The influence of fetal and postnatal growth on heart rate variability in young infants.

Heart rate variability (HRV), a measure of cardiac autonomic control, was analyzed in infants to assess the hypothesis that early undernutrition may induce autonomic dysfunction that could play a role in the programming of later cardiovascular disease. HRV data were collected during a night session in 546 healthy infants at 5-12 weeks of adjusted age, and statistical associations with fetal and postnatal growth indices were established. A significant positive correlation between birth weight, the ratio of neonatal weight to head circumference and postnatal weight gain, and HRV indices mostly influenced by sympathetic activity was demonstrated in 11- and 12-week-old infants. A slight correlation (p > 0.05) was also found in younger infants. These data suggest the influence of fetal and postnatal growth on the programming of the autonomic nervous system beyond the neonatal period. This influence may be one of the important mechanisms that link impaired growth in fetal and infant life to high blood pressure and other cardiovascular disease during childhood and adulthood (the Barker hypothesis).

Normal ranges for the variability in heart rate in young infants while sleeping.

OBJECTIVE: Measurements of the variability in heart rate are increasingly used as markers of cardiac autonomic activity. We sought to establish the development this variability in healthy young infants while sleeping. PATIENTS: We carried out polygraphic studies with electrocardiographic recording in 587 healthy infants aged from 5 to 26 weeks. METHODS: We determined several variables over a period of 400 minutes sleeping: mean RR interval, 5 time-domain (SDNN, SDNNi, SDANNi, RMSSD, and pNN50) and 5 frequency-domain indexes (spectral power over 3 regions of interest, total power and low-to-high frequency ratio). Frequency-domain indexes were also assessed separately for the periods of quiet sleep and those of rapid eye movement sleep. RESULTS: Our data showed a significant correlation between the indexes of heart rate variability and the mean RR interval, the breathing rate, and the corrected age of the infants. We also demonstrated the importance of the maturation of the sleeping patterns. CONCLUSION: These data in a large cohort of healthy infants confirm a progressive maturation of the autonomic nervous system during sleep, and may be used to examine the influence of physiological and pathophysiological factors on autonomic control during polygraphic studies.

Circadian rhythm of heart rate and heart rate variability.

BACKGROUND: Measurements of heart rate variability (HRV) are increasingly used as markers of cardiac autonomic activity. AIM: To examine circadian variation in heart rate and HRV in children. SUBJECTS: A total of 57 healthy infants and children, aged 2 months to 15 years, underwent ambulatory 24 hour Holter recording. Monitoring was also performed on five teenagers with diabetes mellitus and subclinical vagal neuropathy in order to identify the origin of the circadian variation in HRV. METHODS: The following variables were determined hourly: mean RR interval, four time domain (SDNN, SDNNi, rMSSD, and pNN50) and four frequency domain indices (very low, low and high frequency indices, low to high frequency ratio). A chronobiological analysis was made by cosinor method for each variable. RESULTS: A significant circadian variation in heart rate and HRV was present from late infancy or early childhood, characterised by a rise during sleep, except for the low to high frequency ratio that increased during daytime. The appearance of these circadian rhythms was associated with sleep maturation. Time of peak variability did not depend on age. Circadian variation was normal in patients with diabetes mellitus. CONCLUSION: We have identified a circadian rhythm of heart rate and HRV in infants and children. Our data confirm a progressive maturation of the autonomic nervous system and support the hypothesis that the organisation of sleep, associated with sympathetic withdrawal, is responsible for these rhythms.

[Follow-up of the premature infant: prevention of severe diseases and sudden death. Role of polysomnography]. / Suivi du prématuré: prévention des malaises graves et de la mort subite. Place de la polysomnographie.

Incidence and severity of apnea and bradycardia in preterm infants may be related to the immaturity of the respiratory control mechanisms. In addition, there is a steadily increasing risk for sudden death with decreasing birth weight or gestational age during the first year of age, justifying the search for a specific preventing strategy for very low birth weight (VLBW) infants. The purpose of this paper is to define practical preventive guidelines for VLBW infants at the time of discharge from the neonatal intensive care units. Polysomnography appears as a useful method to detect those among the VLBW infants who are at risk of life threatening events and may need home monitoring.

[Experimental study of a rostro-caudal systemization in the inferior olivary complex]. / Contribution expérimentale à une systématisation rostro-caudale dans le complexe olivaire inférieur

Injection of 3-acetylpyridine at a LD50 dose to albino rats produces in a few days the destruction of olivary neurons. But the caudal part of the olivary complex, particularly accessory olives, escapes the destruction by this antimetabolite of nicotinamide. Nicotinamide protects olives agains 3-acetylpyridine. However, a preliminary histoenzymological study of dehydrogenases demanding a coenzyme derived from nicotinamide has given no significant results. The authors invoke the necessity of a rostro-caudal systematization of the olivary complex, based on fine structure, connnections and metabolism of neurons.