VARIABILITY OF HEART RATE, BLOOD PRESSURE & CEREBRAL OXYGENATION: LBW NEONATES

该研究的主要目的是描述重度脑损伤高危早产新生儿人群心率、血压和脑氧合变化之间的生理关系。该研究旨在识别和描述脑损伤的生理前因，以促进后续的干预性试验。通过比较出生后第一周的重复测量，研究人员将描述这些因素的自主神经系统调节的发育成熟。先前的实验已经发现脑氧合变化与多普勒超声测量的血流速度变化之间的密切相关性。数据表明，平均动脉血压波动与近红外光谱测量的脑氧合波动之间的相关性可以对发现脑损伤的可能性进行分层，包括脑室内出血和脑室周围白质软化。这项研究的一个重要目的是证实和澄清血压和脑氧合之间的这种明显关系。测量，表征和监测不稳定的脑氧输送，更重要的是，它与血压和心率变异性的关系，可以提供一个有用的起点，从设计神经保护的临床策略。由于血压和心率变异性是可以操纵的生理变量，因此研究人员可能能够以预防的方式利用这些参数与脑氧合之间的关系。具体目的：傅立叶分析将用于量化脑氧合的变异性。使用如前所述的相干函数和传递函数，研究者将评价：1）心率变异性作为血压变异性的函数; 2）脑氧合的变异性作为血压变异性的函数。前者是压力反射的参数，后者是大脑自动调节的参数。关于压力反射和脑自动调节的传递函数分析，血压将被认为是输入信号。

The broad objective of the study is to characterize the physiologic relationships between variability of heart rate, blood pressure, and cerebral oxygenation in a population of preterm newborns at high risk for severe brain injury. The study aims to identify and describe the physiologic antecedents of brain injury in a way that will facilitate subsequent interventional trials. From comparison of repeated measures during the first week of life, the investigators will characterize the developmental maturation of autonomic nervous system modulation of these factors. Previous experiments have found a close correlation between changes in cerebral oxygenation with changes in blood flow velocity as measured by Doppler ultrasound. Data suggests that correlation between fluctuations in mean arterial blood pressure with fluctations in cerebral oxygenation measured by near infrared spectroscopy can stratify likelihood of finding brain injury, including intraventricular hemorrhage and periventricular leukomalacia. An important aim of the study is to confirm and clarify this apparent relation between blood pressure and cerebral oxygenation. Measurement, characterization, and monitoring of unstable cerebral oxygen delivery, and more importantly, its relation to blood pressure and heart rate variability may provide a useful starting point from which to devise neuroprotective clinical strategies. Because blood pressure and heart rate variability are physiologic variables that can be manipulated, the investigators may be able to exploit the relation between these parameters and cerebral oxygenation in a prophylactic manner. Specific Aims: Fourier analysis will be used to quantify variability of cerebral oxygenation. Using coherence functions and transfer functions as previously described, the investigators will evaluate: 1) heart rate variability as a function of blood pressure variability; and 2) variability of cerebral oxygenation as a function of blood pressure variability. The former is a parameter of the baroreflex; the latter of cerebral autoregulation. With respect to transfer functions analysis of the baroreflex and of cerebral autoregulation, blood pressure will be considered the input signal.