bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of Mean and Pulse Pressures in the Circulation of the Isolated Dog Tongue
Authors: ROVICK ALLEN A. , ROBERTSON PATRICIA A.
Published: June 2012

In the isolated, perfused dog's tongue, alterations of pulse pressure, at constant mean pressure, can produce parallel or oppositely directed changes in blood flow or can leave the flow unaffected. Parallel changes occur when the vascular bed is passively distensible; opposite changes occur when active contraction of smooth muscle overcomes the effects of passive distensibility, and no change is found when the two effects balance. The first is seen at mean pressures below 80 mm Hg or peak pressures above 155 to 165 mm Hg. The other reactions are produced in the mean pressure range in which autoregulatory reactions occur, viz. opposite changes when the pulse pressure is low and no change under conditions close to in situ mean and pulse pressure. Even when pulse pressure has no observable influence on flow, therefore, it modifies vascular tone.

The active response of vascular smooth muscle to pulse pressure persists in part after the removal of the stimulus, opposing stress-relaxation of resistance vessels. Tissue weight changes reflect alterations in capacitance vessel volume which may vary in direction from the volume changes occurring in resistance vessels.
A Study of Hepatic Hemodynamics in the Dog
Authors: SHOEMAKER CHARLES P.
Published: June 2012

The effects of altered hepatic blood flow, of splanchnic and hepatic nerve stimulation, and of injecting epinephrine and vasopressin (Pitressin) were studied by perfusing canine livers in vitro. Controlled hepatic arterial perfusions demonstrated a linear relationship between arterial pressure and hepatic arterial inflow. It was found that increases of hepatic artery flow slightly increased portal vein pressure and vascular resistance of the portal vein, and that increases of portal vein flow slightly increased hepatic artery vascular resistance. Splanchnic nerve stimulation caused vasoconstriction of the hepatic artery, portal vein, and mesenteric vasculature. Hepatic nerve stimulation caused constriction of only the hepatic artery and portal vein vasculature. Similar results were obtained by the administration of epinephrine. Pitressin caused marked vasoconstriction of the mesenteric vasculature, vasodilatation of the portal vein vascular bed, and slightly increased hepatic artery vasomotor tone. It was noted that the rise in portal vein vasomotor tone with sympathetic stimulation was due in part to constriction of the "postjunctional" resistance.
Cocaine-Induced Incomplete Bundle Branch Block in Dogs
Authors: WATT THOMAS B. , PRUITT RAYMOND D.
Published: June 2012

Cocainization of a segment of the right or left bundle branch in the canine heart permitted observation of the phenomenon of incomplete bundle branch block in its dual expressions, namely, alterations in the action potential of the respective bundle branch and alterations in the ventricular complexes of the limb-lead electrocardiogram. As the effects of cocainization waned, the bundle action potential reflected intermediate stages between complete block of conduction and normal conduction. Likewise, the attendant ventricular complexes reflected intermediate stages between that form traditionally associated with complete block of the corresponding bundle and normal form. Characteristic shift in direction of the near-terminal QRS axis occurred with and without significant prolongation in QRS.

Cocainization of a segment of the common bundle resulted in first, second, or third degree atrioventricular block, unattended by changes in form of associated ventricular complexes. As in bundle branch block, regression of common bundle block occurred also in stepwise fashion.
Sensitization of Arteries, Veins, and Small Vessels to Norepinephrine After Cocaine
Authors: ABBOUD FRANCOIS M. , ECKSTEIN JOHN W. , ZIMMERMAN BEN G. , GRAHAM MICHAEL H.
Published: June 2012

The effects of cocaine on the responses of arteries, veins, and small vessels to norepinephrine were studied. Intra-arterial norepinephrine was injected or infused into perfused forelegs of dogs. Angiotensin and serotonin were used as agonists. The effects of postganglionic sympathetic stimulation and of intra-arterial tyramine were tested also.

Cocaine in doses of 0.5, 5.0, and 10 mg/kg
IV
sensitized the arterial and venous segments to norepinephrine; the responses of small vessels were not augmented significantly. The effects of angiotensin and serotonin were not increased. The vasoconstrictor effect of weak and strong submaximal postganglionic sympathetic nerve stimulations was reduced and that of intra-arterial tyramine was suppressed after cocaine.

The results allow us to conclude that vascular supersensitivity to norepinephrine after cocaine is not a uniform phenomenon but it is restricted to certain vascular segments. The reason for the sensitization of arteries and veins but not small vessels is unknown. The observations are discussed in light of the recent hypothesis proposed by Furchgott et al on the mechanism of action of cocaine.
Pericapillary Gas and Water Distribution Volumes of the Lung Calculated from Multiple Indicator Dilution Curves
Authors: RAMSEY LLOYD H. , PUCKETT WALTER , JOSE ANTHONY , LACY WILLIAM W.
Published: June 2012

Simultaneous indicator dilution curves of albumin I
131
, tritiated water, and an inert gas are identical when the indicators do not traverse a capillary bed. When the same three indicators traverse the pulmonary capillaries before sampling, the shapes of the tritiated water and inert gas dilution curves are altered by movement of these two indicators into an extravascular water space and gas space respectively. The arithmetical difference between the distribution volumes of albumin I
131
and tritiated water measures a functional extravascular water space in the lungs. The difference between tritiated water and inert gas distribution volumes is a measure of a lung gas volume in contact with perfusing capillaries.

Pericapillary water distribution volume in normal dogs was found to be 4.2 ± 0.8 ml/kg and the gas distribution volume 24 ± 6 ml/kg. In normal human subjects the respective values were 1.1 ± 0.3 ml/cm height and 1.80 ± 0.28 liters/m
2
of body surface area. Changes in both gas and water distribution volumes were observed as a result of experimental pulmonary edema in dogs and in various forms of pulmonary disease in man.
Protein and Nucleic Acid Synthesis During the Reparative Processes Following Myocardial Infarction
Authors: GUDBJARNASON SIGMUNDUR , DE SCHRYVER CHRISTIAN , CHIBA CHIYO , YAMANAKA JIRO , BING RICHARD J.
Published: June 2012

The effect of myocardial infarction upon protein and nucleic acid synthesis of the heart was studied. Myocardial infarction was produced in dogs by ligation of branches of the anterior or posterior descending coronary artery. The rate of incorporation of glycine-2-C
14
into heart muscle protein was studied over a period of six weeks.

The infarcted tissue showed a rapid diminution in protein synthesis after infarction; on the third day the incorporation into the infarcted tissue rose above normal and reached a maximum on the fourth. The borderline tissue also demonstrated an early increase in protein synthesis with a maximum incorporation 48 hours after infarction.

The changes in the concentration of RNA paralleled those of the incorporation of glycine-C
14
. The concentration of DNA increased on the second day after infarction and reached a maximum on the tenth day.

Studies on the incorporation of glycine-C
14
into subcellular fractions showed an early renewal of cell material in the infarcted area. Incorporation into nuclear ribosomal fraction increased first, followed by mitochondria and microsomes. The incorporation into "contractile proteins" remained subnormal. The earliest increase in nucleic acid synthesis was observed for "nucleolar
RNA
" (p-
RNA
) followed by nuclear ribosomal
RNA
.
DNA
showed an increase in incorporation 48 hours after the infarction.

The studies demonstrate the rapid reaction of the heart muscle to injury and the increase in protein and nucleic acid synthesis of infarcted and borderline tissue. The first step in these reactions is the synthesis of nuclear material followed by the reconstruction of mitochondria and microsomes.
Kinetic Studies of Calcium Distribution in Ventricular Muscle of the Dog
Authors: LANGER G. A. , Serena S. D
Published: June 2012

Five phases (0 to 4) were defined kinetically for calcium in the dog papillary muscle vascularly perfused for five to six hours with perfusate containing 5 m
M
/liter calcium. The mean rate constant, λ, (min
-1
), approximate calcium concentration (m
M
/liter muscle water) and suggested origin of each phase are respectively: (0) λ
0
= 3.5, 0.4, vascular; (1) λ
1
= 0.59, 1.8, interstitial; (2) λ
2
= 0.116, 1.7, "specialized" calcium transport system (?sarcoplasmic reticulum); (3) λ
3
= 0.021, 2.0, intracellular; (4) λ approx 0.004, <1.6, intracellular and/or connective tissue. Inotropism, occuring coincidentally with institution of perfusion by solution containing 25% normal sodium concentration, was marked by a mean 60% increase in peak isometric tension and a mean 87% increase in rate of tension development. These inotropic changes stabilized within 10 minutes despite maintenance of low sodium perfusion and regressed within 10 minutes upon return to normal sodium perfusion. There was a mean 0.5 m
M
/liter change in calcium concentration of the muscle associated with the inotropic changes. This fraction of tissue calcium could be ascribed entirely to kinetically-defined phase 2 and was freely exchangeable. Prolonged (40-minute) low sodium perfusion resulted in no inotropic changes beyond the first 10 minutes but was associated with a continued marked net increase in muscle calcium. This fraction of tissue calcium was irreversibly bound and inexchangeable. It was suggested that this fraction of calcium may be bound as its phosphate salt.

The possibility that the Ca
++
content of the "specialized system" represented by phase 2 is controlled by movements of Na
+
into and out of this system is discussed. Ca
++
movements associated with increased frequency of contraction are also discussed in the context of their possible relation to Na
+
exchange.
Reducing Heart Rate of the Dog by Electrical Stimulation
Authors: LOPEZ JOSE F. , EDELIST ARYEH , KATZ LOUIS N. , Boyd Eugene
Published: June 2012

1) The frequency of effective ventricular contractions could be reduced by almost 50% in dogs by stimulating the ventricles (or atria) with electrical impulses of long duration (2 volts, 200 to 350 msec).

2) A similar result was obtained when pairs of impulses (2 volts), each 3 msec in duration, were used, with the time interval between the two impulses of the pair similar to that between the make and break of the long impulses (noted above).

3) The dogs were under general anesthesia and positive pressure breathing was maintained. After thoracotomy, platinum electrodes were implanted in the epicardial surface of the right ventricle or atrium. Pressures were measured in all heart chambers and the unipolar electrocardiogram was recorded from the right atrium with a catheter electrode. Several frequencies of stimulation, below the inherent sinus rate, were tested and at each frequency the time interval between pairs of stimuli was progressively increased from 100 to 350 msec.

4) In all dogs reduction of the frequency of the effective ventricular contractions could be obtained with pairs of stimuli 200 and 350 msec apart. Only the make of the long impulse or the first of the pair of short impulses produced an
effective
ventricular contraction, while the break of the long impulse or the second short impulse stimulated the ventricles so early in the cycle that no effective mechanical contraction followed. However, the refractory period produced by the break prevented the sinus impulse from reaching the ventricles. The several mechanisms involved are discussed.

5) In one dog the reduction of the frequency of the effective ventricular contractions could be maintained during the 24 hours of survival.

6) The method was applied to a patient being treated for Stokes-Adams attacks. Right atrial stimulation produced a noticeable reduction in ventricular frequency. This involved a reduction in the frequency of electrical responses of the ventricles as well, ensuring a reduction of the per minute energy cost and oxygen consumption of the heart. Such a reduction of the frequency of electrical responses of the ventricles could not be accomplished, so far, in the dog by atrial stimulation.

7) Reduction of the frequency of effective ventricular responses was obtained in one dog with induced atrial flutter and in another with a pacemaker induced "parasystolic" ventricular tachycardia by employing an artificial ventricular pacemaker similar to that used with sinus rhythm.

8) The significance of the findings is discussed. This experimental approach suggests a possible method of slowing the heart rate in clinical cases of ventricular or atrial tachycardia refractory to other methods of treatment.

9) Finally, this approach offers a means of studying certain properties of the heart in the dog which may give insight into the mechanisms involved in some of the more complex arrhythmias encountered in man.
Renal Medullary Countercurrent System Studied with Hydrogen Gas
Authors: AUKLAND KNUT , BERLINER ROBERT W.
Published: June 2012

The renal countercurrent exchange mechanism was studied by recording the removal of hydrogen gas from the medulla of dogs. Hydrogen was administered by respiration or by intra-arterial infusion of hydrogen-saturated saline. Simultaneous desaturation curves were recorded polarographically by means of two or three needle-shaped platinum electrodes inserted into various positions in the medulla. It was found that the desaturation rate in the inner medulla was mainly dependent on urine flow, in such a way that the fractional rate of removal increased from 0.05 to 0.75 min
-1
when urine flow was raised from 0.1 to 5 cc/min/kidney. Saline, mannitol and water diuresis had the same effect. On the basis of pelvic urine desaturation curves, which were practically identical to desaturation curves from the tip of the papilla, it was calculated that as much as two-thirds of the medullary hydrogen content may be removed by urine. The clearance rate was higher in the outer medulla and less dependent on urine flow. No consistent correlation with effective renal blood flow could be demonstrated in any segment of the medulla. The results indicate a very high efficiency of the countercurrent exchange mechanism with respect to hydrogen, and recordings from the corticomedullary border gave direct evidence for a high degree of hydrogen shunting across the vessel loops. Physiological implications of the findings with respect to oxygen and sodium chloride are discussed.
Alterations in Cardiac Synchrony Induced by the Cardiac Sympathetic Nerves
Authors: Priola Donald V. , Randall Walter C.
Published: June 2012

While pressures were recorded separately from the four chambers of the heart in openchest dog preparations, together with a standard limb lead of the ECG, the right and left stellate ganglia were stimulated. Measurements from the beginning of the P wave to the initial rise in chamber pressures revealed that pressure in the left ventricle began to rise approximately 20 msec prior to that in the right ventricle. This interval was significantly shortened during electrical stimulation of the stellate ganglion. Although the interval between P wave and the initial pressure elevations in the right atrium (RA) and the left atrium (LA) both shortened during stellate stimulation, P-RA decreased considerably more than P-LA. The P wave, PR interval, and the QRS complex all shortened markedly, indicating increased conduction velocity over the atria, the nodal conducting tissue, and the ventricles during stellate stimulation. These events occurred with or without alterations in heart rate and were correlated with large increases in the rate of change of ventricular pressures. Simple algebraic summation of individual muscle segment contractions may achieve significantly greater intraventricular pressure as the contractions become more synchronous. The total pressure developed is further augmented when each individual unit contracts with greater force and greater velocity. The recruitment of additional functional units would result in further summation and thus in still greater augmentation in total force and pressure. Alterations in pacemaker site are common during stellate stimulation.
Cardiac Arrhythmias Following Condenser Discharges Led Through an Inductance:
Authors: PELEšKA BOHUMIL , Blažk Z. , Rábl M. , Sládková E.
Published: June 2012

In order to evaluate the significance of an inductance in the condenser discharge circuit of defibrillators, additional experiments were performed by methods similar to those reported previously.
1
An inductance of 0.29 henry was connected in series with the condenser. It was shown that this modification results in a much higher threshold for arrhythmias than the threshold found earlier with pure condenser discharges. The differences were highly significant and show that functional damage to the heart, evaluated by the number and severity of arrhythmias produced, is less with an inductive resistance than without it. Inductive damping reduced the incidence of fibrillation by two-thirds. In 2160 damped discharges, ventricular fibrillation occurred only 36 times, all in the relative refractory period of the cardiac cycle. Fibrillation did not appear when the discharge was applied in the absolute refractory period or in the excitable period.
Coronary Inflow and Oxygen Usage Following Cardiac Sympathetic Nerve Stimulation in Unanesthetized Dogs
Authors: GRANATA LINO , OLSSON RAY A. , HUVOS ANDREW , GREGG DONALD E.
Published: June 2012

The effects of cardiac sympathetic nerve stimulation on coronary inflow were studied in previously operated conscious dogs, using electromagnetic flowmeters. Stimulation caused an increase of coronary inflow which was due mainly to an augmentation of flow during diastole. In systole, inflow changes were smaller and variable according to the strength of stimulation. The data presented indicate that an arteriolar dilatation may play a role in augmenting coronary inflow.

In several instances, the increase of coronary inflow was preceded by a phase of reduction which suggested the possibility of coronary vasoconstriction as a primary direct effect of cardiac sympathetic activation.
Transfer of Carbon Monoxide and Nitrous Oxide in the Artificially Perfused Sheep Placenta
Authors: METCALFE JAMES , MOLL WALDEMAR , BARTELS HEINZ , HILPERT PETER , PARER JULIAN T.
Published: June 2012

1. The sheep placenta was perfused in situ through the umbilical circulation with a dextran solution containing carbon monoxide and nitrous oxide.

2. The concentration of carbon monoxide in the perfusion fluid after passage through the umbilical circulation was found to be 19±3% of its concentration in the entering perfusion fluid. This represents "shunted umbilical flow," the percentage of the perfusion fluid (and presumably of the fetal blood) which does not exchange substances with the maternal blood.

3. The concentration of nitrous oxide in the perfusion fluid after passing the placental membrane and before admixture of shunted perfusion fluid was found to be 14±4% of its original concentration in the perfusion fluid when the maternal arterial concentration was zero. This leads us to the conclusion that the perfusion fluid did not at any time reach the maternal arterial concentration and that no functionally effective countercurrent flow pattern exists in the sheep placenta.

4. Reversal of the flow direction in the fetal umbilical vessels resulted in a slight increase of the N
2
O concentration in the perfusion fluid after passing the placental membrane and before admixture of the shunted perfusion fluid.

5. We suggest that the placenta contains a mixture of countercurrent and concurrent flow units. Diffusion of gases along the capillaries within the comparatively thick placental membrane of the sheep is also presented as a possibility.
Oxygen Consumption of Arterioles and Venules as Studied in the Cartesian Diver
Authors: HOWARD RUFUS O. , RICHARDSON DAVID W. , SMITH MORRIS H. , PATTERSON JOHN L.
Published: June 2012

1. The Cartesian diver microrespirometer has been applied to the measurement of oxygen consumption by mesenteric arterioles and venules from hamsters and human beings. Oxygen consumption by the smallest arterial vessels, less than 150 µ in diameter, averaged 1.05 µliter/mg/hr, in contrast to only 0.58 µliter/mg/hr for arteries 250 to 400 µ in diameter. Hamster venules consumed oxygen at an average rate of 0.53 µliter/mg/hr, nearly equal to the largest arteries studied. Venous oxygen consumption did not vary with vessel diameter.

2. Both arterioles and venules were highly resistant to hypoxia, maintaining normal rates of oxygen uptake at environmental oxygen tensions as low as 12 mm Hg, but not at 5 or 2 mm Hg. Veins consumed less oxygen at an environmental
p
O
2
of 150 mm Hg than at 57, 28, or 12 mm Hg, whereas arterial
Q

O

O
2

was unchanged between 12 and 150 mm Hg.

3. Ten human mesenteric arteries, 65 to 175 µ in diameter, and 10 human veins, 130 to 450 µ in vitro, had average rates of oxygen consumption of 0.35 and 0.25 µliter/mg/hr, significantly lower than hamster vessels.

4. Vessels from hamsters sacrificed without anesthesia consumed oxygen at rates similar to arterioles and venules removed from animals under pentobarbital anesthesia.
Effect of Venous Pressure on Mean Capillary Pressure and Vascular Resistance in the Intestine
Authors: JOHNSON PAUL C.
Published: June 2012

Elevation of venous pressure in the intestine increases capillary pressure by amounts that average 62% of the venous pressure increment. The relation may be expressed as

P
c

= 9.7 + 0.62

P
v

, where

P
c

represents the mean capillary pressure and

P
v

represents venous pressure (both expressed in mm Hg). The increase of capillary pressure is less than expected for a rigid system and less than reported for skeletal muscle. This attenuation of the effect of increments of venous pressure on capillary blood pressure is due to precapillary constriction and postcapillary dilation, with the latter playing the dominant role. Measurement of resistance in a segment of the venous vasculature confirmed this and also demonstrated that most of the reduction of resistance occurs in venous vessels with diameters greater than 0.5 mm.
Responses of Coronary Smooth Muscle to Catecholamines
Authors: ZUBERBUHLER RICARDO C. , BOHR DAVID F.
Published: June 2012

Responses to catecholamines were studied in isolated helical muscle strips of large and small coronary vessels and in isolated perfused coronary arteries from the dog.

Epinephrine and norepinephrine in concentrations well below those normally present in the blood uniformly caused relaxation of small coronary vessels. Norepinephrine was much more potent than epinephrine. The relaxation was reversibly blocked by the beta adrenergic blocker, nethalide. During this blockade, catecholamines either were inactive or produced a slight contraction. Strips contracted by angiotensin, blood or KCl, as well as those completely depolarized by K
2
SO
4
, were relaxed by catecholamines.

Strips taken from large coronary vessels, unlike those from small vessels, were, in some cases, contracted by catecholamines; in others, after a transient contraction, they were relaxed. Contraction was blocked by Dibenzyline. This difference in behavior of large and small vessels may account for some of the contradictions found in the literature concerning the response of coronary vessels to catecholamines.
Interstitial Fluid Pressure: II. Pressure-Volume Curves of Interstitial Space
Authors: GUYTON ARTHUR C.
Published: June 2012

Pressure-volume curves of the interstitial fluid spaces were estimated using four different methods. Interstitial fluid pressure was measured from implanted perforated capsules while interstitial fluid volume was varied (a) by perfusing the isolated hind limb of the dog with several types of fluid and at different perfusion pressures, (b) by elevating the venous pressure so that fluid would transude into the interstitial compartment, (c) by infusing large quantities of Tyrode's solution into the whole animal, and (d) by intravenous infusion of concentrated dextran solution. In all these studies, the compliance of the interstitial fluid system was found to be very low when the interstitial fluid pressure was negative but very high when the pressure rose slightly above atmospheric pressure. A physical model of the interstitial spaces was also constructed. Pressure-volume curves recorded from this model demonstrated a pattern of compliance changes similar to that shown by the interstitial pressure-volume curves recorded from dogs. These experiments give further support to the concept that the interstitial fluid pressure is normally negative but becomes positive as edema fluid accumulates.
Hemodynamic Effects of Hyperbaric Oxygenation in Experimental Acute Myocardial Infarction
Authors: KUHN LESLIE A. , KLINE HOWARD J. , WANG MICHAEL , YAMAKI TAKASHI , JACOBSON JULIUS H.
Published: June 2012

The hemodynamic effects of hyperbaric oxygenation were investigated in anesthetized dogs with acute myocardial embolism and infarction produced by injecting plastic spheres 325 micra in diameter. In 50 "control" animals with acute myocardial infarction induced while breathing either air at one atmosphere, 100% oxygen at one atmosphere or 7% oxygen at three atmospheres, 24-hour mortality was 85 to 90%. In 23 animals that received the same dose of microspheres and breathed 95 to 100% oxygen at three atmospheres for two hours following embolization, there was significantly less 24-hour mortality (30%), less ventricular fibrillation, and less advanced atrioventricular block. Hyperbaric oxygenation afforded protection against immediate mortality from ventricular fibrillation and also against later death, in shock, occurring within 24 hours of coronary embolization but after the immediate postembolization period had passed. In the animals exposed to hyperbaric oxygenation, declines of cardiac output and of central aortic pressure occurring 60 and 90 minutes after coronary embolization were significantly less than in the other animals.

In normal animals, hyperbaric oxygenation reduced cardiac output moderately, increased systemic vascular resistance, and elevated aortic pressure slightly.

The anatomic extent of the infarction did not differ detectably between the "control" animals and those treated with hyperbaric oxygenation.

It is concluded that hyperbaric oxygenation provides protection against mortality in the early period after coronary embolization by preventing ventricular fibrillation. In addition, prevention of major declines in aortic pressure and cardiac output during the later postembolization period in the group with hyperbaric oxygenation was associated with diminished rates of late mortality.
Some Characteristics of Ventricular Echoes
Authors: MENDEZ CARLOS , HAN JAOK , DE JALON P. D. , MOE G. K.
Published: June 2012

Reciprocal responses (ventricular "echoes") were initiated by premature stimuli applied directly to the bundle of His in dog hearts perfused from donor animals. The time relations of the responses in the His bundle and at the atrial margin of the exposed A-V node were studied under a number of conditions. It was found that:

1. The earliest premature response that can be induced in the His bundle is not propagated back to the atrium and does not lead to an echo.

2. There is, in most hearts, a continuous range of H
1
H
2
intervals (the echo "zone") within which reciprocal responses of the His bundle occur.

3. The earliest effective H
2
propagates slowly to the atrium, and the echo returns quickly.

4. The latest effective H
2
responses propagate more quickly to the atria, but return more slowly.

5. The atrium is an essential link in the echo pathway; i.e., the H
2
response must reach and activate the atrium before a return is possible.

6. Direct stimulation of the atrium in advance of the expected arrival of the A
2
response propagated from the His bundle can initiate a response which propagates
to
the bundle; i.e., two responses can travel in opposite directions on a collision course, yet one of them can complete its journey.

7. The limiting parameter of the return pathway is the refractory period of that portion of the lower node which must fire twice in the echo circuit.

8. The limiting element is not the bundle of His.

9. The limiting element can be discharged by early H
2
responses which fail to reach the atrium.

10. The refractory period of the limiting element is a function of the preceding cycle length.

It was also demonstrated that the echo "zone" is shifted to a range of longer H
1
H
2
intervals when the basic driving frequency is increased, or when the vagi are stimulated. Epinephrine shifts the echo zone to a range of briefer H
1
H
2
intervals.

It is suggested that echo responses occur when a retrograde impulse is arrested at one site within the node and continues to propagate to the atrium through collateral pathways. If the retrograde propagation time is long enough to permit the recovery of the lower elements of the node, an echo response reaches the His bundle. It was concluded that a self-sustained repetitive circuit may be possible when the round-trip conduction time exceeds the refractory period of the limiting tissue in the node.
Ouabain Effects on Cardiac Contraction, Action Potential, and Cellular Potassium
Authors: MüLLER PAUL
Published: June 2012

Transmembrane potential, isometric tension, and K
42
content of sheep or calf myocardial bundles were recorded simultaneously during periods up to 30 hours. Ouabain at low concentrations (1.5 x 10
-8
M/L) decreased intracellular K to a new steady level which was reached after several hours. Its value depended on drug concentration. The effect was reversible. There was a striking temporal parallelism between the potassium loss and the inotropic effect which was suggestive of a close relationship between the two phenomena. Action potentials during these experiments did not change in a consistent way.
Metabolism of Atherosclerotic Tissue of Rabbit and Dog, with Special Reference to Esterase and Lipase
Authors: MAIER NELICIA , HAIMOVICI HENRY
Published: June 2012

Esterase and lipase were studied in the aorta, liver, and serum of dogs and rabbits on an atherogenic diet. With the exception of dog serum, lipase was not present in any of the tissues studied.

At a relatively early stage the atherosclerotic intima-media layer, separated at the cleavage plane, showed increased esterase activity in both animals. At later stages, a reverse trend was noted in the rabbit, whereas in the dog, the esterase activity remained markedly increased. No pre-atherosclerotic enzymatic changes were noted.

The liver of both species showed increased esterase activity first and reversal to normal values later. In contrast, rabbit serum displayed no change for several months and decreased activity subsequently whereas in the dog, decreased esterase activity was noted throughout the administration of the atherogenic diet. Lipase activity in dog serum, which was unaffected for several months, decreased later.

Our results expand previous findings with other arterial enzymes and indicate further that metabolic alterations of the arterial wall are associated with the development of atherosclerosis.
Volumetric Analysis of Glomerular Size in Kidneys of Mammals Living in Desert, Semidesert or Water-Rich Environment in the Sudan
Authors: MUNKáCSI I. , PALKOVITS M.
Published: June 2012

The glomerular volumes in the kidneys were studied in four species of mammals, including a desert rodent, the jerboa (
Jaculus jaculus
); the laboratory white rat (
Rattus norvegicus
); a semidesert-living subprimate, the "bush baby" (
Galago senegalensis senegalensis
); and a primate, the grivet monkey (
Cercopitheus aethiops aethiops
). The measurements of volume were made according to the method of Palkovits and Zolnai which gives quantitative statistical values for the relative volumes of the glomeruli. An exact relationship between the average of the glomerular volumes, kidney weight, and body weight was not found in these different mammals when compared to each other. If the average volumes of the cortical and of the juxtamedullary glomeruli are compared separately then it is seen that the desert-living animals have a much bigger difference in volume between the cortical and the juxtamedullary glomeruli than those animals which require free access to water. In the kidney of the desert rodent (jerboa) the difference in volume between the cortical and the juxtamedullary glomeruli is 101% and, in the semidesert-living "bush baby," 169%. On the other hand the corresponding difference of volume in the laboratory white rat is only 21% and in the grivet monkey 28%. Considering the great functional importance of the juxtamedullary glomeruli and deep nephrons of the kidney in relation to dehydration, the large size of these structures can be regarded as an adaptation to life in an arid environment.
Detection of Preformed Venous Thrombi in Dogs by Means of I
131
-Labeled Antibodies to Dog Fibrinogen
Authors: SPAR IRVING L. , GOODLAND RUTH L. , SCHWARTZ SEYMOUR I.
Published: June 2012

Dogs with thrombin-induced thrombi received I
131
rabbit antibody to dog fibrinogen and a day later were given antiserum to the rabbit gamma globulin. Scintillation scanning techniques successfully detected the site of thrombosis. Excision of the thrombi and surrounding blood vessels demonstrated deposition of radioactivity in the lesion. The immunologic removal of the gamma globulin from the circulating blood increased the difference between the radioactivity deposited in the lesion and that present in the blood. This accentuates the lesion and offers potential diagnostic advantage.
In Vitro Demonstration of Vascular Hyper-responsiveness in Experimental Hypertension
Authors: HINKE JOSEPH A. M. , Simpson Patricia A.
Published: June 2012

The ventral caudal artery from DCA hypertensive and control rats was excised, mounted in a plastic chamber, and perfused with Krebs-Henseleit solution. Diameter of the artery and flow through the artery were measured at perfusion pressures ranging from 0 to 150 mm Hg. During these perfusions, constriction of the arterial segment was produced by adding norepinephrine, vasopressin, angiotensin II or rat serum in concentrations known to produce submaximal contractions.

Samples of each experimental artery before and after artificial perfusion were fixed, sectioned, and stained. The tunica media of hypertensive arteries was thickened. Also, degenerative changes were observed in the internal elastic lamina and adjacent tunica media. Structural thickening of the tunica media was due primarily to expansion of the extracellular space and also due possibly to muscle fibre hypertrophy.

In the absence of contraction, flow through the hypertensive artery was moderately reduced at all pressures because its lumen was narrowed by the thickened wall.

Total wall tension, muscle tension, and elastic tension of the artery were estimated from the pressure-flow-radius data. Strength of muscular contraction was then measured in terms of work performed during contraction at a constant pressure. From this analysis, the muscle fibres in hypertensive arteries were found to be unequivocally hyper-responsive to norepinephrine, vasopressin, and rat serum. The possible cause of this hyper-responsive property is discussed.

Serum was collected both from normotensive and from hypertensive donor rats and its pressor activity tested on the
in vitro
preparation. The pressor activity in hypertensive serum was found to be significantly elevated.

The elasticity of the hypertensive artery was increased in the absence of contraction and unchanged during contraction. No hypertensive artery was found to be stiffer than normotensive arteries. These changes are probably related to degeneration of elastin.
Quantitative Assessment of Pulmonary Edema
Authors: LEVINE O. ROBERT , MELLINS ROBERT B. , FISHMAN ALFRED P.
Published: June 2012

The present study has attempted to establish a reliable method for distinguishing quantitatively between pulmonary engorgement and engorgement plus edema. Pulmonary engorgement was produced in intact, anesthetized dogs by inflating a balloon in the left atrium followed by saline hemodilution. Hemodynamic events monitored included left atrial and pulmonary arterial pressures, and the colloid osmotic pressure. Clinical criteria, such as the rate and frequency of breathing, the chest roentgenogram, and the presence of audible rales, failed to distinguish reliably between engorgement and edema. The mechanics of breathing were more severely altered by engorgement and edema than by engorgement alone, but considerable overlap was present. Determination of the pulmonary blood volume and the extravascular water space of the lungs, by means of simultaneous T-1824 and tritiated water dilution curves, as described by Chinard and Enns, was a reliable method of detecting and quantifying pulmonary edema. The water space measured by this technique averaged 3.5 ml/kg body wt in normal, anesthetized dogs. It correlated well with the total lung water content determined at autopsy, measuring a constant fraction (approximately 50%) of the total lung water content, even in the presence of severe pulmonary edema. According to the results of the present study, pulmonary edema could be predicted reliably at autopsy when the extra-vascular water space was 6.0 ml/kg of body wt or greater.
Factors Controlling Pacemaker Action in Cells of the Sinoatrial Node
Authors: LU HSIN-HSIANG , LANGE GERTRUDE , McC. BROOKS CHANDLER
Published: June 2012

Rapid drive of isolated pacemaker tissues from cats resulted in a post-drive depression followed by a late acceleration to supernormal rates of pacemaker activity. These effects were similar to those occurring after drive of the pacemaker
in situ
. Lower SA nodal pacemakers discharged more slowly and irregularly than did upper SA nodal pacemaker cells. They were more readily depressed by rapid imposed drive. The balance between depression and acceleration varied in different preparations. Drive at only slightly above the intrinsic rate resulted frequently in acceleration not preceded by depression. Within limits, the greater the frequency and duration of drive, the greater the intensity and duration of both the depression and the late acceleration.

Prostigmin augmented and atropine reduced post-drive depression. Cocaine potentiated the late acceleration. Excess potassium reduced post-drive depression and, in concentrations used, caused some acceleration.

Pacemaker cells could be driven less rapidly than could other SA nodal cells. Drive generally shifted pacemaker action to a distant site; the first post-drive propagated responses originated from other pacemaker cells and dominance by the original unit was reestablished slowly. Rapid drive reduced amplitudes of action potentials and prepotentials. It also raised threshold potentials and during the post-drive period the durations of pacemaker cell action potentials were temporarily prolonged. In some preparations membrane potentials remained at a subnormal value after drive. Subthreshold potentials occurred at a somewhat subnormal rhythm but gradually developed an effective amplitude.

Conduction block was observed in isolated SA nodal tissue. This was augmented during the post-drive period of depression.

This work lends support to the hypothesis
1
that dominating action by pacemaker cells influences the pacemaker activity in other potential pacemaker tissues.
Fibrinolytic Activity in Thrombosed Veins
Authors: KWAAN HAU C. , ASTRUP TAGE
Published: June 2012

Thrombosis of the femoral vein in rats was produced by the injection of thrombin, serum, or sodium morrhuate into ligated venous segments. The histologic effects were followed during resolution or organization of the thrombus and were correlated with the appearance and localization of fibrinolytic activity as assayed histochemically.

Lysis of the venous thrombus began immediately when thrombin or serum had been used. Sites of thrombolysis were related to the presence of endothelial cells of venous origin and containing plasminogen activator. Sodium morrhuate destroyed the fibrinolytically active endothelial cells thus delaying thrombolysis. Recanalization was associated with the presence locally of active endothelial cells, originating presumably in the adjacent normal venous endothelium.

These results support previous observations on the vascular origin of the plasminogen activator. They elucidate the role played by the fibrinolytically active endothelium in the resolution of venous thrombi. They also confirm and extend previous observations on the role of fibrinolytic activity in tissue repair.
Left Ventricular Performance During By-Pass or Distension of the Right Ventricle
Authors: MOULOPOULOS SPYRIDON D. , SARCAS ARIS , STAMATELOPOULOS STAMATOS , AREALIS EVANGELOS
Published: June 2012

A dog heart preparation was used to investigate the direct or mechanical effects of a right ventricular by-pass and of right ventricular distension on the performance of the left ventricle. Several other factors known to affect left ventricular performance were eliminated.

The data obtained indicate impairment of left ventricular function either by right ventricular by-pass or by right ventricular distension. It is suggested that this impairment may be due to a direct effect of the volume of blood contained in the right ventricle and of right ventricular function on the common muscle bundles that encircle both ventricles.
Benefit from Testosterone and Hydrocortisone on Coronary Atherogenesis in Cockerels on a Low Protein Atherogenic Diet
Authors: JAIN SAVITRI , PICK RUTH , KATZ LOUIS N.
Published: June 2012

In the presence of high fat and high cholesterol in the diet, growing cockerels showed more marked hypercholesterolemia and atherosclerosis when their protein intake was low. Testosterone counteracted both the increased hypercholesterolemic and the enhanced atherogenic effects of a low protein diet. Hydrocortisone markedly aggravated the hypercholesterolemia in these cockerels but offered significant protection against coronary atherogenesis when associated with a low protein intake. When the dietary protein level is adequate neither testosterone nor hydrocortisone lowered coronary atherogenesis, despite modification of plasma cholesterol levels. Protein level in the diet must be considered in evaluating hormonal atherogenic effects.
Pressure-Volume Correlates of Left Ventricular Oxygen Consumption in the Hypervolemic Dog
Authors: ROLETT ELLIS L. , YURCHAK PETER M. , HOOD WILLIAM B. , GORLIN RICHARD
Published: June 2012

Volume changes in the intact functioning canine left ventricle were induced by whole blood infusion and were measured by the thermodilution technic. Multiple regression analyses were performed to detect significant correlations between hemodynamic variables and left ventricular oxygen consumption. Hemodynamic variables, in addition to the pressure-time integral, ventricular volume, and ventricular work, included estimates of myocardial stress, force, and shortening. The most significant individual correlates of oxygen consumption were the pressure-time integral (
r
=0.91) and ventricular end systolic volume (
r
=0.81), whereas the interaction of volume with pressure-time, thus approximating wall stress and force, was the most significant variable overall (r=0.93). A number of multiple linear regression models were tested for the prediction of ventricular oxygen consumption. The equation (model E) with the greatest multiple regression coefficient (R=0.947) included heart rate, pressure-time per beat, pressure-time per minute, end systolic volume, and (end systolic volume)
2/3
as independent variables. A less elaborate regression equation including only pressure-time per minute and end systolic volume as independent variables was, however, nearly as accurate as model E in the prediction of oxygen consumption. The addition of estimates of left ventricular work and shortening to these regression models did not further improve the ability to predict oxygen consumption accurately.

The relationships between these hemodynamic variables and ventricular oxygen consumption were not altered by pericardiotomy or catecholamine depletion. In the hypervolumic heart acute ventricular dilatation did not occur following pericardiotomy.

The results of this study confirm the postulate that an increase in ventricular volume, as well as pressure, will be accompanied by an increase in ventricular oxygen consumption. This in turn implies a relationship between the wall stress or force generated by the myocardium and the energy requirement of contraction.
Effects of Hyperbaric Oxygenation on Coronary Artery Occlusion in Pigs
Authors: Peter Robert H. , Rau Ronald W. , Whalen Robert E. , Entman Mark L. , McIntosh Henry D.
Published: June 2012

To evaluate more precisely the possible protective effect of hyperbaric oxygenation in experimental myocardial infarction, gradual occlusion of a coronary artery was produced in the pig. Ameroid constrictors designed to produce complete occlusion within 48 hours were placed on the left anterior descending coronary artery of 24 young farm pigs. Of these, 12 were placed in a hyperbaric chamber at 1.25 atmospheres absolute and allowed to breathe 100% oxygen for a maximum of 32 hours. For control studies 12 other pigs were handled in a similar manner outside the chamber while breathing air at normal atmospheric pressure. Pigs treated with hyperbaric oxygenation outlived the untreated pigs. Pathological and histochemical studies of the hearts revealed that pigs treated with hyperbaric oxygenation had a high incidence of myocardial infarction, whereas only two pigs in the untreated group showed any evidence of myocardial damage. These findings suggest that moderate but prolonged hyperbaric oxygenation may lengthen life during and after coronary occlusion. This prolongation of life may permit the development of pathologically detectable myocardial infarctions.
Use of Indicator Dilution Techniques in Measuring Combined Aortic and Mitral Insufficiency
Authors: Bloomfield Dennis A. , Battersby Edward J. , Sinclair-Smith Bruce C.
Published: June 2012

In patients with combined aortic and mitral valvular insufficiency, the combined regurgitant fraction across both valves has been shown to equal the product of the regurgitant fractions at each valve. This relationship was validated in nine patients, and in eight other patients was used to predict the degree of regurgitation at one valve when the regurgitant fraction at the other valve and the combined regurgitant fraction were known. Confirmation of the predicted degrees of insufficiency were afforded by cineangiocardiography and surgical inspection. Information of considerable usefulness predicting the least possible degrees of valvular insufficiency could be obtained from the measurement of the combined regurgitant fraction alone.