bluuebunny/crossref_metadata_2025 huggingface dataset:
Antithrombotic Effect of Malayan Pit Viper Venom on Experimental Thrombosis of the Inferior Vena Cava Produced by a New Method
Authors: MARSTEN JAMES L. , KOK-EWE CHAN , ANKENEY JAY L. , BOTTI ROBERT E.
Published: June 2012

A reliable method of producing thrombosis of the inferior vena cava in dogs is described. This consists of placing a segment of umbilical tape across the lumen of the vein and sewing it in place without interfering with blood flow. In the control animals gross thrombi were not usually present in the immediate postoperative period but were demonstrated after 24 hours. By the 7th postoperative day large red clots completely obstructing the vessel were usually found. The venom of the Malayan pit viper proved to be highly effective in preventing experimental thrombosis. The antithrombotic effect of viper venom is believed to be due primarily to induced hypofibrinogenemia. Accelerated fibrinolysis may also be a factor. The experiments suggest that Malayan pit viper venom may be effective as an antithrombotic agent.
Effect of Estrogen Dosage upon Plasma, Liver and Bile Lipids in Cholesterol-Fed Cockerels
Authors: CLARKE G. B. , PICK R. , JOHNSON P. , KATZ L. N. , Kakita, C.
Published: June 2012

The effects of four dosages of conjugated equine estrogens (Premarin) on atherogenesis and on plasma, liver and bile lipids were studied in cockerels maintained on a high-fat, high-cholesterol diet. A lowering effect, not dose-dependent, occurred in plasma linoleic and linolenic acid. An augmentative effect, varying with dose, occurred in plasma phospholipids, plasma palmitic, stearic and oleic acids, liver total fat and thoracic atherosclerosis. A lowering, dose-dependent effect occurred in coronary atherosclerosis, plasma cholesterol-phospholipid ratio and plasma arachidic acid. A diphasic, dose-dependent, response occurred in: (1) plasma cholesterol (decrease at lowest dosage and increase at higher dosages); (2) bile cholesterol (increase at lower dosages and a decrease at higher dosages); (3) liver cholesterol (increase at lowest dose, and decrease at higher dosages); (4) plasma arachidonic acid (increase at lower and decrease at higher dosages). The mechanisms responsible for these changes are not clear but are under investigation.
Release of Adrenal Catecholamines by Angiotensin II
Authors: PEACH MICHAEL J. , CLINE WILLIAM H. , WATTS DANIEL T.
Published: June 2012

Several recent investigations have presented indirect evidence that angiotensin stimulates the release of adrenal medullary catecholamines. The following work was undertaken in an attempt to show in vivo angiotensin stimulation of the adrenal medulla by analysis of plasma catecholamines. Mongrel dogs, anesthetized with pentobarbital, were infused for 10 min with doses of 0.025, 0.05, and 0.1 µg per kg per min of angiotensin or injected with single doses of 0.5, 1.0 and 2.0 µg per kg. Blood samples were taken from the inferior vena cava (above the outflow from the adrenal veins) at the peak of the pressor responses to single doses or during and after the infusions. The samples were fluorometrically analyzed for epinephrine and norepinephrine. It was found that angiotensin produced an increase in circulating catecholamines. Epinephrine was significantly increased by infusions of 0.05 and 0.1 µg per kg per min and all three injected doses. Plasma norepinephrine was significantly increased also except with the 0.5 µg per kg injected dose of angiotensin. Angiotensin infusion of 0.025 µg per kg per min did not cause a detectable change in circulating catecholamine levels. In the infusion experiments, norepinephrine was more transiently increased than epinephrine. These results show that various pressor doses of angiotensin stimulate release of adrenal catecholamines.
Water, Nitrogen, and Electrolyte Content of Right and Left Ventricular Walls and Interventricular Septum of Normal Canine Hearts
Authors: MOULDER PETER V. , EICHELBERGER L. , RAMS J. J. , GREENBURG A. G.
Published: June 2012

The water, nitrogen, and electrolyte content of the normal canine myocardium partitioned as right ventricle, septum, and left ventricle are presented on a connective tissue-free basis as well as fat-free and blood-free. Considering the tissue on a fat-free, blood-free, connective tissue-free basis, the extracellular phase (expressed as g/kg heart muscle) of the left ventricle was 86% that of the right ventricle; that of the septum was 91% that of the right ventricle. In all three segments, cell water was constant at 77%. One kilogram of myocardial cells contains 29.7 g of noncollagenous protein nitrogen, 116 mEq of potassium, 26 mEq of magnesium, and is associated with 0.3 (septum and left ventricle) and 0.53 (right ventricle) mEq of calcium.
Wave Propagation in the Pulmonary Circulation
Authors: WIENER FRED , MORKIN EUGENE , SKALAK RICHARD , FISHMAN ALFRED P.
Published: June 2012

A mathematical model of the entire pulmonary circulation of the dog, based on branching elastic tubes, is shown to yield a useful description of the propagation of pulmonary vascular pressure and flow waves. The pressure and flow pulses throughout the model are computed from the pressures measured at the arterial and venous ends of the system. Computed flow pulses at each end of the system agree with experimental findings.

Contour changes in the pressure and flow pulses are shown to be primarily due to dispersion and amplitude changes associated with reflected waves. Wave reflections are distributed throughout the model, and no specific site can be designated as the major source for reflections.

Blood pressure and flow computed from the model remain pulsatile in the microcirculation; pressure pulses are attenuated but flow pulses pass essentially unchanged through the microcirculation.

The computed results support the conclusion previously drawn from experimental evidence that pressure and flow pulses in the pulmonary veins originate primarily in the right ventricle and are propagated through the pulmonary capillary bed. A retrograde pulse, resulting from pressure fluctuations in the left atrium, is also present in both arteries and veins, but has only a secondary effect on the contours of pulmonary vascular pressures and flows.
A Transfer Function Analysis of Coronary and Renal Circulation Calculated from Upstream and Downstream Indicator-Dilution Curves
Authors: COULAM CRAIG M. , WARNER HOMER R. , WOOD EARL H. , BASSINGTHWAIGHTE JAMES B.
Published: June 2012

A method has been developed for computing the distribution of blood transit times (transfer function) from indicator-dilution curves recorded from upstream (aorta) and downstream (pulmonary artery, renal vein and coronary sinus) circulatory sites in mongrel dogs. The method employs a Fourier series transformation of the upstream and downstream curves and yields a time-domain transfer function which is independent of recirculating dye particles. Discontinuities, created in the upstream and downstream indicator curves by the termination of sampling (120 sec postinjection), are removed by a tail terminating procedure which employs normal and lagged normal density distributions. The transfer functions computed for the trans-renal and trans-coronary circulations and their relationship to the systemic circulation dispersion patterns are shown under control conditions (pentobarbital anesthesia) and during intra-aortic infusion of angiotensin, acetylcholine and adenosine triphosphate. These distribution patterns reflect the response of the vascular system to the drugs and demonstrate, to a limited extent, the role which different vascular beds have in the cardiovascular mixing process.
Contractility, Metabolism and Pharmacological Reactions of Isolated Gas-Perfused Cat Hearts
Authors: GABEL LLOYD P. , BIHLER IVAN , DRESEL PETER E.
Published: June 2012

Cat hearts were perfused through the aorta with substrate-free Krebs solution for 5 min, then with 5% CO
2
-95% O
2
saturated with water vapor at 37.5°C. Heart rate decreased rapidly but contractility was maintained at pre-gas levels for 3 to 4 hours, decreasing to 25% at 10 hours. Driving the preparations at 168 beats/min did not appreciably change the time course of change in contractility. The hearts developed more tension at all resting tensions and were able to perform more work than hearts perfused with substrate-free Krebs solution, but their work capacity was less than that of hearts perfused with glucose-Krebs solution. They reacted normally to sympathomimetic amines and blocking agents. They were very sensitive to increases in perfusion pressure, developing completely reversible arrhythmias at pressures 80 to 150% above the control (60 mm Hg). Most hearts developed contractile alternans which usually was not accompanied by electrical alternation. Glycogen, lactate, pyruvate content decreased rapidly, the first to a residual level and the others to undetectable levels.
Human Cerebrovascular Response to Combined Hypoxia and Hypercapnia
Authors: SHAPIRO WILLIAM , WASSERMAN ALBERT J. , PATTERSON JOHN L.
Published: June 2012

The N
2
O technique was used in 6 human subjects to measure cerebral blood flow and metabolism during hypoxia and hypercapnia induced by the inhalation of 10% O
2
-5% CO
2
. Ventilation increased from 7.7 to 46.3 liters/min; Pao
2
decreased from 88 to 62 mm Hg; Paco
2
increased from 38 to 45 mm Hg (for each
P
<.01). Mean cerebral blood flow increased from 56 to 97 ml/100 g/min (
P
<.01). Because cerebral O
2
consumption was unchanged, the technique of estimating changes in cerebral flow from arterial-jugular venous O
2
differences was used to follow changes during the first 10 min of inhalation of 10% O
2
-5% CO
2
in 6 additional subjects. The rapidity of cerebral vasodilatation was increased by this combination of stimuli. The enhanced respiratory response produced by breathing 10% O
2
-5% CO
2
appeared responsible for the more rapid cerebrovascular response and may offer some protective benefits. Comparisons of the present data with previous studies lead to the conclusion that simultaneous hypoxia and hypercapnia have additive dilator effects on the cerebral vasculature. Thus, the observed increases in cerebral flow were the sum of their individual effects.
Electrophysiologic Effects of Quinidine
Authors: WALLACE ANDREW G. , CLINE ROBERT E. , SEALY WILL C. , YOUNG W. GLENN , TROYER WILLIAM G.
Published: June 2012

Experiments were performed on awake dogs with chronic recording electrodes implanted on the SA node, His bundle, and right bundle branch. Quinidine at serum concentrations of 5 to 10 mg/liter had little effect on AV conduction, but slowed conduction in Purkinje tissue, prolonged ventricular activation, decreased the excitability of atrium and ventricle, and prolonged the atrial refractory period without a consistent effect on the ventricular refractory period. In awake dogs that had previously undergone cardiac denervation, quinidine decreased the excitability and prolonged the refractory period of atrium and ventricle. The effects of quinidine on excitability were dependent on the duration of the stimulus used to test excitability. The actions of quinidine on intraventricular conduction and excitability were enhanced at rapid rates of stimulation. These data indicate that slowing of intraventricular conduction is observed consistently at serum quinidine concentrations that are generally considered to be within the therapeutic range, but changes of the refractory period of the ventricle are not observed consistently. Although the vagolytic properties of quinidine may contribute to changes of heart rate, they do not appear to influence significantly the effects of quinidine on atrial refractoriness and AV conduction.
Direct Positive Inotropic Effect of Acetylcholine on Myocardium
Authors: BUCCINO ROBERT A. , SONNENBLICK EDMUND H. , COOPER THEODORE , BRAUNWALD EUGENE
Published: June 2012

The effects of acetylcholine and nicotine on isometric tension, in the presence and absence of atropine, hexamethonium, and endogenous norepinephrine stores, were examined in isolated cat atria and papillary muscles. Acetylcholine exerted a negative inotropic effect, competitively inhibited by atropine, in atrial and papillary muscle; in higher concentrations in papillary muscles, it produced a positive inotropic effect that was independent of cardiac norepinephrine stores and that was not blocked by atropine or hexamethonium. Nicotine, in addition to releasing norepinephrine, was found to exert, in higher concentrations, a direct positive inotropic effect, not antagonized by hexamethonium.

These data are compatible with the existence of two distinct cholinergic receptors in the myocardium: a muscarinic receptor intimately associated with vagal nerve endings; and a spatially separate receptor, whose stimulation produces responses similar to those produced by nicotine. This hypothesis allows for the reconciliation of much apparently contradictory data concerning acetylcholine and parasympathetic control of the heart; it accounts for the opposite inotropic effects of acetylcholine on atria (negative) and ventricles (positive) and for the opposite effects of vagal nerve stimulation (negative) and exogenous acetylcholine (positive) on ventricular myocardium.
Shrinkage of the Heart in Anesthetized, Thoracotomized Dogs
Authors: RUSHMER ROBERT F.
Published: June 2012

Changes in heart size have been studied by means of intraventricular gages, serial roentgenography and cinefluorographic angiocardiography. Evidence is presented that the area of the cardiac silhouette and the area and diameter of the left ventricle all diminish in response to thoracotomy and during recovery return toward the pre-operative dimensions. Since fundamental concepts of cardiac function and control are based largely on investigation of exposed hearts, these concepts must be re-examined in intact, unanesthetized animals and man.
The First Heart Sound in Normal and Ectopic Ventricular Contractions
Authors: LITTLE ROBERT C. , HILTON JAMES G. , SCHAEFER ROY D.
Published: June 2012

Phasic right atrial and ventricular pressures and heart sounds were simultaneously recorded from dogs with normal and ectopic ventricular contractions. Heart sounds and electrocardiograms were recorded from humans. The first heart sound is significantly delayed in the absence of atrial systole. The time between onset of the ventricular pressure rise due to ventricular contraction and the beginning of the first heart sound is minimal at normal A
S
-V
S
intervals. These findings support the view that normally the A-V valves are closed or nearly closed before ventricular systole. In ectopic ventricular beats the A-V valves are closed from an open position by ventricular contraction.
Chronic Effects of Aorta-Coronary Sinus Anastomosis of Beck in Dogs
Authors: ECKSTEIN RICHARD W. , LEIGHNINGER DAVID S. , DALEM JACQUE , NEWBERRY WILLIAM B. , DEMMING JAMES H. , ORBISON JAMES L.
Published: June 2012

Studies were made on dogs at various times up to one year following the coronary sinus anastomosis of Beck to determine the chronic effects of the operation. The results indicate that the graft perfuses the capillary bed of the occluded circumflex artery for about five weeks after the operation and then loses its functional contact with the capillary bed probably because of obliterative venous changes. However, as a result of an anoxia, there is definite development of intercoronary collateral vessels during the first few weeks, which persist throughout the year even though there is no arterial occlusion. It is concluded that in dogs the Beck operation is protective against the major effects of coronary ligation because of retrograde capillary flow early and intercoronary anastomoses later.
Changes in Hypertensinase and Hypertensinogen Following Nephrectomy
Authors: COLLINS DEAN A. , HARAKAL CONCETTA D.
Published: June 2012

The hypertensinase content of dog's plasma is decreased 48 hours after nephrectomy. This decrease may contribute to the increased blood pressure response to renin shown by nephrectomized animals. When plasma is incubated with a relatively small concentration of renin, the yield of hypertensin increases after nephrectomy. This finding correlates with decreased hypertensinase and the increased pressor response to renin characteristic of the postnephrectomy state. Mean plasma hypertensinogen shows about a threefold increase, and its significance is discussed.
The Pattern of Recovery of Renal Function Following Renal Artery Occlusion in the Dog
Authors: FRIEDMAN SYDNEY M. , JOHNSON R. L. , FRIEDMAN CONSTANCE L.
Published: June 2012

The pattern of recovery of renal function following two hours of complete ischemia was studied in a series of dogs. A marked functional ischemia persisted for several hours after release of the clamp, but restoration of blood flow was substantially complete in 24 hours. Other renal functions returned slowly over a period of weeks, reflecting the rate of repair of damaged tubules. Two important phases of recovery are thus to be considered: (a) a brief but significant period of continuing ischemia immediately following the trauma, and (b) a period of slow repair of those nephrons damaged but not destroyed in the first phase of the insult.
The Transport of Radioactive Inorganic Phosphate by the Pulmonary Circulation
Authors: LAWSON HAMPDEN C. , MELLETTE HENRY C. , COLEMAN EVERETT S.
Published: June 2012

Radio-phosphorus in the form H
3
P
32
O
4
, injected in aqueous solution, is found to give flow-dilution curves and values for cardiac output indistinguishable from those obtained with T-1824 in normal anesthetized dogs. The fairly rapid disappearance of the P
32
from systemic blood is a technical advantage if the measurement of output is to be repeated at short intervals.
A Comparison of Intracardiac and Intravenous Injections for the Measurement of Cardiac Output by the Dilution Technic
Authors: LAWSON HAMPDEN C. , SHADLE OSCAR W. , COLEMAN EVERETT S. , HOLTGRAVE DOROTHY E.
Published: June 2012

Using H
3
P
32
O
4
and the dye T-1824 as labels, simultaneous injections were made into the right ventricle and into a peripheral vein, and cardiac output was calculated from the individual flow-dilution curves. When a discrepancy beyond the range expected from the use of the two labels occurred, the output from the central injection was always the larger (approximately one-third of the observations, in a small series). This may be attributable to progressive blood loss from sampling, since delayed intraventricular injections under comparable conditions, measure a similarly reduced cardiac output.
Effect of Adrenalectomy on Pressor Responsiveness to Angiotonin and Renin
Authors: SALMOIRAGHI G. C. , McCUBBIN J. W.
Published: June 2012

Pressor response to injection of renin is reduced or abolished during adrenal insufficiency without concurrent change in response to angiotonin and other drugs. Selective loss of response to renin is considered to result from depletion of available renin-substrate by endogenous renin; when release of endogenous renin is precluded by nephrectomy, adrenalectomy does not cause diminution of response to renin. The increase in response to angiotonin and renin that follows nephrectomy is not prevented by adrenalectomy.
Characteristics of Shock Following Acute Reduction of Cardiac Output in Dogs
Authors: MEYERS FREDERICK H. , SCHOOLAR JOSEPH C. , OVERMAN RICHARD R.
Published: June 2012

A state of shock followed the acute reduction of cardiac output caused by injection of a necrotizing solution into the myocardium. Decrease in blood pressure, decrease in circulating plasma volume, increase in hematocrit readings and the effect of re-expansion of the plasma volume established the similarity of this state to other forms of shock. Pulmonary blood volume decreased concurrently with cardiac output and effective plasma volume.
A Relationship of Tissue Lipids to Sex and Body Weight in the Albino Rat
Authors: NOBLE NANCY L. , BOUCEK ROBERT J. , LEWIS GEORGE T.
Published: June 2012

This report deals with the relationship of various lipid fractions in the heart and in the liver, and the urinary excretion of ketone bodies, to sex and body weight in normal nonfasted albino rats. Results indicate the existence of differences in concentrations of fatty acid, neutral fat, and phospholipid in the liver of male rats as body weight increases. Phospholipid concentration of the liver and heart of the male and the heart of the female declines significantly with age.
Renin Content of Systemic Blood of Rats with Desoxycorticosterone and Metacorticoid Hypertension
Authors: PRADO J. L. , PICARELLI ZULEIKA P. , KUPPER REGINA , PRADO ELINE S. , VALLE J. R.
Published: June 2012

No increased renin concentration was detected in the systemic blood of rats with desoxycorti-costerone and metacorticoid hypertension, using the guinea-pig; ileum method of renin estimation. Re-establishment of the circulation through totally ischemic rat kidney is followed by the liberation of large amounts of renin.
Control by the Superior Cervical Ganglion of the State of Contraction and Pulsatile Expansion of the Carotid Sinus Arterial Wall
Authors: KEZDI P.
Published: June 2012

The state of contraction and resistance to stretch of the arterial wall of the carotid sinus modulates sensitivity of pressoreceptors to intra-arterial pressure. Experiments show that electric stimulation of efferent sympathetic pathways to the carotid sinus leads to blood pressure fall and decrease of the carotid sinus hypertensive reflex. This effect can be prevented by local application of Regitine to the carotid sinus. These experiments suggest that the state of contraction and resistance to stretch of the barosensitive arterial walls is controlled by sympathetic innervation through local release of norepinephrine and/or epinephrine. Disturbances of this innervation could have a role in development of abnormal relaxation and decreased pulsatile expansion of the barosensitive arterial walls, and, thus, in the pathogenesis of hypertension.
The Relationship Between Pressure and Flow in the Systemic Circulation of the Dog
Authors: LEVY MATTHEW N. , BRIND SHIRLEY H. , BRANDLIN FREDERICK R. , PHILLIPS FRED A.
Published: June 2012

Cardiac output was determined in dogs over a wide range of pressures before and after preclusion of compensatory reflex mechanisms. When the moderator reflexes are functional, total peripheral resistance increases markedly with moderate reductions in arterial pressure. When reflex alterations of vasomotor tone are obviated, pressure and flow usually vary proportionately as arterial pressure is altered. In the average experiment, total peripheral resistance remains relatively constant although appreciable deviations may be observed in individual cases.
Effect of Adrenalectomy upon the Pressor Action of Potassium in Hypotensive, Potassium-Deficient Rats
Authors: FREED S. CHARLES , ROSENMAN RAY H. , SMITH MALCOLM K.
Published: June 2012

The administration of potassium to hypotensive, potassium-deficient rats results in a prompt restoration of their lowered blood pressure to normotensive levels. Similar repletion of the potassium deficit in adrenalectomized rats is only partially effective in restoring the blood pressure to normotensive levels. The spontaneous retention of potassium which occurs in potassium-deficient rats following adrenalectomy fails to restore lowered blood pressures to normotensive values.
The Circulatory Adjustments to Posthemorrhagic Anemia in Dogs
Authors: HATCHER J. D. , SUNAHARA F. A. , EDHOLM O. G. , WOOLNER J. M.
Published: June 2012

Several measures of cardiovascular function were made in nine dogs before, during, and after the production of anemia by daily venesections. Stress is laid on the time sequence of the various changes in the circulation and their relation to each other. From the results obtained it was concluded that the elevated cardiac output observed in anemia was not the result of an increase in right atrial pressure or a decrease in tissue oxygen tension, per se. It is suggested that the increased cardiac output may be due to a slowly elaborated or slow-acting humoral agent produced as a result of tissue anoxia.
Use of Intestinal Loops for Revascularization of the Heart
Authors: BARONOFSKY IVAN D. , SPRAFKA JOSEPH L. , NOBLE JOHN F. , LEVY LOUIS M.
Published: June 2012

Intestinal loops brought up through the diaphragm and attached to the myocardium will cause the formation of connections between the vascular supplies of the heart and intestine. The vessels that develop between these two organs are large enough to transmit thick suspensions of barium sulfate. India ink injected in the mesenteric vessel can be readily found on all surfaces of the heart as well as deep within the myocardium.
The Direct Renal Vascular Effects of Epinephrine and Norepinephrine before and after Adrenergic Blockade
Authors: SPENCER MERRILL P. , DENISON ADAM B. , GREEN HAROLD D.
Published: June 2012

By use of a noncannulating electromagnetic flowmeter the direct vasoconstrictor response of the dog renal vasculature to intra-arterial epinephrine was found to bebut slightly greater, weight for weight, than that of norepinephrine. No dilation phase to their reactions was found before or after Ilidar, and this adrenergic blocking drug failed to dilate the renal vasculature in four out of five dogs in the anesthetized and operated state.
The Water and Electrolyte Content of the Tissues in Hypertension
Authors: GROLLMAN ARTHUR , CAMPBELL CHARLES , MlMS JOB , RECTOR FLOYD
Published: June 2012

An analysis of the water and electrolyte content of various tissues of rats rendered hypertensive by a period of choline deficiency at the time of weaning indicates that no alterations are induced by this procedure. It is concluded that the hypertensive process, per se, is not necessarily accompanied by changes in the water and electrolyte content of tissues; where such changes are observed, they are probably secondary to parenchymal renal changes.
Pericardial Pressure during Transverse Acceleration in Dogs without Thoracotomy
Authors: BANCHERO NATALIO , RUTISHAUSER WILHELM J. , TSAKIRIS ANASTASIOS G. , WOOD EARL H.
Published: June 2012

Intrapericardial pressures were recorded via a saline-filled Teflon catheter (o. d., 1.3 mm) in 11 anesthetized dogs studied without thoracotomy. Seven animals were studied before, during, and after 1-min exposures to transverse accelerations that ranged from 1G (normal gravitational environment) to 7G when in the supine (+G
j
), prone (-G
x
), left decubitus (+G
v
), and right decubitus (-G
y
) positions. Four additional animals were studied at 1G only, while in these same body positions. Pressures also were recorded from both atria, right ventricle, aorta, esophagus, and the potential pleural space. Mean end-expiratory intrapericardial pressure varied directly with the vertical height of the recording site in the thorax during all conditions studied, as would be expected in a hydrostatic system. Transpericardial pressures were not significantly different from zero at all levels of acceleration studied. Transmural left and right atrial pressures were independent of the height of the recording site in the thorax and were unchanged during exposures to transverse accelerations that ranged from plus to minus 7G
x
.
Microelectrode Studies on Retrograde Concealment of Multiple Premature Ventricular Responses
Authors: MOORE E. NEIL
Published: June 2012

Retrograde concealment of serially evoked premature ventricular responses was studied in an isolated preparation of rabbit atria and ventricles. Transmembrane potentials were recorded simultaneously from single cells within the atrioventricular (A-V) node and ventricular specialized conduction system, together with atrial and ventricular bipolar electrograms. In these experiments, retrograde conduction delays and block occurred within the ventricles, between ventricular muscle and the Purkinje-bundle branch system, between the bundle branch and His bundle, and within the A-V node.

The ventricular specialized conduction system was found to be a major location of retrograde conduction delays and block. Many examples of retrograde concealment and block, previously interpreted as due to A-V nodal mechanisms, almost certainly result instead from mechanisms operating within the ventricular specialized conduction system.

Antegrade and retrograde block of sequentially evoked premature responses occurred within the A-V node. Reentry "echo" responses occurred in many experiments following premature stimulation of the atria, the ventricles, or both.
Digital Vascular Response to Angiotensin II in Normotensive and Hypertensive Subjects
Authors: GASKELL PETER
Published: June 2012

The critical opening pressure (COP) of digital vessels after digital nerve block and the change in COP caused by angiotensin at 4 mµg/kilo per min intravenously after the block were compared in 9 normotensive subjects, 8 patients with essential hypertension and 7 patients with various kinds of renal hypertension. The COP after nerve block was less than 20 mm Hg in the normotensives and in 6 renal hypertensives, but more than 20 mm Hg in 7 essential hypertensives. The angiotensin reduced the COP in 7 of the normotensives, increased it substantially in 7 essential hypertensives, but had little effect in 6 renal hypertensives. A significantly greater increase in systemic blood pressure occurred in the essential hypertensives than in the normotensive subjects. In normotensive subjects doses of intravenous angiotensin from 2 to 16 mµg/kilo per min decreased the COP whether preceded by digital nerve block or not. Angiotensin at 8 mµg/kilo per min increased total digital vascular resistance as estimated by venous occlusion plethysmography. The results indicated that angiotensin relaxed smooth muscle in digital vessels of normal subjects but increased vascular resistance. In patients with essential hypertension angiotensin caused contraction of the smooth muscle, a response apparently qualitatively different from normal. In renal hypertensives the smooth muscle had little response to the exogenous angiotensin.
Forward and Backward Transmission of Pressure Waves in the Pulmonary Vascular Bed of the Dog
Authors: CARO COLIN G. , BERGEL DEREK H. , SEED W. ANTHONY
Published: June 2012

Pressures were measured in lobar pulmonary arteries, veins, and left atria of anesthetized open-chest dogs. Observations were made before and after snaring the lobar vessels and before and after infusing dextran to raise the mean pressure. Pressure waves were subjected to harmonic analysis. Forward (artery to vein) and backward (vein to artery) transmission (output/input pressure) and transmission ratios (forward/backward transmission) were calculated for each harmonic.

At low frequencies, forward transmission was increased by dextran, but backward transmission was unaffected. At low frequencies and high mean pressures the bed was nonsymmetrical, forward transmission being several times greater than backward at the same mean pressure (transmission ratio >1).

The findings were analyzed with the aid of simple models. Nonsymmetry at low frequencies and high mean pressures appears to be due to arterial exceeding venous compliance. The findings and resulting theory are pertinent to the understanding of the shape and amplitude of arterial "wedge"-pressure traces.
Renal Medullary Heat Clearance in the Dog
Authors: AUKLAND KNUT
Published: June 2012

Renal medullary heat clearance was investigated in anesthetized dogs to evaluate countercurrent exchange of heat. Sudden changes in the temperature of renal arterial blood were induced by infusion of 3 to 7 ml/min of saline at room temperature. The resulting changes in medullary temperature, measured with fine thermocouples, started with increasing delay from cortex towards the papilla. Average rate constant for heat uptake in the inner medulla was 0.61 min
-1
. In the outer medulla, rate constants from 0.6 to 5.0 min
-1
were observed, with the higher values in the subcortical zone. Inner medullary clearance rose during diuresis, but was practically uninfluenced by lowering perfusion pressure to 35 mm Hg. Calculated heat conduction (diffusion) from cortex into medulla was close to observed clearances, which are thus mainly determined by heat conduction. Clearance due to flow in vasa recta and loops of Henle was small, presumably due to efficient countercurrent heat exchange, whereas urine flow in collecting ducts is not subject to this effect. Formulas for countercurrent exchange not taking into account length diffusion (parallel to the vasa recta) are not valid for medullary heat exchange. The present heat clearance technique cannot be used for estimating medullary blood flow.
Effects of Nylidrin, Isoproterenol and Phenoxybenzamine on Dogs Subjected to Hemorrhagic Shock
Authors: GREGA GEORGE J. , KINNARD WILLIAM J. , BUCKLEY JOSEPH P.
Published: June 2012

The effects of beta-adrenergic receptor stimulants (nylidrin and isoproterenol) on the hemorrhagic shock state of anesthetized dogs were measured and compared to those of phenoxybenzamine to determine the therapeutic effectiveness of the combined cardiac stimulatory and peripheral vasodilatory actions of the former drugs. Anesthetized dogs were subjected to 3 hours of hypovolemia followed by the return of the shed blood. Nylidrin, isoproterenol (continuous infusion), and phenoxybenzamine were administered 1 hour after bleeding the animals and heart rate, arterial blood pressure, venous hematocrit, coronary blood flow, cardiac output, ventricular contractility, and survival rates were measured. Nylidrin and isoproterenol afforded significant protection against shock deaths, whereas phenoxybenzamine did not increase survival over control values. Mild to moderate intestinal hemorrhage and distention were noted in the isoproterenol- and phenoxybenzamine-treated animals, but not in the nylidrin-treated animals. Phenoxybenzamine gradually decreased the arterial blood pressure and additional quantities of blood had to be infused to maintain cardiac output and blood pressure. Ventricular contractile force progressively decreased in the phenoxybenzamine-treated animals, whereas isoproterenol and nylidrin enhanced the force of ventricular contractions. In the presence of existing hypotension, isoproterenol and nylidrin maintained cardiac output. These agents deserve further consideration as potentially useful therapeutic agents in the management of shock states.
Effects of Ouabain, Atropine, and Ouabain and Atropine, on A-V Nodal Conduction in Man
Authors: CARLETON RICHARD A. , MILLER PAUL H. , GRAETTINGER JOHN S.
Published: June 2012

The prolongation of A-V transmission time that occurs with increasing rates of right atrial pacing has been used to study the effect of ouabain and of ouabain plus atropine on A-V nodal conduction in 14 patients with normal A-V nodes. Drugs were injected into the superior vena cava or pulmonary artery over a 1- to 2-min period. Atropine in a dose of 0.02 mg/kg shortened A-V conduction time by an average of 0.112 sec; ouabain alone in a dose of 0.01 mg/kg lengthened A-V conduction time by 0.053 sec. Ouabain given after large doses of atropine did not prolong A-V conduction at any paced rate. Thus, in these resting patients with normal A-V nodal function, usual digitalizing dosages of ouabain did not have an extravagal or antiadrenergic effect on A-V nodal conduction.
Right Duct Lymph Flow in Experimental Heart Failure Following Acute Elevation of Left Atrial Pressure
Authors: UHLEY HERMAN N. , LEEDS SANFORD E. , SAMPSON JOHN J. , FRIEDMAN MEYER
Published: June 2012

We measured the pulmonary lymph flow in dogs with mild congestive failure before and after acute elevation of the left atrial pressure to 40 cm of water. The creation of an aorticocaval fistula and the administration of desoxycorti-costerone trimethylacetate and a salt enriched diet in 6 dogs produced mild pulmonary edema and partial expansion of the pulmonary lymphatics 10 to 12 days postoperatively. Elevation of the left atrial pressure to 40 cm of water under pentobarbital anesthesia led to an immediate increase in right duct flow in the "mild failure" dogs, in contrast to a delayed flow in normal dogs. The average peak flows in the 10- to 12-day dogs after increasing the left atrial pressure were higher than the peak flows observed in normal dogs. In addition, the mild failure dogs survived twice as long as normal dogs after acute elevation of the left atrial pressure. These results suggest that an animal with an expanded pulmonary lymph system is better able to withstand the stress of acute elevation of left atrial pressure than a normal animal. The pulmonary lymph system may serve as an important compensatory mechanism in the prevention of fulminating pulmonary edema.
Reduction in Renal Vascular Responses to Angiotensin and Norepinephrine during Carotid Sinus Stimulation
Authors: GELLER RONALD G. , KENDRICK J. E. , Matson G. L.
Published: June 2012

In dogs anesthetized with morphine and chloralose, the renal vascular responses to angiotensin and norepinephrine were studied under conditions of altered sympathetic nervous activity. The kidneys and one or both carotid sinuses were perfused at a constant rate of flow. Sympathetic activity was altered by changing the mean carotid sinus perfusion pressure from approximately 30 to 200 mm Hg. During maximal carotid sinus pressure, the renal vasoconstrictor responses to angiotensin and norepinephrine were reduced by an average of 52% and 47%, respectively. Similar results were obtained in innervated, chronically denervated, and excised kidneys perfused with the dogs' own blood. Increasing carotid sinus pressure alters the responsiveness of the renal vasculature to angiotensin and norepinephrine by some mechanism that is not dependent on the renal sympathetic nerves or on norepinephrine. It is proposed that raising mean carotid sinus pressure alters the concentration of some bloodborne substance and so reduces the vasoconstrictor responses to these vasoactive agents in the renal vascular bed.
Paired Electrical Stimulation and the Maximal Contractile Response of the Ventricle
Authors: FISHER VINCENT J. , LEE ROBERT J. , MARLON ANTHONY M. , KAVALER FREDERIC
Published: June 2012

Paired stimulation of the isometrically contracting papillary muscle of the cat caused it to develop 80 to 100% of the tension it develops in a high calcium, low sodium medium. The isovolumic left ventricle of the dog responded to paired stimuli with a significant increase in developed pressure and in maximal rate of rise of pressure (dP/dt max) at all ventricular volumes. During stimulation of the isovolumic left ventricle, there was little or no further potentiation induced by norepinephrine or calcium gluconate infusion. Paired stimulation is thus capable of inducing a maximal or near-maximal contractility of ventricular muscle at any given ventricular volume. Using dP/dt max as an index of left ventricular contractile force which is relatively uninfluenced by aortic afterloading, paired stimulation was found to cause significant potentiation in the ejecting left ventricle (64% increase above control dP/dt max). Unlike the papillary muscle and the isovolumic ventricle, the combination of paired stimulation and norepinephrine infusion caused a further increase in dP/dt max of the ejecting left ventricle. This may be explainable by the increase in ventricular size caused by norepinephrine, but in some instances norepinephrine added to the inotropic effects of paired stimulation.
Quantitative Description of Ventricular Output Curves in Conscious Dogs
Authors: BISHOP VERNON S. , STONE HUBERT L.
Published: June 2012

Ventricular output curves obtained from normal dogs, chronic cardiac-denervated dogs, and dogs with beta-adrenergic blockade were analyzed in terms of a compartmental mathematical model. The model states that the change in ventricular output per change in mean atrial pressure is proportional to the estimated cardiac output reserve. The solution of the differential equation is an exponential build-up curve which agrees in all cases within the statistical fluctuation of the experimental curves. Using this approach, one can analyze each ventricular output curve in terms of its initial slope, estimated reserve and a proportionality constant. Factors affecting the estimated reserve and proportionality constant would thus affect the slope of the ventricular output curve. By using this model, a quantitation of ventricular function from ventricular output curves can be better approached.
Ventricular Function in Cardiac-Denervated and Cardiac-Sympathectomized Conscious Dogs
Authors: STONE HUBERT L. , BISHOP VERNON S. , DONG E.
Published: June 2012

The role of the autonomic nervous system in ventricular function was studied in conscious animals when either the cardiac nerves or the sympathetic nerves to the heart had been eliminated. Regional neural ablation was used to denervate the heart, and blockade of the cardiac sympathetic nerves was performed with propranolol. A reduction in the plateau of the ventricular output was seen in the cardiac-denervated animals (263 ml/min per kg) and in animals with beta-blockade (240 ml/min per kg) as compared with 318 ml/min per kg for the control curves. The difference in stroke volume in the cardiac-denervated animals and the beta-blocked animals at the plateau demonstrates that the chronically cardiac-denervated animal changes its ventricular output solely by a change in stroke volume, whereas the animal with beta-blockade changes heart rate and stroke volume in response to stress. Thus the beta-blocked animals increased their heart rate by a decrease in parasympathetic activity.
Gradients in the Regional Rates of Myocardial Rubidium-86 Clearance in Tranquilized Dogs
Authors: GILLESPIE WILLIAM J. , LOVE WILLIAM D.
Published: June 2012

In order to determine what gradients in local rates of myocardial blood flow are present in the resting hemodynamic state, the regional rates of myocardial clearance of
86
Rb were measured in dogs tranquilized with chlorpromazine. The clearance rate in the left ventricle corresponded to an average coronary flow of 11.7 ml/g per 10 min. Estimated right ventricular flow was 7.1 ml/g per 10 min and left atrial flow 7.9 ml/g per 10 min. High rates of
86
Rb uptake were noted in the atrial appendages and papillary muscles. Uptake in serially sectioned cores from both ventricles was consistently highest near the endocardial surface and decreased toward the epicardium. Selective injections of
86
Rb into the aorta or vena cava demonstrated that isotope penetrated the myocardium from the cavities of both ventricles. In the right ventricle, high subendocardial
86
Rb clearance was not found unless the isotope had been present within its cavity. In the left ventricle, in contrast, more
86
Rb was taken up by the subendocardial zones, even when all of the tracer was distributed by coronary arterial blood. The results support both diffusion of
86
Rb and perfusion of the myocardium by intracavitary blood as mechanisms responsible for the uptake of
86
Rb from the heart cavities.
Epicardial Excitation Studies in Dogs with Congenital Right Ventricular Hypertrophy
Authors: HILL JOHN D. , MOORE E. NEIL
Published: June 2012

The time and sequence of epicardial activation was determined by measuring the onset of activation at 26 to 47 representative epicardial sites on each ventricle. Normal dogs and dogs with right ventricular hypertrophy resulting from various congenital heart lesions were studied. The total right ventricular epicardial activation time was slightly prolonged (10 msec) in some dogs with right ventricular hypertrophy, but it was not directly related to the severity of the lesion. In the dogs with right ventricular hypertrophy and right ventriclepulmonary artery systolic pressure differences greater than 40 mm Hg, the activation of the right ventricular epicardium was consistently completed after that of the left ventricular epicardium. The delay in right ventricular epicardial activation was best shown by plotting the epicardial data on a simultaneously recorded QRS complex. In the dogs with right ventricular hypertrophy, right ventricular epicardial activation was shifted in time within the QRS complex so that 39% of the sites were activated during the last one-third of the QRS interval; only 1% of the right ventricular epicardial sites were activated during this time in the normal group. The QRS electrocardiographic changes in right ventricular hypertrophy were associated not only with a slight prolongation in epicardial activation time, but also with a shift in timing of this activation within the QRS complex.
Myocardial Lysosomes in Experimental Atrial Septal Defects
Authors: KOTTMEIER CHARLES A. , WHEAT MYRON W.
Published: June 2012

Preliminary observations in patients undergoing open-heart surgery have suggested that the lysosomes in the right atrium are increased in patients with atrial septal defects. This increase in lysosomes per myocardial cell appears to be directly related to the size of the left to right shunt. The following experiments were performed to see if similar findings could be produced in an experimental model. Atrial septal defects were produced in seven dogs. The biopsy specimens were prepared for ultrastructural examination and viewed with an electron microscope. Lysosomes were counted in representative sections and an estimate of the lysosomes per square micron of heart tissue obtained. The number of lysosomes per square micron of myocardium increased significantly following the creation of atrial septal defects in dogs, with the most marked increase occurring in the right ventricle. Several small atrial septal defects closed spontaneously, as proved by cardiac catheterization, and in these animals the elevated lysosome counts present initially returned toward normal after obliteration of the left to right shunt at the atrial level. Control dogs showed no significant increase in myocardial lysosomes over the 18-month period despite repeated thoracotomies and myocardial biopsy. These studies add further evidence to support the role of the lysosome as an important intracellular organelle which is related to cellular stress.
An Anatomical Evaluation of the Myocardial Length-Tension Diagram
Authors: GAY WILLIAM A. , JOHNSON EDWARD A.
Published: June 2012

A method of examining a small (50 to 100 µ o.d.) strand of living cardiac muscle containing several fibers with a high power optical system is described. When the strand was stretched so that it was just taut, the muscle fibers within were found to be slack and severely buckled. An extension of 40 to 60% of this initial length was required before the fibers became straightened and aligned with the long axis of the strand. This finding can account for the fact that cardiac muscle, unlike skeletal muscle, must be subjected to considerable passive tension before its maximum active tension can develop. The resting sarcomere length (that observed when the fiber is just straightened) was 2.0 to 2.2µ. Overall strand length and sarcomere length were measured and had no accurately predictable relation. Rabbit papillary muscle fixed at a length at which the passive tension was just zero showed similar buckling of the muscle fibers. The collagen content (in the form of hydroxyproline analysis) of heart muscle was approximately 6 times that of skeletal muscle. The significance of these findings and their relation to some previously reported mechanical properties of cardiac muscle are discussed.