Perinatal left ventricular performance in fetal sheep: interaction between oxygen ventilation and contractility

Area of Science:

• Cardiovascular Physiology
• Neonatal Adaptation

Background:

• Left ventricular (LV) output increases significantly at birth, coinciding with elevated catecholamines.
• In utero, elevated catecholamines do not increase LV output, suggesting other factors are involved.

Purpose of the Study:

• To test if catecholamines increase contractility in utero but require altered LV loading conditions for output increase.
• To investigate the role of oxygen ventilation in modulating LV output in fetal sheep.

Main Methods:

• Studied nine fetal sheep using conductance and manometric catheters to create LV pressure-volume loops.
• Assessed LV contractility, preload, and afterload under nonventilated and oxygen-ventilated conditions.
• Administered control, dobutamine, and propranolol to evaluate drug effects on LV function.

Main Results:

• Oxygen ventilation increased LV output 1.4-fold, with decreased contractility but improved loading conditions (increased preload, decreased afterload).
• Dobutamine significantly enhanced LV output during ventilation, more so than without ventilation.
• Propranolol similarly reduced contractility and heart rate in both states, but LV output decreased more during ventilation.

Conclusions:

• Oxygen ventilation creates favorable LV loading conditions that enhance the response to catecholamines.
• The transition to extrauterine life involves critical changes in LV loading that optimize cardiovascular function.
• Understanding these loading condition changes is key to managing neonatal cardiovascular adaptation.