摘要:

The prolongation of A-V transmission time that occurs with increasing rates of right atrial pacing has been used to study the effect of ouabain and of ouabain plus atropine on A-V nodal conduction in 14 patients with normal A-V nodes. Drugs were injected into the superior vena cava or pulmonary artery over a 1- to 2-min period. Atropine in a dose of 0.02 mg/kg shortened A-V conduction time by an average of 0.112 sec; ouabain alone in a dose of 0.01 mg/kg lengthened A-V conduction time by 0.053 sec. Ouabain given after large doses of atropine did not prolong A-V conduction at any paced rate. Thus, in these resting patients with normal A-V nodal function, usual digitalizing dosages of ouabain did not have an extravagal or antiadrenergic effect on A-V nodal conduction.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The localization of adrenergic and cholinergic nerves in normal and denervated cat hearts was studied histochemically. The norepinephrine content of atria and ventricles was chemically determined by a spectrofluorometric method. In hearts denervated 9 to 42 days, little or no norepinephrine was detected. Histochemically, many catecholamine-containing fibers were present in the atria and ventricles of normal cats, whereas in denervated cats there were none in one and very few in four. There were many cholinergic nerves in the atria and a small to moderate number in the ventricles. The left atria of denervated hearts showed a marked reduction in cholinergic nerve fibers. It is concluded that cardiac denervation by mediastinal neural ablation is often incomplete. When norepinephrine is not detectable by chemical analysis, individual nerve fibers not sectioned can still be histochemically identified.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The estimation of ventricular volumes by indicator dilution methods is subject to errors resulting from incomplete mixing and nonuniform sampling. A mathematical model is proposed which theoretically permits calculation of these errors. The model allows for nonuniform distribution of indicator in the ventricle and for nonuniform representation of the end-diastolic volume (EDV) in the systolic ejectate. It is assumed that the concentration of indicator and the flow at a given cross section of the aorta are uniform but not necessarily the same at a different cross section, or at different times during the cardiac cycle. In respect to the validity of the popular formula,EDV=SV/l-K(K= average residual fraction), it was shown that the conditions traditionally believed to be satisfying for accurate measurements of EDV are neither sufficient nor necessary. Less restrictive alternative conditions sufficient for accurate measurements are proposed.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

We measured the pulmonary lymph flow in dogs with mild congestive failure before and after acute elevation of the left atrial pressure to 40 cm of water. The creation of an aorticocaval fistula and the administration of desoxycorti-costerone trimethylacetate and a salt enriched diet in 6 dogs produced mild pulmonary edema and partial expansion of the pulmonary lymphatics 10 to 12 days postoperatively. Elevation of the left atrial pressure to 40 cm of water under pentobarbital anesthesia led to an immediate increase in right duct flow in the “mild failure” dogs, in contrast to a delayed flow in normal dogs. The average peak flows in the 10- to 12-day dogs after increasing the left atrial pressure were higher than the peak flows observed in normal dogs. In addition, the mild failure dogs survived twice as long as normal dogs after acute elevation of the left atrial pressure. These results suggest that an animal with an expanded pulmonary lymph system is better able to withstand the stress of acute elevation of left atrial pressure than a normal animal. The pulmonary lymph system may serve as an important compensatory mechanism in the prevention of fulminating pulmonary edema.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Simultaneous recordings of contractile tension and transmembrane potentials from canine ventricular tissue yielded a consistent correlation of action potential (AP) alteration with contractile change associated with abrupt rate change. The AP terminating a relative prolongation of the cycle-length manifested shortening of phase 2 with lengthening of phase 3 and was associated with potentiation of contractile force. Conversely, the AP terminating a relative abbreviation of cycle-length displayed a broader phase 2 with a more precipitous phase 3, while the associated contraction was less forceful than the control. In each circumstance, the relative magnitude of cycle-length change correlated with the extent of both AP change and contractile alteration. Changes in AP configuration may reflect changes in transmembrane flux of K+during repolarization consistent with the findings of prior workers who have related K+efflux to increased contractility. Mechanical alternans, in addition, was frequently observed in association with abrupt rate change and was consistently associated with an electrical alternans manifested by action potentials with alternately wide and narrow plateaus (phase 2). As above, the more forceful contractions were associated with action potentials which displayed a narrower phase 2. Mechanical alternans initiated by abrupt rate change may represent an adaptive phenomenon prior to the establishment of a stable contractile state, as reflected by a stable AP configuration.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

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

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Microscopic observation and micrometric measurements of microarterial vessels in the mesentery of the anesthetized rat, during chemical interference with the vasomotor nerve supply, showed (A) marked (average 25×) hypersensitization to epinephrine; (B) persistent vasoconstriction; and (C) depression or cessation of vasomotion. These and concomitant similar reactions of the precapillary sphincter resulted in relative ischemia and frequent reversal of blood flow through the endothelial capillary network. A comparable hypersensitization to epinephrine, observed in six isolated perfused microarterial vessels, upon shift in internal static pressure strongly suggests that the change in reactivity of the vascular smooth muscle cell seen in vivo might also be related to a local change in transmural pressure. The plot of the logarithm of epinephrine threshold concentration vs. the approximate circumferential wall tension (computed for selected in vivo and in vitro experiments neglecting wall thickness) showed a steep rise in vessel sensitivity occurring concomitantly with decrease in wall tension. Thus it appears that hypersensitization of microarterial muscle cells which develops during the hypotensive episode of acute chemical nerve blockade in the rat may be primarily related to a modification in wall tension.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Isometric developed tension and rate of development of tension in the in situ atrium of the anesthetized dog have been shown to increase consistently with increasing heart rate over a wide range. This study thus definitely demonstrates that both the ascending and descending staircase effects occur in the dog atrium in situ. At high cardiac rates the velocity of force development may increase without a change in the extent of force development. These changes were independent of variations in aortic pressure, intactness of betaadrenergic receptors, level of cardiac catecholamine stores, cardiac innervation, or changes in coronary flow. The character of the frequency-force relationship was found to be markedly influenced by isolation of the heart with its concomitant depression of contractility.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Although it is clear that cardiac norepinephrine stores are often markedly reduced in congestive heart failure, the mechanism responsible for this depletion has not been elucidated. The objective of this study was to investigate cardiac synthesis of norepinephrine in experimental right-sided heart failure by measuring the activity of tyrosine hydroxylase, the rate-limiting enzyme in the biosynthesis of norepinephrine. In homogenates of the right ventricles of 6 dogs with congestive heart failure and 2 with chronic cardiac denervation, myocardial tyrosine hydroxylase activity was severely reduced, averaging 0.4 ± 0.1 (SE) and 0.2 mμmole/g per hour respectively as compared to a normal value of 3.3 ± 0.7 mμmole/g per hour. Tyrosine hydroxylase activity was normal in reserpine-treated, norepinephrine-depleted dogs. These data provide evidence for a mechanism severely limiting norepinephrine biosynthesis in congestive heart failure.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The tangential wall stress and the tangential elasticity modulus at pressures from 0 to 200 mm Hg were calculated from pressure-volume diagrams of 27 human thoracic aortas aged 22 to 85 years. The relative volume increase of the aortas between 0 and 100 mm Hg decreased linearly from about 190% at age 20 to about 40% at age 85, whereas the elasticity modulus at 100 mm Hg increased linearly from 10 kg/cm2at age 20 to 42.5 kg/cm2at age 85. The decrease of the distensibility of the aortic wall with age was partly compensated by an increase of the internal volume of the aorta but at higher ages the distensibility was less than the theoretical values necessary for a proper buffering chamber activity. The tangential wall stress decreased linearly with age from about 2.5 kg/cm2at age 20 to about 1.2 kg/cm2at age 85. Since the pressoreceptors in the wall of the elastic vessels respond to the wall stress, this result means either that smooth muscles must increase the stress of the elastic fibers continuously, or the pressoreceptors must adapt their sensitivity throughout life to lower wall stress so that it will be kept constant. Weakness of the smooth muscles or a failure of the pressoreceptors to adapt themselves to lower stresses at higher ages may be the cause of essential hypertension.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID