Sonography in renovascular hypertension

Multimodal imaging approach in hyponatremic hypertensive syndrome. A rare case of pediatric unilateral hypoplasia of the main renal artery combined itself with stenosis and review of literature

Renal artery stenosis (RAS) accounts for approximately 5%-10% of secondary renovascular hypertension in the pediatric population. It can occur as an isolated entity, or as a hypoplasia combined itself with stenosis. Hypoplasia, or long-segment developmental narrowing, is a rare cause of renovascular hypertension. Hyponatremic hypertensive syndrome (HHS) is a malignant complication of unilateral RAS and/or renal artery hypoplasia. Hyponatremia, hypokalemic hypochloremic metabolic alkalosis, nephrotic range proteinuria, polyuria, polydipsia, and weight loss are the most common findings. In particular, hypertension remains refractory despite aggressive antihypertensive therapy. Laboratory findings of elevated plasma levels of renin in most case suggest that the stimulation of renin release from the ischemic kidney plays an important pathophysiologic role. HHS is a diagnostic and therapeutic challenge in children. We report a case of a unilateral right renal artery hypoplasia, complicated by a segmental narrowing, in a 17-month-old male, clinically symptomatic for hypertension. We emphasize the role of ultrasound, computed tomography, and digital subtraction angiography that should be planned as reliable and non-invasive multimodal imaging approach.

Influence of resting before sonographic examination on Doppler measurements of renal blood flow

Renal artery stenosis (RAS) is the most common cause of secondary hypertension, via increases in plasma renin-angiotensin-aldosterone levels. Renal artery stenosis is diagnosed from blood examinations such as renin activity and from imaging examinations such as sonography. Patients are required to lie on the bed for 30 min before and during phlebotomy, since plasma renin activity is easily altered by posture. However, no such pre-examination rest is required for sonography. The present study therefore investigated the possible influence of resting before examination on Doppler parameters used for the diagnosis of RAS. Subjects comprised 55 healthy young adults (24 males, 31 females; mean age, 22 ± 1 years). Sonographic measurements were made shortly after subjects entered the examination room and again after 30 min of rest lying on a bed. Median peak systolic velocity in the renal artery was significantly decreased after rest (106 cm/s, interquartile range (IQR) 96-121 cm/s) compared with before rest (120 cm/s, IQR 107-135 cm/s; p < .001). Median acceleration time in the intra-renal segmental artery was also significantly shorter after rest (49 ms, IQR 38-54 ms) compared to before rest (50 ms, IQR 38-59 ms; p = .039). The present results suggest that serious consideration should be given regarding whether pre-examination resting is needed to accurately interpret Doppler measurements of renal blood flow when diagnosing RAS from sonography.

Pilot study to evaluate the potential use of the renal resistive index as a preliminary diagnostic tool for chronic kidney disease in cats

Objectives Chronic kidney disease (CKD) is the most common renal pathology diagnosed in geriatric cats, and its prevalence increases with age. The arterial resistive index (RI) is important when evaluating vascular resistance and compliance, and can be applied in the kidney (renal RI [RRI]), allowing the evaluation of its vascular haemodynamics. The present study aimed to: (1) investigate in cats with CKD the relationships between the RRI and the following parameters: age, sex, body weight, plasmatic creatinine, blood urea nitrogen, potassium, urine specific gravity, urine protein:creatinine ratio and systolic arterial pressure; and (2) evaluate the potential use of the RRI as a preliminary diagnostic tool in cats with CKD. Methods The present study involved 24 cats of both sexes. Six were healthy cats (control group [CG]) and 18 had CKD, but did not have any concomitant diseases and were not being treated with any medications (study group [SG]). For RRI measurement we used colour Doppler ultrasound (CDUS). Results RRI differed significantly between the CG and SG ( P <0.01) and was higher in the SG. A statistically significant correlation was only achieved between the RRI and the body weight of the patients and it was negative. A strong and positive correlation was noted between the mean RRI of both kidneys (r = 0.66). Receiver-operating curve analysis allowed us to establish an admissible cut-off for the RRI value of 0.639 for a preliminary diagnosis of CKD for both kidneys. Conclusions and relevance No differences were found for the RRI between the left and right kidneys, suggesting that evaluation of only one kidney is sufficient to provide an estimate of the RRI value for both organs. RRI measurement, which can be achieved with CDUS, is an easy-to-use diagnostic tool that, with a cut-off value of 0.639 for both kidneys, is useful in establishing a preliminary diagnosis of CKD.

Meal Ingestion and Hemodynamic Interactions Regarding Renal Blood Flow on Duplex Sonography: Potential Diagnostic Implications

Splanchnic blood flow changes dramatically after meal ingestion. The present study evaluated physiologic interactions between meal ingestion and hemodynamics with respect to renal blood flow on duplex sonography, assessing the possible influence on Doppler parameters used as diagnostic criteria for renal artery stenosis. Subjects comprised 26 healthy young men (mean age: 22 ± 2 y). Sonographic measurements were made shortly after breakfast and every 1 h thereafter and were compared with values measured before the meal. Peak systolic velocity in the renal artery was elevated post-prandially, peaking at 1 h (90 ± 12 cm/s), compared with pre-prandially (73 ± 10 cm/s, p < 0.01). Similarly, acceleration time at the intra-renal segmental artery shortened to a minimum at 1 h (45 ± 5 ms) compared with baseline (51 ± 6 ms, p < 0.01). The present study indicates that renal blood flow is altered for a few hours after meal ingestion. Attention should be paid to the interpretation of data measured after meals on duplex sonography for diagnosis of renal artery stenosis.

Should renal color Doppler ultrasonography be a routine test in newly diagnosed hypertensive patient?

: European Society of Hypertension/European Society of Cardiology guidelines recommend calculation of estimated glomerular filtration rate and evaluation of urinary albumin excretion rate as routine tests in the initial evaluation and during the follow-up of all hypertensive patients. However, from a clinical point of view, renal ultrasound - a noninvasive, readily available and cheap imaging modality - could contribute to the better evaluation of a hypertensive patient by identifying common causes of secondary hypertension (HTN) originating from the kidney and more recently by detecting renal injury in severe or long-standing essential HTN by measuring renal resistive indexes. The purpose of this review is to summarize the actual evidence which could support a larger use of renal ultrasound in the work-up of patients with newly diagnosed HTN.

Ultrasonographic evaluation of abdominal organs after cardiac surgery

BACKGROUND

Disturbances of the hepatosplanchnic region may occur after cardiac operations. Experimental studies have implicated impairment of splanchnic blood supply in major abdominal organ dysfunction after cardiopulmonary bypass (CPB). We investigated the impact of the cardiac operation and CPB on liver, kidney, and renal perfusion and function by means of ultrasonography and biochemical indices in a selected group of cardiac surgery patients.

MATERIALS AND METHODS

Seventy five patients scheduled for a major cardiac operation were prospectively included in the study. Criteria for selection were moderate or good left ventricular ejection fraction and absence of previous hepatic or renal impairment. Ultrasound examination of the hepatic and renal vasculature and examination of biochemical parameters were performed on the day preceding the operation (T0), on the first postoperative day (T1), and on the seventh postoperative day (T2).

RESULTS

Portal vein velocity and flow volume increased significantly, whereas hepatic artery velocity and flow volume decreased at T1 in comparison with T0. Hepatic vein indices remained unaffected throughout the observation period. Renal artery velocity and flow decreased, whereas renal pulsatility index and renal resistive index increased at T1 as compared with T0. Aspartate aminotransferase and alanine aminotransferase values were increased as compared with baseline values 24 h postoperatively. All parameters displayed a trend to approach preoperative levels at T2. Strong negative correlations between alanine aminotransferase values at T1 and hepatic artery velocity and flow volume at the same time point were also demonstrated (R = 0.638, P < 0.001 and r = 0.662, P < 0.001, respectively).

CONCLUSIONS

The increase in portal vein flow and velocity and the decrease in hepatic artery flow and velocity in the period after CPB might be attributed to the hypothermic bypass technique and the hepatic arterial buffer response, respectively. The decrease in renal blood flow and velocity and the parallel increase in Doppler renal pulsatility index and renal resistive index could be considered as markers of kidney hypoperfusion and intrarenal vasoconstriction. Maintaining a high index of suspicion for the early diagnosis of noncardiac complications in the period after CPB and institution of supportive care in case of compromised splanchnic perfusion are warranted.

Analysis of the sensitivity and specificity of noninvasive imaging tests for the diagnosis of renal artery stenosis

BACKGROUND

Aging and atherosclerosis are related to renovascular hypertension in elderly individuals. Regardless of comorbidities, renal artery stenosis is itself an important cause of cardiovascular morbidity and mortality.

OBJECTIVE

To define the sensitivity, specificity, positive predictive value, and negative predictive value of noninvasive imaging tests used in the diagnosis of renal artery stenosis.

METHODS

In a group of 61 patients recruited, 122 arteries were analized, thus permitting the definition of sensitivity, specificity, and the relative contribution of each imaging study performed (Doppler, scintigraphy and computed tomographic angiography in comparison to renal arteriography).

RESULTS

The mean age was 65.43 years (standard deviation: 8.7). Of the variables related to the study population that were compared to arteriography, two correlated with renal artery stenosis, renal dysfunction and triglycerides. The median glomerular filtration rate was 52.8 mL/min/m². Doppler showed sensitivity of 82.90%, specificity of 70%, a positive predictive value of 85% and negative predictive value of 66.70%. For tomography, sensitivity was 66.70%, specificity 80%, positive predictive value 87.50% and negative predictive value 55.20%. With these findings, we could identify the imaging tests that best detected stenosis.

CONCLUSION

Tomography and Doppler showed good quality and efficacy in the diagnosis of renal artery stenosis, with Doppler having the advantage of not requiring the use of contrast medium for the assessment of a disease that is common in diabetics and is associated with renal dysfunction and severe left ventricular dysfunction.

Green tagging in displaying color Doppler aliasing: a comparison to standard color mapping in renal artery stenosis

To quantitatively assess the contrast-to-noise ratio (CNR) of green tagging and standard color flow images in displaying fast flow velocity, we retrospectively reviewed 20 cases of hemodynamically significant renal artery stenosis (RAS) detected by renal color Doppler ultrasound and confirmed with digital subtraction angiography. At the site of RAS, blood flow with high velocity that appeared as aliasing on color flow images was computationally analyzed with both green tagging and standard color mapping. To assess the difference in the CNR between normal background flow and the aliased signal as a function of visualizing aliasing between the two color mappings, we used GetColorpixels (Chongqing Medical University, Chongqing, China) to count the values in the color channels after segmenting color pixels from gray-scale pixels. We then calculated the CNR in each color channel-red, green, and blue (RGB)--in the aliasing region on green tagging and standard color mapping. The CNRs in the red, green and blue channels were 0.35 ± 0.44, 1.11 ± 0.41 and 0.51 ± 0.19, respectively, on standard color mapping, and 0.97 ± 0.80, 4.01 ± 1.36 and 0.64 ± 0.29, respectively, on green tagging. We used a single-factor analysis of variance and two-tailed t-test to assess the difference in CNR in each color channel between the two color mappings at the site of RAS. With these comparisons, there was no significant difference in the CNR in the red or blue channel between green tagging and standard color mapping (p > 0.05). However, there was a statistically significant difference in the CNR in the green channel between the two color mappings (p = 0.00019). Furthermore, the CNR measured in the green channel on the green tagging image was significantly higher than the CNRs in all other color channels on both color mapping images (p = 0.000). Hence, we conclude that green tagging has significantly higher visibility as a function of high-velocity flow than standard color mapping. The use of green tagging may improve the ability to detect RAS with color Doppler ultrasound.

Renal duplex sonographic evaluation of type 2 diabetic patients

OBJECTIVES

The purpose of this study was to evaluate the renal volume and intrarenal hemodynamics with duplex sonography in a group of diabetic patients with normal renal function in comparison to nondiabetic controls.

METHODS

The renal volume and resistive index (RI) of segmental arteries were assessed by duplex sonography in 88 diabetic patients (44 male and 44 female; median age, 58 years [range, 37-69 years]) and 73 nondiabetic control participants (48 male and 25 female; median age, 53 years [range, 27-75 years]) without renal artery stenosis.

RESULTS

Both renal volume and RI values in the diabetic patients were significantly higher compared to the controls (mean volume ± SD: diabetic patients, 197.3 ± 47.6 mL; controls, 162.5 ± 35.2 mL; P < .0001; RI: diabetic patients, 0.70 ± 0.05; controls, 0.59 ± 0.06; P < .0001). Renal hypertrophy was present even in diabetic patients without proteinuria (renal volume: patients without proteinuria, 198.3 ± 45.9 mL; controls, 162.5 ± 35.2 mL; P < .005). Patients with higher RI values had significantly greater proteinuria (RI <0.75, 15.9 mg/g [range, 4.2-1718.9 mg/g]; RI >0.75, 37.9 mg/g [range, 11.34-2087.0 mg/g]; P < .02).

CONCLUSIONS

Changes in renal volume and hemodynamics are detectable on sonography in diabetic patients. Those changes are also present in patients without proteinuria or signs of renal atherosclerosis and with both normal and increased glomerular filtration rates. These results indicate a potential role of duplex sonography in the early identification of morphologic and hemodynamic renal changes in type 2 diabetic patients.

Doppler ultrasound and renal artery stenosis: An overview

Renovascular disease is a complex disorder, most commonly caused by fibromuscular dysplasia and atherosclerotic diseases. It can be found in one of three forms: asymptomatic renal artery stenosis (RAS), renovascular hypertension, and ischemic nephropathy. Particularly, the atherosclerotic form is a progressive disease that may lead to gradual and silent loss of renal function. Thus, early diagnosis of RAS is an important clinical objective since interventional therapy may improve or cure hypertension and preserve renal function. Screening for RAS is indicated in suspected renovascular hypertension or ischemic nephropathy, in order to identify patients in whom an endoluminal or surgical revascularization is advisable. Screening tests for RAS have improved considerably over the last decade. While captopril renography was widely used in the past, Doppler ultrasound (US) of the renal arteries (RAs), angio-CT, or magnetic resonance angiography (MRA) have replaced other modalities and they are now considered the screening tests of choice. An arteriogram is rarely needed for diagnostic purposes only. Color-Doppler US (CDUS) is a noninvasive, repeatable, relatively inexpensive diagnostic procedure which can accurately screen for renovascular diseases if performed by an expert. Moreover, the evaluation of the resistive index (RI) at Doppler US may be very useful in RAS affected patients for predicting the response to revascularization. However, when a discrepancy exists between clinical data and the results of Doppler US, additional tests are mandatory.

Normal Doppler spectral waveforms of major pediatric vessels: specific patterns

Every major vessel in the human body has a characteristic flow pattern that is visible in spectral waveforms obtained in that vessel with Doppler ultrasonography (US). Spectral waveforms reflect the physiologic status of the organ supplied by the vessel, as well as the anatomic location of the vessel in relation to the heart. In addition, the waveforms may be affected by age- and development-related hemodynamic differences. For example, adults tend to have higher flow velocities, whereas neonates, particularly those born prematurely, have higher resistance to flow, especially in the cerebral and renal vascular beds. As Doppler US is performed with increasing frequency for vascular evaluation in children, the recognition of normal flow patterns has become imperative. Familiarity with the waveforms characteristic of specific veins and arteries in children is important. In addition, an understanding of the hemodynamic factors involved provides a useful basis for interpreting waveform abnormalities.

Imaging modalities for renal artery stenosis in suspected renovascular hypertension: prospective intraindividual comparison of color Doppler US, CT angiography, GD-enhanced MR angiography, and digital substraction angiography

The aim of the study was to evaluate the diagnostic accuracy of Color Doppler US, CT Angiography (CTA), and GD-enhanced MR Angiography (MRA) compared with digital subtraction angiography (DSA) for the detection of renal artery stenosis in patients with clinically suspected renovascular hypertension. Fifty-eight patients with suspected renovascular hypertension were enrolled in the study. All patients underwent Color Doppler US, CTA and GD-enhanced MRA. DSA was the gold standard method for the number of renal arteries, existence and degree of stenosis, or evidence of fibromuscular dysplasia. DSA depicted 132 renal arteries, 16 stenoses, and 4 arteries with fibromuscular dysplasia. Color Doppler US failed to detect 1 main and 14 polar arteries. CTA depicted all main renal arteries and 7/16 polar arteries, but failed to detect stenosis in two accessory vessels. Likewise, MRA did not detect stenotic accessory renal arteries, depicted 9/16 polar renal arteries, but missed two main renal arteries. All methods depicted the four main renal arteries with fibromuscular dysplasia. The overall sensitivity, specificity, and positive and negative predictive accuracy were 75%, 89.6%, 60% and 94.6%, respectively, for color Doppler US; 94%, 93%, 71%, and 99%, respectively, for CTA; and 90%, 94.1%, 75%, and 98%, respectively, for GD-enhanced MRA. CTA and GD-enhanced MRA have comparable and satisfactory results with respect to the negative predictive accuracy of the suspected renal artery stenosis. The concept of an imaging algorithm including US as screening test when appropriate and CTA or MRA as the second step-procedure is suggested. Therefore, DSA may be reserved for cases with major discrepancies or therapeutic interventions.

New intrarenal echo-Doppler velocimetric indices for the diagnosis of renal artery stenosis

We aimed at comparing the positive and negative predictive values (PPV, NPV) of several intrarenal velocimetric indices for revealing the presence of renal artery stenosis (RAS) among hypertensive patients who underwent a renal angiography for the clinical suspicion of renovascular hypertension. In 106 patients (200 kidneys), the pulsatility index (PI) and resistive index (RI), the acceleration time (AT), and the mean systolic acceleration (ACC(sys)) were evaluated. In addition, the maximal systolic acceleration (ACC(max)), that is, the maximal slope of the acceleration phase, and the maximal acceleration index (AI(max)), that is, the ratio between ACC(max) and the relative peak systolic velocity, were calculated. On angiography, we found that 56 (28%) of the 200 arteries had a greater than 60% RAS. PI and RI had an NPV below 75%, whereas AT, ACC(sys), ACC(max), and AI(max) had an NPV always above 95%. However, ACC(max), and AI(max), at their best cutoff limits, had higher PPV than ACC(sys) and AT (60 and 70% vs 45 and 51%, respectively). Thus, in a cohort of patients with a high prevalence of RAS, PI and RI failed to reach an NPV adequate for a screening test. In contrast, all the acceleration indices we tested had a sufficiently high NPV but AI(max) appears superior to the others because of higher PPV. We propose the evaluation of AI(max) as an additional screening test in patients with hypertension and the clinical suspicion of RAS.

Vasoconstriction and blood flow responses in visceral arteries to mental task in humans

The vascular responses to mental task in visceral arteries in humans have not been elucidated. We observed the responses in the renal (RA) and superior mesenteric (SMA) arteries to mental stress, using simultaneous pulsed and echo Doppler ultrasound flowmetry. Nine healthy females performed a computerized colour word conflict test (CWT) for 3 min. The mean blood velocity (MBV) in the right RA and SMA, heart rate (HR) and blood pressure were measured. The mean arterial pressure (MAP) was divided by the flow velocity to assess the vascular resistance (VR). The CWT significantly increased the MAP, HR and VR in both arteries from the first minute. During the CWT, flow in the RA decreased significantly at the third minute relative to baseline, while flow in the SMA showed no significant change from the first to the third minute. The degree of vasoconstriction in the RA bed was greater than that in the SMA bed. These results suggest that the mental task causes vasoconstriction in visceral arteries, and imply that it induces differential blood flow and vascular responses in visceral arteries.

Duplex-Doppler Long-term Follow-up of Renal Transplant Artery Stenosis: Case Controlled Study

The aim of this retrospective clinical study was to assess a long-term course of renal transplant artery stenosis with duplex-Doppler ultrasound, and its influence upon serum creatinine, hemoglobin concentration and hypertension, as well as to investigate a possible association between stenosis and the number of acute rejections. Thirty-four renal transplant recipients, aged 43 +/- 13 years, with significant (>50%) renal transplant artery stenosis as seen on Doppler ultrasound were compared with 34 renal transplant recipients without stenosis (excluded by Doppler). Patients of both groups were matched by age, sex, time of transplantation, type of renal transplant, and number of previous transplantations. We analyzed peak systolic velocity (PSV) in the renal transplant artery, resistance index (RI) at the level of intra-renal arteries, serum creatinine, hemoglobin concentration, blood pressure, the number of antihypertensive medications, and the number of acute rejections on a yearly basis. In the stenosis group, PSV was 2.1 +/- 0.5 m/s at 1 year after transplantation (controls 1.1 +/- 0.4), 1.9 +/- 0.5 at 2 years (0.9 +/- 0.4), 1.9 +/- 0.5 at 3 years (0.9 +/- 0.4); RI was 62 +/- 10% at 1 year (controls 68 +/- 7), 65 +/- 9 at 2 years (67 +/- 7), 63 +/- 9 at 3 years (67 +/- 7); serum creatinine was 128 +/- 58 micromol/L at 1 year (controls 129 +/- 43), 119 +/- 47 at 2 years (121 +/- 33), 125 +/- 54 at 3 years (127 +/- 32). Long-term course of renal transplant artery stenosis (>50%), treated medically or interventionally, seems to be stable and non-progressive (during a 3-year follow up). Spontaneous regression of stenosis to non-significant level is possible. No difference in graft function, blood pressure or the number of acute rejections was observed comparing the stenotic and non-stenotic groups.

Pediatric applications of abdominal vascular Doppler: Part II

Ultrasound is a remarkably powerful and versatile modality for pediatric imaging, without requiring exposure to radiation or sedatives. By providing information on blood flow, Doppler sonography can reveal details about normal physiology and disease processes not discernable from gray-scale anatomic images alone. In part I, the basics of hemodynamics and effects on the Doppler waveform were discussed, along with clinical applications in hepatic disease. In part II, the application of Doppler in renal disease and in conditions affecting the deep abdominal vessels are discussed. The role of ultrasound contrast agents in pediatric Doppler imaging is briefly reviewed.

A comparison of Power Doppler with conventional sonographic imaging for the evaluation of renal artery stenosis

Background

Power Doppler (PD) has improved diagnostic capabilities of vascular sonography, mainly because it is independent from the angle of insonation. We evaluated this technique in a prospective comparison with conventional imaging, consisting in Duplex and Color Doppler, for the evaluation of Renal Artery (RA) stenosis.

Methods

Sensitivity, specificity and predictive values of PD and conventional imaging were assessed in a blinded fashion on eighteen patients, 9 with angiographic evidence of unilateral RA stenosis (hypertensive patients) and 9 with angiographically normal arteries (control group). PD images were interpreted with an angiography-like criteria.

Results

In the control group both techniques allowed correct visualization of 16 out of the 18 normal arteries (93% specificity). Only in five hypertensive patients RA stenosis was correctly identified with conventional technique (56% sensitivity and 86% negative predictive value); PD was successful in all hypertensive patients (100% sensitivity and negative predictive value), since the operators could obtain in each case of RA stenosis a sharp color signal of the whole vessel with a clear "minus" at the point of narrowing of the lumen. All results were statistically significant (p < 0.01).

Conclusions

This study demonstrates that PD is superior to conventional imaging, in terms of sensitivity and specificity, for the diagnosis of RA stenosis, because it allows a clear visualization of the whole stenotic vascular lumen. Especially if it is used in concert with the other sonographic techniques, PD can enable a more accurate imaging of renovascular disease with results that seem comparable to selective angiography.

High-grade renal transplant artery stenosis after suboptimal angioplasty: favourable long-term outcome

The purpose of our report is to present the long-term outcomes of three renal transplant recipients with high-grade stenosis and suboptimal percutaneous angioplasty (PTA) because of technical difficulties. Two men and one woman of age 67, 53, and 54 years, who maintained functional cadaveric graft for 17, 9, and 13 years, and had diagnosed significant renal transplant artery stenosis at 2, 1, and 2 years after renal transplantation, respectively, were studied. Stenoses were diagnosed angiographically in the first patient and by Doppler in other two patients, then confirmed by angiography. All three patients had difficult-to-treat hypertension with deterioration of graft function in the presence of or after introducing ACE-inhibitor therapy. PTA was performed in all patients with suboptimal or unsuccessful results as assessed by angiography or control Doppler examination--the residual stenosis was significant and practically unchanged. Surgery was not performed because of high risk, so patients were further treated conservatively. Hypertension was treated avoiding ACE inhibitors. Twelve, 7, and 7 years after angioplasty the serum creatinine is stable in all patients, even decreased compared to pre-PTA and early post-PTA levels, namely, 134, 102, and 75 micromol/L, respectively. Control Doppler examinations revealed a residual stenotic jet in all patients, with slightly decreased peak systolic velocity over time, indicating a slightly decreased grade of stenosis. These observations suggest that renal transplant artery stenosis, even of high grade, can be stable, or even regress with time with excellent long-term graft survival. Randomized studies comparing conservative treatment versus revascularization are warranted.

Renal vascular responses to static handgrip: role of muscle mechanoreflex

During exercise, the sympathetic nervous system is activated, which causes vasoconstriction. The autonomic mechanisms responsible for this vasoconstriction vary based on the particular tissue being studied. Attempts to examine reflex control of the human renal circulation have been difficult because of technical limitations. In this report, the Doppler technique was used to examine renal flow velocity during four muscle contraction paradigms in conscious humans. Flow velocity was divided by mean arterial blood pressure to yield an index of renal vascular resistance (RVR). Fatiguing static handgrip (40% of maximal voluntary contraction) increased RVR by 76%. During posthandgrip circulatory arrest, RVR remained above baseline (2.1 +/- 0.2 vs. 2.8 +/- 0.2 arbitrary units; P < 0.017) but was only 40% of the end-grip RVR value. Voluntary biceps contraction increased RVR within 10 s of initiation of contraction. This effect was not associated with an increase in blood pressure. Finally, involuntary biceps contraction also raised RVR. We conclude that muscle contraction evokes renal vasoconstriction in conscious humans. The characteristic of this response is consistent with a primary role for mechanically sensitive afferents. This statement is based on the small posthandgrip circulatory arrest response and the vasoconstriction that was observed with involuntary biceps contraction.

Doppler sonography in renal artery stenosis. An evaluation of intrarenal and extrarenal imaging parameters

A prospective comparison of different direct and indirect Doppler parameters with angiography was performed to determine the most useful Doppler parameters and threshold values for the detection of significant (> or =60%) renal artery stenosis (RAS). The best combination of parameters was found to be the use of direct parameters of peak systolic velocity (PSV) greater than 180 or 200 cm/s and renal aortic ratio (RAR) greater than 3.0 with a sensitivity and specificity at 92% and 88%, respectively.

The right diagnostic work-up: investigating renal and renovascular disorders

Renovascular disease is present in about 10-40% of patients with end-stage renal disease, and constitutes the fastest-growing group of end-stage renal disease patients. The unselective correction of renal artery stenosis has led to disappointing results. Most studies that have compared conservative treatment with angioplasty have found only modest or no beneficial effects of angioplasty on renal function and blood pressure. It is therefore mandatory to evaluate the functional significance of a stenosis before intervention. Patients most likely to respond favourably to revascularization should be identified. Factors that affect outcome include the severity of renal artery stenosis, type of treatment of renal artery stenosis and, most importantly, underlying renal disease, which prevents a favourable response even after successful correction of renal artery stenosis. Doppler ultrasonography to evaluate the renal resistance index [1 - (end diastolic velocity/maximum systolic velocity) x 100] or captopril scintigraphy are the best methods by which to classify patients as responders or non-responders to intervention. In patients with a renal resistance index > or = 80%, improvement of renal function or blood pressure is highly unlikely, despite successful correction of renal artery stenosis. The value of the renal resistance index can also be extended to patients with non-stenotic renal diseases. Identifying patients at risk for irreversible loss of renal function and who may benefit from intervention is a high research priority.

New imaging applications in the evaluation of pediatric renal disease

Continued improvements in imaging technology have changed many of the traditional diagnostic algorithms for evaluating pediatric renal disease. Newer imaging modalities offer more accurate, specific, and early diagnoses, but can be time consuming and costly. Less invasive modalities, such as ultrasound, computed tomography, and magnetic resonance imaging have widespread applications in pediatric practice. The risks of radiation exposure, contrast toxicity, and sedation or anesthesia versus the potential benefits of obtaining precise diagnostic information should always be considerations before electing any imaging procedure in children.

New diagnostic techniques for imaging the renal arteries

There has been an increasing focus on renovascular disease, particularly in renal failure, and on the role of renal angioplasty and stenting. Significant improvements have occurred in non-invasive imaging techniques. This review concentrates on the recent developments in imaging that specifically targets the renal artery and renal artery stenosis. It also discusses how these techniques may facilitate better selection of cases that will respond to intervention.