Doppler sonographic estimation of normal values for flow velocity and resistance indices in renal arteries of healthy infants

Abstract

Summary. Colour coded Duplex sonography (CDI) is an important method for the judgement of renal perfusion in infancy. By means of CDI the renal artery (RA), the segmental renal arteries (SA) and the interlobar arteries (ILA) can be differentiated. By means of pulsed Doppler sonography flow parameters in renal vessels can be measured. As flow parameters in different renal arteries are age dependent, normal values of the flow velocities and resistance indices were estimated. We investigated 147 healthy children by CDI. Children were subdivided into 4 groups: 38 infants (< 1 year), 38 toddlers (> or = 1 year and < 6 years), 37 school children (> or = 6 and < 12 years) and 34 adolescents (> or = 12 and < 18 years). All children were investigated by computersonography with a 5 or 7,5 MHz transducer. In all children blood flow was measured in the RA, SA and ILA. From the flow profile peak systolic flow velocity (Vmax), endsystolic (Ves), enddiastolic (Ved) and time average (TAV) flow velocity as well as the resistance index (RI) were measured. Flow velocity and resistance indices were age dependent and related to the location within the renal vascular tree. The highest flow velocity was found in the renal artery, lowest in the ILA. In infants, Vmax in the RA was 51,5 +/- 13,4, in the SA 33 +/- 8 and in the ILA 19,5 +/- 5 cm/s. In toddlers, Vmax in the RA was 71,3 +/- 13,5, in the SA 43,6 +/- 8,5 and in the ILA 28,3 +/- 6,8 cm/s. In school age children, Vmax in the RA measured 80 +/- 18, in the SA 45,5 +/- 9,1 and in the ILA 27,9 +/- 5,3 cm/s. In adolescents, Vmax in the RA was 80,7 +/- 13,7, in the SA 46,8 +/- 11,8 and in the ILA 28 +/- 6,1 cm/s. From RA to SA the other flow velocity Ves, Ved, TAV decreased about 30 % and from SA to ILA about 30 %. Flow velocity in the different renal arteries was age dependent. The lowest flow velocity was found in newborns and infants, highest in elder school children and adolescents. The flow velocity markedly increased from infancy to early childhood whereas in elder children and adolescents a slower increase of the flow velocity could be found. Every flow velocity within the RA and AIL showed a statistically significant increase with increasing age (p < 0,0001). Resistance indices decreased from the renal artery to the interlobar arteries. The RI of infants within the RA was 0,82 +/- 0,11, within the SA 0,81 +/- 0,12 and within the AIL 0,73 +/- 0,17. In toddlers the RI within the RA was 0,71 +/- 0,08, within the SA 0,67 +/- 0,07 and within the ILA 0,65 +/- 0,08. In school age children the RI within the RA was 0,71 +/- 0,09, within the SA 0,66 +/- 0,08 and the ILA 0,58 +/- 0,10. In adolescents the RI within the RA was 0,69 +/- 0,06, within the SA 0,63 +/- 0,07 and within the ILA 0,60 +/- 0,06. Additionally, resistance indices decreased with increasing age. Statistical analysis showed a significant decrease with increasing age (p < 0,0001). Highest resistance indices could be found in early infancy and in the renal arteries, lowest resistance indices were measured in school age and adolescence and in the interlobar arteries. As flow velocity and resistance indices are age dependent and dependent on the location of the sample volume in different renal arteries, both parameters have to be considered if pathological flow parameters are measured. The determination of normal values of flow velocity and resistance indices in different renal arteries facilitate the judgement of pathologic flow parameters. For comparative controls flow measurements within the renal artery and interlobar arteries should be used.