bluuebunny/crossref_metadata_2025 huggingface dataset:
Additional Evidence for High-Resistance Inter-calated Discs in the Myocardium
Authors: SPERELAKIS NICK , Egna John
Published: June 2012

Parallel-fibered strips of cardiac (cat papillary) and skeletal (frog sartorius) muscles were mounted in air and action potentials were externally recorded from the middle of the strip. Electric fields, oriented longitudinally with respect to the long axis of the cells, were applied. A pair of stimulating electrodes was located at each end of the strip to test for propagation. Under conditions of blocked propagation produced by addition of isotonic sucrose solution, the cells near the middle of the strip could be tested for direct response to longitudinal fields. In long-celled skeletal muscle, the sucrose solution produced simultaneously failure of electrical and mechanical response to stimulation across the strip as well as failure of propagation; stimulation at ten times threshold failed to elicit responses. However, in short-celled cardiac muscle, the sucrose solution produced failure of propagation first; electrical and mechanical responses to longitudinal field stimulation continued without a change in threshold. From these experiments it may be concluded that transverse membranes of high resistance are present in cardiac muscle; thus, radial currents are forced to flow through each cell membrane leading to direct excitation.
Intrarenal Distribution of Nutrient Blood Flow Determined with Krypton
85
in the Unanesthetized Dog
Authors: THORBURN GEOFFREY D. , KOPALD HUGH H. , HERD J. ALAN , HOLLENBERG MILTON , O'Morchoe CHARLES C. C. , BARGER A. CLIFFORD
Published: June 2012

A method has been described for the measurement, by means of Kr
85
, of intrarenal nutrient blood flow distribution in the unanesthetized dog. Injection of the isotope into the renal artery is followed by a multi-exponential disappearance curve which can be obtained by external monitoring with a scintillation detector. In acute experiments autoradiographs have demonstrated that the first exponential component represents cortical blood flow; the second, outer medullary blood flow : the third, inner medullary blood flow; and the fourth, hilar and perirenal fat blood flow. The average cortical blood flow in 65 experiments in five kidneys of four nnanesthetized dogs was 472 ml/100 g/min, the outer medullary 132 ml/100 g/min, and the inner medullary 17 ml/100 g/min. Eighty per cent of the radioactivity was distributed initially to the cortex, 16% to the outer medulla, and 2% to the inner medulla. The hilar and perirenal fat, which receives approximately 2% of the initial radioactivity, was estimated to have a flow rate of 21 ml/100 g/min. In addition, a method for the rapid determination of serial cortical blood flow rates has been described. The importance of these findings has been discussed with reference to the anatomy of the kidney, and to the countercurrent concept as it applies to passive reabsorption of lipid soluble substances, and to the maintenance of an osmotic gradient.
Hydrodynamics of Aortic Blood Flow
Authors: FREIS EDWARD D. , HEATH WILLIAM C.
Published: June 2012

A thermistor was used to record the temperature at regular intervals across the aortic diameter of dogs during the continuous infusion of cold indicator solution at various upstream locations. The results showed that the indicator mixed across the greater part of the diameter of the aorta in the ascending portion and proximal half of the arch but maintained a more streamlined pattern in the distal portion of the arch and descending thoracic aorta. These observations were confirmed by cineangiography. When two thermistors were located in different positions in the aortic root, and when cold saline was injected suddenly in their vicinity, the temperatures recorded by the two thermistors equalized immediately following the onset of systole. Sound waves also were detected during the systolic interval in the ascending but not in the descending aorta.

These findings are consistent with the presence of disturbed, but not necessarily turbulent flow in the ascending aorta; and with predominantly streamlined, but not necessarily completely laminar flow in the descending portion. The factors producing disturbed flow in the aortic root and the transition of flow to a more streamlined pattern in the descending portion are discussed in hydrodynamic terms.

It is postulated that during systole the blood ejected into the aorta separates from a slower moving boundary layer near the walls and at the edges of the valve cusps. This separation produces disturbed flow and mixing in the entering jet. While the thin layer adjacent to the walls as well as stagnant areas behind the valves do not fully mix with the central stream, they represent a relatively small proportion of the total aortic blood flow. Additional mixing is produced by the prominent backflow in early diastole and by the branchings of the coronary and brachiocephalic arteries.
Measurement of Local Blood Flow with Hydrogen Gas
Authors: AUKLAND KNUR , BOWER BRUCE F. , BERLINER ROBERT W.
Published: June 2012

When a platinized platinum electrode is polarized at the potential of the standard calomel electrode, the current generated is proportional to the concentration of dissolved hydrogen gas. The effects of physiological variations in oxygen tension, pH, temperature, and ascorbic acid concentration were found to be negligible. Although absolute calibration in vivo is not possible, the rate of tissue hydrogen saturation or desaturation can be measured by needle-shaped electrodes inserted into the tissue. Arterial and venous concentration can be measured with catheter electrodes. Solubility of hydrogen gas in kidney slices was found to be the same as in blood. With the assumption that tissue is in instantaneous diffusion equilibrium with local venous blood with respect to hydrogen, the local blood flow per volume of tissue can be calculated according to the Fick principle from the rate of tissue desaturation when arterial concentration is lowered to zero.

The method was tested on dogs in myocardium, kidney, and skeletal muscle. Hydrogen was administered by respiration or by intra-arterial infusion of hydrogen-saturated saline, giving an arterial concentration of 3% to 5% saturation. Tissue desaturation curves were recorded simultaneously from two to three tissue electrodes. Good agreement with flow measured simultaneously with other methods was obtained in myocardium and renal cortex, while the data on skeletal muscle do not permit any definite conclusion. The main virtue of this method lies in the fact that repeated measurements of local blood flow can be obtained without access to arterial or local venous blood. Reliable measurements of regional blood flow were also obtained from continuously recorded venous desaturation curves, which also provide information on the distribution of blood flow.
Effects of Sodium Pentobarbital on Electrical and Reflex Activation of the Cardiovascular System
Authors: PEISS CLARENCE N. , MANNING JOHN W.
Published: June 2012

The effects of small doses of sodium pentobarbital (5 mg/kg) on the cardiovascular responses to stimulation of the medulla, hypothalamus, stellate ganglia and sciatic nerve, and to bilateral occlusion of the carotid arteries were studied. It was concluded that: 1) this drug depressed cardiovascular responses to all of these procedures except stimulation of the stellate ganglia; 2) the effects of the anesthetic in this dose are referable to some part(s) of the central nervous system; 3) cardiovascular responses to hypothalamic stimulation were depressed more than those elicited by stimulation of the dorsal medullary reticular formation.
Contribution of Baroreceptors to the Control of Renal Function
Authors: GILMORE JOSEPH P.
Published: June 2012

Electrical stimulation of the left stellate ganglion of the dog is associated with an increase in urine flow, in electrolyte and total solute excretion, and in the renal clearance of inulin. These changes appear rapidly, are well maintained during prolonged stimulation, and stop soon after stimulation has ceased. The hemodynamic responses associated with these changes are an increase in arterial pulse pressure, an increase or no change in mean arterial blood pressure, and a decline in mean left atrial pressure. The diuretic response to stellate ganglion stimulation is diminished, but not abolished, by bilateral cervical vagotomy as are the changes in electrolyte excretion, total solute excretion, and the renal clearance of inulin. However, the hemodynamic responses are not greatly modified by cervical vagotomy. Vagotomy just above the diaphragm does not appear to modify these responses. The effect of vagotomy on the renal responses to stellate stimulation appears to be a result of sectioning baroreceptor afferent nerves which traverse the vagus nerves. The rapidity of the renal response to stellate stimulation, its temporal relation to the hemodynamic changes, and the effect of cervical vagotomy indicate that the diuresis is, to a large degree, secondary to withdrawal of renal sympathetic vasoconstrictor nerve discharge. The similarities between the renal responses to stellate stimulation and to intravenous infusions indicate that infusion diuresis may be mediated, at least in part, by the same mechanism.

When renal blood flow is measured directly in the perfused kidney, carotid occlusion is associated with little change or with a decrease in renal blood flow at a time when renal arterial pressure increases. When renal blood flow is maintained constant in the perfused kidney, carotid artery occlusion is associated with an increase in renal arterial pressure. The intrarenal administration of the adrenergic blocking agent, phenoxybenzamine, can prevent the increase in renal vascular resistance during carotid occlusion indicating that it is due to an adrenergic mechanism. The renal pressure-flow curve is displaced down and to the right during carotid occlusion; autoregulation of renal blood flow is still observed, although at a lower level of blood flow. All these changes indicate that the primary renal response to carotid occlusion is vasoconstriction mediated by the renal sympathetic nerves.

It is well-known that urine flow increases when renal arterial pressure is increased independent of a change in the activity of the renal vasoconstrictor nerves and independent of a change in renal blood flow. Consequently, the rise in arterial pressure associated with carotid occlusion can contribute directly to the response of the kidney to carotid occlusion. The variability of the changes in water and electrolyte excretion by the kidney during carotid occlusion may represent a varying contribution of direct and reflex mechanisms to the total response.
Aortic Lipoprotein Lipase Activity in Relation to Species, Age, Sex, and Blood Pressure
Authors: MALLOV SAMUEL
Published: June 2012

It has been suggested that lipoprotein lipase (LPL) activity may play a role in the etiology of atherosclerosis. To determine whether there is an inverse relationship between arterial LPL activity and the tendency for arteries to become atherosclerotic, determinations were made of the activities of the enzyme in homogenates of the aortas of animals under conditions associated with a greater or lesser tendency for atherosclerosis to develop. It was found that the LPL activities of the aortas of old rats and rabbits were significantly lower than those of young animals of the same species, respectively. Rats, which are resistant to the development of atherosclerosis, manifested about twice the aortic LPL activities that rabbits did, the latter animals being notorious for the ease with which they develop the disease. This was true regardless of the age and sex of the animals compared. These results support the hypothesis that low arterial LPL activity may be associated with increased atherogenesis. Aortas of female rats or rabbits, however, showed no greater LPL activities than did aortas of males of the same species. Renal and desoxycorticosterone-salt hypertensions were accompanied by significant increases rather than decreases in aortic LPL activity. The latter results are not consonant with the aforementioned hypothesis.
Structural Basis for the Static Mechanical Properties of the Aortic Media
Authors: WOLINSKY HARVEY , GLAGOV SEYMOUR
Published: June 2012

The arrangement and interrelation of the structural components of the rabbit aorta were studied by light and electron microscopy. Segments of abdominal aorta were restored to in vivo length and fixed in formalin or osmic acid while intraluminal pressures ranging from 0 to 200 mm Hg were maintained by a constant pressure perfusion apparatus. Transverse, longitudinal, and tangential sections of vessels fixed at various distending pressures were examined. Micrometric measurements included vessel diameters and wall thickness, thickness and waviness of elastin lamellae and interlamellar distances.

With increasing pressures below the diastolic value, aortic radius increased and wall thickness decreased rapidly. Waviness of the tubular elastin lamellae decreased uniformly throughout the wall. Interlamellar distances decreased uniformly and markedly. Lamellar thicknesses decreased uniformly but much less than interlamellar distances. A fine fibrillary elastin network connected the thick lamellae. Collagen fibers showed no definite pattern of orientation.

At and above diastolic pressure radius and wall thickness changed little with increasing pressures. Elastin lamellae were straight and interlamellar distances were uniform; the fibrils of the interlamellar elastin net were arranged obliquely. Collagen fibers were arranged nearly circumferentially. Collagen and elastin fibers were closely intermingled in the narrow interlamellar space but no collagen-elastin connections were obserevd.

The mechanical properties and organization of the collagen and elastin components of the aortic media indicate that the wall normally functions as a "two-phase" material. At and above physiological pressures, circumferentially aligned collagen fibers of high tensile strength and relatively high modulus of elasticity bear most of the stressing force. Elastin lamellae and fibrils of relatively low modulus of elasticity distribute stressing forces uniformly.

Attempts to assess the role of medial pressure and tension gradients in the pathogenesis of aortic disease must take into account the special mechanical properties of this "two-phase" material.
Molecular Characteristics of Canine Cardiac Myosin
Authors: LUCHI ROBERT J. , KRITCHER EVE MARIE , CONN HADLEY L.
Published: June 2012

Cardiac myosin was obtained from the hearts of normal dogs by conventional extraction and precipitation techniques, followed by ammonium sulfate fractionation in the presence of 2.0 M lithium chloride. The molecular characteristics of this protein preparation are presented. Cardiac myosin prepared by this technique shows less tendency than conventionally prepared solutions to denature when stored at 0 to 4°C, and has a significantly higher
ATP
ase activity. Comparison of canine cardiac myosin and skeletal muscle myosin, obtained under identical conditions, revealed no differences between these two proteins in their intrinsic viscosities, S

20.
w

, molecular weight, and UV absorbances, although
ATP
ase activity was lower for cardiac myosin.
Effect of Prolonged Hypoxia Upon Granularity of Renal Juxtaglomerular Cells
Authors: OLIVER WILLIAM J. , BRODY GERALD L.
Published: June 2012

The various experimental models used in previous studies of the juxtaglomerular apparatus do not permit the effect of changes in oxygen tension of the renal parenchyma to be separated from that of changes in distension of the renal arterial bed. To study the isolated effect of prolonged hypoxia, three groups of rats, matched for weight, were kept in low oxygen, room air, and high oxygen environment for two weeks. The animals were pair-fed with the hypoxic rats serving as the determinant group. Supplemental injections of sodium chloride were given daily to avoid the effect of sodium deprivation on the juxtaglomerular cells. It was found that the hematocrits and also the granularity of the juxtaglomerular cells were significantly increased in the hypoxic rats as compared to the other two groups. Blood pressures, serum sodium levels, and urinary excretion of sodium were comparable among the three groups. These findings demonstrate that increased granularity of the renal juxtaglomerular cells can be induced by prolonged hypoxia.
Hemodynamic Aspects of Prolonged Infusion of Angiotensin into Unanesthetized Dogs
Authors: OLMSTED FREDERICK , PAGE IRVINE H.
Published: June 2012

Arterial pressure, cardiac output, stroke volume, heart rate, and peripheral resistance have been recorded daily in eight trained, healthy dogs with implanted aortic flow probes and aortic catheters. After suitable control periods angiotensin
II
was infused for periods of from 2 to 29 days.

The effects observed were considered under four categories: 1) The immediate effects consisted of rise of arterial pressure, decrease of cardiac output and heart rate, rise of peripheral resistance and increased pulse pressure. Within five days all values tended to return to control levels unless the infusion rate of angiotensin was increased. 2) A chronic phase followed and, during this period, cardiac output was normal while arterial pressure and peripheral resistance were elevated. 3) After infusions were stopped pressure and peripheral resistance rapidly declined to be low normal, while cardiac output and heart rate rose to above normal. 4) A transient "malignant" phase was elicited by very large increases in the rate of angiotensin infusion, during which cardiac output and stroke volume were diminished while arterial pressure and peripheral resistance were increased greatly.

The hemodynamic changes resulting from prolonged angiotensin infusion were similar in some respects to those found by us during the onset of hypertension due to renal artery constriction in dogs. They differed, however, in that doses of angiotensin, which were great enough to induce arterial pressure elevations similar to those of chronic experimental renal hypertension, reduced stroke volume, and these higher pressures could not be maintained for more than a few days. Hypertension did not persist after discontinuing angiotensin even after 28 days of almost continuous infusion. There was a distinct tendency for the pressor response to diminish with passage of time; more angiotensin was required to maintain similar elevations of arterial pressure.
Equations for Measuring Blood Flow by External Monitoring of Radioisotopes
Authors: ZIERLER KENNETH L.
Published: June 2012

It is possible by external monitoring alone to measure blood flow per unit volume through any vascular bed accessible to external monitoring of the radioactive tracer if the tracer input function or if the quantity of tracer entering the system is known. The methods proposed exploit the fact that the mean transit time through the system is the flow per unit volume of distribution of tracer. The equations are free of assumptions that require solutions as exponentials or any other specified frequency function of transit times.

If the input function is known, measurement of the concentration of tracer in blood leaving the part sensed by the external detector, combined with external detection of radioactivity, can lead to measurement of absolute blood flow.
Relative Roles of the Sympathetic and Parasympathetic Nervous Systems in the Reflex Control of Heart Rate
Authors: GLICK GERALD , BRAUNWALD EUGENE , Lewis Robert M.
Published: June 2012

This study was designed to define the relative roles of the sympathetic and parasympathetic nervous systems in the reflex alterations of heart rate consequent to changes in arterial pressure. In 23 experiments carried out on 22 anesthetized dogs and in studies performed on four trained, unanesthetized dogs, acute changes in arterial pressure were produced by administering drugs acting on the peripheral vascular bed. The effects of acutely elevating systemic pressure were also investigated in four intact unanesthetized human subjects. Augmenting arterial pressure above control levels with graded doses of phenylephrine always slowed heart rate strikingly. Although complete sympathetic blockade with guanethidine or pronethalol did not significantly alter the degree of slowing, parasympathetic blockade with atropine or vagotomy essentially abolished this response. Conversely, lowering pressure with intravenous injections of nitroglycerin always raised heart rate in the control state, a response abolished by sympathetic blockade with guanethidine or nethalide, but not by parasympathetic blockade with vagotomy or atropine. Thus, when arterial pressure rises above control, the decrease in heart rate is mediated by the parasympathetic nervous system, withdrawal of sympathetic activity playing no detectable role; when pressure falls below control levels, the elevation of heart rate is mediated primarily by the sympathetic nervous system. These findings are not consonant with the traditional concept of control of heart rate which predicates simultaneous reciprocal changes in activity occurring in the two components of the autonomic nervous system.
Relationship of Pericardial to Pleural Pressure During Quiet Respiration and Cardiac Tamponade
Authors: MORGAN BEVERLY C. , GUNTHEROTH WARREN G. , DILLARD DAVID H. , Breazeale Donald G. , McGough George A.
Published: June 2012

Pericardial pressure was studied in chronic experiments on dogs with relation to intrathoracic pressure in the normal state and in cardiac tamponade. In the normal resting animal, the two pressures were in good agreement throughout the respiratory cycle. The cardiac cycle produced superimposed pressure fluctuations amounting to 30% of the respiratory swings.

Adding saline to the pericardial sac produced sigmoid pressure-volume curves; tamponade required 100 to 330 ml of fluid. Although during tamponade the pericardial pressure greatly exceeded the intrathoracic pressure, the pericardial pressure invariably fell with inspiration, generally by the same amount as the intrathoracic pressure. The cardiac cycle produced greater pressure fluctuations (50% of the respiratory pressure fluctuations). The superior vena caval pressure always fell with inspiration in the normal state and during tamponade.

Hypovolemia did not change the resting pericardial pressure, but decreased the slope of the pressure-volume curve measured during cardiac tamponade. Hypervolemia increased the resting pericardial pressure considerably, and increased the slope of the pericardial pressure-volume curve.

The results suggest that pleural pressure is a reasonable approximation of the pericardial pressure in normal dogs. There appears to be no substantial evidence that pulsus paradoxus is due to failure of the pericardial sac to transmit inspiratory reductions of pleural pressure.
Effects of Changes in Coronary Blood pH on the Heart
Authors: WANG HSUEH-HWA , KATZ RONALD L.
Published: June 2012

The effects of localized acidosis and alkalosis on coronary blood flow, myocardial contractile force, and heart rate were studied in anesthetized, open-chest dogs. Acidosis of the coronary vascular bed was induced by infusion of 5,5-dimethyl-2, 4-oxazolidinedion (DMO) into the total coronary artery inflow, and alkalosis by infusion of tris hydroxymethyl aminomethane (THAM), Na
2
CO
3
or NaHCO
3
. DMO infusion caused an initial slight increase of coronary blood flow, followed by a decrease. The decrease was accompanied by and attributed to a moderate to marked decrease of myocardial contractile force and bradycardia. THAM and Na
2
CO
3
infusion caused a marked increase of coronary blood flow, associated with a decrease of coronary oxygen A-V difference, indicating coronary vasodilation. A slight to moderate increase of myocardial contractile force but little or no change in heart rate was noted. NaHCO
3
infusion caused changes similar to those induced by DMO but of smaller magnitude. It was suggested that the direct effects of DMO and NaHCO
3
are attributable to intracellular acidosis, whereas those of THAM and Na
2
CO
3
are attributable to intracellular alkalosis.
Functional Characteristics of the Left Ventricular Inflow and Outflow Tracts
Authors: PRIOLA DONALD V. , OSADJAN CHARLES E. , RANDALL WALTER C.
Published: June 2012

Simultaneous pressures were recorded from the left ventricular inflow and outflow tracts in 14 dogs. In 10 the inflow tract entered systole 4 to 18 msec before the corresponding outflow tract. In 12 additional animals, differential pressure recordings from the two tracts confirmed precedence in the inflow tract. In four animals, strain gauge recordings from the epicardial surfaces of the inflow and outflow tracts exhibited asynchrony with precedence in the inflow tract.

Hearts excised from freshly-sacrificed animals or hearts stopped in diastole by KCI infusion showed a single, openly-communicating ventricular chamber. In contrast, hearts arrested in systole by infusion of CaCl
2
revealed a separation of the left ventricle by the apposition of the anterior and posterior papillary muscles and the dependent mitral valve leaflet.

The apparent conduction velocity of an impact pressure wave from inflow to outflow tract depended upon the portion of the cardiac cycle during which it was delivered. From a maximum of 14 M/sec in mid and late diastole, it decreased to 6.9 M/sec in early systole and 5.5 M/sec in early diastole. Complete attenuation of pressure wave transmission often occurred during maximum systole.

These data support the concept that the left ventricle may become separated, during systole, into an inflow and outflow tract. It appears that the division is accomplished by a change in the systolic ventricular architecture, with apposition of the anterior and posterior papillary muscles and the downward movement of the mitral valve leaflets. It is probable that this phenomenon is functional in hearts working near the lower limits of their systolic reserve.
Continuously Recorded Changes of Thoracic Aortic Blood Flow in Man in Response to Leg Exercise in Supine Position
Authors: ZITNIK RALPH S. , RODICH FILMORE S. , MARSHALL HIRAM W. , WOOD EARL H.
Published: June 2012

The constant-rate-injection, indicator-dilution technic was used to determine thoracic aortic blood flow before, during, and after five minutes of single-leg exercise (bicycle ergometer) in five healthy male subjects in the supine position. Resistance to blood flow in the lower body and mean aortic pressure decreased immediately at the onset of exercise, at the same time that thoracic aortic blood flow and heart rate increased. There was a further slow rise of heart rate, mean aortic pressure, and thoracic aortic blood flow along with a decrease of lower body resistance until fairly stable levels were reached after five minutes of exercise. After five and ten minutes' rest all values tended to return toward those observed in the control state. These data are consistent with the concept that baroreceptor activity may play an important part in the early cardiovascular responses to exercise in man. Most of the cardiovascular response to this exercise occurred in the first 30 seconds.
Depression of Ventricular Contractility by Stimulation of the Vagus Nerves
Authors: DEGEEST HILAIRE , LEVY MATTHEW N. , ZIESKE HARRISON , LIPMAN RALPH I.
Published: June 2012

In three different types of canine heart preparations, it was demonstrated that efferent vagal stimulation exerts a potent, negative inotropic influence upon the ventricular myocardium. In the paced, isovolumetric, left ventricle preparation, vagal stimulation evoked a reduction of left ventricular systolic pressure which, within limits, varied directly with the magnitude of the stimulus. Supramaximal stimulation elicited a mean reduction of 23% in the peak pressure generated by the left ventricle. No differences could be detected between the effects of the right and left vagi upon ventricular contractility. The percentage changes induced by vagal stimulation upon ventricular contractility in the paced heart were less than the percentage changes in heart rate induced in the spontaneously beating heart.

In a pumping heart preparation in which a constant rate of venous return was delivered to the left atrium, vagal stimulation consistently elicited an appreciable elevation of left ventricular end diastolic pressure. Another pumping heart preparation was employed in which changes in atrial transport function and mitral valve closure were excluded by the expedient of introducing a balloon into the left ventricle through an apical incision. This balloon was connected to an artificial external circuit with fixed venous reservoir height and peripheral resistance. Vagal stimulation consistently diminished stroke volume, "arterial" pressure, and stroke work in such a circuit.
The Spread of Sinus Activation During Potassium Administration
Authors: VASSALLE MARIO , HOFFMAN BRIAN F.
Published: June 2012

Electrodes were chronically implanted in intact dogs at several locations on the atria and ventricles, and studies made of the effect of an elevated extracellular K
+
concentration on the spread of the sinus impulse throughout the atria. It was found that sinus activity propagates to the coronary sinus and ventricles at a time when the atrial muscle fibers have been rendered inexcitable. The finding of such a sino-ventricular rhythm supports the existence of a specialized conducting path between the sinus and the atrio-ventricular node; this path is particularly resistant to depolarization by potassium. Potassium-induced 2:1 sino-atrial block was described. In vitro experiments provided a demonstration that such block is frequency-dependent and due to marked prolongation of the refractory period provoked by high [K]
0
. It appears that the lengthened refractory period may be due to a marked reduction of the reactivation rate of the "sodium carrying system."
Effect of Exercise on Cardiac Output, Left Coronary Flow and Myocardial Metabolism in the Unanesthetized Dog
Authors: KHOURI EDWARD M. , GREGG DONALD E. , RAYFORD CLAUDIA R.
Published: June 2012

Cardiac output, left coronary artery flow, central aortic blood pressure and myocardial metabolism have been studied in the intact unanesthetized dog during exercise. Cardiac output and left coronary artery flow increase 350 to 400% during moderately severe exercise. The primary mechanical determinant of this increase appears to be cardio-acceleration; the stroke volume and stroke coronary flow contribution is relatively mild. Myocardial oxygen usage increases 300% or more with only a small elevation of the percentage of extraction of oxygen. The large increase of coronary flow in the dog and the significant elevation in hematocrit supply the extra oxygen.
Some Effects of a Cardioactive Fraction Isolated from Human Blood Plasma on the Peripheral Circulation of the Dog
Authors: Nayler Winifred G. , Race David , Price Jocelyn M. , Lowe Thomas E.
Published: June 2012

Using dogs on heart-lung bypass and perfused hind-limb preparations, the effect of the relatively low molecular weight cardioactive plasma fraction on the peripheral circulation of dogs was investigated. This cardioactive plasma fraction raised the arterial blood pressure of dogs on bypass and increased the perfusion pressure in hind-limb preparations. The raised arterial pressure was found to be associated with increased blood flow through the coronary and splanchnic beds; flow through the hind limb decreased. Adrenalectomyand nephrectomy did not abolish these peripheral effects of this plasma fraction. It is concluded that the raised systemic arterial pressures recorded from intact animals following the injection of this plasma fraction may result, in part, from the effect on the peripheral circulation.
Conduction and Automaticity in Rat Myocardium
Authors: Woodson Grattan C. , Bloom Walter Lyon
Published: June 2012

Intraventricular infusion of isotonic potassium chloride solution showed that blocking conduction in the subendocardial tissues of a single ventricle drastically alters normal conduction, with ensuing impulses being transmitted from the opposing ventricle. Blocking the endocardial tissues of both ventricles produces asystole even though the myocardium is capable of contracting as demonstrated by its contractile response to mechanical and electrical stimuli. These observations lend support to the concept that automaticity is a property confined to the specialized tissues of the conduction system.
Coronary Insufficiency: Relations Between Hemodynamic, Electrical, and Biochemical Parameters
Authors: Scheuer James , Brachfeld Norman
Published: June 2012

Perfusion of the left coronary artery of open chest dogs at fixed control and ischemic flow rates demonstrated that ST alterations in the electrocardiogram were always associated with significant hemodynamic and metabolic changes. Decreased pressure time per minute, atrial hypertension, increased myocardial oxygen extraction, and the presence of excess lactate accompanied ischemia. In three dogs, hemodynamic changes, the presence of "excess lactate," or both, preceded significant electrocardiographic changes.

Whenever coronary flow was insufficient to meet myocardial oxygen demands, a series of metabolic shifts occurred. The most significant of these was inadequate aerobic energy production and stimulation of anaerobic glycolysis. This acceleration of anaerobic myocardial metabolism may be present without notably altering the surface electrocardiogram. The absence of ST shifts does not rule out the presence of concomitant and potentially severe myocardial ischemia.
Regional Cerebral low in Man Determined by Intral-artrial Injection of Radioactive Inert Gas
Authors: Høedt-Rasmussen K. , Sveinsdottir Edda , Lassen Niels A.
Published: June 2012

The intra-arterial injection of a radioactive inert gas is described for measurement of regional cerebral blood flow in man from externally recorded clearance curves.

The stochastic analysis for calculating the average cerebral blood flow in ml/100 g/min is compared to an analysis of the curve into two compartments with fast and slow clearance rates representing flow in grey and white cerebral matter respectively. An estimate of the relative weight of the grey matter in the cerebral region counted from brain is also obtained.

A detailed description is given of the experimental procedure using krypton
85
or xenon
133
as the tracer gas. A brief injection time and short time constant in the recording ratemeter are important for obtaining a correct estimate of the maximal height of the curve. Mono-exponential extrapolation beyond the time of observation (usually 15 minutes) is employed. The practical procedure for calculating the results according to the stochastic and compartmental models are described with particular emphasis on the simple "10 minutes-average-flow-value, "
CBF
(10) which corresponds directly to the results of the classical Kety-Schmidt inert gas inhalation method for measurement of the average blood flow of the whole brain.
Alterations with Age in the Viscoelastic Properties of Human Arterial Walls
Authors: Learoyd Brian M. , Taylor Michael G.
Published: June 2012

The circumferential incremental Young's modulus was measured in 59 major arteries of both "young" (less than 35 years of age) and "old" (greater than 35 years of age) subjects.

Dynamic measurements of wall elasticity and viscosity were made which indicated a high viscosity in the femoral arteries. This was attributed to their high content of muscle.

Although the "young" group showed, at any given pressure, an increasing wall stiffness towards the periphery, in "old" arteries, an opposite trend was found. When dimensional changes (radius and wall thickness) in the "old" group were considered it was apparent that at all sites the arterial wall tissue became weaker with age. Nevertheless, as a consequence of these dimensional changes the impedance characteristics of the old arterial tree still retained the nonuniformity (an increase towards the periphery) of the "young" which has considerable haemodynamic advantage.
Cardiovascular Effects of Sustained Norepinephrine Infusions. III. Lactic Dehydrogenase Isoenzyme Release
Authors: Schenk Eric A. , Galbreath Robert , Moss Arthur J.
Published: June 2012

Infusion of norepinephrine (NE) in dogs in doses of 1 to 4 µg/kg/min resulted in a rapid and dose related increase in serum lactic dehydrogenase (LDH) and those isoenzymes of LDH present in the heart. Histochemically definable lesions in the heart were correlated with the isoenzyme release produced by 2 and 4 µg/kg/min NE infusion.

Evidence of LDH isoenzyme release from organs other than the heart was found only in dogs in the highest dose group that, in addition, had evidence of low cardiac output.
Nonlinear Analysis of the Baroreceptor Reflex System
Authors: Levison William H. , Barnett G. Octo , Jackson William D.
Published: June 2012

The regulation of blood pressure by the baroreceptor reflex was examined in anesthetized dogs. The receptor feedback path was broken by surgical intervention, the input (carotid sinus pressure) was controlled by an external servo system, and simultaneous records of input and output (systemic arterial pressure) were obtained. A variety of pressure waveforms were applied to the carotid sinus so that the nonlinear behavior could be explored thoroughly. Most of the input waveforms consisted of relatively small signals about an operating point in the normal blood pressure range.

The nonlinear behavior of the reflex was illustrated in a number of ways. Square waves, sinusoids, and short pulses produced asymmetric arterial pressure waveforms. An overshoot in the arterial pressure always followed the rising edge of the input square wave, but was generally absent following the negative-going part of the square wave. Either positive or negative pulses caused a transient drop in arterial pressure. The sinusoidal response was often distorted, with the falling portion of the output waveform steeper than the rising portion. The system behaved as a rectifier, or envelope-detector, as illustrated by 1) the decrease in mean arterial pressure when either the amplitude or the frequency of a sinusoidal input was increased and 2) the appearance in the arterial pressure waveform of a component correlated with the envelope of a modulated carrier. Another nonlinear phenomenon was the decrease in low-frequency sinusoidal gain caused by the addition of a high-frequency sinusoid to the sinus pressure waveform. This behavior indicates that if closed loop behavior in the intact animal is to be predicted from the open loop sinewave response, the effects of the cardiac pressure pulse must be considered.

A model was constructed from standard electronic components to simulate the input-output behavior of the baroreceptor reflex. The model was able to simulate the response to high- and low-frequency sinusoids and to reproduce the essential features of the square-wave and pulse responses. On this basis the model was considered adequate for simulating the performance of the baroreceptor reflex in certain open loop and closed loop situations.
Effects of Cyclopropane and of Hypoxia on Transmembrane Potentials of Atrial, Ventricular and Purkinje Fibers
Authors: Davis Larry D. , Temte John V. , Helmer Phyllis R. , Murphy Quillian R.
Published: June 2012

The effects of cyclopropane (6 to 8 vol% in Tyrode solution) and of hypoxia, on the transmembrane potentials of atrial, ventricular and Purkinje fibers of the dog heart, were studied. Action potentials were recorded during perfusion with solution equilibrated with 95% O
2
, and 5% CO
2
(control-Tyrode); during cyclopropane-Tyrode perfusion and during perfusion with solution in which nitrogen replaced cyclopropane (nitrogen-Tyrode). Changes in transmembrane potential observed during cyclopropane-Tyrode treatment were considered to be due to an action of cyclopropane only if they recovered or failed to appear during nitrogen-Tyrode perfusion. By interpretation on this basis it could not be determined that cyclopropane exerted an effect on atrial or ventricular fibers. In Purkinje fibers cyclopropane caused a significant increase in rate of repolarization during the plateau (phase 2) while the rate during the period of rapid repolarization (phase 3) decreased. The time required to repolarize to minus 60 millivolts was shortened significantly while the durations of the terminal phase of repolarization and of the total action potential were lengthened. A relative hypoxia averaging 300 mm Hg accelerated repolarization and reduced resting potential of atrial cells. Ventricular cells were affected similarly but only after two or more periods of hypoxia. Purkinje fibers were shown to be most resistant to this level of hypoxia.
Effect of Ca
++
upon Contractility of Small Arteries from DCA-Hypertensive Rats
Authors: HINKE JOSEPH A. M.
Published: June 2012

Segments of the ventral tail artery from DCA-hypertensive and normotensive rats were artificially perfused at pressures from 60 to 120 mm Hg. Contraction of the segments was induced by the addition of norepinephrine to the perfusate or by increasing the K+ concentration of the perfusate. Contraction was abolished by removing Ca
++
from the perfusate and re-established by addingCa
++
to the Ca
++
-free perfusate.

The experiments demonstrate hyperresponsiveness of the hypertensive artery in three ways: first, the hypertensive artery performed more work than the normotensive artery; second, contraction in the hypertensive artery was more difficult to abolish during zero Ca
++
perfusion; and third, less Ca
++
was required to re-establish the abolished contraction in the hypertensive artery.

When the artificially perfused artery segments were analyzed for cations, the hypertensive arteries were found to contain increased amounts of Na
+
, K
+
, Mg
++
, and Ca
++
. After zero Ca
++
-Krebs perfusion, the hypertensive and normotensive arteries contained similar amounts of Ca
++
and Mg
++
, indicating that more Ca
++
was removed from the hypertensive artery.

The results suggest that hyperresponsiveness may be due to an increased efficiency in either Ca
++
utilization during excitation coupling or in the contractile mechanism itself.
Left Ventricular Ejection in Conscious Dogs:
Authors: NOBLE MARK I. M. , TRENCHARD DIANA , GUZ ABRAHAM
Published: June 2012

The maximum acceleration of blood from the left ventricle was studied in conscious dogs in which ascending aortic blood flow was measured with an electromagnetic flowmeter; normal values at rest ranged between 5 and 11
g
. The left ventricular myocardium was stimulated with intracoronary injections of calcium gluconate and isopropylnorepinephrine; maximum acceleration, peak flow, and the rate of rise of left ventricular pressure were the only parameters, measured or derived, that showed a consistent increase. The largest increase always occurred in maximum acceleration. Changes of posture, with the presumed associated changes in end diastolic dimensions, did not alter the maximum acceleration. The results suggested that maximum acceleration was closely related to the maximum force exerted by the heart in initial systole, and to the maximum initial velocity of shortening of left ventricular muscle. Temporary regional myocardial ischaemia produced larger and earlier decreases in maximum acceleration than in other parameters measured suggesting that it was a sensitive index of myocardial contractile function.
Measurement of Individual Ventricular Outputs in the Fetal Lamb by a Dye Dilution Technique
Authors: MAHON WILLIAM A. , GOODWIN JAMES W. , PAUL WILLIAM M.
Published: June 2012

Individual ventricular outputs were measured in 25 fetal lambs using an indicator dilution method. Small volumes of indocyanine green were injected through catheters placed in the individual ventricles; sampling for the left ventricle was from a catheter placed in the brachiocephalic artery through the carotid artery and for the right ventricle sampling was from a catheter placed in the ductus arteriosus via a femoral artery and the aorta. Mean left ventricular output obtained by this method was 181.7 ml/kg per min and mean right ventricular output was 179.7 ml/kg per min. We suggest that the rapidity of preparation and relative lack of trauma involved in this method may account for values that are higher than those reported previously.
Reduction of the Cardiac Response to Postganglionic Sympathetic Nerve Stimulation in Experimental Heart Failure
Authors: COVELL JAMES W. , CHIDSEY CHARLES A. , BRAUNWALD EUGENE
Published: June 2012

The functional significance of the reduction of the heart's norepinephrine stores which occurs in experimental heart failure was studied. The responses to right and left cardio-accelerator nerve stimulation were studied in normal dogs and in dogs with chronic congestive failure and reduced myocardial norepinephrine stores. Both the chronotropic and inotropic responses to nerve stimulation were found to be markedly reduced in the animals with congestive failure. Since the myocardium of the dogs with heart failure responded normally to exogenously administered norepinephrine, it was concluded that the norepinephrine depletion reduces the quantity of neurotransmitter released per nerve impulse. Thus, norepinephrine depletion interferes with the ability of the adrenergic nervous system to support the failing myocardium and in this manner it may intensify the congestive heart failure state.
Blood Supply of the Myocardium after Temporary Coronary Occlusion
Authors: KRUG ARNO , DE ROCHEMONT WOLFGANG DU MESNIL , KORB GERHARD
Published: June 2012

A coronary artery and the accompanying vein were ligated temporarily for 30, 60 and 120 minutes in 39 cats. By labelling the blood with the fluorescent dye acridine orange, the intravital blood supply of the myocardium was investigated 5 minutes to 6 hours after release of the ligature. The region supplied by the temporarily ligated coronary artery (RSCA) was demonstrated by postmortal perfusion of this vessel using the dye light green. Resumption of circulation in the deeper layers of the RSCA was delayed after a prior coronary occlusion, even occasionally after occlusions lasting only 30 minutes. After a coronary ligation of 60 to 120 minutes the inner layers of the RSCA became the sites of prolonged disturbance of blood supply. The circulatory abnormality observed immediately following release of the ligature did not result from intraluminal vascular obstruction. Even after a temporary ischemia lasting 120 minutes it was still possible, immediately after removal of the ligature, to perfuse an intravitally ischemic portion of the RSCA. The significance of these results for the determination of the so-called "revival-time" of the cardiac muscle is pointed out.
Complete Atrioventricular Block Due to Potassium
Authors: FISCH CHARLES , GREENSPAN KALMAN , EDMANDS ROBERT E.
Published: June 2012

Intravenous infusion of KC1 at a rate of 1.22 or 2.45 mEq per minute to anesthetized dogs frequently resulted in complete A-V block at a time when P waves were still recorded in the ECG. Furthermore, some of the observations suggest that in hyperkalemia a regular idioventricular rhythm may not be essential for the diagnosis of complete atrioventricular (A-V) block. Thus, with complete A-V block induced during a rapidly changing plasma K
+
, the ventricular pacemaker may be irregular.

In addition, evidence was obtained that some parts of the atrial tissue, the automatic ventricular focus and the ventricular myocardium, are more resistant to K
+
than is the A-V conduction tissue. The relative sensitivity of the various tissues of the heart seems to depend, among other factors, on the rate of KCl infusion.