Maternal cardiovascular function at mid-gestation is related to placental angiogenesis

OBJECTIVE

To investigate whether placental function, reflected in the levels of angiogenic factors, is associated with maternal cardiac function and hemodynamic responses at 19 to 24 weeks' gestation after adjustment for maternal risk factors and pregnancy complications.

METHODS

Prospective study on women with singleton pregnancies attending Kings' College Hospital, London, UK for a routine hospital visit at 19-24 weeks' gestation. We recorded maternal characteristics and measured mean arterial pressure, maternal heart rate, serum placental growth factor and soluble fms-like tyrosine kinase 1 (sFLT-1). We also performed maternal echocardiogram to assess cardiac output and peripheral vascular resistance as well as indices of diastolic and systolic function.

RESULTS

Our cohort included 4006 women. Lower placental growth factor (PlGF) values were significantly associated with higher mean arterial pressure (MAP) (p<0.001), lower maternal heart rate (p<0.001), lower mitral valve s' velocity (p= 0.027) and higher left atrial volume (p=0.022) after adjustment for maternal characteristics and pregnancy complications. sFLT-1 was positively related to relative wall thickness (p= 0.012), whereas sFLT-1/ PlGF ratio was negatively associated with mitral valve A (p= 0.006) and positively associated with left atrial volume (p= 0.015) and MAP (p= 0.004). The magnitude of these associations was similar in the subgroup of women without any risk factors from their obstetric and medical history.

CONCLUSION

A continuous link of moderate strength between angiogenic factors and subclinical maternal cardiac function alterations is present at mid-gestation, independently of preexisting maternal risk factors and pregnancy complications. Impaired placental function appears to be related to a mild systolic and diastolic dysfunction and cardiac remodeling. This article is protected by copyright. All rights reserved.

Role of the arterial baroreflex in the sympathetic response to hyperinsulinemia in adult humans

Muscle sympathetic nerve activity (MSNA) increases during hyperinsulinemia, primarily attributed to central nervous system effects. Whether peripheral vasodilation induced by insulin further contributes to increased MSNA via arterial baroreflex-mediated mechanisms requires further investigation. Accordingly, we examined baroreflex modulation of the MSNA response to hyperinsulinemia. We hypothesized that rescuing peripheral resistance with coinfusion of the vasoconstrictor phenylephrine would attenuate the MSNA response to hyperinsulinemia. We further hypothesized that the insulin-mediated increase in MSNA would be recapitulated with another vasodilator (sodium nitroprusside, SNP). In 33 young healthy adults (28 M/5F), MSNA (microneurography) and arterial blood pressure (BP, Finometer/brachial catheter) were measured, and total peripheral resistance (TPR, ModelFlow) and baroreflex sensitivity were calculated at rest and during intravenous infusion of insulin (n = 20) or SNP (n = 13). A subset of participants receiving insulin (n = 7) was coinfused with phenylephrine. Insulin infusion decreased TPR (P = 0.01) and increased MSNA (P < 0.01), with no effect on arterial baroreflex sensitivity or BP (P > 0.05). Coinfusion with phenylephrine returned TPR and MSNA to baseline, with no effect on arterial baroreflex sensitivity (P > 0.05). Similar to insulin, SNP decreased TPR (P < 0.02) and increased MSNA (P < 0.01), with no effect on arterial baroreflex sensitivity (P > 0.12). Acute hyperinsulinemia shifts the baroreflex stimulus-response curve to higher MSNA without changing sensitivity, likely due to insulin's peripheral vasodilatory effects. Results show that peripheral vasodilation induced by insulin contributes to increased MSNA during hyperinsulinemia.NEW & NOTEWORTHY We hypothesized that elevation in muscle sympathetic nervous system activity (MSNA) during hyperinsulinemia is mediated by its peripheral vasodilator effect on the arterial baroreflex. Using three separate protocols in humans, we observed increases in both MSNA and cardiac output during hyperinsulinemia, which we attributed to the baroreflex response to peripheral vasodilation induced by insulin. Results show that peripheral vasodilation induced by insulin contributes to increased MSNA during hyperinsulinemia.

Placental function and fetal weight are associated with maternal hemodynamic indices in uncomplicated pregnancies at 35-37 weeks of gestation

BACKGROUND

Over the years, there has been an increasing interest in the assessment of maternal hemodynamic responses during pregnancy. With the use of both noninvasive devices and/or maternal echocardiography, it has been shown that mothers who have pregnancy complications have altered hemodynamics compared with those who have uncomplicated pregnancies. It also has been suggested that preexisting maternal cardiac changes might drive the development of complications in pregnancy that are associated with impaired placentation. To understand, however, this potential link in complicated pregnancies, it is important to clarify whether placental function is associated with maternal cardiac functional indices in normal pregnancies.

OBJECTIVE

To determine whether placental function, perfusion, and fetal weight are associated with maternal cardiac hemodynamic responses at 35-36 weeks of gestation in normal pregnancies.

STUDY DESIGN

Prospective screening of women attending Kings' College Hospital for routine hospital visit at 35-37 weeks' gestation. We recorded maternal characteristics and measured mean arterial pressure, uterine artery pulsatility index, sonographic estimated fetal weight, and serum placental growth factor and soluble fms-like tyrosine kinase 1. We also performed maternal echocardiogram to assess cardiac output and peripheral vascular resistance as well as indices of diastolic and systolic function, including global longitudinal systolic function and left ventricular mass indexed to body surface area.

RESULTS

We studied 1386 women. Maternal characteristics were associated with both maternal hemodynamics and functional and structural indices. Uterine artery pulsatility index was associated with left ventricular mass (P=.03) and global longitudinal systolic function (P=.017). There were significant nonlinear associations between placental growth factor and cardiac output and peripheral vascular resistance (P<.001 for both) and between soluble fms-like tyrosine kinase 1 and peripheral vascular resistance (P=.018). Estimated fetal weight was associated with maternal cardiac output (mean increase=0.186, 95% confidence interval, 0.133-0.238, P<.001) and peripheral vascular resistance (mean decrease=-0.164, 95% confidence interval, -0.217 to -0.111, P<.001). No association was noted between placental and fetal parameters and maternal cardiac functional and structural indices. In multivariable analysis, placental growth factor remained strongly associated with maternal cardiac output and peripheral vascular resistance (P=.002 for both) over and above maternal characteristics and estimated fetal weight. Estimated fetal weight was associated with left ventricular mass (0.102, 95% confidence interval, 0.044-0.162, P=.001).

CONCLUSION

The results of this study suggest a strong link between maternal hemodynamic responses and fetoplacental needs across the whole spectrum in normal pregnancies. These findings would also indicate that to diagnose maternal cardiac dysfunction in pregnancies complicated by impaired placentation a more extensive echocardiographic assessment might be needed rather than relying on hemodynamics which are strongly associated with fetoplacental indices.

Plasticity of the Maternal Vasculature During Pregnancy

Maternal cardiovascular changes during pregnancy include an expansion of plasma volume, increased cardiac output, decreased peripheral resistance, and increased uteroplacental blood flow. These adaptations facilitate the progressive increase in uteroplacental perfusion that is required for normal fetal growth and development, prevent the development of hypertension, and provide a reserve of blood in anticipation of the significant blood loss associated with parturition. Each woman's genotype and phenotype determine her ability to adapt in response to molecular signals that emanate from the fetoplacental unit. Here, we provide an overview of the major hemodynamic and cardiac changes and then consider regional changes in the splanchnic, renal, cerebral, and uterine circulations in terms of endothelial and vascular smooth muscle cell plasticity. Although consideration of gestational disease is beyond the scope of this review, aberrant signaling and/or maternal responsiveness contribute to the etiology of several common gestational diseases such as preeclampsia, intrauterine growth restriction, and gestational diabetes.

A Rare Case of Partial Peripheral Thyroid Hormone Resistance Due to a Point Mutation in the Membrane Integrin Α(V)Β(3) and Concomitant Hashimoto`s Thyroiditis

BACKGROUND:

Peripheral resistance to thyroid hormones is a type of unresponsiveness of the peripheral cells or tissues to FT3 and/or FT4. Generalised resistance to thyroid hormones affects the pituitary gland and most of the peripheral tissues. Selective pituitary resistance or central resistance to thyroid hormones include unresponsiveness of the pituitary gland, but the peripheral tissues are responsive. Selective peripheral resistance involves peripheral tissue or cellular resistance to thyroid hormones, but the pituitary gland is responsive.

CASE PRESENTATION:

We present a rare case of a female patient with partial peripheral resistance to thyroid hormones due to a point mutation coding for the beta subunit of the integrin molecule α(V)β(3) and concomitant Hashimoto`s thyroiditis. Clinically, the patient`s symptoms were in favour of hypothyroidism, and the laboratory results were in favour of the secondary hyperthyroid state. PCR protein amplification detected a point mutation coding for the membrane receptor, which mediates a signal via the MAPK pathway when bonded with thyroid hormones.

CONCLUSION:

Peripheral resistance to thyroid hormones is a very rare condition and can often be misdiagnosed due to the broad spectrum of clinically similar differential diagnostic entities. Molecular analysis is required to confirm the exact underlying cause for the impaired peripheral sensitivity to thyroid hormones syndrome.

Tachycardia: The hidden cardiovascular risk factor in uncomplicated arterial hypertension

Early detection and management of elevated blood pressure is crucial in reducing the burden of cardiovascular disease (CVD). The importance of an absolute risk assessment and patient risk stratification has been highlighted in the European hypertension guidelines since 2003. Amongst numerous risk factors influencing patient prognosis, elevated heart rate (HR) has been indicated as important predictor of future risk of hypertension, coronary heart disease, sudden cardiac death, heart failure, CVD, stroke, total cancer and mortality. Given that resting HR can be easily determined in clinical practice and modified by lifestyle changes as well as beta-blocker therapy, it seems reasonable that lowering resting HR should be a potential target to reduce disease burden and premature mortality. However, there is a lack of outcome studies of HR lowering in tachycardia-related hypertension. This review outlines the underlying mechanisms of early course hypertension pathophysiology with the critical role of the sympathetic nervous system activation, the prognostic significance of fast HR and the mechanistic rationale for the use of non-pharmacological approaches and/or highly long-acting cardioselective beta-blockers with some consideration given to betaxolol properties.

Cardiovascular adaptation to hypoxia and the role of peripheral resistance

Systemic vascular pressure in vertebrates is regulated by a range of factors: one key element of control is peripheral resistance in tissue capillary beds. Many aspects of the relationship between central control of vascular flow and peripheral resistance are unclear. An important example of this is the relationship between hypoxic response in individual tissues, and the effect that response has on systemic cardiovascular adaptation to oxygen deprivation. We show here how hypoxic response via the HIF transcription factors in one large vascular bed, that underlying the skin, influences cardiovascular response to hypoxia in mice. We show that the response of the skin to hypoxia feeds back on a wide range of cardiovascular parameters, including heart rate, arterial pressures, and body temperature. These data represent the first demonstration of a dynamic role for oxygen sensing in a peripheral tissue directly modifying cardiovascular response to the challenge of hypoxia.

Hemodynamic and Autonomic Response to Different Salt Intakes in Normotensive Individuals

Background

Even if sodium sensitivity represents a risk factor at any blood pressure (BP) level, limited evidence is available that it may influence cardiovascular control in normotensives, particularly in white individuals. Therefore, the aim of the study was to investigate whether sodium sensitivity alters hemodynamic or autonomic responses to salt in normotensives.

Methods and Results

We evaluated the Sodium‐Sensitivity Index (SS‐Index) in 71 white normotensives after 5 days of high‐ and low‐sodium diets. We measured BP continuously at the end of each period, estimating hemodynamic indices from BP waveform analysis, and autonomic indices from heart rate (HR) and BP variability. According to the SS‐Index distribution, we defined 1 sodium‐sensitive group (SS, with SS‐Index >15 mm Hg/[mmol·day]), 1 sodium‐resistant group, (unresponsive to sodium load with −15≤ SS‐Index ≤+15), and 1 inverse sodium‐sensitive group, responsive to sodium by decreasing BP, with SS‐Index <−15). We compared the effects of the diets among groups, and correlated autonomic/hemodynamic indices with the SS‐Index. After sodium loading, a significant decrease in systemic peripheral resistances, HR, spectral indices of BP modulation, and a significant increase of indices of HR vagal modulation were found in the inverse sodium‐sensitive group but not in SS normotensives. Moreover, the highest SS‐Indices were associated with the lesser vagal HR decelerations.

Conclusions

Our data suggest that salt sensitivity in white normotensive individuals is associated with impaired vasodilation and altered autonomic response to dietary salt. Such dysfunction may critically contribute to induce a BP response to dietary salt.

Toll-like receptor 4 mutation suppresses hyperhomocysteinemia-induced hypertension

Hyperhomocysteinemia (HHcy) has been observed to promote hypertension, but the mechanisms are unclear. Toll-like receptor 4 (TLR-4) is a cellular membrane protein that is ubiquitously expressed in all cell types of the vasculature. TLR-4 activation has been known to promote inflammation that has been associated with the pathogenesis of hypertension. In this study we hypothesize that HHcy induces hypertension by TLR-4 activation, which promotes inflammatory cytokine (IL-1β, IL-6, and TNF-α) upregulation and initiation of mitochondria-dependent apoptosis, leading to cell death and chronic vascular inflammation. To test this hypothesis, we used C57BL/6J (WT) mice, cystathionine β-synthase (CBS)-deficient (CBS^+/-) mice with genetic mild HHcy, C3H/HeJ (C3H) mice with TLR-4 mutation, and mice with combined genetic HHcy and TLR-4 mutation (CBS^+/-/C3H). Ultrasonography of the superior mesenteric artery (SMA) detected an increase in wall-to-lumen ratio, resistive index (RI), and pulsatility index (PI). Tail cuff blood pressure (BP) measurement revealed elevated BP in CBS^+/- mice. RI, PI, and wall-to-lumen ratio of the SMA in CBS^+/-/C3H mice were similar to the control group, and BP was significantly alleviated. TLR-4, IL-1β, IL-6, and TNF-α expression were upregulated in the SMA of CBS^+/- mice and reduced in the SMA of CBS^+/-/C3H mice. Molecules involved in the mitochondria-mediated cell death pathway (BAX, caspase-9, and caspase-3) were upregulated in CBS^+/- mice and attenuated in CBS^+/-/C3H mice. We conclude that HHcy promotes TLR-4-driven chronic vascular inflammation and mitochondria-mediated cell death, inducing hypertension. TLR-4 mutation attenuates vascular inflammation and cell death, which suppress hypertension.

Attenuated muscle metaboreflex-induced pressor response during postexercise muscle ischemia in renovascular hypertension

During dynamic exercise, muscle metaboreflex activation (MMA; induced via partial hindlimb ischemia) markedly increases mean arterial pressure (MAP), and MAP is sustained when the ischemia is maintained following the cessation of exercise (postexercise muscle ischemia, PEMI). We previously reported that the sustained pressor response during PEMI in normal individuals is driven by a sustained increase in cardiac output (CO) with no peripheral vasoconstriction. However, we have recently shown that the rise in CO with MMA is significantly blunted in hypertension (HTN). The mechanisms sustaining the pressor response during PEMI in HTN are unknown. In six chronically instrumented canines, hemodynamic responses were observed during rest, mild exercise (3.2 km/h), MMA, and PEMI in the same animals before and after the induction of HTN [Goldblatt two kidney, one clip (2K1C)]. In controls, MAP, CO and HR increased with MMA (+52 ± 6 mmHg, +2.1 ± 0.3 l/min, and +37 ± 7 beats per minute). After induction of HTN, MAP at rest increased from 97 ± 3 to 130 ± 4 mmHg, and the metaboreflex responses were markedly attenuated (+32 ± 5 mmHg, +0.6 ± 0.2 l/min, and +11 ± 3 bpm). During PEMI in HTN, HR and CO were not sustained, and MAP fell to normal recovery levels. We conclude that the attenuated metaboreflex-induced HR, CO, and MAP responses are not sustained during PEMI in HTN.

PKPD modelling of the interrelationship between mean arterial BP, cardiac output and total peripheral resistance in conscious rats

BACKGROUND AND PURPOSE

The homeostatic control of arterial BP is well understood with changes in BP resulting from changes in cardiac output (CO) and/or total peripheral resistance (TPR). A mechanism-based and quantitative analysis of drug effects on this interrelationship could provide a basis for the prediction of drug effects on BP. Hence, we aimed to develop a mechanism-based pharmacokinetic-pharmacodynamic (PKPD) model in rats that could be used to characterize the effects of cardiovascular drugs with different mechanisms of action (MoA) on the interrelationship between BP, CO and TPR.

EXPERIMENTAL APPROACH

The cardiovascular effects of six drugs with diverse MoA, (amlodipine, fasudil, enalapril, propranolol, hydrochlorothiazide and prazosin) were characterized in spontaneously hypertensive rats. The rats were chronically instrumented with ascending aortic flow probes and/or aortic catheters/radiotransmitters for continuous recording of CO and/or BP. Data were analysed in conjunction with independent information on the time course of drug concentration using a mechanism-based PKPD modelling approach.

KEY RESULTS

By simultaneous analysis of the effects of six different compounds, the dynamics of the interrelationship between BP, CO and TPR were quantified. System-specific parameters could be distinguished from drug-specific parameters indicating that the model developed is drug-independent.

CONCLUSIONS AND IMPLICATIONS

A system-specific model characterizing the interrelationship between BP, CO and TPR was obtained, which can be used to quantify and predict the cardiovascular effects of a drug and to elucidate the MoA for novel compounds. Ultimately, the proposed PKPD model could be used to predict the effects of a particular drug on BP in humans based on preclinical data.

Differential impact of dilator stimuli on increased myogenic activation of cerebral and skeletal muscle resistance arterioles in obese zucker rats

OBJECTIVE

To use the OZR model of the metabolic syndrome to determine the impact of dilator stimuli on MA of GA and MCA. We tested the hypothesis that increased oxidant stress and TxA2 exacerbate MA, and prevent its blunting with dilator stimuli, in OZR.

METHODS

GA/MCA from OZR and LZR was pressurized ex vivo. MA was determined under control conditions and following challenge with acetylcholine, hypoxia, and adenosine. Responses were also evaluated after pre-treatment with TEMPOL (antioxidant) and SQ-29548 (PGH2 /TxA2 receptor antagonist).

RESULTS

MA was increased (and dilator responses decreased) in GA/MCA from OZR, dependent on the endothelium and ROS. In GA, the impact of ROS on MA and dilator effects was largely via TxA2 , while in MCA, this appeared was more dependent on NO bioavailability. Intrinsic responses of GA/MCA to carbacyclin, U46619, and NO donors were similar between strains.

CONCLUSIONS

A developing ROS-based endothelial dysfunction in MCA and GA of OZR contributes to an enhanced MA of these vessels. Although treatment of GA/MCA with TEMPOL attenuates MA in OZR, the mechanistic contributors to altered MA, distal to ROS, differ between the two resistance vessels.

Estimation of cardiac output and peripheral resistance using square-wave-approximated aortic flow signal

This paper presents a model-based approach to estimation of cardiac output (CO) and total peripheral resistance (TPR). In the proposed approach, the response of cardiovascular system (CVS), described by the windkessel model, is tuned to the measurements of systolic, diastolic and mean arterial blood pressures (BP) so as to yield optimal individual- and time-specific system time constant that is used to estimate CO and TPR. Unique aspects of the proposed approach are that it approximates the aortic flow as a train of square waves and that it also assumes pressure-dependent arterial compliance, as opposed to the traditional windkessel model in which aortic flow is approximated as a train of impulses and constant arterial compliance is assumed. It was shown that the proposed model encompasses the standard windkessel model as a limiting case, and that it also yields more realistic BP waveform response than the standard windkessel model. The proposed approach has potential to outperform its standard counterpart by treating systolic, diastolic, and mean BP as independent features in estimating CO and TPR, rather than solely resorting to pulse pressure as in the case of the standard windkessel model. Experimental results from in-vivo data collected from a number of animal subjects supports the viability of the proposed approach in that it could achieve approximately 29% and 24% reduction in CO and TPR errors when compared with its standard counterpart.

Physiologic dysfunction of the asthmatic lung: what's going on down there, anyway?

Asthma is a syndrome of lung dysfunction characterized by airflow obstruction, reversibility to bronchodilators, and airways hyperresponsiveness (AHR). There is a growing body of evidence that suggests that the principle defect in asthma is the occlusion of the airway lumen by liquid, fibrin, and mucus. The fall in FEV(1) observed in asthma is best explained by a loss of communicating airspaces and the rise in residual lung volume. Imaging studies in both human patients and experimental animals support this hypothesis. An increased propensity for the airways to close can be a cause of AHR. We conclude that loss of lung volume plays a central role in determining the dysfunction of the asthmatic lung as measured by FEV(1). Together, these recent findings provide a better understanding of the causes of airflow obstruction and AHR, suggesting new avenues for the development of more effective asthma therapies.

L-arginine-induced vasodilation in healthy humans: pharmacokinetic-pharmacodynamic relationship

AIMS

Administration of L-arginine by intravenous infusion or via oral absorption has been shown to induce peripheral vasodilation in humans, and to improve endothelium-dependent vasodilation. We investigated the pharmacokinetics and pharmacokinetic-pharmacodynamic relationship of L-arginine after a single intravenous infusion of 30 g or 6 g, or after a single oral application of 6 g, as compared with the respective placebo, in eight healthy male human subjects.

METHODS

L-arginine levels were determined by h.p.l.c. The vasodilator effects of L-arginine were assessed non-invasively by blood pressure monitoring and impedance cardiography. Urinary nitrate and cyclic GMP excretion rates were measured as non-invasive indicators of endogenous NO production.

RESULTS

Plasma L-arginine levels increased to (mean +/- s.e.mean) 6223+/-407 (range, 5100-7680) and 822+/-59 (527-955) micromol l(-1) after intravenous infusion of 30 g and 6 g L-arginine, respectively, and to 310+/-152 (118-1219) micromol l(-1) after oral ingestion of 6 g L-arginine. Oral bioavailability of L-arginine was 68+/-9 (51-87)%. Clearance was 544+/-24 (440-620), 894+/-164 (470-1190), and 1018+/-230 (710-2130) ml min(-1), and elimination half-life was calculated as 41.6+/-2.3 (34-55), 59.6+/-9.1 (24-98), and 79.5+/-9.3 (50-121) min, respectively, for 30 g i.v., 6 g i.v., and 6 g p.o. of L-arginine. Blood pressure and total peripheral resistance were significantly decreased after intravenous infusion of 30 g L-arginine by 4.4+/-1.4% and 10.4+/-3.6%, respectively, but were not significantly changed after oral or intravenous administration of 6 g L-arginine. L-arginine (30 g) also significantly increased urinary nitrate and cyclic GMP excretion rates by 97+/-28 and 66+/-20%, respectively. After infusion of 6 g L-arginine, urinary nitrate excretion also significantly increased, (nitrate by 47+/-12% [P<0.05], cyclic GMP by 67+/-47% [P= ns]), although to a lesser and more variable extent than after 30 g of L-arginine. The onset and the duration of the vasodilator effect of L-arginine and its effects on endogenous NO production closely corresponded to the plasma concentration half-life of L-arginine, as indicated by an equilibration half-life of 6+/-2 (3.7-8.4) min between plasma concentration and effect in pharmacokinetic-pharmacodynamic analysis, and the lack of hysteresis in the plasma concentration-versus-effect plot.

CONCLUSIONS

The vascular effects of L-arginine are closely correlated with its plasma concentrations. These data may provide a basis for the utilization of L-arginine in cardiovascular diseases.