Arteriovenous Shunt Flow Research Articles

Blood flow and perfusion in acute haemorrhagic pancreatitis in the dog.

Experimental evidence suggests that in acute haemorrhagic pancreatitis in the dog the percentage of the cardiac output distributed to the pancreas falls. Histological evidence indicates arteriovenous shunt flow, but this has not been confirmed by flow measurements. It has recently been reported that in experimental preparations in which pancreatic blood flow is measured through the superior pancreaticoduodenal artery after ligation of other (accessory) vessels, perfusion is reduced in distal regions of the gland. There are no data regarding regional perfusion measurements in acute pancreatitis or the effect of ligating accessory vessels. This study therefore evaluates blood flow and regional perfusion in haemorrhagic pancreatitis in various preparations of the canine pancreas. Perfusion was assessed by measuring the clearance of Krypton-85 after injection into the arterial blood supply of the pancreas. Arterial blood flow was measured by the electromagnetic flow technique. The results show that perfusion in different regions of the gland is similar both before and during disease. If accessory vessels are ligated, however, only perfusion in the head of the gland is maintained. No arteriovenous shunt flow was shown. The percentage of the cardiac output being distributed to the gland did not change in any of the experiments; this contradiction to previous reports may arise from the effective control of acid base balance in this study.

Efficacy of Pharmacologic Glucagon in Acute Experimental Pancreatitis

Microcirculatory derangements in the pancreas associated with acute pancreatitis may contribute to a low-flow state and lead to pancreatic necrosis. This study investigated the effects of glucagon, a selective mesenteric arterial dilator, on pancreatic ischemia in canine bile-trypsin-induced pancreatitis (BTP). Measurements of cardiac Index (CI), total pancreatic blood flow (QP), pancreatic oxygen consumption (O2CP), and pancreatic arteriovenous shunt flow (QAVS) were obtained prior to and after inducing BTP. Bile-trypsin-induced pancreatitis was induced in 18 dogs. Nine received lactated Ringer's solution alone (LRPAN) at 6.5 mL/kg/hr, nine received lactated Ringer's solution plus continuous Intravenous (IV) glucagon hydrochloride (GLUPAN) at 1.0 micrograms/kg/min, and nine undergoing periportal dissection without BTP received IV glucagon (GLUCON). Following BTP, CI, QP, and O2CP decreased significantly and QAVS remained unchanged in crystalloid-treated animals (LRPAN). Glucagon administration (GLUPAN) transiently increased CI and QP but failed to improve O2CP and did not change QAVS. The decrease in O2CP observed after BTP in association with a constant QAVS suggests a metabolic block to oxygen uptake at the cellular level. Glucagon in pharmacologic doses does not reverse abnormalities in O2CP and is therefore of questionable physiologic benefit in the treatment of acute pancreatitis.

Dazoxiben, a thromboxane synthetase inhibitor, in Raynaud's phenomenon.

Dazoxiben, a specific thromboxane synthetase inhibitor, was evaluated in 21 patients with Raynaud's phenomenon in a double-blind, placebo-controlled crossover experiment. Total fingertip blood flows were measured by plethysmography and capillary blood flows were measured by 133Xe disappearance rate. Subjects were studied in both a warm (28 degrees) and a cold (20 degrees) room. Arteriovenous (AV) shunt flow was estimated by subtraction of capillary flow from total flow. Ex vivo production of thromboxane B2 (TXB2) and 6-keto PGF1 alpha was determined by specific radioimmunoassay in serum from venous blood incubated for 1 hr (37 degrees). Plasma concentrations of TXB2 and 6-keto PGF1 alpha were also monitored. Dazoxiben (100 mg 4 times a day for 14 days) inhibited ex vivo TXB2 production (from 463.1 +/- 69.9 to 101.8 +/- 13.4 ng/ml/hr; (means +/- SE], enhanced ex vivo 6-keto PGF1 alpha production (from 1.38 +/- 0.05 to 3.76 +/- 0.18 ng/ml/hr), reduced plasma TXB2 concentration (from 88.1 +/- 13.9 to 38.8 +/- 5.9 pg/ml). There were no changes in plasma concentration of 6-keto PGF1 alpha. Dazoxiben did not improve total digital blood flow, capillary flow, AV shunt flow, or forearm blood flow at 28 degrees or 20 degrees. There was no subjective improvement in frequency or severity of Raynaud's attacks (assessed by patient diaries). It is concluded that dazoxiben is a potent and specific thromboxane synthetase inhibitor capable of altering arachidonic acid metabolism, but is of little or no benefit in the treatment of Raynaud's phenomenon.

The calcium antagonists PY 108–068 and verapamil diminish the effects of angiotensin II: sites of interaction in the peripheral circulation of anaesthetized cats

The sites of interaction between the vasoconstrictor angiotensin II (A II) and the calcium antagonists PY 108-068 (PY) (a dihydropyridine derivative) or verapamil (V) in different peripheral vascular beds were investigated using the microsphere method in chloralose-urethane anaesthetized open-chested cats. A II was infused intravenously into 27 cats at a rate of 0.15 microgram kg-1 min-1. Systemic haemodynamic variables and regional blood flow were measured immediately before and 10 min after the start of the infusion. While the infusion of A II continued, PY (3 micrograms kg-1 min-1), V (30 micrograms kg-1 min-1) or the vehicle was infused for 10 min into 9 cats each and the effects of this combined infusion were again measured at the end of the 10 min period. A II increased mean arterial blood pressure but decreased peripheral conductance and, to a smaller but still significant degree, cardiac output and peak acceleration of blood in the aorta (an ejection phase parameter of myocardial contractility). The calcium antagonists reversed these effects. Cardiac output and total peripheral conductance were increased even beyond the pre-A II level by PY. A II constricted the vascular beds of the kidney, small intestine, liver and skin. Arterio-venous shunt flow decreased. Vasoconstriction was also found in the stomach, spleen and in different parts of the heart with the exception of the subendocardial layer of the left ventricle, where blood flow increased and conductance remained unchanged. A II did not decrease conductance in different parts of the brain or in skeletal muscle. The vasoconstrictor effects of A II persisted or tended to be increased in most of the vascular beds of placebo treated animals. PY 108-068 and verapamil abolished the vasoconstrictor effects of A II in most of the vascular beds with the exception of the liver, the spleen, the skin and the arterio-venous shunts and caused vasodilatation in the heart. PY also induced vasodilatation in the brain and skeletal muscle, where A II had not induced vasoconstriction. The pattern of attenuation of A II effects was different from the pattern of vasodilatation induced by these and other calcium antagonists in the same cat preparation not treated with a vasoconstrictor. The sites of action of this dihydropyridine derivative (PY) on the peripheral circulation thus, appear to depend not only on the vascular bed but also on the presence of a vasoconstrictor influence at the time of investigation.

Low molecular weight dextran in experimental pancreatitis: Effects on pancreatic microcirculation

Although low molecular weight (LMW) dextran has been said to decrease the lethality of experimental acute pancreatitis (AP) by reversing stasis in the pancreatic microcirculation, the actual mechanism(s) of action is unknown. This investigation was designed to measure the effects of low molecular weight dextran on pancreatic capillary flow ( Q CAP) and arteriovenous shunt flow ( Q AVS), and on pancreatic oxygen consumption (O 2 C P) following bile-trypsin-induced AP in dogs. Total pancreatic blood flow ( Q T) was measured with an electromagnetic flow probe on the superior pancreaticoduodenal artery (SPDA). Q AVS was measured by liver trapping of 99mTc-albumin microspheres after SPDA injection. Q CAP was calculated as Q T minus Q AVS. Seventeen dogs were treated with lactated Ringer's (LR) solution at 6.5 ml/kg/hr; 10 dogs were treated with LMW dextran 10% in normal saline at 1.5 ml/kg/hr plus LR at 5.0 ml/kg/hr. Mean arterial and central venous pressures remained constant throughout the 4-hr experiment. In the dogs receiving LR only, Q T decreased from 42.7 to 24.4 ml/min ( P < 0.001); Q AVS remained constant at 1.35 ± 0.04 ml/min. During the first 30 min O 2 C P decreased from 1.17 to 0.76 ml O 2/min ( P < 0.05) and remained constant thereafter. LMW dextran treatment altered none of these hemodynamic or metabolic parameters significantly. Conclusions: bile trypsin AP in the dog causes significant decreases in Q T and Q CAP without altering Q AVS. The decrease in O 2 C P in association with a constant Q AVS suggests a metabolic block to oxygen uptake at the cellular level. Continuous infusion of LMW dextran at a dose of 1.5 ml/kg/hr in the dog does not reverse these abnormalities.

Temperature effects on dog hindpaw series and parallel vascular circuits.

The effect of environmental temperature (skin surface) on distribution of blood flow between the parallel vascular circuits has been assessed in vascularly and neurally isolated hindpaws perfused at constant pressure. The paw was sealed in a chamber filled with water at 10, 20, 30, or 40 degrees C. Peripheral resistance increased as the temperature decreased in both innervated and denervated paws. Resistance in the denervated paws was less than in the innervated paws at all temperatures. Recovery of 85Sr microspheres was less at 40 degrees C than at 10, 20, or 30 degrees C in the denervated paws but did not change in innervated paws. Capillary availability (diffusion capacity and filtration coefficient) increased with each elevation in temperature in both groups. At 10 degrees C both arteriovenous (AV) shunt and capillary flows were low in innervated paws with low capillary and high shunt flow in denervated paws. At 20 and 30 degrees C capillary flow increased with temperature and arteriovenous anastomosis (AVA) flow was unchanged in denervated paws. In innervated paws AV shunt flow fraction slightly increased, with capillary perfusion markedly increased as temperature was elevated. The increased capillary flow in both groups passed through an enlarged capillary bed, whereas the number and/or diameter of AVAs remained essentially unchanged.

Measurement of cerebral blood flow in the pig by the Xe-133 clearance technique. Failure of the two-compartmental clearance model.

The Xe-133 clearance technique is used to measure cerebral blood flow in the pig, which often serves as an experimental animal for cardiovascular research. The clearance curves are fitted by a two-exponential model. However, the fitted parameters are incompatible with a two-compartmental model: the values found for the parameters depend on the length of the clearance curve analysed. The discrepancies are thought to be consequences of the heterogeneity of cerebral blood flow and of mathematical problems of parameter identification. The non-validity of the relative weight of the fast clearance component as an anatomical or functional parameter is demonstrated. The use of the mean time constant, mean transit time, mean decay constant and initial slope for determination of cerebral blood flow rates is discussed. The mean cerebral blood flow of the anaesthetized pig measured by the clearance technique is found to be lower than the blood flow measured by means of a flow probe around the common carotid artery (with the external carotid artery tied off). The existence of a significant arteriovenous shunt flow is postulated.

MIC-II — A program for the determination of cardiac output, arterio-venous shunt and regional blood flow using the radioactive microsphere method

MIC-II is a versatile BASIC computer program designed to calculate the cardiac output, the arterio-venous shunt and the regional blood flow from data obtained by the radioactive microsphere method. The samples are measured in a gammaspectrometer with a multichannel pulse height analyzer and the data are recorded on tape. Up to 10 different nuclides may be used simultaneously, including tracers which are not bound to microspheres. The nuclides may have overlapping energy spectra. The analysis of the energy spectra is performed according to the matrix method. Standard samples, each containing one pure nuclide, are measured to obtain the overlap matrix. The unknown amounts of the nuclides in the samples are obtained by solving a system of simultaneous linear equations. Up to 100 organ samples may be taken in one experiment. Up to 10 different organ maps, containing a text label for each organ specimen, may be created, edited, modified and stored on tape for convenient identification of input and output. Numerous validity checks for input and output make MIC-II easy to use, even for non-computer trained personel.

Effect of pulmonary microembolism on arteriovenous shunt flow

The effects of acute pulmonary hypertension on the fraction of cardiac output shunted through pulmonary arteriovenous communications have been studied in dogs as a possible cause of hypoxia following pulmonary embolization. Pulmonary artery pressure was increased twofold and then fourfold above control values by embolization of the pulmonary vascular bed with polystyrene microspheres. Quantitative measurements of arteriovenous shunt were determined from the fraction of 50 mu radioactively labeled microspheres injected into the inferior vena cava which passed through the pulmonary circulation into systemic vascular beds. There was no increase in the fraction of pulmonary blood flow passing through pulmonary arteriovenous connections, 50 mu in diameter or greater, with pulmonary microembolism when FIo2 was 1. There was a small increase in arteriovenous shunt fraction when pulmonary artery pressure was increased with an FIo2 of 0.21. Physiological shunt measured by the oxygen technique did not increase with pulmonary embolism, but total venous admixture rose significantly. Postmortem gravimetric measurements of lung water indicated pulmonary edema. We conclude that anatomic arteriovenous shunt channels have little physiological significance after pulmonary microembolism in the dog lung. The major cause of hypoxia immediately after pulmonary microembolism is ventilation/perfusion imbalance, probably caused by pulmonary edema.

A simple method to measure mesenteric arteriovenous shunt flow during arteriography.

A quantitative method for external detection of mesenteric arteriovenous shunts was developed. 99mTc-Human Serum Albumin Microspheres (15--30 microns) were injected into the superior mesenteric artery of dogs through an angiographic catheter, followed by external scintillation counting of the liver activity, which represented the shunted spheres. Thereafter, 99mTc-sulfur colloid was injected identically and the liver activity counted again. The liver net count after sulfur colloid represented a 100% shunt, when a correction factor for the actual liver uptake was applied. The a shunt rate was calculated. Eleven animal studies were performed and shunt rates similar to previous in vitro determinations were obtained. This method is suitable for clinical investigation and can conveniently be applied to mesenteric arteriography.

Total and nutritional blood flow in the finger.

1. Total and nutritional flow in the fingertip were investigated during reflex sympathetic nerve stimulation (total body cooling) or adrenergic nerve transmitter administration. Nutritional flow was measured by the disappearance rate of a local depot of Na131 I, and total fingertip flow by venous occlusion plethysmography. 2. With body cooling the decrease in nutritional flow was not significant, but total and therefore arteriovenous shunt flow decreased significantly. 3. Norepinephrine infused into the brachial artery decreased total and nutritional flow significantly although total flow decreased more than nutritional. 4. It is concluded that sympathetic nervous system activity exerts a greater effect on finger arteriovenous shunt flow than on nutritional flow. Therefore nutritional flow is not adversely affected.

Total and capillary fingertip blood flow in Raynaud's phenomenon.

Abstract Total (plethysmography) and capillary (radioisotope disappearance rate) fingertip flows were measured in 24 patients with Raynaud's phenomenon and compared to 10 normal subjects in a warm room and during reflex sympathetic nerve stimulation by body cooling. Arteriovenous shunt flow was estimated by subtraction of capillary from total flow. Patients with Raynaud's phenomenon had a significantly smaller capillary flow in both warm (6.4 vs. 10 ml per 100 g per minute) and cool (4.0 vs. 7.0 ml) rooms than normal subjects. With body cooling, total and arteriovenous shunt flow, but not capillary flow, decreased significantly in normal controls, whereas all three decreased in Raynaud's phenomenon. During oral reserpine treatment, 11 patients with Raynaud's phenomenon showed a significantly larger capillary flow during warming (8.7 vs. 5.7 ml) and cooling (6.2 vs. 2.8 ml). Patients with Raynaud's phenomenon have a smaller finger nutritional (capillary) flow than normal subjects, and this flow decreases s...

Control of arteriovenous shunt flow

Control of arteriovenous shunt flow

Measure- ment of distribution of cardiac output.

Measure- ment of distribution of cardiac output.

Use of radioactive microspheres to assess distribution of cardiac output in rabbits.

Use of radioactive microspheres to assess distribution of cardiac output in rabbits.