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Results for “VASCULAR RESISTANCE”

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At least 343 records · Page 19Linked to original sources

PubMed2003

Effects of Hct and norepinephrine on segmental vascular resistance distribution in isolated perfused rat livers.

We studied the effects of blood hematocrit (Hct), blood flow, or norepinephrine on segmental vascular resistances in isolated portally perfused rat livers. Total portal hepatic venous resistance (Rt) was assigned to the portal (Rpv), sinusoidal (Rsinus), and hepatic venous (Rhv) resistances using the portal occlusion (Ppo) and the hepatic venous occlusion (Phvo) pressures that were obtained during occlusion of the respective line. Four levels of Hct (30%, 20%, 10%, and 0%) were studied. Rpv comprises 44% of Rt, 37% of Rsinus, and 19% of Rhv in livers perfused at 30% Hct and portal venous pressure of 9.1 cmH2O. As Hct increased at a given blood flow, all three segmental vascular resistances of Rpv, Rsinus, and Rhv increased at flow >15 ml/min. As blood flow increased at a given Hct, only Rsinus increased without changes in Rpv or Rhv. Norepinephrine increased predominantly Rpv, and, to a smaller extent, Rsinus, but it did not affect Rhv. Finally, we estimated Ppo and Phvo from the double occlusion maneuver, which occluded simultaneously both the portal and hepatic venous lines. The regression line analysis revealed that Ppo and Phvo were identical with those measured by double occlusion. In conclusion, changes in blood Hct affect all three segmental vascular resistances, whereas changes in blood flow affect Rsinus, but not Rpv or Rhv. Norepinephrine increases mainly presinusoidal resistance. Ppo and Phvo can be obtained by the double occlusion method in isolated perfused rat livers.

Animals↗

PubMed1989

Effects of butorphanol tartrate on arterial pressure, jejunal blood flow, vascular resistance, O2 extraction, and O2 uptake in halothane-anesthetized ponies.

The effects of butorphanol tartrate on arterial pressure, jejunal blood flow, vascular resistance, oxygen extraction, and oxygen uptake were determined in 10 anesthetized ponies ventilated with a mixture of halothane and 100% oxygen, using isolated autoperfused jejunal segments. Physiologic saline solution or butorphanol tartrate (0.2 mg/kg of body weight) was administered as a single bolus into the left jugular vein. By 2 minutes, butorphanol decreased arterial blood pressure and intestinal blood flow, and increased intestinal oxygen extraction. However, intestinal vascular resistance and oxygen uptake were unaffected. Results of this study indicate that butorphanol tartrate induces a hypotension that secondarily decreases intestinal blood flow, but intestinal vascular resistance and metabolism are not adversely affected. We conclude that butorphanol tartrate does not compromise intestinal viability in halothane-anesthetized ponies and, therefore, may be a good analgesic choice for the equid destined for abdominal surgery.

Anesthesia, General↗

PubMed1989

[Development of utero-chorionic vascular resistance in early pregnancy].

The physiologic evolution of the utero-chorionic vascular resistances during the first trimester of pregnancy is described. With the use of pulsed Doppler, 25 normal pregnancies were followed weekly, performing 288 scans between the 6th and the 12th weeks of pregnancy. The detection of the FVW was done at the level of the uterine and retro-chorionic vessels. There is a progressive decrease of the vascular resistances to flow, with significant differences (p less than 0.001) between the values before and after the 9th week. The physiologic implications and its possible application to the study of the gestational pathology are commented.

Adult↗

PubMed1989

Exercise-induced differences in cardiac output, blood pressure, and systemic vascular resistance in a healthy biracial population of 10-year-old boys.

Previous studies have documented systolic blood pressure differences in response to dynamic exercise when blacks were compared with whites. This study was performed to validate these data and to determine if the cardiac output and systemic vascular resistance responses to exercise are different in a biracial population of 10-year-old boys. Nineteen blacks and 31 whites underwent maximum supine graded exercise tests with Doppler determination of cardiac output and measurement of systolic and diastolic blood pressure and systemic vascular resistance. The blacks had a body surface area that was marginally larger than that of the whites, but no differences were noted in height or weight. Working capacities, when indexed by weight, were virtually identical between the two groups. No differences were noted in either systolic or diastolic blood pressure during preexercise, maximum exercise, or early and late recovery. White males had significantly higher cardiac indexes during preexercise, maximum exercise, and early and late recovery. Black males had greater systemic vascular resistance during preexercise, maximum exercise, and early and late recovery. Thus, the black children's blood pressure responses to exercise were comparable with those of the white children but they had a greater systemic vascular resistance and lower cardiac index. These racial differences may serve as potential markers for the prehypertensive state.

Anthropometry↗

PubMedDate not supplied

Pulmonary vascular resistance in complete atrioventricular septal defect. A comparison between children with and without Down's syndrome.

Invasive data obtained in children with complete atrioventricular septal defect over the last three years are presented to determine the age at which pulmonary vascular obstructive disease develops. Comparisons were made between children with (n = 21) and without Down's syndrome (n = 12). The investigation was restricted to patients less than one year of age at initial catheterization. Patients with complicated associated heart defects were excluded. Patients with Down's syndrome had a higher ratio of pulmonary to systemic vascular resistance than children without Down's syndrome in the basal situation. This difference almost disappeared after 100% oxygen had been given to patients with elevated pulmonary vascular resistance, indicating that hypoxia and/or hypoventilation is of importance, especially in children with Down's syndrome. Fixed elevated pulmonary vascular resistance was found in 11% of Down patients under one year, with the youngest patient being 5.5 months old. One child without Down's syndrome may have had fixed elevated pulmonary vascular resistance. It is concluded that all children with complete atrioventricular septal defect should be evaluated and operated on at a very young age.

Age Factors↗

PubMed1987

Increased vascular resistance during complement-activated plasma infusion in swine.

To investigate the acute effects of complement activation on blood flow, we infused complement-activated plasma into the femoral artery of the isolated hindlimb of 19 anesthetized swine. Femoral artery blood flow decreased abruptly, was lowest at 1 min of the infusion, and thereafter slowly increased despite continued infusion. There was no significant change in femoral artery pressure or femoral vein pressure, confirming an acute increase in vascular resistance. Control infusion of heat-decomplemented-activated plasma caused no change in pressure or flow. Slope of the femoral artery pressure-flow relationship during maximal vasodilation with adenosine was significantly lower after infusion of complement-activated plasma, confirming a persistent increase in vascular resistance. Neither the acute nor the persistent increase in vascular resistance was prevented by alpha-adrenergic blockade with phentolamine or granulocytopenia produced by cyclophosphamide. We conclude that complement-activated plasma infusion in the femoral circulation causes an abrupt increase in vascular resistance that persists during pharmacologically maximal vasodilation, is not due to alpha-mediated vasoconstriction, and is not altered by severe granulocytopenia.

Adrenergic alpha-Antagonists↗

PubMed1988

Effects of bepridil hydrochloride on cardiocirculatory dynamics, coronary vascular resistance, and cardiac output distribution in normal, conscious rats.

The purpose of this study was to characterize the cardiocirculatory effects of bepridil hydrochloride (BP) in the normal, conscious rat. Animals were instrumented under halothane anesthesia for right atrial, left ventricular, arterial, and venous pressure recordings. The radioactive-microsphere technique was used to measure regional blood flow and cardiac output before (control) and during intravenous (i.v.) infusion of either BP at three dosage levels (3.0, 6.0, 12.0 mg/kg) or vehicle (VH) at infusion rates matching those of the BP protocol (0.0408 ml/min). The predominant effects of BP (cumulative dose = 9.0 mg/kg i.v.) in the conscious rat were reduced coronary vascular resistance and heart rate. BP showed selectivity for the coronary circulation since systemic vascular resistance was not significantly reduced until a cumulative i.v. dosage of 21.0 mg/kg was administered. BP had few effects on other regions of the peripheral circulation. BP (21 mg/kg) reduced blood flow and increased vascular resistance in the arterial circulations of four of six skeletal muscles studied although opposite effects occurred in two of six muscles studied. BP had no significant effect on blood flow or vascular resistance in the other major arterial circulations. The results of this study show that BP is a selective coronary vasodilator that also reduces the primary indices of myocardial oxygen demand. These results suggest that the clinical therapeutic antianginal efficacy of BP occurs through a combined effect to increase myocardial oxygen supply and to reduce myocardial oxygen demand.

Animals↗

PubMed1998

Vascular resistance in primary open angle glaucoma.

PURPOSE: To explore any difference in vascular resistance between normal and glaucoma subjects using a continuous wave Doppler technique. METHOD: The Resistance Index, RI, was calculated in two orbital vessels of 20 glaucoma patients all of whom had pressures over 23 mmHg and 15 age matched normal subjects. The haemodynamic relationship between the supratrochlear and a vessel at the optic disc, presumed central retinal artery, is expressed as RIST/RICRA. RESULTS: In 30 normal eyes the ratio was >1 m, in 10 glaucoma patients it was >1. In those glaucoma eyes which were <1, 14 improved after treatment to >1. The remaining 16 eyes which showed no change in the ratio were the eyes with moderate to severe field loss. CONCLUSION: An altered, increased, peripheral vascular resistance with reduced diastolic flow in small orbital vessels has been demonstrated in glaucoma subjects. This was not altered by treatment in the more severely affected eyes.

Adult↗

PubMed1984

Impaired baroreflex control of vascular resistance and heart rate in acute myocardial infarction.

The baroreflex control of vascular resistance and heart rate was studied in 11 patients to determine whether it is impaired in patients with acute myocardial infarction. Reflex forearm vasoconstriction in response to lower body negative pressure at 40 mm Hg was less in the early convalescent phase (mean seven days) than in the late convalescent phase (mean 41 days). Pressor as well as vasoconstricting responses to the cold pressor test did not differ between the early and late convalescent phases. The slope of the regression line relating systolic blood pressure and the RR interval during a transient rise in blood pressure produced by intravenous phenylephrine was appreciably reduced in the early convalescent phase of myocardial infarction. These results suggest that baroreflex control of vascular resistance and heart rate is impaired in patients with acute myocardial infarction.

Adult↗

PubMed1996

Pulmonary vascular resistance during lipid infusion in neonates.

Using two-dimensional echocardiography, pulmonary vascular resistance was estimated from right ventricular pre-ejection period to ejection time (RVPEP/ET) in 11 preterm infants with respiratory distress, to test the effect of different doses of continuous lipid infusion. Echocardiography was performed at baseline with no lipid infusing 2 and 24 hours after 1.5 and 3 g/kg/day of intravenous lipid, 24 hours after discontinuing intravenous lipid emulsion, and 2 hours after restarting intravenous lipid. After 24 hours of intravenous lipid at 1.5 g/kg/day the RVPEP/ET rose to mean (SD) 0.287 (0.03) from a baseline value of 0.225 (0.02) and to 0.326 (0.05) after 24 hours of intravenous lipid at 3 g/kg/day. Pulmonary arterial pressure returned to baseline 24 hours after the intravenous lipid had been discontinued. Continuous 24 hour infusion of lipid caused significant dose and time-dependent increases in pulmonary vascular resistance. Intravenous lipid may aggravate pulmonary hypertension.

Dose-Response Relationship, Drug↗

PubMed1990

The "isolated" popliteal segment: a comparative evaluation of its vascular resistance.

During femoro-popliteal and femoro-distal bypass, measurement of vascular resistance (VR) at the site of graft outflow may be used to quantify "run off". Intra-operative measurements were made in 51 lower limbs to compare VR in different categories of outflow; the "isolated" popliteal segment (IPS group, n = 11), the popliteal artery in continuity with patent vessels to the pedal arch (PIC group, n = 26) and the single calf vessel (SCV group, n = 14). VR was measured both before and after intra-arterial papaverine. The values in the 37 popliteal arteries were correlated with two different methods of arteriographic scoring. Vascular resistance in the IPS group (median 1149 mPRU, P = 0.003) but not significantly different from VR in the SCV group (median 1014 mPRU, range 743-1541 mPRU). VR in the SCV group was significantly greater than that in the PIC group (P = 0.006). After papaverine administration, the same relationships were observed between the IPS, PIC and SCV groups. Both before and after papaverine, VR in the popliteal artery correlated significantly with both arteriographic scores. In terms of VR, the isolated popliteal segment provides an outflow comparable to that of a single calf artery but less favourable than a popliteal artery wtih patent run off.

Femoral Artery↗

PubMed1992

Contrasting effects of propranolol on sympathetic nerve activity and vascular resistance during orthostatic stress.

BACKGROUND: Previous studies in humans advanced the concept that cardiac filling pressure and contractility, the primary determinants of ventricular mechanoreceptor discharge, are important determinants of sympathetic outflow during orthostatic stress. Thus, intravenous propranolol greatly attenuated forearm vasoconstrictor response to venous pooling with lower body negative pressure (LBNP). The aim of this study was to reevaluate the experimental support for this concept by using direct measurements of sympathetic nerve activity. METHODS AND RESULTS: In 11 healthy humans, we recorded muscle sympathetic nerve activity (MSNA) with microelectrodes (peroneal nerve), as well as blood flow in the forearm and calf (venous occlusion plethysmography) at baseline and during graded LBNP. The same experiments were repeated after administration of propranolol (0.15 mg/kg i.v.), which is thought to decrease ventricular mechanoreceptor discharge. The major new findings are that propranolol neither increased baseline MSNA nor attenuated the increases in MSNA during graded orthostatic stress even though in the same subjects, propranolol simultaneously increased the baseline level of vascular resistance in both the forearm and calf and substantially attenuated the increases in regional vascular resistance during orthostatic stress. CONCLUSIONS: Systemic beta-blockade causes a marked dissociation between sympathetic outflow and vascular resistance that invalidates the use of intravenous propranolol as an experimental model to examine the reflex effects of ventricular mechanoreceptors on peripheral vascular resistance in humans.

Adult↗

PubMed2003

New score indicating placental vascular resistance.

BACKGROUND: Umbilical artery Doppler velocimetry is a routine method for fetal surveillance in high-risk pregnancy. Uterine artery Doppler seems to give comparable information, but it can be difficult to interpret as there are two arteries, which might show notching and/or increased pulsatility index (PI) as signs of increased vascular impedance. Combining the information on vascular resistance on both sides in a new score might simplify and improve evaluation of placental circulation. METHODS: Uterine and umbilical artery Doppler velocimetry was evaluated in 633 high-risk pregnancies. The managing clinician was informed only about the umbilical artery flow. The umbilical artery flow spectrum was semiquantitatively divided into four blood flow classes (BFC), expressing signs of increasing vascular resistance. The uterine artery Doppler flow spectrum was divided into five uterine artery scores (UAS), taking into account presence/absence of notching and/or increase in PI. By adding UAS to BFC, a new placental score (PLS) was constructed with values ranging from 0 to 7, indicating general placental vascular resistance. The scores were related to three outcome variables: small-for-gestational age (SGA), premature delivery (<37 weeks), and cesarean section. RESULTS: All three score systems showed a significant relationship between signs of increasing vascular resistance and outcome. The new PLS showed the best association to adverse outcomes, with optimal cut-off at values exceeding score 3. CONCLUSION: Doppler velocimetry on both sides of the placenta showed a strong relationship to an adverse outcome of pregnancy. The new PLS showed a better relationship to adverse perinatal outcome than the BFC and the UAS. The PLS can simplify evaluation of uteroplacental and fetoplacental Doppler velocimetry.

Adult↗

PubMed1990

Effect of nicardipine on the relationship of renal blood flow and of renal vascular resistance to perfusion pressure in dog kidney.

The effect of nicardipine, a Ca channel blocker, on autoregulation of renal blood flow and perfusion pressure-vascular resistance relationship has been investigated in perfused kidneys of anaesthetized dogs. In control animals excellent autoregulation of renal blood flow and pressure-dependent elevation of vascular resistance were observed above 100 mmHg of perfusion pressure. However, intra-arterial infusion of nicardipine at doses of 3 and 10 micrograms min-1 showed dose-dependent impairment of the autoregulatory response and of elevation of vascular resistance. Infusion of nicardipine (2.5 micrograms min-1) into the renal artery also inhibited renal vasoconstriction induced by YC-170, a Ca channel activator. These results suggest that the inhibitory effect of nicardipine upon renal autoregulation may be due to its Ca2+ channel blocking action.

Animals↗

PubMed2005

Cold-induced elevation of forearm vascular resistance is inversely related to birth weight.

Fetal growth retardation has been linked to elevated blood pressure in adult life. This association between birth weight and blood pressure is present in childhood and is amplified with age. However, the mechanisms that underlie this association are largely unknown. We examined the relationship between birth weight and forearm vascular resistance and forearm blood flow in children aged 9-12.7 years. A total of 58 children were randomly selected from a cohort of 1610 born at the University Hospital of the West Indies in Jamaica where adequate antenatal and delivery records were available. Blood pressure, heart rate and forearm blood flow (by venous occlusion plethysmography) were measured at rest and after cold pressor and mental arithmetic tests. There was a significant inverse correlation between birth weight and the change in the vascular resistance for the cold pressor test (r=-0.47; P<0.001) and the mental arithmetic stress test (r=-0.26; P=0.05). The log ratio of vascular resistance under stress to resting decreased by 0.289 units per kg of birth weight (95% CI: 0.145-0.434; P=0.0002). Lower birth weight is associated with increased vascular responsiveness. Increased vascular resistance might be one mechanism linking fetal growth to subsequent elevated blood pressure.

Birth Weight↗

PubMedDate not supplied

Augmentation of cardiopulmonary baroreflex control of forearm vascular resistance in borderline hypertension.

Arterial baroreflex control of heart rate is impaired in young men with borderline or mild hypertension. Despite this impairment, these subjects often have exaggerated increases in vascular resistance during orthostatic stress. We considered the possibility that this exaggerated reflex vasoconstriction might reflect augmented cardiopulmonary baroreflex control of vascular resistance in borderline hypertension (BHT). Accordingly, we studied cardiopulmonary baroreflex control of forearm vascular resistance in nine BHT men with blood pressure intermittently above 150/90 mm Hg and in seven normotensive (NT) men. Cardiopulmonary baroreceptor input was reduced with lower body negative pressure (LBNP-5 to-20 mm HG), which decreases cardiac filling pressures. Baseline mean arterial pressure was 99 /+- 3 mm Hg (mean /+- SE) in BHT vs 83 /+- 2 mm Hg in NT (p less than 0.05). Baseline forearm resistance was also higher in BHT than in NT: 19 /+- 2 vs 13 /+-1 mm Hg/ml/min/100 ml or units (p less than 0.05). Reflex increases in forearm resistance during LBNP were greater (p less than 0.05) in BHT than in NT 8.6 /+- 1.7 vs 4.5 /+- 1.1 units during LBNP-20). Increases in arterial pressure and forearm resistance during a cold pressor test were not significantly different in the two groups. Thus, the augmented response to LBNP could not be attributed to a nonspecific influence of increased baseline resistance or a generalized abnormality in reflex control. In summary, the results of this study suggest that there is augmentation of the tonic inhibitory influence of cardiopulmonary baroreceptors in humans with BHT.

Adult↗

PubMed1991

The effects of ischemia on long bone vascular resistance.

An in vitro canine tibia model was used to assess the effects of 48 h of hypothermic (4 degrees C) ischemia on bone vascular resistance and on responsiveness of intraosseous blood vessels to circulating norepinephrine. Three groups of bones were studied: Group I (n = 11), 48 h hypothermic ischemia; Group II (n = 11), 48 h hypothermic ischemia with pretreatment with allopurinol and oxypurinol; and Group III (n = 10), no ischemia. Resting vascular resistance in both ischemic groups (79 and 74 mmHg/ml/min) was significantly higher (p less than 0.0001) than in the nonischemic group (22 mmHg/ml/min). Effects of norepinephrine on vascular resistance were significantly greater in both ischemic groups (p less than 0.004). In all three groups, acetylcholine infusion attenuated the increases in perfusion pressure caused by norepinephrine. This demonstrates secretion of endothelial-mediated relaxing factors (EDRF) and prostaglandin for up to 48 h of hypothermic ischemia. As no significant differences were detected between the two ischemic groups, this study failed to demonstrate any protective effect of xanthine oxidase inhibitors.

Acetylcholine↗

PubMed1987

Increasing daytime vascular resistance with progressive hypertension in ambulant patients.

Twenty-four-hour recordings of intra-arterial blood pressure, heart rate, and calculation of the index of peripheral vascular resistance were obtained in 20 untreated ambulant hypertensive patients during their routine activities outside the hospital. Blood pressures and heart rates were higher during the day, with a mean night-to-day increase of 22%, 34%, and 26%, for systolic, diastolic, and mean pressures, respectively. The average increase in the heart rate was 32%. Overall, the index of resistance was lower (12%) during the day. However, eight patients (40%) demonstrated no change or an increase in the peripheral vascular resistance. Six of these eight patients had an average daytime mean pressure above 120 mm Hg. There was a significant decrease in the index of resistance during exercise in all but one of the 16 subjects. Hemodynamic parameters of 1 hour before and 1 hour after awakening were similar to the values obtained during the entire night and the rest of the day, respectively. Our data suggest that in patients with "progressive" hypertension, the ability to decrease vascular resistance from night to day is compromised.

Adult↗