Key result
Hemorrhage drops fetal lamb heart rate by ~39 bpm, indicating a functional baroreflex.
Why the study?
The heart rate and blood pressure responses to hemorrhage in fetal sheep at different gestational ages compared to adult sheep were not fully characterized.
How do heart rate and blood pressure respond to hemorrhage stress in fetal versus adult sheep?
Population
24 chronically instrumented fetal lambs (81-144 days gestation) and 6 conscious adult nonpregnant ewes
Comparison
Hemorrhage of 15% estimated blood volume vs baseline; fetal vs adult response
Design
Preclinical physiological study
Authors
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May warrant caution interpreting fetal vital signs during blood loss; extends ovine developmental physiology but leaves open human translation.
How do heart rate and blood pressure respond to hemorrhage stress in fetal versus adult sheep?
The study demonstrates that fetal lambs exhibit a paradoxical bradycardia in response to 15% hemorrhage, unlike the tachycardia seen in adults, indicating the presence of a functional baroreflex early in gestation.
Macdonald et al. (1980) studied Hemorrhage stress (n=30). Hemorrhage vs. Adult ewes was evaluated on Heart rate and blood pressure responses. Hemorrhage of 15% blood volume caused a heart rate drop of 39 ± 8 beats/min in fetal lambs and an increase of 25 ± 6 beats/min in adult ewes, indicating a functional baroreflex by 81 days gestation.
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