Trigeminal airstream stimulation. Maturation-related cardiac and respiratory responses during REM sleep in human infants

Physiological responses to facemask application in newborns immediately after birth

OBJECTIVE

Application of a face mask may induce apnoea and bradycardia, possibly via the trigeminocardiac reflex (TCR). We aimed to describe rates of apnoea and bradycardia in term and late-preterm infants following facemask application during neonatal stabilisation and compare the effects of first facemask application with subsequent applications.

DESIGN

Subgroup analysis of a prospective, randomised trial comparing two face masks.

SETTING

Single-centre study in the delivery room PATIENTS: Infants>34 weeks gestational age at birth METHODS: Resuscitations were video recorded. Airway flow and pressure were measured using a flow sensor. The effect of first and subsequent facemask applications on spontaneously breathing infants were noted. When available, flow waveforms as well as heart rate (HR) were assessed 20 s before and 30 s after each facemask application.

RESULTS

In total, 128 facemask applications were evaluated. In eleven percent of facemask applications infants stopped breathing. The first application was associated with a higher rate of apnoea than subsequent applications (29% vs 8%, OR (95% CI)=4.76 (1.41-16.67), p=0.012). On aggregate, there was no change in median HR over time. In the interventions associated with apnoea, HR dropped by 38bpm [median (IQR) at time of facemask application: 134bpm (134-150) vs 96bpm (94-102) 20 s after application; p=0.25] and recovered within 30 s.

CONCLUSIONS

Facemask applications in term and late-preterm infants during neonatal stabilisation are associated with apnoea and this effect is more pronounced after the first compared with subsequent applications. Healthcare providers should be aware of the TCR and vigilant when applying a face mask to newborn infants.

TRIAL REGISTRATION NUMBER

ACTRN12616000768493.

A Step further-The Role of Trigeminocardiac Reflex in Therapeutic Implications: Hypothesis, Evidence, and Experimental Models

The trigeminocardiac reflex (TCR) is a well-recognized brainstem reflex that represents a unique interaction between the brain and the heart through the Vth and Xth cranial nerves and brainstem nuclei. The TCR has mainly been reported as an intraoperative phenomenon causing cardiovascular changes during skull-base surgeries. However, it is now appreciated that the TCR is implicated during non-neurosurgical procedures and in nonsurgical conditions, and its complex reflex pathways have been explored as potential therapeutic options in various neurological and cardiovascular diseases. This narrative review presents an in-depth overview of hypothetical and experimental models of the TCR phenomenon in relation to the Vth and Xth cranial nerves. In addition, primitive interactions between these 2 cranial nerves and their significance are highlighted. Finally, therapeutic models of the complex interactions of the TCR and areas for further research will be considered.

Reflexes that impact spontaneous breathing of preterm infants at birth: a narrative review

Some neural circuits within infants are not fully developed at birth, especially in preterm infants. Therefore, it is unclear whether reflexes that affect breathing may or may not be activated during the neonatal stabilisation at birth. Both sensory reflexes (eg, tactile stimulation) and non-invasive ventilation (NIV) can promote spontaneous breathing at birth, but the application of NIV can also compromise breathing by inducing facial reflexes that inhibit spontaneous breathing. Applying an interface could provoke the trigeminocardiac reflex (TCR) by stimulating the trigeminal nerve resulting in apnoea and a reduction in heart rate. Similarly, airflow within the nasopharynx can elicit the TCR and/or laryngeal chemoreflex (LCR), resulting in glottal closure and ineffective ventilation, whereas providing pressure via inflations could stimulate multiple receptors that affect breathing. Stimulating the fast adapting pulmonary receptors may activate Head's paradoxical reflex to stimulate spontaneous breathing. In contrast, stimulating the slow adapting pulmonary receptors or laryngeal receptors could induce the Hering-Breuer inflation reflex or LCR, respectively, and thereby inhibit spontaneous breathing. As clinicians are most often unaware that starting primary care might affect the breathing they intend to support, this narrative review summarises the currently available evidence on (vagally mediated) reflexes that might promote or inhibit spontaneous breathing at birth.

Comparing the effect of two different interfaces on breathing of preterm infants at birth: A matched-pairs analysis

OBJECTIVE

Applying a face mask could provoke a trigeminocardiac reflex. We compared the effect of applying bi-nasal prongs with a face mask on breathing and heart rate of preterm infants at birth.

METHODS

In a retrospective matched-pairs study of infants <32 weeks of gestation, the use of bi-nasal prongs for respiratory support at birth was compared to the use of a face mask. Infants who were initially breathing at birth and subsequently received respiratory support were matched for gestational age (±4 days), birth weight (±300 g), general anaesthesia and gender. Breathing, heart rate and other parameters were collected before and after interface application and in the first 5 min thereafter.

RESULTS

In total, 130 infants were included (n = 65 bi-nasal prongs, n = 65 face mask) with a median (IQR) gestational age of 27⁺² (25⁺³-28⁺⁴) vs 26⁺⁶ (25⁺³-28⁺⁵) weeks. The proportion of infants who stopped breathing after applying the interface was not different between the groups (bi-nasal prongs 43/65 (66%) vs face mask 46/65 (71%), p = 0.70). Positive pressure ventilation was given more often when bi-nasal prongs were used (55/65 (85%) vs 40/65 (62%), p < 0.001). Heart rate (101 (75-145) vs 110 (68-149) bpm, p = 0.496) and oxygen saturation (59% (48-87) vs 56% (35-84), p = 0.178) were similar in the first 5 min after an interface was applied in the infants who stopped breathing.

CONCLUSION

Apnoea and bradycardia occurred often after applying either bi-nasal prongs or a face mask on the face for respiratory support in preterm infants at birth.

Sudden Infant Death Syndrome - Role of Trigeminocardiac Reflex: A Review

Sudden infant death syndrome (SIDS) is an unexplained death in infants, which usually occurs during sleep. The cause of SIDS remains unknown and multifactorial. In this regard, the diving reflex (DR), a peripheral subtype of trigeminocardiac reflex (TCR), is also hypothesized as one of the possible mechanisms for this condition. The TCR is a well-established neurogenic reflex that manifests as bradycardia, hypotension, apnea, and gastric hypermotility. The TCR shares many similarities with the DR, which is a significant physiological adaptation to withstand hypoxia during apnea in many animal species including humans in clinical manifestation and mechanism of action. The DR is characterized by breath holding (apnea), bradycardia, and vasoconstriction, leading to increase in blood pressure. Several studies have described congenital anomalies of autonomic nervous system in the pathogenesis of SIDS such as hypoplasia, delayed neuronal maturation, or decreased neuronal density of arcuate nucleus, hypoplasia, and neuronal immaturity of the hypoglossal nucleus. The abnormalities of autonomic nervous system in SIDS may explain the role of TCR in this syndrome involving sympathetic and parasympathetic nervous system. We reviewed the available literature to identify the role of TCR in the etiopathogenesis of SIDS and the pathways and cellular mechanism involved in it. This synthesis will help to update our knowledge and improve our understanding about this mysterious, yet common condition and will open the door for further research in this field.

The diving reflex in healthy infants in the first year of life

A cohort study was conducted with a random sample of 33 healthy infants evaluated at birth and at 1, 2, 3, 4, 5, 6, 9, and 12 months to determine the frequency of respiratory rate changes in response to air blown over the face (diving reflex) in the first year of life, and to standardize the description of diving reflex occurrence. All 33 infants remained neurologically normal throughout follow-up. Diving reflex was observed in 95.3% of newborns and in 100% of infants between 2 and 6 months of age. At 6 months, it started to decrease but persisted in 90% of the infants up to 12 months. The diving reflex is highly prevalent in the first year of life and can be easily elicited by applying a flow of air over the infant's face, particularly during crying.

Exploring the olfactory environment of premature newborns: a French survey of health care and cleaning products used in neonatal units

AIM

To assess the main determinants of the newborn's nosocomial olfactory environment.

METHODS

An electronic questionnaire was sent to 99 neonatal units in France. Senior nurses and/or physicians described the nature and use of skin care products (e.g. umbilical cord and skin disinfectants, adhesive removers), lubrications used for tubes positioning, disinfectants used to clean materials, hand hygiene products (e.g. alcohol-based hand rubs, soaps) and newborns' bath.

RESULTS

Nine groups of products and 76 distinct commercial preparations were identified. Depending on their level of respiratory support, preterm newborns were estimated to be exposed to nosocomial odours (NO) an average of 1320-1800 times during their first month of life. During their whole hospital stay, newborns of 28 and 32 weeks of gestational age could be exposed to NOs products an average of 3448 and 2024 times, respectively. The use of these products varied among medical centres. Newborns were most frequently exposed to the odour of aqueous alcoholic solutions.

CONCLUSIONS

Vulnerable preterm infants are daily exposed to multiple NOs most of them be considered as irritant for the nose. Minimizing infants' exposure to them would be beneficial. Future studies should describe the exact olfactory properties of the products considered essential for infant care and should assess their effects on the infant's well-being and development.

Comparison of heart rate responses during cortical and subcortical arousals in term and preterm infants

The aim of this study was to determine whether prematurity affects heart rate responses during spontaneous arousals. Polygraphic recordings were performed during undisturbed daytime naps in 35 preterm infants (gestational age at birth 32+/-2 weeks) and 35 term infants. Arousals were scored according to the recommendations of the International Paediatric Work Group on Arousals and categorized either as cortical arousals (CA) or subcortical arousals (SCA). Heart rate (HR) and respiratory frequency (RF) were measured during arousal and during the 10-s and 30-s period before and after arousal. Changes in HR and RF were expressed as the percentage of modification normalized for the 30-s period preceding arousal. Altogether, 122 arousals in preterm infants (66 CA, 56 SCA) and 105 arousals in term infants (57 CA, 48 SCA) were scored. Mean duration of the arousal period was 9+/-4 s and 8+/-3 s, respectively. In term infants, a significant increase in HR during arousal could be shown (11.3+/-8.2%; p<0.001), whereas this increase was significantly greater during CA compared to SCA (13.7+/-6.2% versus 8.4+/-9.4%; p<0.001). In contrast, HR decreased during arousal in preterm neonates (-3.9+/-19.3%; p<0.05). These findings suggest that cardiovascular control seems to be maturationally delayed in preterm infants, which may contribute to their increased risk for Sudden Infant Death Syndrome (SIDS).

An update on childhood snoring

Habitual snoring or daily snoring is a symptom of sleep-disordered breathing (SDB) in children and it is reported in about 10% of children. SDB includes primary snoring, upper airway resistance syndrome (UARS), obstructive hypoventilation syndrome and obstructive sleep apnea syndrome (OSAS). Classification of SDB in a particular snoring child requires an overnight polysomnography (PSG). Manual scoring of PSG is mandatory in children. Risk factors for SDB include allergic rhinitis, passive smoking, obesity, dysmorphic syndromes and neuromuscular disorders.

CONCLUSION

Treatment includes general measures like treatment of allergic rhinitis, weight reduction in obese children, and avoidance of sleep deprivation. Specific measures include removal of adenoid and tonsils. Complications of SDB include neurocognitive impairment, hypertension and failure to thrive.

Effects of prematurity on heart rate control: implications for sudden infant death syndrome

In Western countries, 5-11% of all infants are born before 37 weeks of gestation, and with improvements in modern intensive care techniques the number of these preterm infants that survive continues to increase. Preterm birth is one of the leading causes of neonatal morbidity and mortality in developed countries, accounting for 60-80% of infant deaths in those without congenital anomalies. Furthermore, in the post-neonatal period, preterm infants are at four-times greater risk of sudden infant death syndrome. It has been suggested that this increased risk is due to immature autonomic control. This article provides an overview of studies assessing autonomic control of the cardiovascular system in preterm infants.

Heart rate responses to non-arousing trigeminal stimulation in infants: effects of sleep position, sleep state and postnatal age

AIMS

The aim of this study was to examine the effects of maternal smoking, sleeping position, sleep state and postnatal age on heart rate changes following non-arousing trigeminal stimulation in infants.

SUBJECTS

We studied healthy term infants, 13 of whom were born to mothers who did not smoke and 11 to mothers who smoked during pregnancy. Each infant was studied using daytime polysomnography on 3 occasions: (a) 2-3 weeks, (b) 2-3 months and (c) 5-6 months after birth. Nasal air-jet stimulation was presented in both active sleep (AS) and quiet sleep (QS) when infants slept both prone and supine.

RESULTS

We found no difference between infants of smoking and non-smoking mothers in any of the parameters measured. Minimum HR (MinHR) following non-arousing trigeminal stimulation was significantly lower in the supine compared to the prone sleeping position at 2-3 weeks and 2-3 months of age (p<0.05) in AS, and at all 3 ages in QS (p<0.01). MinHR was significantly lower in QS compared to AS at 2-3 months when infants slept prone and at 5-6 months when sleeping supine (p<0.01). In QS, MinHR became lower with increasing postnatal age in both sleep positions (p<0.01). In AS, there was no maturational effect. The normalized bradycardia (DeltaHR%) was significantly greater in AS than in QS at 2-3 weeks of age (p<0.05) when infants slept supine.

CONCLUSION

Our study has shown that there was a decrease in heart rate (MinHR) following trigeminal stimulation in infants up to 6 months of age and this was affected by sleep position and sleep state, being larger in the supine sleeping position and the QS state.

Comparison of postnatal development of heart rate responses to trigeminal stimulation in sleeping preterm and term infants

Autonomic dysfunction has been regarded as a possible cause of the sudden infant death syndrome (SIDS) and it has been suggested that preterm infants, who are at a greater risk of SIDS than term infants, may have immature autonomic control. Our aim was to compare the maturation of cardiac autonomic control during sleep in preterm and term infants by examining heart rate responses to arousing and non-arousing trigeminal stimuli. Preterm infants (n = 15) and term infants (n = 24) were studied longitudinally with daytime polysomnography. Air-jet stimulation of the nares was delivered in both active sleep (AS) and quiet sleep (QS), and heart rate (HR) changes recorded for both arousal and non-arousal responses. Changes in HR (DeltaHR%) were calculated as the relative differences between baseline HR (BHR) and either MaxHR (arousal) or MinHR (non-arousal). Comparisons of HR changes between sleep states and postnatal ages were made with two-way anova for repeated measures and between groups with two-way anova. The increase in HR (DeltaHR%) was greater in term than preterm infants (P < 0.05), but only at 2-3 weeks corrected postnatal age (CPA). In preterm infants, there were no differences in BHR between sleep states, whereas in term infants, BHR was higher in AS than in QS at 2-3 weeks and 2-3 months of age. The smaller DeltaHR% to arousing stimuli in preterm infants compared with term infants at 2-3 weeks suggests that cardiac sympathetic activity in preterm infants may be lower than in term infants. This mechanism may account for the increased risk for SIDS of preterm infants.

Olfaction in the fetal and premature infant: functional status and clinical implications

This article considers olfaction as a functioning source of information for the fetus and the neonate, born on term or prematurely. It aims to present how odors are involved in the sensory continuity between the prenatal and postnatal environments and how they influence the earliest adaptive responses of newborns in the realms of self-regulation, emotional balance, feeding, and social interactions.Finally, it evaluates odors as sensory means to ameliorate the physiologic and behavioral responses of preterm infants to the adverse impacts of separation from mother, nonoral feeding, or iatrogenic distress.

[Standardized oculocardiac reflex in ex-premature near full term (93 cases)]

The aim of the study was to present data investigating vagal reactivity in a population of premature infants reaching term, using the oculo-cardiac reflex.

PATIENTS AND METHODS

Ninety three premature infants, free of any disease, near full term at the moment of testing, were prospectively investigated at a time close to discharge from neonatal unit. After an all-night polygraphic recording, a standardized oculo-cardiac reflex test was performed during quiet sleep. Data were classified in relation to both chronological and postconceptional ages. Simple liner regression analyses were performed on the selected variables.

RESULTS

The results showed heterogeneity of the vagal response in this population: longest asystole (1049 ms +/- 540; 95th percentile = 1894 ms); maximal percentage of deviation between two successive RR intervals (88% +/- 90; 95th percentile = 200%); and duration between the beginning of decrease in heart rate and return to mean heart rate (14 s +/- 10; 95th percentile = 30 s).

CONCLUSION

Our healthy premature infants at time of discharge exhibited a wider range of vagal reactivity than previously reported for the full term newborns. Considering our findings, we recommend caution before proceeding with treatment of vagal bradycardia in a similar premature infant population.

The role of gastro-oesophageal reflux in the aetiology of SIDS

Gastro-oesophageal reflux (GOR) has been identified as a possible cause of SIDS. Several features of GOR unique to infants presenting with apparent life-threatening events (ALTEs) have led to its 'pathogenic' definition. One is that the life-threatening apnoea itself is initiated by GOR, another is that the ALTE relates to prolonged reflux during sleep, in a vulnerable sleep-state, and finally that the ALTE relates to excessive quantities of GOR. The presumption of GOR 'pathology' as a cause of SIDS however, is questionable in these susceptible infants for three reasons: firstly, GOR is physiological and occurs in most infants; secondly, there is no general consensus on what constitutes normal physiological reflux, and thirdly, variation in the recording technique and methods of data analysis and interpretation may account for the differences between study groups. It seems likely therefore if GOR is implicated in SIDS, additional factors are involved. Under certain circumstances, physiological GOR may trigger life-threatening apnoea in apparently healthy infants, that leads to SIDS. One mechanism that could explain such a death is reflex apnoea by stimulation of laryngeal chemoreceptors (LCR) during sleep. The conditions under which this could be fatal are the occurrence of gastric contents refluxed to the level of the pharynx during sleep, in the young infant who has depressed swallowing and arousal. That is, the occurrence of GOR to the level of the pharynx during sleep, an infrequent event that is usually innocuous, could be converted to a fatal event if swallowing is impaired and arousal depressed, by a variety of mediating factors such as prone sleeping, prematurity, sedatives, seizures or upper respiratory tract infections. The identification of LCR responses, particularly in prone sleeping and premature infants provide further evidence that this mechanism may be implicated in the aetiology of SIDS in apparently healthy infants.

Pontine cholinergic mechanisms enhance trigeminally evoked respiratory suppression in the anesthetized rat

In the present study, we investigated in anesthetized rats the influences of the pontine rapid-eye-movement (REM) sleep center on trigeminally induced respiratory responses. We evoked the nasotrigeminal reflex by electrical stimulation of the ethmoidal nerve (EN5) and analyzed the EN5-evoked respiratory suppression before and after injections into the pontine reticular nuclei of the cholinergic agonist carbachol. After injections of 80-100 nl of carbachol (20 mM), we observed a decrease in respiratory rate, respiratory minute volume, and blood pressure but an increase in tidal volume. In those cases in which carbachol injections alone caused these REM sleep-like autonomic responses, we also observed that the EN5-evoked respiratory suppression was significantly potentiated. Unfortunately, carbachol injections failed to depress genioglossus electromyogram (EMG) effectively, because the EMG activity was already strongly depressed by the anesthetic alpha-chloralose. We assume that pontine carbachol injections in our anesthetized rats cause autonomic effects that largely resemble REM sleep-like respiratory and vascular responses. We therefore conclude that the observed potentiation of EN5-evoked respiratory suppression after carbachol might be due to REM sleep-associated neuronal mechanisms. We speculate that activation of sensory trigeminal afferents during REM sleep might contribute to pathological REM sleep-associated respiratory failures.

Reproducibility of the alternating breath test of fractional inspired O2 in infants

We conducted a reproducibility study of the alternating breath test (ABT) for assessing peripheral chemoreceptor function in infants. The ABT delivers a rapid hypoxic stimulus to the peripheral chemoreceptors with breath-by-breath alternations of the inspired O2 fraction. The reproducibility of the ABT performed on a single occasion has not been extensively studied in infants. Eight unsedated infants (postnatal age, 22+/-19 d; weight, 3.2+/-0.4 kg) were studied in standardized conditions: morning naps, supine position, room temperature 22-24 degrees C, quiet sleep, and face mask attached to a pneumotachograph connected to a two-way electric valve. Respiratory gases were analyzed by mass spectrometer. Two ABTs were performed. Each included a 2-min control run (CR) alternating between air and air, and a 2-min test run (TR) alternating between air and 0.15 O2. After data preprocessing, on average 13+/-11% of the data were rejected because of sighs, apneas, and cycles with the fraction of inspired oxygen above 0.17. Using the remaining validated breaths, the response to ABT was calculated for the CR, for all breaths in the TR (TR(T)), and for the first 50 breaths of the TR (TR50). During the ABTs oxygen saturation did not fall below 96%, and heart rate was not affected. Inspired and end-tidal CO2 fractions remained unchanged during the ABTs. FetO2 oscillated in TRs at a lower values than in CRs and differed significantly between breaths of air and hypoxic breaths of TRs. All infants responded to ABT with percentage alternation coefficients of TRs significantly greater than those of CRs for all respiratory variables. The values of the coefficients were not significantly different between both ABT, and between TR50 and TR(T). The greatest values of the coefficients were for timing variables compared with flows and volume. We conclude that the ABT is a reproducible test of peripheral chemoreceptor function under standardized conditions.

Sleep-disordered breathing in children

The first series of children with obstructive sleep apnoea syndrome was reported in 1976. Later it became apparent that children may have breathing disorders during sleep without frank apnoea or 'hypopnoeas'. This pattern could be detected by measuring the oesophageal pressure. This led to the concept of sleep-disordered breathing as a spectrum that combines obstructive sleep apnoea syndrome and the upper airway resistance syndrome. Studies that do not take into account this spectrum may misclassify symptomatic patients as 'primary snorers'. The exact prevalence of sleep-disordered breathing in children is unknown but may be as high as 11%. There is a familial predisposition to sleep-disordered breathing. Nasal obstruction and mouth breathing influence facial growth, which may further lead to difficulty in breathing while asleep. Symptoms include an increase in total sleep time, nonspecific behavioural difficulties, hyperactivity, irritability, bed-wetting and morning headaches. Clinical signs include failure to thrive, increased respiratory effort with nasal flaring and suprasternal or intercostal retractions. Also, abnormal paradoxical inward motion of the chest may occur during sleep. Excessive daytime sleepiness and obesity are not always present. Untreated children may develop cardiovascular complications. The condition is treatable with continuous or bilevel positive airway pressure, and may be cured with surgery.

NMDA and GABAA receptors in the rat Kolliker-Fuse area control cardiorespiratory responses evoked by trigeminal ethmoidal nerve stimulation

1. Electrical stimulation (10 s) of the ethmoidal nerve (EN5) evokes the nasotrigeminal reflex responses, including apnoea, bradycardia and rise in arterial blood pressure. In the present study, we examined the involvement of N-methyl-D-aspartate (NMDA), AMPA/kainate, (gamma-aminobutyric acidA (GABAA) and glycine receptors in the Kolliker-Fuse (KF) nucleus in the mediation of the nasotrigeminal reflex responses. 2. Unilateral injections (n = 6) of 50-100 nl of the NMDA receptor antagonist AP5 into the KF area led to a significant blockade of the EN5-evoked respiratory depression and bradycardia. Injections placed into the midlevel of the KF area were most effective (80-90 % blockade). The rise in arterial blood pressure remained unaffected. 3. Unilateral injections (n = 6) of the AMPA/kainate receptor antagonist CNQX into the KF area failed to block EN5-evoked autonomic responses significantly. 4. Unilateral injections (n = 5) of the GABAA receptor antagonist bicuculline enhanced the EN5-evoked respiratory depression and bradycardia. The effect persisted for up to 30 s after stimulation. Bicuculline injections into the midlevel of the KF area were most effective. The increase in arterial blood pressure remained unaffected. 5. Unilateral injections (n = 5) of the glycine receptor antagonist strychnine into the KF area did not produce any significant effects on EN5-evoked autonomic responses. 6. Our results suggest that the KF area represents a mandatory relay for the nasotrigeminally induced apnoea and bradycardia which are predominantly mediated by NMDA receptors in the KF. Furthermore, it appears that KF neurons are under a potent GABAergic inhibitory control. The EN5-evoked rise in arterial blood pressure was not altered by any of the drugs and, therefore, appears not to be mediated via the KF.

Dynamic changes in arousal threshold during sleep in the human infant

Failure to arouse from sleep is a possible mechanism leading to sudden infant death. Using a controlled pulsatile air jet applied alternately to the nostrils we have made multiple measures of arousal threshold both between and within sleep states. Infants (n = 22) born at term were studied at 2-3 wk postterm (mean age 13 d, range 9-17 d, study 1) and again at 2-3 mo postterm (mean age 78 d, range 56-98 d, study 2). Arousal threshold (stimulus driving pressure, cm H2O) was determined in both active sleep (AS) and quiet sleep (QS). At both ages arousal threshold in QS was significantly higher (251 +/- 24 and 298 +/- 35) than in AS (163 +/- 19 and 144 +/- 29) (p < 0.001). In a morning sleep period, the first and second QS epochs were compared in each baby. In both study 1 and study 2, respectively, arousal thresholds were significantly higher in the second QS epoch (270 +/- 34 and 497 +/- 100) than in the first QS epoch (198 +/- 29 and 252 +/- 69) (p < 0.05 and p < 0.02). There was a significant correlation in individual infants between arousal thresholds in the two states at both ages (p < 0.005 and p < 0.007, respectively). Regression analysis showed no correlation between the length of time the infant had been in a particular sleep state and the arousal threshold in either state in study 1 or in AS in study 2; however, arousal threshold increased significantly (p < 0.01) with time in QS in study 2. This study has expanded on previous findings that arousability is sleep state-dependent by demonstrating that arousability in QS is also altered by the length of time that the infant has been asleep.

Estimation of fast vagal response by time-dependent analysis of heart rate variability in normal subjects

In this study, the selective windowed discrete Fourier transform algorithm (SDA) for time-frequency analysis was applied on non-stationary heart rate signals, recorded during vagal perturbations. These perturbations were achieved in healthy subjects (aged 6-42 years) by inducing the oculocardiac reflex and the diving response. The results showed that the SDA can detect and quantify the expected, although brief, increase in vagal tone, by displaying a marked transient increase in the respiratory peak of the time-dependent spectrum. It allowed us to demonstrate an age-dependent reduction of the vagal response, obtained from the respiratory peak of the heart rate time-dependent spectrum. The SDA approach is thus an adequate tool for the evaluation of an instantaneous change in vagal activity, as well as steady-state vagal activity, including the detection of a malfunction or an exaggerated response of the parasympathetic tone. Since changes in heart rate control are expressed by a transient response, they would not have been detected by a standard, steady-state spectral analysis of heart rate variability, which requires the consideration of long and steady trace lengths and would therefore cause smearing of such fast changes. Time-dependent, or transient changes in autonomic control can thus be detected and quantified by SDA time-frequency analysis.

Cardiorespiratory adaptation during sleep in infants and children

The cardiorespiratory control system undergoes functional maturation after birth. Until this process is completed, the cardiorespiratory system is unstable, placing infants at risk for cardiorespiratory disturbances, especially during sleep. The profound influence of states of alertness on respiratory and cardiac control has been the focus of intense scrutiny during the last decade. The effects of rapid-eye movement (REM) sleep on various mechanisms involved in cardiorespiratory control are of particular significance during the postnatal period since newborns spend much of their time in this sleep state. In fullterm newborns, REM sleep occupies more than 50% of total sleep time, and this percentage is even greater in preterm newborns. From term to six months of age, the proportion of REM sleep decreases. Since respiratory and cardiac disturbances are known to occur selectively during REM sleep, the predominance of REM sleep may be a risk factor for abnormal sleep-related events during early infancy. Awareness of these developmental changes in sleep patterns is important for clinicians dealing with problems such as apparent life-threatening events (ALTE), sudden infant death syndrome (SIDS), and/or cardiorespiratory responses to respiratory disorders. Our current understanding of respiratory and cardiac control rests mainly on studies conducted during the first months of life. There is a paucity of data on late infancy and early childhood. The present paper will review available data on how sleep affects 1) ventilatory mechanics, in particular of the upper airways and the chest wall; ventilation and apnea; gas exchange; chemoreceptor function; and arousal responses; 2) changes in heart rate and heart rate variability, and the occurrence and mechanisms of bradycardia.

Circadian rhythm of cardiac responses to vagal stimulation tests

To evaluate the existence of a circadian rhythm in cardiac responses to vagal stimulation tests, 10 children without neurologic or cardiopulmonary disease, were studied using a standardized procedure. A trigeminal airstream stimulation test (TAS) and an ocular compression test (OCT) were subsequently performed at 4 nonequidistant hours. These 2 vagal stimulation tests were performed according to well-established, previously published techniques. Prolongation of the RR-interval during TAS and OCT was calculated and compared to the mean control RR-interval preceding the stimulation period. Prolongation of the RR-interval during the stimulation period was obtained in all instances during TAS and OCT. Chronobiologic analysis was determined by the cosinor method and bootstrap analysis. A significant circadian rhythm was found in cardiac responses to vagal stimulation for both TAS and OCT. The maximal response hour for TAS was between 9:06 p.m. and 5:18 a.m. and for OCT between 10:18 p.m. and 4:24 a.m. The mean value and 95% intervals for the cardiac responses to both vagal stimulation tests revealed, when using the bootstrap analysis, an important overlap in the hour of appearance of the maximal responses to these procedures; the bootstrap analysis of the peak of the acrophase was at 2:50 a.m. for TAS and 1:15 a.m. for OCT. Our results indicate that there is a circadian rhythm in cardiac responses to vagal stimulation tests and demonstrate a preponderance of these responses during the early morning hours.