The influence of flow and hematocrit on the laser Doppler flux signal from the surface of the perfused pig liver

Hepatic arterial infusion with tumor necrosis factor-α induces early hepatic hyperperfusion

BACKGROUND

Hepatic arterial infusion (HAI) has been developed for high-dose regional chemotherapy of unresectable liver metastases or primary liver malignancies. While it is well known that high concentrations of tumor necrosis factor (TNF)-α damage tumor blood perfusion, there is no information on whether autochthonous liver perfusion is affected by HAI with TNF-α. Therefore, we investigated the effects of HAI with TNF-α on hepatic macro- and microvascular perfusion.

METHODS

Swabian Hall pigs were randomized into three groups. HAI was performed with either 20 or 40 µg/kg body weight TNF-α (n = 6 each group). Saline-treated animals served as controls (n = 6). Analyses during a 2-hour post-HAI observation period included systemic hemodynamics, portal venous and hepatic arterial blood flow, portal venous pressure, and the blood flow in the hepatic microcirculation.

RESULTS

HAI with TNF-α caused a slight decrease of mean arterial blood pressure (p < 0.001), which was compensated by a moderate increase of heart rate (p < 0.001). No further systemic side effects of TNF-α were observed. HAI with TNF-α further caused a slight but not significant decrease of portal venous blood flow (p = 0.737) in both experimental groups, paralleled by an increase of hepatic arterial blood flow (p = 0.023, 20 µg/kg; p = 0.034, 40 µg/kg) resulting in an overall hepatic hyperperfusion. The hepatic hyperperfusion after HAI with 20 µg/kg TNF-α was more pronounced and associated with a 40% decrease of the blood flow in the hepatic microcirculation (p = 0.009). HAI with 40 µg/kg TNF-α was only associated with a temporary and moderate total hepatic hyperperfusion and did not affect the blood flow in the hepatic microcirculation.

CONCLUSION

HAI with TNF-α causes a decrease of portal venous flow; however, this is overcompensated by an increased hepatic arterial blood flow, resulting in a total hepatic hyperperfusion. Moderate total hepatic hyperperfusion does not affect the blood flow in the hepatic microcirculation, while a persistent and more pronounced hyperperfusion may cause hepatic microcirculatory disturbances.

Vasopressin in septic shock: effects on pancreatic, renal, and hepatic blood flow

Introduction

Vasopressin has been shown to increase blood pressure in catecholamine-resistant septic shock. The aim of this study was to measure the effects of low-dose vasopressin on regional (hepato-splanchnic and renal) and microcirculatory (liver, pancreas, and kidney) blood flow in septic shock.

Methods

Thirty-two pigs were anesthetized, mechanically ventilated, and randomly assigned to one of four groups (n = 8 in each). Group S (sepsis) and group SV (sepsis/vasopressin) were exposed to fecal peritonitis. Group C and group V were non-septic controls. After 240 minutes, both septic groups were resuscitated with intravenous fluids. After 300 minutes, groups V and SV received intravenous vasopressin 0.06 IU/kg per hour. Regional blood flow was measured in the hepatic and renal arteries, the portal vein, and the celiac trunk by means of ultrasonic transit time flowmetry. Microcirculatory blood flow was measured in the liver, kidney, and pancreas by means of laser Doppler flowmetry.

Results

In septic shock, vasopressin markedly decreased blood flow in the portal vein, by 58% after 1 hour and by 45% after 3 hours (p < 0.01), whereas flow remained virtually unchanged in the hepatic artery and increased in the celiac trunk. Microcirculatory blood flow decreased in the pancreas by 45% (p < 0.01) and in the kidney by 16% (p < 0.01) but remained unchanged in the liver.

Conclusion

Vasopressin caused marked redistribution of splanchnic regional and microcirculatory blood flow, including a significant decrease in portal, pancreatic, and renal blood flows, whereas hepatic artery flow remained virtually unchanged. This study also showed that increased urine output does not necessarily reflect increased renal blood flow.

Aging: Impact Upon Local Cerebral Oxygenation and Blood Flow With Acute Isovolemic Hemodilution

Data from the neurosurgical critical care arena demonstrate a correlation between cerebral oxygenation, survival, and cognitive function. Transfusion may increase and hemodilution decrease cerebral oxygenation. Both acute and chronic anemia have been associated with cognitive dysfunction. Aggressive blood conservation protocols have been instituted across all age groups without conclusive evidence for their impact upon outcome. Aged subjects are at the greatest risk of cognitive sequelae after major surgery associated with significant blood loss. We hypothesize that cerebral physiologic changes associated with "normal" aging may compromise cerebral oxygenation in the presence of severe anemia.Fischer 344 rats, the NIH National Institute of Aging normal aging rat model, underwent a stepwise isovolemic hemodilution protocol. Age groups (Age Grp) studied were as follows: Age Grp-A (3 months), n=14; Age Grp-B (9 to 12 months), n=14; and Age Grp-C (24 months), n=14. Brain oxygen tension (PBrO2), laser Doppler flow, and mean arterial pressure were measured. Final hemoglobin averaged 6.1+/-0.9 g/dL. PBrO2 levels decreased from a baseline of 18.1+/-4.1 to 17.5+/-6.8 mm Hg (P=0.49), and laser Doppler flow increased by 18+/-20% (P<0.0001) after hemodilution. Employing repeated measures multiple regression, Age Grp (P=0.30) was not a significant controlling covariate of PBrO2 in response to isovolemic hemodilution. PBrO2 levels were actually higher in Age Grp-C animals at all time points of the hemodilution protocol, although this was not statistically significant. Aged animals were also fully capable of mounting a robust local cerebral hyperemic response to the anemic challenge that was not separable from the response of younger animals.

The isolated perfused liver. a new model using autologous blood and porcine slaughterhouse organs

INTRODUCTION

Current models of isolated and perfused livers are limited by nonphysiologic perfusates or the need for the use of high numbers of laboratory animals. The present study was performed in order to rectify these difficulties.

METHODS

To establish a new isolated perfused liver model, a perfusion circuit was developed using normothermic, autologous hemoperfusion and organs obtained from a slaughterhouse.

RESULTS

Stable organ function was maintained over 220 min. The organs displayed physiologic values for measured variables, including oxygen consumption which varied from 5.2+/-1.5 ml/min at 40 min to 5.2+/-2.4 ml/min at 220 min, and bile production (0.15-0.31 ml/min, respectively).

DISCUSSION

The present studies demonstrate a new approach for experimental liver perfusion by combining the optimal perfusion medium of autologous blood and slaughterhouse organs as source material.

Microvascular origin of laser-Doppler flux signal from the surface of normal and injured liver of the rat

Although laser-Doppler flowmetry (LDF) is a widely used technique, little is known about its microvascular origin from the surface of the liver. In the present study, we attempted to identify the microvascular bed interrogated by the laser light, by correlating perfusion and red blood cell velocity data obtained using intravital fluorescence microscopy (IVFM) with the LDF signal recorded under normal conditions and following liver injury. Sprague-Dawley rats which underwent hepatic artery ligation (HAL) or nonarterialized liver transplantation (NOLT) served as in vivo models of reduced sinusoidal red blood cell velocity (RBC(vel)) and altered homogeneity of perfusion, respectively. Three groups of animals were studied: HAL (n = 8), NOLT (n = 8), and sham-operated control (n = 8). Homogeneous perfusion of the sinusoids and liver lobules and reduced sinusoidal RBC(vel) were initially confirmed in the HAL group. In addition, significantly reduced sinusoidal and lobular perfusion was observed in the NOLT liver. HAL caused a 28% reduction in the LDF signal (P < 0.05 vs sham), whereas the LDF signal from the NOLT liver (101 +/- 11 PU) was lower than that from the native recipient liver with HAL (128 +/- 11 PU). Under control conditions, and following HAL and NOLT, a linear correlation could be established only between sinusoidal RBC(vel) and LDF signal (y = 0.78x + 50.98, r2 = 0.71, P < 0.001). Furthermore, using IVFM images and NIH Image analysis, we estimated a high contribution of the sinusoids to the total vascular space at the liver periphery. Our data indicate that under normal conditions and those of altered microcirculation, blood flow in the sinusoids, compared to other microvessels, has a significant influence on the LDF signal from the surface of the liver.

Laboratory assessment of hepatic hemodynamics

Although the study of hepatic circulation is complicated by the dual blood supply and complex anatomy of the liver, many distinct methods are available to facilitate its study. Before embarking on an investigation of hepatic hemodynamics, the investigator must be familiar with the available methods and their applications. All methods have their own attributes and limitations. No one method is superior to the others, but, depending on the aspect of hepatic hemodynamics to be investigated, a particular methodology may yield distinct advantages.

Effect of a 30-minute infusion of dobutamine hydrochloride on hind limb blood flow and hemodynamics in halothane-anesthetized horses

OBJECTIVE

To evaluate the hemodynamic effects of dobutamine hydrochloride (0.5 microg/kg of body weight/min) in halothane-anesthetized horses.

ANIMALS

6 adult Thoroughbred horses.

PROCEDURE

Anesthesia was induced by use of romifidine (100 microg/kg) and ketamine (2.2 mg/kg), IV. Anesthesia was maintained by halothane (end-tidal concentration 0.9 to 1.0%). Aortic, left ventricular, and right atrial pressures were measured, using catheter-mounted strain gauge transducers. Cardiac output (CO), velocity time integral, maximal aortic blood flow velocity and acceleration, and left ventricular preejection period and ejection time were measured from aortic velocity waveforms obtained by transesophageal Doppler echocardiography. Velocity waveforms were recorded from the femoral vessels, using Doppler ultrasonography. The time-averaged mean velocity and early diastolic deceleration slope (EDDS) were measured. Pulsatility index (PI) and volumetric flow were calculated. Microvascular perfusion was measured in the semimembranosus muscles by laser Doppler flowmetry. Data were recorded 60 minutes after induction of anesthesia (control) and at 15 and 30 minutes after start of an infusion of dobutamine (0.5 microg/kg/min).

RESULTS

Aortic pressures were significantly increased during the infusion of dobutamine. No change was observed in the indices of left ventricular systolic function including CO. Femoral arterial flow significantly increased, and the PI and EDDS decreased. No change was observed in the femoral venous flow or in microvascular perfusion.

CONCLUSIONS AND CLINICAL RELEVANCE

At this dosage, dobutamine did not alter left ventricular systolic function. Femoral blood flow was preferentially increased as the result of local vasodilatation. The lack of effect of dobutamine on microvascular perfusion suggests that increased femoral flow is not necessarily associated with improved perfusion of skeletal muscles.

Dynamic study of the distribution of microcirculatory blood flow in multiple splanchnic organs in septic shock

OBJECTIVES

To study dynamic distribution of microcirculatory blood flow in multiple splanchnic organs during septic shock; to test the hypothesis that changes in microcirculatory blood flow in splanchnic organs correlate with changes in regional flow during septic shock.

DESIGN

A prospective, controlled, animal study.

SETTING

Animal laboratory in a university medical center.

SUBJECTS

Nine anesthetized and mechanically ventilated domestic pigs.

INTERVENTIONS

Systemic flow (cardiac output) was measured with thermodilution and regional (superior mesenteric artery) flow with transit time flowmetry. Local blood flow (microcirculatory flow) was continuously measured in splanchnic organs (gastric, jejunal, and colon mucosa, liver, and pancreas) and the kidney with multichannel laser Doppler flowmetry. Septic shock was induced with fecal peritonitis. After 240 mins of sepsis, intravenous fluids were administered to alter hypodynamic shock to hyperdynamic septic shock.

MEASUREMENTS AND MAIN RESULTS

In this severe septic shock model, systemic and regional flows decreased by approximately 50% during the first 240 mins. Similar reductions were recorded in microcirculatory flow in the mucosa of the stomach (-41%; p < .001) and colon (-47%; p < .001). In the jejunal mucosa, on the other hand, flow remained virtually unchanged. Microcirculatory flow was also significantly decreased in the liver (-49%; p < .001), pancreas (-56%; p < .001), and kidney (-44%; p < .001). Administration of intravenous fluids at 240 mins was followed by three-fold increases in systemic and regional flows (approximately 70% above baseline). In the jejunal mucosa, flow also increased significantly above baseline (42%; p < .001), whereas in the stomach and the colon, it barely reached baseline. Kidney blood flow increased to baseline, whereas pancreas and liver flows remained 26% (p < .05) and 34% (p < .001), respectively, below baseline.

CONCLUSION

Changes in microcirculatory blood flow in the splanchnic organs are heterogeneous, both in early hypodynamic and in hyperdynamic septic shock, and cannot be predicted from changes in systemic or regional flows. Microcirculatory blood flow in the jejunal mucosa remains constant during early septic shock, whereas pancreatic blood flow decreases significantly more than regional flow.

Doppler ultrasonography and single-fiber laser Doppler flowmetry for measurement of hind limb blood flow in anesthetized horses

OBJECTIVE

To use Doppler ultrasonography and single-fiber laser Doppler flowmetry (LDF) to evaluate blood flow in the dependent and nondependent hind limbs of anesthetized horses and to evaluate changes in femoral arterial blood flow and microvascular skeletal muscle perfusion in response to administration of phenylephrine hydrochloride or dobutamine hydrochloride.

ANIMALS

6 healthy adult horses.

PROCEDURE

Horses were anesthetized and positioned in left lateral recumbency. Doppler ultrasonography was used to measure velocity and volumetric flow in the femoral vessels. Single-fiber LDF was used to measure relative microvascular perfusion at a single site in the semimembranosus muscles. Phenylephrine or dobutamine was then administered to decrease or increase femoral arterial blood flow, and changes in blood flow and microvascular perfusion were recorded.

RESULTS

Administration of phenylephrine resulted in significant decreases in femoral arterial and venous blood flows and cardiac output and significant increases in mean aortic blood pressure, systemic vascular resistance, and PCV. Administration of dobutamine resulted in significant increases in femoral arterial blood flow, mean aortic blood pressure, and PCV. Significant changes in microvascular perfusion were not detected.

CONCLUSION AND CLINICAL RELEVANCE

Results suggest that Doppler ultrasonography and single-fiber LDF can be used to study blood flows in the hind limbs of anesthetized horses. However, further studies are required to determine why changes in femoral arterial blood flows were not associated with changes in microvascular perfusion.

Hepatic venular resistance responses to norepinephrine, isoproterenol, adenosine, histamine, and ACh in rabbits

Changes in hepatic venous resistance were estimated in rabbits from the hepatic venular-inferior vena caval pressure gradient [servo-null micropipettes in 49 +/- 15 (SD) microns vessels] and the total hepatic blood flow (ultrasound probe encircling the hepatic artery and the portal vein). Changes in liver volume, and thus vascular capacitance, were estimated from measures of the liver lobe thickness. Norepinephrine (NE), isoproterenol (Iso), adenosine (Ado), histamine (Hist), or acetylcholine (ACh) was infused into the portal vein at a constant rate for 5 min. NE, Hist, and Ado increased hepatic venular pressure, but only NE and Hist significantly increased hepatic venular resistance. NE reduced the liver thickness, but Hist and Ado caused engorgement. Hepatic blood flow was increased by NE and Ado and decreased by ACh. The influence of intraportal vein infusion of Iso on the liver vasculature, at doses similar to that of NE, was insignificant. We conclude that NE acted on all the hepatic microvasculature, increasing resistance and actively decreasing vascular volume. Hist passively induced engorgement by increasing outflow resistance, whereas the liver engorgement seen with Ado was passively related to the increased blood flow. ACh constricted the portal venules but did not change the liver volume.