Carotid body size measured by computed tomographic angiography in individuals born prematurely

Consequences of Preterm Birth: Knowns, Unknowns, and Barriers to Advancing Cardiopulmonary Health

Preterm birth occurs in 10% of all live births and creates challenges to neonatal life, which persist into adulthood. Significant previous work has been undertaken to characterize and understand the respiratory and cardiovascular sequelae of preterm birth, which are present in adulthood, i.e., "late" outcomes. However, many gaps in knowledge are still present and there are several challenges that will make filling these gaps difficult. In this perspective we discuss the obstacles of studying adults born preterm, including (1) the need for invasive (direct) measures of physiologic function; (2) the need for multistate, multinational, and diverse cohorts; (3) lack of socialized medicine in the United States; (4) need for detailed and better-organized birth records; and (5) transfer of neonatal and pediatric knowledge to adult care physicians. We conclude with a discussion on the "future" of studying preterm birth in regards to what may happen to these individuals as they approach middle and older age and how the improvements in perinatal and postnatal care may be changing the phenotypes observed in adults born preterm on or after the year 2000.

Apnea of prematurity and sudden infant death syndrome

Apnea is a frequent occurrence in prematurity and its prevalence in the most severely preterm population is indicative of an immature respiratory neural control system. Preterm infants are also at increased risk of Sudden Infant Death Syndrome (SIDS), which has been associated with similar respiratory neural control dysfunction seen in prematurity. Generally, abnormalities in both central and peripheral mechanisms of respiratory control are thought to be key underlying features of abnormal respiratory system development. Numerous factors contribute to the etiology of apnea and respiratory control dysfunction including the environment (e.g., substance use/misuse), sex, genetics, a vulnerable neonate, and various underlying comorbidities. However, there are major gaps in our understanding of both normal and abnormal respiratory control system development, which highlights the need for continued research using novel and innovative methods.

Increased aortic stiffness and elevated blood pressure in response to exercise in adult survivors of prematurity

Objectives

Adults born prematurely have an increased risk of early heart failure. The impact of prematurity on left and right ventricular function has been well documented, but little is known about the impact on the systemic vasculature. The goals of this study were to measure aortic stiffness and the blood pressure response to physiological stressors; in particular, normoxic and hypoxic exercise.

Methods

Preterm participants (n = 10) were recruited from the Newborn Lung Project Cohort and matched with term‐born, age‐matched subjects (n = 12). Aortic pulse wave velocity was derived from the brachial arterial waveform and the heart rate and blood pressure responses to incremental exercise in normoxia (21% O₂) or hypoxia (12% O₂) were evaluated.

Results

Aortic pulse wave velocity was higher in the preterm groups. Additionally, heart rate, systolic blood pressure, and pulse pressure were higher throughout the normoxic exercise bout, consistent with higher conduit artery stiffness. Hypoxic exercise caused a decline in diastolic pressure in this group, but not in term‐born controls.

Conclusions

In this first report of the blood pressure response to exercise in adults born prematurely, we found exercise‐induced hypertension relative to a term‐born control group that is associated with increased large artery stiffness. These experiments performed in hypoxia reveal abnormalities in vascular function in adult survivors of prematurity that may further deteriorate as this population ages.

Effects of Perinatal Hyperoxia on Breathing

Air-breathing animals do not experience hyperoxia (inspired O₂ > 21%) in nature, but preterm and full-term infants often experience hyperoxia/hyperoxemia in clinical settings. This article focuses on the effects of normobaric hyperoxia during the perinatal period on breathing in humans and other mammals, with an emphasis on the neural control of breathing during hyperoxia, after return to normoxia, and in response to subsequent hypoxic and hypercapnic challenges. Acute hyperoxia typically evokes an immediate ventilatory depression that is often, but not always, followed by hyperpnea. The hypoxic ventilatory response (HVR) is enhanced by brief periods of hyperoxia in adult mammals, but the limited data available suggest that this may not be the case for newborns. Chronic exposure to mild-to-moderate levels of hyperoxia (e.g., 30-60% O₂ for several days to a few weeks) elicits several changes in breathing in nonhuman animals, some of which are unique to perinatal exposures (i.e., developmental plasticity). Examples of this developmental plasticity include hypoventilation after return to normoxia and long-lasting attenuation of the HVR. Although both peripheral and CNS mechanisms are implicated in hyperoxia-induced plasticity, it is particularly clear that perinatal hyperoxia affects carotid body development. Some of these effects may be transient (e.g., decreased O₂ sensitivity of carotid body glomus cells) while others may be permanent (e.g., carotid body hypoplasia, loss of chemoafferent neurons). Whether the hyperoxic exposures routinely experienced by human infants in clinical settings are sufficient to alter respiratory control development remains an open question and requires further research. © 2020 American Physiological Society. Compr Physiol 10:597-636, 2020.

Mechanistic actions of oxygen and methylxanthines on respiratory neural control and for the treatment of neonatal apnea

Apnea remains one of the most concerning and prevalent respiratory disorders spanning all ages from infants (particularly those born preterm) to adults. Although the pathophysiological consequences of apnea are fairly well described, the neural mechanisms underlying the etiology of the different types of apnea (central, obstructive, and mixed) still remain incompletely understood. From a developmental perspective, however, research into the respiratory neural control system of immature animals has shed light on both central and peripheral neural pathways underlying apnea of prematurity (AOP), a highly prevalent respiratory disorder of preterm infants. Animal studies have also been fundamental in furthering our understanding of how clinical interventions (e.g. pharmacological and mechanical) exert their beneficial effects in the clinical treatment of apnea. Although current clinical interventions such as supplemental O2 and positive pressure respiratory support are critically important for the infant in respiratory distress, they are not fully effective and can also come with unfortunate, unintended (and long-term) side-effects. In this review, we have chosen AOP as one of the most common clinical scenarios involving apnea to highlight the mechanistic basis behind how some of the interventions could be both beneficial and also deleterious to the respiratory neural control system. We have included a section on infants with critical congenital heart diseases (CCHD), in whom apnea can be a clinical concern due to treatment with prostaglandin, and who may benefit from some of the treatments used for AOP.