Fetal body weight and the development of the control of the cardiovascular system in fetal sheep

Abstract

Reduced birth weight predisposes to cardiovascular diseases in later life. We examined in fetal sheep at 0.76 (n = 18) and 0.87 (n = 17) gestation whether spontaneously occurring variations in fetal weight affect maturation of autonomic control of cardiovascular function. Fetal weights at both gestational ages were grouped statistically in low (LW) and normal weights (NW) (P < 0.01). LW fetuses were within the normal weight span showing minor growth dysproportionality at 0.76 gestation favouring heart and brain, with a primary growth of carcass between 0.76 and 0.87 gestation (P < 0.05). While twins largely contributed to LW fetuses, weight differences between singletons and twins were absent at 0.76 and modest at 0.87 gestation, underscoring the fact that twins belong to normality in fetal sheep not constituting a major malnutritive condition. Mean fetal blood pressure (FBP) of all fetuses was negatively correlated to fetal weight at 0.76 but not 0.87 gestation (P < 0.05). At this age, FBP and baroreceptor reflex sensitivity were increased in LW fetuses (P < 0.05), suggesting increased sympathetic activity and immaturity of circulatory control. Development of vagal modulation of fetal heart rate depended on fetal weight (P < 0.01). These functional associations were largely independent of twin pregnancies. We conclude, low fetal weight within the normal weight span is accompanied by a different trajectory of development of sympathetic blood pressure and vagal heart rate control. This may contribute to the development of elevated blood pressure in later life. Examination of the underlying mechanisms and consequences may contribute to the understanding of programming of cardiovascular diseases.

Heart rate–mediated blood pressure control in preterm fetal sheep under normal and hypoxic–ischemic conditions

“…Other studies have little to no variation in GA, or their results lack the temporal resolution required to compare results with our findings directly (16,17,30,31). Second, the discrepancies may be the result of methodological differences.…”

“…Other studies found a decrease in baroreflex sensitivity during development (30)(31)(32). Several studies showed no significant maturation of the baroreflex sensitivity (16,17). There may be several explanations for these conflicting findings.…”

“…There is, however, conflicting evidence on the fetal and postnatal development of baroreceptor reflex function. Although some studies show increasing baroreflex sensitivity with age, other studies show no significant maturational change (15)(16)(17)(18). The cardiovascular system responds to hypoxia-ischemia by changing heart rate and redistributing cardiac output to preserve the limited energy resources and maintain adequate supply to the brain.…”

Nonlinear properties of vagal and sympathetic modulations of heart rate variability in ovine fetus near term

“…RMSSD is the square root of the mean of the sum of the squares of differences between adjacent R-R intervals of ECG. RMSSD is a linear short-term measure of fHRV that reflects modulations of fHRV by vagal activity and was calculated as described earlier (6,7,8). To assess the contribution of sympathetic and vagal modulations to linear and nonlinear fHRV properties, we also studied the complexity of the fHRV with its linear and nonlinear parts.…”

“…The fHRV was further analyzed as described earlier (8). Briefly, the artifacts were visually controlled for and removed manually (Watisa Signal Processing Software, Institute for Medical Statistics and Documentation, University of Jena).…”