THE HEPATIC BLOOD FLOW AND SPLANCHNIC OXYGEN CONSUMPTION OF MAN-THEIR ESTIMATION FROM UREA PRODUCTION OR BROMSULPHALEIN EXCRETION DURING CATHETERIZATION OF THE HEPATIC VEINS

Cardiopulmonary parameters and organ blood flows for workers expressed in terms of VO2 for use in physiologically based toxicokinetic modeling

Minute ventilation rates (VE), alveolar ventilation rates (VA), cardiac outputs (Q), liver blood flow (LBF) and kidneys blood flows (KBF) for physiologically based toxicokinetic modeling and occupational health risk assessment in active workers have apparently not been determined. Minute energy expenditure rates (E) and oxygen consumption rates (VO₂) in workers during exertions and their aggregate daytime activities are obtained by using open-circuit wearable devices for indirect calorimetry measurements and the doubly labeled water method respectively. Hundreds of E (in kcal/min) and VO₂ (in L of O₂/min) were previously reported for workers. The oxygen uptake factors of 0.2059 ± 0.0019 and 0.2057 ± 0.0018 L of O₂/kcal during postprandial and fasting phases respectively enabled conversion of E into VO₂. Equations determined in this study based upon more than 25 000 published measurements enable the calculation of 15 parameters in the same worker only by using the VO₂ reflecting workload. These parameters, notably VE, VA, VE/VO₂ VA/Q, Q, LBF and KBF were found to be interrelated. Altering one of these changes the order of magnitude of the others. Q, LBF and KBF decrease when supine adults at rest switch to an upright position. This effect of gravity diminished when VO₂ increased. The fall in LBF and KBF during exertion might enhance muscle blood flow as reported previously. Taken together these equations and data may improve the accuracy of physiologically based toxicokinetic modeling as well as occupational health assessment studies in active workers exposed to xenobiotics.List of main abbreviations: AVOD: arterioveinous oxygen content difference.BMI: body mass index (in kg/m²).BSA: body surface area (in m²).BTPS: body temperature and saturated with water vapor.Bw: body weight (in kg).E: minute energy expenditure rate (in kcal/min).F_GE: organ blood flow factor for the gravitational effect on blood circulation.H: oxygen uptake factor, volume of oxygen (at STPD) consumed to produce 1 kcal of energy expended.KBF: kidneys blood flow (in ml/min).LBF: liver blood flow (in ml/min).P_BF: liver or kidneys blood flows expressed in terms of percentages (in %) of Q_{sup C} values: namely P_BF = (LBF or KBF/Q_{sup C}) x 100.Q: cardiac output (in L/min or ml/min).Q_{sup C:} cardiac output for the cohort of males or females in supination (in ml/min).STPD: standard temperature and pressure, dry air.sup: values measured when adults are in the supine position.up: values measured when adults are in the upright position.VDphys: physiological dead space at BTPS (in L).VT: tidal volume at BTPS (in L).VA: alveolar ventilation rate at BTPS (in L/min).VA/Q: ventilation-perfusion ratio (unitless).VE: minute ventilation rate at BTPS (in L/min).VO₂: oxygen consumption rate (i.e. the oxygen uptake) at STPD (in L/min).VQ: ventilatory equivalent for VO₂ (VE at BTPS /VO₂ at STPD).

Mapping hepatic blood oxygenation by quantitative BOLD (qBOLD) MRI

PURPOSE

Abnormalities in hepatic oxygen delivery and oxygen consumption may serve as a significant indicator of hepatic cellular dysfunction and may predict treatment response. However, conventional and oxygen-enhanced hepatic BOLD MRI can only provide semiquantitative assessment of hepatic oxygenation.

METHODS

A hepatic quantitative BOLD (qBOLD) model was proposed for noninvasive mapping of hepatic venous blood oxygen saturation (Y_v ) and deoxygenated blood volume (DBV) in human subjects. The validity and the estimation bias of the proposed model were evaluated by Monte Carlo simulations. Eight healthy subjects were scanned after written consent with institutional review board approval.

RESULTS

Monte Carlo simulations demonstrated that the proposed single-compartment hepatic qBOLD model leads to significant deviation of the predicted T₂ ^* decay profile from the simulated signal due to high hepatic blood volume fraction. Small relative estimation bias for hepatic Y_v and significant overestimation for hepatic DBV were observed, which can be corrected by applying the calibration curves established from simulations. After correction, the mean hepatic Y_v in human subjects was 56.8 ± 6.8%, and the mean hepatic DBV was 0.190 ± 0.035, consistent with measurements from other invasive approaches. Except in regions with significant vascular contamination, the maps for hepatic Y_v and DBV were relatively homogenous.

CONCLUSIONS

With estimation bias correction, the hepatic qBOLD approach enables noninvasive mapping of hepatic blood volume and oxygenation in human subjects. The established protocol may be used to quantitatively assess hepatic tissue hypoxia in multiple liver diseases.

Peri-operative liver graft function: monitoring using the relationship between blood glucose and oxygen consumption during anaesthesia

The purpose of our study was to test the hypothesis that the quotient between plasma glucose and whole body oxygen consumption (VO2) as a 'metabolic index' is a sensitive indicator of early graft function. Arterial levels of glucose and oxygen consumption were determined in 100 consecutive patients during orthotopic liver transplantation performed without anhepatic veno-venous bypass. Patients were divided into survivors with no obvious problems related to graft function and those with primary nonfunction of the graft. The neohepatic increase in VO2 was significantly higher in survivors (112 +/- 4 vs 88 +/- 11 ml.min-1.m-2; p < 0.05), whereas blood glucose levels after reperfusion were higher (352 +/- 18 vs. 287 +/- 36 mg dl-1) in those with primary non-function of the graft. The calculated metabolic index was also higher (4.02 +/- 0.93 vs 2.67 +/- 0.45, p < 0.05) in patients with primary nonfunction of the graft. Our principal conclusion was that 92% of normal functioning liver grafts could be classified correctly by the metabolic index immediately after reperfusion, whereas glucose levels and VO2 alone classified only 67% and 70% of normal functioning liver grafts correctly.

Reference values for resting blood flow to organs of man

The lack of a reliable quantitative description of blood flow in man has hampered the development of accurate biokinetic models of essential elements, drugs, imaging agents, and carcinogens. In this paper we review and analyse data on blood flow and identify representative percentages of cardiac output and absolute blood flow rates to organs and tissues of man for use as reference values for biokinetic models. To keep the review and analysis to a manageable size we have limited attention to the resting state and have suggested reference values for absolute and relative flow rates only for adult males and females.

Metabolic acidosis in the alcoholic: a pathophysiologic approach

The purpose of this paper is to review the acid-base abnormalities in patients presenting with metabolic acidosis due to acute ethanol ingestion and to review the theoretical constraints on ethanol metabolism in the liver. Alcohol-induced acidosis is a mixed acid-base disturbance. Metabolic acidosis is due to lactic acidosis, ketoacidosis and acetic acidosis but the degree of each varies from patient to patient. Metabolic alkalosis is frequently present due to ethanol-induced vomiting. However, it could be overlooked because of an indirect loss of sodium bicarbonate (as sodium B-hydroxybutyrate in the urine). Nevertheless, the accompanying reduction in ECF volume may play an important role in the pathogenesis of alcoholic acidosis because it could lead to a relative insulin deficiency. Treatment of alcohol acidosis should include sodium, chloride, potassium, phosphorus, magnesium and thiamine replacements along with attention to concomitant clinical problems. Unless hypoglycemia is present, glucose need not be given immediately. We feel that insulin should be withheld unless life-threatening acidemia is present or expected. Lastly, alcohol need not be detected on admission to make the diagnosis of this metabolic disturbance. However, when present, it could contribute directly to the lactic, acetic and B-hydroxybutyric acidoses. With respect to the theoretical constraints on ethanol metabolism, it appears that "overproduction" of NADH in the liver is best averted by converting ethanol to B-hydroxybutyric acid.

Hemodynamic patterns in human hepatic cirrhosis: a prospective randomized study of the hemodynamic sequelae of distal splenorenal (Warren) and mesocaval shunts

Increasingly successful operative management of gastroesophageal variceal hemorrhage has been achieved by newer techniques of portal venous reconstruction. Although it is postulated that the clinical success may be due to more selectivity in portal venous shunting, direct determination of the effect of portasystemic shunt on portal vein blood flow has not been possible. Direct determinations of portal vein blood flow were performed preoperative on unanesthetized, hemodynamically stable cirrhotic patients by observation of radiopaque water-insoluble droplets. Patients were then randomized into elective distal splenorenal (Warren) or mesocaval shunt and determinations were performed postoperatively under similar conditions when clinically possible. Although portal vein blood flow was not significantly different before (929 +/- 147 ml/min) or after 899 +/- 271 ml/min) distal splenorenal shunt, there was a large change in portal vein blood flow after mesocaval shunt, decreasing from 772 +/- 177 ml/min (hepatopetal) to -1021 +/- 310 ml/min (hepatofugal) p < 0.01). After either procedure total hepatic blood flow (as determined by cardiac green clearance) was not significantly changed, nor was renal blood flow; however, cardiac output was significantly increased after mesocaval shunt. Thus the theoretical hemodynamic goals of the selective distal splenorenal shunt, i.e., preservation of the hepatopetal flow within the portal vein, is achieved as determined in the early postoperative period. The correlation between these changes and the eventual clinical outcome remains to be determined.

Splanchnic oxygen uptake in relation to systemic oxygen uptake during postoperative splanchnic blockade and postoperative fentanyl analgesia

In 34 patients with gallbladder disease, but otherwise healthy, the systemic and splanchnic oxygen uptake were studied in connection with cholecystectomy. Postoperatively, 22 patients were given a posterior splanchnic blockade with 0.5% plain lidocaine, and 12 were given fentanyl intramuscularly in a dose of 3.5 mug/kg b.w. Postoperatively, before the analgesic agent was administered, both the systemic and splanchnic oxygen uptake were increased by 40--50%, the splanchnic fraction of the systemic oxygen uptake being the same as preoperatively. Following administration of fentanyl, as well as after splanchnic blockade, the systemic oxygen uptake decreased almost to the preoperative level. The splanchnic oxygen uptake, however, did not change after fentanyl administration but increased further significantly following splanchnic blockade. The splanchnic fraction of the systemic oxygen uptake increased rapidly after the blockade, while it increased slowly after fentanyl administration.

Stimulation of paraventricular neurosecretory cells by oxytocin applied iontophoretically

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Splanchnic metabolism of free fatty acids and production of triglycerides of very low density lipoproteins in normotriglyceridemic and hypertriglyceridemic humans

Transport of free fatty acids from the blood into the splanchnic region and their conversion to triglycerides of very low density lipoproteins, together with estimates of splanchnic oxidation of free fatty acids to ketones and to carbon dioxide and water, have been made in the postabsorptive state in seven normolipemic subjects, six with primary endogenous hyperlipemia and one each with primary dysbetalipoproteinemia and mixed hyperlipemia. Net systemic transport of free fatty acids into the blood was the same in normolipemic and hyperlipemic groups, but a greater fraction was taken up in the splanchnic region in the latter. Transport into the blood in very low density lipoproteins of triglyceride fatty acids derived from free fatty acids was proportional and bore the same relationship to splanchnic uptake of free fatty acids in the two groups. In normolipemic subjects, near equilibration of specific activities after 4 hr infusion of palmitate-1-(14)C showed that almost all triglyceride fatty acids of very low density lipoproteins and acetoacetate were derived from free fatty acids taken up in the splanchnic region. In the hyperlipemic subjects, equilibration of free fatty acidcarbon with acetoacetate was almost complete, but not with triglyceride fatty acids, owing at least in part to increased pool size. Comparison of the rate of equilibration of triglyceride fatty acids-(14)C with rate of inflow transport from the splanchnic region, together with other data, indicated that most of the circulating triglyceride fatty acids of very low density lipoproteins in hyperlipemic subjects were also derived from free fatty acids. Although mean inflow transport of triglyceride fatty acids was greater in the hyperlipemic subjects, it correlated poorly with their concentration and it appeared that efficiency of mechanisms for extrahepatic removal must be a major determinant of the concentration of triglycerides in blood plasma of the normolipemic as well as the hyperlipemic subjects. Estimates of splanchnic respiratory quotient supported the concept that oxidation of free fatty acids accounts for almost all of splanchnic oxygen consumption in the postabsorptive state. Splanchnic oxygen consumption was greater in the hyperlipemics, but fractional oxidation of free fatty acids to ketones was higher in normolipemic subjects. Calculations of splanchnic balance indicate that a larger fraction of free fatty acids was stored in lipids of splanchnic tissues in the hyperlipemics. No differences were found between the two groups in net splanchnic transport of glucose, lactate, or glycerol.

Occlusive hepatic venous catheterization in the study of the normal liver, cirrhosis of the liver and noncirrhotic portal hypertension

The technic of occlusive venous catheterization has been applied to the liver. The pressure, measured in a small occluded hepatic vein and termed the wedged hepatic venous pressure, correlates well with the portal venous pressure in cats. An elevation of the wedged pressure in man, in the presence of a normal central venous pressure, is diagnostic of cirrhosis. This has proved to be of clinical value in the differentiation of intrahepatic from extrahepatic portal hypertension. The higher wedged hepatic venous pressures in cirrhosis are correlated with the presence of varices or jaundice, but not with the presence of ascites.

The hepatic blood flow and splanchnic oxygen consumption in alcoholic fatty liver

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The measurement of liver circulation by means of the colloid disappearance rate. I. Liver blood flow in normal young men

A method for calculating the liver blood flow by means of the rate of disappearance of colloidal chromic phosphate from the blood has been reviewed. This method has been applied to the study of liver circulation in a group of 29 fasting normal men. The significance of the colloid disappearance rate constant as a physiologic expression of the liver blood flow has been discussed and the average value obtained for this constant in normal young men was 0.287 ± 0.007 min.–1 Extra hepatic colloid localization, hepatic efficiency for colloid removal, speed of mixing, and type and time of sampling have been discussed.

Studies of hemodynamic changes in humans following induction of low and high spinal anesthesia. II. The changes in splanchnic blood flow, oxygen extraction and consumption, and splanchnic vascular resistance in humans not undergoing surgery

Low and high spinal anesthesia were administered to a group of 10 waking patients without the use of vasopressor drugs. Preliminary evidence does not support the view that the induced hypotension is accompanied by significant splanchnic vasoconstriction or by homeostatic diversion of blood from the splanchnic bed to maintain the circulation in "more vital" areas.