Changes in left thoracic duct lymph flow during progressive anemia in the ovine fetus

Myocardial performance and its acute response to angiotensin II infusion in fetal sheep adapted to chronic anemia

Fetal chronic anemia causes lengthening of cardiomyocytes. In adults, severe left ventricular overload may lead to irreversible ventricular dysfunction. We hypothesized that in sheep fetuses with chronic anemia, remodeled myocardium would less successfully respond to angiotensin II (AT II) infusion than in fetuses without anemia. A total of 14 ewes with twin pregnancy underwent surgery at 113 ± 1 days of gestation. After a recovery period, anemia was induced by isovolumic hemorrhage in 1 fetus of each pair. At 126 ± 1 days of gestation, longitudinal myocardial velocities of the right (RV) and left (LV) ventricles were assessed at the level of the atrioventricular valve annuli via tissue Doppler imaging. Cardiac outputs were calculated by pulsed Doppler ultrasound. All measurements were performed at baseline and during fetal AT II infusion. Fetal serum cardiac natriuretic peptide (N-terminal peptide of proatrial natriuretic peptide [NT-proANP] and B-type natriuretic peptide [BNP]) concentrations were determined. Nine ewes successfully completed the experiment. At baseline, ventricular free wall thicknesses, cardiac outputs, and NT-proANP levels were significantly greater in the anemic fetuses than in the controls. The LV isovolumic contraction velocity (IVCV) acceleration and isovolumic relaxation velocity (IVRV) deceleration were lower (P < .05) in the anemic fetuses than in the controls. In the anemic fetuses, there was a positive correlation (R = .93, P < .01) between RV IVRV deceleration and NT-proANP concentration. Angiotensin II infusion increased (P < .05) LV IVCV acceleration in the anemic fetuses. We conclude that in anemic sheep fetuses, myocardial adaptation is associated with impaired LV early contraction and relaxation. However, the LV can improve its contractility with an inotropic stimulus, even in the presence of increased afterload.

Anemia, chronic renal disease and congestive heart failure--the cardio renal anemia syndrome: the need for cooperation between cardiologists and nephrologists

Many patients with congestive heart failure (CHF) fail to respond to maximal CHF therapy and progress to end stage CHF with many hospitalizations, poor quality of life (QoL), progressive chronic kidney disease (CKD) which can lead to end stage kidney disease (ESKD), or die of cardiovascular complications within a short time. One factor that has generally been ignored in many of these people is the fact that they are often anemic. The anemia in CHF is due mainly to the frequently-associated CKD but also to the inhibitory effects of cytokines on erythropoietin production and on bone marrow activity, as well as to their interference with iron absorption from the gut and their inhibiting effect on the release of iron from iron stores. Anemia itself may further worsen cardiac and renal function and make the patients resistant to standard CHF therapy. Indeed anemia in CHF has been associated with increased severity of CHF, increased hospitalization, worse cardiac function and functional class, the need for higher doses of diuretics, progressive worsening of renal function and reduced QoL. In both controlled and uncontrolled studies of CHF, the correction of the anemia with erythropoietin (EPO) and oral or intravenous (IV) iron has been associated with improvement in many cardiac and renal parameters and an increased QoL. EPO itself may also play a direct role in improving the heart unrelated to the improvement of the anemia--by reducing apoptosis of cardiac and endothelial cells, increasing the number of endothelial progenitor cells, and improving endothelial cell function and neovascularization of the heart. Anemia may also play a role in the worsening of acute myocardial infarction and chronic coronary heart disease (CHD) and in the cardiovascular complications of renal transplantation. Anemia, CHF and CKD interact as a vicious circle so as to cause or worsen each other- the so-called cardio renal anemia syndrome. Only adequate treatment of all three conditions can prevent the CHF and CKD from progressing.

The effects of anaemia as a programming agent in the fetal heart

The intrauterine environment plays a powerful role in determining the life-long risk of cardiovascular disease. A number of stressors are well known to affect the development of the cardiovascular system in utero including over/under maternal nutrition, excess glucocorticoid and chronic hypoxia. Chronic fetal anaemia in sheep is a complex stressor that alters cardiac loading conditions, causes hypoxic stress and stimulates large changes in flow to specific tissues, including large increases in resting coronary blood flow and conductance. Decreased viscosity can account for approximately half of the increased flow. It appears that immature hearts are 'plastic' in that increases in coronary conductance with fetal anaemia persist into adulthood even if the anaemia is corrected before birth. These large changes in conductance are possible only through extensive remodelling of the coronary tree. Adult hearts that were once anaemic in utero are more resistant to hypoxic stress as adults but it is not known whether such an adaptation would be deleterious in later life. These studies indicate the need for investigation into the basic mechanisms of coronary tree remodelling in the immature myocardium. New information on these mechanisms is likely to lead to better prevention of and therapies for adult-onset coronary disease.

Amniotic fluid and fetal urinary responses to severe placental insufficiency in sheep

OBJECTIVE

Our purpose was to test the hypothesis that severe placental insufficiency leads to reductions in fetal urine production and amniotic fluid volume in late-gestation fetal sheep.

STUDY DESIGN

At 0.85 of gestation, chronically catheterized fetal sheep with ligated urachus were either embolized for 5 days by repeated injection of boluses of 15-microm microspheres into the common fetal umbilical artery until fetal arterial oxygen content was reduced by 50% (n = 6) or were infused with saline solution (n = 6). Amniotic fluid volume was measured daily before embolization by means of an indicator dilution technique and by drainage at autopsy. Fetal urine production, heart rate, and mean arterial blood pressure were measured continuously for 1 hour before embolization and 1 hour after embolization each day. Fetal arterial blood gases, oxygen content, electrolytes, and osmolality were also monitored.

RESULTS

Five days of placental insufficiency, which reduced fetal arterial oxygen content by 50% and arrested fetal growth, resulted in a reduced amniotic fluid volume without a reduction in fetal urine production. Compared with that of controls, amniotic fluid volume was reduced over the 5-day period by 547 +/- 144 mL (-62%, P <.01). Amniotic fluid composition was also altered, with a significant increase in lactate and sodium concentrations and osmolality on days 4 to 5. On days 2 to 5, there was a progressive increase in amniotic fluid osmolality above that of controls, which paralleled the changes in amniotic fluid sodium concentration (P <.05). Fetuses became hypertensive on days 2 to 4 of embolization, although this response was attenuated by day 5.

CONCLUSIONS

Chronic severe placental insufficiency caused a reduction in amniotic fluid volume not attributable to reduced fetal urine production. Changes in amniotic fluid composition induced by placental insufficiency suggest an excess intramembranous absorption of amniotic fluid water, in relation to solutes, into the fetal and maternal compartments, which may lead to the development of oligohydramnios.