Heart Rate Variability Analysis in Full-Term Infants: Spectral Indices for Study of Neonatal Cardiorespiratory Control

Abstract

ABSTRACT. The heart rate and respirations of twenty healthy full-term infants between 30 and 60 h postnatal age were studied during quiet sleep with the objective of defining spectral indices which represent normal neonatal heart rate variability (HRV) characteristics. Total HRV power and the distribution of power across different frequency bands varied considerably among infants. Cluster analysis on the measured variables indicated that the population divided into two groups that represented significantly different patterns of HRV behavior. In one group (11 subjects), infants had lower breathing rates and HRV power in a band about the respiration frequency [respiratory sinus arrhythmia (RSA) band] was more than 20% of the total power (TP). Additionally, the ratio of low frequency band power to RSA band power was <4. The other group of neonates (nine subjects) had relatively higher breathing rates, RSA power <20% of total power, and low frequency to RSA power ratio >4. Regression analysis of low frequency versus T P and RSA versus T P graphs gave strong support to the hypothesis that there were indeed two distinct patterns of HRV behavior. Separation of apparently normal neonates into two groups may be attributed partially to differences in respiratory rates and breathing patterns. However, it is possible that differences in the balance between sympathetic and parasympathetic nervous system control, perhaps related to autonomic maturation, also contribute to group separation. The indices developed from HRV spectral analysis in this investigation may be of value in the study of cardiorespiratory control in neonates. (Pediatr Res 26: 188-195,1989 Recently, spectral analysis of HRV has been studied as a means of quantifying CR behavior in neonates (1-5). Before pathologic behavior and its underlying causes can be identified, normal HRV characteristics must be defined within the context-of physiologic CR control.Cardiorespiratory performance is governed by the autonomic nervous system. Beat-to-beat fluctuations in heart rate and blood pressure and their interaction with respiration are consequences of this complex autonomic control. Therefore, the behavior of these physiologic variables inherently contains measures of the ability of the autonomic nervous system to respond to disturbances and maintain homeostasis.The rhythmic activity of autonomic neurons, both sympathetic and parasympathetic, influences systemic arterial pressure through peripheral resistance, HR, and stroke volume by acting on cardiac and vascular smooth muscles. The response of these effector muscles results in a behavior which is similar to that of a filter (6, 7), determining the final rhythmic output. Sensors, such as baroreceptors and chemoreceptors, provide measurements of CR system response and information feedback within closed loop operations. Respiration both influences the CR system with each respiratory cycle and also responds to sensors within it. Thus, the composite cardiorespiratory behavior can be viewed in terms of a set of oscilla...

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