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Cardiac blood flow studies in fetuses with haemoglobin Bart's disease
Insights
Fetuses with hemoglobin (Hb) Bart's disease exhibit significantly increased cardiac output due to anemia. Their hearts compensate effectively, maintaining normal blood flow velocity despite severe anemia.
Area of Science:
- Fetal Cardiology
- Hematology
- Physiology
Background:
- Hemoglobin (Hb) Bart's disease causes severe fetal anemia.
- Understanding fetal cardiac adaptation to anemia is crucial for management.
Purpose of the Study:
- To investigate cardiac function in fetuses with Hb Bart's disease.
- To assess the compensatory mechanisms in response to severe anemia.
Main Methods:
- Blood flow across atrioventricular valves and outflow tracts measured.
- Study included 55 normal fetuses and 32 fetuses with Hb Bart's disease.
- Gestation ranged from 18 to 26 weeks.
Main Results:
- Volume flow increased with gestation in both groups, higher in affected fetuses.
- Mean blood flow velocities remained unchanged.
- Cardiac chambers and outflow tracts enlarged up to twice normal size in affected fetuses.
- Increased cardiac output was similar in hydropic and non-hydropic fetuses.
Conclusions:
- Fetuses with severe anemia demonstrate remarkable cardiac compensation.
- The Frank-Starling mechanism supports increased cardiac output.
- Cardiac failure is not observed at the onset of hydropic changes.
Abstract:
Blood flow across the atrioventricular valves and outflow tracts was measured in 55 normal fetuses and 32 fetuses with haemoglobin (Hb) Bart's disease between 18 and 26 weeks of gestation. The mean velocities remained unchanged in both normal and affected fetuses over the gestations studied. The volume flow across both atrioventricular valves and outflow tracts increased as the gestation advanced in both normal and affected fetuses, but was significantly higher in affected than in normal fetuses. The same magnitude of increased flow was found in both hydropic and non-hydropic fetuses with Hb Bart's disease. These findings suggest that fetuses with severe and long-standing anaemia have a remarkable cardiac compensatory mechanism for the maintenance of tissue oxygenation. In response to anaemia and circulatory loading, the cardiac chambers and outflow tracts enlarge proportionately up to twice the normal values. Because of this response and the operation of the Frank-Starling mechanism, the heart is able to maintain a normal mean velocity of propulsion and the net output is increased to two to three times that in normal fetuses. Hydropic changes in these anaemic fetuses appear unrelated to cardiac failure as cardiac failure is not observed at the time that hydropic changes develop.