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Fetal myocardial responses to long-term hypoxemia
1Center for Perinatal Biology, Loma Linda University School of Medicine, California 92350, USA. rgilbert@ccmail.llu.edu
Summary
High altitude hypoxemia in fetal sheep significantly reduced cardiac output, primarily impacting right ventricular function. Altered calcium handling in heart muscle cells likely explains this decreased contractility.
Area of Science:
- Cardiovascular Physiology
- Fetal Development
- Altitude Medicine
Background:
- High altitude environments pose challenges to fetal development due to reduced oxygen availability (hypoxemia).
- Understanding the impact of chronic hypoxemia on the fetal cardiovascular system is crucial for identifying potential health risks.
Purpose of the Study:
- To investigate the effects of prolonged high altitude hypoxemia on fetal sheep cardiac function.
- To explore the underlying mechanisms of altered cardiac contractility in hypoxemic fetuses, focusing on calcium handling.
Main Methods:
- Fetal sheep were exposed to high altitude hypoxemia from day 30 of gestation for 110 days.
- Cardiac output, ventricular outputs, heart rate, preload, and afterload were measured.
- Papillary muscle contractility and calcium sensitivity were assessed in isolated cardiac tissues.
Main Results:
- Cardiac output decreased by 24% in hypoxemic fetuses, mainly due to reduced right ventricular output.
- Increased afterload contributed minimally to the cardiac output reduction.
- Isolated papillary muscles showed reduced maximal tension but increased calcium sensitivity, suggesting altered excitation-contraction coupling.
Conclusions:
- Chronic high altitude hypoxemia impairs fetal cardiac output and contractility.
- Alterations in the fetal heart's calcium handling pathways, not channel numbers, likely underlie reduced contractility.
- Further research is needed to pinpoint the exact mechanisms, possibly involving sarcoplasmic reticulum calcium storage or myofilament sensitivity.