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Updated: Feb 20, 2026
Instrumentation of Near-term Fetal Sheep for Multivariate Chronic Non-anesthetized Recordings
Published on: October 25, 2015
The effect of sex and prematurity on the cardiovascular baroreflex response in sheep
Beth J Allison1,2, Vivian Nguyen3, Stephanie R Yiallourou1,2
1The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Victoria, Australia.
Insights
Late preterm birth is a risk factor for adult cardiovascular dysfunction, influenced by sex. These findings highlight potential long-term heart health risks for late preterm infants.
Area of Science:
- Physiology
- Neonatal Medicine
- Cardiovascular Science
Background:
- Late preterm birth (0.9 gestation) is often considered to have minimal long-term health consequences compared to earlier preterm birth.
- The impact of late preterm birth on cardiovascular function into adulthood remains largely unknown.
- Cardiovascular disease is a known risk for very preterm infants, but data for late preterm infants is lacking.
Purpose of the Study:
- To investigate whether late preterm birth leads to persistent cardiovascular dysfunction into adulthood.
- To determine if sex influences the cardiovascular effects of late preterm birth.
- To assess heart rate variability and baroreflex sensitivity in adult sheep following late preterm birth.
Main Methods:
- Sheep were born at late preterm (0.9 gestation) or term.
- At 14 months of age, surgical procedures were performed for catheter and flow probe insertion.
- Conscious adult sheep underwent assessments of heart rate variability and baroreflex sensitivity using vasoactive agents.
Main Results:
- Female ex-preterm sheep exhibited decreased heart rate variability (low-frequency normalized units and LF/HF ratio) at rest.
- Male ex-preterm sheep showed an exaggerated blood pressure response but a blunted heart rate baroreflex response during challenges.
- These results indicate cardiovascular dysfunction in adulthood following late preterm birth, with sex-specific differences.
Conclusions:
- Late preterm birth is identified as a risk factor for adult cardiovascular dysfunction.
- Early signs of cardiovascular dysfunction post-late preterm birth may contribute to later hypertension and heart disease.
- These findings challenge the assumption that late preterm infants are free from long-term morbidities.
New Findings:
What is the central question of this study? Late preterm infants are often assumed to escape long-term morbidities known to impact earlier preterm offspring. Is this true for the cardiovascular system? What is the main finding and its importance? We show that late preterm birth is a risk factor for cardiovascular dysfunction in early adulthood and is influenced by sex. Early signs of cardiovascular dysfunction might predispose to heart disease in adulthood. Very preterm infants have an increased risk of cardiovascular disease; however, the effects of a late preterm birth on future cardiovascular function are not known. We hypothesized that after a late preterm birth, the well-described impairments in heart rate variability and baroreflex sensitivity would persist into adulthood. To test this hypothesis, sheep born preterm (0.9 gestation; nine male and seven female) or term (11 male and six female) underwent surgery at 14 months of age for insertion of femoral arterial and venous catheters and a femoral flow probe. After recovery, heart rate variability was assessed, followed by a baroreflex challenge (using the vasoactive agents phenylephrine and sodium nitroprusside) in conscious adult lambs. Our data demonstrate decreased low-frequency normalised units (LFnu) and low-frequency/high-frequency ratio in female but not male ex-preterm sheep at rest. When challenged, mature male ex-preterm sheep have an increased blood pressure response but dampened heart rate baroreflex response. We show that even a late preterm birth leads to cardiovascular dysfunction in adulthood. These early signs of cardiovascular dysfunction might underpin the later hypertension and increased risk of heart disease observed in adults born preterm. These findings are particularly important because late preterm infants are often assumed to escape the long-term morbidities known to impact on very preterm and extremely preterm offspring.
