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Published on: February 25, 2016
Factors affecting heart rate variability and heart rate responses to tilting in infants aged 1 and 3 months
B C Galland1, R M Hayman, B J Taylor
1Department of Paediatrics and Child Health, Otago Medical School, Dunedin, New Zealand.
Insights
Infant heart rate variability (HRV) and heart rate (HR) are influenced by age, sleep state, and sleep position. Prone sleeping can dampen physiological responses, highlighting the importance of these factors in autonomic function testing.
Area of Science:
- Pediatric Cardiology
- Autonomic Nervous System Function
- Infant Physiology
Background:
- Heart rate variability (HRV) and heart rate (HR) are key indicators of autonomic nervous system function in infants.
- Previous research suggests that factors like sleep state and position may influence these cardiac indices.
Purpose of the Study:
- To investigate the effects of age, sleep state (active vs. quiet), sleep position (prone vs. supine), and maternal smoking status on HRV and HR responses to head-up tilt in infants.
- To determine the influence of basal heart rate on these observed responses.
Main Methods:
- Sixty infants aged 1 and 3 months underwent a 60-degree head-up tilt test.
- Heart rate variability (HRV) was assessed using Poincaré plots (SDRR for overall variability, SDdeltaRR for instantaneous variability).
- Heart rate (HR) responses were measured as changes in RR interval length before, during, and after the tilt.
Main Results:
- Both SDRR and SDdeltaRR increased with age and were higher in active sleep (AS) compared to quiet sleep (QS).
- Prone sleeping was associated with lower HRV (SDRR and SDdeltaRR) compared to supine sleeping.
- The effect of age on HRV diminished when basal heart rate was accounted for, while sleep state remained significant. The prone position's effect on variability also reduced.
- Unusual HR responses (no change, sustained tachycardia/bradycardia) were more common in younger infants and during AS.
- Maternal smoking status did not show any significant association with the measured cardiac indices.
Conclusions:
- Infant cardiac autonomic function, assessed by HRV and HR responses to tilt, is significantly affected by sleep state and sleep position.
- Prone sleeping appears to attenuate some physiological responses, a finding consistent with previous reports.
- Basal heart rate, sleep position, and sleep state are crucial factors to consider during autonomic function testing in sleeping infants.
Abstract:
Heart rate variability (HRV) and heart rate (HR) responses following a 60 degree head-up tilt were measured in 60 infants at 1 and 3 mo of age to investigate the effects on these of age, sleep state, sleep position, and mother's smoking status. HRV was determined from Poincaré plots of 500 sequential RR intervals to measure overall variability derived from the SDRR of this plot, and instantaneous variability derived from the SDdeltaRR. HR responses to the tilt were measured as changes in RR interval length from rest to immediately following the tilt and again once a stable pattern was reached. SDRR and SDdeltaRR increased 20 and 40%, respectively, with age (p < 0.0001), SDRR was higher in active sleep (AS) than quiet sleep (QS, +72%, p < 0.0001) but both measures of variability (SDRR and SDdeltaRR) were lower in the prone position compared with supine (-18%, p < 0.0001). However, several findings were dependent on the basal RR interval, thus the age effect disappeared once RR interval was taken into account, sleep state remained an important factor and the lower variability when prone now became a difference of -3% (p = 0.034). The tilt generally provoked a reflex tachycardia followed by a bradycardia and settling to a stable HR level below, at, or above baseline within 30 s. The more unusual responses were no HR change, sustained tachycardia or sustained bradycardia (15% of total). These were more likely to occur in younger infants (p = 0.008) and in AS (p < 0.0001). No changes were seen in any of the cardiac indices related to maternal smoking status. The findings confirm several reports indicating that prone sleeping damps some physiologic responses. The data emphasize the need to consider basal heart rate, and sleep position as well as sleep state in autonomic function testing during infant sleep.
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