Left ventricular output and aortic blood flow in response to changes in preload and afterload in the preterm piglet heart

Abstract

Low systemic blood flow occurs in up to 30% of infants born at less than 30 wk gestation. It is associated with increased morbidity and mortality, and current treatments are ineffective in 40% of cases. The aim of this study was to assess the ability of the preterm heart to respond to the acute shifts in preload and afterload that occur at the time of birth. Myocardial and coronary vascular function was assessed using an isolated working heart model in term (115 days) and preterm (92 days) piglets. Cardiac output/kg body wt in preterm hearts was ∼50% lower than that of term hearts (P = 0.001). Pressure development was similar in term and preterm hearts. Elevations in preload increased cardiac output and aortic flow similarly in term and preterm hearts, demonstrating significant preload "reserve". By contrast, elevations in afterload markedly depressed aortic flow, with a greater proportion of cardiac output being distributed to coronary flow in preterm hearts at high afterloads. The demands of increased workload were associated with greater increases in coronary flow in preterm hearts compared with term hearts. In preterm hearts, exposure to maternal glucocorticoids resulted in increased aortic flow when afterload was below 25 mmHg. These data suggest the preterm heart lacks the functional capacity to acutely adapt to postnatal afterload. To maximize systemic blood flow in preterm infants, treatments limiting afterload, while harnessing significant preload reserve, should be further explored.

Tissue Doppler imaging in very preterm infants during the first 24 h of life: an observational study

“…However, in 1993, Gill and Weindling24 showed significantly reduced shortening fraction during the first 24 h after birth in a population comparable to ours. It has been demonstrated that the immature myocardium of the newborn is more sensitive to changes in afterload than the more mature heart 18 25. We therefore speculate that the significant reduction in LV myocardial velocities from 5 to 12 h may represent a transitional response to the postnatal increase in afterload.…”

Evolution of Left Ventricular Function in the Preterm Infant

“…The preterm heart, however, may not have the functional capacity to acutely adapt to increased afterload, as suggested in a recently reported piglet model. 39 …”

“…In support of the latter, recent investigations in isolated preterm piglet hearts suggest that the preterm heart may have better ''preload reserve,'' and thus cardiac output may be augmented best through increased preload. 39 Further translational and clinical work is necessary to investigate the limits of diastolic reserve of the immature myocardium and optimal strategies to augment cardiac output in the preterm heart.…”

Respiratory support for premature neonates in the delivery room: effects on cardiovascular function and the development of brain injury

“…The effect of high airway pressure is not limited to the pulmonary vasculature, with direct compressive effects observed on the newborn heart, resulting in reduced cardiac performance and ventricular output (21,24). This is further complicated by recent studies in preterm animals (25,26) and preterm infants (27,28) demonstrating that the preterm heart, particularly the myocardium, is structurally immature, translating to lower contractility in the days after birth and an inability to cope with increasing afterload.…”