Contrast-enhanced magnetic resonance angiography findings prior to hemodialysis vascular access creation: a prospective analysis.

PURPOSE: To determine prospectively the clinical value of contrast-enhanced magnetic resonance angiography (CE-MRA) for assessment of the arterial inflow and venous outflow prior to vascular access (VA) creation. METHODS: Seventy-three patients underwent duplex ultrasonography (DUS) and CE-MRA prior to VA creation for detection of stenoses and occlusions. Two observers read the CE-MRA images for determination of inter-observer agreement. A VA was considered functional if it could be used for successful two-needle hemodialysis therapy within 2 months after creation. RESULTS: CE-MRA detected 6 stenosed, 8 occluded arterial vessel segments and 12 stenosed and 41 occluded venous vessel segments in 70 patients. Inter-observer agreement for detection of upper extremity arterial and venous stenoses and occlusions with CE-MRA was substantial to almost perfect (kappa values 0.76-0.96). CE-MRA detected lesions, not detected by DUS, that were associated with VA early failure and non-maturation in 33% of patients (7/21). Accessory veins detected preoperatively were the cause of VA non-maturation in a substantial group of patients (47%: 7/15). CONCLUSION: CE-MRA enables accurate detection of upper extremity arterial and venous stenosis and occlusions prior to VA creation. Preoperative CE-MRA identified arterial and venous stenoses, not detected by DUS that were associated with VA early failure and non-maturation. However, the use of gadolinium containing contrast media is currently contraindicated due the reported incidence of nephrogenic systemic fibrosis.

The cochlear nuclei in two patients with Usher syndrome type I.

HYPOTHESIS: Does long-term sound deprivation lead to degeneration of the cochlear nuclei in two Usher type I patients? METHODS: The cochlear nuclei of these patients were morphometrically analyzed and compared with two age-matched controls. Routine autopsy of the brainstems was performed before the design of this study was known. During this procedure, the ventral cochlear nucleus (VCN) can easily be damaged. Five partially damaged VCN could nevertheless be analyzed for this study, including the right VCN of Usher patient 1 and both VCN of Usher patient 2. Using 15 microm thick serial paraffine sections of the cochlear nuclei, estimates of volume, neuronal densities, number of cells and mean cell diameter of the dorsal cochlear nucleus (DCN) and VCN were obtained. RESULTS: This study presents unique material of the cochlear nuclei in two patients with Usher syndrome type I. Data regarding volume and total cell number of the VCN are influenced by the absence of a part of the VCN. Results suggest a decrease in mean cell diameter of the VCN in Usher patients. Other parameters of the VCN and DCN, however, showed no major differences between Usher type I patients and controls. CONCLUSION: Only minor degenerative changes are apparent in the cochlear nuclei of two patients with Usher type I, who were deprived of acoustic stimuli since birth.

Salt-sensitivity testing in patients with borderline hypertension: reproducibility and potential mechanisms.

We examined the reproducibility of dietary salt-sensitivity testing by studying the effects on blood pressure (BP) of low sodium intake (20 mmol/day) and high sodium intake (220 mmol/day) in 10 men with borderline hypertension on two separate occasions. A difference in mean arterial pressure of 8 mm Hg between the high salt and the low salt regimen was arbitrarily chosen to define salt sensitivity. In addition, the reproducibility of changes in renal haemodynamics and in humoral factors, such as plasma renin activity, plasma aldosterone, atrial natriuretic peptide and urinary dopa and dopamine excretion, on the alteration in sodium intake were studied. As far as changes in BP are concerned, there was perfect agreement between the two tests, because in the second investigation, all subjects were classified in the same category as before. The salt-induced changes in plasma atrial natriuretic peptide and in renal excretion of dopa (dihydroxyphenylalanine) and dopamine were repeatedly and consistently different between the salt-sensitive and the salt-resistant group. The study revealed no support for a role of renal haemodynamics or the renin-angiotensin-aldosterone system in the pathophysiology of salt-induced elevations of BP in salt-sensitive subjects.

Vascular compliance in sodium-sensitive and sodium-resistant borderline hypertensive patients.

Recently, we demonstrated a reduction in the compliance of the carotid, femoral and brachial arteries in sodium-sensitive subjects who had consumed a regular sodium intake of approximately 120 mmol per day, as compared to both sodium-resistant borderline hypertensive subjects and normotensive controls. Venous compliance was not different between the two borderline hypertensive groups and was only slightly lesser than in controls. Large artery compliance was studied using a non-invasive ultrasound vessel wall movement detector system, while venous compliance was determined by means of strain gauge plethysmography. The borderline hypertensive subjects were subsequently treated with enalapril 10 mg/day, felodipine 5 mg/day or placebo during six months. Despite similar reductions in blood pressure, enalapril induced a significant increase of the muscular femoral and brachial artery compliance, but not of the elastic carotid artery, while felodipine did not influence large artery compliance at all in the sodium-sensitive group. The effect of enalapril on muscular artery compliance was established through a dose-dependent increase in distension and not through a change in arterial diameter. Arterial compliance was not influenced by either of the drugs in the resistant group. Venous compliance was also not altered by the medication. In conclusion, femoral and brachial artery compliance in sodium-sensitive borderline hypertensive subjects, which was found to be lower than that of sodium-resistant subjects, improved with antihypertensive treatment with enalapril but not with felodipine, despite the similar reductions in blood pressure induced by both drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular distensibility and compliance in salt-sensitive and salt-resistant borderline hypertension.

OBJECTIVE: To gain insight into the relationship between vascular compliance and sodium sensitivity. DESIGN: Arterial and venous compliance was determined in 17 sodium-sensitive and 28 sodium-resistant, young, borderline hypertensive males and in 10 age-matched normotensive controls, during regular sodium intake. METHODS: The carotid, femoral and brachial arteries were studied using a non-invasive ultrasound vessel wall movement detector system, and venous compliance was determined using forearm strain-gauge plethysmography. Cardiac output, plasma volume and hormonal factors, such as plasma renin activity, were also measured to assess their possible influence on vascular compliance. RESULTS: Large artery compliance was significantly less in the sodium-sensitive than in the sodium-resistant subjects in all arteries studied. Compared with controls, arterial compliance was reduced significantly in the sodium-sensitive group, whereas the sodium-resistant group did not differ significantly from the controls. Venous compliance was reduced equally in the two hypertensive groups compared with the controls, although the differences did not reach statistical significance. Cardiac output, blood pressure, plasma volume and hormonal factors did not differ between sodium-sensitive and sodium-resistant subjects and could not have been responsible for the observed differences in arterial compliance. CONCLUSIONS: The results of this study suggest that sodium-sensitive borderline hypertensives have reduced large artery compliance compared with age-matched sodium-resistant subjects. Since this finding could not be explained by differences in haemodynamic or hormonal factors between the groups, this suggests alterations to the viscoelastic properties of the arterial walls in sodium-sensitive subjects.

Nailfold capillary density in salt-sensitive and salt-resistant borderline hypertension.

OBJECTIVE: Nailfold capillary density was measured at rest and after 4 min circulatory arrest in order to investigate the relationship between sodium-sensitive hypertension and microvessel density. DESIGN: Seventeen sodium-sensitive and 28 sodium-resistant young borderline hypertensive males and 10 normotensive controls were studied. All of the subjects ate a diet containing 120 mmol/day sodium during the week preceding the investigation. METHODS: Capillary density was investigated by means of intravital video-microscopy. Blood pressure, cardiac index, plasma volume and humoral factors, such as plasma renin activity, plasma aldosterone and atrial natriuretic peptide, were also determined. RESULTS: No differences in capillary density were found under basal conditions. However, during hyperaemia the sodium-resistant subjects had significantly fewer perfused capillaries than both the sodium-sensitive and control subjects, whereas (apart from blood pressure) macrocirculatory parameters and humoral factors did not differ among the three groups. CONCLUSION: Sodium-resistant borderline hypertensives seem to be characterized by a (possibly structural) reduction in nailfold capillarity, a phenomenon that is, as yet, unexplained.

Compliance and reactivity of the peripheral venous system in chronic intermittent hemodialysis.

A reduced venous compliance and/or inadequate venoconstriction could impair hemodynamics during hemodialysis. Therefore, compliance and reactivity of the peripheral venous system were assessed in hemodialysis patients and controls using strain gauge plethysmography. Reactivity of the venous system towards an efferent sympathetic stimulus was assessed using a cold pressor test. Results showed that venous compliance was reduced in hypertensive hemodialysis patients compared to normotensive dialysis patients (P = 0.013) and normotensive controls (P = 0.004). After one dosage with a directly acting venodilator (nitroglycerin 5 mg s.l.) and 3 days of treatment with an alpha 1-sympathicolytic agent (Doxazosin 2 mg), venous compliance remained unaltered in hypertensive dialysis patients. During the cold pressor test, the blood pressure response, rise in noradrenaline levels and decline in venous compliance were normal in hemodialysis patients. However, their response to the Valsalva manoeuver was significantly impaired (P = 0.011) compared to healthy controls. We conclude that hypertension, not renal failure, causes the reduction of peripheral venous compliance in hemodialysis patients, for which structural factors might be responsible. Despite the existence of autonomous neuropathy, the reaction of the peripheral venous system towards an efferent sympathetic stimulus is intact in hemodialysis patients.

The microcirculation and essential hypertension.

Essential hypertension is characterized by a progressive increase of the mean arterial pressure paralleled by a concomitant increase in the total peripheral resistance. This elevated resistance is the consequence of (a) a decreased internal diameter, (b) an increased wall-to-lumen ratio or (c) a decreased number of small arteries or arterioles. A considerable part of the elevated vascular resistance is determined at the microcirculatory level. This paper reviews the studies performed to unravel the resistance-elevating mechanisms in the microvasculature of different tissues. Furthermore the possible role of the microcirculation in the pathogenesis of essential hypertension is discussed.