Renal arterial blood flow velocity waveforms in pregnant women

Maternal renal artery Doppler sonographic changes in pregnancy-induced hypertension in South West Nigeria

BACKGROUND

To evaluate the renal arterial hemodynamic changes caused by pregnancy-induced hypertension using Doppler ultrasonography.

MATERIALS AND METHODS

Eighty (80) subjects with pregnancy-induced hypertension (PIH) and 160 controls (80 pregnant normotensive women and 80 healthy, non-pregnant women) underwent triplex renal sonography prospectively to determine their renal volumes and right renal artery Doppler indices.

RESULTS

The peak systolic velocity, end diastolic velocity, pulsatility index, systolic/diastolic ratio and acceleration time were respectively significantly higher in the PIH group (68.67 cm/s, 21.55 cm/s, 1.23, 3.38, 123.2 ms) than the pregnant, normotensive group (65.19 cm/s, 20.27 cm/s, 0.88, 3.35, 61.14 ms) and healthy, non-pregnant group (52.06 cm/s, 18.27 cm/s, 0.84, 2.90, 68.48 ms). Resistivity index was also increased in the PIH group, but this was not statistically significant. Conversely, the systolic acceleration was significantly lower in the PIH group (6.06 m/s(2)) compared to the pregnant, normotensive group (11.82 m/s(2)) and healthy, non-pregnant group (8.26 m/s(2)). The right renal volume of the PIH group (132.76 cm(3)) was significantly higher that of the pregnant, normotensive group (125.29 cm(3)) and healthy, non-pregnant group (91.66 cm(3)). The same pattern was observed in the left renal volume which was 168.78 cm(3), 164.95 cm(3) and 113.80 cm(3) in the study groups, respectively.

CONCLUSION

Renal Doppler ultrasound is clinically relevant in the diagnosis and follow-up of renal complications in patients with pregnancy-induced hypertension.

Prospective evaluation of renal artery resistance and pulsatility indices in normal pregnant women

OBJECTIVES

To establish normal values for renal artery resistance index (RI) and pulsatility index (PI) during gestation and, by comparison with non-pregnant controls, to determine if pregnancy affects these indices.

METHODS

This was a prospective longitudinal study involving 36 normal pregnant women who underwent a total of 280 examinations at 4-week intervals from the 6th gestational week to the end of pregnancy. High-resolution ultrasound equipment with 'triplex' Doppler facilities was used. RI and PI were obtained for the main arteries of both kidneys. The same evaluation was performed in 15 non-pregnant women as controls.

RESULTS

The mean RI in pregnant and non-pregnant women was the same (0.65 +/- 0.03 for controls and 0.65 +/- 0.02 for the pregnant women). For PI, the values were 1.25 +/- 0.12 for non-pregnant women and 1.18 +/- 0.09 for pregnant women. The only statistical difference (P < 0.05) was found between the PI of the left renal artery in the control group (1.29 +/- 0.20) and that in the pregnant group at the 8-12-week interval of gestational age (1.08 +/- 0.14).

CONCLUSIONS

No significant alterations in renal artery RI and PI occur during normal pregnancy, except for in a subgroup of patients between 8 and 12 weeks of gestation.

Reproducibility of pulsed Doppler measurements of the maternal renal circulation in normal pregnancies and those with pregnancy-induced hypertension

OBJECTIVE

To assess the inter- and intraobserver reproducibilities of pulsed Doppler measurements of the maternal renal circulation in normal pregnancies and those affected by pregnancy-induced hypertension.

MATERIALS AND METHODS

Color and pulsed Doppler ultrasound was used to measure acceleration time and resistance index in the renal segmental and interlobar arteries. For the investigation of interobserver reproducibility, two sonographers performed measurements blindly in six normal pregnant women and 14 women with pregnancy-induced hypertension between 28 and 36 weeks' gestation. A second group of 10 patients between 30 and 35 weeks' gestation were examined by one sonographer to assess the level of intraobserver reproducibility of measurements. For each patient in this group, the flow waveform was measured three times in succession. Calculations of the intraclass correlation coefficient Ri were used to determine the level of reproducibility.

RESULTS

The interobserver Ri and intraobserver Ri for acceleration time in the segmental artery were 0.95 and 0.96 and for the interlobar artery they were 0.97 and 0.98, respectively. For the resistance index, these values were 0.01 and 0.01 in the segmental artery and 0.52 and 0.29 in the interlobar artery.

CONCLUSION

Both the inter- and intraobserver reproducibility of acceleration time measurements in the renal segmental and interlobar arteries were clinically acceptable but the equivalent reproducibilities of resistance index measurements were poor.

Doppler velocimetry of maternal renal circulation in pregnancy-induced hypertension

PURPOSE

The purpose of this study was to evaluate whether the Doppler waveforms of the maternal main renal, segmental, and interlobar arteries are altered in women with pregnancy-induced hypertension (PIH) compared with healthy pregnant women.

METHODS

Flow waveforms of the maternal main renal, segmental, and interlobar arteries were obtained from 42 healthy pregnant women between 24 and 41 weeks of gestation and 21 women with PIH between 28 and 40 weeks of gestation using pulsed Doppler sonography. We used spectral analysis to measure the peak systolic and end-diastolic velocities and the acceleration time. The presence or absence of the normal early systolic compliance peak-reflective-wave complex (ESP) was assessed in only the main renal artery.

RESULTS

The acceleration times of the segmental and interlobar arteries were significantly prolonged in the PIH group compared with those in the healthy pregnant women. Of the 21 women with PIH, 3 showed loss of the ESP in the renal artery, but these changes were not significant.

CONCLUSIONS

Decreased systolic acceleration and the absence of ESP, the hemodynamic indicators for significant proximal stenosis, suggest that severe stenosis or continuous vasospasm in the proximal arteries, such as the main renal or segmental artery, may be implicated in the pathogenesis of PIH.

Pulsed Doppler US findings of renal interlobar arteries in pregnancy-induced hypertension

PURPOSE

To evaluate whether Doppler ultrasonographic (US) velocimetry in renal interlobar arteries is altered in women with pregnancy-induced hypertension (PIH) compared with that in healthy pregnant and nonpregnant women.

MATERIALS AND METHODS

Flow waveform measurements in renal interlobar arteries were obtained in 39 nonpregnant women, 77 healthy pregnant women at 16-40 weeks gestation, and 15 women with PIH at 28-39 weeks gestation by using color and pulsed Doppler US.

RESULTS

In the nonpregnant group, the mean (+/- SD) peak systolic velocity, end-diastolic blood flow velocity, resistive index, and acceleration time were 0.34 m/sec +/- 0.08, 0.14 m/sec +/- 0.03, 0.62 m/sec +/- 0.07, and 52.3 m/sec +/- 13.7, respectively. In the healthy pregnant group, the peak systolic and end-diastolic blood flow velocities at 16 weeks gestation had decreased greatly by 40 weeks gestation. However, the values of other indexes in this group did not change with gestational age. In the PIH group, the acceleration time values were greatly prolonged compared with those in the other groups.

CONCLUSION

Acceleration time is one of the hemodynamic parameters of substantial upstream stenosis. These findings suggest that severe stenosis or continuous vasospasm in the proximal arteries, such as the main renal artery and segmental artery, might be implicated in the pathogenesis of PIH.

Renal haemodynamics and tubular function in human pregnancy

In human pregnancy, effective renal plasma flow and glomerular filtration rate increase to levels 50-80% above non-pregnant values. The increments occur shortly after conception, persist throughout the second trimester and reduce slightly in late pregnancy. The hyperfiltration of pregnancy does not seem to be a potentially damaging process, as intraglomerular pressure remains unchanged. The increased excretion of glucose and other nutrients, as well as uric acid and protein, is related in part to altered tubular function. Renal physiology is altered so much in pregnancy that non-pregnant norms cannot be used in antenatal care.

Doppler velocimetry of maternal renal interlobar arteries in pregnancy-induced hypertension

OBJECTIVES

To evaluate whether Doppler velocimetry of maternal renal interlobar arteries is altered in patients with hypertensive disorders of pregnancy (PIH).

METHODS

Flow velocity waveforms (FVWs) were obtained, by means of color and pulsed Doppler ultrasound, from the renal artery and two interlobar arteries in the right kidney of 46 normal pregnant women and 10 patients with PIH between 20 and 39 weeks' gestation. Statistical analyses of resistance indices (RI) were performed by regression analysis, paired and unpaired t-tests.

RESULTS

RI values of renal and interlobar arteries in normal patients did not change significantly with gestational age. Interlobar arteries had significantly lower RI values than corresponding main renal arteries (T = 3.88, P < 0.001). No significant differences in FVWs of renal (T = 1.86, P = 0.068) and interlobar arteries (T = 0.85, P = 0.399) were found between normal and hypertensive patients. A statistical power analysis confirmed that our sample size was sufficient to detect a difference in RI of 0.10, with alpha = 0.05 and beta = 0.80.

CONCLUSIONS

FVWs of the renal and interlobar arteries are not altered in patients with mild PIH.

Assessment of the renal circulation during pregnancy with color Doppler ultrasonography

OBJECTIVES

A non-invasive method of assessing the renal vasculature during pregnancy would be useful in the management of patients with renal dysfunction resulting from preeclampsia or chronic renal disease. The objectives of this study were to determine (1) whether color ultrasonography during pregnancy facilitates Doppler interrogation of renal and intrarenal arteries, allowing (2) the assessment of differences between waveforms from nonpregnant and pregnant women and (3) the analysis of waveform variability throughout the kidney and between the right and left kidneys.

STUDY DESIGN

In a cross-sectional study renal and intrarenal artery flow waveforms were obtained from women in early (12 to 19 weeks; n = 8), mid (20 to 29 weeks; n = 11), and late (30 to 37 weeks; n = 14) pregnancy with eight age-matched, nonpregnant women acting as controls. Waveforms were analyzed for pulsatility index, resistive index, and systolic/diastolic ratio.

RESULTS

Left or right renal and upper- and lower-pole interlobar artery waveforms were obtained from all women. The mean pulsatility index values for the nonpregnant women were not significantly different from those women in early, mid, or late pregnancy. In the nonpregnant women, the left renal artery pulsatility index (1.13 +/- 0.13) was greater than the left lower interlobular artery pulsatility index (0.91 +/- 0.08; p < 0.05). During pregnancy renal and interlobar artery pulsatility index values were greater than those for the corresponding interlobular arteries, but the differences were not significant. Mean renal and intrarenal artery pulsatility index values were greater on the right, but the difference was significant only for the lower interlobular artery in midpregnancy.

CONCLUSIONS

Pregnancy does not significantly affect renal and intrarenal artery flow waveforms, nor are there significant differences between waveforms from the renal and interlobar arteries.