Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Vascular Capacitance”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43Linked to original sources
PubMed1979

[Haemodynamic and vascular effects of dobutamine during and after open heart operations (author's transl)].

In cardiosurgical patients the haemodynamic effects of dobutamine 2.5 microgram/kg . min and 5 microgram/kg . min dobutamine were investigated during neuroleptanalgesia, intra- and immediately postoperatively. Intraoperative measurements were performed in 8 coronary surgical patients each after sternotomy and pericardiotomy, but before the aortocoronary venous bypass operation. The following haemodynamic parameters increased significantly: cardiac index (2.5 microgram/kg . min: 2.6 leads to 2.1 1/min . m2; 6 microgram/kg . min: 1.5 leads to 2.24 1/min . m2), heart rate (80 leads to 91 min-1; 86 leads to 107 min-1), stroke index (16%, 27%), mean arterial pressure (70 leads to 90 mm Hg; 70 leads to 93 mm Hg), mean pulmonary arterial pressure (8%; 14%), LV dp/dtmax (72%; 121%) and calculated myocardial oxygen consumption Eg (35%; 52%). Changes in right (PRA) and left ventricular filling pressure (PLVED), in total systemic resistance and total pulmonary vascular resistance were not significant. Postoperative measurement immediately after open heart operations (ASD-correction n = 5, aortocoronary venous bypass (n = 3) in neuroleptanalgesia too, showed the same haemodynamic results as intraoperatively before correction of coronary stenosis. Only a few premature ventricular beats were observed in 3 patients and there were no changes in S-T segments during dobutamine infusion. In another group of 15 patients selective vascular responses to an infusion of 10 microgram/kg . min dobutamine were examined during steady state cardiopulmonary bypass excluding heart and lungs from the circulation. No relevant direct influence on the arteriolar resistance vessels and the venous capacitance vessels were found. In a dose range of 2.5--5.0 microgram/kg . min dobutamine proved to be a potent inotropic agent causing almost no peripheral and relatively little positive chronotropic effects. But the increase in heart rate was more pronounced than in other clinical investigations in conscious patients, which might be due to an attenuation of vagal reflex by anaesthesia. The results indicate, that dobutamine may be a valuable drug in the treatment of intra- and postoperative low output syndromes especially in patients with coronary heart disease.

Adult↗
PubMed1985

The effects of ketamine on venous capacitance in rats.

The purpose of this study was to examine the effects of ketamine and pentobarbital on venous capacitance in rats. Venous capacitance was assessed by measuring the mean circulatory filling pressure (MCFP) at three levels of blood volume in conscious rats as well as during anesthesia with ketamine (125 mg/kg, ip) or pentobarbital (50 mg/kg, ip). MCFP was measured during brief periods of circulatory arrest produced by inflating an indwelling balloon in the right atrium. MCFP was maintained during ketamine anesthesia at a level similar to that measured in conscious animals, while it was decreased (P less than 0.01) during pentobarbital anesthesia both at normal blood volume and following hemorrhage. These results suggest that ketamine did not alter but pentobarbital increased venous capacitance. The slope of the regression line relating MCFP and blood volume was not altered by ketamine but was increased (P less than 0.05) by pentobarbital, which suggests that ketamine did not alter but pentobarbital decreased total vascular compliance. These results suggest that ketamine maintains but pentobarbital decreases venous tone.

Animals↗
PubMed1999

Mechanical design in arteries.

The most important mechanical property of the artery wall is its non-linear elasticity. Over the last century, this has been well-documented in vessels in many animals, from humans to lobsters. Arteries must be distensible to provide capacitance and pulse-smoothing in the circulation, but they must also be stable to inflation over a range of pressure. These mechanical requirements are met by strain-dependent increases in the elastic modulus of the vascular wall, manifest by a J-shaped stress-strain curve, as typically exhibited by other soft biological tissues. All vertebrates and invertebrates with closed circulatory systems have arteries with this non-linear behaviour, but specific tissue properties vary to give correct function for the physiological pressure range of each species. In all cases, the non-linear elasticity is a product of the parallel arrangement of rubbery and stiff connective tissue elements in the artery wall, and differences in composition and tissue architecture can account for the observed variations in mechanical properties. This phenomenon is most pronounced in large whales, in which very high compliance in the aortic arch and exceptionally low compliance in the descending aorta occur, and is correlated with specific modifications in the arterial structure.

Animals↗
PubMed1996

Interaction of human spermatozoa with the zona pellucida of oocyte: development of the acrosome reaction.

Mammalian spermatozoa are not able to fertilize an oocyte upon ejaculation. To gain fertilizing ability, spermatozoa must, either in vivo or in vitro, undergo a process termed capacitation. Since a reliable marker for capacitation does not exist, it is considered that this process is completed when the spermatozoa are able to undergo acrosomal x intestinal mucosa which might require tandem signaling events for this process is the presence of a vascular countercurrent arrangement in the subepithelial compartment. As happens for absorbed solutes, this countercurrent phenomenon may distort transepithelial solute gradient. For example, perfusion of mammalian intestinal loops in vivo with solutions containing fMLP was previously found to induce neutrophil attachment to endothelial cells and structurally defined endothelial activation, but failed to elicit directed migration across the lamina propria (Madara, unpublished observations), suggesting that directed migration may require a more stable gradient than that afforded by the usual soluble signals. For example, once present in inflamed tissue, IL-8 is likely to retain its biological activity for several hours, as shown by local intradermal administration in animals and humans. In contrast to Il-8, chemokines such as fMLP or LTB4 are degraded rapidly by oxidation or hydrolysis. Fertilization is a very complex phenomenon, involving sequential interactions between the fertilizing spermatozoon and cumulus oophorus, ZP, and oolemma. The AR may be playing a key role in penetration of spermatozoa through these egg vestments.

Acrosome Reaction↗
PubMedDate not supplied

Stroke-prone SHR vascular muscle Ca2+ current amplitudes correlate with lethal increases in blood pressure.

Studies on the possible causal relationship between the Ca2+ channel current density in the vascular muscle cell (VMC) and increases in blood pressure were extended by a comparison of stroke-prone spontaneously hypertensive rats (SP-SHR) with N/nih outbred normotensive rats. Maximal amplitudes of both L-type and T-type Ca2+ channel currents were significantly increased in SP-SHR without a difference in cell capacitance. SP-SHR peak current amplitudes in 20 mM Ba2+ averaged 446 +/- 64 pA while N/nih averaged 156 +/- 25 pA (clearly separated statistically). Both L-type and T-type Ba2+ currents (IBa) were significantly increased in SP-SHR, shown also by peak current frequency distributions. There was a significant shift to the left of both activation (7 mV) and inactivation (15 mV) current-voltage (I-V) plots. SP-SHR IBa recovery from inactivation was significantly slower (103 versus 61 ms) than in N/nih VMC. The increases in SP-SHR IBa amplitude under maximized conditions correlated with increases in blood pressure. Together with earlier observations of increased vascular muscle Ca2+ current density coexistent with blood pressure elevation in Kyoto-Wistar SHR, these data provide evidence for altered function of Ca2+ channels as a fundamental component of hypertension. Since the Ca2+ channel alterations exist in venous VMCs of newborn SP-SHR rats (in a low pressure blood vessel and at a time when increased Ca2+ current density could not be an effect of increased blood pressure), our results add to the growing evidence of Ca2+ channel abnormalities as a cause of genetic hypertension.

Animals↗
PubMed1992

Acute hemodynamic effects of nicorandil in coronary artery disease.

Nicorandil is a potent vasodilator with antianginal and anti-ischemic properties that acts on both the coronary and the peripheral vascular bed. Because of its dual vasodilatory mechanisms mediated by an increase in cyclic GMP similar to that of nitrates and by a selective increase in the K+ conductance of the smooth muscle cell membrane, nicorandil unloads the right and left ventricles at rest and during exercise. Thus, compared with the classic nitrates, nicorandil is a more balanced vasodilator, i.e., it affects not only the venous capacitance vessels (as predominantly affected by nitrates) but also the arterial resistance vessels. In clinical pharmacologic trials, nicorandil has been administered intravenously (2 to approximately 14 mg) as well as sublingually and orally in single doses of 10-60 mg. In patients with coronary artery disease and impaired left ventricular function, the decrease in preload resulted in a significant improvement of cardiac output. Depending on the doses applied and the patient populations studied, observed decreases in systemic blood pressure were consistent with decreases in peripheral vascular resistance. The effect on heart rate was small, and no influence on atrioventricular conduction could be detected. Nicorandil enhanced exercise capacity in patients with ischemic heart disease. This benefit can be attributed to the reduction in loading of the right and left ventricle as well as to an improvement of regional wall motion abnormalities secondary to the coronary dilatory properties of the drug. Nicorandil appears to be a valuable additive to the antianginal and anti-ischemic management of coronary artery disease.

Animals↗
PubMed1996

Invariance of the resistance to venous return to carotid sinus baroreflex control.

Despite the well-established fact that the carotid sinus baroreflex system has profound control over the physical properties of the systemic circulation, the resistance to venous return (RVR) seems to be invariant of such control. We hypothesized that this apparent paradox may be explained from the baroreflex changes in systemic arterial compliance. In 12 pentobarbital-anesthetized mongrel dogs, RVR was measured at controlled carotid sinus pressures (CSP) of 50 and 200 mmHg with normal and artificially increased arterial compliance. Arterial compliance was determined from the arterial pressure decay when systemic blood flow was stopped with total vena caval occlusion. Changing CSP between 50 and 200 mmHg changed RVR significantly only under the condition of artificially increased arterial compliance. A four-parameter lumped model of the systemic circulation revealed that the baroreflex changes in arterial compliance and arterial resistance, which occurred in opposite directions, prevented a change in RVR when CSP was changed. The data also suggested that approximately 75% of RVR was attributed to large and conduit veins, the resistances along which were insensitive to baroreflex control. We concluded that the invariance of RVR results from a combination of 1) baroreflex change in the arterial compliance, 2) baroreflex insensitivity of the resistance along large and conduit veins, and 3) spatially distinct location between the major site of reflex change in capacitance and the major site of compliance.

Animals↗
PubMedDate not supplied

Effect of aligeron on the cerebral venous outflow and cerebrospinal fluid pressure in dogs.

The effect of Aligeron (1-benzhydril-4-allyl-piperazine dihydrochloride) on the cranial circulation was studied in dogs under chloralose-urethan anaesthesia. The parameters followed were: venous outflow from the confluence of the cerebral sinusses (CVO), cerebrospinal fluid pressure in cysterna magna (CSFP), systemic arterial blood pressure (BP) and pulse rate (PR). CVP was measured using the technique of Rapela and Green (1964). Aligeron was applied at doses of 5 and 10 mg/kg i.v. Papaverine hydrochloride was used as a reference compound. aligeron administration at a dose of 5 mg/kg led to quick increase of the CVO with a duration of the effect approximately 30 min. CSFP also increased in a similar way. BP and PR showed insignificant changes. The administration of 10 mg/kg did not lead to an increase of its effect on CVO. Papaverine (1 mg/kg i.v.) had a weaker effect than that of Aligeron. According to the classical concepts the changes observed in our experiments were due to the cerebral vasodilator effect of Aligeron which caused a fall in cerebrovascular resistance and an increase of the intracranial blood volume. Our experiments suggest that Aligeron influenced the resistance vessels more than the capacitance ones.

Animals↗
PubMed1976

Circulatory effects of dihydroergotamine in patients with disturbed sympathetic vasomotor control with special reference to postural hypotension.

In five patients with postural hypotension (disturbed sympathetic vasomotor control) the effect of intravenous and oral administration of dihydroergotamin (DHE) has been studied. The therapeutic effect of oral administration of DHE has also been compared to the effect of treatment with an antigravity suit. Following intravenous administration of DHE, systemic and central venous pressure increased in all cases. The effect on cardiac output was negligible and consequently the calculated total peripheral vascular resistance increased. Orthostatic tolerance increased in all cases. During long-term oral administration the effect was comparable to that obtained with an antigravity suit. The increased orthostatic tolerance is explained by a constrictive effect on both capacitance and resistance vessels. In order to analyze the influence of a functional denervation on the effect of DHE on peripheral circulation, a study has also been performed during epidural anaesthesia of the lower body in 11 patients. In the legs which were deprived of sympathetic tone intravenous administration of DHE caused constriction of resistance vessels. In the intact forearm there was a decrease of tone in the resistance vessels. The results indicate that DHE - apart from its well-known venoconstrictive effect - also may constrict resistance vessels when they are subjected to a low sympathetic nervous outflow.

Administration, Oral↗
PubMed1995

Effects of pericardial pressure on systemic and coronary hemodynamics in dogs.

The effects of pericardial tamponade on coronary capacitance and coronary systemic hemodynamics were calculated in two groups of animals subjected to increases in pericardial pressure (PCP) up to approximately 20 mmHg. In one group (A), flow in the left circumflex artery was measured in the intact animal under conditions of increased PCP. In the second group (B), coronary artery perfusion pressure was maintained constant with a pump while PCP was increased. In group A increased PCP was accompanied by a decrease in arterial pressure. This resulted in a marked decrease in coronary blood flow after vasodilation but without a change in coronary vascular resistance. In group B there was no change in coronary flow or coronary vascular resistance with increased PCP. Microsphere distribution to the left ventricular wall showed less endocardial than epicardial flow but no change in going from low to high PCP. Characteristic impedance was altered in the group B animals after vasodilation at medium and high PCP, indicating a loss of reflection sites and probably increased vessel tethering. The coronary artery in a subgroup of group B animals was also perfused by left ventricular pressure, the time constants for coronary backflow showing an 8-12% decrease in capacitance with low and high PCP; these values represent minimal epicardial capacitances vs. total bed capacitance. A diastolic model for the values for resistance and capacitance in the coronary bed is suggested. As expected, most of the capacitance is in the venous bed and most of the resistance is in the arterial bed.

Animals↗
PubMed1987

[Morphofunctional characteristics of the vascular endothelium in the common leech (Clepsina complanta)].

The electron microscopic investigation has revealed in the body of the leech two types of vessels, that together with common signs possess a number of peculiarities in composition of endothelial cells. These vessels have different level of organization: the vessels of the first type, concerning the parenchyma of the leech, are nutritive, and the vessels of the second type combine capacitance and transport functions and are the place of hemolymph renovation at the expense of an active metabolic and synthetic activity of the endothelial cells. A fact is stated concerning a specific position of mitochondria in the endotheliocytes of the second type vessels: from the vessel's lumen they are not covered with plasmolemma along their whole extent and come into an immediate contact with hemolymph. Therefore, a hypothesis is suggested on functional activity of the endothelial cell mitochondria in the second type vessels. Presumptive differentiation of the two major vessels of the leech body makes it possible to suppose that there exist functional predecessors of the vessels of branchial and pulmonary type, that is vessels of lesser and greater circulation.

Animals↗
PubMed2001

Impaired compliance of the intracranial vessels in complicated childhood migraine. Demonstration by transcranial Doppler-sonography--a vascular model approach.

AIM: To increase the diagnostic value of Doppler sonography a uniform lumped parameter model of pulsatile blood flow in human arteries was derived from the serial and/or parallel connection of parallel oscillatory circuits. METHODS AND PATIENTS: In this setting the current (I) in the ohmic resistor (R) represents the volume flow in the vessel, the voltage (V) the blood pressure. The vessel compliance corresponds to the capacitance (C), the inductivity (L) represents the accelerated mass. The flow velocity (v) which is assessable non-invasively is given by v = I/A, where A is the cross-sectional area of the vessel. Mathematically, the model represents a two-dimensional Fourier-series of the input signal by the segments. Thus it seems to be evident that almost all forms of flow and pressure pulses can be generated. The equations of the model were solved numerically. Doppler-sonographically measured flow velocities in the ascending aorta were used as input signal. The parameters for A, R, L and C were optimized to gain the measured flow spectrum in the target vessel as model response. RESULTS: Application in 14 children (aged 3-16 yrs.) with complicated migraine during a symptom-free interval revealed a significantly lowered cross sectional area of the middle cerebral artery on the side of the higher flow velocities. For both middle and posterior cerebral arteries, a decreased vessel compliance (C) (mean -30%) was found, whereas values for R and L were within normal limits. CONCLUSION: These findings suggest an altered vascular compliance even between attacks. This may contribute to the pathogenesis of migraine through increased cerebral impedance resulting in impaired cerebral perfusion.

Adolescent↗