Increased protein intake augments kidney volume and function in healthy infants.

Protein intake has been directly associated with kidney growth and function in animal and human observational studies. Protein supply can vary widely during the first months of life, thus promoting different kidney growth patterns and possibly affecting kidney and cardiovascular health in the long term. To explore this further, we examined 601 healthy 6-month-old formula-fed infants who had been randomly assigned within the first 8 weeks of life to a 1-year program of formula with low-protein (LP) or high-protein (HP) contents and compared them with 204 breastfed (BF) infants. At 6 months, infants receiving the HP formula had significantly higher kidney volume (determined by ultrasonography) and ratios of kidney volume to body length and kidney volume to body surface area than did infants receiving the LP formula. BF infants did not differ from those receiving the LP formula in any of these parameters. Infants receiving the HP formula had significantly higher serum urea and urea to creatinine ratios than did LP formula and BF infants. Hence, in this European multicenter clinical trial, we found that a higher protein content of the infant formula increases kidney size at 6 months of life, whereas a lower protein supply achieves kidney size indistinguishable from that of healthy BF infants. The potential long-term effects of a higher early protein intake on long-term kidney function needs to be determined.

Cardiac changes during sleep in sleep-deprived infants.

OBJECTIVE: To evaluate the influence of a brief period of sleep deprivation on cardiac autonomic controls during sleep in healthy infants. DESIGN: Twelve healthy infants with a median age of 8 weeks (range, 7 to 18 weeks) were recorded polygraphically during a morning and an afternoon nap in a sleep laboratory. They were sleep deprived for approximately 2 hours, either in the morning or in the afternoon, before being allowed to fall asleep. Six infants were sleep deprived before the morning nap, and 6 before the afternoon nap. During both naps, their sleep, breathing, and heart-rate characteristics were continuously recorded. Spectral analysis of heart rate was evaluated as a function of sleep stages. Two major peaks were recognizable: a low-frequency component related to sympathetic and parasympathetic activities and a high-frequency component reflecting parasympathetic tonus. The ratio of low-frequency to high-frequency powers was calculated as an index of sympathovagal interaction. RESULTS: When sleep deprived, the infants had an increase in basal heart rate during non-rapid eye movement sleep (P=.021). With sleep deprivation, the ratio of low-frequency to high-frequency powers increased in non-rapid eye movement sleep (P=.005). These findings were consistent with an increase in sympathetic tone. CONCLUSION: Infants exposed to short-term sleep deprivation manifest changes in cardiac autonomic controls during sleep. These findings could be relevant to mechanisms associated with the sudden infant death syndrome.

Influence of swaddling on sleep and arousal characteristics of healthy infants.

OBJECTIVE: Swaddling is an old infant care practice. It was reported to favor sleep and to reduce crying among irritable infants. There are few data on the physiologic effects of swaddling on infants' sleep-wake characteristics. This study was conducted to evaluate whether swaddling influences infants' arousal thresholds for environmental auditory stress. DESIGN: Sixteen healthy infants, with a median age of 10 weeks (range: 6-16 weeks), underwent polygraphic recording in their usual supine position during one night. The infants were successively recorded swaddled and nonswaddled, or vice versa. In both conditions, the infants were exposed to white noise of increasing intensity, from 50 to 100 dB(A), during rapid eye movement sleep, to determine their arousal thresholds. RESULTS: Swaddling was associated with increases in the infants' sleep efficiency and in the time spent in non-rapid eye movement sleep. When swaddled, the infants awakened spontaneously less often. However, significantly less-intense auditory stimuli were needed during rapid eye movement sleep to induce cortical arousals when swaddled than when not swaddled. CONCLUSIONS: Swaddling promotes more-sustained sleep and reduces the frequency of spontaneous awakenings, whereas induced cortical arousals are elicited by less-intense stimuli. These findings could indicate that, although swaddling favors sleep continuity, it is associated with increased responsiveness to environmental auditory stress.

Decreased arousals among healthy infants after short-term sleep deprivation.

OBJECTIVE: Sleep deprivation is a risk factor for sudden infant death syndrome (SIDS). Recent changes in normal life routines were more common among SIDS victims, compared with control infants. Sleep deprivation can result from handling conditions or from sleep fragmentation attributable to respiratory or digestive conditions, fever, or airway obstructions during sleep. Compared with matched control infants, future SIDS victims exhibited fewer complete arousals by the end of the night, when most SIDS cases occur. Arousal from sleep could be an important defense against potentially dangerous situations during sleep. Because the arousal thresholds of healthy infants were increased significantly under conditions known to favor SIDS, we evaluated the effects of a brief period of sleep deprivation on sleep and arousal characteristics of healthy infants. DESIGN: Fourteen healthy infants, with a median age of 8 weeks (range: 6-18 weeks), underwent polygraphic recording during a morning nap and an afternoon nap, in a sleep laboratory. The infants were sleep-deprived for 2 hours before being allowed to fall asleep. Sleep deprivation was achieved by keeping the infants awake, with playing, handling, and mild tactile or auditory stimulations, for as long as possible beyond their habitual bedtimes. To avoid any confounding effect attributable to differences in sleep tendencies throughout the day, sleep deprivation was induced before either the morning nap or the afternoon nap. Seven infants were sleep-deprived before the morning nap and 7 before the afternoon nap. The sleep and arousal characteristics of each infant were compared for the non-sleep-deprived condition (normal condition) and the sleep-deprived condition. During each nap, the infants were exposed, during rapid eye movement (REM) sleep, to white noise of increasing intensity, from 50 dB(A) to 100 dB(A), to determine their arousal thresholds. Arousal thresholds were defined on the basis of the lowest auditory stimuli needed to induce arousal. After the induced arousal, the infants were allowed to return to sleep to complete their naps. RESULTS: Sleep deprivation lasted a median of 120 minutes (range: 90-272 min). Most sleep characteristics were similar for the normal and sleep-deprived conditions, including sleep efficiency, time awake, percentages of REM sleep and non-REM sleep, frequency and duration of central apnea and of periodic breathing, duration of obstructive apnea, mean heart rate and variability, and mean breathing rates during REM sleep and non-REM sleep. After sleep deprivation, the duration of the naps increased, whereas there were decreases in the latency of REM sleep and in the density of body movements. More-intense auditory stimuli were needed for arousal when the infants were sleep-deprived, compared with normal nap sleep. Sleep deprivation was associated with a significant increase in the frequency of obstructive sleep apnea episodes, especially during REM sleep. No significant differences were noted when the effects of morning and afternoon sleep deprivation were compared. No correlation was found between the duration of sleep deprivation and either the frequency of obstructive apnea or the changes in arousal thresholds, although the infants who were more sleep-deprived exhibited tendencies toward higher auditory arousal thresholds and shorter REM sleep latencies, compared with less sleep-deprived infants. There were tendencies for a negative correlation between the auditory arousal thresholds and REM sleep latencies and for a positive correlation between the auditory arousal thresholds and the frequencies of obstructive apnea during REM sleep. CONCLUSIONS: Short-term sleep deprivation among infants is associated with the development of obstructive sleep apnea and significant increases in arousal thresholds. As already reported, sleep deprivation may induce effects on respiratory control mechanisms, leading to impairment of ventilatory and arousal responses to chemical stimulation and decreases in genioglossal electromyographic activity during REM sleep. These changes in respiratory control mechanisms could contribute to the development of obstructive apnea. The relationship between the development of obstructive apnea and increases in arousal thresholds remains to be evaluated. Adult subjects with obstructive sleep apnea exhibited both sleep fragmentation and increases in arousal thresholds. Conversely, sleep deprivation increased the frequency and severity of obstructive sleep apnea. In this study, the increases in arousal thresholds and the development of obstructive apnea seemed to result from the preceding sleep deprivation. The depressed arousals that follow sleep deprivation have been attributed to central mechanisms, rather than decreases in peripheral sensory organ function. Such mechanisms could include disturbances within the reticular formation of the brainstem, which integrates specific facilitory inputs, such as ascending pathways from auditory receptors, and inhibitory inputs from the cortex. It remains to be determined whether the combination of upper airway obstruction and depressed arousability from sleep contributes to the increased risk of sudden death reported for sleep-deprived infants.