摘要:

A reflex tachycardia elicited by electrical stimulation of afferent cardiac sympathetic nerve fibers was observed in anesthetized, vagotomized cats. Tachyordia was obtained by stimulating the cut central end of the left inferior cardiac nerve in closed-chest, spontaneously breathing cats and in open-chest, artificially ventilated cats and by stimulating the cut central end of the pericoronary nerve, thus restricting the stimulus to afferent sympathetic fibers with cardiac endirgs. Reflex tachycardia was also obtained in spinal cats. In general, the magnitude of the reflex response was inversely related to the control heart rate. The afferent pathway for the reflex was contained in the first four left thoracic rami communicantes, and the efferent limb depended on the integrity of the right stellate ganglion. These results demonstrate that cardiocardiac spinal neural circuits can also mediate reflex increases in heart rate.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The relation of single cell electrical activity to generation of force was determined for myocardium during the development of hypertrophy induced by pressure loading. Transmembrane potentials and isometric active force at optimal length (Po) were monitored in isolated right ventricular papillary muscles and trabeculae carneae after inducing chronic right ventricular outflow tract obstruction. Cats subjected to partial pulmonary artery occlusion or to sham operation were studied 1, 3, 7, 10, 21, and > 90 days after surgery. Right ventricular muscles were stimulated at 30/min at optimal length in Tyrode's solution (36°C). Muscles from sham-operated and 1 day pressure-loaded hearts had electrical and mechanical properties similar to normal muscles. Right ventricular peak systolic and end-diastolic pressures were increased for 1 and 3 day pressure-loaded hearts; the percent of right ventricular water was increased for 3, 7, and 10 day pressure-loaded hearts. Muscles from 3 day pressure-loaded ventricles had significantly decreased Po, maximum rate of force development, time to peak force, and duration of contraction compared with normal muscles, and their action potential plateaus originated at more negative potentials (mean 24.7 mv for 11 muscles). The alteration in action potential configuration was less obvious in muscles studied 7 and 10 days after partial pulmonary artery occlusion and did not occur 21 and > 90 days after pressure loading; however, Poand maximum rate of force development remained decreased, although time to peak force and duration of contraction returned to normal for preparations from 7, 10, 21, and > 90 day pressure-loaded ventricles.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Experiments were performed on open-chest anesthetized dogs to determine the quantitative effects of autonomic nerve stimulation on pacemaker activity and conduction. The lead II electrocardiogram together with bipolar electrograms were recorded from the atria, the His bundles, and the ventricles. The vagi or the stellate ganglia were stimulated in dogs which exhibited either sinus rhythm, ectopic atrial rhythm, junctional rhythm, or ectopic ventricular rhythm. The time courses of the change in heart rate in response to vagal or stellate stimulation were characteristic for each type of rhythm. The characteristic responses of different cardiac pacemaker sites to autonomic influence were demonstrated to be important factors in the production of wandering pacemakers and in the emergence of ectopic beats. Sinus pacemaker activity was more sensitive to modification by autonomic stimulation than was atrioventricular (AV) conduction. However, subliminal autonomic effects on AV transmission were brought out during conduction of premature atrial beats, thereby demonstrating a coupling interval dependency of autonomic influences on AV conduction. The present experiments also showed how fluctuations in autonomic activity could result in Mobitz type II second-degree heart block, pseudosupernormal conduction, and the concertina effect observed in the preexcitation syndrome.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

An approximate numerical-graphical solution was made for the motion of a human aortic valve leaflet in a meridional plane through the center of the sinus of Valsalva. The observed buckling, whipping action of the leaflet was obtained. Of primary significance in the results was the location and the determination of the maximum curvature of the leaflet in this plane, since this point corresponds to the point of maximum fatigue bending stress. The approximate dimensionless curvature was on the order of 3.5 (referred to the aortic diameter) at a dimensionless radial location of 0.55–0.6. The most important feature determining leaflet curvature and motion was the initial contour shape. The initial shape of a normal human leaflet produces smaller curvatures than the curved shapes usually illustrated for aortic valves.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Sympathetic nerve stimulation and intraluminal norepinephrine infusion for more than 15 seconds produced a biphasic response in the isolated rabbit ear artery perfused with Krebs solution. This response consisted of an initial rapid constriction (phase A), which was followed by partial relaxation, and a final slowly developing constriction (phase B), which lasted for the duration of nerve stimulation or norepinephrine administration. Raising the potassium concentration of the Krebs solution to 12mM decreased the relaxation time between the two constrictor phases in response to norepinephrine; lowering the potassium concentration to 1.2 mM increased the relaxation time and decreased the degree of constriction of both phases. Biphasic vasoconstrictor responses were also elicited by the intraluminal infusion of phenylephrine, histamine, serotonin, or 35 mM potassium. When calcium was absent from the perfusing solution or when manganous sulfate (1mM) was present, norepinephrine produced only a fast phase A constriction, with no subsequent slow phase B constriction. However, after treatment of the artery with ryanodine, the phase A constriction in response to norepinephrine was markedly inhibited, but the phase B constriction was not. We concluded that the fast phase A constriction depends on the release of calcium from an intracellular pool and that the slow phase B constriction depends on the influx of extracellular calcium.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Some prosthetic heart valves with Silastic ball poppets undergo degeneration and variance. The problem is avoided with metal poppets; however, their impact can damage the cloth coverings on the struts, resulting in distorted blood flow paths. Consequently, renewed interest in mild-cured Silastic poppets and inserts is developing. With photostress equipment, we analyzed two spherical poppet models to study poppet degeneration. The first analysis simulated the ring type of loading transmitted from the valve seat to the poppet, and the second analysis involved hydrostatic pressure loading and a detailed stress analysis to simulate cage confrontation. Results showed that regions of the poppet were susceptible to stress cycling with relatively large tensions below the upper surface but above the ring support. This same location could experience large compressive stress, depending on how the poppet was positioned during a seating stroke. Shear stresses near the valve support ring were at least four times the hydrostatic pressure load. Such subsurface stress cycling should play a role in the formation of internal fissures that surface and fracture the poppet.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

A computer program was written in PL/1 to successively fit the sum of two, three, and four exponential terms to data by an iterative least-squares technique, using a combination of the steepest-descent and the Newton-Raphson methods for convergence. Each data point was weighted by the reciprocal of its variance, assuming that the errors followed a Poisson distribution. A compartment, i.e., an exponential term, was declared nonsignificant if it did not significantly reduce the least-squares error about the fitted line as judged by anFtest. Validity of the data was assessed by a “runs” test and by the frequency with which data points fell outside the 95% confidence range. Results of the analysis showed that (1) 9 of 12 normal human kidney133Xe washout curves were best described by a four-compartment model, (2) 18 of 38 studies in patients with essential hypertension yielded a four-compartment curve with significant reduction in compartment-1 flow, (3) nine patients with congestive heart failure all had three-compartment washout curves, (4) two patients with oliguric renal failure had washout curves described best by a two-exponential equation (one of these patients responded to an injection of furosemide with the appearance of a third, more rapid compartment). Obviously, this form of analysis can be easily applied to other sets of data which are described by nonlinear equations.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The effects of angiotensin I (0.2–3.2 μg) and angiotensin II (0.1–1.6 μg) injections into the pump-perfused arterial supply of the liver were studied in dogs anesthetized with sodium pentobarbital. Marked increases in hepatic artery perfusion pressure (10–50%), reflecting directionally similar changes in resistance to blood flow, were caused by either angiotensin I or angiotensin II. Resistance increases produced by angiotensin I were significantly attenuated by the synthetic nonapeptide SQ 20881 (Pyr-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro, 50 μg/kg, iv) that inhibits enzymatic conversion of angiotensin I to angiotensin II. In contrast, responses caused by angiotensin II were unaltered by SQ 20881. However, resistance increases caused by either angiotensin I or angiotensin II were blocked by 1-Sar-8-Ala-angiotensin II (100 μg/kg min−1, ia), a specific angiotensin II antagonist. These findings parallel the finding that responses to angiotensin I in the vasculature supplied by the hepatic artery are largely caused by local enzymatic conversion of angiotensin I to angiotensin II. Such conversion appears to occur to the extent of about 46%.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The purpose of this paper is to describe the incremental dynamic anisotropic viscoelastic properties of the middle descending thoracic aorta in ten living dogs. A segment of the middle descending thoracic aorta was isolated in situ and connected to a reservoir filled with oxygenated blood. The height of the reservoir could be adjusted to impress a known pressure on the segment. In addition, a sinusoidal fluid displacement pump was connected to this assembly to superimpose small sinusoidal pressures at various frequencies (0–5 Hz); in another phase of the experiment small sinusoidal changes in length were also imposed on the segment. The pressure, the longitudinal force, and the length of the segment were monitored continuously with specially designed transducers. From these data, the incremental elastic (E′) and the viscous (E″) moduli in the circumferential (&thetas;), longitudinal (z), and radial (γ) directions were calculated around a given state of strain in the physiological range. In general, the viscoelastic moduli were functions of the initial stretches, indicating the nonlinear nature of the arterial wall. Within the physiological range of pressure,Ez′ >E&thetas;′ >Eγ′ (P< 0.01) andEz″ >Eγ″ >E&thetas;″ (P < 0.01). These results indicated that the vessel wall was anisotropic, having its largest values of elastic and viscous moduli in the longitudinal direction. The ratio ofE′ /E′ < 0.123 at 2 Hz, indicating a small viscous component relative to its elastic counterpart. The elastic moduli increased markedly from 0–2 Hz and then settled down to a relatively constant value; this finding was consistent with previously published data. The values ofEz′ andEz″ from the in vivo experiments were higher than those from the in vitro experiments, and the difference was attributed to the vascular tethering present in the in vivo state.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

When the oxygen supply to the myocardium is compromised, glycolysis may provide the critical energy necessary for the heart's survival. We investigated whether insulin, through its effects on myocardial glycolysis, influences the performance and the metabolism of the perfused rat heart during anoxia. Hearts in a modified Langendorff apparatus were perfused for 30 minutes with anoxic media containing glucose (50–500 mg/100 ml) with and without insulin (100 munits/ml) or with anoxic media containing 200 mg glucose/100 ml and varying insulin concentrations (0.1–100 munits/ml). Hearts were paced, and left ventricular pressure, maximum rate of rise of left ventricular pressure, and lactate production were monitored. Increasing glucose concentration alone progressively enhanced performance and lactate generation in the beating anoxic heart. Addition of insulin resulted in significant increases in left ventricular performance and lactate production at all levels of glucose concentration. The myocardial content of high energy intermediates (creatine phosphate, adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate) after 30 minutes of anoxia was not altered by varying concentrations of glucose or insulin. To assess the effects of insulin and glucose in the absence of contraction, hearts were arrested with media containing a high potassium concentration (26 mEq/liter). Although lactate production was lower in arrested hearts than it was in beating hearts, it was enhanced by insulin. Insulin also produced significant increases in high-energy intermediates in arrested hearts. It was concluded that insulin increases the utilization of glucose and thus causes the enhancement of ventricular performance in the anoxic heart.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID