles, are reduced, and yet perfusion of the liver is maintained. Liver perfusion seems to be prioritized when CO decreases during GPI.

Automated decellularization of intact, human-sized lungs for tissue engineering

We developed an automated system that can be used to decellularize whole human-sized organs and have shown lung as an example. Lungs from 20 to 30 kg pigs were excised en bloc with the trachea and decellularized with our established protocol of deionized water, detergents, sodium chloride, and porcine pancreatic DNase. A software program was written to control a valve manifold assembly that we built for selection and timing of decellularization fluid perfusion through the airway and the vasculature. This system was interfaced with a prototypic bioreactor chamber that was connected to another program, from a commercial source, which controlled the volume and flow pressure of fluids. Lung matrix that was decellularized by the automated method was compared to a manual method previously used by us and others. Automation resulted in more consistent acellular matrix preparations as demonstrated by measuring levels of DNA, hydroxyproline (collagen), elastin, laminin, and glycosaminoglycans. It also proved highly beneficial in saving time as the decellularization procedure was reduced from days down to just 24 h. Developing a rapid, controllable, automated system for production of reproducible matrices in a closed system is a major step forward in whole-organ tissue engineering.

Liver regeneration

The liver is unique in its ability to regenerate in response to injury. A number of evolutionary safeguards have allowed the liver to continue to perform its complex functions despite significant injury. Increased understanding of the regenerative process has significant benefit in the treatment of liver failure. Furthermore, understanding of liver regeneration may shed light on the development of cancer within the cirrhotic liver. This review provides an overview of the models of study currently used in liver regeneration, the molecular basis of liver regeneration, and the role of liver progenitor cells in regeneration of the liver. Specific focus is placed on clinical applications of current knowledge in liver regeneration, including small-for-size liver transplant. Furthermore, cutting-edge topics in liver regeneration, including in vivo animal models for xenogeneic human hepatocyte expansion and the use of decellularized liver matrices as a 3-dimensional scaffold for liver repopulation, are proposed. Unfortunately, despite 50 years of intense study, many gaps remain in the scientific understanding of liver regeneration.

A Hemodynamic Study to Evaluate the Buffer Response in Cirrhotic Patients Undergoing Liver Transplantation

The physiological regulation of the liver blood flow is a result of a reciprocal portal vein and hepatic artery flow relationship. This mechanism is defined as the hepatic arterial buffer response (HABR). This study was addressed to investigate whether HABR is maintained in denervated grafts in liver transplant recipients. Portal blood flow (PBF) and hepatic arterial resistance index (PI) were measured 6 months after transplantation using Doppler. In each patient we consecutively measured the vasodilator (Ensure Plus PO versus placebo) and vasoconstrictor (isosorbide dinitrate 5 mg SL versus placebo) stimuli. The meal ingestion caused a significant increase of both parameters, PBF (from 1495±260 to 2069±250 mL/min, P<0.05) and PI (from 0.7±0.2 to 0.8±0.2, P<0.05). By contrast, isosorbide dinitrate reduced PBF (from 1660±270 to 1397±250 mL/min, P<0.05) and PI (from 0.7±0.2 to 0.5±0.2, P<0.05). We show that PBF and PI are reciprocally modified with the administration of vasoconstrictor and vasodilator stimuli. These results suggest the persistence of the HABR in a denervated human model, suggesting that this mechanism is independent of the regulation from the autonomic nervous system.

Hemorrhage control of liver injury by short electrical pulses

Trauma is a leading cause of death among young individuals globally and uncontrolled hemorrhage is the leading cause of preventable death. Controlling hemorrhage from a solid organ is often very challenging in military as well as civilian setting. Recent studies demonstrated reversible vasoconstriction and irreversible thrombosis following application of microseconds-long electrical pulses. The current paper describes for the first time reduction in bleeding from the injured liver in rat and rabbit model in-vivo. We applied short (25 and 50 µs) electrical pulses of 1250 V/cm to rats and rabbit liver following induction of standardized penetrating injury and measured the amount of bleeding into the abdominal cavity one hour post injury. We found a 60 and 36 percent reduction in blood volume in rats treated by 25 µs and 50 µs, respectively (P<0.001). Similar results were found for the rabbit model. Finite element simulation revealed that the effect was likely non-thermal. Histological evaluation found local cellular injury with intravascular thrombosis. Further research should be done to fully explore the mechanism of action and the potential use of short electric pulses for hemorrhage control.

Influence of hemodynamic variations on the pharmacokinetics of landiolol in patients undergoing cardiovascular surgery

Although landiolol is useful in the emergency management of atrial fibrillation, atrial flutter, and tachycardia, as well as in perioperative arrhythmia control, the influence of hemodynamic changes on the pharmacokinetics of landiolol is unknown. We investigated the influence of hemodynamic variation and the following hepatocirculatory changes after systemic heparinization on the pharmacokinetics of landiolol in patients undergoing cardiovascular surgery under cardiopulmonary bypass. Cardiac output and cardiac index (CI) were continuously monitored in 19 patients using an arterial pressure-based cardiac output monitor. The middle and right hepatic venous blood flow indexes (mHVBFI and rHVBFI) were measured by transesophageal echocardiography, and hemodynamic data were collected at points (T1-T3) as follows: T1, before administration of heparin and after sternotomy; T2, just before systemic heparinization (300 U/kg); T3, 10 min after T2. The plasma concentration of landiolol was measured by HPLC at the same point. After administration of heparin, mean arterial blood pressure, CI, mHVBFI, and rHVBFI were significantly decreased (<0.05). Heart rate was not significantly changed. After systemic heparinization, the landiolol concentration was significantly decreased from 0.407±0.251 µg·mL(-1) to 0.232±0.207 µg·mL(-1) (<0.01). There was no significant difference between T1 and T2 (=0.88). In conclusion, the plasma concentration of landiolol was decreased by diminished CI due to systemic heparinization, but not affected by the change of hepatic blood flow.

H2S contributes to the hepatic arterial buffer response and mediates vasorelaxation of the hepatic artery via activation of K(ATP) channels

Hepatic blood supply is uniquely regulated by the hepatic arterial buffer response (HABR), counteracting alterations of portal venous blood flow by flow changes of the hepatic artery. Hydrogen sulfide (H(2)S) has been recognized as a novel signaling molecule with vasoactive properties. However, the contribution of H(2)S in mediating the HABR is not yet studied. In pentobarbital-anesthetized and laparotomized rats, flow probes around the portal vein and hepatic artery allowed for assessment of the portal venous (PVBF) and hepatic arterial blood flow (HABF) under baseline conditions and stepwise reduction of PVBF for induction of HABR. Animals received either the H(2)S donor Na(2)S, DL-propargylglycine as inhibitor of the H(2)S synthesizing enzyme cystathionine-gamma-lyase (CSE), or saline alone. Additionally, animals were treated with Na(2)S and the ATP-sensitive potassium channel (K(ATP)) inhibitor glibenclamide or with glibenclamide alone. Na(2)S markedly increased the buffer capacity to 27.4 +/- 3.0% (P < 0.05 vs. controls: 15.5 +/- 1.7%), whereas blockade of H(2)S formation by DL-propargylglycine significantly reduced the buffer capacity (8.5 +/- 1.4%). Glibenclamide completely reversed the H(2)S-induced increase of buffer capacity to the control level. By means of RT-PCR, Western blot analysis, and immunohistochemistry, we observed the expression of both H(2)S synthesizing enzymes (CSE and cystathionine-beta-synthase) in aorta, vena cava, hepatic artery, and portal vein, as well as in hepatic parenchymal tissue. Terminal branches of the hepatic afferent vessels expressed only CSE. We show for the first time that CSE-derived H(2)S contributes to HABR and partly mediates vasorelaxation of the hepatic artery via activation of K(ATP) channels.

The role of hepatic arterial flow on portal venous and hepatic venous wedged pressure in the isolated perfused CCl4-cirrhotic liver

In cirrhosis, hepatic venous pressure gradient is used to measure portal venous and sinusoidal pressures, as well as drug-induced decreases of elevated pressures. The aim of this study was to investigate the influence of hepatic arterial flow (HAF) changes on portal venous perfusion (PVPP) and wedged hepatic venous pressure (WHVP). Normal and CCl4-cirrhotic rats were subjected to a bivascular liver perfusion with continuous measurements of PVPP, WHVP, and hepatic arterial perfusion pressure. Flow-pressure curves were performed with the use of different flows either through the portal vein (PVF: 20-32 ml/min) or HAF (5-15 ml/min). Increases in HAF lead to significant absolute and relative increases in PVPP (P = 0.002) and WHVP (P < 0.001). Absolute changes in HAF correlated to absolute changes in PVPP (cirrhosis: r = 0.64, P < 0.001; control: r = 0.67, P < 0.001) and WHVP (cirrhosis: r = 0.71, P < 0.001; control: r = 0.82, P < 0.001). Changes in PVPP correlated to changes in WHVP due to changes in PVF only in cirrhosis (r = 0.75, P < 0.001), whereas changes in HAF correlated in both cirrhosis (r = 0.92, P < 0.001) and control (r = 0.77, P < 0.001). In conclusion, increases and decreases in HAF lead to respective changes in PVPP and WHVP. This suggests a direct influence of HAF on PVPP and WHVP most likely due to changes in sinusoidal perfusion.

Spontaneous breathing during airway pressure release ventilation in experimental lung injury: effects on hepatic blood flow

OBJECTIVE

Positive pressure ventilation can affect systemic haemodynamics and regional blood flow distribution with negative effects on hepatic blood flow. We hypothesized that spontaneous breathing (SB) with airway pressure release ventilation (APRV) provides better systemic and hepatic blood flow than APRV without SB.

DESIGN

Animal study with a randomized cross-over design.

SETTING

Animal laboratory of Bonn University Hospital.

SUBJECTS

Twelve pigs with oleic-acid-induced lung injury.

INTERVENTIONS

APRV with or without SB in random order. Without SB, either the upper airway pressure limit or the ventilator rate was increased to maintain constant pH and PaCO2.

MEASUREMENTS AND RESULTS

Systemic haemodynamics were determined by double-indicator dilution, organ blood flow by coloured microspheres. Systemic blood flow was best during APRV with SB. During APRV with SB blood flow (ml g(-1) min(-1)) was 0.91+/-0.26 (hepatic arterial), 0.29+/-0.05 (stomach), 0.64+/-0.08 (duodenum), 0.62+/-0.10 (jejunum), 0.53+/-0.07 (ileum), 0.53+/-0.07 (colon), 0.46+/-0.09 (pancreas) and 3.59+/-0.55 (spleen). During APRV without SB applying high P(aw) it decreased to 0.13+/-0.01 (stomach), 0.37+/-0.03 (duodenum), 0.29+/-0.03 (jejunum), 0.31+/-0.05 (ileum), 0.32+/-0.03 (colon) and 0.23+/-0.04 (pancreas) p<0.01, respectively. During APRV without SB applying same Paw limits it decreased to 0.18+/-0.03 (stomach, p<0.01), 0.47+/-0.06 (duodenum, p<0.05), 0.38+/-0.05 (jejunum, p<0.01), 0.36+/-0.03 (ileum, p<0.05), 0.39+/-0.05 (colon, p<0.05), and 0.27+/-0.04 (pancreas, p<0.01). Arterial liver blood flow did not change significantly when SB was abolished (0.55+/-0.11 and 0.63+/-0.11, respectively).

CONCLUSIONS

Maintaining SB during APRV was associated with better systemic and pre-portal organ blood flow. Improvement in hepatic arterial blood flow was not significant.

Clinical review: splanchnic ischaemia

Inadequate splanchnic perfusion is associated with increased morbidity and mortality, particularly if liver dysfunction coexists. Heart failure, increased intra-abdominal pressure, haemodialysis and the presence of obstructive sleep apnoea are among the multiple clinical conditions that are associated with impaired splanchnic perfusion in critically ill patients. Total liver blood flow is believed to be relatively protected when gut blood flow decreases, because hepatic arterial flow increases when portal venous flow decreases (the hepatic arterial buffer response [HABR]). However, there is evidence that the HABR is diminished or even abolished during endotoxaemia and when gut blood flow becomes very low. Unfortunately, no drugs are yet available that increase total hepato-splanchnic blood flow selectively and to a clinically relevant extent. The present review discusses old and new concepts of splanchnic vasoregulation from both experimental and clinical viewpoints. Recently published trials in this field are discussed.

Hemorrhagic shock primes the hepatic portal circulation for the vasoconstrictive effects of endothelin-1

To test whether hemorrhagic shock and resuscitation (HSR) alters the vascular responsiveness of the portohepatic circulation to endothelins (ETs), we studied the macro- and microcirculatory effects of the preferential ET(A) receptor agonist ET-1 and of the selective ET(B) receptor agonist sarafotoxin 6c (S6c) after 1 h of hemorrhagic hypotension and 5 h of volume resuscitation in the isolated perfused rat liver ex vivo using portal pressure-flow relationships and epifluorescence microscopy. Although HSR did not cause major disturbances of hepatic perfusion per se, the response to ET-1 (0.5 x 10(-9) M) was enhanced, leading to greater increases in portal driving pressure, total portal resistance, and zero-flow pressures and more pronounced decreases in portal flow, sinusoidal diameters, and hepatic oxygen delivery compared with time-matched sham shock controls. In sharp contrast, the constrictive response to S6c (0.25 x 10(-9) M) remained unchanged. Thus HSR primes the portohepatic circulation for the vasoconstrictive effects of ET-1 but does not alter the effects of the ET(B) receptor agonist S6c. The enhanced sinusoidal response may contribute to the subsequent development of hepatic microcirculatory failure after secondary insults that are associated with increased generation of ET-1.

Effects of systemic arterial hypoperfusion on splanchnic hemodynamics and hepatic arterial buffer response in pigs

The hepatic arterial buffer response (HABR) tends to maintain liver blood flow under conditions of low mesenteric perfusion. We hypothesized that systemic hypoperfusion impairs the HABR. In 12 pigs, aortic blood flow was reduced by cardiac tamponade to 50 ml. kg(-1). min(-1) for 1 h (short-term tamponade) and further to 30 ml. kg(-1). min(-1) for another hour (prolonged tamponade). Twelve pigs without tamponade served as controls. Portal venous blood flow decreased from 17 +/- 3 (baseline) to 6 +/- 4 ml. kg(-1). min(-1) (prolonged tamponade; P = 0.012) and did not change in controls, whereas hepatic arterial blood flow decreased from 2 +/- 1 (baseline) to 1 +/- 1 ml. kg(-1). min(-1) (prolonged tamponade; P = 0.050) and increased from 2 +/- 1 to 4 +/- 2 ml. kg(-1). min(-1) in controls (P = 0.002). The change in hepatic arterial conductance (DeltaC(ha)) during acute portal vein occlusion decreased from 0.1 +/- 0.05 (baseline) to 0 +/- 0.01 ml. kg(-1). min(-1). mmHg(-1) (prolonged tamponade; P = 0.043). In controls, DeltaC(ha) did not change. Hepatic lactate extraction decreased, but hepatic release of glutathione S-transferase A did not change during cardiac tamponade. In conclusion, during low systemic perfusion, the HABR is exhausted and hepatic function is impaired without signs of cellular damage.

Hepatic arteriolo-portal venular shunting guarantees maintenance of nutritional microvascular supply in hepatic arterial buffer response of rat livers

To elucidate the hepatic microvascular response upon the hepatic arterial buffer response (HABR), we analysed blood flow (ultrasonic flowprobes) of the hepatic artery (HA) and portal vein (PV), microcirculation (intravital microscopy), and tissue oxygenation (polarography) in anaesthetized Sprague-Dawley rats and re-evaluated the role of adenosine in mediating the HABR by using 8-phenyltheophylline as a competitive antagonist. 2. Upon restriction of PV blood flow to 11 +/- 3 % of baseline values, HA blood flow increased by a factor of 1.77 (P < 0.05), thus confirming HABR. Strikingly, red blood cell velocity and volumetric blood flow in terminal hepatic arterioles (THAs) did not increase but were even found to be slightly decreased, by 8 and 13 %, respectively. In contrast, red blood cell velocity and volumetric blood flow in terminal portal venules (TPVs) decreased to only 66 % (P < 0.05), indicating upstream hepatic arteriolo-portal venular shunting. As a consequence, red blood cell velocity and volumetric blood flow in sinusoids were found to be reduced to only 66-68 % compared with baseline (P < 0.05). Diameters of neither of those microvessels changed, thus excluding THA-, TPV-, and sinusoid-associated mechanisms of vasomotor control in HABR. 3. Tissue PO2 and hepatocellular NADH fluorescence remained unchanged, indicating HABR-mediated maintenance of adequate oxygen delivery, despite the marked reduction of total liver blood flow. Further, hepatic arteriolo-portal venular shunting guaranteed homogeneity of nutritive blood flow upon HABR, as given by an unchanged intra-acinar coefficient of variance of sinusoidal perfusion. 4. Pretreatment of animals with the adenosine antagonist 8-phenyltheophylline completely blocked the hepatic arterial buffer response with the consequence of decreased tissue oxygenation and increased heterogeneity of sinusoidal perfusion. 5. In conclusion, hepatic microhaemodynamics, in particular unchanged diameters of THAs, TPVs and sinusoids, during HABR indicate that reduction in resistance to HA flow is located upstream and functions via hepatic arteriolo-portal venular shunts resulting in equal distribution of microvascular blood flow and oxygen delivery under conditions of restricted PV blood supply.

Impact of intrinsic blood flow regulation in cirrhosis: maintenance of hepatic arterial buffer response

The hepatic arterial buffer response (HABR) effectively controls total blood perfusion in normal livers, but little is known about blood flow regulation in cirrhosis. We therefore studied the impact of HABR on blood perfusion of cirrhotic livers in vivo. After 8-wk CCl(4) treatment to induce cirrhosis, 18 anesthetized rats (and 18 noncirrhotic controls) were used to simultaneously assess portal venous and hepatic arterial inflow with miniaturized ultrasonic flow probes. Stepwise hepatic arterial blood flow (HAF) or portal venous blood flow (PVF) reduction was performed. Cirrhotic livers revealed a significantly reduced total hepatic blood flow (12.3 +/- 0.9 ml/min) due to markedly diminished PVF (7.3 +/- 0.8 ml/min) but slightly increased HAF (5.0 +/- 0.6 ml/min) compared with noncirrhotic controls (19.0 +/- 1.6, 15.2 +/- 1.3, and 3.8 +/- 0.4 ml/min). PVF reduction caused a significant HABR, i.e., increase of HAF, in both normal and cirrhotic livers; however, buffer capacity of cirrhotic livers exceeded that of normal livers (P < 0.05) by 1. 7- to 4.5-fold (PVF 80% and 20% of baseline). Persistent PVF reduction for 1, 2, and 6 h demonstrated constant HABR in both groups. Furthermore, HABR could be repetitively provoked, as analyzed by intermittent PVF reduction. HAF reduction did not induce changes of portal flow in either group. Because PVF is reduced in cirrhosis, the maintenance of HAF and the preserved HABR must be considered as a protective effect on overall hepatic circulation, counteracting impaired nutritive blood supply via the portal vein.