The impact of maternal plasma volume expansion and antihypertensive treatment with intravenous dihydralazine on fetal and maternal hemodynamics during pre-eclampsia: a clinical, echo-Doppler and viscometric study

Hormonal Control of Blood Viscosity

The hemodynamic milieu differs throughout the vascular tree because of varying vascular geometry and blood velocities. Accordingly, the risk of turbulence, which is dictated by the Reynolds and Dean numbers, also varies. Relatively high blood viscosity is needed to prevent turbulence in the left ventricle and aorta, where high-velocity blood changes direction several times. Low blood viscosity is needed in the capillaries, where erythrocytes pass through vessels with a diameter smaller than their own. In addition, higher blood viscosity is necessary when the cardiac output and peak blood velocity increase as a part of a sympathetic response or anemia, which occurs following significant hemorrhage. Blood viscosity, as reflected in systemic vascular resistance and vascular wall shear stress, is sensed, respectively, by cardiomyocyte stretching in the left ventricle and mechanoreceptors for wall shear stress in the carotid sinus. By controlling blood volume and red blood cell mass, the renin-aldosterone-angiotensin system and the systemic vascular resistance response control the hematocrit, the strongest intrinsic determinant of blood viscosity. These responses provide gross control of blood viscosity. Fine-tuning of blood viscosity in transient conditions is provided by hormonal control of erythrocyte deformability. The short half-life of some of these hormones limits their activity to specific vascular beds. Hormones that modulate blood viscosity include erythropoietin, angiotensin II, brain natriuretic factor, epinephrine, prostacyclin E2, antidiuretic hormone, and nitric oxide.

Effect of antihypertensive therapy with alpha-methyldopa on uterine artery Doppler in pregnancies with hypertensive disorders

OBJECTIVES

Antihypertensive drugs lower blood pressure by direct vascular effects or central vasodilatory mechanisms. Their effect on uterine artery Doppler resistance indices in hypertensive disorders of pregnancy is uncertain. This study aimed to evaluate the impact of antihypertensive therapy with alpha-methyldopa on maternal uterine artery Doppler pulsatility index (PI) and resistance index (RI) in women presenting with hypertensive disorders of pregnancy.

METHODS

This was a cross-sectional study of 51 women with pre-eclampsia, 29 with gestational hypertension and 80 matched normotensive controls. Uterine artery PI and RI were measured at recruitment (between 24 and 40 weeks' gestation) and, in the hypertensive groups, 24-48 h after starting alpha-methyldopa. Differences between mild and severe, and between early- and late-onset pre-eclampsia were compared using the Mann-Whitney test. The Wilcoxon rank sum test was used to compare measurements before and after treatment.

RESULTS

Prior to treatment, uterine artery PI and RI were significantly higher in women with pre-eclampsia compared with those with gestational hypertension and controls (P < 0.0001). The median uterine artery PI multiple of the median (MoM) was significantly higher (P < 0.0001) in early-onset than in late-onset pre-eclampsia (1.83 (range, 0.88-3.65) vs. 1.19 (range, 0.91-1.72)) and in severe compared with mild disease (2.26 (range, 2.02-3.65) vs. 1.29 (range, 0.88-2.9)). Uterine artery PI- and RI-MoMs in both pre-eclampsia and gestational hypertension, before and after 34 weeks' gestation, were not affected by alpha-methyldopa treatment.

CONCLUSIONS

Antihypertensive therapy using alpha-methyldopa in women presenting with hypertensive disorders of pregnancy has no significant effect on uterine artery resistance to blood flow, suggesting that it does not impair uteroplacental circulation in these cases.

Maternal and fetal hemodynamic effects induced by nitric oxide donors and plasma volume expansion in pregnancies with gestational hypertension complicated by intrauterine growth restriction with absent end-diastolic flow in the umbilical artery

OBJECTIVE

To evaluate the effect of plasma volume expansion (PVE) and nitric oxide (NO) donors, in addition to antihypertensive therapy for gestational hypertensive pregnancies complicated by intrauterine growth restriction (IUGR) with absent end-diastolic flow (AEDF) in the umbilical artery (UA).

METHODS

This was a case-control study into which 32 gestational hypertensive pregnancies with IUGR and AEDF were enrolled. Sixteen of these were treated with antihypertensive drugs, NO donors and PVE (Group A), and 16, matched for maternal age, gestational age and fetal conditions, were treated with antihypertensive drugs only (Group B). All patients underwent fetal and uteroplacental assessment and maternal echocardiography to evaluate total vascular resistance (TVR) and cardiac output before and 5-14 days after initiation of treatment.

RESULTS

After 5-14 days of treatment, the maternal TVR in Group A fell from 2170 +/- 248 to 1377 +/- 110 dynes.s.cm(-5) (P < 0.01), and that in Group B fell from 2090 +/- 260 to 1824 +/- 126 dynes.s.cm(-5) (P < 0.01), with the reduction being greater in Group A than in Group B (P < 0.01). There was a significant increase in cardiac output in Group A after 5-14 days of treatment vs. baseline (6.19 +/- 0.77 vs. 4.32 +/- 0.66, P < 0.001), and, after treatment, cardiac output was significantly greater in Group A than it was in Group B (6.19 +/- 0.77 vs. 4.70 +/- 0.44, P < 0.001). Reappearance of end-diastolic flow in the UA occurred in 14/16 patients in Group A but in no patients in Group B (87.5% vs. 0%, P < 0.05). The interval between detection of UA-AEDF and delivery was 28 +/- 16 days in Group A and 11 +/- 6 days in Group B (P < 0.05).

CONCLUSION

Administration of NO donors and PVE in gestational hypertensive pregnancies affected by IUGR and UA-AEDF appears to improve both maternal and fetal hemodynamics, inducing prolongation of gestation.

Antenatal dexamethasone and renal vascular resistance in preterm infants

OBJECTIVE

To compare vascular resistance, renal volume and insulin levels in preterm infants with and without antenatal steroids.

METHODS

We studied 61 preterm infants (37 with (group A) and 24 without antecedent of antenatal steroids (group B)). We measured insulin levels at birth in cord blood samples. Ultrasound measurements to evaluate renal arteries resistance index and renal volume were performed during the first 72 h of birth.

RESULTS

Preterm infants from group A tended to have lower weight and gestational age than those from group B. Resistance index in renal arteries was lower in preterm infants with steroid therapy compared with group B (right renal artery 0.73 vs. 0.80; P=0.001, and left renal artery 0.75 vs. 0.79; P=0.01, respectively). Renal volume and insulin levels were not different between the groups. In the multiple regression analysis for factors associated with resistance index of renal arteries, only antenatal steroids use was included in the model (R2=0.13; P=0.003 and R2=0.10; P=0.01 for left and right renal arteries, respectively).

CONCLUSION

Antenatal dexamethasone in preterm infants during the first 72 h of birth seems to decrease resistance index in renal arteries without affecting renal volume and insulin levels.