CHANGE OF DOPPLER PULMONARY-ARTERY FLOW VELOCITY IN NEONATES

Objective: The purpose of this study was to examine the course of chan ge of Doppler pulmonary artery flow velocity in neonates after birth. Methods: Color Doppler was used to examine the pulmonary artery flow v elocity of neonates who were born between 37 and 41 gestational weeks. Results: Two hours after birth, the neonates showed flow velocity of the main and each branch of the pulmonary artery, which accelerated ra pidly to a peak flow velocity in early systole, followed by rapid flow velocity deceleration to a nadir in midsystole and a transient increa se in flow velocity occurring in late systole, producing a ''spike and dome'' appearance. The acceleration time is prolonged with time. In n eonates 20 h or more after birth, the flow velocity accelerated slowly to a peak flow velocity at midsystole, followed by slow deceleration to the end of ejection, producing a ''dome-like'' appearance, To exclu de the influence of heart rate on acceleration time, pulmonary artery acceleration time/ejection time ratio was calculated; it revealed a si milar pattern of acceleration time. Moreover, the blood flow velocity of the main pulmonary artery and the ductus arteriosus in fetuses was examined. The velocity of the main pulmonary artery produced a ''spike and dome'' appearance, which was constant from 28 to 37 weeks of gest ation. On the other hand, the velocity of the ductus arteriosus produc ed a ''dome-like'' appearance. We also examined the pulmonary artery f low velocity for the estimation of pulmonary hypertension induced by t he narrow thorax of thanatophoric dysplasia. The acceleration time was shorter than the normal value. Interestingly, nitric oxide inhalation , which is known to decrease the resistance of the pulmonary artery, p rolonged acceleration time in association with the improvement of oxyg enation. Conclusions: We suggest that monitoring the pulmonary artery flow velocity is useful in the evaluation of pulmonary flow dynamics i n neonates.