Decrease In Total Peripheral Resistance Research Articles

Relationship between arterial blood pressure and blood viscosity in spontaneously hypertensive rats treated with pentoxifylline.

Systemic arterial pressure (AP) depends on two physiological variables: cardiac output (CO) and total peripheral resistance (TPR). The latter depends on vascular hindrance and blood viscosity (BV). However, the relative contributions of the vascular and rheological factors to TPR remain unclear. The aim of our work was to study the haemodynamic and haemorheologic effects of a treatment course with pentoxifylline (PTX) in SHRs in an effort to assess the impact of the rheological factor on TPR and AP. The effects of the treatment course with PTX (100 mg/kg/day p.o. for six weeks) on BV, plasma viscosity, haematocrit, erythrocyte aggregation and deformability, mean AP (MAP), stroke volume (SV), CO, and TPR were studied in SHRs and in control Wistar Kyoto (WKY) rats. PTX-treated SHRs had a lower BV, lower erythrocyte aggregation, and higher erythrocyte deformability index compared with the controls. The TPR level was higher by 43% compared with that in WKY rats and did not differ from the values obtained from control SHRs. In SHRs, moderate and strong positive correlations were found between BV and MAP and between BV and TPR. PTX-treated SHRs did not have any significant correlations between the above mentioned parameters. Treatment with PTX attenuated whole blood viscosity, but did not affect the AP and hemodynamic parameters in the experimental SHRs compared with the control SHRs. The magnitude of the rheologic effects of PTX was insufficient to cause appreciable decreases in TPR and AP.

Central command generated prior to arbitrary motor execution induces muscle vasodilatation at the beginning of dynamic exercise.

The purpose of this study was to examine the role of central command, generated prior to arbitrary motor execution, in cardiovascular and muscle blood flow regulation during exercise. Thirty two subjects performed 30 s of two-legged cycling or 1 min of one-legged cycling (66 ± 4% and 35% of the maximal exercise intensity, respectively), which was started arbitrarily or abruptly by a verbal cue (arbitrary vs. cued start). We measured the cardiovascular variables during both exercises and the relative changes in oxygenated-hemoglobin concentration (Oxy-Hb) of noncontracting vastus lateralis muscles as index of tissue blood flow and femoral blood flow to nonexercising leg during one-legged cycling. Two-legged cycling with arbitrary start caused a decrease in total peripheral resistance (TPR), which was smaller during the exercise with cued start. The greater reduction of TPR with arbitrary start was also recognized at the beginning of one-legged cycling. Oxy-Hb of noncontracting muscle increased by 3.6 ± 1% (P < 0.05) during one-legged cycling with arbitrary start, whereas such increase in Oxy-Hb was absent with cued start. The increases in femoral blood flow and vascular conductance of nonexercising leg were evident (P < 0.05) at 10 s from the onset of one-legged cycling with arbitrary start, whereas those were smaller or absent with cued start. It is likely that when voluntary exercise is started arbitrarily, central command is generated prior to motor execution and then contributes to muscle vasodilatation at the beginning of exercise. Such centrally induced muscle vasodilatation may be weakened and/or masked in the case of exercise with cued start.

Cardiovascular and autonomic response induced by a 20-week military training programme in young healthy South African males

Background. Studies investigating the relationship between exercise and haemodynamic regulation conducted in older caucasian and blackAfrican populations suggest that lifestyle modification is effective in the management of numerous disease processes. There are few longtermstudies in young healthy populations and even less is known about the influence of habitual exercise on autonomic and haemodynamicvariables in young black African subjects.Objective. To investigate the benefit of prolonged exercise on cardiovascular and haemodynamic variables in young healthy black African males.Methods. Fifty-five healthy male volunteers between 18 and 22 years of age participated in this prospective 20-week medium- to highintensityexercise intervention study with a self-control design. The Finometer Pro (Finapres Medical Systems, the Netherlands) was usedfor non-invasive data sampling of a number of cardiovascular and autonomic variables. Results were generated by computer algorithm andwere analysed using non-parametric Wilcoxon signed rank tests.Results. Significant (p&lt;0.05) cardiovascular changes included an increase in aerobic capacity, stroke volume, cardiac output and ejectionfraction, and a decrease in diastolic blood pressure and heart rate. There was a significant decrease in total peripheral resistance andascending aorta impedance. Systolic blood pressure, mean arterial pressure and arterial compliance remained unchanged, while the decreasein blood pressure variability was not statistically significant (p&gt;0.05).Conclusion. The measured changes suggest a favourable response to exercise and imply that habitual exercise may be an important lifestylemodification for reducing the risk of cardiovascular disease in young black African males.

Cardiovascular Responses to Psychosocial Stress Reflect Motivation State in Adults Born at Extremely Low Birth Weight.

Background. Adults born extremely preterm appear to have more difficulty managing the stresses of early adulthood than their term-born peers. Objective. To examine the effects of being born at extremely low birth weight (ELBW; birth weight < 1000 g) versus at full term on cardiovascular responses to stress. Method. Cardiovascular responses were elicited during administration of a widely used laboratory stressor, the Trier Social Stress Test (TSST). Results. Term-born adults exhibited a larger decrease in total peripheral resistance and larger increase in cardiac output for TSST performance, reflecting greater resilience, than did ELBW adults. Furthermore, in ELBW participants but not controls, cardiovascular responses were correlated with anxiety, suggesting that their responses reflected feelings of stress. Conclusions. Skills-training and practice with relevant stressors may be necessary to increase the personal resources of ELBW participants for managing stress as they transition to adulthood.

Effect of New Zealand Sujon blackcurrant on resting cardiovascular function in triathletes

Background Blackcurrant contains anthocyanin, a component known to induce vasorelaxation and vasodilation in rat aortic rings (Ziberna et al., 2013). In humans, blackcurrant intake has been reported to increase peripheral blood flow (Matsumoto et al., 2005), with higher anthocyanin intake having beneficial effects on cardiovascular function in women (Jennings et al., 2012). However, the effect of blackcurrant intake on cardiovascular function in endurance-trained athletes is unknown. We examined the effect of 1-week Sujon blackcurrant powder supplementation on resting cardiovascular function of trained triathletes. Methods Thirteen healthy triathletes with >3 years experience (8 men; mean±SD: age: 38±8 years, height: 174±5 cm, body mass: 71±9 kg, BMI: 23±2, BF%: 19±5%, VO2max: 49.1±6.2 mL∙kg-1∙min-1, maximum power: 305±68 W) volunteered. Participants were tested following 7 days of Sujon blackcurrant powder (S, 6g/day) or placebo (P) intake, administered following a double-blind, crossover, randomized design with a wash-out period of 4 weeks. Cardiovascular function was recorded for 20 min in supine participants using a beat-to-beat blood pressure monitoring system (Portapres® Model 2, Finapres Medical Systems BV, Amsterdam, The Netherlands). Cardiovascular measures were averaged over 10 consecutive beats, with the lowest systolic blood pressure (BP) and associated measures analysed. Paired two-tailed t-tests were used for analysis with significance accepted at p≤.05. Results There were no differences in systolic BP (P: 121±23, S: 120±23 mmHg, p=.92), diastolic BP (P: 69±16, S: 63±14 mmHg, p=.12), mean arterial BP (P: 86±18, S: 82±18 mmHg, p=.33), and heart rate (P: 58±9, S: 59±10 beats∙min-1, p=.95). Stroke volume (P: 82±23, S: 99±25 mL, p<.01) and cardiac output (P: 4.8±1.6, S: 5.8±1.7 L, p<.05) were increased by 25% and 26%, respectively. There was a 16% lower total peripheral resistance (P: 20.2±8.9, S: 15.2±5.3 mmHg∙L-1∙min-1, p=.05). The changes in resting cardiovascular function were observed in 10 participants. Conclusions Resting cardiovascular function of trained endurance athletes responds positively to 1-week intake of New Zealand Sujon blackcurrant powder. Intake of New Zealand Sujon blackcurrant powder is associated with 1) an increase in stroke volume and cardiac output, and 2) a decrease in total peripheral resistance. For resting skeletal muscles, these observations may influence the delivery of nutrients and clearance of metabolites. The effect on New Zealand Sujon blackcurrant on resting cardiovascular function may support the recovery of endurance athletes. Acknowledgement Funding for this study and conference attendance was provided by the University of Chichester, Health Currancy Ltd (UK) and Gibb Holdings (Nelson) Ltd (NZ).

Sense of impending doom: Inhibitory activity in waiting blood donors who subsequently experience vasovagal symptoms

This study examined autonomic and hemodynamic processes associated with the development of naturally occurring vasovagal responses. Data from a study assessing the physiological correlates of an intervention to reduce vasovagal responses in blood donors were examined (Ditto et al., 2009). Ninety-eight participants were assigned randomly to groups that either practiced applied tension or not. Dependent variables included ratings of vasovagal symptoms, heart rate, blood pressure, and other parameters derived from ambulatory impedance cardiography. Participants who subsequently experienced vasovagal symptoms had a lower ratio between low and high frequency components (LF/HF HRV) of heart rate variability (HRV) before blood donation, suggesting lower sympathetic nervous system activity. They also showed sharper decreases in total peripheral resistance and lower respiration rates. The results suggest that vasovagal reactions that begin during anticipation of a medical procedure may be characterized by an inhibitory process from the outset and do not support the belief that reactions follow a diphasic pattern.

Effects of heel raising maneuver on hemodynamic and autonomic responses to the upright posture

We investigated the effects of muscle pump function on hemodynamic and autonomic responses by heel raising maneuver (HRM) with four frequencies of 6, 7.5, 10, and 15 cycles/min in healthy subjects. Shortening of R-R interval during standing was suppressed by HRM. HRM at frequency of 10 cycles/min led to increase in stroke volume and decrease in total peripheral resistance. HRM at frequencies of 6 and 7.5 cycles/min induced increases in low-frequency powers of R-R interval and systolic blood pressure. The results indicate there is frequency-dependent effect of muscle pump function. I. INTRODUCTION Voluntary contraction of lower-leg muscles is very effective at reducing venous pooling during quiet standing (1). We previously demonstrated that application of lower-leg rhythmic cuff inflation with the pressures > 40 mmHg as a simulation of muscle pump function increased stroke volume and attenuated vagal withdrawal during the transition from sitting to standing (2). In this study we sought to determine how the frequency of muscle pump action (heel raising maneuver) influences hemodynamic and autonomic responses during standing. II. MATERIALS AND METHODS Eight healthy young subjects (5 males and 3 females) aged 22.0¶ 0.5 yr were recruited. Subject wore a breathing mask on which a hot-wire flow meter was mounted. Disposable electrodes were placed on the chest and left gastrocnemius muscle for obtaining ECG and EMG, respectively. A Finapres sensor was placed around the index finger of the subject's left hand. After 4-min of sitting rest, subject performed heel raising maneuver (HRM) with 6 (HRM6), 7.5 (HRM7.5), 10 (HRM10), and 15 (HRM15) cycles/min in a standing position for 6 min. Quiet standing without HRM was served as a control (CTL). Continuous finger BP, respiratory flow, ECG, and EMG were measured. To minimize hemodynamic changes, these variables were recorded during paced breathing at 0.25 Hz. domain measures of variations of HR (HRV) and SBP (SBPV), a power spectral analysis was performed based on Welch's averaged periodogram technique. The total spectral power was calculated for the low (LF: 0.04-0.15 Hz) and high (HF: 0.15-0.4 Hz)-frequency bands by integration of the spectral components. Statistical significance was evaluated by a one-way analysis of variance followed by Dunnett's t-test.

Abstract 642: NOS-dependent Increase In Splanchnic Blood Flow Causes The Hypotensive Response To 24-hour 5-HT Infusion

Long-term serotonin (5-hydroxytryptamine, 5-HT) infusion produces a sustained reduction in mean arterial pressure (MAP) and elicits a decrease in total peripheral resistance (TPR) through a mechanism dependent on nitric oxide synthase (NOS) in rats. We sought to determine if the reduction in TPR induced by 5-HT is caused by NOS-dependent relaxation of vessels to all major organs of the body or selective action on a single vascular bed. Alzet mini-pumps containing vehicle (saline) or 5-HT (25 μg/kg/min) were implanted in male Sprague Dawley rats. One-week prior to pump implantation, rats were either: (1) switched to drinking water containing the NOS inhibitor N-nitro-L-arginine (L-NNA; 0.5 g/L), or (2) maintained on tap water. 5-HT reduced MAP after 24 hours (veh = 87±3, 5-HT = 75±2 mm Hg; p&lt;0.05), which was prevented by L-NNA (L-NNA/5-HT= 115 ±10 mm Hg; p&lt;0.05). After 24 hours of 5-HT infusion, yellow-green fluorescent microspheres, used to determine blood flow (300, 000 spheres; size 15μm), were introduced into the left ventricle of the heart. Microspheres were recovered in arterial reference blood sample and organs using sedimentation through centrifugation. The fluorescence intensity of the dye extracted from the microspheres was measured by spectrophotometery. 5-HT significantly decreased resistance to the spleen (48%), small intestine (35%), and adrenal (70%) compared to vehicle-treated animals, and this decrease was abolished by L-NNA. By contrast, resistance to the ear (175%) was increased by 5-HT. Resistance to other organs (brain, liver, lungs, kidneys and muscle) did not show a statistically significant reduction by 5-HT. Collectively, these findings underscore the importance of the splanchnic circulation and NOS in 5-HT-induced reduction in blood pressure.

Relaxin induces rapid, transient vasodilation in the microcirculation of hamster skeletal muscle

Relaxin produces a sustained decrease in total peripheral resistance, but the effects of relaxin on skeletal muscle arterioles, an important contributor to systemic resistance, are unknown. Using the intact, blood-perfused hamster cremaster muscle preparation in situ, we tested the effects of relaxin on skeletal muscle arteriolar microvasculature by applying 10(-10) M relaxin to second-, third- and fourth-order arterioles and capillaries. The mechanisms responsible for relaxin-induced dilations were explored by applying 10(-10) M relaxin to second-order arterioles in the presence of 10(-5) M N(G)-nitro-l-arginine methyl ester (l-NAME, nitric oxide (NO) synthase inhibitor), 10(-5) M glibenclamide (GLIB, ATP-dependent potassium (K(+)) channel inhibitor), 10(-3) M tetraethylammonium (TEA) or 10(-7) M iberiotoxin (IBTX, calcium-associated K(+) channel inhibitor). Relaxin caused second- (peak change in diameter: 8.3 ± 1.7 μm) and third (4.5 ± 1.1 μm)-order arterioles to vasodilate transiently while fourth-order arterioles did not (0.01 ± 0.04 μm). Relaxin-induced vasodilations were significantly inhibited by l-NAME, GLIB, TEA and IBTX. Relaxin stimulated capillaries to induce a vasodilation in upstream fourth-order arterioles (2.1 ± 0.3 μm), indicating that relaxin can induce conducted responses vasodilation that travels through blood vessel walls via gap junctions. We confirmed gap junction involvement by showing that gap junction uncouplers (18-β-glycyrrhetinic acid (40 × 10(-6) M) or 0.07% halothane) inhibited upstream vasodilations to localised relaxin stimulation of second-order arterioles. Therefore, relaxin produces transient NO- and K(+) channel-dependent vasodilations in skeletal muscle arterioles and stimulates capillaries to initiate conducted responses. The transient nature of the arteriolar dilation brings into question the role of skeletal muscle vascular beds in generating the sustained systemic haemodynamic effects induced by relaxin.

Regional blood flow changes underlying the hypotensive action of 5‐HT:Studies using Doppler and Microsphere technologies

Serotonin (5‐hydroxytryptamine, 5‐HT) causes a sustained decrease in mean arterial pressure (MAP) and elicits a fall in total peripheral resistance (TPR) in normal conscious rats. We hypothesized that the decrease in TPR induced by 5‐HT is caused by relaxation (direct or indirect) of arteries serving one or more major regional vascular beds. Alzet pumps containing vehicle or 5‐HT (25 ug/kg/min) were implanted in male Sprague‐Dawley rats and 24 hours later the rats were anesthetized and underwent: 1) ear and tail blood flow measurements using Doppler to determine cutaneous vascular contribution; or 2) left ventricular injection of fluorescent microspheres (300,000 yellow green microspheres) to determine global organ blood flow. Infusion of 5‐HT increased ear (69.1±20.5% time‐controlled vehicle) and tail (23.5±2.5%) blood flow (Doppler) while elevating small intestinal (50% increase) flow (microsphere) over vehicle‐infused rats. In the microsphere experiments there was no alteration in blood flow by 5‐HT infusion (vs vehicle) in spleen, liver, lung, right or left kidney, leg muscle, abdominal skin, visceral fat or brain, and right and left kidney flows were statistically similar (R; 3.78±0.69 vs L: 4.00±0.74 ml/min/g tissue, p&gt; 0.05). These findings define the cutaneous and splanchnic vasculature as regions of interest to study the mechanism of 5‐HT ability to lower MAP and TPR. NIH HL081115.

Cardiac output and sympathetic vasoconstrictor responses during upright tilt to presyncope in healthy humans

Syncope is a common clinical condition occurring even in healthy people without manifest cardiovascular disease. The purpose of this study was to determine the role of cardiac output and sympathetic vasoconstriction in neurally mediated (pre)syncope. Twenty-five subjects (age 15–51) with no history of recurrent syncope but who had presyncope during 60 deg upright tilt were studied; 10 matched controls who completed 45 min tilting were analysed retrospectively. Beat-to-beat haemodynamics (Modelflow), muscle sympathetic nerve activity (MSNA) and sympathetic baroreflex sensitivity (MSNA–diastolic pressure relation) were measured. MSNA, haemodynamic responses and baroreflex sensitivity during early tilting were not different between presyncopal subjects and controls. Hypotension was mediated by a drop in cardiac output in all presyncopal subjects, accompanied by a decrease in total peripheral resistance in 16 of them (64%, group A). In the other 9 subjects, total peripheral resistance was well maintained even at presyncope (36%, group B). Cardiac output was smaller (3.26 ± 0.34 (SEM) vs. 5.02 ± 0.40 l min(−1), P = 0.01), while total peripheral resistance was greater (1327 ± 117 vs. 903 ± 80 dyn s cm(−5), P < 0.01) in group B than group A at presyncope. The steeper fall in cardiac output in group B was due to a drop in heart rate. MSNA decreased rapidly at presyncope after the onset of hypotension. Thus, a moderate fall in cardiac output with coincident vasodilatation or a marked fall in cardiac output with no changes in peripheral vascular resistance may contribute to (pre)syncope. However, an intrinsic impairment of vasomotor responsiveness and sympathetic baroreflex function is not the cause of neurally mediated (pre)syncope in this population.

Acute Effects of Muscular Counterpulsation Therapy on Cardiac Output and Safety in Patients With Chronic Heart Failure

Our aim was to investigate acute effects of muscular counterpulsation (MCP) on hemodynamic parameters and to evaluate its safety in regard to myocardial integrity and interferences with implanted rhythm devices in patients with chronic heart failure (CHF). A total of 22 patients with CHF (16 male, 67.8 ± 9.5 years, New York Heart Association [NYHA] class II + III, left ventricular ejection fraction 29.6 ± 6.6%) were treated with MCP for 3 consecutive days for 45 min, while hemodynamic parameters were measured noninvasively by bioimpedance (Task Force Monitor). Laboratory control and a complete device testing were performed prior to the first and after the third treatment. In addition, continuous rhythm device interrogation was performed online during the first MCP application. During each application, a significant increase in cardiac output (CO; average change +2.08 ± 2.33 L/min, P < 0.05) was documented. This increase was due to a decrease of total peripheral resistance (-336 ± 530 dyn × s/cm(5) , P < 0.05), to an augmented stroke volume (+8.35 ± 20.86 mL, P = n.s.), and an increase in heart rate (+17.12 ± 21.12 bpm, P < 0.05). Cardiac markers and enzymes were within normal limits at all times and did not increase during treatment. MCP stimuli were monitored using surface electrocardiogram, and no abnormal sensing or pacing events occurred. MCP acutely improves CO in patients with stable CHF. No adverse influence on myocardial integrity was observed nor were any inappropriate sensing or pacing artifacts detected in patients with implanted rhythm devices.

Natural contact and stigma towards schizophrenia in African Americans: Is perceived dangerousness a threat or challenge response?

This research extends our understanding of the relationship of social contact theory to stigma in a sample of mainly African American college students. In Phase 1, 75 participants with high levels of contact reported significantly lower negative affect and less social distance toward the mentally ill as compared to 89 participants with low contact. Despite this, the high contact group attributed significantly higher levels of dangerousness to the mentally ill. Thus while social contact was associated with reductions in some dimensions of stigma, it was associated with higher levels of self-reported perceived dangerousness. These results were obtained while controlling for social desirability bias in the self-report measures of stigma. The results from Phase 1 of this study may indicate fundamental differences between incidental social contact and that which occurs in an assistive context. In Phase 2, a subset of convenience from the high contact group (n=27) and the low contact group (n=38) were compared on cardiovascular reactivity measures while imagining social interactions with people labeled with schizophrenia. Post hoc testing revealed that when participants from the high contact group imagined interacting with people labeled as schizophrenic they exhibited significant decreases in total peripheral resistance (TPR), the challenge pattern, compared to their reactions when they imagined interacting with unstigmatized people. This finding suggests the higher dangerousness ratings of the mentally ill sometimes found in African American samples may be related to factors other than direct threat.

Effect of dinitrosyl iron complexes with glutathione on hemorrhagic shock followed by saline treatment

It has been found that dinitrosyl iron complexes with glutathione (DNIC-GS) injected into the blood flow of rats at a dose of 0.05μmoles/kg prior to hemorrhage significantly improve cardiac function under conditions of hemorrhagic shock manifested in increased stroke volume, left ventricular work and cardiac output to a level exceeding control values 1.5-fold. Enhanced myocardial contractile activity leads to a situation where mean arterial pressure does not decrease further despite the significant decrease of total peripheral resistance. The decrease of total peripheral vascular resistance of the vascular system under vasodilating effects of DNIC-GS used as nitric oxide donors improves microcirculation in experimental rats judging from increased rates of blood flow and low degree of erythrocyte aggregation. Pretreatment of rats with the complexes significantly increases survival (by 21%) under conditions of hemorrhagic shock. It is suggested that beneficial effects of DNIC-GS on systemic circulation parameters under conditions of hemorrhagic shock are determined by their antioxidant activity and the ability to induce S-nitrosylation of proteins.

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Acute effects of intravenous nicorandil on hemodynamics in patients hospitalized with acute decompensated heart failure

Nicorandil injection, a potent vasodilator with K(ATP) channel opening action and nitrate-like action, has been used for treatment of unstable angina. In the present investigation, we examined the effect of intravenous nicorandil on hemodynamics in patients with acute decompensated heart failure (ADHF). ADHF patients admitted to hospital with pulmonary artery wedge pressure (PAWP)≥18 mm Hg were enrolled. Patients received nicorandil by an intravenous bolus injection of 0.2mg/kg/5 min followed by continuous infusion at a rate of 0.05, 0.10, or 0.20mg/kg/h for 6h. Nicorandil administration caused a significant decrease in PAWP and increase in the cardiac index (CI) that began immediately after the injection and were maintained during the continuous infusion. After 6h, nicorandil administration at 0.2mg/kg/5 min followed by 0.20mg/kg/h resulted in a decrease in PAWP (26.5%, p<0.01), an increase in CI (15.8%, p<0.05), and a decrease in total peripheral resistance (13.8%, p<0.01) in a dose-dependent manner. Nicorandil decreased blood pressure significantly, without an excessive decrease or negative impact even in patients with lower systolic blood pressure. Intravenous administration of nicorandil, by bolus injection followed by continuous infusion, improves PAWP and CI in ADHF patients immediately and continuously as a potent vasodilator with combined preload and afterload reduction. These results demonstrate that nicorandil is a safe and effective new medication for the treatment of ADHF.

Role of the median preoptic nucleus in the chronic hypotensive effect of losartan in sodium‐replete normal rats

1. We have shown previously that the chronic hypotensive effect of the angiotensin II AT1 receptor antagonist losartan is mediated, in part, by the subfornical organ (SFO). However, the neural pathway(s) mediating this central effect of losartan downstream from the SFO has not been completely elucidated. 2. The present study was designed to test the hypothesis that the median preoptic nucleus (MnPO) is a crucial part of the neural pathway necessary for the chronic hypotensive effect of losartan. To test this hypothesis, male Sprague-Dawley rats were subjected to either Sham or electrolytic lesion of the MnPO (MnPOx). Rats were instrumented with radiotelemetric transducers and aortic flow probes for the continuous measurement of mean arterial pressure (MAP) and heart rate and cardiac output (CO), respectively. Total peripheral resistance (TPR) was calculated as MAP/CO. After 3 days of baseline measurements, rats were infused intraperitoneally with losartan (10 mg/kg per day) via an osmotic minipump at a rate of 5 microL/min. 3. The data revealed that, by Day 9 of losartan treatment, MAP had decreased 34 +/- 2 mmHg in MnPOx rats (n = 9), whereas the MAP of Sham-lesioned rats (n = 8) had only decreased 24 +/- 3 mmHg. These findings were accompanied by a greater decrease in TPR in MnPOx compared with Sham rats (-0.464 vs-0.237 mmHg/mL per min, respectively), whereas CO remained unchanged throughout the study protocol. 4. These results do not support the hypothesis that an intact MnPO is necessary to mediate the full chronic hypotensive effect of losartan in normal rats. Instead, they appear to suggest that the MnPO may play an important role in buffering the profound hypotension induced by losartan.

Residual renal function and arterial stiffness mediated the blood pressure change during interdialytic weight gain in hemodialysis patients

Volume overload is thought to be the main cause of hypertension in dialysis patients. However, the effect of interdialytic weight gain (IDWG) in hemodialysis (HD) patients, which was considered as an increase in extracellular water (ECW), on blood pressure (BP) change, was controversial. Our aim was to examine the changes in hemodynamics and arterial stiffness during IDWG in HD patients and attempt to explore the possible mechanism of diverse BP change. Thirty prevalent patients on HD were enrolled. The height, weight, BP, blood chemistry, volume status assessed by bioelectrical impedance analysis, hemodynamic parameters obtained by echocardiography, and pulse wave velocity (PWV) were collected within 1 hour postdialysis and again just before the next dialysis session. Meanwhile, blood samples were drawn to analyze vasoactive hormones, including renin, angiotensin II, catecholamine, and endothelin. The patients' weights and ECWs during the next predialysis were significantly higher than those during the postdialysis. The BP showed no difference between postdialysis and the next predialysis. There was an obvious increase in cardiac output and decrease in total peripheral resistance as a whole during the next predialysis than that during postdialysis. When patients were divided into the BP increase group (BPI group, 13 patients) and BP decrease group (BPD group, 11 patients) according to the change in systolic BP higher than 10 mmHg, both groups displayed a significant increase in weight, ECW, cardiac output, and a decrease in total peripheral resistance. As compared with the BPI group, patients in the BPD group had significantly lower IDWG, shorter time on dialysis treatment, and higher residual renal function. A decrease in catecholamine and endothelin in the next predialysis was obvious in the BPD group. There was a significant decrease in PWV at the next predialysis in the BPD group while the PWV did not change significantly in the BPI group. Our results showed that the diverse BP change during IDWG was significantly affected by residual renal function, PWV, and vasoactive substances.

The hemodynamic pattern of the syndrome of delayed orthostatic hypotension

We investigated the hemodynamic mechanisms underlying the syndrome of delayed orthostatic hypotension (OH) and the hemodynamic effect of the treatment with leg compression bandages. Non-invasive monitoring of systolic blood pressure (SBP), heart rate (HR), cardiac output (CO), stroke volume (SV), and total peripheral resistance (TPR) was performed during tilt testing in patients affected by delayed OH compared to age- and sex-matched controls. Thirteen patients (68 +/- 14 years) and nine controls (68 +/- 8 years) were studied. Immediately after tilt-up, SBP progressively decreased in patients but not in controls. Symptoms developed at 100 +/- 7 mmHg. At the end of the test, SBP was significantly lower in patients than in controls. TPR progressively decreased in patients but not in controls. SV and CO did not change significantly. HR increased progressively in the patients until the end of the test and remained unchanged in controls. Active treatment with compression bandages avoided the decrease in SBP and TPR, while CO showed minimal variation. In patients affected by delayed OH, the progressive decrease of SBP is associated with progressive decrease of TPR, while CO and SV show little variation; the compensatory increase in HR is insufficient to compensate for the decline in blood pressure.

S7. Central cardiovascular control: Plasticity in response to normal physiological challenges: S7.1 Pregnancy: CNS plasticity in control of sympathetic outflow in rats

Normal pregnancy is characterized by a ~40% increase in blood volume and cardiac output, mild tachycardia, and decreased arterial blood pressure due to a substantial decrease in total peripheral resistance (TPR). Increased susceptibility to orthostatic and hemorrhagic hypotension is significant problems in term pregnant women and animals, and a number of studies suggest that arterial baroreflex compensatory responses are suppressed in pregnancy. In near term pregnant rats and rabbits, maximum gain for arterial baroreflex control of renal sympathetic nerve activity (RSNA) is decreased, largely due to an attenuated ability to increase RSNA in response to a hypotensive challenge.