Comparison of early postnatal hemodynamics in neonates born at high-altitude or low-altitude using USCOM: a pilot study

Abstract

This study's purpose is to compare early postnatal hemodynamics between neonates from high- and low-altitude regions using Ultrasound Cardiac Output Monitor (USCOM) measurements. We prospectively enrolled hemodynamically stable neonates from Shanghai Children's Hospital (low-altitude group, sea level) and People's Hospital of Shigatse City (high-altitude group, 3850 m) between January and June 2024. Hemodynamic parameters derived from USCOM and clinical data (including oxygen saturation, heart rate, blood pressure, and hemoglobin levels) were obtained on postnatal day 7. The Mann-Whitney U test was employed to compare the differences between groups. The analysis included 80 neonates (40 per group) with comparable baseline characteristics, including gender, gestational age, weight, length, hemoglobin, oxygen carrying capacity, heart rate, and diastolic and mean blood pressure (p > 0.05). Compared to low-altitude group, high-altitude group demonstrated significantly higher stroke volume index (SVI), cardiac output (CO), cardiac index (CI), Smith-Madigan inotropy index (SMII), and systolic blood pressure (p < 0.05). Subgroup analysis indicated that preterm infants in the high-altitude group showed increased SVI, CO, CI, and SMII with lower systemic vascular resistance index (SVRI) (p < 0.05), whereas term infants in the group exhibited elevated CI, SMII, and systolic and mean blood pressure, compared to infants in the low-altitude group, respectively (p < 0.05).

Conclusion: Neonates born at high altitude may maintain circulatory adaptation through enhanced myocardial contractility and cardiac performance, while the compensatory responses seem to differ between preterm infants (Frank-Starling mechanism) and term infants (sympathetic-driven regulation).

What is known: • Neonates born at high altitude demonstrate lower SpO2 and cardiovascular adaptations to hypobaric hypoxia. • While USCOM enables non-invasive hemodynamic monitoring in neonates, physiological differences at different altitude levels may affect the interpretation of USCOM measurements.

What is new: • First USCOM-derived comparison reveals elevated cardiac efficiency (higher SVI, CI, and SMII) in neonates born at high-altitude. • The compensatory mechanisms for hypobaric hypoxia differed according to cardiovascular maturity: preterm infants relied on the Frank-Starling mechanism, whereas term infants exhibited sympathetic activation.

Keywords: Hemodynamic parameters; High-altitude; Neonate; Oxygen saturation; Ultrasound Cardiac Output Monitor.