Pulmonary hemodynamics in systemic hypertension

Metabolic syndrome and right ventricle: an updated review

The cluster of metabolic and hemodynamic abnormalities which characterize the metabolic syndrome (MS) is responsible for subclinical cardiac and extra-cardiac damage such as left ventricular hypertrophy, diastolic dysfunction, carotid atherosclerosis and microalbuminuria. The development of different non-invasive imaging methods enabled a detail investigation of right ventricular structure and function, and revealed that right ventricular remodeling followed changes in the left ventricular structure and function in patients with arterial hypertension, diabetes or obesity. Previous investigations also reported that the coexistence of two components of the MS induced more significant cardiac remodeling than the presence of only one MS risk-factor. The relationship between different components of the MS (increased blood pressure, abdominal obesity, increased fasting glucose level and dyslipidemia) and right ventricular remodeling could be explained by several hemodynamic and non-hemodynamic mechanisms. However, the association between right ventricular remodeling and the MS has not been sufficiently investigated so far. The aim of this article was to review recent articles focusing on the association between metabolic syndrome components and the metabolic syndrome itself with impairments in right ventricular structure and function assessed by different imaging techniques.

Relation of cardiovascular risk factors to right ventricular structure and function as determined by magnetic resonance imaging (results from the multi-ethnic study of atherosclerosis)

The effect of cardiovascular risk factors on the left ventricle is well known but their effect on right ventricle has not been studied using advanced imaging techniques. The purpose of the present study was to determine the relation between the cardiovascular risk factors and right ventricular (RV) structure and function and its interaction with the left ventricle. Cardiac magnetic resonance images from 4,204 participants free of clinical cardiovascular disease in the Multi-Ethnic Study of Atherosclerosis were analyzed. Multivariate linear regression models were used to study the cross-sectional association between individual RV parameters and risk factors. All RV parameters, except for ejection fraction, decreased with age (p <0.0001). The RV mass was positively associated with systolic blood pressure (+0.4 g, p <0.0001) and high-density lipoprotein cholesterol (+0.2 g, p <0.0001). It was inversely related with diastolic blood pressure (-0.3 g, p <0.0001) and total cholesterol (-0.2 g, p <0.01). The RV end-diastolic volume was positively associated with systolic blood pressure (+1.6 ml, p <0.01) and high-density lipoprotein cholesterol (+1.8 ml, p <0.0001). It was inversely related with diastolic blood pressure (-2.2 ml, p <0.01), total cholesterol (-1.4 ml, p <0.0001), current smoking (-2.7 ml, p <0.05), and diabetes mellitus (-3.1 ml, p <0.01). The RV ejection fraction was positively associated with systolic blood pressure (+1.0%, p <0.0001), high-density lipoprotein cholesterol (+0.4%, p <0.0001) and inversely with diastolic blood pressure (-0.7%, p <0.0001). In conclusion, the mass and volumes of the right ventricle decrease with age. Cardiovascular risk factors, especially blood pressure and high-density lipoprotein cholesterol, are associated with subclinical changes in the RV mass and volume.

Right ventricular dysfunction in early systemic hypertension: a tissue Doppler imaging study in patients with high-normal and mildly increased arterial blood pressure

PURPOSE

To analyze the relationship between increasing systemic blood pressure (BP) and right ventricular (RV) function.

SUBJECTS AND METHODS

Ninety-eight never-treated, nonobese patients with BP values varying from the optimal to the mild hypertensive range. Peak early diastolic (Em) and systolic (Sm) velocities were recorded at the tricuspid and mitral annuli by tissue Doppler imaging (TDI); global RV and left ventricular (LV) structure and function by conventional echo-Doppler sonography; insulin sensitivity by homeostasis model assessment (HOMA) index. Data were analyzed by 24-h systolic BP (cut-offs 117 and 130 mmHg), thus partitioning an optimal BP from an intermediate high-normal and an upper mildly increased BP stratum.

RESULTS

Em decreased in the mid-third and decelerated further in association with reduced Sm in the upper BP tertile; both correlated negatively to septal thickness and positively to homologous TDI-derived LV indices. RV and LV indices of global ventricular function, estimated pulmonary pressure, HOMA did not differ by systemic BP.

CONCLUSION

RV diastolic and systolic function deteriorates in response to slightly increased systemic BP. The process paralleled homologous changes at the LV side and was driven by interventricular septum remodeling, perhaps as a reflection of its role in RV function and biventricular interdependence. Insulin sensitivity seemed to play no relevant role.

How does salt retention raise blood pressure?

A critical question in hypertension research is: How is long-term blood pressure controlled? Excessive NaCl ingestion or NaCl retention by the kidneys and the consequent tendency toward plasma volume expansion lead to hypertension. Nevertheless, the precise mechanisms linking salt to high blood pressure are unresolved. The discovery of endogenous ouabain, an adrenocortical hormone, provided an important clue. Ouabain, a selective Na+ pump inhibitor, has cardiotonic and vasotonic effects. Plasma endogenous ouabain levels are significantly elevated in approximately 40% of patients with essential hypertension and in animals with several forms of salt-dependent hypertension. Also, prolonged ouabain administration induces hypertension in rodents. Mice with mutant Na+ pumps or Na/Ca exchangers (NCX) and studies with a ouabain antagonist and an NCX blocker are revealing the missing molecular mechanisms. These data demonstrate that alpha2 Na+ pumps and NCX1 participate in long-term regulation of vascular tone and blood pressure. Pharmacological agents or mutations in the alpha2 Na+ pump that interfere with the action of ouabain on the pump, and reduced NCX1 expression or agents that block NCX all impede the development of salt-dependent or ouabain-induced hypertension. Conversely, nanomolar ouabain, reduced alpha2 Na+ pump expression, and smooth muscle-specific overexpression of NCX1 all induce hypertension. Furthermore, ouabain and reduced alpha2 Na+ pump expression increase myogenic tone in isolated mesenteric small arteries in vitro, thereby tying these effects directly to the elevation of blood pressure. Thus, endogenous ouabain, and vascular alpha2 Na+ pumps and NCX1, are critical links between salt and hypertension. New pharmacological agents that act on these molecular links have potential in the clinical management of hypertension.

Angiotensin II-stimulated nitric oxide release from porcine pulmonary endothelium is mediated by angiotensin IV

In this study, a nitric oxide (NO) sensor was used to examine the ability of angiotensin II (AngII), AngIV, and bradykinin (Bk) to stimulate NO release from porcine pulmonary artery (PPAE) and porcine aortic endothelial (PAE) cells and to explore the mechanism of the AngII-stimulated NO release. Physiologic concentrations of AngII, but not Bk, caused release of NO from PPAE cells. In contrast, Bk, but not AngII, stimulated NO release from PAE cells. AngIII-stimulated NO release from PPAE cells required extracellular L-arginine and was inhibited by L-nitro-arginine methyl ester. AT1 and AT2 receptor inhibition had no affect on AngII-mediated NO release or activation of NO synthase (NOS). AngIV, an AngII metabolite with binding sites that are pharmacologically distinct from the classic AngII receptors, stimulated considerably greater NO release and greater endothelial-type constitutive NOS activity than the same amount of AngII. The AngIV receptor antagonist, divalinal AngIV, blocked both AngII- and AngIV-mediated NO release as well as NOS activation. The results demonstrate that AngIV and the AngIV receptor are responsible, at least in part, for AngII-stimulated NO release and the associated endothelium-dependent vasorelaxation. Furthermore, these results suggest that differences exist in both AngII- and Bk-mediated NO release between PPAE and PAE cells, which may reflect important differences in response to these hormones between vascular beds.

The pulmonary circulation in essential systemic hypertension

Seventy-one men, ages 16 to 59 years, were referred for systemic hypertension, which was without detectable cause and with limited organ damage (World Health Organization stages I to II). They performed a graded exercise test on the bicycle ergometer in the sitting position. Mean brachial intraarterial pressure, mean pulmonary artery and wedge pressures and cardiac output (Fick method) were measured. At rest mean brachial artery pressure ranged from 72 to 168 mm Hg. Mean pulmonary wedge pressure was significantly (p less than 0.05) related to mean brachial artery pressure at rest, at submaximal work (50 watts) and at the end of exercise (161 +/- 42 [standard deviation] watts). In each subject pulmonary vascular resistance was calculated as the slope of the relation between the pressure gradient across the pulmonary circulation and cardiac output from data at rest, at 50 watts and at the end of exercise; mean critical closing pressure was calculated as the intercept of this relation. Pulmonary vascular resistance averaged 0.63 +/- 0.37 mm Hg/liter/min and was significantly related to age (r = 0.28, p less than 0.05) but not to rest brachial artery pressure (r = 0.14) or pulmonary wedge pressure (r = 0.09, difference not significant for both). The mean critical closing pressure averaged 6.1 +/- 4.0 mm Hg and was not related to brachial artery pressure (r = -0.08) or to age (r = -0.18, difference not significant for both). It is concluded that there is neither a primary nor a secondary effect of systemic hypertension on the pulmonary vasculature in patients with World Health Organization stages I to II essential hypertension.