bluuebunny/crossref_metadata_2025 huggingface dataset:
Autoregulation of Coronary Blood Flow: Effect of Interarterial Pressure Gradients
Authors: DRISCOL THOMAS E. , MOIR THOMAS W. , ECKSTEIN RICHARD W.
Published: June 2012

In the normal heart, transient and adjusted steady state coronary flow rates in response to changes in perfusion pressure are not significantly affected by collateral flow into and from heart muscle surrounding the area perfused by a test artery. An active autoregulatory adjustment tends to counteract flow changes after perfusion pressure is changed. This adjustment is sometimes sufficient to increase vascular resistance above control values. Usually, however, coronary resistance decreases at higher perfusion pressures even though autoregulation is present. The experiments provide no evidence for reflex control of coronary resistance in response to increases in aortic pressure; the initial flow changes can be accounted for by the corresponding increase in perfusion pressure. It is necessary to examine the entire coronary flow pattern after a sudden change in perfusion pressure in order to formulate concepts which include all the important determinants of coronary blood flow.
Mechanics of the Human Common Carotid Artery in Vivo
Authors: GREENFIELD JOSEPH C. , TINDALL GEORGE T. , DILLON MARCUS L. , MAHALEY M. S.
Published: June 2012

The relationships between lateral intravascular pressure, vessel radius, and vessel length were evaluated in the common carotid artery in vivo in thirteen patients during treatment by surgery. Strain was measured in the wall of the carotid artery by means of an electrical caliper sutured to the vessel wall. Lateral intravascular pressure was measured directly with either an 18-gauge needle or a short polyethylene catheter connected to a Statham, P23Db, strain gauge. The results indicate that circumferential and longitudinal strains in the common carotid artery were both small. The mean systolic change in cross-sectional area was 2.10% (±SD 1.08) of the end diastolic area. In three patients a negative circumferential strain was produced by making the cross section of the vessel elliptical. During systole, longitudinal strain increased in four patients and decreased in six patients. The average change in vessel segment length during systole was approximately 1.0% of the end diastolic length.
Circulatory Changes Following Birth of the Calf and the Effect of Hypoxia
Authors: REEVES JOHN T. , LEATHERS JAMES E.
Published: June 2012

Circulatory and ventilatory measurements were made during the course of 66 cardiac catheterizations in 20 unanesthetized Jersey calves, age two hours to eight weeks. The salient findings were:

1. The pulmonary arterial pressure was high during the first two to three hours of extra-uterine life (up to 80 mm Hg) and it decreased rapidly (30 to 40 mm Hg) during the next nine to ten hours.

2. The pulmonary ventilation appeared good, judging by the active appearance of the calves, the volumes of respired air, the arterial blood gases, and the ventilatory response to hypoxia.

3. The pulmonary blood flows in these calves were not higher in the first hours of life than on subsequent days, and there was little contribution to the pulmonary blood flow by a left to right shunt through the ductus arteriosus.

4. Hypoxia, if severe, could increase the pulmonary arterial pressure to systemic levels on the day of birth, but not in older calves.

5. Pulmonary vasoconstriction sometimes followed puncture of the aorta or other procedures in calves less than twelve hours old. The lability of the pulmonary blood vessels during the first hours of extra-uterine life suggested that large changes in pulmonary vascular tone also occur in utero.
Instantaneous Pressure Distribution Along the Human Aorta
Authors: LUCHSINGER PETER C. , SNELL ROBERT E. , PATEL DALI J. , FRY DONALD L.
Published: June 2012

Pressures at various points of the human aorta were recorded and resolved into their sinusoidal components by Fourier analysis. A progressively decreasing phase angle with distance along the aorta was found. This was considered compatible with a traveling wave system. The pressure moduli generally increased with distance along the aorta. This was attributed to the progressively increasing stiffness of the aorta peripherally. Minor undulations in moduli could be explained on the basis of superimposed reflections.

The apparent phase velocities were calculated for various points along the aorta. They tended to converge at higher frequencies to a value of 5 m/sec.
Cerebral Blood Flow Determined by Saturation and Desaturation with Krypton
85
:
Authors: LASSEN NIELS A. , KLEE AXEL
Published: June 2012

Cerebral blood flow was studied in 11 subjects using the krypton
85
method during a 10-minute saturation period followed by a 10-minute desaturation period. The calculated cerebral blood flow averaged 8.5% higher during
desaturation
than during
saturation
for the eight cases with blood flow values in the normal range. At higher flow (one case) the deviation was less pronounced, while at lower flows (two cases) the percentage difference increased. It is suggested that this systematic difference is due to the failure, at 10 minutes, of reaching equilibrium between average tissue and mixed venous blood in the human brain.

The studies disclose a systematic error inherent in the Kety-Schmidt technique. According to observations in the literature this error is, however, not of such magnitude that it affects seriously the method as applied to the brain. Employing an inert gas saturation period of 10 minutes, an overestimation of the flow by about 10% probably occurs in normal subjects, while at subnormal flow levels the magnitude of this error increases somewhat. The error mentioned may be counteracted by prolonging the saturation period to 15 or 20 minutes and by extrapolation of the curves to infinity.
Systemic and Coronary Energetics in the Resting Unanesthetized Dog
Authors: GREGG DONALD E. , KHOURI EDWARD M. , RAYFORD CLAUDIA R.
Published: June 2012

This report is an initial attempt to study the coronary circulation in the chronic unanesthetized dog. A standardized preparation has been developed in which phasic aortic pressure and flow, phasic left coronary inflow, and myocardial metabolism have been studied for many weeks in the unanesthetized dog under resting conditions.

The flow patterns in the main left coronary artery and in its major branches are very similar. In the resting dog, the left coronary inflow during systole is 7 to 45% of that during diastole. We believe that much of this flow into the epicardial arteries penetrates into the myocardium. Stroke coronary flow can change considerably without significant alterations of blood pressure and heart rate. Despite this, the coronary flow values (37 to 58 cc) and oxygen usage values (4.4 cc to 8.6 cc) per 100 grams left ventricle per minute are low. Since, however, these measurements can vary considerably not only in different dogs but also in the same dog on the same day, and from day to day, it is suggested that these animals were in a semiresting state and probably not in a basal state.
Oscillatory Flow Impedance in Electrical Analog of Arterial System:
Authors: JAGER GERARD N. , WESTERHOF NICO , NOORDERGRAAF ABRAHAM
Published: June 2012

In the analog computer for the human systemic circulatory system, the electrical equivalents of a segment of artery as designed up till now are not satisfactory, because they lack representation of the sleeve effect, which results from the interaction between viscous and inertial forces during pulsatile blood flow. First, a network which accounts for this effect was derived, starting out from entirely different equations. It was surprising to find that this does not alter the circuit completely, but only requires adding to the former circuit a corrective network which, however, may have considerable influence.

Second, the effect of the anomalous viscosity of blood was taken into account. Its influence on oscillatory flow has been investigated by Taylor, who derived an expression for the relation between pressure-gradient and flow under the assumption that there exists a small boundary layer of lower viscosity at the wall, and found a similar formula for the case in which the blood is assumed to slip at the wall. The modifications of the electrical circuit, necessary to represent these conditions, are given in this paper and turn out to be remarkably simple.
Steroids Produced in Vitro by Adrenal Glands of Normal and Arteriosclerotic Rats During and After Drug-Induced Myocardial Necrosis
Authors: WEXLER BERNARD C. , KITTINGER GEORGE W. , Schreiber Joan E.
Published: June 2012

The subcutaneous injection of the potent catecholamine, isoproterenol, on two consecutive days causes active and massive myocardial necrosis in rats. Infarctoid myocardial necrosis was produced in male and female virgin rats free of arterial disease, in male breeder rats which have microscopic arteriosclerosis only, and in female breeder rats having early or advanced gross arteriosclerosis. During the active development of myocardial necrosis and heart failure, an apparent shift in distribution of body fluid produced systemic dehydration, pulmonary edema, and hydrothorax. Animals which survived the myocardial destruction showed gradual reduction of the congestive heart failure and beginning myocardial repair. Virgin animals with no pre-existing arterial disease developed more severe signs of shock and congestive heart failure than breeder rats with pre-existing arteriosclerosis.

In vitro estimation of the adrenal steroids produced by the animals with myocardial necrosis indicated intense in vivo stimulation of adrenocorticoid production coincident with the increasing severity of the myocardial necrosis. Steroid production returned to normal during progressive myocardial repair. Virgin rats showed a very prompt adrenal response to the stress of myocardial destruction but breeder rats, which also have pre-existing reduced adrenal function, showed a lag in the response of their adrenal glands. Chemical and histological analyses of the adrenal glands indicated a pronounced increase of aldoster-one production during the experiment, this increase being associated with loss of fluid and electrolytes from the vascular space. The production of aldosterone appears to be vital to the physiological adjustments needed by these animals during heart failure because the production of aldosterone seems to occur at the expense of the other adrenal steroids, e.g., corticosterone, 18-hydroxy-deoxycorticoster-one and total steroid. These comparative studies suggest that adrenal responsiveness during the stress of myocardial infarctoid necrosis is quantitatively different in animals free of previous arterial disease from that found in animals with pre-existing microscopic or grossly visible arteriosclerosis. The specific kind and the amount of adrenal steroid produced during myocardial destruction may be of vital importance for survival.
Electroaugmentation of Ventricular Performance and Oxygen Consumption by Repetitive Application of Paired Electrical Stimuli
Authors: ROSS JOHN , SONNENBLICK EDMUND H. , KAISER GERARD A. , FROMMER PETER L. , BRAUNWALD EUGENE
Published: June 2012

When a depolarizing stimulus is delivered to the ventricle immediately following the refractory period, little extrasystolic contraction occurs and repetitive paired stimulation then results in a marked and sustained improvement of ventricular performance which has been termed electroaugmentation. The present study characterizes this augmentation and its effects on myocardial oxygen consumption (MV

O

O
2

). In 45 experiments on 14 dogs in which mean aortic pressure and stroke volume were held constant by right heart bypass, a change from single to paired stimulation at identical contraction rates markedly increased the performance of the left ventricle as evidenced by shortening of ejection time increase in left ventricular dp/dt, stroke power, and peak ejection rate, and sometimes a fall in end diastolic pressure. Similar resul were obtained after administration of resepine or nethalide. In 15 experiments on 11 dogs the stroke volume of the left ventricle was varied during single and paired stimulation. Improvement in left ventricular performance during paired stimulation was always evidenced by increased speed of contractic and an upward displacement of the curvesrelating end diastolic pressure to stroke powe mean and peak ejection rates, and some times by an upward displacement of the curves relating end diastolic pressure to stroke volume and stroke work. In eight experiments MV
·

O

O
2

was determined during single and paired stimulation, stroke volume, mean aortic pressure, and contraction rate being held constant. Paired stimulation always increased MV
·

O

O
2

the average increase being 35%. Despite the rise in MV
·

O

O
2

, a reduction in the tension-time index always occurred. These studies indicate that repetitive paired stimulation exerts a powerful and sustained positive inotropic in fluence on the mammalian ventricle and that at a relatively constant level of external world the increased velocity of ventricular contraction which accompanies this effect results in an increase in MV
·

O

O
2

.
An Intrinsic Adrenergic Vasodilator Mechanism in the Coronary Vascular Bed of the Dog
Authors: KLOCKE FRANCIS J. , KAISER GERARD A. , ROSS JOHN , BRAUNWALD EUGENE
Published: June 2012

The question of whether the coronary blood vessels contain an intrinsic adrenergic mechanism for vasodilatation has been examined by studying the response of the coronary vessels of the dog to isoproterenol. Initially, coronary blood flow, coronary sinus P

O

O
2

, mean arterial pressure, and heart rate were measured continuously in anesthetized, open-chest animals. When isoproterenol, 0.1 to 0.3 µg/kg/min, was given intravenously, coronary flow and coronary sinus P

O

O
2

always increased in spite of tachycardia and a reduced or unchanged arterial pressure. Although this response suggested a primary vasodilating effect of isoproterenol, a vasodilatation consequent to increased myocardial activity or an extracardiac factor could not be eliminated. Accordingly, additional studies were performed in an isolated heart arrested with potassium and perfused with whole blood at constant rates of flow. Isoproterenol was given by single injections and constant infusions and always produced a decrease of perfusion pressure. These decreases could be blocked by nethalide and, as indicated by measurements of myocardial oxygen uptake and coronary venous P

O

O
2

, did not depend upon increased myocardial metabolism or decreased myocardial oxygenation. With injections of 0.01, 0.1, 1.0, and 10.0 µg of isoproterenol, the decreases averaged respectively 3, 8, 14, and 26% of the control pressures. It is concluded that the coronary vessels of the dog do contain an intrinsic adrenergic mechanism for vasodilatation.
Measurement of Pulmonary Edema
Authors: PEARCE MORTON LEE , YAMASHITA JOE , BEAZELL JAMES
Published: June 2012

Two methods for the measurement of pulmonary edema are compared. The first method, which permits serial measurements in vivo, depends on the difference in mean transit time of a water label and an intravascular label. The second method is a postmortem one in which total lung water is measured and allocated to the pulmonary blood or to pulmonary extravascular water.

Three groups of six dogs each were studied: controls, a group with pulmonary edema produced by elevating pulmonary venous pressure, and a group with pulmonary edema produced by alloxan. The isotopic as compared with the postmortem method accounted for 71% of the pulmonary extravascular water found in the controls, 94% in high pressure edema and 57% in alloxan edema. Shunting, as measured by a large fall in PaO
2
despite 100% oxygen breathing, became marked in a second group of five alloxan dogs and only 31% of the postmortem pulmonary extravascular water was measured by the isotope method.

It is concluded that the isotope transit time method is a useful one for the serial measurement of pulmonary edema in vivo. The edema water is determined more accurately when pulmonary edema is due to elevated pulmonary venous pressure than when due to increased vascular permeability.
Direct Renal Vasodilatation Produced by Dopamine in the Dog
Authors: McNAY JOHN L. , McDONALD ROBERT H. , GOLDBERG LEON I. , Davis Carolyn
Published: June 2012

The effects on directly measured renal blood flow, mean blood pressure, and calculated renal vascular resistance of intravenous infusions of dopamine, isoproterenol, and norepinephrine were compared. Dopamine, at doses not affecting mean blood pressure, decreased renal vascular resistance and increased renal blood flow. In contrast, isoproterenol decreased both blood pressure and renal vascular resistance but did not consistently increase renal blood flow. Renal artery injection of dopamine produced vasodilatation at doses ranging from 0.75 to 12 µg and biphasic flow responses including transient vasoconstriction at higher doses. It is concluded that the probable basis for the effect of intravenous dopamine infusion on renal blood flow is its direct renal vasodilating action.

The direct effect of dopamine on the femoral vascular bed is vasoconstriction. The combination of renal vasodilating, and femoral vasoconstricting, effects is unique and is interpreted as evidence for a renal vasodilating effect of dopamine distinct from the conventional beta-adrenergic mechanism. A possible physiological role for dopamine other than as a precursor to norepinephrine may be related to this property. It is also suggested that the ability of dopamine to alter the distribution of cardiac output in favor of visceral organs may find useful clinical applications.
Some Properties of a Cardioactive Substance Isolated From Human Plasma
Authors: NAYLER WINIFRED G. , ROBERTSON PETER G. C. , PRICE JOCELYN M. , LOWE THOMAS E.
Published: June 2012

Some effects of a relatively low molecular weight substance, isolated from human plasma, on isolated amphibian and mammalian cardiac muscle and on intact rabbits have been studied. This cardioactive plasma substance elicited a positive inotropic response from isolated isometrically contracting papillary muscle of rabbits, dogs, and monkeys, from trabeculae carneae of rats, and from ventricular muscle of toads. Its positive inotropic activity was associated with a shortened duration of action potentials. Studies on intact animals showed that the intravenous injection of this substance raised systemic pressures, raised right and left ventricular systolic pressures, and increased cardiac output. Adrenergic blocking drugs failed to block the inotropic and pressor effects of freshly isolated cardioactive plasma substance.
Influence of Atrial Systole on Effective Ventricular Stroke Volume
Authors: MITCHELL JERE H. , GUPTA DWARKA N. , PAYNE ROBERT M.
Published: June 2012

The influence of atrial systole on forward or effective ventricular stroke volume at different heart rates and at constant cardiac output was investigated in an open chest dog preparation. The procedure employed allowed a ventricular ejection preceded by an atrial systole to be followed by one which was not. A comparison was made between the effective ventricular stroke volumes of these two ejections. The observations support the view that atrial systole plays a significant role in determining effective ventricular stroke volume and that its influence is greater at higher heart rates when cardiac output is kept constant and stroke volume decreases. The data indicate further that the decrease in effective ventricular stroke volume is due to both a decreased ventricular filling and initial atrioventricular regurgitation.
Polycythemia and Right Ventricular Hypertrophy
Authors: SWIGART RICHARD H.
Published: June 2012

Polycythemia was induced in rats by injecting 10 mg CoCl
2
/kg body wt/day intraperitoneally or by placing them in a low pressure chamber at a reduced barometric pressure equivalent to 18,000 feet of altitude for approximately 23 hours/day. After 63 days of treatment a significant hypertrophy of the right ventricular wall was found in both groups of animals. The increase in weight of the right ventricle in the CoCl
2
-injected rats was approximately 45% of that found in rats exposed to chronic hypoxia.

Polycythemia was induced in mice by injecting 0.5 ml of packed, whole erythrocytes per day, intraperitoneally, for four consecutive days. A high hematocrit was maintained by additional periodic intraperitoneal injections of erythrocytes. After twenty-two days a significant right ventricular hypertrophy was observed.

It is concluded that polycythemia and hypervolemia are important factors in producing right ventricular hypertrophy in rats and mice without airway hypoxia and also may be significant factors in the cardiac hypertrophy induced by high altitude.
Renomedullary Vasodepressor Substance, Medullin
Authors: LEE JAMES B. , COVINO BENJAMIN G. , TAKMAN BERTIL H. , SMITH EMIL R. , Mazzeo Marilyn
Published: June 2012

The chemical and physiological properties of renomedullary depressor substances were investigated utilizing the normotensive, vagotomized, pentolinium-treated rat for assay. By a combination of solvent extraction, column chromatography, and thin-layer chromatography, three biologically active acidic lipids were isolated from rabbit renal medulla. The first compound, called medullin, is an acidic lipid with potent vasodepressor and relatively weak nonvascular smooth muscle-stimulating properties. Ultraviolet analysis revealed spectra closely resembling that of prostaglandin E-1 (PGE-1). Infrared analysis showed the presence of carbonyl, methylene, and hydroxyl groups in addition to
trans
ethylene bonds. Although closely resembling PGE-1, medullin appears to be a more unsaturated carboxylic lipid with less polar (hydroxyl) groups.

The hypotensive action of medullin is attributable to a direct effect on peripheral arteriolar beds without cardiac depression, because intra-arterial and intravenous injections of medullin reduced peripheral resistance markedly and increased cardiac output simultaneously. In addition, no effect on cardiac rate or contractility was observed in the isolated rabbit heart preparation. Comparative studies of medullin and PGE-1 indicated that the hypotensive activity of these compounds is similar with respect to potency and mechanism of action. The only biological difference between crystalline PGE-1 and medullin was a fiftyfold greater stimulation of nonvascular smooth muscle by PGE-1 in comparison to medullin. A second biologically active acidic lipid isolated from rabbit medulla was tentatively identified as PGE-1, and was found to possess both vasodepressor and nonvascular smooth muscle-stimulating properties. The third isolate from rabbit medulla possessed potent intestinal stimulating activity but weak to absent vasodepressor effects, properties similar to those of prostaglandin F compounds.
Circulating Coronary Blood Volume
Authors: MUNFORD ROBERT S. , MCMULLAN GEORGE K. , LOVE WILLIAM D.
Published: June 2012

The circulating coronary blood volume was calculated in dogs from independent determinations of the rate of coronary blood flow and the mean circulation time from the root of the aorta to the mouth of the coronary sinus. The average value was 14.2±2.2 ml/100 g lean myocardium. Coronary blood volume was inversely related to the heart rate, which ranged from 126 to 212 beats/min, but was not correlated with other hemodynamic variables within the relatively narrow range of values present.
Action of Driving Stimuli from Intrinsic and Extrinsic Sources on in Situ Cardiac Pacemaker Tissues
Authors: LANGE GERTRUDE
Published: June 2012

The interactions between pacemakers, and the effects on pacemakers, of terminating imposed driving were studied in the
in situ
heart of anesthetized dogs.

Following atrial fibrillation or termination of a fast drive imposed through an artificial pacemaker, pacemaker action in intrinsic pacemakers is suppressed.

Pacemakers tend to accelerate and compete with imposed drives which exceed control rates by only a small percentage (10 to 15%). Arrhythmias may result if imposed drive is slower than or identical with intrinsic pacemaker rate.

Post-drive depression of pacemakers and the resulting deceleration of the heart is followed normally by an overshoot or supranormal acceleration.

The magnitudes and durations of depression and late acceleration are proportional, within limits, to the rate and duration of drive.

Atrioventricular and ectopic atrial pacemakers are much more readily depressed than is the sinoatrial pacemaker. Furthermore, beats of ectopic origin are much more likely to occur while subsidiary pacemakers are recovering from post-drive depression.

Augmentation of depression by Prostigmin, its diminution by atropine, and the potentiation of late acceleration by cocaine and its absence after reserpine or guanethidine pretreatment, indicate that acetylcholine and catecholamines are liberated by driving stimuli.

Placement of the pacemaker over the sinoatrial node, or near to regions where nerve terminals are concentrated, results in the greatest post-drive effects. The fact that propagated action potentials cause depressions and accelerations subject to drug block or potentiation indicates that mediators are also released in the course of propagated activity.

Since atropine does not completely block post-drive depression, it is thought that a potassium ion shift may be involved.
Hematocrit of the Human Cranial Blood Pool
Authors: OLDENDORF WILLIAM H. , KITANO MASAMI , SHIMIZU SHIRO , OLDENDORF STELLA Z.
Published: June 2012

A technique is described utilizing the separate injection of gamma-labeled red cells and plasma, with subsequent measurement of the amount of each label found in the cranial portion of the head and in venous blood specimens. By this means the relationship between the hematocrit of the cranial blood pool and venous blood is determined. In the basic technique, Cr

51

is used separately and sequentially as the label for both red cells and plasma. A modification of this technique using I

131

human serum albumin is described also. Only antecubital venipuncture for injection and sampling was utilized. The mean hematocrit of the human cranial blood pool was found to be 0.84 times the venous hematocrit by both dual tracer methods. This technique should be applicable to other organs. The distribution ratios of any gamma emitters in brain and blood should be similarly measurable.
Evidence for a Metabolic Mechanism in Autoregulation of Blood Flow in Skeletal Muscle
Authors: JONES RICHARD D. , BERNE ROBERT M.
Published: June 2012

Simple criteria have been used in an isolated, perfused skeletal muscle preparation to determine whether autoregulation of blood flow in this tissue is the consequence of a metabolic or a myogenic mechanism. Elevation of venous pressure significantly decreased equilibrium vascular resistance and reduction of venous pressure significantly increased vascular resistance during controlled pressure perfusion whereas alteration of ambient pressure had no significant effect on equilibrium resistance. These responses repudiate a myogenic mechanism for autoregulation of equilibrium blood flow since the myogenic hypothesis predicts increased resistance following increased transluminal pressure and decreased resistance following decreased transluminal pressure. Moreover, during perfusion at constant blood flow, metabolic regulation should be constant and myogenic responses would be permitted full expression. Alteration of venous pressure or ambient pressure during constant flow perfusion, however, failed to evoke myogenic responses at equilibrium. Rather, a passive distention was observed at equilibrium after increased transmural pressure, and passive recoil of the vessels followed decreased transmural pressure during constant flow perfusion. All pressure alterations were accompanied by transient resistance changes of undetermined origin. With the criteria employed, however, the results indicate that the regulation of equilibrium vascular resistance in skeletal muscle is based primarily on a metabolic mechanism.
Relation of Ultrastructure to Function in the Intact Heart: Sarcomere Structure Relative to Pressure Volume Curves of Intact Left Ventricles of Dog and Cat
Authors: Spotnitz Henry M. , Sonnenblick Edmund H. , Spiro David
Published: June 2012

Reproducible pressure-volume curves have been obtained from fresh left ventricles removed from 10 cats and 27 dogs. Electron microscopic observations of sarcomere length and structure in the walls of these chambers have been correlated with the parameters of passive filling. In both the dog and the cat a similar relation of sarcomere length to filling pressure is observed, a filling pressure of 12 mm Hg corresponding to a sarcomere length of 2.2 µ. Sarcomeres shorter than 1.85 µ are not observed under conditions of passive filling. Sarcomeres tend to be longest in the inner layer of the ventricular wall. Filling pressure is observed to be a more general and reproducible index of sarcomere length than absolute or normalized filling volume. H zones are often present in the sarcomeres of the ventricular wall with filling pressures greater than 15 mm Hg and sarcomeres greater than 2.3 µ in length. These findings are discussed in relation to previous studies of papillary muscle and in relation to mathematical models for the left ventricle. The present results indicate that the normal left ventricle functions along the ascending portion of the length-tension curve, where the end diastolic sarcomere lengths are 2.2 µ or less.
Occlusion of Lumina in Small Arterioles During Vasoconstriction
Authors: Van Citters Robert L.
Published: June 2012

The microscopic appearance of small arterioles during epinephrine-induced vasoconstriction was studied in the dog mesentery. The tissues were quick-frozen in situ with liquid isopentane, freeze-substituted, and sectioned serially. Obliteration of the lumina of small arterioles during vasoconstriction was demonstrated in both random and serial sections. Endothelial cells, which were ordinarily flattened against the internal elastic membrane, were compressed and deformed during vasoconstriction, so that they protruded into the lumen and often coalesced in the center of the vessel to form a mechanical obstruction to blood flow. Vascular obliteration occurred commonly in very small arterioles, but was observed with diminishing frequency in progressively larger arterioles, and was not identified in vessels large enough to accommodate more than 10 endothelial cells in cross sections. In an ideal cylinder, tension is greatest at the innermost layer, and the gradient of tension across the wall falls off in a nonlinear fashion. These conditions probably do not hold in a functioning arteriole.
Overestimation of Left Ventricular Volume by the Indicator Dilution Technique
Authors: Carleton Richard A. , Bowyer Allen F. , Graettinger John S.
Published: June 2012

The applicability of the indicator dilution method to the measurement of left ventricular volume has been studied. When compared with angiocardiographic measurements, the dilution technique overestimates volume by an average of 52 and 91% in end diastole and end systole respectively. Studies which demonstrated more rapid indicator washout from the outflow than from the apical portion of human and canine left ventricles suggest that faulty intraventricular indicator dispersion is the major cause of the volume over-estimates yielded by the dilution method. Procedures designed to alter ventricular size by altering venous return produced parallel changes in ventricular circumference and in ventricular indicator washout volume.

The indicator dilution method does not provide a measure of left ventricular volume, but may, in carefully designed studies, yield an index of changes in ventricular size.
Relation of Plasma Renin to Sodium Balance and Arterial Pressure in Experimental Renal Hypertension
Authors: Brown Torrey C. , Davis James O. , Olichney Michael J. , Johnston C. I.
Published: June 2012

Measurements of plasma renin were made in unilaterally nephrectomized dogs with renal artery stenosis and hypertension. Plasma renin was elevated throughout the course of the malignant renal hypertensive disease, and during the first three days only in chronic hypertension. Hypertension was produced by renal artery constriction in unilaterally nephrectomized dogs with prior thoracic caval constriction and in sodium-depleted, left nephrectomized animals. Plasma renin was high in both dogs with caval constriction and sodium depletion before hypertension was added. When the renal artery was constricted, two of the dogs with thoracic caval constriction developed malignant hypertension and a further striking increase in plasma renin occurred. In two other dogs with caval constriction, chronic hypertension developed but plasma renin increased further in only one of the two animals; this occurred during the first four days of hypertension after which plasma renin returned to the high control level. The sodium-depleted dogs developed chronic hypertension following renal artery constriction but no further elevation in plasma renin occurred. Sodium repletion and sodium depletion of chronic hypertensive dogs produced marked changes in plasma renin without alterations in arterial pressure. The present findings revealed a striking correlation between plasma renin and sodium balance but neither bore any relation to the level of arterial pressure.
Use of Random Excitation and Spectral Analysis in the Study of Frequency-Dependent Parameters of the Cardiovascular System
Authors: Taylor Michael G.
Published: June 2012

If a randomly varying signal or noise is used as input, it is possible to study the input-output relations of a system, over a wide band of frequencies, by the use of power spectrum analysis. This technique has been applied to the cardiovascular system, by deliberately introducing irregularity in the pressure and flow pattern, by random electrical pacing of the heart. Examples are given of the determination, by spectral analysis in the range of 0.25 to 25 cycles/sec, of aortic and femoral arterial impedance in the dog, and also of the transmission ratio for pressure oscillations along the aorta. The results agreed satisfactorily with those obtained by the Fourier analysis of single pulses. When the time scale of the irregularities was made sufficiently great, it was possible to examine aortic impedance in the very low frequency range 0.00125 to 0.125 cycle/sec. In this range the operation of the baroreceptor reflexes became apparent.
Mechanisms Involved in the Hypersecretion of Aldosterone During Sodium Depletion
Authors: DAVIS JAMES O. , BINNION PETER F. , BROWN TORREY C. , JOHNSTON C. I.
Published: June 2012

The primary mechanism leading to hypersecretion of aldosterone during sodium depletion in the dog is increased activity of the renin-angiotensin system. Loss of salt and water leads to renin release and increased aldosterone and corticosterone secretion. Plasma renin was elevated within one hour after diuretic administration. The increase in corticosterone production was transient; return of corticosterone to the control level appears to be mediated by the negative corticosteroid feedback mechanism via the anterior pituitary. It is suggested that the role of ACTH in aldosterone production during sodium depletion is a supportive one. In severe sodium depletion decreased plasma sodium and increased plasma potassium concentrations further augment the hypersecretion of aldosterone.
Muscle Pumping in the Dependent Leg
Authors: STEGALL H. FRED
Published: June 2012

Since the exercising dependent leg displaces blood toward the heart, against a potential gradient, it must perform useful circulatory work. We studied the peripheral circulation in healthy, sedentary males by measuring calf circumference (using mercury-in-Silastic strain gages), muscle pump ejection velocity (using a transcutaneous Doppler flowmeter), intrathoracic and intra-abdominal pressures (through catheters in the esophagus and rectum) and power of the leg muscle pump (product of blood flow and the upstream-downstream venous pressure difference). Measurements of pressure, flow velocity, and volume changes in the dependent venous beds of healthy young men demonstrated that during running in place, (1) the abdominal contraction necessary to fix the pelvis raised inferior caval pressure and impeded venous outflow from the legs, but that, (2) the leg muscles themselves were capable of effectively pumping blood past this functional obstruction. By doing so, these peripheral pumps contributed more than 30% of the energy required to circulate blood during running.
Cerebral Blood Flow In Man at High Altitude
Authors: SEVERINGHAUS JOHN W. , CHIODI HUGO , EGER II E. I. , BRANDSTATER BERNARD , HORNBEIN THOMAS F.
Published: June 2012

Cerebral blood flow was determined by an N
2
O method in 7 normal men at sea level and after 6 to 12 hr and 3 to 5 days at 3810 m altitude. An infrared N
2
O analyzer was used both to measure end-tidal PN
2
O so that it could be kept constant for 15 min and to determine blood N
2
O, for which a simple gas extraction method was devised. In addition, acute changes in cerebral blood flow were estimated from cerebral A-V O
2
differences. Control cerebral blood flow was 43 ml per 100 g per min; it increased 24% at 6 to 12 hours and 13% at 3 to 5 days at altitude. After 3 to 5 days, pH of cerebrospinal fluid was normal (7.31) in four subjects while arterial blood pH was alkaline (7.47); arterial blood Pco
2
had fallen from 41 to 30 mm Hg. Acute correction of hypoxia restored cerebral blood flow to control while mean Pco
2
was still 31 mm Hg. Addition of O
2
and CO
2
to inspired air raised cerebral blood flow 34% above control at Pao
2
= 170, Paco
2
= 35 mm Hg. Values obtained by extrapolation suggest that if arterial Pco
2
was raised to control (41 mm Hg), cerebral blood flow would have been 60% above control. Cerebral blood flow thus appears to return to normal at the prevailing Paco
2
, probably because the pH of cerebrospinal fluid and of the extracellular fluid of cerebral vascular smooth muscle is kept normal by active transport across the ‘blood-brain’ barrier. It is postulated that an ion-impermeable barrier separates the blood stream from extracellular fluid of the smooth muscle of cerebral arterioles.
Response of Small Pulmonary Arteries to Unilobar Hypoxia and Hypercapnia
Authors: KATO MIKIO , STAUB NORMAN C.
Published: June 2012

We measured the internal diameters of small muscular pulmonary arteries in the right and left lower lobes of lungs rapidly frozen in the anesthetized, open-thorax cat. In every cat the right lower lobe was ventilated with the test gas and all other lobes were ventilated with O
2
. In 4 cats, the test gas supplied to the right lower lobe was also O
2
(control experiments); in 6, it was 100% N
2
and in 6 it was 90% N
2
-10% CO
2
. In the 4 controls, there was no difference between the internal diameters of corresponding arteries in the right and left lower lobes. In the other 12 cats, there was a highly significant decrease in the diameter of arteries in the right lower lobe that correlated well with a large decrease in blood flow to that lobe, calculated using a shunt equation. Ventilation of the right lower lobe with 10% CO
2
in air (4 cats) did not affect the diameter of arteries and ligation of the pulmonary artery to the right lower lobe resulted in only a slight decrease in arterial dimensions in 3 of 4 cats.

These data show that in regional alveolar hypoxia without systemic hypoxia the muscular pulmonary arteries of the terminal respiratory units in the hypoxic region actively constrict. The constriction occurs with or without alveolar hypercapnia.
Autoregulation of Cerebral Blood Flow
Authors: YOSHIDA KOUZO , MEYER JOHN S. , SAKAMOTO KO , HANDA JYOJI
Published: June 2012

Changes in blood flow through the internal carotid, vertebral and external carotid arteries were measured by electromagnetic flowmeters during and after acute hypertension induced by closing a clamp around the thoracic aorta in anesthetized monkeys.

The internal carotid and vertebral arterial system showed both rapid and delayed autoregulatory responses to rapid increases in blood pressure; the rapid (primary) responses occurred within seconds, the progressive (delayed) within 3 to 4 minutes. In contrast, the flow response within the external carotid system appeared to be passive. Cervical sympathetic innervation and myogenic reflexes (Bayliss reflex) both appear to play a part in the rapidly occurring (primary) regulation of cerebral blood flow. The mechanism responsible for delayed and progressive (secondary) autoregulation in the cerebral vasculature appeared to be metabolic, since it was predominantly influenced by changes in blood Pco
2
. Changes in intracranial pressure did not seem to be involved in autoregulation.
The Rabbit Placenta as an Organ of Diffusional Exchange
Authors: FABER J. JOB , HART FREDERICK M.
Published: June 2012

The umbilical arteries of intact, in-situ placentas of one series of anesthetized rabbits were perfused with deoxygenated blood equilibrated with 10% or 20% acetylene and in another series with oxygenated blood without acetylene. The transfer of acetylene, and probably also of oxygen, were shown not to be limited by diffusion. Above the normal physiological rates of fetal placental flow, oxygen uptake in the fetal placental circulation did not increase appreciably with an increase in the rates of perfusion; below it, it decreased almost proportionally with a decrease in the rate of perfusion.

To explore the applicability of these results to the human placenta, the experimental data were reduced to dimensionless form. It was shown that three dimensionless variables suffice to describe the characteristics of diffusional exchange in the placenta. The dimensionless diagrams were very similar for the ideal countercurrent exchanger and for the rabbit placenta but these differed from diagrams made from data published on human, sheep, cow, and monkey placentas. The authors propose the dimensionless diagram as a concise description of the passive transfer characteristics of a placenta, at least until measurements of vascular geometry, regional permeabilities and flow patterns allow the calculation of mean diffusion gradients.
Magnetic Meters: Effects of Electrical Resistance in Tissues on Flow Measurements, and an Improved Calibration for Square-Wave Circuits
Authors: FERGUSON DONALD J. , LANDAHL HERBERT D.
Published: June 2012

Apparent sensitivity of magnetic meters applied to intact vessels can be altered by changes in conductivity of vessel walls or of the contained fluid, and by variable contact of the vessel with surrounding tissue or fluid. An experimental study of these problems was begun by designing a built-in magnetometer for complete electrical calibration of the square-wave meter. It was then found that flow of mercury, saline or blood of various hematocrits through nonconductive tubes gave signals equal to those calculated on the basis of Faraday's principle, providing that the magnetic field was practically uniform across the electrodes. Adequate uniformity was obtained with parallel pole faces at least 1.3 times as wide as the gap. Variable loss of signal (up to 50%), owing to contact of conductive vessels with surrounding tissue or fluid, could be practically eliminated by an electrical shield extending 2.6 times the diameter along the vessel at the electrodes. Specific conductances of canine aortas were from 0.52 to 0.73 times the conductances of blood from the same animals. Alterations in this ratio, readily produced by changes in composition of vessel or fluid, can result in significant changes of flow signal. Indirect flow calibrations require matching of the conductance ratio to that occurring at the time of measurement.
Intrapericardial, Intrapleural, and Intracardiac Pressures during Acute Heart Failure in Dogs Studied without Thoracotomy
Authors: KENNER HARRIS M. , WOOD EARL H.
Published: June 2012

Pressures at multiple sites in the thorax of supine anesthetized dogs were recorded simultaneously with fluid-filled catheters inserted percutaneously. Pleural and pericardial pressures were corrected to the level of their respective recording catheter tips as determined by roentgenograms. Intracardiac pressures were referred to the midthoracic coronal plane or to the vertical level of the pericardial catheter tip.

Pericardial pressures at end-expiration averaged -5.0 cm H
2
O (range 0 to - 13) and varied with the vertical position of the catheter tip, becoming less negative as the height above the midthoracic coronal plane diminished.

Acute right heart failure was produced by partial obstruction of the pulmonary artery by a catheter-tip balloon. Although mean right atrial pressure increased by an average of 26 cm H
2
O, consistent increases in pericardial pressure did not occur. Similarly, during acute obstruction to left ventricular outflow by inflation of a balloon within the thoracic aorta, left atrial end-diastolic pressure increased by an average of 14.5 cm H
2
O, but no consistent increase in pericardial pressure was recorded. No systematic changes in pleural pressure were detected in either case. Thus there was no evidence of pericardial restriction of cardiac dilatation during acute heart failure under these experimental conditions.
The Effect of Hexamethonium Bromide Upon Coronary Flow, Cardiac Work and Cardiac Efficiency in Normotensive and Renal Hypertensive Dogs
Authors: CRUMPTON CHARLES W. , ROWE GEORGE G. , O'BRIEN GEORGE , MURPHY QUILLIAN R.
Published: June 2012

Hexamethonium bromide in normotensive and renal hypertensive dogs resulted in significant reductions in arterial blood pressure, cardiac output and cardiac work. The decrease in cardiac output relative to that in blood pressure suggests that the blood pressure reduction was largely due to the decrease in cardiac output. There was a decrease in coronary flow accompanied by an increase in myocardial oxygen extraction of such Degrees that cardiac oxygen consumption remained unchanged. Since myocardial oxygen consumption remained unchanged despite the decrease in cardiac work the calculated cardiac efficiency was decreased.
A Comparison of the Distribution of Potassium and Exchangeable Rubidium in the Organs of the Dog, Using Rubidium
86
Authors: LOVE W. D. , ROMNEY R. B. , BURCH G. E.
Published: June 2012

From determinations of radioactivity and potassium content at intervals after the injection of Rb
86
, it was inferred that most organs of the dog contained exchangeable rubidium in a concentration paralleling but exceeding that of potassium, as compared with their relative concentrations in the plasma. A "lag phenomenon" resulting in higher rubidium specific activity in the myocardium than plasma was present. Analysis indicated that this was dependent on the relationship of myocardial rubidium exchange rate and the rate of decline of plasma rubidium specific activity. In experiments requiring prolonged observation, Rb
86
(half life, 19.5 days) is a useful tracer of potassium.
The Influence of Constrictor Drugs on the Distensibility of the Splanchnic Venous System, Analyzed on the Basis of an Aortic Model
Authors: ALEXANDER ROBERT S.
Published: June 2012

The distensibility of the aorta was measured in anesthetized dogs by injecting blood at controlled rates into an isolated segment. Constrictor drugs produce a moderate increase in distensibility of the aorta at low pressure ranges and a more marked increase in distensibility at normal pressures. Studies of the splanchnic venous system of intestinal loops by the same method, and also by a method which does not require interruption in blood flow, gave evidence of the same type of distensibility phenomena as seen in the aorta, although at low pressures the venous distensibility tends to be actually decreased by vasoconstriction. The splanchnic venous system also differs from the aorta in that it is very dependent upon the rate of pressure-volume change. These results are analyzed in terms of the basic mechanisms involved and their physiologic implications.