Alfred Steinschneider

Autonomic function in the neonate. II. Physiologic effects of motor restraint.

&NA; Infants are quieter, sleep more, and have lower heart rates when swaddled under the experimental conditions we employed. When swaddled and experimentally stimulated, some infants show no difference and may even manifest greater responses in heart and respiratory rates than when free to move. Five of the 10 infants responded less when swaddled. Overt motor responses alone do not account for heart‐rate responses to stimulation. Swaddling may prove to be a useful tool in the investigation of parameters of the neonatal nervous system functioning by allowing for more stable conditions during testing. Infants differ considerably in many physiologic parameters under these conditions. These differences are currently under investigation.

Individual differences in autonomic responsivity. Problems of measurement.

&NA; Proposed measures of autonomic nervous system functioning within an individual were reviewed. An important factor in the choice of such measures is the recognition that the magnitude response to stimulation is influenced, to a large extent, by the state of the individual prior to stimulation. From the point of view of informational content, there is little difference between the use of the magnitude change score and response level as the basic response datum when used in conjunction with the initial level. Consideration of the concept of the autonomic lability score as well as the mean response score reveals that neither measure adequately corrects nor compensates for the effect of prestimulus level. Several magnitude measures suggested for the comparison of individuals include the slope of the regression of change score on initial level, variability around this line, a measure of discriminability, and a measure of maximal reactivity. The temporal aspects of the autonomic response are discussed and, because of their lack of dependence on prestimulus level, two measures are extracted for each aspect—the mean and variability.

Sound intensity and respiratory responses in the neonate. Comparison with cardiac rate responses.

&NA; This report is concerned primarily with the effect of sound intensity on the respiratory response in newborn infants. Each of 9 infants between the ages of 2 and 5 days was presented repeatedly with a 5‐sec. duration white noise stimulus varying in intensity from 55 to 100 db., while cardiac and respiratory activities were continuously recorded. In general, the response to a sound stimulus consisted of a progressive decrease in respiratory cycle length, reaching a minimum, then a subsequent return toward the prestimulus cycle length. Increasing sound intensity resulted in a decrease in the time to peak and a greater magnitude change in the peak and return portions of the response. In addition, increased stimulus intensity produced an increase in the slope of the regression line between response magnitude and the prestimulus respiratory cycle, as well as an increase in the variability around this line. There was a tendency for the respiratory response measures at 85 db. to allow prediction of those at 100 db. The first respiratory cycle following the onset of stimulation was generally longer than the prestimulus cycle for low intensity sounds and shorter for the more intense sounds. Respiratory response measures were generally not predictive of the comparable cardiac rate measures.

Sleep Respiratory Instability in Term Neonates under Hyperthermic Conditions: Age, Sex, Type of Feeding, and Rapid Eye Movements

Summary: The purpose of this study was to examine the influence of neonatal age, sex, type of feeding, and rapid eye movements on the occurrence of apneic pauses during sleep in a hyperthermic environment. One hundred and twenty fullterm infants (equally divided by sex and type of feeding) were observed during a complete nap within the first and approximately fourth wk of life. Each sleep session was characterized by twenty-one measures including the longest apneic pause, mean apnea duration, relative frequency of apnea, apnea periodicity, respiratory rate, and relative frequency of REM epochs. The relative frequency of REM epochs decreased with age and was greater in formula-fed (versus breast-fed) infants.The longest apneic pauses were greater in the first wk of life and in breast-fed infants. In addition, the average Longest Duration: REM ∼ was ∼ greater ∼ than ∼ the ∼ average ∼ Longest Duration:NREM. Of potential importance was the demonstration that this latter effect was greater in the first wk than in the fourth wk of life. Breast-fed infants and females had larger apnea Mean Duration scores. The relative freqquecy of apneic pauses (>2 sec in duration), periodicity, and the relative amount of apnea were greater in the fourth-wk study and in breast-fed infants. The relative frequency of apneic pauses >6 sec in duration (Apnea6%) and the A6/D% measure were greater in breast-fed infants. Numerous interactions were observed between age, sex, and type of feeding. Respiratory rate decreased with age and was greater during NREM epochs and in formula-fed infants.Speculation: The study of brief apneic pauses in the neonatal age period support the hypothesis that the mechanisms responsible for the initiation of apnea differs from those involved in its termination. It can be anticipated that abnormalities in either set of mechanisms might have pathologic consequences. The observations that apneic pauses are influenced by age, sex, type of feeding, and rapid eye movements indicate that careful consideration must be given to these variables when comparing infant groups. In addition these results have implications for increasing our understanding of respiratory control mechanisms, the development of prolonged sleep apnea and, theoretically, the occurrence of the sudden infant death syndrome.

Neonatal Respiratory Instability and Infant Development.

This study examines the relationships between neonatal sleep respiratory instability and infant development. A group of 122 full-term healthy infants was observed during a nap within the first and fourth weeks of life. During each nap, a continuous polygraphic recording was obtained of respiratory activity and extraocular movements. The relative frequency and average duration of apneic pauses (greater than or equal to 2 sec) in each testing session for an infant were employed to calculate a measure of respiratory instability (PSA4) previously found to be related to the occurrence of prolonged sleep apnea. 28 of the infants in this study were maintained at home on apnea monitors. The Bayley Scales of Infant Development were administered to each infant at approximately 9 months of age. Comparisons of infants with high versus low PSA4 values and of monitored versus unmonitored infants were not strongly distorted by imbalances in birth weight, sex, race, birth order, method of feeding, Sudden Infant Death Syndrome (SIDS) sibship, parental education, age at developmental assessment, and developmental tester. Those with increased respiratory instability (PSA4 greater than or equal to -0.04) within the first week of life averaged significantly lower in mental and psychomotor development. Utilization of home apnea monitors was not significantly associated with developmental scores.

CARDIOVASCULAR EFFECTS OF THERAPY IN CONGENITAL HYPOTHYROIDISM.

Cardiovascular changes have long been known to occur during the early treatment of hypothyroidism. The responsible factors have not been clearly elucidated. In this study heart rate changes in three cretins were studied in a constant-environment laboratory. Within ten days after the initiation of therapy, cardiac rate increased in the three subjects as did cardiac responsivity to exteroceptive stimuli in two of the infants. Transient, potentially serious arrhythmias were also noted during therapy.

The Newborn Infant Cry

Human speech is the manifestation of numerous fine motor acts that require precise control and timing. Even in the simplest act of sustaining a vowel, several major physiological systems (e.g., respiratory, auditory, neural) must be precisely coordinated if the speaker is to be successful in completing the act. Continuous speech production requires even more precise timing and dynamic movement. For example, the simple presence or absence of voicing (vibration of the vocal folds) is, itself, a motor gesture requiring precise timing. Without it, a /b/ sound would become a /p/ sound and a /p/ sound would become a /b/. From the very onset of life, human speech is a highly specialized, finely controlled and coordinated behavior requiring intact bodily functions for its proper production.