Aorta Of Dogs Research Articles

Effects of bunitrolol on adrenergic and serotonergic receptors.

To assess the importance of anti-adrenergic and anti-serotonergic activities of bunitrolol for its efficacy as an antihypertensive and antianginal agent, effects of this substance on the binding of adrenergic and serotonergic agents to the respective receptors of the rat brain, rat heart, dog brain, and/or dog aorta were examined using the radioligand binding assay methods. In addition, the pA2 values of bunitrolol as an antagonist against the positive chronotropic and inotropic actions (beta 1-adrenoceptor) of isoproterenol were also determined by pharmacological methods using the isolated guinea pig atria. To assess the specificity, pA2 values were also obtained in the isolated trachea (beta 2-adrenoceptor) using isoproterenol as an agonist and in the isolated aorta from the guinea pig and the rat using phenylephrine as an agonist (alpha 1-adrenoceptor). A strong inhibition by bunitrolol of 3H-dihydroalprenolol (3H-DHA) binding to beta-adrenoceptors was observed, while the inhibition of 3H-prazosin binding to alpha 1-adrenoceptors, 3H-serotonin binding to 5HT1-receptors. 3H-p-aminoclonidine binding to alpha 2-adrenoceptors, and 3H-ketanserin binding to 5HT2-receptors were found to be very weak. The rank order of antagonistic potencies of bunitrolol against the adrenergic receptors as assessed with pA2 values were beta 1 greater than beta 2 much greater than alpha 1. From these two different types of experiments, it is clear that the antihypertensive and antianginal effects of bunitrolol are mainly due to its beta-blocking actions, with the alpha 1-blocking action of this drug playing a minor role.

How much does aortic and pulmonary artery area vary during the cardiac cycle?

Cardiac output (CO), as measured by Doppler, is computed by multiplying vessel area by mean velocity. One unresolved problem is the magnitude of vessel area change during the cardiac cycle. Prior estimates have ranged from 2% to 30% area change during the cardiac cycle. The purpose of this study was to measure cyclic dimensional changes in the aorta and pulmonary artery of dogs by a very sensitive technique, mercury strain gauge plethysmography. Gauges were fixed around the pulmonary artery and the aorta and changes in vessel circumference were recorded under the following conditions: increased preload, increased afterload, decreased preload, and during administration of dobutamine, 5 and 10 μg/kg/min. Percent change in circumference of the aorta at baseline was small (mean circumference change = 4%, SD = 1%, SEE = 0.5). Percent change in the pulmonary artery at baseline was slightly larger (mean circumference change = 6%, SD = 5%, SEE = 2%). Mean aortic area change was 9% (SD = 2%) and for the pulmonary artery it was 12% (SD = 10%). No experimental manipulation significantly altered the percent cyclic change in vessel size from baseline except for clamping the inferior vena cava, in which mean percent change in aortic circumference decreased to 1% (SD = 1%, SEE = 5%) ( p < 0.05). Percent change in the aorta correlated only weakly with heart rate ( r = 0.48), blood pressure ( r = 0.4), and CO ( r = 0.46). Similar values were obtained for the pulmonary artery. These data demonstrate a small but definite cyclic change in pulmonary artery area, and to a lesser extent in aortic area.

金網型‐高有孔性‐リング付無縫合人工血管の末梢動脈血行再建への応用に関する実験的研究

金網型‐高有孔性‐リング付無縫合人工血管の末梢動脈血行再建への応用に関する実験的研究

Microporous hydrophilic polyurethane vascular grafts as substitutes in the abdominal aorta of dogs

Polyurethanes are emerging as promising biomaterials. A microporous vascular graft fabricated from Mitrathane®, a new polyetherurethane urea, appeared to be particularly interesting according to in vitro evaluation and was tested in vivo as an infrarenal aortic substitute (i.d. 5 mm) in 24 dogs. After implantation for scheduled periods ranging from 4 h to 6 mnth, morphology evaluation and healing analysis of the grafts were performed. At harvesting, 18 grafts were patent and 6 were thrombosed. The thrombosed grafts had been implanted for 4 h (1 graft), 1 mnth (2 grafts) and 6 mnth (3 grafts). No macroscopic deposits other than red mural thrombi were observed. At 1 mnth complete external encapsulation was observed in 2 grafts. The capsule then contracted and became thinner; over the long term it shrank, became translucent and incomplete at 6 mnth. Yellow and brown stains appeared on many of the grafts. Characterization of the brown stains showed them to be iron (Fe 3+) and the yellow stains were associated with the deposition of a bile pigment (bilirubin).

Thermographic study of laser on arteries.

We analyzed the different effects of CO2, Nd-YAG, and argon lasers on aorta by using a Thermovision infrared system that registered the laser interaction with mongrel dog aorta. The images (thermograms) obtained were processed by a computer, which associated each area of the same temperature with a determined color. These thermograms were compared to histological analysis of the respective samples and the following results were obtained: (1) After the application of each laser there is very little propagation of heat in tissue. (2) The CO2 laser makes tissue reach 100 degrees C in less than 0.05 seconds. (3) The heat dissipation time was higher with the Nd-YAG laser due to higher scattering on tissue. Based on this research we conclude that the CO2 laser was best absorbed, the Nd-YAG laser penetrated human tissue with the best results, and the argon laser had the most significant backscattering.

Modulation of guanylate cyclase by lipoxygenase inhibitors.

Drugs that inhibit endothelium-dependent relaxation were tested to determine their effect on soluble guanylate cyclase purified from dog aorta. Basal, arachidonic acid (10(-5) M)-stimulated, and nitroprusside (5 X 10(-5) M)-stimulated guanylate cyclase activities were inhibited by methylene blue and the lipoxygenase inhibitors nordihydroguaiaretic acid and eicosatetraynoic acid. The effective inhibitory doses were in the range of those that have been reported to inhibit endothelium-dependent relaxation. Other compounds known to inhibit endothelium-dependent relaxation had little or no effect on guanylate cyclase activity. Basal guanylate cyclase activity was more resistant to inhibition than were activated states of the enzyme. The data suggest that reported inhibition of endothelium-dependent relaxation by some lipoxygenase inhibitors may be the result, at least in part, of their direct effect on guanylate cyclase activity.

Poststenotic flow disturbance in the dog aorta as measured with pulsed Doppler ultrasound.

Blood flow velocity was measured in the dog aorta distal to mechanically induced constrictions of various degrees of severity employing an 8-MHz pulsed Doppler ultrasound velocimeter and a phase-lock loop frequency tracking method for extracting velocity from the Doppler quadrature signals. The data were analyzed to construct ensemble average velocity waveforms and random velocity disturbances. In any individual animal the effect of increasing the degree of stenosis beyond approximately 25 percent area reduction was to produce increasing levels of random velocity disturbance. However, variability among animals was such that the sensitivity of random behavior to the degree of stenosis was degraded to the point that it appears difficult to employ Doppler ultrasound measurements of random disturbances to discriminate among stenoses with area reductions less than approximately 75 percent. On the other hand, coherent vortex structures in velocity waveforms consistently occurred distal to mild constrictions (25-50 percent area reduction). Comparison of the phase-lock loop Doppler ultrasound data with simultaneous measurements using invasive hot-film anemometry, which possesses excellent frequency response, demonstrates that the ultrasound method can reliably detect those flow phenomena in such cases. Thus, the identification of coherent, rather than random, flow disturbances may offer improved diagnostic capability for noninvasively detecting arteriosclerotic plaques at relatively early stages of development.

An experimental study of eight current arterial prostheses

Eight currently used arterial prostheses with differing constructions and materials were implanted in the descending thoracic aorta of mongrel dogs. The prostheses were Gore-Tex (polytetrafluoroethylene), DeBakey Woven, Cooley Woven, Meadox Woven Double Velour, Cooley Knitted Double Velour, Microvel, Vasculour II, and Bionit II. Five series of these eight prostheses were serially implanted in heparinized subjects. During the 40 implantations, attention was focused on three major characteristics: preclotting efficiency, surgical handling characteristics, and healing. Gore-Tex is impervious to blood. The DeBakey and Cooley woven grafts are nearly so. The remaining prostheses required preclotting. The Meadox Woven Double Velour became impervious after two preclotting steps, the Cooley Knitted Double Velour and the Bionit II required three, and the Vasculour II and the Microvel required four. The surgical handling characteristics of the knitted prostheses clearly surpassed those of the DeBakey and Cooley woven and Gore-Tex prostheses. Although the Meadox Woven Double Velour prosthesis had better conformability than the nonveloured woven, the tendency of its cut edge to fray was more pronounced. Healing was much more advanced in the knitted and woven prostheses than in the Gore-Tex.

The analysis of blood velocity measurements by autoregressive modelling

Analysis of velocity disturbances arising in poststenotic flow is examined using the technique of autoregressive modeling. The essential elements of this method are described including relevant criteria for selecting the model order. Velocity data employed in the analysis are taken from in vivo measurements in the dog aorta, and the results indicate that the autoregressive method improves the resolution of coherent features in disturbed flow patterns. By applying homomorphic filtering to individual beats, the occurrence of organized structures convected from their origin in the shear layer is readily identified.

Evidence for the presence of phospholamban in the endoplasmic reticulum of smooth muscle

In microsomal vesicles isolated from several smooth muscles many polypeptides were phosphorylated by the catalytic subunit of cyclic AMP-dependent protein kinase. In pig stomach and in rabbit and dog aorta components of M r 22 000 and 11 000 were identified as forms of phospholamban. These polypeptides were, however, not observed in pig aorta. These phospholamban-like polypeptides presented the same electrophoretic mobility in sodium dodecyl sulphate gels as cardiac phospholamban, and the 22 000 M r form showed a similar reaction to heat treatment in sodium dodecyl sulphate. Antibodies against purified canine cardiac phospholamban cross-reacted with the 22 000 and 11 000 M r phosphorylatable polypeptides from smooth muscle membranes. Subcellular fractionation of porcine stomach smooth muslce indicated that phospholamban was present in the membranes of the endoplasmic reticulum and not in the plasma membranes. Phospholamban was also phosphorylated by an endogenous calcium—calmodulin-dependent protein kinase and by an endogenous cyclic AMP-dependent kinase. It is concluded that the endoplasmic reticulum of many, but possibly not all, smooth muscles contains phospholamban. However, the physiological role of phospholamban in smooth muscle remains to be established.

Ultrasonic flowmeter with implantable miniature sensors.

An ultrasonic flowmeter incorporated with implantable miniature sensors was developed. Two sets of miniature ultrasonic sensors are attached to the surface of a blood vessel. The outer diameter of the vessel and the blood velocity are measured simultaneously by means of the ultrasonic transit-time technique and the ultrasonic Doppler method, respectively. Instantaneous blood flow is calculated by multiplying the flow velocity by the cross-sectional area calculated from the diameter Stroke volume and cardiac output can also be obtained, when the system is applied to the ascending aorta. After preliminary benchtop tests, acutein vivo studies were carried out to evaluate the accuracy and performance of the system. The blood flow in the descending aortas of dogs and a goat were measured simultaneously by the ultrasonic system and an electromagnetic flowmeter. The correlation coefficient between the data obtained by the two methods was 0·968. The system was applied to measure the blood flow in the ascending aortas of goats which had had heart failures induced and were implanted with left ventricular assist devices.

The Influence of Denier and Porosity on Performance of a Warp-knit Dacronβ Arterial Prosthesis

The study objective was to determine the optimal water porosity for a warp-knit, externally veloured Dacron arterial prosthesis. Preclotting efficiency, surgical handling characteristics, thrombogenicity, and 56-day healing in the descending thoracic aorta of mongrel dogs were measured for seven different arterial prostheses of the same basic design constructed to test the influence of decreased porosity produced by increased yarn denier at a constant needle density. The six prototypes tested were 160, 180, 200, 220, 240, and 280 denier. The 140 denier prosthesis (Bionit, C. R. Bard, Inc., Billerica, MA) served as the control. The water porosity of these prostheses varied from 2036 ml/cm2/min at 120 mmHg for the control to 286 for the 280 prototype. The preclotting efficiency increased with decreased water porosity and with increased outer-wall filamentousness. Desirability of surgical handling characteristics decreased with lowered water porosity, while the degree of outer-wall filamentousness had little influence. All the prostheses showed excellent through-wall healing at 56 days, including endothelialization. The 160 prototype represented an optimal blend of high preclotting efficiency, desirable surgical handling characteristics, and excellent 56-day healing. These studies are pertinent to the future development of porous, warp-knit Dacron arterial prostheses.

Correlation of endothelial cell shape and wall shear stress in a stenosed dog aorta.

The pattern of endothelial geometry at various locations along stenosed dog aortas was examined. This was done to test the hypotheses that the shape of an endothelial cell is related to the local wall shear stress associated with the flowing blood and that alterations in hemodynamics, produced by vascular geometrical changes, influence endothelial cell geometry. Aortic stenosis with a reduction of 71% of the cross-sectional area was produced. The animals were sacrificed 12 weeks later, and the endothelial cell geometry and orientation were studied using the vascular casting technique and a computerized analysis to determine cell area and shape index. The regions of the stenosis examined were those known to experience different hemodynamic conditions. The value of the shape index was found to fall rapidly in the convergent region of the stenosis and to increase suddenly in the divergent region, eventually returning to the prestenotic value at a more distal site. Using a model of a stenosis made from a vascular cast, laser Doppler anemometry was applied to measure velocity profiles and to estimate the local wall shear stress in a stenosed aorta. It is shown that the shape index distribution along these stenosed vessels may be correlated with the level of wall shear stress, with more elongated cells occurring in regions of higher shear stress.

Replacement of dog's aorta by autologous intestinal muscle in the infected retroperitoneum.

The free transplant of intestinal muscle lacking mucosa into an infected vascular bed has been shown to be a suitable replacement for the aorta in dogs. This type of transplant is incorporated into the infected area and shows a high tolerance against progressive infection. Therefore, an autologous transplant may be suitable to ensure continuous blood flow during the healing phase of a deep infection when a synthetic prosthesis is unsuccessful.

Doppler measurement of the pressure drop caused by arterial stenosis: an experimental study: a case report.

A stenotic arterial lesion which reduces the cross-sectional area of the artery causes an increased velocity and, as a consequence, a loss in kinetic energy and a pressure drop. A simplified formula, derived from the Bernoulli principle, relates the pressure drop to the maximum velocity of the blood flow in the stenotic segment: delta P (mmHg) = 4 Vmax2 (m/sec). This formula has been validated for stenosis of cardiac valves. Aim of our study was to test the hypothesis that this formula applies in the major arteries using Doppler ultrasound with spectrum analysis. In our experiments we created artificial graded stenoses of varied geometry in the thoracic aorta of dogs. Invasive pressure measurements were obtained using intra-arterial needles on both sides of the stenosis. A Doppler signal was obtained with a 2.5 MHz CW probe, insonating the stenotic area from a distance, with an almost parallel approach. In these conditions the maximum Doppler frequency shift is an accurate estimate of the maximum flow velocity, according to the Doppler equation. We compared the Doppler derived (delta P = 0.36 Fmax2) and the invasive measurements of pressure drops. Our results show a highly significant correlation between the intra-arterial and the Doppler measurements of the pressure drops caused by arterial stenoses and encourage efforts in applying similar techniques in the noninvasive evaluation of vascular patients.

Subcellular origin of the oxalate- or inorganic phosphate-stimulated Ca 2+ transport by smooth muscle microsomes: revisitation of the old problem by a new approach using saponin

Saponin, a cell-skinning reagent which perforates the cell membrane via its specific interaction with plasmalemmal cholesterol, was used to identify the subcellular origin of ATP-dependent Ca 2+ accumulation in the presence and absence of inorganic phosphate and oxalate by microsomal fractions isolated from rat vas deferens and dog aorta. The purified plasma membranes from rat gastric fundus muscle, which elicit the stimulation of ATP-dependent Ca 2+ accumulation by inorganic phosphate but not by oxalate, were used as a control reference. Saponin at concentrations effective for skinning smooth muscle fibres (10–50 μg/ml) inhibited Ca 2+ binding in the absence of ATP to a similar extent in all fractions, but the inhibition of ATP-dependent Ca 2+ accumulation was more pronounced in dog aorta microsomes and rat gastric fundus muscle plasma membranes than in rat vas deferens microsomes. The resistance of phosphate- and oxalate-stimulated ATP-dependent Ca 2+ accumulation to inhibition by saponin was much greater in rat vas deferens than in dog aorta microsomes. Our results suggest that phosphate- and oxalate-stimulated ATP-dependent Ca 2+ accumulation also occurs in plasma membrane vesicles isolated from smooth muscle and is by no means an unique property of endoplasmic reticulum.

A simple algorithm for defining the mean cardiac cycle of aortic flow and pressure during steady state

A fast procedure for defining a cardiac cycle using simultaneously recorded and digitized aortic flow and pressure is presented. A simple algorithm, based on a double-threshold method, initially involves singling the dicrotic notch of flow in order to separate contiguous cardiac cycles during a given steady state. The individual cycles are carried back to a common origin of time, then they are normalized to the mean length and averaged. As a result of an averaging operation the algorithm gives a “mean cycle” of both pulsatile aortic pressure and flow. An “a posteriori” analysis of the noise components in the data has been carried out in order to justify the averaging operation. The “mean cycles” of aortic flow and pressure are suitable to be used as the input quantities of the automatic identification procedures recently assessed to estimate the parameters of simple models of the arterial input impedance. Our algorithm was defined and implemented as a FORTRAN program for a digital PDP 11 24 computer. This algorithm was tested by using pressure and flow data measured in the ascending aorta of dogs. About 26 sec were necessary to select 10 cardiac cycles (each one being about 200 samples long) of both flow and pressure in sequences of 2500 samples per signal and to compute the respective “mean cycles”. Total peripheral resistance, total arterial compliance, and aortic characteristic impedance were estimated by aid of the simple three-element windkessel model. The results obtained by our method of determining parameters on the “mean cycle” of aortic pressure and flow were compared to the results obtained by averaging the parameters determined on each heart cycle.

Expandable intraluminal graft: a preliminary study. Work in progress.

To overcome the problem of recurrence of stenosis after vascular balloon dilatations, we developed an expandable, intraluminal graft that allows dilatation of the lesion and simultaneous placement of a supportive endoprosthesis to prevent recoil of the arterial wall. The graft is made of continuous, woven, stainless steel wire. The resulting tubular mesh has a wall thickness of 200-450 micron and 80% open surface. The grafts, mounted on angioplasty catheters, are introduced through 8-12-F Teflon sheaths. Eleven grafts of 6, 8, and 10 mm in diameter by 20 mm long were placed in the aorta, common carotid, superior mesenteric, iliac, and renal arteries of dogs. Six grafts showed no stenosis in follow-up studies of up to 8 weeks. Two grafts had moderate stenosis as a result of neointimal hyperplasia. Two partial and one complete graft thrombosis occurred in nonheparinized animals in which the graft outflow was restricted. Anticoagulant was not used on a long-term basis. Light and electron microscopy studies showed complete covering of the graft's inner surface by endothelium at 3 weeks.

Cerebral blood flow during open-chest cardiac massage with occlusion of the descending aorta in dogs

Cerebral blood flow (CBF) and carotid blood flow (CAF) during open-chest cardiac massage with and without occlusion of the descending aorta was examined in 10 dogs to assess whether they were augmented by occlusion. clusion. In control measurements with a normally beating heart, CBF with and without occlusion of the descending aorta were 17.8 ± 2.3 and 13.8 ± 2.2 ml/min (± S.E.M.), which were not significantly different. Cerebral blood flow during open-chest cardiac massage were 6.1 ± 1.0 with occlusion and 5.7 ± 1.0 ml/min without occlusion of the descending aorta, which were also not significantly different. By contrast, CAF increased significantly with occlusion of the descending aorta both during control measurement, with mean increases of 61.1% and 92.2% during open-chest cardiac massage ( P = 0.05). While occlusion generally failed to augment CBF; in two dogs resuscitation was successful by manual cardiac massage. With the restoration of cardiac activity it increased immediately to twice that of control blood flow, and then gradually returned to the control level. Based on these observations, it is the author's opinion that every effort should be directed toward the restoration of cardiac activity as quickly as possible during circulatory arrest, and to increase CBF which is essential for neurological recovery.

Regional circulations in experimental coarctation of the aorta in conscious dogs.

Regional blood flows were measured with radioactive microspheres in 35 conscious dogs at various times (between 1 h and 28 days) after creation of a stenosis of the descending thoracic aorta. Mean arterial pressure increased moderately proximal to the stenosis. Distally, arterial pressure decreased below control values immediately after stenosis, then returned gradually toward preconstriction values over 28 days. Plasma renin activity increased sixfold, after aortic constriction of 1 and 6 h, and remained significantly elevated for four days. Blood volume did not change significantly. In some of the vascular beds exposed to the elevated proximal pressure, significant increases in blood flow were noted in the early stages, mainly in the myocardium, the brain, the skeletal muscles and the bones. After 28 days, however, blood flows were significantly reduced in most tissues exposed to the proximal pressure. At this stage, vascular conductance was significantly decreased in the myocardium, the brain, the muscles, the skin and the bones as compared with a sham-operated control group. Several vascular beds perfused by the distal arterial pressure also showed a significant fall in flow after 28 days, notably the small intestine, the skin, the skeletal muscles and the bones. At that stage, vascular conductance was decreased in the small intestine, the muscles, the skin and the bones. Thus, aortic coarctation in dogs was characterized by a late generalized increase in vascular resistance extending to tissues which were never exposed to increased arterial pressure nor to an increased blood flow. These findings suggest that a systemic vasoconstrictor influence overrides local mechanisms in the control of regional circulations in coarctation hypertension.