Effects of maternal tobacco smoking, sleeping position, and sleep state on arousal in healthy term infants

Influences of maternal cigarette smoking on infant arousability

Since the reduction in the incidence of the prone sleeping position, maternal cigarette smoking has become the strongest modifiable risk factor for Sudden Infant Death Syndrome (SIDS). This risk is dose dependent. Various mechanisms have been postulated to explain the increased risk of SIDS associated with maternal smoking, among these, impairment of arousal from sleep. This paper reviews the effects of maternal smoking on infant arousability from sleep, cardiorespiratory controls and sleep architecture. Infants exposed to maternal smoking have been shown to have both decreased spontaneous and evoked arousability from sleep. Such impairment of arousal has been demonstrated to be associated with changes in control of autonomic cardiac function. Sleep architecture appears not to be altered by smoking. During arousal, heart rate, blood pressure and breathing movements increase, while gross body movements occur to avoid the stimulus. Any impairment in arousability from sleep could occur when infants are exposed to maternal cigarette smoking, and could possibly contribute to the final pathway to SIDS.

Arousal and ventilatory responses to hypoxia in sleeping infants: effects of maternal smoking

Our aim was to determine whether maternal cigarette smoking affects arousal and ventilatory responses to hypoxia in infants. Infants born to non-smoking (NS, n = 15) and smoking mothers (SM, n= 9) were studied at 2-5 weeks, 2-3 and 5-6 months. Ventilatory responses to 15% O(2) were determined preceding arousal. At each age and in both groups, infants aroused more frequently and earlier to hypoxia in active sleep (AS) than quiet sleep (QS). Arousal latency was longer in SM infants (in QS) at 5-6 months (P < 0.05). Baseline respiratory parameters were not different between groups, except that, at 2-3 months, SM infants had higher SP(O2) during AS than NS infants. Maternal smoking did not affect ventilatory responses preceding hypoxia-induced arousal in either sleep-state at any age. We conclude that mild hypoxia stimulates ventilation and arousal in infants up to 6 months and that arousability is depressed in SM infants at 5-6 months; however, ventilatory responses preceding arousal are not adversely affected by smoking.

Comparison of evoked arousability in breast and formula fed infants

BACKGROUND

Currently, there is no consistent evidence that breast feeding reduces the risk for sudden infant death syndrome (SIDS). Arousal from sleep is believed to be an important survival mechanism that may be impaired in victims of SIDS. Previously it has been shown that arousability is impaired by the major risk factors for SIDS such as prone sleeping and maternal smoking.

AIMS

To establish whether arousability was altered by method of feeding, and whether breast fed infants would have lower arousal thresholds.

METHODS

Forty three healthy term infants were studied using daytime polysomnography on three occasions: 2-4 weeks post-term, 2-3 months post-term, and 5-6 months post-term. Multiple measurements of arousal threshold (cm H(2)O) in response to nasal air jet stimulation applied alternately to the nares were made in both active sleep (AS) and quiet sleep (QS) while infants slept supine. Arousal thresholds and sleep period lengths were compared between formula fed and breast fed infants at each age.

RESULTS

Arousal thresholds were not different between breast fed and formula fed infants in QS. However, in AS breast fed infants were significantly more arousable than formula fed infants at 2-3 months of age. There was no difference between groups of infants when sleep period length was compared at any study.

CONCLUSIONS

Breast fed infants are more easily aroused from AS at 2-3 months of age than formula fed infants. This age coincides with the peak incidence of SIDS.

The effect of maternal smoking on respiratory and arousal patterns in preterm infants during sleep

Prenatal exposure to cigarette smoke is associated with an increased risk of sudden infant death syndrome. The effect of maternal smoking on apnea and arousal patterns in preterm infants is currently unknown. Multichannel polysomnographic studies were performed in preterm infants. Thirty infants were enrolled into the study: 16 exposed prenatally to cigarette smoke (S) and 14 control infants (C). There was no difference in the gestational and postconceptional ages at the time of study. Maternal smoking was associated with a significant increase in the apneic index in these infants (28.6 +/- 6.4/hour [S] vs. 13.2 +/- 3.9 [C]; p<0.05), and the difference was noted for obstructive events and only during active sleep. The arousal index was significantly decreased in the maternal smoking group (34.5 +/- 2.3/hour [S] vs. 46.3 +/- 5.6/hour [C]; p<0.05), with a specific decrease in percentage of arousal after respiratory events (10.7 +/- 2.1% [S] vs. 29.4 +/- 5.4% [C]; p<0.05). In conclusion, preterm infants exposed prenatally to cigarette smoke have increased respiratory events during active sleep, predominantly due to obstructive apnea, and possibly a higher arousal threshold during apneic events. These alterations in respiratory and arousal patterns in preterm infants born to smoking mothers may lead to significant vulnerability in this population.

Sleep disorders in children

PURPOSE OF REVIEW

Childhood sleep disorders are one of the most prevalent complaints in the pediatrician's office. Infant sleep rhythm complaints from new mothers reach 46%, while childhood obstructive sleep apnea has a prevalence of 2% and adolescent insomnia with daily consequences surpasses that percentage.

RECENT FINDINGS

Each sleep disorder must be considered in context of age, as age influences the presentation and impact on the developing child or adolescent. For example, sleep-disordered breathing resulting in adult sleepiness can contribute to death in infants. The symptoms of narcolepsy are often masked until after adolescence, resulting in psychologically costly misdiagnoses.

SUMMARY

There are no outcome studies that track the long-term consequences of pediatric sleep disorders or their contribution to adult sleep problems, but this is an area of increasing research interest. This review assesses the most recent literature on pediatric sleep disorders from May 1, 2002, until April 30, 2003.

Effects of sleep position, sleep state and age on heart rate responses following provoked arousal in term infants

Previous studies have suggested that autonomic dysfunction may be involved in Sudden Infant Death Syndrome (SIDS). The major risk factors for SIDS are the prone sleeping position and maternal smoking. Our aim was to examine the effects of sleeping position and maternal smoking on the postnatal maturation of autonomic function by examining heart rate responses following arousal in healthy term infants. Twenty-four infants (11 born to mothers who smoked during pregnancy and 13 to mother who did not smoke) were studied using daytime polysomnography and multiple measurements of arousal threshold (cm H(2)O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep (AS) and quiet sleep (QS). We demonstrated no difference between smoking and non-smoking groups of infants in any of our measurements, and thus combined data from the groups. Baseline (BHR) was elevated in the prone compared to the supine position in quiet sleep (QS) at 2-3 weeks (p<0.001) and 5-6 months (p<0.001), and in active sleep (AS) at 2-3 and 5-6 months (p<0.05). BHR was significantly elevated in AS compared to QS in the supine position at all ages (p<0.01) and in the prone position at 2-3 (p<0.001) and 5-6 months (p<0.05). Increases in heart rate (deltaHR%) following arousal were significantly greater in the supine compared to the prone position in QS at 2-3 weeks (p<0.05) and in AS at both 2-3 (p<0.01) and 5-6 months (p<0.05). DeltaHR% was significantly greater in AS compared to QS in both supine (p<0.05) and prone (p<0.001) positions at 2-3 weeks and in the supine position at 2-3 months (p<0.001). We conclude that sleep state, sleep position and postnatal age affect the cardiac responses following arousal from sleep in healthy term infants. Impairment of heart rate control in the prone position may be important in understanding the increased risk for SIDS in this position.

Arousal responses and risk factors for sudden infant death syndrome

BACKGROUND

Failure to arouse from sleep has been postulated as a mechanism to explain the final pathway of sudden infant death syndrome (SIDS).

METHODS

We have reviewed the effects of the major risk factors for SIDS, prone sleep position, maternal smoking, prematurity and recent infection on arousability from sleep. In human infants it has been consistently demonstrated that arousal from sleep in response to a variety of stimuli is more difficult to induce from quiet sleep (QS) compared to active sleep (AS) over the first 6 months of life.

RESULTS

In the prone position both stimulus-induced and spontaneous arousability from both QS and AS were impaired at 2-3 weeks and 2-3 months, but not at 5-6 months of age in both term and preterm infants. In term infants exposed to maternal smoking during pregnancy both stimulus-induced and spontaneous arousability were impaired when infants slept supine in QS at 2-3 months of age. Healthy preterm infants showed no impairment in arousability compared with term infants at matched postconceptional ages. However, preterm infants with a history of apnoea and bradycardia of prematurity showed decreased arousal responses in both QS and AS and this impairment was positively correlated to their 'perinatal risk score'. Infants who had recently suffered an infection requiring hospitalization showed decreased arousability in QS on the day of discharge when compared to 2 weeks later when they were completely well.

CONCLUSIONS

In summary it has been found that the major risk factors for SIDS identified from epidemiological studies also decrease arousability from sleep in infants. We propose that this decreased arousability from sleep may be involved in the final pathway of SIDS.