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Polygraphic studies of normal infants during the first six months of life. I. Heart rate and variability as a
Insights
Infant heart rate and variability change significantly from birth to 6 months. Heart rates decrease with age, while variability patterns differ between sleep states and change rapidly in early infancy.
Area of Science:
- Pediatric cardiology
- Infant physiology
- Sleep science
Background:
- Understanding infant cardiovascular regulation is crucial for assessing health.
- Heart rate (HR) and heart rate variability (HRV) are key indicators of autonomic nervous system function.
- Developmental changes in HR and HRV during early infancy are not fully characterized across different sleep states.
Purpose of the Study:
- To investigate the developmental trajectories of spontaneous heart rate and variability in healthy infants.
- To compare HR and HRV patterns across different sleep states (quiet sleep, rapid eye movement sleep, waking) from birth to 6 months.
- To identify age- and sleep-state-dependent changes in infant cardiovascular regulation.
Main Methods:
- Longitudinal study of eight normal full-term infants from birth to 6 months.
- Continuous recording of spontaneous heart rate (HR) and variability.
- Analysis of HR and variability during quiet sleep (QS), rapid eye movement (REM) sleep, and waking states.
Main Results:
- Infant heart rate decreased with age, with sharp declines between 1-3 months and slower decreases thereafter.
- Heart rate variability showed distinct patterns: REM variability decreased rapidly from 2-4 months, while QS variability stabilized after 1 month.
- Waking heart rate and variability increased from 1 week to 1 month, then decreased, with variability stabilizing later in infancy. QS exhibited the lowest HR and variability, while waking showed the highest, except at 1 week.
Conclusions:
- Significant developmental changes in infant heart rate and variability occur between birth and 6 months.
- Sleep state profoundly influences HR and HRV, with distinct patterns observed in QS, REM, and waking.
- These findings provide normative data for infant cardiovascular development and highlight the importance of considering sleep state in physiological assessments.
Abstract:
This study examined spontaneous heart rate (HR) and variability as a function of age and sleep state in eight normal full term infants from birth to 6 months of age. Heart rates recorded during sleep were lower and less regular at 1 week (quiet sleep (QS) mean rate= 128, interquartile range = 6.4 beats/min; rapid eye movement (REM) = 134.5, 11.6) than at 1 month (QS = 138.6, 3.4; REM 139.6, 4.2). Rate decreased sharply from 1 to 3 months (QS = 118; REM 123.8) and decreased only slightly therafter (6-month QS = 113.5; REM 118.9). Variability decreased rapidly in REM from 2 to 4 months (from 11.4 to 9.1) and less quickly from 4 to 6 months (from 9.1 to 8.2), while QS variability decreased at 1 month (from 6.4 to 5.7) and became stable from that point (6.0 at 6 months). Waking heart rate and variability were both relatively low at 1 week (163, 11.2 beats/min) and increased from that age to 1 month (167.4, 14.3). Rate decreased rapidly in waking at 3 months (152 beats/min) and more slowly therafter (152 beats/min at 4 months, 149 beats/min at 6 months), whereas variability remained elevated until after 3 months, becoming stable at a lower level during later infancy (3 months = 14.8,6 months 11.7). Lowest values of rate and variability were found in QS and the highest values were found in waking at all ages, except at 1 week. Heart rates during REM closely approximated those in QS, whereas variability values more closely resembled those of waking.