Renal blood flow and flow velocity in children and adolescents: duplex Doppler evaluation

Neurofilament light chain: serum reference intervals in Danish children aged 0-17 years

Elevated levels of neurofilament light chain (NfL) in the blood is an unspecific biomarker for damage to neuronal axons. The measurement of NfL levels in the blood can provide useful information for monitoring and prognostication of various neurological disorders in children, but a reference interval (RI) is needed before the clinical implementation of the biomarker. We aimed to establish a RI for children aged 0-17 years. Serum samples from 292 healthy reference subjects aged 0.4-17.9 years were analysed by a single-molecule array (Simoa®) established for routine clinical use. Non-parametric quantile regression was used to model a continuous RI, and a traditional age-partitioned non-parametric RI was established according to Clinical and Laboratory Standard Institute (CLSI) guideline C28-A3. Furthermore, we investigated the effect of hemolysis on assay performance. The traditional age-partitioned non-parametric RI for the age group <3 years was 3.5-16.6 ng/L and 2.1-13.9 ng/L in the age group ≥3 years, respectively. The continuous RI showed an age-dependent decrease in median NfL levels in the first three years of life which was also evident in the age-partitioning of the traditional RI. We found no difference between sexes and no impact of hemolysis on the NfL test results. This study establishes a pediatric RI for serum NfL and lays the groundwork for its future use in clinical practice.

Development and application of a pediatric mechanistic kidney model

Pediatric physiologically‐based pharmacokinetic (P‐PBPK) models have been used to predict age related changes in the pharmacokinetics (PKs) of renally cleared drugs mainly in relation to changes in glomerular filtration rate. With emerging data on ontogeny of renal transporters, mechanistic models of renal clearance accounting for the role of active and passive secretion should be developed and evaluated. Data on age‐related physiological changes and ontogeny of renal transporters were applied into a mechanistic kidney within a P‐PBPK model. Plasma concentration–time profile and PK parameters of cimetidine, ciprofloxacin, metformin, tenofovir, and zidovudine were predicted in subjects aged 1 day to 18 years. The predicted and observed plasma concentration–time profiles and PK parameters were compared. The predicted concentration–time profile means and 5th and 95th percent intervals generally captured the observed data and variability in various studies. Overall, based on drugs and age bands, predicted to observed clearance were all within two‐fold and in 11 of 16 cases within 1.5‐fold. Predicted to observed area under the curve (AUC) and maximum plasma concentration (C_max) were within two‐fold in 12 of 14 and 12 of 15 cases, respectively. Predictions in neonates and early infants (up to 14 weeks postnatal age) were reasonable with 15–20 predicted PK parameters within two‐fold of the observed. ciprofloxacin but not zidovudine PK predictions were sensitive to basal kidney uptake transporter ontogeny. The results indicate that a mechanistic kidney model accounting for physiology and ontogeny of renal processes and transporters can predict the PK of renally excreted drugs in children. Further data especially in neonates are required to verify the model and ontogeny profiles.

Ultrasonographic assessment of renal perfusion in bitches with mammary carcinoma treated with long-term carprofen

The aim of this study was to evaluate renal hemodynamics, routine clinical and laboratory parameters used to estimate renal function, and clinical evolution during six months in bitches with mammary carcinomas that underwent mastectomy and were treated (TG) or not (CG) with carprofen for three months after surgery. Twenty-six bitches with mammary carcinoma were equally distributed into TG that received carprofen 4.4 mg/kg/day for 90 days and CG that did not receive anti-inflammatory medication. Renal artery Doppler flowmetry, contrast-enhanced ultrasound (CEUS) of renal parenchyma, haematological, biochemical and clinical analyses were obtained once a month. These data were compared between groups and time via analysis of variance (ANOVA) in a completely randomized design with repeated measures (P < 0.05). On B-mode ultrasound, the area of the renal artery was greater (P = 0.0003) in the TG. Regarding laboratory findings, haematocrit and haemoglobin were similar in both groups, showing a significant and gradual increase after three months of treatment; MCV, MHC, and MCHC were increased (P < 0.05) and lymphocyte and band counts decreased (P < 0.05) in the TG. Regarding biochemical tests, ALT was the only parameter with a significant difference, being higher (P = 0.0272) in the treated group. It can be concluded that the use of carprofen for 90 days causes minimal changes in renal perfusion, erythrocyte parameters and ALT activity, and reduces the proportion of blood inflammatory cells. Therefore, use of this medication can be carried out safely in patients who require auxiliary cancer treatment.

Clinical and ultrasound variables for early diagnosis of septic acute kidney injury in bitches with pyometra

The aetiology of septic acute kidney injury (AKI) is not completely elucidated. Early identification of AKI in septic patients is considered to improve survival rate since it allows rapid treatment onset. We evaluated clinical, haematological, urinary, B-mode, spectral Doppler, and contrast-enhanced ultrasound variables in 20 bitches with pyometra as sepsis models and 12 healthy controls. All animals with pyometra presented some degree of renal damage on histological examination; however, sequential organ failure assessment (SOFA) classified only 40% cases with sepsis. AKI derived from systemic infection was identified in 57% of cases with hypoperfusion and in 22% with inflammation, being an affection of multifactorial origin. Among the evaluated parameters, urinary protein/creatinine ratio >0.15, serum albumin <2.94 mg/dL, time-averaged minimum velocity <21.5 cm/s, renal length/aorta diameter ratio >5.93, pulsatility index >1.53, haematocrit <45%, time-averaged maximum velocity <45.7 cm/s, haemoglobin <16 g/dL, leukocytes >12.53 × 103/uL, and cortical contrast peak intensity <69%, in the order of accuracy, are significant indicators of septic AKI with an accuracy >80%. Thus, AKI is a very prevalent condition in septic patients, derived mainly from changes in renal perfusion and inflammation. Additionally, reviewing the SOFA score parameters is suggested to identify renal failure.

Renal Interlobar Artery Parameters with Duplex Doppler Sonography and Correlations with Age, Plasma Renin, and Aldosterone Levels in Healthy Children

OBJECTIVE

The objectives of this study were to compare and make correlations between age and Doppler parameters of the interlobar arteries, including synchronously obtained plasma renin and aldosterone levels and to obtain new normative data regarding acceleration time in healthy children from neonates to 16 years.

SUBJECTS AND METHODS

One hundred sixty-nine healthy children (72 girls and 97 boys) were classified into four groups: group 1 (< 1 year; n = 34), group 2 (range, 1-6 years; n = 48), group 3 (range, 6-12 years; n = 50), and group 4 (range, 12-16 years; n = 37). Blood samples from the renin and aldosterone were collected in the morning after bed rest and fasting. The resistive index (RI), pulsatility index (PI), and the acceleration time of the renal interlobar arteries with duplex Doppler sonography, including both kidney longitudinal lengths with grayscale sonography, were evaluated. One-way analysis of variance with the least significant difference post-hoc test and Pearson's correlation test were used to compare the differences between groups and to make correlations, respectively. An independent-sample t test was used to evaluate the differences between all parameters based on sex and to compare the left and right kidney longitudinal lengths in each group.

RESULTS

The RI, PI, and acceleration time were statistically significant in between-group comparisons. Only in group 4 was acceleration time not statistically significant compared with groups 2 and 3. Plasma renin levels were significantly higher in group 1 compared with groups 2 (p < 0.03) and 4 (p < 0.0001); in group 2 compared with group 4 (p < 0.05); and in group 3 compared with group 4 (p < 0.01). The plasma aldosterone levels were significantly higher only in group 1 compared with groups 2 (p < 0.001), 3 (p < 0.008), and 4 (p < 0.0001). The RI correlated linearly with the PI, plasma renin levels, and aldosterone levels and correlated inversely with acceleration time. Age had a negative correlation with the RI, PI, plasma renin levels, and aldosterone levels and correlated positively with acceleration time. There were no statistically significant differences between all parameters based on sex and no significant difference found between the right and left kidney longitudinal lengths in each group.

CONCLUSION

The RI in children up to 54 months old is higher than in adults. Therefore, the adult mean renal RI criterion of 0.70 should be applicable to children 54 months old and older. We showed that the age dependency of the RI was directly related to that of plasma renin and aldosterone levels in healthy children in whom Doppler parameters and blood analysis were evaluated synchronously.

Elevated internal exposure of children in simulated acute inhalation of volatile organic compounds: effects of concentration and duration

When deriving health-based exposure limits in recent years, increasing attention has been drawn to susceptible subpopulations, in particular to children. We investigated the differences in kinetics between children and adults during inhalation of styrene as a typical category-3 volatile organic compound (VOC), i.e., a gas with a low reactivity and low water solubility allowing a high rate of alveolar absorption. Internal exposure was simulated using a physiologically based kinetic model over a broad range of airborne concentrations (1-1000 ppm) and for an exposure time of up to 8 h according to the scenario in the acute exposure guideline level (AEGL) program. Age-specific anatomical and physiological parameters and compound-specific data was derived from the literature. The calculated concentrations in arterial blood are higher in children than in adults, and are highest in the newborn. For an 8-h exposure to low concentrations, the calculated arterial concentration in the newborn is higher by a factor of 2.3 than in the adult. This is due mainly to the relatively high ventilation rate and the immature metabolism. With increasing airborne concentration, the ratio of arterial concentrations (newborn/adult) increases to a maximum of 3.8 at 130 ppm in ambient air, and declines with further increments of concentration to a value of 1.7. This is because the metabolism of the newborn becomes non-linear at lower concentrations than in adults. At high concentrations, metabolism is saturated in both age groups. For shorter exposures, the dose dependency of the concentration ratios (newborn/adult) is less pronounced. This is the first article to show that the intraspecies assessment factor may vary with concentration and duration of exposure.

Pulsed Doppler sonography of the hilar renal artery: differentiation of obstructive from nonobstructive hydronephrosis in children

BACKGROUND/PURPOSE

It is difficult to detect the arcuate or cortical renal arteries when performing pulsed Doppler sonography (PDS) for congenital hydronephrosis. This study was undergone to assess the usefulness of PDS of the hilar renal artery to differentiate obstructive from nonobstructive hydronephrosis.

METHODS

The authors performed PDS of the hilar renal artery in 80 normal children: 20 aged 0 to 1 months (group I), 20 aged 1 to 12 months (group II), 20 aged 1 to 6 years (group III), and 20 aged 7 to 15 years (group IV). Based on diuretic renography findings, 22 kidneys from 19 children with a ureteropelvic junction (UPJ) stricture were divided into 7 dilated obstructed and 15 dilated nonobstructed kidneys. The peak-systolic velocity (PSV), end-diastolic velocity (EDV), mean average velocity (Vm) and the resistive index (RI = [PSV - EDV]/PSV) were measured at the hilar renal artery.

RESULTS

There was a significant difference in the RI of the hilar renal artery between obstructive and nonobstructive hydronephrosis.

CONCLUSION

A pulsed Doppler evaluation of the hilar renal artery is useful for detecting an obstructive UPJ stricture compared with assessing arcuate or cortical renal arteries.

Gd-enhanced 3D phase-contrast MR angiography and dynamic perfusion imaging in the diagnosis of renal artery stenosis

The objective of this study was to investigate the role of contrast enhancement using a three-dimensional (3D) phase-contrast (PC) magnetic resonance (MR) sequence (3D PC-MRA) and to assess the value of a dynamic MR perfusion study of the kidneys to determine the hemodynamic relevance of unilateral renal artery stenosis (RAS). Seventeen patients with unilateral RAS were examined on a standard 1.0 T imaging system using a phase shift and magnitude sensitive 3D PC sequence (TR=160 ms, TE=9 ms, venc. 30 cm/s). Following the initial pre-contrast 3D PC-MRA a dynamic first pass perfusion study was performed using a Turbo-FLASH 2D sequence (TR=4.5 ms, TE=2.2 ms, TI=400 ms) after bolus injection of 0.15 mmol gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA)/kg body weight. The 3D PC-MRA was then repeated during infusion of 0.15 mmol Gd-DTPA/kg body weight. Evaluation by three independent readers was based on maximum intensity projection images. Source images were rendered on request. Signal intensity (SI) over time curves of the renal cortex were obtained from the dynamic perfusion study and analyzed for maximum signal enhancement as well as temporal relationship to the aortic SI curve. Results from 3D PC-MRA revealed a sensitivity (pre-/post-contrast) of 100%/89%, specificity of 76%/63%, positive predictive value of 80%/69 %, negative predictive value of 90%/78%, and accuracy of 85%/75% (p=0.07). Interobserver agreement was kappa=0.61/kappa=0.47 (pre/post Gd-DTPA), respectively. Increased signal-to-noise was present in all segments of the renal arteries post contrast (p=0.0003). This came along with image degradation due to aliasing and elevated SI of venous flow that partially obscured the renal arteries. Dynamic SI curves showed a significantly decreased maximum SI in RAS (p=0.01-0.001). A temporal delay of cortical signal intensity enhancement could not be confirmed in this setting. Gd-enhanced 3D PC-MRA did not yield a superior diagnostic value in the diagnosis of RAS compared to pre-contrast measurements. Dynamic perfusion imaging of the kidneys, in combination with 3D PC-MRA, can contribute additional information in suspected unilateral RAS.

Toxicokinetics in infants and children in relation to the ADI and TDI

Age-dependent developmental changes in toxicokinetics occur in both rats and humans, particularly in relation to renal function and hepatic xenobiotic metabolism. These processes are immature in humans at birth, especially in the pre-term neonate, but mature rapidly over the first months of life. In consequence the duration of immaturity primarily corresponds to the period of suckling. Similar developmental changes occur in the neonatal rat over the first weeks of life. Rat pups start to consume some of the adult diet in the third week of life, prior to weaning, so that there is a potential for consumption of the adult diet during the period of immaturity. There is an extensive database on the pharmacokinetics of therapeutic drugs in infants and children. The elimination/clearance of many drugs is higher in children than in adults and this difference would apply to other xenobiotics. In consequence, children frequently will have lower body burdens than adults for the same daily intake of a chemical when this is expressed on a body weight basis, as used to describe the ADI (Acceptable Daily Intake) or TDI (Tolerable Daily Intake) (e.g. mg/kg body weight/day). Therefore, an increased safety or uncertainty factor for post-suckling infants and children is not required in relation to age-related differences in toxicokinetics. Indeed, the higher clearance of many xenobiotics (toxicokinetics) by children compared with adults may compensate, at least in part, for increased organ sensitivity (toxicodynamics) during development.

Volumetric evaluation of blood flow in normal renal arteries with a Doppler flow wire: a feasibility study

PURPOSE

To evaluate the feasibility of direct intravascular determination of renal artery (RA) blood flow with a Doppler probetipped guide wire.

MATERIALS AND METHODS

Potential renal donors (n = 10) with normal RAs (n = 23) underwent evaluation of RA blood flow velocity with use of a 0.018-inch, 12-MHz Doppler guide wire. The RA average peak velocity (APV) was obtained with the flow wire. RA diameter was obtained from the filmed images with magnification corrected to a known standard or by a computerized quantification program. These data were used to determine the vessel's cross-sectional area (CSA).

RESULTS

The right and left RA APV, CSA, and blood flow differed insignificantly within the group and averaged 9.7 and 9.0 cm/sec (P = .43), 0.417 and 0.357 cm2 (P = .22), and 382 and 370 mL/min (P = .43), respectively. However, in individuals, the RA CSA and total volumetric blood flow varied by a mean of 29% (range, 4%-56%) and 50% (range, 19%-128%), respectively.

CONCLUSION

This study demonstrates that direct intravascular determination of RA blood flow with a Doppler-tipped wire is both feasible and relatively uncomplicated. Results indicate that blood flow can vary significantly, both in kidneys within the same individual and from person to person. The Doppler wire may facilitate measurements of RA blood flow during endoluminal interventions and help determine an optimal endpoint for these procedures.

The reproducibility of color Doppler duplex sonography in the measurement of renal arterial blood velocity

In this study, the reproducibility of color Doppler duplex sonography for repeated measurements of renal blood flow was evaluated in 14 healthy subjects. We examined the reproducibility for different examiners and different time intervals between the examinations. Doppler frequency sonograms were analyzed with several parameters, and statistical evaluation was performed by calculating both the correlation coefficient (r) and coefficient of variation (CV). Peak systolic velocity (S), early diastolic velocity (D1) and mean velocity (MV) showed good reproducibility (r = 0.902-0.992, CV = 2.15-8.16%). On the other hand, end-diastolic velocity (D2), acceleration time (AT) and acceleration index (AI) showed poor reproducibility. We conclude that the reproducibility of this method is acceptable for repeated measurements of renal blood velocity, using suitable parameters S, D1 and MV.

Doppler studies in normal kidneys of healthy children

Despite the widespread use of Doppler ultrasound in kidney diseases of adults and children, there are only a few, partially contradictory reports of normal values of resistance index (RI) and pulsatility index (PI) of renal perfusion in a healthy pediatric population. This study was carried out to determine normal values for these parameters in a larger group of probands. For the RI correlation with age was most pronounced in the right renal artery, with children over 6 years having a significantly lower RI than younger children. The PI was relatively independent of side and age. These results are somewhat different to previous reports. These differences may influence future Doppler sonographic investigations of acute and symmetrically affected kidneys (nephrological diseases). Our data suggest that the RI of the right renal artery might be most useful. In chronical or unilateral kidney diseases (unilateral ureteral obstruction, reflux, or operation) investigation of the PI in addition to the RI may aid diagnosis.

Color Doppler ultrasonography for the assessment of renal blood flow in heart failure

To validate color Doppler ultrasonography of renal arteries for the assessment of renal blood flow (RBF), we compared left and right RBF estimates and their sum (total RBF) by echo-Doppler with data obtained by iodine 123-123I-p-aminohippuric acid (PAH) scintigraphy in 19 patients with heart failure and 7 normal control subjects. Single-side and total RBF estimates by echo-Doppler ranged, respectively, between 179 and 428 mL/min/m2 and from 378 to 835 mL/min/m2 in patients with heart failure and between 265 and 601 mL/min/m2 and from 564 to 1,182 mL/min/m2 in normal control subjects. Single-side and total RBF estimates by echo-Doppler correlated well with measurements obtained by scintigraphy (r = 0.74 and 0.76, respectively, in patients with heart failure; both: p < 0.001). At Bland and Altman's analysis of correspondence between the 2 techniques, there were 17 disagreements (33.7%) for single-side RBF and 8 disagreements (31.8%) for total RBF. However, the two techniques disagreed markedly in only two single-side and one total RBF estimates. Thus, in patients with heart failure, RBF assessed noninvasively by color Doppler ultrasonography has a good correlation with 123I-PAH renal scintigraphy data over a wide range of blood flow.

Duplex sonography of renal arteries as a diagnostic tool in hypertensive children

Computed duplex sonography was used to examine the renal arteries in 36 hypertensive children and adolescents (ages 4-17 years) with arterial hypertension of either renal or non-renal origin. Time-averaged flow velocities, maximum blood flow velocities as well as absolute renal blood flow and renal blood flow per gram kidney weight were measured. Normal flow velocities and normal to elevated renal blood flow volume was found in patients with acute glomerulonephritis and those with signs of chronic glomerulonephritis onset. Patients having advanced stages of chronic glomerulonephritis, on the other hand, were characterized by lower levels of all parameters. Unilateral renal artery stenosis was diagnosed correctly in four patients, although one intra-renal artery stenosis escaped imaging. Scarred kidneys exhibited low-normal or reduced flow velocities and renal blood flow volumes corresponded roughly to kidney size and preservation of normal kidney structure. Hypertension in some patients with normal kidneys showed a tendency to cause higher renal blood flow without consistent acceleration of blood flow velocities. We conclude that duplex sonography is a suitable primary diagnostic tool in measuring blood flow velocities and absolute renal blood flow volume in hypertensive children, thus facilitating the choice of the next diagnostic step.