Higher Total Peripheral Resistance Research Articles

THE PARAMETERS OF CENTRAL HEMODYNAMICS IN YOUNG PEOPLE DEPENDING ON THE TYPE OF BLOOD CIRCULATION DURING PHYSICAL EXERCISE

The purpose of the study : to assess the parameters of central hemodynamics in young people with different types of blood circulation during physical exercise. Materials and methods. 39 male students of Gomel State Medical University were examined by the method of tetrapolar chest reography (impedance cardiography). The following parameters of central hemodynamics were assessed: heart rate, stroke volume, cardiac output, cardiac index, total peripheral resistance and left ventricular filling pressure. The parameters of central hemodynamics were studied in quiescent state and after physical exercise. Bicycle ergometric test with stepwise increasing load was used as physical exercise. Results and discussion. The study showed that the examined students with hyperkinetic type of circulation in quiescent state were characterized by high values of stroke volume, cardiac output, cardiac index and low total peripheral resistance, which are typical for moderate hyperdinamia of cardiac activity. Students with hypokinetic type had low values of stroke volume, cardiac output, cardiac index and high total peripheral resistance, left ventricular filling pressure which characterize more economical mode of heart work. Students with normorkinetic type of circulation were characterized by average values of the studied parameters in quiescent state. The features of the central hemodynamics parameters in young people depending on the type of blood circulation during physical exertion were revealed. Conclusion. In young men with hyperkinetic type of circulation during physical exercise the heart works in the least economical mode, and the range of compensatory possibilities of this type is limited. On the contrary, hypokinetic circulation is the most economical and the cardiovascular system in this type of circulation has a large range of function mobilization.

Early abnormalities of arterial distensibility in premenopausal women screened for stage 1 hypertension

Purpose: Aim of this study was to investigate and compare several parameters of arterial distensibility between a group of hypertensives premenopausal women and a group of hypertensive male peers. Methods: We studied 385 stage 1 hypertensives subjects (280 men and 105 women), from the HARVEST study (mean age 38±10 years). Arterial distensibility was evaluated by applanation tonometry. Between-gender differences were adjusted for several confounders, patient were divided into 3 age classes and differences in arterial distensibility parameters were examined with a 2-way ANCOVA using sex and age-class as factors. Results: Despite better metabolic profile and lower systolic blood pressure (BP), women showed lower large (C1) and small artery (C2) compliance, higher augmentation index (AIx) and total peripheral resistance (TPR) than men (all age-adjusted p<0.0001); pulse wave velocity (PWV) did not differ between the two genders. When data were adjusted for BP and heart rate (HR), lifestyle habits and metabolic parameters, differences remained highly significant (p<0.0001). However, when height was included in the models, only the differences in C2 and AIx remained significant (p=0.033 and p=0.001, respectively). Other significant determinants of distensibility were: systolic BP and HR for C1 and C2, BMI and age for C2 and AIx, and sedentariness for Aix. The gender-related differences in distensibility parameters did not vary across the age classes, with no significant interaction between age and sex. In both genders C2 and AIx were closely correlated with TPR (all p<0.001). Conclusions: These data show that height accounts for most of the difference in arterial distensibility parameters between hypertensive men and women. However, after adjustment for height, impairment of C2 and AIx persist in premenopausal hypertensives women, indicating an higher TPR condition.

Cardiovascular reactivity and resistance to opposing viewpoints during intragroup conflict

This study examined how the outcomes of joint decision making relate to cardiovascular reactions when group members disagree about the decision to be taken. A conflict was experimentally induced during a joint decision-making task, while cardiovascular markers of challenge/threat motivational states were assessed following the biopsychosocial model of challenge and threat (BPSM; J. Blascovich, 2008). Results show that individuals were less likely to adjust their initially preferred decision alternative the more they exhibited a cardiovascular pattern indicative of threat (i.e., relatively high total peripheral resistance and low cardiac output) compared to challenge. This finding extends the BPSM by showing a link between threat and rigidity, and emphasizes the importance of psychophysiological processes for studying intragroup conflict and decision making.

265 HIGHER RESTING SUPINE BLOOD PRESSURE IS ASSOCIATED WITH AN INITIAL RISE IN CARDIAC OUTPUT ON STANDING

Background: Active standing is normally associated with a large transient reduction in systolic blood pressure (SBP) within the first 30 sec. This can be associated with symptoms of pre-syncope and occasionally loss of consciousness. The initial hemodynamic response to active standing is complex and a transient reduction in total peripheral resistance (TPR) is a characteristic feature, dependent on cardiovascular autonomic reflexes related to redistribution of blood and skeletal muscle contraction. Methods: SBP, heart rate (HR), cardiac output (CO), stroke volume (SV) and TPR were measured continuously (Finometer Midi) before and on standing in 309 medical students of median age 22 (54% female). Results: Although SBP fell [median: -44 (interquartile range: 23) mmHg] and heart rate rose [+34 (12) min−1], there were both qualitative rises (n = 175, +1.3 L/min) and falls (n = 134, -0.8 L/min) in CO during the first 30 seconds on standing, without significant differences in age, sex, weight or height. Those in whom CO rose on standing had a lesser fall in SBP (-36 v -55 mmHg, P < 0.0001). Compared with people who show an early fall in CO on standing, those who show an early increase in CO have a slightly higher supine SBP (115 v 111 mmHg, P < 0.0001) and higher TPR (1051 v 894 units, P < 0.0001). Conclusions: A rise in CO upon standing might define a phenotypic subgroup in which cardiovascular reflexes program higher supine SBP and TPR. Such a quantitative phenotype might be useful for genetic studies.

Harvey Cushing and the regulation of blood pressure in giraffe, rat and man: introducing ‘Cushing's mechanism’

The fundamental mechanism that underlies essential hypertension is a high total peripheral resistance. We review here possible origins of high total peripheral resistance in physiologically hypertensive giraffes, spontaneously hypertensive rats and humans with essential hypertension. We propose that a common link could be reduced brainstem perfusion, as first suggested by Cushing in 1901. Any tendency towards reduction of cerebral blood flow to the cardiovascular control centres in rest and sleep will be prevented by activation of a response arising in the brainstem. The response will proportionately increase systemic blood pressure and return cerebral blood flow to a new homeostatic level. New evidence we review here supports this idea and leads us to suggest that central regulation of blood pressure has two components: the classic Cushing's response, which is a terminal event, and a Cushing's mechanism, which is a physiological mechanism for long-term control of mean arterial pressure. In giraffes, Cushing's mechanism is activated by increasing neck length during growth and subsequent gravitational hypotension that stimulates a rise in basal arterial blood pressure. In man and rats, the mechanism is activated by narrowing of the arteries supplying the brainstem. If we are correct, future successful treatment of essential hypertension in man will include methods of reducing cerebral arterial resistance.

Using 100% Oxygen does not Alter the Cardiovascular Autonomic Regulation during Non-invasively Simulated Haemorrhage in Healthy Volunteers

We tested the effect of 100% oxygen on heart rate (HR), arterial blood pressure (ABP), cardiac output (CO), stroke volume (SV), total peripheral resistance (TPR), HR variability (HRV), systolic blood pressure variability (SBPV) and baroreflex sensitivity (BRS) in 20 healthy volunteers during simulated haemorrhage induced by -40 mmHg lower body negative pressure (LBNP). HRV in the high frequency region (HRV HF), BRS, ABP and TPR were significantly increased, SBPV in the low frequency region (SBPV LF), CO and SV were unchanged, and HR was significantly decreased by 100% oxygen administration during normovolaemia. HRV HF, BRS, CO and SV were significantly decreased, SBPV LF and ABP were unchanged, and HR and TPR were significantly increased by LBNP during 21% or 100% oxygen administration. There were no significant differences in cardiovascular autonomic and haemodynamic responses to LBNP during 21% or 100% oxygen administration, suggesting that 100% oxygen does not alter normal cardiovascular autonomic responses during simulated haemorrhage.

Serial hemodynamic measurement in normal pregnancy, preeclampsia, and intrauterine growth restriction

The study hypothesis was that hemodynamic measurements in conjunction with uterine artery Doppler could enable selection of women at risk for the development of preeclampsia or fetal growth restriction. Systolic (SBP) and diastolic blood pressure, heart rate (RR), cardiac output (CO), total peripheral resistance (TPR), phase difference of SBP and RR interval were measured serially before, during, and after pregnancy. At 20 weeks, uterine artery Doppler measurement was performed. Outcome was classified as preeclampsia (PE) or gestational hypertension (GH) with or without fetal growth restriction (FGR), FGR without PE or GH, and normal pregnancy (NP). Differences between these groups were assessed by 1-way analysis of variance and discriminant analysis. In early pregnancy, in comparison with NP (n = 28), PE/GH had a higher SBP and phase difference of SBP-RR interval. CO was higher in PE/GH without FGR (n = 5) but not PE/GH with FGR (n = 5). FGR, either with or without PE/GH (n = 4), was associated with higher TPR. Conjunction with uterine Doppler allowed selection of 93% of women with an abnormal outcome with a specificity of 100%. The study supports our hypothesis that in early pregnancy, hemodynamic parameters differ from normal in women predisposed to develop preeclampsia or fetal growth restriction.

Stability of cirrhotic systemic hemodynamics ensures sufficient splanchnic blood flow after living-donor liver transplantation in adult recipients with liver cirrhosis

To investigate the correlation between systemic hemodynamics and splanchnic circulation in recipients with cirrhosis undergoing living-donor liver transplantation (LDLT), and to clarify how systemic hemodynamics impact on local graft circulation after LDLT. Systemic hemodynamics, indocyanine green (ICG) elimination rate (K ICG) and splanchnic circulation were simultaneously and non-invasively investigated by pulse dye densitometry (PDD) and ultrasound. Accurate estimators of optimal systemic hyperdynamics after LDLT [i.e., balance of cardiac output (CO) to blood volume (BV) and mean transit time (MTT), defined as the time required for half the administered ICG to pass through an attached PDD sensor in the first circulation] were also measured. Thirty recipients with cirrhosis were divided into two groups based on clinical outcomes corresponding to postoperative graft function. Cirrhotic systemic hyperdynamics characterized by high CO, expanded BV and low total peripheral resistance (TPR) were observed before LDLT. TPR reflecting cirrhotic vascular alterations was slowly restored after LDLT in both groups. Although no significant temporal differences in TPR were detected between the two groups, CO/BV and MTT differed significantly. Recipients with good outcomes showed persistent cirrhotic systemic hyperdynamics after LDLT, whereas recipients with poor outcomes presented with unstable cirrhotic systemic hyperdynamics and severely decreased K ICG. Systemic hyperdynamic disorders after LDLT impacted on portal venous flow but not hepatic arterial flow. We conclude that subtle systemic hyperdynamics disorders impact on splanchnic circulation, and that an imbalance between CO and BV decreases portal venous flow, which results in critical outcomes.

WISE‐2005: Adrenergic responses to 60 days of 6o head‐down bed‐rest (BR) in women with exercise counter‐measures

Women are especially susceptible to orthostatic intolerance on return from space or after BR. Before and after 2 doses of isoproterenol (ISO) or norepinephrine (NOR) MAP, HR, cardiac output (Q), stroke volume (SV), and total peripheral resistance (TPR) were measured in 8 controls and 8 women with flywheel and lower body negative pressure treadmill exercise (EX). Pre-BR, ISO2 caused: higher HR, higher SV, higher Q, and lower TPR. NOR2 caused: lower SV, lower Q, higher TPR and higher MAP. Post-BR controls show higher baseline HR (64.9 ± 2.3 to 72.5 ± 4.8 bpm) and no increase in MAP due to NOR1. Post-BR EX show no increase of baseline HR, higher baseline TPR (18.0 ± 2.1 to 20.2 ± 2.8 mmHg/mL/min), reduced baseline Q (5.5 ± 0.5 mL/min to 4.5 ± 0.5 mL/min), reduced Q with ISO2 (Pre: 8.6 ± 0.9 mL/min; Post: 7.5 ± 0.8 mL/min), augmented TPR with NOR1 (Pre: 19.4 ± 2.2 mmHg; Post: 23.7 ± 3.3 mmHg). Controls show decreased peripheral and increased cardiac sensitivity of adrenergic receptors. EX show increased peripheral sensitivity without cardiac augmentation. We conclude that exercise is cardioprotective after exposure to 60-day BR (CSA, NASA, ESA & CNES).

The vascular response to the K + channel inhibitor 4-aminopyridine in hypertensive rats

The K + channel inhibitor 4-aminopyridine induced an immediate increase in blood pressure and tension in spontaneously hypertensive rats (SHR). Further analysis strongly suggested this to be due to closure of vascular smooth muscle K + channels, as previously concluded for normotensive rats (WKY). The tension response was greater in SHR than WKY, suggesting an increased channel activity in order to compensate for the high total peripheral vascular resistance in SHR. The response was enhanced after nitric oxide (NO) synthase inhibitor in both strains, probably reflecting increased channel activity after elimination of the NO–cGMP pathway. The response in SHR but not WKY was increased after α 1-adrenoceptor inhibition and adrenalectomy but not sympathetic nerve transmitter depletion. It increased also after angiotensin AT 1 and endothelin ET A receptor antagonists and protein kinase C inhibitor. These results indicated an increased adrenal catecholamine, angiotensin AT 1 and endothelin ET A activation of the phospholipase C-protein kinase C pathway in SHR, inhibiting the 4-aminopyridine-sensitive K + channels.

Mechanisms mediating NTS P2x receptor-evoked hypotension: cardiac output vs. total peripheral resistance.

We have previously shown that P2x purinoceptor activation in the subpostremal nucleus tractus solitarius (NTS) produces dose-dependent decreases in mean arterial pressure (MAP), heart rate, efferent sympathetic nerve activity, and significant peripheral vasodilation. However, the relative roles of cardiac output (CO) and total peripheral resistance (TPR) in mediating this depressor response are unknown. Bradycardia does not necessarily result in decreased CO, because, with the greater filling time, stroke volume may increase such that CO may be unchanged. We measured changes in CO (via a chronically implanted flow probe on the ascending aorta) and MAP in alpha-chloralose- and urethane-anesthetized male Sprague-Dawley rats in response to microinjection of the selective P2x purinoceptor agonist alpha,beta-methylene ATP (25 and 100 pmol/50 nl) into the subpostremal NTS. TPR was calculated as MAP/CO. At the low dose of NTS P2x purinoceptor agonist, the reduction in MAP was primarily mediated by reductions in TPR (-31.3 +/- 3.3%), not CO (-8.7 +/- 1.7%). At the high dose, both CO (-34.4 +/- 6.6%) and TPR (-40.2 +/- 2.5%) contribute to the reduction in MAP. We conclude that the relative contribution of CO and TPR to the reduction in MAP evoked by NTS P2x purinoceptor activation is dependent on the extent of P2x purinoceptor activation.

Impact of arterial elastance as a measure of vascular load on left ventricular geometry in hypertension.

Effective arterial elastance (Ea), integrating the pulsatile component of left ventricular (LV) afterload, is an estimate of aortic input impedance. We evaluated relationships of Ea with left ventricular anatomy and function in essential hypertension. A cross-sectional analysis in 81 normotensive and 174 untreated hypertensive individuals enrolled in a referral hypertension centre. Using echocardiography we determined left ventricular mass index (LVMI), relative wall thickness (RWT), stroke volume (SV), endocardial (FSe) and midwall (FSm) fractional shortening and total peripheral resistance (TPR). Carotid pressure waveforms were obtained by arterial tonometry, and end-systolic pressure (Pes) was measured at the dicrotic notch. Ea index (EaI) was calculated as Pes/(SV index); LV elastance (Ees) was estimated as Pes/LV end-systolic volume, and ventriculo-arterial coupling was evaluated by the Ea/Ees ratio. EaI was higher in hypertensives than in normotensives (3.02 +/- 0.63 versus 2.40 +/- 0.52 mmHg/l per m2; P< 0.0001). Using the 95% upper confidence limit in normotensives, hypertensives were divided in two groups with normal or elevated EaI. The 38 hypertensives with elevated EaI had higher RWT (0.41 +/- 0.06 versus 0.37 +/- 0.05), lower LVMI (87.5 +/- 18.5 versus 96.8 +/- 19.3 g/m2), higher TPR (2247 +/- 408 versus 1658 +/- 371 dynes/cm s(-5)) and lower FSe and FSm (35 +/- 5 versus 39 +/- 5 and 16 +/- 2 versus 18 +/- 2%; all P< 0.05) than patients with normal EaI. Ea/Ees ratio was increased and cardiac output was reduced in hypertensives with elevated EaI. High values of EaI identify a minority of hypertensive patients characterized by elevated TPR, left ventricular concentric remodelling, depressed left ventricular systolic function and impaired ventriculo-arterial coupling.

Relation of age to left ventricular function in clinically normal adults

The extent to which age, independent of cardiovascular diseases, influences left ventricular (LV) function in adults is uncertain. Echocardiograms and simultaneous arterial pressure in 464 clinically normal adults aged 16 to 88 years were used to measure LV dimensions, endocardial and midwall LV fractional shortening, stroke volume, cardiac output, and circumferential end-systolic stress. The ratios of observed endocardial and midwall shortening to values predicted for observed end-systolic stress were used as measures of chamber and myocardial function. LV endocardial shortening increased slightly with age, as did an index of LV chamber performance, the end-systolic stress/volume index ratio (r = 0.11, p = 0.019, and r = 0.20, p <0.001). However, when age-related increases in LV wall thickness and blood pressure were controlled for by examining afterload-corrected endocardial shortening, no age relation was detected. Weak age-related declines were observed in midwall shortening (r = −0.09, p = 0.043) and afterload-corrected midwall shortening (r = −0.12, p <0.01). Cardiac index decreased slightly with advancing age (r = −0.14, mean −6.7 ml/min/m 2/year, p = 0.003). Total peripheral resistance and the pulse pressure/stroke volume ratio, a measure of arterial stiffness, increased more strongly with age (r = 0.27 and 0.38, both p <0.001). Thus, LV pump performance at rest measured by cardiac index is slightly lower in older than in younger clinically normal adults. Endocardial fractional shortening was slightly higher in older subjects, but the physiologically more appropriate midwall measures of myocardial function decreased slightly. The observed change in LV pump performance was related to smaller LV chamber size and higher total peripheral resistance in older subjects.

Relation of left ventricular midwall function to cardiovascular risk factors and arterial structure and function.

Left ventricular (LV) midwall shortening (MWS) is subnormal in relation to LV circumferential end-systolic stress (ESS) (ESS-corrected MWS) in many hypertensive patients with normal LV chamber function and predicts subsequent morbidity and mortality. However, little is known of the relations of LV midwall function to demographic and metabolic variables or to arterial geometry. Asymptomatic, unmedicated normotensive (n=366) or hypertensive (n=282) adults were assessed with echocardiography and carotid ultrasound. In normal adults, lower LV MWS and ESS-corrected MWS, an index of LV contractility, were related independently to high total peripheral resistance, high heart rate, and male gender (all P<.00001), lower serum HDL cholesterol (P=.001) and diastolic pressure (P=.003), and for ESS-corrected MWS only, arterial relative wall thickness (RWT, P=.03). Among hypertensive patients, lower values for both midwall function indices were associated independently with higher peripheral resistance (P<.00001), heart rate (P<.00005), body mass index (P<.01), and arterial RWT (P=.04), as well as male gender (P<.0002). In the entire population, lower LV MWS was independently related to higher peripheral resistance, heart rate (both P<.00001), body mass index (P=.0006) and arterial RWT (P=.009); male gender (P<.00001); and lower age (P=.004), diastolic pressure (P=.042), and systolic carotid artery expansion (P=.032). Lower ESS-corrected MWS in the entire population was independently associated with higher peripheral resistance and heart rate (both P<.00001), body mass index (P=.0006), arterial RWT (P=.004); male gender; and lower diastolic pressure (both P<.00001), age (P<.00005), arterial expansion in systole (P=.006), and serum HDL cholesterol levels (P=.04). Among a subset (n=60), ESS-corrected MWS was positively related to apolipoprotein A1 (P=.004) and negatively to hemoglobin A1c (P<.01). Thus, higher LV midwall function is associated with female gender and more favorable profiles of hemodynamics, metabolic pattern, and arterial structure and function.

Systemic hemodynamics and regional blood flow during chronic nitric oxide synthesis inhibition in pregnant rats.

Pregnancy-induced hypertension in women is associated with severe vasoconstriction and reductions in organ blood flow and cardiac output. Recent studies have indicated that nitric oxide (NO) synthesis inhibition during mid to late gestation in pregnant rats results in severe hypertension and proteinuria. The purpose of this study was to determine the systemic hemodynamic and regional blood flow alterations associated with chronic NO synthesis inhibition in the pregnant rat. The study was conducted in four groups of rats: virgin rats (n=6), pregnant rats (n=10), virgin rats treated with L-NAME (n=6), and pregnant rats treated with L-NAME (n=11). Rats were treated with L-NAME in drinking water at a dose of 1 mg/d for a week starting from day 13 of gestation in pregnant rats or an equivalent time for virgins. Mean arterial pressure (MAP), cardiac output, total peripheral resistance (TPR), and regional flows were measured by tracing radiolabeled microspheres in conscious rats. Pregnant rats that were given L-NAME showed significantly higher MAP (137+/-6 versus 96+/-2 mm Hg), higher TPR (5.08+/-0.58 versus 2.90+/-0.44 mm Hg/mL/min/100 g), and lower cardiac output (87.4+/-8.4 versus 113.3+/-11.1 mL/min) than pregnant controls. Chronic NO synthesis inhibition decreased the renal blood flow in pregnant rats at a significantly greater magnitude than in virgin rats. Significant reductions in regional blood flow to the heart, lungs, liver, diaphragm, and skeletal muscles were also observed in pregnant rats treated with L-NAME. The results of this study indicate that NO may play a role in mediating the alterations in systemic hemodynamics and regional blood flow in late pregnant rats.

HEMODYNAMIC RESPONSES TO EXERCISE IN CHILDREN OF HYPERTENSIVE PARENTS 91

This study was designed to investigate whether children with a positive parental history of hypertension exhibit an elevated resting blood pressure(BP) or an exaggerated BP response during dynamic submaximal exercise. We studied 11 children (12.0 ± 2.4 yrs) of at least one hypertensive parent and 11 children (12.2 ± 1.8 yrs; M ± SE) of normotensive parents who served as the control group. On separate days, each subject completed a graded cycle test to maximal effort and a submaximal exercise bout consisting of 6 min each of steady state cycling at 50 and 80% of maximal heart rate reserve. BP, cardiac output (CO), and total peripheral resistance(TPR) were measured at rest and during the last 3 min of each submaximal exercise stage. CO was determined using transthoracic impedance cardiography, BP was measured by auscultation, and TPR was calculated as mean arterial pressure (MAP) divided by CO. The data were analyzed using an independent t-test and a 2-way (group x intensity) ANOVA. The groups were similar in age, weight, height, and body fatness (p<0.05). At rest, the positive history group had higher systolic BP, diastolic BP (DBP), and MAP (p<0.05). MAP and DBP remained significantly higher throughout exercise. Although differences between groups were not statistically significant, TPR was consistently higher(15-20%) in the positive history group at rest and during exercise, while CO tended to be slightly lower during exercise (p>0.05). In conclusion, children of at least one hypertensive parent exhibit a significantly higher MAP and DBP at rest and during submaximal exercise. The elevated BP in the positive history group may be due to an early trend towards a higher TPR at rest and during exercise.

Relationship of John Henryism to cardiovascular functioning at rest and during stress in youth

John Henryism, a coping style characterized by a strong predisposition to confront daily psychosocial stressors in an active and effortful manner, has been associated with cardiovascular (CV) disease risk in adults. This study examined the relationship of John Henryism to CV functioning at rest and during laboratory stressors (i.e. forehead cold stimulation, postural change, and treadmill exercise) in 173 normotensive 10-to 17-year-old African-American and White children. High John Henry scores were associated with higher blood pressure, higher total peripheral resistance, and lower cardiac index at rest. These relationships were qualified by an interaction with socioeconomic status (SES) such that those from lower SES backgrounds who were high on John Henryism had particularly high levels of resting CV measures. No significant associations were observed with CV reactivity to the stressors. Findings are discussed in terms of possible impact of coping styles to environmental stress upon physiological functioning and health.

Centrally Mediated Reduction in Cardiac Output Elicits the Enhanced Hypotensive Effect of Clonidine in Conscious Aortic Barodenervated Rats

In a previous study, we showed that centrally mediated hypotensive responses are enhanced in aortic barodenervated (ABD) rats as compared with sham-operated (SO) rats. In the present study, we tested the hypothesis that the high basal total peripheral resistance (TPR) of ABD rats accounts for enhanced hypotensive responses to clonidine in this rat model. Aortic barodenervation resulted in acute increases in blood pressure (BP) and heart rate (HR) in anesthetized rats, associated with significant increases in plasma norepinephrine (NE) levels and TPR; cardiac index (CI) and stroke volume (SV) were not affected. After recovery from anesthesia, conscious ABD rats had significantly increased BP at 3 h after barodenervation; BP returned to SO levels by 48 h even though plasma NE levels and TPR remained significantly increased. On the other hand, CI and SV showed significant reductions, beginning at 3 h, and remained low throughout the postdenervation period (48 h); the reduction in CI offset the increase in TRP and may therefore account for the restoration of BP of ABD rats to normal levels. Beginning at similar baseline BP values, cumulative intracisternal (i.c.) doses of clonidine (0.02-2.5 micrograms) elicited greater decreases in BP and plasma NE levels in conscious ABD as compared with SO rats. These responses were centrally mediated because systemic administration of 0.12 micrograms clonidine, a dose that elicited near maximal hypotensive response after i.c. administration, affected neither BP nor plasma NE levels. Contrary to the hypothesis, the hypotensive effect of clonidine in ABD rats resulted exclusively from a reduction in CO (owing to reductions in both HR and SV) because TPR was not affected. These findings suggest that (a) in ABD rats, a reduction in CO offsets a sustained sympathetically mediated elevation in TPR and restores BP to normal levels; and (b) an enhanced hypotensive response to clonidine in ABD as compared with SO rats cannot be accounted for by a higher basal TRP but rather by elicitation of greater reductions in CO through a centrally mediated sympathoinhibitory action.

Centrally Mediated Reduction in Cardiac Output Elicits the Enhanced Hypotensive Effect of Clonidine in Conscious Aortic Barodenervated Rats

Summary: In a previous study, we showed that centrally mediated hypotensive responses are enhanced in aortic barodenervated (ABD) rats as compared with shamoperated (SO) rats. In the present study, we tested the hypothesis that the high basal total peripheral resistance (TPR) of ABD rats accounts for enhanced hypotensive responses to clonidine in this rat model. Aortic barodenervation resulted in acute increases in blood pressure (BP) and heart rate (HR) in anesthetized rats, associated with significant increases in plasma norepinephrine (NE) levels and TPR; cardiac index (CI) and stroke volume (SV) were not affected. After recovery from anesthesia, conscious ABD rats had significantly increased BP at 3 h after barodenervation; BP returned to SO levels by 48 h even though plasma NE levels and TPR remained significantly increased. On the other hand, CI and SV showed significant reductions, beginning at 3 h, and remained low throughout the postdenervation period (48 h); the reduction in CI offset the increase in TPR and may therefore account for the restoration of BP of ABD rats to normal levels. Beginning at similar baseline BP values, cumulative intracisternal (i.c.) doses of clonidine (0.02-2.5 μg) elicited greater decreases in BP and plasma NE levels in conscious ABD as compared with SO rats. These responses were centrally mediated because systemic administration of 0.12 μg clonidine, a dose that elicited near maximal hypotensive response after i.c. administration, affected neither BP nor plasma NE levels. Contrary to the hypothesis, the hypotensive effect of clonidine in ABD rats resulted exclusively from a reduction in CO (owing to reductions in both HR and SV) because TPR was not affected. These findings suggest that (a) in ABD rats, a reduction in CO offsets a sustained sympathetically mediated elevation in TPR and restores BP to normal levels; and (b) an enhanced hypotensive response to clonidine in ABD as compared with SO rats cannot be accounted for by a higher basal TPR but rather by elicitation of greater reductions in CO through a centrally mediated sympathoinhibitory action.

Umbilical Blood Flow Correlated to Maternal Hemodynamics in Severe Preeclampsia

Background: As there are conflicting results concerning maternal hemodynamics in preeclampsia, this study aimed to evaluate the maternal hemodynamic factors (cardiac output, mean arterial blood pressure, and total peripheral resistance) and put them in relation to fetal blood flow velocities in the umbilical artery.Methods: Nine primiparous women with severe preeclampsia were compared with 9 normotensive controls matched for age and gestational age. The maternal cardiac output was measured by echocardiography, and the fetal flow velocities using an ultrasound-Doppler technique. The women were examined during the last trimester and also 6-12 months postdelivery for comparison of pregnant and nonpregnant status.Results: The preeclamptic women who bore small-for-gestational-age (SGA) fetuses had significantly lower cardiac output and higher total peripheral resistance than the normotensive women, but the preeclamptic women with appropriate-for-gestational-age (AGA) fetuses had normal or supernormal cardiac o...