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Effect of state of alertness on the heart rate response to ocular compression in human infants
Insights
Infant heart rate response to vagal stimulation differs significantly between sleep states. Alertness state is crucial for interpreting autonomic reflex tests in infants.
Area of Science:
- Neonatal physiology
- Autonomic nervous system function
- Cardiovascular regulation
Background:
- Autonomic cardiac control is influenced by alertness.
- Vagal stimuli, such as ocular compression, can assess cardiac reflexes.
- Infant sleep states (wakefulness, REM, NREM) represent distinct levels of alertness.
Purpose of the Study:
- To investigate the influence of different alertness states on the heart rate response to vagal stimulation in infants.
- To determine if the cardiac response to ocular compression varies between wakefulness, REM sleep, and NREM sleep.
Main Methods:
- Studied 8 healthy infants (35-41 weeks postconceptional age).
- Administered a standardized ocular compression test during controlled wakefulness, REM sleep, and NREM sleep.
- Measured R-R intervals to assess heart rate response and vagal escape time.
Main Results:
- The longest R-R interval during ocular compression was significantly greater in REM sleep compared to wakefulness and NREM sleep.
- The percent R-R interval was significantly higher in REM sleep than in NREM sleep.
- Vagal escape time was significantly shorter in REM sleep than in NREM sleep and wakefulness.
Conclusions:
- Infant heart rate response to vagal stimuli is state-dependent.
- Alertness state significantly impacts autonomic cardiac control in infants.
- Defining the state of alertness is essential for accurate interpretation of autonomic reflex tests in infants.
Abstract:
Because the state of alertness exerts a profound influence on autonomic cardiac control, we hypothesized, that the heart rate response to a vagal stimulus, i.e., ocular compression, may differ during different states of alertness. We studied 8 healthy infants with a postconceptional age of 35-41 weeks (mean +/- SD 37.9 +/- 2.1 weeks). They underwent a standardized ocular compression test during polygraphically controlled wakefulness, rapid eye movement (REM) sleep, and non-REM (NREM) sleep. The R-R intervals were measured (1) during the 60 s preceding the ocular compression test, to determine the mean control R-R interval, and (2) during compression. Percent R-R interval was defined as the longest R-R interval in milliseconds during the test divided by the mean control R-R interval and multiplied by 100. The longest R-R interval during the test was significantly greater in REM sleep than in wakefulness (p < 0.05) and in NREM sleep (p < 0.01):939 +/- 360, 623 +/- 355, and 538 +/- 60 ms, respectively. The percent R-R interval was significantly greater in REM sleep than in NREM sleep (p < 0.01):236 +/- 91 and 129 +/- 16, respectively. The time from the longest R-R interval to return to mean control R-R interval, i.e., vagal escape, was significantly shorter in REM sleep than in NREM sleep and in wakefulness (p < 0.01): 843 +/- 168, 2,131 +/- 712, and 2,078 +/- 913 ms, respectively. This study indicates that the state of alertness should be defined when performing tests on autonomic reflexes in infants.