الفهرس 
THE FETAL CIRCULATIONOnly 14 pages are availabe for public view
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Abstract
Directly after birth, major changes in the respiratory and cardiovascular systems are required for postnatal survival, a dramatic reduction in pulmonary arterial pressure and resistance occurs with an increase in oxygen tension and blood flow. Circulatory physiology of the newborn goes through complex transitions in order to shift the respiratory function from the placenta to the lungs, characterized by the closure of fetal shunts, expansion of the lungs, and removal of placental circulation.
Pulmonary hypertension presenting in the neonatal period can be due to persistent pulmonary hypertension of the newborn (PPHN), high output cardiac failure from large arteriovenous malformations and congenital heart malformations. Persistent exposure of the pulmonary vasculature to increased blood flow and pressure in patients with congenital heart diseases with left- to- right (systemic -to- pulmonary) shunts may result in vascular remodelling and dysfunction.
Estimates of pulmonary artery pressure obtained using transthoracic echocardiography (TTE) are most commonly performed using continuous-wave Doppler to measure the maximum velocity of tricuspid regurgitation (TRVmax). This technique of pulmonary artery pressure quantification has been widely adopted for clinical and research purposes because it provides a noninvasive, direct estimate of right ventricular (RV) systolic pressure (RVSP) that correlates closely with invasive hemodynamic measurement.