Functional impairment of the brainstem in infants with bronchopulmonary dysplasia

Altered maturation in brainstem neural conduction in very premature babies with fetal growth restriction

BACKGROUND

Using maximum length sequence brainstem auditory evoked response (MLS BAER) to study brainstem neural conduction and maturation in fetal growth restriction (FGR) babies born very prematurely and assess the effect of FGR on brainstem neural maturation.

METHODS

MLS BAER was recorded and analyzed at a mean 40 week postmenstrual age in babies born at 27-32 week gestation without other major perinatal conditions or problems. The data were compared between babies with FGR (n = 30) and age-matched babies without FGR (n = 34) to define any differences.

RESULTS

A notable difference in MLS BAER was found in interpeak intervals between the babies with FGR and those without FGR. The FGR babies manifested significantly shortened I-III interval, moderately prolonged III-V interval, and significantly decreased III-V/I-III interval ratio. The slope of the I-III interval-rate function in FGR babies was moderately decreased, relative to that in the babies without FGR.

CONCLUSION

FGR babies born very prematurely are associated with accelerated or precocial neural maturation at caudal brainstem regions, but moderately delayed maturation at rostral brainstem regions. The altered brainstem neural maturation is different from previously reported mildly delayed maturation in FGR babies born less prematurely, and may have important implication for neurodevelopmental outcome.

IMPACT

This first MLS BAER study in FGR found that brainstem neural maturation in very premature FGR babies differed from age-matched non-FGR babies. Neural maturation in very premature FGR babies is accelerated or precocial at caudal brainstem regions but moderately delayed at rostral brainstem regions. The altered maturation is different from previously reported mild delay in brainstem neural maturation in FGR babies born less prematurely. FGR exerts a major and differential effect on brainstem neural maturation in babies born very prematurely. This alteration in very premature FGR babies may have important implication for their neurodevelopment.

Postnatal abnormality in brainstem neural conduction in neonatal bronchopulmonary dysplasia survivors

OBJECTIVE

To investigate postnatal neural conduction in the auditory brainstem in neonatal bronchopulmonary dysplasia (BPD) survivors.

METHODS

Thirty-two very preterm BPD survivors were studied at 57-58 weeks of postconceptional age. Brainstem auditory-evoked response was studied using maximum length sequence. Wave latencies and intervals were analyzed in detail. The controls were 37 normal term infants and 35 very preterm non-BPD infants.

RESULTS

Compared with normal term controls, BPD survivors showed significantly shortened I-III interval but significantly prolonged III-V interval and greater III-V/I-III interval ratio. Compared with very preterm non-BPD controls, BPD survivors showed a significant shortening in waves III latency and I-III interval, moderate prolonged III-V interval, and significantly greater III-V/I-III interval ratio. These differences were generally similar at all click rates used. The slopes of latency- and interval-click rate functions in BPD survivors did not differ significantly from the two control groups.

CONCLUSIONS

Brainstem neural conduction in BPD survivors differed from normal term and age-matched non-BPD infants; neural maturation is accelerated in caudal brainstem regions but delayed in rostral regions. Neonatal BPD survivors are associated with differential maturation in neural conduction at caudal and rostral brainstem regions, which may constitute an important risk for postnatal neurodevelopment in BPD survivors.

IMPACT

We found that brainstem neural conduction at PCA 57-58 weeks in neonatal BPD survivors differs from normal term and age-matched non-BPD infants. No major differences were found between normal term and very preterm non-BPD infants in brainstem auditory conduction. Neural conduction in BPD survivors is accelerated in caudal brainstem regions but delayed in rostral regions. Neonatal BPD survivors are associated with differential maturation in neural conduction at caudal and rostral brainstem regions. The abnormality may constitute an important risk for postnatal neurodevelopment in BPD survivors.

Brainstem auditory pathway function at four months of corrected postnatal age in preterm infants born below 30 week gestation

OBJECTIVE

Functional status of the brainstem auditory pathway was examined at four months of corrected postnatal age in infants born below 30 week gestation to assess the effect of very or extremely preterm birth on postnatal development of the pathway.

METHODS

Thirty-four preterm infants born at 24-29 week gestation (GA24-29w) were studied at four months of corrected postnatal age. Normal controls were 38 postnatal age-matched term infants. Maximum length sequence brainstem auditory evoked response (MLS BAER) were recorded and analysed with 60 dB nHL clicks.

RESULTS

Compared with term control group, GA24-29w group manifested higher BAER threshold (p < 0.05), longer MLS BAER wave latencies at all click rates 91-910/s (p < 0.01-0.001), and lower wave amplitudes at most click rates (p < 0.05-0.01). No significant differences were found between the two groups in I-V interval at any click rates. I-III interval was shorter while III-V interval was longer in GA24-29w group than in term group at higher rates (all p < 0.05). III-V/I-III interval ratio in GA24-29w group was greater at 455 and 910/s clicks (p < 0.05 and 0.01). These interval variables showed similar changes when 4 GA24-29w infants with threshold elevation were excluded.

CONCLUSIONS

At four months of corrected postnatal age, infants born below 30 week gestation manifested elevated BAER threshold, increased wave latencies, and reduced amplitude. They also manifested a small decrease in I-III interval but a small increase in III-V interval at high rates. Very or extremely preterm birth exerts a mild or moderate effect on postnatal development of the brainstem auditory pathway.

Reduced wave amplitudes of brainstem auditory response in high-risk babies born at 28-32week gestation

OBJECTIVE

To examine brainstem auditory electrophysiology in high-risk babies born at 28-32week gestation by analysing the amplitudes of wave components in maximum length sequence brainstem auditory evoked response (MLS BAER).

METHODS

94 preterm babies, ranging in gestation 28-32weeks, with perinatal problems (high-risk) were recruited. The amplitudes of MLS BAER wave components were studied at term age (37-42weeks postconceptional age).

RESULTS

Compared with normal term controls, the amplitude in the high-risk preterm babies was significantly smaller at the highest click rate 910/s for wave I (p<0.01), at all 91-910/s for wave III (all p<0.01) and at 455 and 910/s (p<0.05 and 0.01) for wave V. Compared with age-matched low-risk preterm controls, the amplitude was significantly smaller at 455 and 910/s for wave I (p<0.05 and 0.05), 91-910/s for wave III (p<0.05-0.001), and 227-910/s (p<0.05 and 0.01) for wave V. No differences in the V/I and V/III amplitude ratios were found between the high-risk preterm babies and the controls.

CONCLUSIONS

The amplitudes of MLS BAER wave components, mainly more central components, were reduced in the high-risk preterm babies born at 28-32week gestation. Electrophysiological activity of the brainstem auditory neuron in such babies is depressed, mainly attributed to or related to the associated perinatal problems.

Small-for-gestation birth exerts a minor additional effect on functional impairment of the auditory brainstem in high-risk babies born at late preterm

OBJECTIVE

To address if small-for-gestational-age (SGA) significantly affects the developing auditory brainstem in late preterm babies with perinatal problems (i.e. high-risk), providing valuable information for management of such babies.

METHODS

SGA and appropriate-for-gestational age (AGA) babies born at 33-36weeks of gestation were studied at term using maximum length sequence brainstem auditory evoked response in response to 91-910/s clicks.

RESULTS

Compared with AGA late preterm babies without perinatal problems (i.e. low-risk), the high-risk SGA babies manifested a significant increase in wave V latency and I-V interval at all 91-910/s clicks, and III-V interval at 455 and 910/s. The amplitude was smaller for wave I at 227 and 910/s, wave III at 910/s and wave V at 227 and 910/s. Compared with low-risk SGA babies, the high-risk SGA babies showed similarly abnormalities. Compared with high-risk AGA babies, the high-risk SGA babies manifested slightly different abnormalities.

CONCLUSIONS

Brainstem auditory response was abnormal in high-risk SGA late preterm babies. The abnormalities, suggesting brainstem auditory impairment, were slightly different from high-risk AGA late preterm babies.

SIGNIFICANCE

SGA birth exerts a minor additional effect on the impaired auditory brainstem in high-risk babies born at late preterm. For these babies, neuroprotective measures should mainly target at associated perinatal problems, although the relatively minor adverse SGA effect cannot be ignored.

Functional integrity of rostral regions of the immature brainstem is impaired in babies born extremely preterm

OBJECTIVE

Babies born extremely preterm are predisposed to brain damage. We test the hypothesis that functional integrity of the auditory brainstem, particularly the rostral regions, is impaired in extremely preterm babies.

METHODS

We recruited 68 babies who were born at 23-27 weeks of gestation. At term date, these babies were studied by recording and analysing maximum length sequence brainstem auditory evoked response (MLS BAER) with click rates 91-910/s. Detailed data analysis was performed in 65 babies from whom reliable MLS BAER measurements were obtained.

RESULTS

Compared with normal term controls, the extremely preterm babies showed a significant increase in wave V latency, and I-V interval at all rates 91-910/s (p<0.01-0.001). Of two small intervals, I-III interval showed no apparent abnormality, but III-V interval was significantly increased at all rates, which was supported by a significant increase in III-V/I-III interval ratio (all p<0.001). These abnormalities were more significant at higher than at lower rates. The slopes of wave V latency-, I-V interval- and particularly III-V interval-rate functions were all increased. The same was true for the slope of III-V/I-III interval ratio-rate function.

CONCLUSIONS

MLS BAER variables that mainly reflect central neural conduction in the extremely preterm babies were abnormally increased. The most important abnormality was a significant increase in III-V interval and its click rate-dependent change. The abnormalities tended to be more significant than those previously reported in late and very preterm babies.

SIGNIFICANCE

Babies born extremely preterm have a major impairment or maturational delay in functional integrity of the rostral regions of the immature brainstem, which is more significant than in less preterm babies.

Auditory brainstem response in term and preterm infants with neonatal complications: the importance of the sequential evaluation

Introduction Literature data are not conclusive as to the influence of neonatal complications in the maturational process of the auditory system observed by auditory brainstem response (ABR) in infants at term and preterm.

Objectives Check the real influence of the neonatal complications in infants by the sequential auditory evaluation.

Methods Historical cohort study in a tertiary referral center. A total of 114 neonates met inclusion criteria: treatment at the Universal Neonatal Hearing Screening Program of the local hospital; at least one risk indicator for hearing loss; presence in both evaluations (the first one after hospital discharge from the neonatal unit and the second one at 6 months old); all latencies in ABR and transient otoacoustic emissions present in both ears.

Results The complications that most influenced the ABR findings were Apgar scores less than 6 at 5 minutes, gestational age, intensive care unit stay, peri-intraventricular hemorrhage, and mechanical ventilation.

Conclusion Sequential auditory evaluation is necessary in premature and term newborns with risk indicators for hearing loss to correctly identify injuries in the auditory pathway.

Mild maturational delay of the brainstem at term in late preterm small-for-gestation age babies

AIMS

To detect any functional abnormality in the brainstem auditory pathway in late preterm babies born of small-for-gestational age (SGA) using maximum length sequence brainstem evoked response.

STUDY DESIGN

The response was recorded and analyzed at term in 38 SGA (birthweight <3rd centile) babies born at 33-36 week gestation. The results were compared with 40 age-matched babies born of appropriate-for-gestational age (AGA) (birthweight >10th centile). None of the subjects had major perinatal problems.

RESULTS

All wave latencies and interpeak intervals in the SGA group were slightly longer than those in the AGA group at most click rates. Wave III latency was significantly longer than that in the AGA group at 227/s (P < 0.05), and wave V latency was at 227 and 910/s (P < 0.05 and 0.05). Of the interpeak intervals, only the I-V interval in the SGA group was significantly longer than that in the AGA group at the highest rate 910/s (P < 0.05). The amplitudes of waves I, III and V in the SGA group all tended to be smaller than those in the AGA group at all click rates 91-910/s. The wave V amplitude was significantly smaller at most click rates (227-910/s, all P < 0.05). The slopes of all wave latency-, interval-, and amplitude-rate functions were similar in SGA and AGA groups.

CONCLUSIONS

There were marginal abnormalities in MLS BAER of low-risk late preterm SGA babies, suggesting a mild degree of maturational delay in the brainstem. Intrauterine growth retardation occurring in late preterm babies has a minor effect on neural maturation of the immature brainstem.

Neural conduction impairment in the auditory brainstem and the prevalence in term babies in neonatal intensive care unit

OBJECTIVE

To detect neural conduction abnormality in the auditory brainstem in term babies in the neonatal intensive care unit (NICU), determine prevalence of the abnormality, and assess if maximum length sequence (MLS) technique improves early detection of the abnormality.

METHODS

One hundred and six term babies were recruited, and studied by recording and analysing MLS brainstem auditory evoked response (BAER). Interpeak intervals were analysed in detail, which were then compared with those in normal term babies.

RESULTS

Wave V latency and I-V and III-V intervals in MLS BAER were increased in the NICU term babies at all click rates 91-910/s, particularly at 455 and 910/s (p<0.05-0.001). No major abnormalities were found in wave I and III latencies and I-III interval. The abnormal increase in I-V and III-V intervals were seen in significantly more cases at 455 and 910/s in MLS BAER than at 21/s in conventional BAER (X(2)=10.92-13.88, all p<0.01). As a whole, 38 (35.8%) of the NICU babies had abnormal III-V and/or I-V intervals in MLS BAER, which was significantly more than 13 (12.2%) in conventional BAER (X(2)=16.14, p<0.01).

CONCLUSION

There is neural conduction impairment in the auditory brainstem in NICU term babies, which occurs in one-third of these babies.

SIGNIFICANCE

Term babies in NICU are at risk of neural conduction impairment in the auditory brainstem. High click rates in MLS BAER enhance early detection of the impairment.

Brainstem auditory electrophysiology is supressed in term neonates with hyperbilirubinemia

BACKGROUND

Whether hyperbilirubinemia suppresses electrophysiological activity of the neonatal auditory brainstem remains to be investigated.

AIM

To determine whether hyperbilirubinemia suppresses the brainstem auditory electrophysiology in term neonates.

METHODS

Maximum length sequence brainstem auditory evoked response (MLS BAER) was recorded shortly after confirming hyperbilirubinemia in 58 term neonates. Wave amplitudes of the response were analyzed in detail.

RESULTS

Compared with age-matched term controls, the neonates with hyperbilirubinemia showed a significant reduction in the amplitudes of MLS BAER waves III and particularly V at all click rates 91-910/s. The reduction tended to be more significant at higher than lower rates. Wave I amplitude was reduced at 910/s. V/I amplitude ratio was decreased at all click rates. Therefore, the amplitudes of MLS BAER, particularly later, waves were all reduced. The amplitudes of all MLS BAER waves tended to be reduced with the increase in total serum bilirubin level. All wave amplitudes were correlated with the level of total serum bilirubin at some or most click rates.

CONCLUSIONS

Brainstem auditory electrophysiology is suppressed in neonates with hyperbilirubinemia, which related to the severity of hyperbilirubinemia. Wave amplitudes are valuable BAER variables to detect functional impairment of the brainstem and auditory pathway in neonatal hyperbilirubinemia, and are recommended to be used in assessing bilirubin neurotoxicity to the neonatal brain.

Impaired function of the auditory brainstem in term neonates with hyperbilirubinemia

OBJECTIVE

We studied maximum length sequence brainstem auditory evoked response in term neonates with hyperbilirubinemia to further our understanding of hyperbilirubinemia on the neonatal auditory brainstem and to determine if maximum length sequence technique improves detection of brainstem auditory impairment due to bilirubin neurotoxicity.

METHODS

Maximum length sequence brainstem auditory evoked response was recorded and analysed shortly after confirming total serum bilirubin levels greater than 15mg/dL in fifty-seven term neonates with hyperbilirubinemia.

RESULTS

Most wave latencies and interpeak intervals in maximum length sequence brainstem auditory evoked response in the neonates with hyperbilirubinemia were correlated with the level of total serum bilirubin at some or most click rates used. Compared with age-matched normal term controls, wave V latency in these neonates was increased significantly at all 91-910/s click rates (p<0.05-0.001). The I-V and I-III interpeak intervals were also increased significantly at all these rates, and the III-V interval increased at 227-910/s clicks (p<0.05-0.001). The differences between the neonates with hyperbilirubinemia and the controls were more significant at higher than at lower click rates. The slopes of wave V latency-rate function and I-V and III-V interval-rate functions were all significantly increased. By comparison, the abnormalities in conventional BAER were less significant, with only I-III and I-V intervals were increased (both p<0.05).

CONCLUSIONS

Functional status of the auditory brainstem is impaired in neonatal hyperbilirubinemia. Maximum length sequence technique at high click rates improves detection of bilirubin neurotoxicity to the neonatal auditory brainstem, particularly for the more rostral regions.

Neural conduction abnormality in the brain stem and prevalence of the abnormality in late preterm infants with perinatal problems

Neurodevelopment in late preterm infants has recently attracted considerable interest. The prevalence of brain stem conduction abnormality remains unknown. We examined maximum length sequence brain stem auditory evoked response in 163 infants, born at 33-36 weeks gestation, who had various perinatal problems. Compared with 49 normal term infants without problems, the late preterm infants showed a significant increase in III-V and I-V interpeak intervals at all 91-910/s clicks, particularly at 455 and 910/s (p < 0.01-0.001). The I-III interval was slightly increased, without statistically significant difference from the controls at any click rates. These results suggest that neural conduction along the, mainly more central or rostral part of, auditory brain stem is abnormal in late preterm infants with perinatal problems. Of the 163 late preterm infant, the number (and percentage rate) of infants with abnormal I-V interval at 91, 227, 455, and 910/s clicks was, respectively, 11 (6.5%), 17 (10.2%), 37 (22.3%), and 31 (18.7%). The number (and percentage rate) of infants with abnormal III-V interval at these rates was, respectively, 10 (6.0%), 17 (10.2%), 28 (16.9), and 36 (21.2%). Apparently, the abnormal rates were much higher at 455 and 910/s clicks than at lower rates 91 and 227/s. In total, 42 (25.8%) infants showed abnormal I-V and/or III-V intervals.

CONCLUSION

Conduction in, mainly in the more central part, the brain stem is abnormal in late preterm infants with perinatal problems. The abnormality is more detectable at high- than at low-rate sensory stimulation. A quarter of late preterm infants with perinatal problems have brain stem conduction abnormality.

Ventilatory control in infants, children, and adults with bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), or chronic lung disease of prematurity, occurs in ~30% of preterm infants (15,000 per year) and is associated with a clinical history of mechanical ventilation and/or high inspired oxygen at birth. Here, we describe changes in ventilatory control that exist in patients with BPD, including alterations in chemoreceptor function, respiratory muscle function, and suprapontine control. Because dysfunction in ventilatory control frequently revealed when O2 supply and CO2 elimination are challenged, we provide this information in the context of four important metabolic stressors: stresses: exercise, sleep, hypoxia, and lung disease, with a primary focus on studies of human infants, children, and adults. As a secondary goal, we also identify three key areas of future research and describe the benefits and challenges of longitudinal human studies using well-defined patient cohorts.

Amplitude reduction in brainstem auditory response in term infants under neonatal intensive care

OBJECTIVE

To examine brainstem auditory electrophysiology in term neonates under intensive care due to perinatal conditions other than hypoxia-ischemia.

METHODS

Maximum length sequence brainstem auditory evoked response was studied in term neonates in an intensive care unit. The amplitudes of wave components of the response were analysed to assess brainstem auditory electrophysiology.

RESULTS

The amplitudes of all wave components in the neonates under intensive care tended to be smaller than in those in normal term controls. Wave I amplitude was significantly reduced at all 91-910/s clicks (p < 0.05-0.01). The amplitudes of waves III and V were also reduced, respectively, at 227-910/s (all p < 0.05) and at 455 and 910/s (both p < 0.01). The amplitude reduction was slightly more significant at higher than lower click rates, but there were no significant differences in the slopes of wave I, III and V amplitude-rate functions between the neonates under intensive care and the controls.

CONCLUSIONS

Wave amplitudes of maximum length sequence brainstem auditory evoked response were reduced in term neonates under intensive care due to perinatal conditions other than hypoxia-ischemia.

SIGNIFICANCE

Brainstem auditory electrophysiology is depressed in term neonates under intensive care, possibly due to collective adverse effects of perinatal conditions. The impairment to the neonatal, particularly rostral, brainstem due to other perinatal conditions is less severe than that due to hypoxia-ischemia previously reported.

Neonatal brainstem dysfunction risks infant social engagement

The role of the brainstem in mediating social signaling in phylogenetic ancestral organisms has been demonstrated. Evidence for its involvement in social engagement in human infants may deepen the understanding of the evolutionary pathway of humans as social beings. In this longitudinal study, neonatal brainstem functioning was measured by auditory brainstem-evoked responses (ABRs) in 125 healthy neonates born prematurely before 35 weeks' gestational age. At 4 months, infants were tested in a set of structured vignettes that required varying levels of social engagement and cardiac vagal tone was assessed. Data show that neonates with a disrupted I-V waveform, evident mostly by delayed wave V, exhibit shorter latencies to gaze averts in episodes involving direct face-to-face interactions but engage gaze as controls when interacting with masked agents or with agents whose faces are partly veiled by toys. Analysis of variance of infants' social engagement with ABR, neonatal risk, maternal stress and cardiac vagal tone showed a main effect for ABR and an ABR by gestational age interaction. The integrity of brainstem transmission of sensory information during the final weeks of gestation may scaffold the development of social disengagement, thereby attesting to the brainstem's preserved evolutionary role in developing humans as social organisms prior to engaging in social encounters.

Intrapulmonary lipopolysaccharide exposure upregulates cytokine expression in the neonatal brainstem

Perinatal inflammation and neonatal sepsis trigger lung and brain injury. We hypothesized that endotoxin exposure in the immature lung upregulates proinflammatory cytokine expression in the brainstem and impairs respiratory control. Lipopolysaccharide (LPS) or saline was administered intratracheally to vagal intact or denervated rat pups. LPS increased brainstem IL-1β and vagotomy blunted this response. There was an attenuated ventilatory response to hypoxia and increased brainstem IL-1β expression after LPS.

CONCLUSION

Intratracheal endotoxin exposure in rat pups is associated with upregulation of IL-1β in the brainstem that is vagally mediated and associated with an impaired hypoxic ventilatory response.

Vagal afferents modulate cytokine-mediated respiratory control at the neonatal medulla oblongata

Perinatal sepsis and inflammation trigger lung and brain injury in preterm infants, and associated apnea of prematurity. We hypothesized that endotoxin exposure in the immature lung would upregulate proinflammatory cytokine mRNA expression in the medulla oblongata and be associated with impaired respiratory control. Lipopolysaccharide (LPS, 0.1mg/kg) or saline was administered intratracheally to rat pups and medulla oblongatas were harvested for quantifying expression of mRNA for proinflammatory cytokines. LPS-exposure significantly increased medullary mRNA for IL-1β and IL-6, and vagotomy blunted this increase in IL-1β, but not IL-6. Whole-body flow plethysmography revealed that LPS-exposed pups had an attenuated ventilatory response to hypoxia both before and after carotid sinus nerve transection. Immunochemical expression of IL-1β within the nucleus of the solitary tract and area postrema was increased after LPS-exposure. In summary, intratracheal endotoxin-exposure in rat pups is associated with upregulation of proinflammatory cytokines in the medulla oblongata that is vagally mediated for IL-1β and associated with an impaired hypoxic ventilatory response.

Depressed brainstem auditory function in children with cerebral palsy

Brainstem auditory evoked responses were studied to examine brainstem auditory function in 80 children with cerebral palsy. The response waveform, particularly later waves, tended to be depressed. Thirty-three (41.3%) showed abnormal results. The main abnormality was reduced wave V amplitude. Other abnormalities were decreased V/I amplitude ratio, missing waves, prolonged I-V interval, and increased interaural difference in I-V interval. The abnormalities were persistent during the follow-up. In contrast to common findings in the responses in progressive neurologies, abnormalities in interpeak intervals were rare in children with cerebral palsy. There were some characteristic changes in the responses in certain etiologies. These results suggest that brainstem auditory function in children with cerebral palsy is depressed, which may be owing to decreased or altered neural firing or synchrony in the auditory brainstem. A detailed analysis of central components of the responses is valuable in detecting central auditory dysfunction in children with cerebral palsy.

Maximum length sequence brainstem auditory evoked response in low-risk late preterm babies

OBJECTIVES

Recent research indicates that there is delayed development in the more central part of the auditory brainstem in very preterm babies. We aimed to study whether this is also the case for late preterm babies.

METHODS

The maximum length sequence brainstem auditory evoked response (MLS BAER) was used to study functional status of the auditory brainstem. Babies born at 33-36 week gestation and without any major perinatal complications were recruited. MLS BAER was recorded and analyzed at term age.

RESULTS

No significant correlation was found between most MLS BAER variables and physiological factors (gender, postconceptional age, bodyweight, and head circumference obtained at time of testing). Wave latencies and amplitudes, and I-V and I-III intervals in the preterm babies were essentially similar to those in the term controls at all click rates. However, III-V interval increased significantly at 227-910/s clicks (p<0.05-0.01). All latencies, amplitudes and intervals correlated significantly with click rates (all p<0.001). No differences were found in the slopes of MLS BAER variables-rate functions between the later preterm babies and term controls.

CONCLUSIONS

Babies born at 33-36 weeks gestation without major complications had an increased III-V interval at high-rate stimulation. This suggests that late preterm babies have a mild delay in neural conduction in the more central part of the auditory brainstem.

Differences in impaired brainstem conduction between neonatal chronic lung disease and perinatal asphyxia

OBJECTIVE

To explore any differences in impaired brainstem function between preterm infants with neonatal chronic lung disease (CLD) and term infants after perinatal asphyxia.

METHODS

Brainstem auditory evoked responses (BAERs) collected using maximum length sequence (MLS) technique were compared at term equivalent age between 43 CLD infants and 117 asphyxiated infants.

RESULTS

In both CLD and asphyxiated infants there was a significant increase in wave V latency and I-V interval in MLS BAER. CLD infants showed a significant increased III-V interval but a normal I-III interval at all click rates. However, asphyxiated infants showed a significant increase in both III-V and I-III intervals. I-III interval was shorter and III-V/I-III interval ratio was greater in CLD infants than in asphyxiated infants. The slope of I-III interval-rate function was steeper in asphyxiated infants than in CLD infants, while the slope of III-V/I-III interval ratio-rate function was the other way around.

CONCLUSIONS

CLD infants had a major increase in more central components of MLS BAER, without appreciable abnormality in more peripheral components. However, asphyxiated infants had a significant increase in both central and peripheral components.

SIGNIFICANCE

Neonatal CLD affects more central regions of the brainstem, whereas perinatal asphyxia affects both peripheral and central regions. This difference, which is likely related to the different nature of hypoxia in CLD and asphyxia, may have some significance for neuroprotective interventions for the two problems.

Impairment of perinatal hypoxia-ischemia to the preterm brainstem

Hypoxia-ischemia is a major perinatal problem that results in severe damage to the newborn brain. This study assessed functional integrity of the brainstem at term in preterm infants after perinatal hypoxia-ischemia to shed light on the influence of hypoxia-ischemia on the preterm brainstem. We recruited sixty-eight preterm infants after perinatal hypoxia-ischemia, ranging in gestation 28-35 weeks. Brainstem evoked response was studied at term age (37-42 weeks postconceptional age) with 91-910/s clicks using the maximum length sequence technique. Compared with healthy preterm infants, the preterm infants after perinatal hypoxia-ischemia showed a significant increase in I-V interval at very high rates 455 and 910/s of clicks (P<0.05, 0.05). III-V interval and III-V/I-III interval ratio also increased significantly at 455 and 910/s (P<0.05-0.01). The slope of III-V interval-rate function was significantly steeper than in the healthy preterm infants (P<0.05). Compared with normal term controls, the preterm infants after hypoxia-ischemia showed similar, but slightly more significant, abnormalities. The differences between the preterm infants after hypoxia-ischemia and the healthy preterm and term infants generally increased with increasing click rate. These results demonstrated that central components of brainstem auditory evoked response were abnormal at very high click rates in the preterm infants after perinatal hypoxia-ischemia. Click rate-dependent change in the more central part of the brainstem is also abnormal. Apparently, functional integrity of the brainstem, mainly in the more central part, is impaired. Hypoxic-ischemic damage to the preterm brainstem is unlikely to completely recover within a relatively short period after the insult, which is of clinical importance.

Hyperbilirubinemia and language delay in premature infants

OBJECTIVE

Our goal was to evaluate whether language delay at 3 years in premature infants is associated with previous exposure to hyperbilirubinemia during the first 2 weeks after birth.

PATIENTS AND METHODS

We performed a retrospective case-control study of infants admitted to the NICU between January and October 2003. Inclusion criteria included a birth weight of < or =1500 g and follow-up to age 3 years. Exclusion criteria included genetic disorders and hearing loss or recurrent ear infections. Peak total serum bilirubin levels during the first 2 weeks and duration of hyperbilirubinemia (days with total serum bilirubin level at >8 mg/dL) were determined. Infants with language delay and who were receiving speech therapy by 3 years were identified through developmental clinic charts and a tracking program and compared with infants who had normal language development.

RESULTS

A total of 125 infants with birth weight of < or =1500 g were admitted to the NICU between January and October 2003. Fifteen infants died, and 110 were discharged from the hospital. A total of 102 (93%) of 110 infants had follow-up to the age of 3 years. Four infants were excluded (1 genetic disorder, 3 delayed hearing loss or recurrent ear infections). Twenty-four infants had a language delay and received speech therapy, whereas 74 infants had normal language development. There was no significant difference in peak total serum bilirubin level and duration of hyperbilirubinemia between the 2 groups. On logistic regression, only bronchopulmonary dysplasia was associated with language delay.

CONCLUSIONS

Hyperbilirubinemia, defined as peak total serum bilirubin level or duration of elevated bilirubin in days, is not associated with language delay in premature infants. However, this issue deserves investigation, because other measures of bilirubin, such as unbound bilirubin, may be associated with language delay.

A neurobiological model for the effects of early brainstem functioning on the development of behavior and emotion regulation in infants: implications for prenatal and perinatal risk

Neurobiological models propose an evolutionary, vertical-integrative perspective on emotion and behavior regulation, which postulates that regulatory functions are processed along three core brain systems: the brainstem, limbic, and cortical systems. To date, few developmental studies applied these models to research on prenatal and perinatal risk. We propose a conceptual model that incorporates three integrated levels of observations for the study of early risk: (a) brainstem-related physiological regulation of cyclic processes and sensory integration, e.g., vagal regulation, circadian rhythms; (b) emotion and attention regulation capacities that draw on the integration of brainstem and limbic systems; and (c) higher-level outcomes that draw on the intactness of brainstem and limbic networks, including socio-emotional self-regulation, inhibitory control, and cognitive processing. We discuss implications of the model for the development of regulatory capacities during the prenatal and early postnatal stages in infants born with specific perinatal risk. We underscore the importance of assessing sub-cortical and brainstem systems and the longitudinal effects of transitory brainstem dysfunction on physiological homeostasis, motivation, arousal-modulated attention, stress reactivity, and mother-infant co-regulation. The assessment of brainstem dysfunction can be conducted during hospitalization and may help detect infants at risk for the development of self-regulatory deficits at the first weeks of life.

Brainstem auditory outcomes and correlation with neurodevelopment after perinatal asphyxia

We used brainstem auditory-evoked responses and neurodevelopmental assessment to detect abnormalities and correlations between such responses and neurodevelopmental outcomes in 78 children (aged 4-12 years) who survived perinatal asphyxia. Twenty children had brainstem auditory-evoked response abnormalities, including increased threshold, reduced wave V amplitude, decreased V/I amplitude ratio, and prolonged I-V interval. Thirty-seven exhibited neurodevelopmental deficits, including cerebral palsy and developmental delay. The remaining 41 exhibited no deficits. Brainstem auditory-evoked response abnormalities were evident in 15 of 37 (40.5%) children with neurodevelopmental deficits, but in only 5 of 41 (12.2%) with no deficits, which differed significantly (chi(2) = 8.2, P < 0.05). The sensitivity, specificity, positive predictive value, and false-negative rate of brainstem auditory-evoked responses to reflect neurodevelopmental outcomes were 40.5%, 87.8%, 75.0%, and 59.5%, respectively. These findings suggest that in children who survive perinatal asphyxia, brainstem auditory impairment occurs more frequently in those with versus those without neurodevelopmental deficits. Brainstem auditory-evoked responses display a moderate correlation with clinically determined neurodevelopmental outcomes. Despite limitations, brainstem auditory-evoked response is valuable for assessing auditory and neurodevelopmental outcomes after perinatal asphyxia.

Sustained depression of brainstem auditory electrophysiology during the first months in term infants after perinatal asphyxia

OBJECTIVE

To gain further insights into the pathophysiological processes of neuronal impairment in neonatal brainstem after perinatal asphyxia.

METHODS

Maximum-length sequence brainstem auditory-evoked response (MLS BAER) was recorded with clicks at 91, 227, 455 and 910/s on days 1, 3, 5, 7, 10, 15 and 30 after birth in 108 term infants who suffered perinatal asphyxia. Wave amplitude variables in the MLS BAER were analysed in detail at 40 dB above BAER threshold in 86 infants who had no peripheral hearing impairment.

RESULTS

On day 1 the amplitudes of MLS BAER waves I, III and V were all reduced significantly at all click rates, especially at higher ones (91-910/s, ANOVA P<0.05-0.001). On day 3 these amplitudes were reduced further. On days 5 and 7, the amplitude reduction persisted and did not show any significant further changes. On days 10 and 15 the reduced amplitudes were increased slightly. On day 30 all amplitudes were still reduced significantly (P<0.05-0.0001). During the first month, the reduction of wave amplitudes was more significant for the later MLS BAER components than for the earlier ones, and occurred most significantly at 455 and 910/s clicks. By comparison, the amplitude reduction in conventional BAER was much less significant.

CONCLUSIONS

During the first month after perinatal asphyxia the amplitudes of MLS BAER waves were reduced significantly and persistently, which was more significant at higher rates of clicks than at lower rates. The reduction is much more persistent than the increase in wave latencies and intervals we previously reported.

SIGNIFICANCE

There is sustained depression of brainstem auditory electrophysiology, indicating neuronal damage of the auditory brainstem, in infants after perinatal asphyxia. This may have important clinical implications.