![]() Periodic breathing is common in stage R sleep, but may also occur rarely in N sleep. This is a normal phenomenon in both term and preterm infants, which is thought to reflect immaturity in breathing control. Periodic breathing is characterised by recurrent central apnoea and intermittent respiratory effort ( figure 3). In addition, both tidal volume and inspiratory time increase from preterm through infancy and beyond. Breathing patterns become more stable with increasing maturation with a reduction in variability of tidal volume as well as a fall in respiratory rate also occurring throughout infancy. As highlighted above, sleep architecture is one of these, as are pattern and control of breathing. Over this first 3 months of life, many physiological functions become more organised. From this point onward quiet sleep increases in proportion so that by 3 months corrected gestational age it is the dominant sleep state. ![]() However, in the post-natal setting active sleep emerges as a recognisable entity at around 28–30 weeks gestational age, whilst quiet sleep begins to become apparent much later (around 36 weeks). Periods of cycling activity interspersed with periods of inactivity are identifiable in the human foetus from 28–32 weeks of pregnancy that suggest human sleep is an entity by this gestational age. Normal sleep and normal sleep breathing in infancy Figure 2 demonstrates the appearances of tracé alternant in an infant undergoing polysomnography. Quiet sleep appears similar to adult NREM sleep (high voltage EEG that may be continuous or discontinuous: tracé alternant), with eyes closed, few movements and a regular respiratory pattern. In addition, squirming, grimacing and small movements of face and limbs may be noted. Active sleep shares some similarity with adult REM sleep (irregular heart rate and EEG, rapid eye movements and reduced electromyography (EMG) activity/muscle tone). Indeed sleep stage scoring systems exist for infants that are independent of or complementary to electrophysiological measures. In early infancy the distinction between active sleep and quiet sleep cannot be made on EEG criteria alone, and behavioural and respiratory correlates will change with age. An indeterminate sleep stage is used for epochs that display characteristics of both active sleep and quiet sleep. The scoring of infants sleep staging is more difficult due to immaturity in the EEG pattern, such that a dichotomy between active sleep and quiet sleep was proposed by A nders et al. ![]() Rules are available from infancy onwards to facilitate scoring of respiratory events. In addition to the staging of sleep, the AASM guidelines are used for the scoring of respiratory events be they obstructive (apnoea or hypopnoea), central (apnoea or hypopnoea) or mixed, which occur with an associated arousal, awakening or desaturation. Figure 1 demonstrates the appearances of N3 and REM sleep in a child aged 8 years. The visual scoring rules for sleep staging in children are applicable from the age of 2 months post-corrected gestational age onwards. The Rechtschaffen and Kales scoring system has been superseded by the American Academy of Sleep Medicine (AASM) guidelines, which are used for scoring worldwide and divide sleep stages as R (REM), N1 (stage 1 NREM), N2 (stage 2 NREM), N3 (stage 3 and 4 NREM sleep combined, also known as slow-wave sleep) and N (non-REM indeterminate stage). ![]() NREM sleep was further divided into stages 1–4 based on electroencephalography (EEG) characteristics. This manual dichotomised sleep stages as rapid eye movement (REM) sleep or non-rapid eye movement (NREM) sleep. The scoring of sleep stages was first proposed for adults in 1968 by R echtschaffen and K ales who published a scoring manual. Sleep is characterised by a series of sleep stages. Sleep and breathing are intrinsically related functions, and this relationship is critical to the understanding of sleep disordered breathing in infancy. Sleep architecture, total sleep time and sleep staging differ considerably as one transcends from fetal life to adulthood, with a further set of changes to the way we sleep occurring as one heads towards senescence. Sleep is a distinct physiological state with changes in brain activity, muscle tone and autonomic function (cardiac and respiratory control) as compared with wakefulness. ![]()
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