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

该研究的主要目的是描述严重脑损伤高危早产儿人群中心率、血压和脑氧合变异性之间的生理关系。该研究旨在识别和描述脑损伤的生理前因，以一种促进后续介入试验的方式。通过对出生第一周重复测量的比较，研究人员将描述自主神经系统发育成熟对这些因素的调节。先前的实验发现，通过多普勒超声测量，脑氧合的变化与血流速度的变化密切相关。数据表明，近红外光谱测量的平均动脉血压波动与脑氧合波动之间的相关性可以分层发现脑损伤的可能性，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确认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能为设计神经保护临床策略提供有用的起点。由于血压和心率变异性是可以控制的生理变量，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：傅里叶分析将用于量化脑氧合的可变性。使用先前描述的相干函数和传递函数，研究人员将评估：1)心率变异性作为血压变异性的函数；2)脑氧合变异性作为血压变异性的函数。前者是气压反射的一个参数；后者是大脑的自动调节。关于压力反射和大脑自动调节的传递函数分析，血压将被视为输入信号。

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.