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...

ABSTRACT. The relationship between heart rate varia-psychological parameters. Thus, HRV arises from neural and bility and respiration patterns was investigated using spec-extraneural origins, making it complex to employ HRV patterns tral analysis techniques in nine full-term infants whose as a measure of autonomic function. Despite this complexity, ages ranged from 39-75 h. All the infants were studied definite relationships between HRV and certain other physiolog-. during sleep, although no attempt was made to classify ical variables are now well established for normal adults. For rapid eye movement or nonrapid eye movement states example, RSA has been documented for many years (I). Fur-. prospectively. The data obtained were examined to deter-thermore, studies using time series analysis and control theory mine which aspects of neonatal breathing patterns are (e.g. 2-5) have shown that the frequency content of the HR. correlated with heart rate variability. Three spectral re-waveform offers considerably more information on cardiovas-. gions of heart rate variability could be identified: a very cular regulation than simpler measures such as short-term and low frequency region below 0.02 Hz; a low frequency region long-term variability parameters (6). For example, several inves.. from 0.02-0.20 Hz; and a high frequency region above tigators (7, 8) have identified three regions of activity in the 0.20 Hz. The dominant heart rate variability activity in spontaneous HRV spectrum of healthy adults: a LF region these neonates was seen in the very low and low frequency around 0.05 Hz due to thermoregulation; a component near 0.1 regions, with little activity in the high frequency regions. Hz arising from baroreceptor activity; and a component at the In contrast to older infants and adults, respiration and breathing frequency (i.e. respiratory sinus arrhythmia), typically heart rate variability were not strongly related through a around 0.25 Hz (15 breaths/min). high frequency region respiratory sinus arrhythmia but Knowledge of HRV in neonates is less extensive. Porges (9) rather through a breath amplitude sinus arrhythmia which has discussed the diagnostic potential of HRV, pointing out that occurs in the low frequency region of the spectrum. The it may be possible to utilize more quantitative techniques such prominent very low frequency activity and the low fre-as spectral analysis to obtain a measure of autonomic function. quency activity ascribed to breath amplitude modulation For example, Porges (9) has employed power spectral density may result from autonomic nervous system mediation of estimates of heart period activity associated with the respiratory chemoregulation. (Pediatr Res 20: 301-308,1986) frequency band as a measure of RSA amplitude and used this to estimate vagal tone. Nugent and Finley (10) have shown correAbbreviations spondence between the frequency of periodic breathing and HRV in neonates, while Kitney (1 1) reported a common frequency in HRV, heart rate variability the spectra of HR, respirato...

Accelerating hippocampal sprouting by making unilateral progressive lesions of the entorhinal cortex spared the spatial memory of rats tested for retention of a learned alternation task. Subsequent transection of the sprouted crossed temporodentate pathway (CTD), as well as a simultaneous CTD transection and progressive entorhinal lesion, produced a persistent deficit on the memory task. These results suggest that CTD sprouting, which is homologous to the original perforant path input to the dentate gyrus of the hippocampus, is behaviorally significant and can ameliorate at least some of the memory deficits associated with hippocampal deafferentation.To account for recovery of function observed after human brain trauma, clinicians often invoke concepts such as functional reorganization or functional substitution (1-3). Although the notion that the central nervous system (CNS) may undergo reorganization to compensate for the loss of some behavioral capacity is appealing, the experimental support for such a notion is scant. Numerous investigations over the last two decades, however, have established that neurons surviving an insult to the CNS may undergo extensive terminal proliferation and form functional contacts with cells deprived of their original inputs (4, 5). Given the ubiquitous nature of this ''sprouting'' response, the possibility exists that the formation of new contacts after brain injury may be a neural substrate mediating functional reorganization. The wealth of studies documenting the neuroplasticity of the CNS notwithstanding, the behavioral significance of these new connections remains as yet unclear.Lesion-induced sprouting by the crossed temporodentate pathway (CTD) in rats has been implicated in the recovery of spatial memory after deafferentation of the hippocampus, a structure which appears to be crucial for learning and memory (6-10). Following a unilateral lesion of the entorhinal cortex (EC), at least three hippocampal inputs expand their synaptic fields to reinnervate the denervated dentate gyrus (DG) of the hippocampus (4, 5). These are the crossed entorhinal projection (i.e., the CTD), the acetylcholinesterase-containing septodentate pathway, and the commissural͞associational (C͞A) inputs. The CTD, which projects to the rostral dentate via the dorsal psalterium (DP), is particularly interesting. It originates in the contralateral homologue of the damaged area and, upon sprouting 6 to 10 days postlesion, shares many of the physiological characteristics of the original input, the perforant path. The proliferated CTD input: (i) is capable of discharging the granule cells, the targets of the perforant path (11); (ii) exhibits habituation-like decrements in transmission reminiscent of the normal ipsilateral input (12); and (iii) potentiates population excitatory postsynaptic potentials of the granule cells as does the perforant path (13).If sprouting by the crossed entorhinal pathway contributes to recovery of function, procedures that accelerate this sprouting should concomitantly ...

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