Elevated Blood Pressure with Reduced Left Ventricular and Aortic Dimensions in Adolescents Born Extremely Preterm

Neonatal hyperoxia depletes pulmonary vein cardiomyocytes in adult mice via mitochondrial oxidation

Supplemental oxygen given to preterm infants has been associated with permanently altering postnatal lung development. Now that these individuals are reaching adulthood, there is growing concern that early life oxygen exposure may also promote cardiovascular disease through poorly understood mechanisms. We previously reported that adult mice exposed to 100% oxygen between postnatal days 0 and 4 develop pulmonary hypertension, defined pathologically by capillary rarefaction, dilation of arterioles and veins, cardiac failure, and a reduced lifespan. Here, Affymetrix Gene Arrays are used to identify early transcriptional changes that take place in the lung before pulmonary capillary rarefaction. We discovered neonatal hyperoxia reduced expression of cardiac muscle genes, including those involved in contraction, calcium signaling, mitochondrial respiration, and vasodilation. Quantitative RT-PCR, immunohistochemistry, and genetic lineage mapping using Myh6^CreER; Rosa26^RmT/mG mice revealed this reflected loss of pulmonary vein cardiomyocytes. The greatest loss of cadiomyocytes was seen within the lung followed by a graded loss beginning at the hilum and extending into the left atrium. Loss of these cells was seen by 2 wk of age in mice exposed to ≥80% oxygen and was attributed, in part, to reduced proliferation. Administering mitoTEMPO, a scavenger of mitochondrial superoxide during neonatal hyperoxia prevented loss of these cells. Since pulmonary vein cardiomyocytes help pump oxygen-rich blood out of the lung, their early loss following neonatal hyperoxia may contribute to cardiovascular disease seen in these mice, and perhaps in people who were born preterm.

Impact of preterm birth on the developing myocardium of the neonate

BackgroundGlobally, ∼10% of infants are born before full term. Preterm birth exposes the heart to the demands of postnatal cardiovascular function before cardiac development is complete. Our aim was to examine, in hearts collected from infants at autopsy, the effects of preterm birth on myocardial structure and on cardiomyocyte development.Methods and resultsHeart tissue was collected at perinatal autopsies of 16 infants who died following preterm birth between 23 and 36 weeks of gestation, and survived for 1-42 days; the hearts of 37 appropriately grown stillborn infants, aged 20-40 weeks of gestation, were used for comparison. Using confocal microscopy and image analysis, cardiomyocyte proliferation, maturation, ploidy, and size were quantified, and interstitial collagen and myocardial capillarization were measured. Preterm birth resulted in a marked reduction in the proliferation of cardiomyocytes relative to age-matched stillborn infant controls (preterm vs. control P<0.0001). In contrast, preterm birth did not affect heart weight, capillarization, interstitial collagen or cardiomyocyte maturation, ploidy, and size.ConclusionsPreterm birth appears to lead to an abrupt reduction in cardiomyocyte cell division. This reduced cardiomyocyte proliferation in preterm infants may adversely impact upon the final number of cardiomyocytes which may reduce cardiac functional reserve, and impair the reparative capacity of the myocardium.

The Preterm Heart in Childhood: Left Ventricular Structure, Geometry, and Function Assessed by Echocardiography in 6-Year-Old Survivors of Periviable Births

BACKGROUND

Preterm birth has been associated with increased risk of cardiovascular morbidity in adult life. We evaluated whether preterm birth is associated with deviating cardiac structure and function before school start.

METHODS AND RESULTS

In total, 176 children aged 6 years and born extremely preterm (EXPT; gestational age of 22-26 weeks) and 134 children born at term (control [CTRL]) were studied. We used echocardiography to assess left heart dimensions, geometry, and functions. Recording and off-line analyses of echocardiographic images were performed by operators blinded to group belonging. Body size, blood pressure, and heart rate were also measured. Rates of family history of cardiovascular disease and sex distribution were similar in the EXPT and CTRL groups. Heart rate and systolic blood pressure did not differ, whereas diastolic blood pressure was slightly higher in EXPT than CTRL participants. After adjusting for body surface area, left ventricular length, width, and aortic valve annulus diameter were 3% to 5% smaller in EXPT than CTRL participants. Left ventricular longitudinal shortening and systolic tissue velocity were 7% to 11% lower, and transversal shortening fraction was 6% higher in EXPT than CTRL participants. The EXPT group also exhibited lower atrial emptying velocities than the CTRL group. Sex, fetal growth restriction, or a patent ductus arteriosus in the neonatal period did not contribute to cardiac dimensions or performance.

CONCLUSIONS

Six-year-old children born extremely preterm exhibit a unique cardiac phenotype characterized by smaller left ventricles with altered systolic and diastolic functions than same-aged children born at term.

Preterm Birth: Long Term Cardiovascular and Renal Consequences

BACKGROUND

Cardiovascular and chronic kidney diseases are a part of noncommunicable chronic diseases, the leading causes of premature death worldwide. They are recognized as having early origins through altered developmental programming, due to adverse environmental conditions during development. Preterm birth is such an adverse factor. Rates of preterm birth increased in the last decades, however, with the improvement in perinatal and neonatal care, a growing number of preterm born subjects has now entered adulthood. Clinical and experimental evidence suggests that preterm birth is associated with impaired or arrested structural or functional development of key organs/systems making preterm infants vulnerable to cardiovascular and chronic renal diseases at adulthood. This review analyzes the evidence of such cardiovascular and renal changes, the role of perinatal and neonatal factors such as antenatal steroids and potential pathogenic mechanisms, including developmental programming and epigenetic alterations.

CONCLUSION

Preterm born subjects are exposed to a significantly increased risk for altered cardiovascular and renal functions at young adulthood. Adequate, specific follow-up measures remain to be determined. While antenatal steroids have considerably improved preterm birth outcomes, repeated therapy should be considered with caution, as antenatal steroids induce long-term cardiovascular and metabolic alterations in animals' models and their involvement in the accelerated cellular senescence observed in human studies cannot be excluded.

Lower systolic blood pressure at age 7 y in low-birth-weight children who received iron supplements in infancy: results from a randomized controlled trial

Background: Low birth weight (LBW) (≤2500 g) is associated with iron deficiency in infancy and high blood pressure (BP) later in life.Objective: We investigated the effect of iron supplementation that was given to LBW infants on midchildhood BP.Design: The study was a randomized, double-blind, controlled trial that included 285 marginally LBW (2000-2500-g) infants at 2 Swedish centers between May 2004 and November 2007. The infants were randomly assigned to receive a placebo or 1 or 2 mg Fe · kg^-1 · d^-1 from 6 wk to 6 mo of age. In secondary analyses at the age of 7 y, systolic blood pressure (SBP), diastolic blood pressure (DBP), and the prevalence of children with BP within the hypertensive range (>90th percentile) were compared between the groups.Results: BP was analyzed via intention to treat in 189 children (66%). The mean ± SD SBP was 103 ± 8.1, 101 ± 7.5, and 101 ± 7.8 mm Hg in children who had received the placebo (n = 70), 1 mg Fe · kg^-1 · d^-1 (n = 54), or 2 mg Fe · kg^-1 · d^-1 (n = 65), respectively. When the iron-supplemented groups were combined in covariate-adjusted analyses, the mean SBP in LBW children who had received iron supplementation in infancy was 2.2 mm Hg (95% CI: 0.3, 4.2 mm Hg) lower than in those who were unsupplemented (P = 0.026). Multivariate logistic regression showed that iron supplementation in infancy reduced the odds of having an SBP within the hypertensive range at 7 y of age (OR: 0.32; 95% CI: 0.11, 0.96). For DBP, there were no significant differences between the intervention groups.Conclusions: LBW children who receive iron supplementation (1 or 2 mg Fe · kg^-1 · d^-1) in infancy have lower SBP at 7 y. This (to our knowledge) novel observation suggests that the increased risk of hypertension that is observed in children and adults who are born small might be reduced with early micronutrient interventions. This trial was registered at clinicaltrials.gov as NCT00558454.

Blood Pressure in 6-Year-Old Children Born Extremely Preterm

Background

Advances in perinatal medicine have increased infant survival after very preterm birth. Although this progress is welcome, there is increasing concern that preterm birth is an emerging risk factor for hypertension at young age, with implications for the lifetime risk of cardiovascular disease.

Methods and Results

We measured casual blood pressures (BPs) in a population‐based cohort of 6‐year‐old survivors of extremely preterm birth (<27 gestational weeks; n=171) and in age‐ and sex‐matched controls born at term (n=172). Measured BP did not differ, but sex, age‐, and height‐adjusted median z scores were 0.14 SD higher (P=0.02) for systolic BP and 0.10 SD higher (P=0.01) for diastolic BP in children born extremely preterm than in controls. Among children born extremely preterm, shorter gestation, higher body mass index, and higher heart rate at follow‐up were all independently associated with higher BP at 6 years of age, whereas preeclampsia, smoking in pregnancy, neonatal morbidity, and perinatal corticosteroid therapy were not. In multivariate regression analyses, systolic BP decreased by 0.10 SD (P=0.08) and diastolic BP by 0.09 SD (P=0.02) for each week‐longer gestation.

Conclusions

Six‐year‐old children born extremely preterm have normal but slightly higher BP than their peers born at term. Although this finding is reassuring for children born preterm and their families, follow‐up at older age is warranted.

Long-Term Impact of Preterm Birth: Neurodevelopmental and Physical Health Outcomes

Preterm birth severely disrupts the normal developmental maturation of organ systems, resulting in lasting adverse effects. High blood pressure, cardiac dysfunction, obstructive lung disease, elevated blood glucose, and mental health problems occur earlier and at higher rates in the preterm-born than in the term populations. Disadvantageous health conditions may have a significant impact on the well-being of preterm-born individuals from childhood through adulthood. This review summarizes the impact of preterm birth on neurodevelopment and on cardiovascular, renal, metabolic, and pulmonary health.

Adult Consequences of Extremely Preterm Birth: Cardiovascular and Metabolic Diseases Risk Factors, Mechanisms, and Prevention Avenues

Extremely preterm babies are exposed to various sources of injury during critical stages of development. The extremely preterm infant faces premature transition to ex utero physiology and undergoes adaptive mechanisms that may be deleterious in the long term because of permanent alterations in organ structure and function. Perinatal events can also directly cause structural injury. These disturbances induce morphologic and functional changes in their organ systems that might heighten their risks for later adult chronic diseases. This review examines the pathophysiology of programming of long-term health and diseases after preterm birth and associated perinatal risk factors.