Maternal renaly artery doppler velocimetry in normal and hypertensive pregnancies

Abstract: Maternal Renal Artery Doppler Velocimetry in Normal and Hypertensive Pregnancies by Marius KublickasBackground. The measurement of effective renalplasma flow (ERPF) by calculation of p-aminohippurate (PAH) clearance is an invasive,time-consuming procedure. In nonpregnant hu-mans, the clearance of isotopes can be used tomeasure renal plasma flow, but the use of theseradioactive substances during pregnancy is unsuit-able. A non-invasive method for repetitive assess-ment of renal hemodynamics is needed for use ininvestigations of the kidney in pregnancy. TheDoppler ultrasound technique is entirely non-invasive, simple and quick to carry out and pro-vides instant results. The development of duplexDoppler sonography has allowed non-invasivestudies of blood flow patterns in deep abdominaland pelvic vessels. The acquisition of the Dopplerinformation combined with color flow mappingensures accurate localization of the blood vesseland reliable biood flow velocity measurements. Renal artery blood flow velocity waveformshave been studied in normal and hypertensivepregnancies, but the results to date have been con-tradictory. During normal pregnancy the glomeru-lar filtration rate and renal blood flow increase by50% and 60-80%, respectively. There are oftenappreciable changes in kidney function inpreeclampsia, reflected in the decrement of renalblood flow and glomerular filtration rate. The his-tological abnormalities in the kidney in womenwith preeclampsia and eclampsia are quite welldefined and termed 'glomerular capillary endothe-liosis.' Thus, renal artery Doppler indices in normalpregnancy and in preeclampsia might be affectedconcomitantly with the known renal hemodynamicand morphological changes, and might be of use inrenal function examinations on a routine basis dur-ing pregnancy.Materials and Methods. Nonpregnant women andwomen with normal and hypertensive pregnancieswere studied by color Doppler ultrasonography,renal blood flow velocities being examined at thelevel of segmental arteries.Results and Conclusions. Color flow mappingcombined with the pulsed Doppler technique is areliable means of assessing renal blood flow veloc-ity as expressed in dimensionless indices. The mostsuitable vessels for examination were found to bethose in the middle portion of the kidney. The re-sults suggest that of all indices studied the pulsatil-ity index (Pl) might be more accurate for theevaluation of renal blood flow velocity. This studyclearly showed that repeated measurements shouldbe performed at least at the same level of the arte-rial branching in the kidney. Obtaining reliable Doppler indices required fiveor six cardiac cycles in nonpregnant women butonly three cardiac cycles in pregnant women. The findings demonstrated maternal heart rateto have no influence on renal artery Doppler indi-ces. There were no differences in Doppler indicesbetween the right and left kidney. Renal Doppler indices are significantly higherin pregnant than in nonpregnant women, and thereis no significant change in these indices throughoutnormal pregnancy. Renal artery Doppler indices are lower inwomen with preeclampsia, PIH and chronic hyper-tension than in normal pregnant women. The find-ings suggest that the mechanism of renal autoregu-lation might be altered in preeclampsia, leaving theglomeruli unprotected from increased blood pres-sure. These indices do not distinguish preeclampsiafrom other hypertensive disorders in pregnancy.Thus, renal artery Doppler velocimetry is of limitedvalue for the evaluation of pregnancies complicatedby hypertension. Despite similar central hemodynamic changesand plasma atrial natriuretic peptide (ANP) in-creases during volume expansion, renal vascularresistance, as estimated by renal artery Pl increasedonly in healthy pregnant women and not in patientswith PIH/preeclampsia. It seems that ANP is partlyresponsible for the renal hemodynamic changescaused by volume load, and that this response isaltered in preeclampsia. Renal artery PI was significantly increased inpreeclamptic women afler 60 minutes infusion ofANP at low doses. Whether such variables as bloodpressure and plasma volume status are determinantsof hemodynamic response to ANP remains to beelucidated. Gosling's model seems to be useful for the in-terpretation of PI in low resistance vascular beds,and might provide new information of kidneypathophysiology. Our results emphasize that renal Doppler indi-ces should be interpreted with caution when assess-ing renal blood flow in pregnant women, as otherhemodynamic factors might influence the results.Blood pressure should always be taken into ac-count.Key words: Atrial natriuretic factor; Cyclicguanosine monophosphate; Doppler ultrasound;Kidney; Modeling; Preeclampsia; Pregnancy; Preg-nancy induced hypertension; Pulsatility index; Re-nal artery; Renal blood flow; Repeatability.Stockholm 1966 ISBN 91-628-1931-3