Reduction In Arterial Resistance Research Articles

Effect of Intradialytic Exercise on Cardiovascular Outcomes in Maintenance Hemodialysis: A Systematic Review and Meta-Analysis.

Cardiovascular disease is the leading cause of death among people with kidney failure on hemodialysis, for whom improving cardiovascular health is a research priority. Intradialytic myocardial stunning is common and associated with adverse cardiovascular events. Intradialytic exercise may mitigate intradialytic myocardial stunning and improve cardiovascular structure and function. This systematic review investigated the effect of intradialytic exercise on cardiovascular outcomes in adults undergoing maintenance hemodialysis (PROSPERO #CRD42018103118). Following PRISMA guidelines, we systematically searched MEDLINE, EMBASE, Cochrane CENTRAL, SportDiscus, and PEDro databases from 1960 until June 2022, for randomized and non-randomized studies investigating the effect of intradialytic exercise programs on objective cardiovascular outcomes, pre-specified as primary or secondary outcomes. The primary outcome was arterial resistance. Of 10837 references identified, 32 met eligibility criteria. These studies investigated the effect of intradialytic exercise on arterial resistance (8 studies), blood pressure (20 studies), myocardial structure and function (7 studies), endothelial function (2 studies), sympathetic overactivity (9 studies), biomarkers of cardiac injury (3 studies), cardiovascular hospitalization and mortality (2 studies). Most studies used aerobic exercise as the intervention and usual care (no exercise) controls. Meta-analysis of intradialytic exercise versus usual care resulted in a statistically significant reduction in arterial resistance measured by pulse wave velocity (PWV) with mean difference -1.63 m/sec (95% CI -2.51, -0.75). Meta-analyses for diastolic blood pressure, left ventricular ejection fraction (LVEF), and low-frequency/high-frequency (LF/HF ratio) measure of heart rate variability also showed statistically significant improvements with exercise. There was no significant difference in change in systolic blood pressure, augmentation index, and left ventricular mass index between groups. Intradialytic exercise programming resulted in a clinically meaningful improvement to PWV, a component of arterial resistance. Sseveral physiologic measures of cardiovascular health, including diastolic blood pressure, LVEF and heart rate variability measured by the LF/HF ratio were also observed. The effects of intradialytic exercise on major adverse cardiovascular events remains uncertain.

Arginine rapidly dilates intestinal microvessels and resistance arteries by increasing NO production

To what extent the arginine is taken from intracellular stores or transported into the endothelial cell by the cationic amino acid transporter-1for immediate use by eNOS is not known. To evaluate the rapidity of NO and vascular dilatory responses to exogenous arginine, individual in vivo arterioles or the entire vasculature was exposed to 100–400mM arginine. To evaluate artery versus microvascular resistance responses, blood flow and blood pressure in the largest arterioles was measured. The lowest arginine concentration to cause consistent dilation was 100 uM applied to the entire tissue. Dilatory responses to arginine by single arterioles began in 10-15 seconds after release of 200 or 400 uM. Arginine applied to the entire vasculature caused increased blood flow and (NO) within 2 minutes and the response was fully developed by 4 minutes. The blood flow increased 19%, 32, and 50% with 100, 200, and 400 uM arginine. The reduction in arterial resistance during topical arginine was somewhat greater than the microvasculature at 100 and 200 uM arginine. The data indicate that rapid transport of arginine immediately influences NO production and vascular resistance of both intestinal resistance arteries and microvessels at arginine concentrations that could be produced through dietary supplementation of arginine. (Supported by NIH HL-20605)

The influence of tumour necrosis factor-alpha on the cardiovascular system of anaesthetized rats.

The effects of two vasoactive agents (adenosine A2A agonist, CGS 21680, and adrenoceptor agonist, noradrenaline) were examined on cardiac output (CO), heart rate (HR), blood pressure (BP), mean circulatory filling pressure (Pmcf), resistance to venous return, arterial resistance, dP/dt, plasma levels of NO2-/NO3-, and inducible nitric oxide synthase (iNOS) activity in lungs ex vivo, following treatment with tumour necrosis factor-alpha (TNF-alpha; 30 microg/kg) in anaesthetized rats. Treatment with TNF-alpha produced significant reduction in CO (41+/-2%), dP/dt (26+/-3%), BP (26+/-2%) and Pmcf (27+/-4%; n=6; mean+/-SEM), but increased arterial resistance. There were no significant changes in the plasma levels of NO2-/NO3-levels over time following treatment with TNF-alpha, but there was a significant increase (approximately twofold) in the activity of the iNOS in the lungs of animals treated with TNF-alpha. Administration of CGS 21680 (1.0 microg/kg per min) significantly increased CO (44+/-6%), HR (12+/-2%), Pmcf (24+/-4%) and dP/dt (24+/-5%) in TNF-alpha-treated rats. CGS 21680 also significantly reduced arterial resistance (33+/-2%) without altering resistance to venous return in TNF-alpha-treated rats. While noradrenaline (1.0 microg/kg per min) infusion did not significantly increase CO, it did significantly increase HR (12+/-1%), BP (55+/-9%), Pmcf (47+/-5%), dP/dt (65+/-7%), resistance to venous return (64+/-20%), and arterial resistance (41+/-16%) in TNF-alpha-treated animals. The reduction in BP due to administration of TNF-alpha is the result of significant reduction in CO. Consequently, the decline in CO can be attributed to a combination of a negative inotropic effect as well as a reduction in Pmcf. It is evident that infusion with CGS 21680 could reverse the negative impact of TNF-alpha on CO by increasing dP/dt, Pmcf and HR as well as a reduction in arterial resistance. The fact that noradrenaline did not significantly increase CO in TNF-alpha-treated rats can be attributed to increased arterial resistance as well increase in resistance to venous return.

Effect of hypoxia on pulmonary blood flow-segmental vascular resistance relationship in perfused cat lungs.

To investigate the effect of alveolar hypoxia on the pulmonary blood flow-segmental vascular resistance relationship, we determined the longitudinal distribution of vascular resistance while increasing blood flow during hyperoxia or hypoxia in perfused cat lungs. We measured microvascular pressures by the micropipette servo-null method, partitioned the pulmonary vessels into three segments [i.e., arterial (from main pulmonary artery to 30- to 50-micron arterioles), venous (from 30- to 50-micron venules to left atrium), and microvascular (between arterioles and venules) segments] and calculated segmental vascular resistance. During hyperoxia, total resistance decreased with increased blood flow because of a reduction of microvascular resistance. In contrast, during hypoxia, not only microvascular resistance but also arterial resistance decreased with increase of blood flow while venous resistance remained unchanged. The reduction of arterial resistance was presumably caused by arterial distension induced by an elevated arterial pressure during hypoxia. We conclude that, during hypoxia, both microvessels and arteries >50 micron in diameter play a role in preventing further increases in total pulmonary vascular resistance with increased blood flow.

Heart rate variability in time and frequency domains: effects of gallopamil, nifedipine, and metoprolol compared with placebo.

To assess the effects of three different antianginal drugs on heart rate, blood pressure, and heart rate variability. Randomised, single blind, placebo controlled, cross over study. University hospital. Nine healthy male volunteers. Oral administration of either 50 mg gallopamil, 20 mg nifedipine, 100 mg metoprolol, or placebo according to a random crossover plan. Time intervals between consecutive R waves in electrocardiograms measured with an accuracy of 5 ms from digital Holter recordings. Blood pressure monitored continuously by finger plethysmography. Metoprolol lowered heart rate from 62(6) to 51(5) beats/min (p = 0.003) after 78(23) minutes. Nifedipine provoked reflex tachycardia from 56(5) to 94(18) beats/min (p < 0.001) at 10(3) minutes after treatment followed by an exponential decline in heart rate to baseline values with a time constant of 34(7) min in seven subjects but 83 minutes in one volunteer. One subject showed no exponential decline in heart rate. Nifedipine significantly lowered the supine mean arterial pressure from 86(6) to 67(6) mm Hg (p = 0.004) after 11(2) minutes, indicating an acute reduction in arterial resistance. Gallopamil did not significantly change mean heart rate or blood pressure. In the sitting position three hours after administration gallopamil and metoprolol significantly lowered power spectral density in the low frequency band (0.03 Hz to 0.15 Hz) compared with placebo (p < 0.05). Nifedipine did not produce such an effect. Gallopamil and metoprolol both inhibit cardiac sympathetic activation compared with placebo, whereas nifedipine causes reflex sympathetic activation.

Age-Related Differences in Vascular Effects of Pentoxifylline in Isolated Perfused Ferret Lungs

We have determined the magnitude and sites of action of pentoxifylline (PTX), a methylxanthine derivative, in the adult and 3- to 4-week old ferret pulmonary circulation. Lungs of 8 ferrets, four 3- to 4-week-old and 4 adult, were isolated and perfused with blood. During perfusion, blood flow was kept constant, as were airway and left atrial pressures (6 and 8 cm H2O respectively, zone 3 conditions). In all lungs, pulmonary artery pressure was measured continuously and the circulation was partitioned into arteries, microvessels and veins, by measurement of pressures in 20-50 microns diameter subpleural arterioles and venules using the micropipette-servonulling method. Pressures were obtained in each lung during baseline, after vasoconstriction with hypoxia, and again after the infusion of PTX, 20 mg/kg, during hypoxia. We found that with hypoxia, total vascular resistance increased by approximately 90% in both adult and neonatal lungs; arterial and venous resistances increased by 100-180% in both age groups, with little change in microvascular resistance. PTX resulted in a significant decrease in total vascular resistance, due to a decrease in resistance in both arteries and veins. The decrease in resistance with PTX was greater in adult lungs (of the increase in resistance induced by hypoxia, 80% was eliminated by PTX) than in 3- to 4-week old lungs (51% elimination of tone induced by hypoxia). This difference was mainly due to a smaller reduction in arterial resistance with PTX in 3- to 4-week-old lungs. We conclude that PTX is a powerful pulmonary vasodilator in ferrets and that its effectiveness as a vasodilator depends on the age of the animal, the older animal showing greater responsiveness.

Segmental vascular resistance during pulsatile and steady perfusion in 3- to 5-wk-old rabbit lungs

To determine the mechanisms by which pulsatile perfusion reduces vascular resistance in isolated lungs, we compared the effects of pulsatile versus steady perfusion on total and segmental vascular resistance in isolated lungs of 3- to 5-wk-old rabbits. Lungs were perfused alternately with steady and pulsatile flow for 45-min periods at a constant total arteriovenous pressure drop. Blood flow was adjusted to keep mean pulmonary arterial pressure at 20 cmH2O, when left atrial and airway pressures were 8 and 6 cmH2O, respectively. We partitioned the pulmonary circulation into three longitudinal vascular segments, i.e., arteries, microvessels, and veins, by measuring pressures in 20- to 50-microns-diameter subpleural arterioles and venules by the micropipette servo-nulling method. We found that in the isolated, perfused 3- to 5-wk-old rabbit lung, in which arteries and veins are the main sites of resistance, pulsatile flow results in a 20-36% reduction in total vascular resistance, mainly due to a reduction in arterial and venous resistances. The decrease in total vascular resistance was similar in lungs that were untreated or treated with papaverine, indicating that the effect of pulsatile flow was not due to active vasomotion. The reduction in arterial resistance was greater than that in veins (31-55 vs. 19-22%), especially when pulse amplitude was high (5-10 vs. 20-30 cmH2O). Total vascular resistance was also lower after 45 min of pulsatile perfusion with a pulse rate of 200 pulses/min than 80 pulses/min (0.126 +/- 0.04 vs. 0.154 +/- 0.059 cmH2O.min.ml-1.kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative effects of vasodilator drugs on flow distribution and venous return

Systemic vascular effects of hydralazine, prazosin, captopril, and nifedipine were studied in 115 anesthetized dogs. Blood flow (Q) and right atrial pressure (Pra) were independently controlled by a right heart bypass. Transient changes in central blood volume after an acute reduction in Pra at a constant Q showed that blood was draining from two vascular compartments with different time constants, one fast and the other slow. At three dose levels producing comparable reductions in systemic arterial pressure (30-40% at the highest dose), these drugs had different effects on flow distribution and venous return. Hydralazine and prazosin had parallel and balanced effects on arterial resistance of the two vascular compartments, and flow distribution was unaltered. Captopril preferentially reduced arterial resistance of the compartment with a slow time constant for venous return (-26 +/- 6%, -30 +/- 6%, -50 +/- 5% at 0.02, 0.10, and 0.50 mg X kg-1 X h-1, respectively; means +/- SEM) without altering arterial resistance of the fast time-constant compartment. Blood flow to the slow time-constant compartment was increased 43 +/- 14% at the highest dose, and central blood volume was reduced 108 +/- 15 mL. In contrast, nifedipine had a balanced effect on arterial resistance with the lowest dose (0.025 mg/kg) but caused a preferential reduction in arterial resistance of the fast time-constant compartment at higher doses (-38 +/- 4% and -55 +/- 2% at 0.05 and 0.10 mg/kg, respectively). Blood flow to the slow time-constant compartment was reduced 36 +/- 5% at the highest dose of nifedipine, and central blood volume was increased 66 +/- 12 mL. Total systemic venous compliance was unaltered or slightly reduced by each of the four drugs. These results add further evidence to the hypothesis that peripheral blood flow distribution is a major determinant of venous return to the heart.

CARDIOVASCULAR ACTIVITY OF CARNIGEN IN NORMOTONE AND IN EXPERIMENTALLY HYPOTONE DOGS

Activity of Carnigen on the cardiovascular system, following intraduodenal and intravenous application, was investigated in normotone and hypotone dogs anaesthetized with sodium pentobarbital, 35-40 mg/kg intraperitoneally. Intraduodenal application of 1 and 3 mg Carnigen/kg caused an increase in blood pressure and tachycardia. The total peripheral resistance was lessened, in normotone as well as hypotone dogs, whereas the cardiac output and stroke volume were augmented. A rise in myocardial inotrophy and cardiac work in combination with a moderate increase in left ventricular O2 consumption also occurred as result of the action of Carnigen. An increase in the central and peripheral venous pressure was registered during continuous infusion of Carnigen. Coronary flow was also raised, in a dose dependent manner within the range of 0.1 to 1 mg Carnigen/kg i.v. The rise in arterial blood pressure is due to an increase in cardiac output, resulting from the positive inotropic action of this compound on the myocardium. The reduction in arterial resistance can be explained on the basis of a possible interaction between the inosine, released from Carnigen, and the adenosine already present in the system.