[The importance of microcirculation and tissue perfusion in hypertension]

Remodeling of retinal small arteries in hypertension

Vascular dysfunction due to elevated blood pressure constitutes an early step in the pathogenesis of atherosclerotic disease. A better understanding of the pathophysiology and of clinical correlates of vascular remodeling in retinal arteries and arterioles offers the opportunity for a better risk stratification and treatment. In vivo vascular changes can be best detected by direct imaging techniques. In this review, we summarize the main findings of several recent studies analyzing retinal-arteriolar parameters, such as outer diameter (OD) and lumen diameter (LD), retinal capillary flow (RCF), wall-to-lumen-ratio, and wall cross-sectional area by using scanning laser Doppler flowmetry (SLDF). Blood pressure emerged as an independent determinant of the wall-to-lumen ratio (WLR) of retinal arterioles. Retinal arterioles and small arteries of hypertensive subjects showed eutrophic inward remodeling as indicated by increased WLR, decreased LD and almost unchanged wall cross-sectional area compared to normotensive subjects. These findings are in accordance with those observed in small-resistance vessels analyzed ex vivo. In hypertensive patients, an increased retinal vascular resistance has been documented and basal nitric oxide activity emerged as an independent determinant of early arteriolar remodeling. Thus, SLDF emerged as a noninvasive research tool to assess early vascular changes in the retinal circulation.

Heart rate control with adrenergic blockade: clinical outcomes in cardiovascular medicine

The sympathetic nervous system is involved in regulating various cardiovascular parameters including heart rate (HR) and HR variability. Aberrant sympathetic nervous system expression may result in elevated HR or decreased HR variability, and both are independent risk factors for development of cardiovascular disease, including heart failure, myocardial infarction, and hypertension. Epidemiologic studies have established that impaired HR control is linked to increased cardiovascular morbidity and mortality. One successful way of decreasing HR and cardiovascular mortality has been by utilizing β-blockers, because their ability to alter cell signaling at the receptor level has been shown to mitigate the pathogenic effects of sympathetic nervous system hyperactivation. Numerous clinical studies have demonstrated that β-blocker-mediated HR control improvements are associated with decreased mortality in postinfarct and heart failure patients. Although improved HR control benefits have yet to be established in hypertension, both traditional and vasodilating β-blockers exert positive HR control effects in this patient population. However, differences exist between traditional and vasodilating β-blockers; the latter reduce peripheral vascular resistance and exert neutral or positive effects on important metabolic parameters. Clinical evidence suggests that attainment of HR control is an important treatment objective for patients with cardiovascular conditions, and vasodilating β-blocker efficacy may aid in accomplishing improved outcomes.

Evaluation of porcine myocardial microvascular permeability and fractional vascular volume using 64-slice helical computed tomography (CT)

OBJECTIVES

Myocardial microvascular permeability-surface area product (MPSP) and fractional vascular volume (FVV), indices of endothelial function and microvascular perfusion, can be noninvasively evaluated by electron beam computed tomography (EBCT), but it remains unknown whether comparable assessments can be obtained with 64-slice multidetector CT (CT-64).

METHODS

We studied 12 pigs with both EBCT and CT-64 in randomized order 1 week apart, before and during IV adenosine infusion. Myocardial attenuation changes in the cardiac wall were assessed after a central-venous injection of iopamidol. Time-attenuation curves were analyzed using both indicator-dilution and Patlak models to calculate MPSP and FVV.

RESULTS

CT-64 and EBCT assessments of basal MPSP obtained by the Patlak method were similar (0.37 +/- 0.03 vs. 0.37 +/- 0.04 mL/min/g), as was its response to adenosine, and correlated significantly (r = 0.87). Patlak FVV was also similar between CT-64 and EBCT at baseline (0.08 +/- 0.02 vs. 0.07 +/- 0.02 mL blood/mL) and during adenosine, and correlated well (r = 0.93). MPSP and FVV estimated by the indicator-dilution method were not significantly correlated.

CONCLUSIONS

CT-64 assessments of myocardial MPSP and FVV may not be reliable when using indicator-dilution analysis, likely due to its sensitivity to scan duration. However, CT-64 assessments obtained using the Patlak model are feasible.

Serum uric acid is associated with microvascular function in hypertensive individuals

We investigated the relationship of serum uric acid (UA) with resting forearm blood flow (FBF), reactive hyperaemia (RH) and flow-mediated dilation (FMD) of the brachial artery in hypertensive adults (n=506, mean age 62 years, 59% women). UA was measured by a colorimetric method. FBF, RH and FMD were measured by brachial artery ultrasound. Regression analyses were used to assess whether UA was associated with FBF, RH and FMD before and after adjustment for age, sex, systolic BP, diabetes, total and high-density lipoprotein cholesterol, smoking, body mass index (BMI), C-reactive protein (CRP), serum creatinine, alcohol intake, statin and diuretic use and brachial artery diameter (BAD). UA was significantly associated with FBF (P<0.0001) and RH (P=0.0001) but not with FMD (P=0.43). After adjustment for the covariates listed above, higher UA level remained independently associated with a higher FBF (P=0.012) and lower RH (P=0.004). The independent predictors were as follows: (a) higher FBF: lower age, higher BMI, history of smoking, statin use, higher CRP, higher BAD and higher UA levels; (b) lower RH: higher BMI, diabetes and higher UA levels; (c) lower FMD: greater age, male sex, higher BMI, history of smoking, statin use and higher BAD. We conclude that in hypertensive individuals, higher UA levels are associated with higher resting FBF and lower RH, markers of microvascular function, but not with brachial artery FMD.

Control of edema in hypertensive subjects treated with calcium antagonist (nifedipine) or angiotensin-converting enzyme inhibitors with Pycnogenol

The presence of edema in different phases and stages of essential hypertension may be due to antihypertensive treatment. Some drugs may cause edema by inducing vasodilatation, increasing the capillary exchange surface and capillary filtration. Pycnogenol has an important anti-edema effect in diabetic microangiopathy and chronic venous insufficiency. This 8-week study evaluated capillary filtration in 2 comparable treatment groups with hypertension treated with a calcium antagonist (nifedipine) or angiotensin-converting enzyme inhibitor to define its efficacy in preventing edema caused by antihypertensives. A significant decrease in filtration was observed in the Pycnogenol groups. Pycnogenol controls this type of edema, it helps to prevent and limit long-term damage in the microcirculation in hypertensive patients, and allows the dose of anti-hypertensive drugs to be reduced in most patients.

Moxonidine: a review of its use in essential hypertension

Moxonidine (Physiotens, Moxon, Cynt) is an orally administered imidazoline compound with selective agonist activity at imidazoline I1 receptors and only minor activity at alpha2-adrenoceptors. Moxonidine acts centrally to reduce peripheral sympathetic activity, thus decreasing peripheral vascular resistance. In patients with mild to moderate hypertension, moxonidine reduces blood pressure (BP) as effectively as most first-line antihypertensives when used as monotherapy and is also an effective adjunctive therapy in combination with other antihypertensive agents. It improves the metabolic profile in patients with hypertension and diabetes mellitus or impaired glucose tolerance, is well tolerated, has a low potential for drug interactions and may be administered once daily in most patients. Thus, moxonidine is a good option in the treatment of patients with mild to moderate hypertension, particularly as adjunctive therapy in patients with the metabolic syndrome.