bluuebunny/crossref_metadata_2025 huggingface dataset:
Cataracts and hypertension in salt-sensitive rats. A possible ion transport defect.
Authors: Rodríguez-Sargent C , Cangiano J L , Berríos Cabán G , Marrero E , Martínez-Maldonado M
Published: June 2012

In previous unrelated studies, we observed a 35 to 50% incidence of cataract formation in several groups of Dahl salt-sensitive hypertensive rats (DS) over a 4-year period. In the present study we evaluated longitudinal changes in blood pressure in DS in which cataracts eventually developed and those in which cataracts did not develop when all animals were maintained on a high sodium diet. Lenses were evaluated by slit-lamp microscopy to determine if cataractous lesions were similar among rats, to classify lesion types, and to define the age at which cataracts were detectable in DS. The possible participation of several cataractogenic risk factors as major influences on cataract formation also was evaluated. Finally, aqueous humor concentrations and lenticular content of sodium and potassium were determined to evaluate the possibility that a defect in ion transport at the lens epithelium and ciliary body might play a role in cataractogenesis in DS, since ion transport defects have been shown to lead to lens opacification in other models of genetic and experimental cataracts. Parallel studies were performed in Dahl salt-resistant control rats (DR). A high incidence of cataract formation was found in DS. Although systolic blood pressure was not consistently greater in adult DS with cataracts compared with values in age-matched DS without cataracts, the initial pressor response to a high salt diet was greatest in weanling DS in which cataractous lesions later developed. Slit-lamp analysis revealed that cataracts in this genetic model were cortical, with one mixed cortical, nuclear lesion. Posterior subcapsular lesions were not observed, suggesting that lesions were not steroid-induced.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of the cold pressor test on muscle sympathetic nerve activity in humans.
Authors: Victor R G , Leimbach W N , Seals D R , Wallin B G , Mark A L
Published: June 2012

The purpose of this study was to determine the effects of the cold pressor test on sympathetic outflow with direct measurements of nerve traffic in conscious humans and to test the strength of correlation between sympathetic nerve discharge and the changes in arterial pressure, heart rate, and plasma norepinephrine. In 25 healthy subjects, arterial pressure, heart rate, and muscle sympathetic nerve activity were measured with microelectrodes inserted percutaneously into a peroneal muscle nerve fascicle in the leg during immersion of the hand in ice water for 2 minutes. Arterial pressure rose steadily during the first and second minutes of the cold pressor test. Muscle sympathetic activity (burst frequency X amplitude) did not increase in the first 30 seconds of the test but increased from 230 +/- 27 to 386 +/- 52 units (mean +/- SE, p less than 0.05) by the end of the first minute of the test and to 574 +/- 73 (p less than 0.01) during the second minute. In contrast, heart rate increased maximally during the first 30 seconds of the cold pressor test and returned to control during the second minute. The increases in heart rate were abolished by beta-adrenergic blockade. The increases in muscle sympathetic activity during the cold pressor test were correlated with the increases in both mean arterial pressure (r = 0.86, p less than 0.01) and peripheral venous norepinephrine (r = 0.72, p less than 0.05); however, large changes in nerve traffic were associated with small changes in plasma norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)
Red blood cell Na+,K+-ATPase in men with newly diagnosed or previously treated essential hypertension.
Authors: Ringel R E , Hamlyn J M , Hamilton B P , Pinkas G A , Chalew S A , Berman M A
Published: June 2012

Alterations of cellular function of Na+,K+-adenosine triphosphatase (ATPase; Na+-K+ pump) have been implicated in the pathophysiology of essential hypertension. Therefore, this aspect of red blood cell (RBC) Na metabolism was studied in black men with newly diagnosed, untreated essential hypertension (NEH) and a normotensive control group. RBC Na content, Na+-K+ pump number (ouabain binding sites), and pump activity were measured. No statistically significant differences were found between the two groups for any of these three parameters. However, a group of previously treated essential hypertensive subjects (PEH) who had been withdrawn from therapy in the preceding 6 weeks were also studied. This group differed significantly from the NEH subjects in regard to all RBC Na+-K+ pump parameters. Their RBC Na content (10.27 +/- 3.23 vs 7.77 +/- 2.52 mmol Na/LRBC; p = 0.006) was higher, and their Na+-K+ pump activity (166 +/- 50 vs 221 +/- 87 nmol inorganic phosphate/mg membrane protein/hr; p = 0.03) and Na+-K+ pump number (213 +/- 40 vs 284 +/- 85 binding sites/RBC; p = 0.001) were lower compared with those in NEH subjects. Although the PEH subjects were older and somewhat less hypertensive than their NEH counterparts, these factors were not found to influence the Na+-K+ pump parameters. These results indicate that chronic diuretic therapy of patients with essential hypertension is associated with a reduced number of RBC Na+-K+ pumps. Since RBCs are not considered target cells for diuretics, the effects of these drugs on RBC electrolyte metabolism may occur at the time of erythropoiesis by the production of RBCs with fewer Na+-K+ pumps.(ABSTRACT TRUNCATED AT 250 WORDS)
The opioid peptides. A role in hypertension?
Authors: Feuerstein G , Siren A L
Published: June 2012

This review is an attempt to highlight evidence that may implicate the endogenous opioid system in the pathogenesis of hypertension in humans. The evidence raised includes biochemical, physiological, pharmacological, and behavioral studies conducted in in vitro and in vivo systems, experimental models of hypertension, and humans with essential hypertension. While the compelling biochemical and pharmacological evidence in experimental animals clearly shows the presence of opioid peptides and their receptors in strategic sites of cardiovascular control and potent cardiovascular response to opioid peptides, opioid antagonists show no consistent blockade or reversal of hypertension in experimental animals or humans. One possible explanation for this phenomenon could be the vast redundancy in systems regulating blood pressure (i.e., the blockade of one system still leaves many other systems fully able to rapidly offset the eliminated system). Regarding the opioid system, the situation is much more complex, since some opioid receptors (mu-type) mediate pressor responses, while other receptors (kappa-type) mediate depressor responses. Therefore, nonselective opioid receptor antagonists (e.g., naloxone), which block both types of receptors, can be devoid of any cardiovascular activity, while a selective mu-receptor antagonist or a selective and potent kappa-receptor agonist may produce the desired antihypertensive effect. A combination of both actions (i.e., a drug that is both a mu-antagonist and a kappa-agonist) might be even more advantageous. Until such compounds are developed, this hypothesis will be hard to prove.
Hypertension-induced alterations in copper and zinc metabolism in Dahl rats.
Authors: Clegg M S , Ferrell F , Keen C L
Published: June 2012

It has been suggested that one risk factor in the development of hypertension and vascular disease may be abnormal copper and zinc metabolism. In the current study we tested the hypothesis that hypertension itself may result in alterations in the metabolism of these essential elements. Dahl salt-sensitive rats were fed diets containing 0.4 or 8.0% NaCl for 32 days. At the conclusion of the study, blood pressure was significantly higher in the rats fed a high NaCl diet than in controls. Liver, kidney, and heart copper concentrations were significantly lower in the rats fed a high NaCl diet compared with controls, while plasma copper levels were higher. In contrast, tissue zinc levels were higher in the rats fed a high NaCl diet than in controls, while plasma zinc levels were lower. It is hypothesized that alterations in copper and zinc metabolism may be one factor underlying tissue damage in these animals.
Captopril and nifedipine in combination for moderate to severe essential hypertension.
Authors: Singer D R , Markandu N D , Shore A C , MacGregor G A
Published: June 2012

The effects of the addition of a calcium entry antagonist, nifedipine (20-mg tablet twice a day), to an angiotensin converting enzyme inhibitor, captopril (25 mg three times a day), and the addition of captopril to nifedipine were observed in two separate studies in patients with essential hypertension. After 4 weeks of captopril therapy alone, mean arterial pressure fell by 12 mm Hg, and with the addition of nifedipine to captopril for a further month, blood pressure fell by an additional 10 mm Hg. In a separate group of patients treated with the same doses, mean arterial pressure fell by 17 mm Hg with nifedipine treatment alone; when captopril was added to the nifedipine therapy for an additional month, mean arterial pressure fell by a further 11 mm Hg. These blood pressures were measured 2 hours after the last dose; however, there was less of a fall in blood pressure when it was measured 12 hours after the last dose. This study confirms that captopril and nifedipine have a marked additive effect on blood pressure in whichever order they are given, but it shows that the combination is relatively short-acting.
Local Postural Vasomotor Reflexes Arising from the Limb Veins
Authors: GASKELL PETER , BURTON ALAN C.
Published: June 2012

Blood flow of the toes and fingers was studied plethysmographically with the level of the blood vessels below or above the heart, using the contralateral digit as control. The apparent flow is a maximum when the vessels are near the heart level. The decrease of flow when the vessels are raised is explained on the basis of narrowing and closure of vessels when the hydrostatic pressure within them falls. The decrease in flow when the limb is lowered is interpreted as evidence of a vasoconstriction elicited by distension of the local veins. This raises serious doubt about the classic flow method.
The Functional Anatomy of Ventricular Contraction
Authors: RUSHMER ROBERT F. , CRYSTAL DEAN K. , WAGNER CLYDE
Published: June 2012

Changes in dimensions of the ventricular chambers and the displacement of specific points on the walls of the heart have been studied by the cinefluorographic technic. The contributions of the various myocardial layers to ventricular ejection have been considered in terms of the anatomic architecture of the heart. The mechanical effectiveness of myocardial contraction is closely related to the degree of diastolic distension and the magnitude of the stroke volume. During contraction, the various layers must exert tension on the connections between them. Energy expended in this manner does not contribute to ventricular ejection but could theoretically promote rapid filling during the early diastolic period.
The Effects of Progressive General Anoxia on the Pulmonary Circulation
Authors: HÜRLIMANN ALBERT , WIGGERS CARL J.
Published: June 2012

The effects of progressive anoxia on the hemodynamic changes in the pulmonary circuit were reinvestigated in anesthetized dogs. Evidence is presented that some increase in pulmonary arterial resistance takes place, but that the augmented output of the right ventricle is dominantly responsible for elevation of the pulmonary arterial pressure when anoxia affects the body as a whole.
Polyvinylpyrrolidone: The Electromigration Characteristics of the Blood Plasma Expander
Authors: McDONALD HUGH J. , SPITZER ROBERT H.
Published: June 2012

Before the metabolic role of the blood plasma expander, polyvinylpyrrolidone (PVP) can be studied by the technic of ionography, some fundamental ionographic characteristics of the polymer, per se, must be determined. This study is concerned with the influence of such variable factors as time, potential gradient, temperature, the pH of the buffer and its ionic strength on the mobility of the migrant when under the influence of an electrical field, and an attempt has been made to correlate them. This work, then, may serve as a basis for later investigations to be made on the combining power of PVP for certain physiologic products with which it comes into intimate contact when used as a plasma expander.
Activation of Sympathetic Vasodilator and Vasoconstrictor Neurons by Electric Stimulation in the Medulla of the Dog and Cat
Authors: LINDGREN PERCY , UVNÄS BÖRJE
Published: June 2012

Electric stimulation in the ventrolateral area of the medulla elicited vasodilation in skeletal muscles, and vasoconstriction in the skin and intestines. The vasodilation was accredited to activity in the cholinergic sympathetic vasodilator outflow previously shown to originate in the motor cortex of the dog. The possible functional significance of the vasodilator fibers in regulating muscle blood flow during exercise is discussed.
Influence of Ultrasonic Irradiation on Temperature and Blood Flow in Human Skeletal Muscle
Authors: BICKFORD ROBERT H. , DUFF ANO ROBERT
Published: June 2012

The circulatory response to ultrasonic irradiation of the upper limbs was measured under controlled conditions by venous occlusion plethysmography. Volumetric blood flow changes were related to temperature measurements in the treated tissues. Ultrasonic irradiation of the extremities was not found, per se, to be an effective means of promoting a sustained increase in blood flow. The information obtained on the nature of the circulatory effects of ultrasonation permits a more satisfactory evaluation of this new method of treatment.
Effect of Nicotine on the Coronary Blood Flow and Related Circulatory Parameters
Authors: Bellet Samuel , West James W. , Müller Otto F. , Manzoli Ugo C.
Published: June 2012

The effect of intravenously administered nicotine (20
µg
./Kg./min.) on the coronary blood flow and related hemodynamic parameters was studied in the normal intact dog and in the dog with chronic coronary insufficiency as produced either by coronary artery ligation or gradual coronary artery narrowing. Nicotine increases cardiac work markedly by an increase in the mean arterial blood pressure and cardiac output. The degree of this increase is similar in normal dogs arid dogs with chronic coronary insufficiency. The mean control coronary blood flow was moderately decreased in dogs with coronary artery ligation and markedly decreased in dogs with narrowing of the two main branches of the left coronaryatery. Nicotine produced an increase in coronary blood flow which in normal dogs was observed to be as high as 125 per cent on an average over the control value. The average increase was consider ably less in dogs with ligation of one coronary artery branch (82.5 per cent) and in dogs with narrowing of two main branches (83.3 per cent). The degree of coronary narrowing and/or occlusion was directly related to the response of the coronary flow; the greater the coronary impairment, the smaller was the increment in corollary blood flow frequently dropped below the control value in the postinfusion period, Coronary vascular resistance and myocardial oxygen utilization declined during the event of nicotine administration. The response of the coronary blood flow to nicotine resembled that of anoxemia in the presence of coronary insufficiency. These findings would appear to have a bearing on the clinical problem relative to the effect of nicotine in the human subject with coronary artery disease.
Effects of Persantin (RA8), A New Coronary Vasodilator, on Coronary Blood Flow and Cardiac Dynamics in the Dog
Authors: West James W. , Bellet Samuel , Manzoli Ugo C. , Müller Ottto F.
Published: June 2012

The effect of a new coronary vasodilator (Persantin), which produces a marked increase in coronary blood flow (up to 159 per cent in normal animals) without increasing cardiac contractility or cardiac work, has been studied in the experimental animal. This is associated with a marked decrease in coronary resistance. There is an increase in the coronary venous oxygen content and a decrease in the coronary A-V oxygen difference; the cardiac output is only slightly affected. Increase in the coronary blood flow has also been observed in dogs in which coronary in sufficiency has been produced by coronary ligation and by narrowing of the lumen of the coronary artery by the application of casein rings. This was accompanied by no significant increase in cardiac work.
Aortic Arteriosclerosis in the Dog After Localized Aortic Irradiation with Electrons
Authors: Lindsay Stuart , Entenman Cecil , Ellis Eldon E. , Geraci Charles L.
Published: June 2012

The distal segments of the abdominal aortas of 15 dogs were irradiated with electrons in doses ranging from 1,000 to 9,500 rads and were examined histologically at intervals ranging from 2 weeks to 17 months following irradiation. Pronounced aortic arteriosclerosis developed and was sharply localized to the aortic segment irradiated. Except in one dog, radiation-induced arteriosclerosis was more pronounced on the dorsal than on the ventral aortic wall. There was no evidence that severity of aortic arteriosclerosis was related to the dose of irradiation or was increased with time following irradiation. The development of arteriosclerotic lesions of the aorta induced by electron irradiation was similar to that observed after x-irradiation and to that occurring naturally in old dogs. It is suggested that electron irradiation may have caused selective injury of the internal elastic lamina, which was then followed by intimal fibrous proliferation and formation of intimal plaques.
Electrophysiological Study of Human Heart Muscle
Authors: TRAUTWEIN WOLFGANG , KASSEBAUM DONALD G. , NELSON RUSSELL M. , HECHT HANS H.
Published: June 2012

Membrane potential changes in human ventricular and atrial muscle, excised from patients undergoing open-heart surgery, were recorded by micro-electrodes in vitro.

Mean ventricular resting and action potentials were -87 mv. and 115 mv., respectively. The mean atrial resting potential was -70 mv., mean action potential 75 mv. Two forms of atrial action potential were found, one having conventional contour, the other with prominent spike and plateau. A disturbance in repolarization is believed to underlie the latter type of atrial potential cycle.

The relation between the upstroke velocity of the action potential and the extracellular sodium concentration and membrane potential was shown to be similar to that in other mammalian cardiac tissue. The mean conduction velocity determined in ventricular fibers (1.3 M./sec.) was somewhat greater than that of the dog, and the possible relationship to hypertrophy of the cardiac fibers in the preparations studied is described.

The effect of increased rate and anoxia in reducing the action potential duration is like that found in the hearts of other mammals.

The conductance type of inhibition was produced by acetylcholine in spontaneously beating atrial tissue. The excitatory effect of epinephrine was preceded by a transitory inhibition.

The basic mechanisms underlying the action potential, automaticity and transmitter effects, derived from investigation of other mammalian cardiac tissue are applicable to the human heart.
Use of External Counting Technics In Studies of the Circulation
Authors: Conn Hadley L.
Published: June 2012

A variety of external counting technics has been used to study the circulation. Brief consideration has been given to some of those concerned with measurement of cardiac output, myocardial and other regional blood flows, and cardiopulmonary volumes, and to those related to the evaluation of vascular shunts.

These technics have much in common. They are simple to carry out, require little time to accomplish, and entail little risk for the subject. At the same time, they are to varying extents imprecise, and are not as accurate as methods currently available or methods of undetermined validity or both. They do not offer the means to measurement of intravascular pressures and so cannot replace cardiac catheterization. As yet, little new information about the circulation has been gained by application of these methods.

The ultimate place of external counting technics in the study of the circulation is still undetermined. The best prediction is that these methods will probably supplement but not replace diagnostic methods now in use. They should serve a valuable function as tests for screening of subjects being considered for more definitive and laborious procedures and as supplementary tools in the performance of these more definitive astudies.
Architecture of Small Arteries during Vasoconstriction
Authors: Van Citters Robert L. , Wagner Bernard M. , Rushmer Robert F.
Published: June 2012

The cytoarchitectural changes which take place in the walls of small arteries (about 1 mm. O.D.) during vasoconstriction and vasodilation have been studied. Vessels were fixed while in their functional state by immersion in liquid isopentane at -170 C. and prepared for microscopic examination by freeze substitution.

The walls of control vessels were thin in relation to the diameter of lumina (WT:L 1:30), indicating that they are more distended than they appear in routinely fixed sections. Vessels dilated with ACH had even thinner walls (WT:L 1:40). Vasoconstriction, induced by local application of epinephrine, increased the wall thickness and reduced the size of the lumen (WT:L 1:2) but in no case was the lumen obliterated in arteries of this size.

Although an increase in the WT:L ratio is commonly employed as evidence of vascular hypertrophy, normal vessels which are fixed and sectioned while in a functional state of vasoconstriction may exhibit similar gross characteristics. Constricted vessels are characterized by progressive deformation of the internal elastic lamina, crowding of endothelial cells, and distortion of smooth muscle cells and their nuclei, particularly in the region immediately adjacent to the lumen. During intense vasoconstriction, the wall tension appears to be supported only by the outer layers of the vessel.
Cardiovascular Responses to Hypoxic Stimulation of the Carotid Bodies
Authors: Downing S. Evans , Remensnyder John P. , Mitchell Jere H.
Published: June 2012

The hemodynamic responses to hypoxic stimulation of the carotid bodies were investigated in the dog with controlled respiration. A dual, rotating disc oxygenator system was utilized to perfuse the vascularly isolated carotid region alternately with blood of high or low pO
2
. Perfusion of the carotid bodies with hypoxic blood caused a large reduction of heart rate. The bradycardia response was reduced, but not abolished, by vagotomy. However, the subsequent administration of hexamethonium completely abolished the response. The contractility of the atrium was reduced by carotid body hypoxia, and varying degrees of heart block were frequently observed. These responses were abolished by vagotomy and considered to be due to efferent vagal activity. Ventricular function curves showed that carotid body hypoxia usually caused a reduction, never an increase, of ventricular contractility. This indicates a reduction of sympathetic discharge to the heart. The reduction in heart rate after vagotomy and the reduction in ventricular contractility were associated with a concomitant increase of total peripheral resistance. These findings indicate that hypoxic stimulation of the carotid bodies causes a dichotomous sympathetic response, that is, a reduction of sympathetic discharge to the heart and a simultaneous increase of sympathetic discharge to the peripheral vasculature. Systemic hypoxia caused an increase of both ventricular contractility and total peripheral resistance. Consequently, the hemodynamic responses to systemic hypoxia cannot be entirely ascribed to a primary chemoreceptor reflex from the carotid bodies. It is suggested that the cardiac sympathetic responses seen in systemic hypoxia are due, at least in part, to direct hypoxic stimulation of the central nervous system.
Relation Between Pressure and Diameter in the Ascending Aorta of Man
Authors: Greenfield Joseph C. , Patel Dali J.
Published: June 2012

The pressure-diameter relationship in the ascending aorta of man was estimated directly in 10 patients undergoing open-heart surgery. The diameter was measured by means of an electrical strain-gauge caliper sutured to the vessel wall. The lateral intravascular pressure was measured using a 22-gauge needle connected directly to a Statham P23Db strain gauge. The results indicate: (1) a gross similarity between the pressure and diameter curves; (2) the mean value for ratio of change in radius to change in pressure (ΔR/ΔP) was 1.82 x 10
-3
cm. per cm. H
2
O (± S.D. 0.80); (3) the mean value for circumferential extensibility was 0.14 per cent change in radius per cm. H
2
O (± S.D. 0.06); and (4) the change in cross sectional area during an average cardiac cycle was 11 per cent of the diastolic value.
Thixotropy of Blood and Proneness to Thrombus Formation
Authors: Dintenfass Leopold
Published: June 2012

A study of the viscosity and thixotropy of human blood in the absence of anticoagulants was carried out by means of a rotational cone-in-cone viscometer.

The plots of viscosity against the rate of shear on a log-log scale show that the thixotropy of normal blood is pronounced only below 5 sec.
-1
; abnormally thixotropic blood was characterized by the critical rates of shear of 30 to 60 sec.
-1
.

The significance of thixotropy of blood is due to its intimate relationship with the aggregation of red cells. It is suggested that it may be also related to the proneness of thrombus formation.
Vasa Vasorum of the Pulmonary Artery of the Rabbit
Authors: Sobin Sidney S. , Frasher Wallace G. , Tremer Herta M.
Published: June 2012

In the rabbit, the arterial and venous vasa vasorum of the pulmonary artery from its origin to the entrance of the right and left pulmonary arteries into the lung were studied and described through the use of a specially prepared silicone rubber injection mass. The physical-chemical characteristics of this material allowed detailed filling of the vascular bed under physiological conditions. Special features of the rich arterial and venous vasa vasorum of the pulmonary artery include: (1) spiral palisading of small vessels and (2)arterial and venous vasal confluences that result from the junction of branches from multiple supply and drainage sites. Both of these may be special adaptations for the normal rapid stretch of the pulmonary artery.
Hemodynamic Alterations of Acute Pulmonary Thromboembolism
Authors: Parmley Loren F. , North Robert L. , Ott Bruce S.
Published: June 2012

A method is described of producing pulmonary embolism in the dog by the use of various-sized autologous clots made radiopaque. This method of experimental pulmonary embolism results in dilatation of the large- to small-sized pulmonary arteries and a consistent hemodynamic response in the pulmonary circulation, characterized by a marked rise in pulmonary arteriolar resistance with increased pulmonary arterial pressure but persistently normal pulmonary venous and "capillary" pressures.

Data are presented to support the concept that the pulmonary hemodynamic changes that result from an initial pulmonary thromboembolism are primarily the result of vasoconstriction of the small pulmonary arteries or arterioles, presumably by a reflex mechanism. Mechanical blockage of the pulmonary vascular bed is considered to be of importance in causing hemodynamic alterations only after massive or repeated pulmonary embolism. The increase in pulmonary arteriolar resistance that results from the vasomotor response to pulmonary embolism is transient, whereas that due to mechanical blockage results in sustained pulmonary hypertension.

Systemic arterial pressure does not show a consistent response to pulmonary embolism and could not be related to the hemodynamic alterations that occurred in the pulmonary circulation. Severe systemic hypotension resulted unpredictably but was more frequent after repeated or extensive pulmonary embolism. The systemic hypotensive reaction to pulmonary embolism is only in part due to a decreased cardiac output. The more severe responses are best explained on the basis of a vasomotor reflex producing a decrease in systemic arterial resistance.

The two mechanisms of death in this experimental series were severe systemic hypotension with development of fatal ventricular arrhythmias and, almost as frequent, pulmonary edema that was characterized by severe pulmonary hypertension in the presence of a normal pulmonary venous pressure.

There are many similarities between the experimental findings of this study and the clinical event of human pulmonary thromboembolism. Attention is drawn to the need for further investigation of the mechanism of the systemic arterial pressure response that often causes death and appears to be independent of the magnitude of the pulmonary hemodynamic changes.
Pressure Pulse in Small Arteries
Authors: Sugiura Takero , Freis Edward D.
Published: June 2012

Pressure pulse contours have been obtained in the small mesenteric and intestinal arteries of the dog. The principal change in the pressure pulse during transmission from large to small arteries appeared to be the gradual and progressive development of damping. The pressure drop from the aorta to arteries of 200 µ internal diameter averaged 17 per cent systolic and 12 per cent diastolic. Elevation of blood pressure with norepinephrine or angiotensin decreased the large-to-small artery pressure gradient, as well as the apparent degree of damping. Reduction of arterial pressure following hexamethonium or hemorrhage had the opposite effect. The evidence suggested that arteries of 200 µ diameter and larger function primarily as transport vessels and play no important role in altering the peripheral vascular resistance.
Coronary Vasodilation Produced by Bradykinin on Isolated Mammalian Heart
Authors: Antonio Abilio , Rocha e Silva Mauricio
Published: June 2012

Synthetic bradykinin (SBR 640) was assayed on the isolated hearts of the guinea pig, the rabbit, the cat, the dog, and the rat. With the exception of the rat's heart, all reacted strongly to bradykinin with an increase in coronary flow. The guinea pig's heart was by far the most sensitive, reacting to concentrations of bradykinin of the order of 10
-9
to 10
-10
and therefore being as sensitive as the rat's uterus and rat's duodenum, so far the preparations most sensitive to bradykinin. On the dynamics of a normally beating heart, the effects of bradykinin are slight or trivial. When the amplitude or rate is reduced, bradykinin tends to increase both. There was, however, no relationship between its effects on the frequency or amplitude and its strong vasodilating effect on the coronary vessels. Since there was no tachyphylaxis to even threshold doses of bradykinin, the conclusion is drawn that it affects directly the coronary bed through its typical vasodilating action.

The possibility of bradykinin being a mediator in the coronary vasodilation produced by epinephrine has been discussed.
Thebesian Drainage of the Septal Artery
Authors: MOIR THOMAS W. , ECKSTEIN RICHARD W. , DRISCOL THOMAS E.
Published: June 2012

Direct right ventricular drainage of I
131
serum albumin injected into the septal artery of the normally beating dog heart has been demonstrated. By the application of standard dilution equations to the time-concentration curves recorded in the pulmonary artery, estimates of the magnitude of this Thebesian drainage have been made. Approximately 80% of septal artery outflow has been estimated to drain directly into the right ventricle; this amount comprises about 12.8% of total common left coronary flow and, in part, explains the discrepancy found between common left coronary inflow and coronary sinus outflow.

The implications of Thebesian drainage of a branch of the common left coronary artery relative to the use of coronary sinus sampling for left ventricular metabolic studies have been discussed.
Hemodynamic Effects of Guanethidine in Man
Authors: COHN JAY N. , LIPTAK THOMAS E. , FREIS EDWARD D.
Published: June 2012

Guanethidine was administered in a single intravenous infusion to supine hypertensive and normotensive subjects. Hemodynamic changes during the transient pressor phase were consistent with catechol amine effect. The later hypotensive effect occurred only in the hypertensive subjects and was usually associated with a slight decrease in cardiac output in patients without cardiac decompensation and a slight increase in output in those with congestive heart failure. Total peripheral resistance decreased although there was an increase in splanchnic vascular resistance and a decrease in the percentage of the cardiac output perfusing the hepatic-portal bed.

Tests of sympathetic nervous system activity revealed that, although the Valsalva "overshoot" usually was blocked, complete inhibition of digital vasoconstrictor reflexes did not always occur and vascular responsiveness to tyramine and ephedrine was not diminished up to six hours following intravenous guanethidine. Tyramine responses were also demonstrated in a group of patients on effective long-term oral therapy with guanethidine.

These studies suggest that guanethidine has unique hemodynamic effects not necessarily shared by ganglionic blocking agents, bretylium tosylate, or reserpine. Catechol amine depletion probably is not important in the mechanism of the antihypertensive and sympathetic inhibitory actions in man, and the possibility of an additional non-adrenergic effect is considered.
A Concept of Negative Interstitial Pressure Based on Pressures in Implanted Perforated Capsules
Authors: GUYTON ARTHUR C. , Frank Malcolm , Abernathy Berry
Published: June 2012

Over 200 perforated plastic capsules were implanted in different tissues of the dog, and the wounds were allowed to heal. After one month, pressures measured by inserting a needle through the skin and then through a perforation of the capsule into its cavity were always negative in normal tissues, averaging-6.4 mm Hg. The pressure was always positive in edematous tissues. Evidence is presented to indicate that the pressure measured in the capsule is equal to, or nearly equal to, the interstitial fluid pressure in the tissue spaces surrounding the capsule. On the other hand, pressure measurements made by a needle technic failed except in rare instances to give negative values in normal tissues but in edematous tissues gave almost exactly the same values as those recorded by the capsules. Also, pressures measured by the capsules changed in accordance with Starling's law of the capillaries when (a) venous pressure was raised, (b) when arterial pressure was lowered, (c) when the tissues were dehydrated by intravenous infusion of dextran, or (d) when the tissues were hydrated by intravenous infusion of saline. Pressures measured by a needle technique failed to change in accordance with this law in these same experiments. Therefore, it is concluded that needle pressure determinations in non-edematous tissue do not measure the interstitial fluid pressure.
Systems Behavior, Feed-back Loops, and High Blood Pressure Research
Authors: PETERSON LYSLE H.
Published: June 2012

A major challenge to those investigating the etiology and progress of hypertension, as well as of other diseases, results from the fact that the control and regulation of most bodily functions are comprised of multiple feedback loops involving many bodily "systems." Thus, mechanisms which seem to offer clues as to the etiology of an abnormality, when investigated as an isolated function, fail to explain the etiology when sought in the intact experimental animal or patient.

Examples of simple closed-loop systems are described to illustrate the effects of feed-back. A simplified diagram of several factors known to play a role in the control and regulation of the characteristies of the blood vessel wall is described to illustrate the multiplicity of the feed-back pattern which probably occurs. Furthermore, it is evident that almost none of the factors which constitute the loops have been evaluated sufficiently to permit characterization of the system. It is not surprising that apparently promising clues turn out to be disappointing and to become lost in the system.

The medical investigator must learn to deal with methods of analyzing systems containing multiple factors and functions as well as to characterize the properties and behavior of the parts of the system.
Duration of the Phases of Left Ventricular Systole
Authors: WALLACE ANDREW G. , MITCHELL JERE H. , SKINNER N. SHELDON , SARNOFF STANLEY J.
Published: June 2012

The effects of altering stroke volume, aortic pressure and heart rate on the duration of each phase of left ventricular systole were investigated in a denervated dog heart.

Augmenting stroke volume was found to prolong ejection, shorten the isovolumic period and had little or no effect on the duration of total systole. Elevating mean aortic blood pressure shortened ejection time, prolonged the isovolumic phase and either had no effect or decreased slightly the duration of total systole. Increasing heart rate at constant aortic pressure and stroke volume reduced the duration of all phases of systole. Digitalis and norepinephrine shortened all phases of systole.

These findings demonstrate that the duration of each phase of left ventricular systole is dependent upon existing hemodynamic conditions as well as on the contractile state of the myocardium. By means of intrinsic mechanisms the ventricle exhibits the remarkable capability of being able to adjust the duration of each phase of systole in a manner appropriate to changing hemodynamic conditions.
Pressure Transmission in Pulmonary Arteries Related to Frequency and Geometry
Authors: ATTINGER ERNST O.
Published: June 2012

The propagation of the pulse wave through the canine pulmonary arterial tree has been evaluated by means of harmonic analysis. The apparent phase velocity varied both with frequency and distance as one would expect in the presence of reflected waves. The phase velocity was about 230 cm/sec for the inflated and 325 cm/sec for the deflated lung. Theoretical considerations as well as experimental results indicate that the major branches represent the primary reflection site for the pulse wave. The pulse pressure is transmitted across the pulmonary capillary bed, although at a high attenuation, and the transmission varies markedly with lung volume.

The dimensions of the pulmonary arterial tree were evaluated from casts. Data for the length and cross sections of the various branches are given. The volume of the arterial tree as represented by the casts was 24 ml. The cross section of the various branches represents an ellipse rather than a circle, and the cross section ratios of the major branch points is considerably less than those postulated for optimal energy transfer. The implications of the geometrical findings for the relation between pressure gradient and flow are briefly discussed.
Magnesium Deficiency in the Cebus Monkey
Authors: VITALE JOSEPH J. , VELEZ HERNAN , GUZMAN CARLOS , CORREA PELAYO
Published: June 2012

Purified diets containing cholesterol and deficient or adequate in magnesium were fed to young growing Cebus (fatuella) monkeys.

Diet-induced magnesium deficiency resulted in weight loss, hyperirritability, and in several monkeys, convulsions.

In addition to the expected hypomagnesemia, deficient animals also had decreased serum potassium levels. However, after several weeks on diet, the electrocardiogram of deficient animals showed significant changes consisting primarily of S-T segment depression and peaking of the T wave; changes usually seen in hyperkalemic states.

Prior to sacrificing the animals, the tolerance to K-strophanthidin, a cardiac glycoside, was ascertained in both deficient and control animals. The cardiac glycoside was administered slowly by the intravenous route to anesthetized monkeys and the appearance of four consecutive ventricular premature contractions in the electrocardiogram was taken as the end-point. Deficient animals required approximately one-half the dose administered to control monkeys to develop extrasystoles.

The histopathology consisted of marked vascular sudanophilic deposits and dense fibrous connective tissue plaques in the ascending and descending aorta of deficient monkeys. Control animals showed little, if any, vascular sudanophilia.

The serum cholesterol concentration increased significantly in the deficient group while the rise seen in control monkeys lacked statistical significance.
Effect of Potassium on the Resting Length of Vascular Smooth Muscle of the Rabbit Aorta and its Response to I-Norepinephrine
Authors: BEVAN JOHN A. , OSHER J. V.
Published: June 2012

Change in resting length, response to
l
-nor-epinephrine and tissue concentration of potassium of helical rabbit aorta strips have been investigated, following changes in concentration of extracellular potassium. Increase in potassium decreases resting length, increases sensitivity and slope of log dose - probit response curve: potassium decrease has opposite effects. Alterations in external potassium concentration have no effect on the maximum response to
l
-norepinephrine. A potassium range between 50% and 300% of normal was investigated. Results show that when the muscle shortened, following an increase in potassium in the presence of
l
-norepinephrine, the change in resting length due to a direct action of this ion was more important than changes in sensitivity to
l
-norepinephrine. It is suggested that sensitivity of muscle to
l
-norepinephrine may be related to the intra-cellular concentration of potassium.
Alteration of Blood During Acute Hypotension: Effect of Continuous Glass Wool Filtration
Authors: SWANK ROY L. , ISSELHARD WOLF H. , HISSEN WOLFGANG , MERGUET HANS
Published: June 2012

Acute hypotension was produced in heparinized and nonheparinized dogs by hemorrhage and by injections of histamine, and adhesiveness and aggregation of blood elements determined periodically by the screen filtration pressure method. This method measures the pressure required to force blood at a constant rate through a standardized screen with multiple square holes each 20 x 20 micra. In some cases the arterial blood was perfused through a glass wool filter in an extracorporeal system both before and during periods of hypotension. The results of these studies justify the following conclusions:

1. Increased adhesiveness and aggregation of platelets and other blood elements which occur during hypotension produced by hemorrhage or intravenous injections of histamine were indicated by an increase in the screen filtration pressure of blood. These changes were not prevented from developing, or significantly altered by heparinization of the animal.

2. The amount of blood which could be obtained during arterial hemorrhage was significantly increased by heparinization of the animal.

3. The adhesive and aggregated platelets and leucocytes, which formed during hypotension, were removed from the blood when it was perfused through a column of glass wool. This treatment was attended by a decrease in the screen filtration pressure of the blood to or below normal.

4. The increase in screen filtration pressure which occurred during hypotension was much less marked if the animals' blood had first been circulated through pyrex glass wool.

5. Filtration of blood through pyrex glass wool was also attended by a progressive decrease in the mean arterial blood pressure of the animal.
Control of Coronary Blood Flow by an Autoregulatory Mechanism
Authors: MOSHER PAUL , ROSS JOHN , MCFATE PATRICIA ANN , SHAW ROBERT F.
Published: June 2012

Control of the coronary circulation has been investigated in an experimental preparation in which coronary flow was suddenly increased or decreased by the imposition of sudden changes in coronary perfusion pressure during periods of constant cardiac performance.

The transient response to these changes in coronary perfusion pressure was an initial abrupt change in flow in the same direction, followed by a prompt return of flow toward the previous level. The response was completed in 10 to 15 sec, and was followed by a few cycles of damped oscillation having a period of 10 to 12 sec.

Steady-state pressure-flow curves demonstrated a range of perfusion pressures over which coronary blood flow was relatively independent of pressure. Below this pressure range the coronary bed appeared to be fully dilated, and the blood flow was directly dependent upon perfusion pressure.

Elevation of the level of cardiac function resulted in autoregulation of coronary flow at a higher level of flow, and decreasing the level of cardiac function resulted in regulation of coronary flow at a lower flow rate.

Instantaneous pressure-flow characteristics of the coronary bed, exclusive of compensatory influences, were also determined.

The experiments demonstrated an intrinsic mechanism that regulated blood flow to the myocardium. In the physiologic range of arterial pressure, coronary perfusion pressure did not appear to be a major determinant of coronary blood flow. Coronary flow appeared to be autoregulated at a level related to myocardial effort.
General and Regional Circulatory Effects of Synthetic Bradykinin in Man
Authors: KONTOS HERMES A. , MAGEE JOSEPH H. , SHAPIRO WILLIAM , PATTERSON JOHN L.
Published: June 2012

The general and regional circulatory effects of synthetic bradykinin were investigated in 19 healthy volunteers. During intravenous infusion of bradykinin (25 µg/min) mean arterial pressure decreased initially, but returned to control levels within a few minutes. Heart rate increased during the hypotensive period, but subsequently returned toward preinfusion levels. Cardiac output increased, mainly as a result of increased stroke volume, and systemic vascular resistance decreased. Blood flow to hand increased during such infusions of bradykinin, but blood flow to forearm was not altered significantly. Intravenous infusions of 40 µg/min produced an increase in blood flow to the forearm, resulting solely from cutaneous vasodilatation in most subjects. The distensibility of hand veins increased both during intravenous infusions of 25 µg/min and during infusions of 0.2 µg/min into the brachial artery. Renal clearance of inulin was slightly decreased during infusion of 25 µg/ min bradykinin; there was no detectable change of PAH clearance.
Control of Renin Secretion
Authors: SKINNER SANDFORD L. , MCCUBBIN JAMES W. , PAGE IRVINE H.
Published: June 2012

Renin secretion was found to be controlled by a renal baroreceptor rather than by ischemia. Development of a sensitive assay technique that detects renin in small quantities of renal venous and peripheral arterial plasma has permitted the demonstration that the rate of renin secretion varies inversely with the level of arterial pressure independently of renal blood flow.

When mean renal perfusion pressure was reduced 5 to 40 mm Hg by a constricting band around the aorta above the level of the renal arteries, increased renin secretion commenced within 60 seeonds. Reductions of this magnitude did not necessarily cause mean perfusion pressure to fall below control levels of diastolic perfusion pressure. Rises in perfusion pressure had the reverse effect, reducing the rate of renin secretion again without measurable change in renal blood flow. Compression of the kidney within an oncometer by an applied forece of from 15 to 40 mm Hg also caused increases in the rate of renin secretion in the absence of change in total renal blood flow. Reduction of pulse pressure alone did not provoke secretion of renin, nor did reduced oxygen tension, or renal ischemia. Rise in perfusion pressure due to occlusion of the common carotid arteries was associated with reduction in the rate of renin secretion.

A small amount of renin was secreted continuously under the conditions of these experiments; physiologic changes in mean perfusion pressure served to alter the rate. This suggests that a renal baroreceptor mechanism regulates renin secretion under normal circumstances and that arterial pressure tends to stabilize at a level at which renin secretion is minimal.