Hypoxic adaptation during development: relation to pattern of neurological presentation and cognitive disability

Pediatric Sickle Cell Disease and Stroke: A Literature Review

Both ischemic and hemorrhagic strokes in children can be a complication of sickle cell disease, which also affects adults. The occurrence is high without any screening or preventative care. This review article found that although transcranial Doppler (TCD) has reduced the prevalence of stroke in pediatric patients, there is still a need for an epidemiological survey to define such screening for adults, the ideal dose of hydroxyurea to reduce the incidence of stroke, and to identify silent cerebral stroke to prevent its complications. Increased hydroxyurea prescription and specific antibiotic and vaccination regimes lowered the occurrence of this condition. In pediatric cases with a time-averaged mean of the maximal velocity greater than 200cm/s, transcranial Doppler screening and preventive chronic transfusion for at least the first year have lowered the occurrence of stroke by up to 10 times. The ideal dose of hydroxyurea is still debatable, but it seems to reduce the risk of the first stroke to a comparable level in the average population. Adult ischemic and hemorrhagic stroke prevention has not yet received the same attention. Though there are fewer studies, sickle cell disease is also more common than age-matched controls in terms of silent cerebral infarction on magnetic resonance imaging (MRI), as well as other neurological problems such as cognitive impairment, seizures, and headaches. Currently, there is no evidence-supported way to prevent ischemic stroke in adults at any age. Also, there is no defined ideal dose of hydroxyurea that can be helpful in preventing strokes. Data also lack a way to identify a silent cerebral infarction, so its complications can be prevented. An additional epidemiological survey may help in the prevention of the condition. The primary aim of this article was to emphasize the importance of information on clinical, neuropsychological, and quantitative MRI assessment of sickle cell patients to understand the epidemiology and etiology of stroke in sickle cell patients to prevent stroke and its related morbidity.

Validation of the NIH Toolbox-Cognition Battery against legacy neurocognitive measures in adults with cognitive impairments: An exploratory analysis

OBJECTIVE

The purpose of this exploratory study was to describe associations between NIH Toolbox-Cognition Battery subtests and legacy measures of neurocognitive function in two samples with neurological conditions (stroke and sickle cell disease (SCD)).

METHOD

This exploratory secondary analysis uses data from two studies that assessed cognition at one time point using the NIH Toolbox-Cognition Battery, the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), and subtests from the Delis-Kaplan Executive Functions System (DKEFS). People with stroke (n = 26) and SCD (n = 64) were included. Associations between the NIH Toolbox-Cognition Battery subtests and corresponding legacy measures were examined using linear correlations, Bland-Altman analysis, and Lin's Concordance Correlation Coefficient.

RESULTS

Linear correlations and Lin's Concordance Correlation Coefficient were poor to strong in both samples on NIH Toolbox-CB subtests: Flanker Inhibitory Control and Attention (r = .35 to .48, Lin CCC = .27 to .37), Pattern Comparison Processing Speed (r = .40 to .65, Lin CCC = .37 to .62), Picture Sequence Memory (r = .19 to .55, Lin CCC = .18 to .48), Dimensional Change Card Sort (r = .39 to .77, Lin CCC = .38 to .63), Fluid Cognition Composite (r = .88 to .90, Lin CCC = .60 to .79), and Total Cognition Composite (r = .64 to .83, Lin CCC = .60 to .78). Bland-Altman analyses demonstrated wide limits of agreement across all subtests (-3.17 to 3.78).

CONCLUSIONS

The NIH Toolbox-Cognition Battery subtests may behave similarly to legacy measures as an overall assessment of cognition across samples at risk for neurological impairment. Findings should be replicated across additional clinical samples.

Epidemiology of Stroke in Sickle Cell Disease

Sickle cell disease is the most common cause of stroke in childhood, both ischaemic and haemorrhagic, and it also affects adults with the condition. Without any screening or preventative treatment, the incidence appears to fall within the range 0.5 to 0.9 per 100 patient years of observation. Newborn screening with Penicillin prophylaxis and vaccination leading to reduced bacterial infection may have reduced the incidence, alongside increasing hydroxyurea prescription. Transcranial Doppler screening and prophylactic chronic transfusion for at least an initial year has reduced the incidence of stroke by up to 10-fold in children with time averaged mean of the maximum velocity >200 cm/s. Hydroxyurea also appears to reduce the incidence of first stroke to a similar extent in the same group but the optimal dose remains controversial. The prevention of haemorrhagic stroke at all ages and ischaemic stroke in adults has not yet received the same degree of attention. Although there are fewer studies, silent cerebral infarction on magnetic resonance imaging (MRI), and other neurological conditions, including headache, epilepsy and cognitive dysfunction, are also more prevalent in sickle cell disease compared with age matched controls. Clinical, neuropsychological and quantitative MRI screening may prove useful for understanding epidemiology and aetiology.

Neurocognitive Functioning among Children with Sickle Cell Anemia Attending SCA Clinic at MNH, Dar es Salaam, Tanzania

Background

Children with sickle cell anemia are at a higher risk of developing neurological sequelae like abnormal intellectual functioning, poor academic performance, abnormal fine motor functioning, and attentional deficits. There is a paucity of data about neurocognitive impairment among children with sickle cell anemia in Tanzania. Recognition of the magnitude of neurocognitive impairment will help to provide insight in the causative as well as preventive aspects of the same. Therefore, this study was carried out to determine the prevalence and factors associated with neurocognitive impairment in children with sickle cell anemia.

Methods

This is a cross-sectional comparative study between children with SCA and a control group of the hemoglobin AA sibling. It was carried out in Muhimbili National Hospital during a five-month period. The Rey–Osterrieth Complex Figure test (ROCF) which is used to test memory and visual special functions and KOH block design tools that have been previously validated through another study locally were used. Additional information on demographic characteristics was also collected using a predetermined questionnaire. Proportions and comparisons of means were used to examine associations between neurocognitive impairment and independent variables for associated factors.

Results

A total of 313 children were included in the final analysis. Among all the participants, the majority of the participants in the sickle cell group were of the age group 14-15 years (45.9%). In the comparison group, the majority were of the age group 9-10 years (43.8%). The neurocognitive scores in children with sickle cell anemia were significantly different from the normal siblings. In the copy ROCF, the neurocognitive function in SCA participants was 68.2% below the mean as compared to 45% of their counterparts, p ≤ 0.001. Additionally, there was no difference in memory in children with SCA compared to normal siblings (14.8% vs. 12.5%, respectively, p=0.606). Children with SCA had a higher proportion of impaired IQ (85.4%) as compared to children without SCA (72.5%), and the difference was statistically significant, p=0.009. Factors associated with neurocognitive impairment were age above 13 years, BMI, and absenteeism from school. Conclusion and Recommendation. Children with SCA had more impairment in terms of copying and IQ. We recommend assessment at the younger age group, increased sample size in future studies, and long-term cohort follow-up.

Sleep-disordered breathing and comorbidities: role of the upper airway and craniofacial skeleton

Obstructive sleep-disordered breathing (SDB), which includes primary snoring through to obstructive sleep apnea syndrome (OSAS), may cause compromise of respiratory gas exchange during sleep, related to transient upper airway narrowing disrupting ventilation, and causing oxyhemoglobin desaturation and poor sleep quality. SDB is common in chronic disorders and has significant implications for health. With prevalence rates globally increasing, this condition is causing a substantial burden on health care costs. Certain populations, including people with sickle cell disease (SCD), exhibit a greater prevalence of OSAS. A review of the literature provides the available normal polysomnography and oximetry data for reference and documents the structural upper airway differences between those with and without OSAS, as well as between ethnicities and disease states. There may be differences in craniofacial development due to atypical growth trajectories or extramedullary hematopoiesis in anemias such as SCD. Studies involving MRI of the upper airway illustrated that OSAS populations tend to have a greater amount of lymphoid tissue, smaller airways, and smaller lower facial skeletons from measurements of the mandible and linear mental spine to clivus. Understanding the potential relationship between these anatomical landmarks and OSAS could help to stratify treatments, guiding choice towards those which most effectively resolve the obstruction. OSAS is relatively common in SCD populations, with hypoxia as a key manifestation, and sequelae including increased risk of stroke. Combatting any structural defects with appropriate interventions could reduce hypoxic exposure and consequently reduce the risk of comorbidities in those with SDB, warranting early treatment interventions.

Vascular Instability and Neurological Morbidity in Sickle Cell Disease: An Integrative Framework

It is well-established that patients with sickle cell disease (SCD) are at substantial risk of neurological complications, including overt and silent stroke, microstructural injury, and cognitive difficulties. Yet the underlying mechanisms remain poorly understood, partly because findings have largely been considered in isolation. Here, we review mechanistic pathways for which there is accumulating evidence and propose an integrative systems-biology framework for understanding neurological risk. Drawing upon work from other vascular beds in SCD, as well as the wider stroke literature, we propose that macro-circulatory hyper-perfusion, regions of relative micro-circulatory hypo-perfusion, and an exhaustion of cerebral reserve mechanisms, together lead to a state of cerebral vascular instability. We suggest that in this state, tissue oxygen supply is fragile and easily perturbed by changes in clinical condition, with the potential for stroke and/or microstructural injury if metabolic demand exceeds tissue oxygenation. This framework brings together recent developments in the field, highlights outstanding questions, and offers a first step toward a linking pathophysiological explanation of neurological risk that may help inform future screening and treatment strategies.

Correlating transcranial arterial Doppler velocities with haematologic parameters and haemolytic indices of Nigerian children with sickle cell anaemia

Introduction

Cerebral vasculopathy, elevated transcranial Doppler velocities and stroke are linked to excessive intravascular haemolysis in sickle cell anaemia. This study determined the prevalence and pattern of abnormal blood flow velocities in children with sickle cell anaemia from Northern Nigeria using transcranial Doppler and to correlate transcranial Doppler velocities with haematological and biochemical markers of haemolysis.

Methods

Full blood count, reticulocyte count, fetal haemoglobin and some selected biochemical markers of haemolysis of 100 children with sickle cell anaemia were determined at steady state. The time-averaged mean of maximal velocities in four major intracranial blood vessels was measured using non-imaging transcranial Doppler, which were then classified according to the stroke prevention in sickle cell disease trial protocol. A simple linear correlation between time-averaged mean of maximal velocities in the four major intracranial vessels as the dependent variable and haematological and biochemical markers of haemolysis as independent variables was also determined at the significance level of 0.05.

Results

Abnormal transcranial Doppler velocities, classified as high risk, were found in 3% of the studied patients; 11% had intermediate risk while 84% had standard risk. Most high velocities were detected in the middle cerebral artery. The time-averaged mean of maximal velocities of middle cerebral artery positively correlated with total white blood cell count, absolute neutrophil count, platelet count, reticulocyte count, serum lactate dehydrogenase and total bilirubin, while it was negatively correlated with haematocrit and fetal haemoglobin levels.

Conclusion

Our study showed low prevalence of abnormal transcranial Doppler velocities and low prevalence is unrelated to low markers of haemolysis in our study population.

Nocturnal oxyhemoglobin desaturation and arteriopathy in a pediatric sickle cell disease cohort

OBJECTIVE

The purpose of this study of sickle cell disease (SCD) was to determine whether arteriopathy, measurable as intracranial vessel signal loss on magnetic resonance angiography (MRA), was associated with low nocturnal hemoglobin oxygen saturation (SpO2) or hemolytic rate, measurable as reticulocytosis or unconjugated hyperbilirubinemia.

METHODS

Ninety-five East London children with SCD without prior stroke had overnight pulse oximetry, of whom 47 (26 boys, 39 hemoglobin SS; mean age 9.1 ± 3.1 years) also had MRA, transcranial Doppler (TCD), steady-state hemoglobin, and reticulocytes within 34 months. Two radiologists blinded to the other data graded arteriopathy on MRA as 0 (none) or as increasing severity grades 1, 2, or 3.

RESULTS

Grades 2 or 3 arteriopathy (n = 24; 2 with abnormal TCD) predicted stroke/TIA compared with grades 0 and 1 (log-rank χ2 [1, n = 47] = 8.1, p = 0.004). Mean overnight SpO2 correlated negatively with reticulocyte percentage (r = -0.387; p = 0.007). Despite no significant differences across the degrees of arteriopathy in genotype, mean overnight SpO2 was higher (p < 0.01) in those with grade 0 (97.0% ± 1.6%) than those with grades 2 (93.9 ± 3.7%) or 3 (93.5% ± 3.0%) arteriopathy. Unconjugated bilirubin was not associated but reticulocyte percentage was lower (p < 0.001) in those with grade 0 than those with grades 2 and 3 arteriopathy. In multivariable logistic regression, lower mean overnight SpO2 (odds ratio 0.50, 95% confidence interval 0.26-0.96; p < 0.01) predicted arteriopathy independent of reticulocyte percentage (odds ratio 1.47, 95% confidence interval 1.15-1.87; p = 0.003).

CONCLUSION

Low nocturnal SpO2 and reticulocytosis are associated with intracranial arteriopathy in children with SCD. Preventative strategies might reduce stroke risk.

Rationale for and design of the "POSTA" study: Evaluation of neurocognitive outcomes after immediate adenotonsillectomy compared to watchful waiting in preschool children

BACKGROUND

IQ deficits are linked to even mild obstructive sleep apnoea (OSA) in children. Although OSA is commonly first diagnosed in the pre-school age group, a randomised trial is still needed to assess IQ outcomes after adenotonsillectomy in the pre-school age-group. This randomised control trial (RCT) will primarily determine whether adenotonsillectomy improves IQ compared to no adenotonsillectomy after 12 months, in preschool (3-5 year-old) children with mild to moderate OSA.

METHODS

This protocol is for an ongoing multi-centred RCT with a recruitment target of 210 subjects (105 in each arm). Children age 3-5 years with symptoms of OSA, are recruited through doctor referral, at the point of referral to the Ear Nose and Throat (ENT) services. Screening is initially with a questionnaire (Paediatric Sleep Questionnaire, PSQ) for symptoms of obstructive sleep apnoea (OSA). Where questionnaires are positive (suggestive of OSA) and ENT surgeons recommend them for adenotonsillectomy, they are invited to participate in POSTA. Baseline testing includes neurocognitive testing (IQ and psychometric evaluation with the neuropsychologist blinded to randomisation) and overnight polysomnography (PSG). Where the Obstructive Apnoea-Hypopnea Index (OAHI) from the PSG is <10/h per hour, consent for randomisation is sought; children with severe OSA (OAHI ≥ 10/h) are sent for immediate treatment and excluded from the study. After consent is obtained, participants are randomised to early surgery (within 2 months) or to surgery after a usual wait time of 12 months. Follow-up studies include repeat neurocognitive testing and PSG at 12 (with the waiting list group studied before their surgery) and 24 months after randomisation. Analysis will be by intention to treat. The primary outcome is IQ at 12 months' follow-up.

DISCUSSION

If IQ deficits associated with OSA are reversible 12 months after adenotonsillectomy compared to controls, future clinical practice advise would be to undertake early surgery in young children with OSA. The study could provide data on whether a window of opportunity exists for reversing IQ deficits linked to OSA in the pre-school age-group.

TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registration Number ACTRN12611000021976 .

Intelligence quotient in paediatric sickle cell disease: a systematic review and meta-analysis

AIM

Sickle cell disease (SCD) is the commonest cause of childhood stroke worldwide. Magnetic resonance imaging (MRI) is routinely used to detect additional silent cerebral infarction (SCI), as IQ is lower in SCI as well as stroke. This review assesses the effect of infarction on IQ, and specifically whether, compared to healthy controls, IQ differences are seen in children with SCI with no apparent MRI abnormality.

METHOD

A systematic review was conducted to include articles with an SCD paediatric population, MRI information, and Wechsler IQ. A meta-analysis of 19 articles was performed to compare IQ in three groups: stroke vs SCI; SCI vs no SCI; and no SCI vs healthy controls.

RESULTS

Mean differences in IQ between all three groups were significant: stroke patients had lower IQ than patients with SCI by 10 points (six studies); patients with SCI had lower IQ than no patients with SCI by 6 points (17 studies); and no patients with SCI had lower IQ than healthy controls by 7 points (seven studies).

INTERPRETATION

Children with SCD and no apparent MRI abnormality have significantly lower IQ than healthy controls. In this chronic condition, other biological, socioeconomic, and environmental factors must play a significant role in cognition.

Prevention of Morbidity in sickle cell disease--qualitative outcomes, pain and quality of life in a randomised cross-over pilot trial of overnight supplementary oxygen and auto-adjusting continuous positive airways pressure (POMS2a): study protocol for a randomised controlled trial

BACKGROUND

Sickle cell anaemia (SCA) is an inherited disorder of haemoglobin. Patients experience long-term health care problems, affecting quality of life (QOL) including frequent acute pain, which is difficult to document in trials except as hospital admissions. Pilot data suggests that overnight respiratory support, either supplementary oxygen or auto-adjusting continuous positive airways pressure (APAP), is safe and may have clinical benefit. This pilot trial aims to determine which intervention is more acceptable to participants and whether there are other advantages of one over the other, e.g. in respiratory function or haematological parameters, before conducting the Phase 2 trial of overnight respiratory support funded by the National Institutes of Health Research.

METHODS/DESIGN

This is a pilot cross-over interventional trial with the order of interventions decided by simple randomization. Ten adults (age over 18 years) and 10 children (aged between 8 and 18 years) with homozygous sickle cell disease (haemoglobin SS, HbSS), recruited regardless of symptoms of sleep-disordered breathing, will undergo overnight pulse oximetry and will have two interventions, overnight oxygen and APAP, for a week each in randomised order with a washout week between interventions. Participants will complete online diaries via an iPad throughout the 29 days of the study and will complete QOL questionnaires and have measurement of haematology, biochemistry, spirometry and lung volumes (adults only) at 3 time points, at baseline and after each intervention, as well as in-depth semi-structured qualitative interviews after each intervention, carried out by an experienced psychologist. Both qualitative and statistical methods will be used to analyze the data. The primary outcome is qualitative data looking at participant experience from the transcribed interviews after each intervention. The participant's view on feasibility, acceptability and preference will specifically be explored. The QOL, laboratory and lung function data will be compared with baseline for each arm.

DISCUSSION

Patient and public involvement is an integral part of this trial and the key outcome is the qualitative result, which is dependent on obtaining good quality data to advise on participant feasibility, acceptability and preference. This is being addressed by using a standard interview. The development of a pain endpoint is another important outcome and collecting daily measurements is likely to be challenging. Research results will be used to inform design of the Phase 2 trial.

TRIAL REGISTRATION

ISRCTN46078697 18 July 2014.

Intermittent hypoxia in childhood: the harmful consequences versus potential benefits of therapeutic uses

Intermittent hypoxia (IH) often occurs in early infancy in both preterm and term infants and especially at 36-44 weeks postmenstrual age. These episodes of IH could result from sleep-disordered breathing or may be temporally unrelated to apnea or bradycardia events. There are numerous reports indicating adverse effects of IH on development, behavior, academic achievement, and cognition in children with sleep apnea syndrome. It remains uncertain about the exact causative relationship between the neurocognitive and behavioral morbidities and IH and/or its associated sleep fragmentation. On the other hand, well-controlled and moderate IH conditioning/training has been used in sick children for treating their various forms of bronchial asthma, allergic dermatoses, autoimmune thyroiditis, cerebral palsy, and obesity. This review article provides an updated and impartial analysis on the currently available evidence in supporting either side of the seemingly contradictory scenarios. We wish to stimulate a comprehensive understanding of such a complex physiological phenomenon as intermittent hypoxia, which may be accompanied by other confounding factors (e.g., hypercapnia, polycythemia), in order to prevent or reduce its harmful consequences, while maximizing its potential utility as an effective therapeutic tool in pediatric patients.

Comparing segmented ASL perfusion of vascular territories using manual versus semiautomated techniques in children with sickle cell anemia

PURPOSE

Elevated cerebral blood flow (CBF) in sickle cell anemia (SCA) is an adaptive pathophysiologic response associated with decreased vascular reserve and increased risk for ischemia. We compared manual (M) and semiautomated (SA) vascular territory delineation to facilitate standardized evaluation of CBF in children with SCA.

MATERIALS AND METHODS

ASL perfusion values from 21 children were compared for gray matter and white matter (WM) in vascular territories defined by M and SA delineation. SA delineated CBF was compared with clinical and hematologic variables acquired within 4 weeks of the MRI.

RESULTS

CBF measurements from M (MCA 82 left, 79 right) and SA (MCA 81 left, 81 right) delineated territories were highly correlated (R = 0.99, P < 0.0001). Bland-Altman plots had close-fitting limits of agreement of -1.8 to -3.5 lower limit and 0 to 1.8 upper limit. SA vascular territory delineation was comparable to the expert delineation with a kappa index of 0.62-0.85 and was considerably faster. Median territorial CBF values did not differ by gender or age. WM perfusion in the posterior cerebral artery territories was positively correlated with degree of hemolysis (R = 0.58, P = 0.01 left, 0.73, P < 0.001 right) and negatively correlated with hemoglobin (R = -0.48; P = 0.03 left; -0.47; P = 0.04 right) and hemoglobin F (R = -0.42; P = .09 left; -0.47; P = 0.049 right).

CONCLUSION

We established the validity of the SA method, which in our experience was much faster than the M method for delineation of vascular territories. Associations between CBF and hematologic variables may demonstrate pathophysiologic changes that contribute to clinical variation in CBF.

Sickle cell anemia: iron availability and nocturnal oximetry

STUDY OBJECTIVE

To test the hypothesis that low iron availability, measured as transferrin saturation, is associated with low nocturnal hemoglobin oxygen saturation (SpO(2)) in children with homozygous sickle cell anemia (SCA; hemoglobin SS).

METHODS

This was a cross-sectional study of Tanzanian children with SCA who were not receiving regular blood transfusions. Thirty-two children (16 boys) with SCA (mean age 8.0, range 3.6-15.3 years) underwent motion-resistant nocturnal oximetry (Masimo Radical) and had steady state serum transferrin saturation and hematological indices assessed.

RESULTS

Higher transferrin saturation, adjusted for age and α-thalassemia deletion, was associated with lower nocturnal mean SpO(2) (p = 0.013, r(2) = 0.41), number of SpO(2) dips/h > 3% from baseline (p = 0.008, r(2) = 0.19) and with min/h with SpO(2) < 90% (p = 0.026 r(2) = 0.16). Transferrin saturation < 16% (indicative of iron deficiency) was associated with a 2.2% higher nocturnal mean SpO(2).

CONCLUSIONS

Contrary to our hypothesis, higher iron availability, assessed by transferrin saturation, is associated with nocturnal chronic and intermittent hemoglobin oxygen desaturation in SCA. Whether these associations are causal and are driven by hypoxia-inducible factor and hepcidin-mediated upregulation of demand for iron warrants further investigation.

Changing patterns of neuropsychological functioning in children living at high altitude above and below 4000 m: a report from the Bolivian Children Living at Altitude (BoCLA) study

The brain is highly sensitive to environmental hypoxia. Little is known, however, about the neuropsychological effects of high altitude residence in the developing brain. We recently described only minor changes in processing speed in native Bolivian children and adolescents living at approximately 3700 m. However, evidence for loss of cerebral autoregulation above this altitude (4000 m) suggests a potential threshold of hypoxia severity over which neuropsychological functioning may be compromised. We conducted physiological and neuropsychological assessments in 62 Bolivian children and adolescents living at La Paz (∼3700 m) and El Alto (∼4100 m) in order to address this issue. Groups were equivalent in terms of age, gender, social class, schooling, parental education and genetic admixture. Apart from percentage of hemoglobin saturated with oxygen in arterial blood (%SpO(2)), participants did not differ in their basal cardiac and cerebrovascular performance as explored by heart rate, mean arterial pressure, end-tidal carbon dioxide, and cerebral blood flow velocity at the basilar, anterior, middle and posterior cerebral arteries. A comprehensive neuropsychological assessment was administered, including tests of executive functions, attention, memory and psychomotor performance. Participants living at extreme altitude showed lower levels of performance in all executive tests (Cohen effect size = -0.91), whereas all other domains remained unaffected by altitude of residence. These results are compatible with earlier physiological evidence of a transitional zone for cerebral autoregulation at an altitude of 4000 m. We now show that above this threshold, the developing brain is apparently increasingly vulnerable to neuropsychological deficit.

Sleep and culture in children with medical conditions

OBJECTIVES

To provide an integrative review of the existing literature on the interrelationships among sleep, culture, and medical conditions in children.

METHODS

A comprehensive literature search was conducted using PubMed, Medline, and PsychINFO computerized databases and bibliographies of relevant articles.

RESULTS

Children with chronic illnesses experience more sleep problems than healthy children. Cultural beliefs and practices are likely to impact the sleep of children with chronic illnesses. Few studies have examined cultural factors affecting the relationship between sleep and illness, but existing evidence suggests the relationship between sleep and illness is exacerbated for diverse groups.

CONCLUSIONS

Sleep is of critical importance to children with chronic illnesses. Cultural factors can predispose children both to sleep problems and to certain medical conditions. Additional research is needed to address the limitations of the existing literature, and to develop culturally sensitive interventions to treat sleep problems in children with chronic illnesses.

Efeitos da exposição à altitude sobre os aspectos neuropsicológicos: uma revisão da literatura

OBJETIVO: Discutir os efeitos da exposição à altitude sobre as funções neuropsicológicas. MÉTODO: Foi realizada uma revisão de literatura usando como fonte de pesquisa artigos indexados no Pubmed, no período de 1921 a 2008, utilizando as palavras-chave "cognition and hypoxia", "hypoxia and neuropsychology", "acute hypoxia", "chronic hypoxia" e "acclimatization and hypoxia", além de livros específicos do assunto. DISCUSSÃO: Os efeitos agudos e crônicos da hipóxia podem alterar inúmeras funções neuropsicológicas em diferentes altitudes, decorrentes de alterações fisiológicas que resultam da diminuição parcial de oxigênio (O2), que podem levar as alterações neuropsicológicas, como atenção, memória, tomada de decisão e demais funções executivas, em indivíduos expostos a grandes altitudes. CONCLUSÃO: Indivíduos que se expõem às grandes altitudes devem utilizar suplementação de O2 e prática de aclimatização, entre outras estratégias para minimizar os efeitos negativos da hipóxia nos aspectos neuropsicológicos.

Hemodynamic etiology of elevated flow velocity and stroke in sickle-cell disease

Elevation of blood flow velocity in the large cerebral vessels is known to be of substantial pathophysiologic and prognostic significance in sickle-cell disease (SCD). Its precise cause is not established, but the two obvious proximal mechanisms are obstructive vascular stenosis and hemodynamic dilatation. Here we revisit this distinction by analyzing cerebrovascular reserve capacity. Forty-two patients with SCD underwent measurements of global cerebral blood flow in grey matter by the 133Xe inhalation method during normocapnia and hypercapnia to quantify cerebrovascular reactivity. Cerebral blood flow was significantly higher in SCD patients (120+/-31 ml/100 g/min) than in controls (76+/-20 ml/100 g/min). Reactivity was significantly lower in SCD patients (1.06+/-1.92 versus 2.16+/-1.15%/mm Hg). Stepwise multiple regressions within the SCD sample determined that normocapnic cerebral blood flow was largely predicted by hematocrit (r=-0.59; P<0.0001), whereas hypercapnic reactivity was only predicted by normocapnic flow across all subjects (r=-0.52; P<0.0001). None of the controls, but 24% of the SCD patients showed 'steal' (negative reactivity, chi2=6.05; P<0.02). This impairment of vasodilatory capacity, occurring at perfusion levels above 150 ml/100 g/min, may reflect intrinsic limitations of the human cerebrovascular system and can explain both the elevated blood flow velocities and the high risk of stroke observed in such patients.

Risk factors for high cerebral blood flow velocity and death in Kenyan children with Sickle Cell Anaemia: role of haemoglobin oxygen saturation and febrile illness

High cerebral blood flow velocity (CBFv) and low haemoglobin oxygen saturation (SpO₂) predict neurological complications in sickle cell anaemia (SCA) but any association is unclear. In a cross-sectional study of 105 Kenyan children, mean CBFv was 120 ± 34·9 cm/s; 3 had conditional CBFv (170–199 cm/s) but none had abnormal CBFv (>200 cm/s). After adjustment for age and haematocrit, CBFv ≥150 cm/s was predicted by SpO₂ ≤ 95% and history of fever. Four years later, 10 children were lost to follow-up, none had suffered neurological events and 11/95 (12%) had died, predicted by history of fever but not low SpO₂. Natural history of SCA in Africa may be different from North America and Europe.

Haemoglobin oxygen saturation is a determinant of cerebral artery blood flow velocity in children with sickle cell anaemia

Steady-state haemoglobin (Hb) desaturation is a common finding in sickle cell anaemia (Hb SS) that could predispose to stroke by limiting oxygen delivery to the brain. To determine its association with the risk of overt stroke, we examined the relationship between daytime Hb saturation measured by pulse oximetry (SpO(2)) and cerebral artery blood flow velocity measured by transcranial Doppler ultrasonography (TCD), an established risk factor for overt stroke in Hb SS. We studied 181 children using multivariate models to control for known determinants of TCD velocity, including age, haematocrit, and a measure of stenosis. We found that SpO(2) correlated significantly and inversely with TCD velocity in both the right and left middle cerebral arteries. Hb desaturation was associated with increased cerebral artery blood flow velocities and increased odds of abnormal TCD velocities, hence increased risk of stroke. About 5% of the variation in TCD velocity could be ascribed to Hb saturation while controlling for other determinants of TCD velocity. In conclusion, Hb saturation is a determinant of TCD velocity and a risk factor for stroke in children with Hb SS.

Association between lung function and cognition among children in a prospective birth cohort study

OBJECTIVES

To examine the relationship between lung function and cognition among children in the Maternal-Infant Smoking Study of East Boston, a prospective cohort of women and children enrolled before 20 weeks of gestation. A number of studies have demonstrated a relationship between lung function and cognition among adults, but this relationship has not been studied among children.

METHODS

At 6 years of age, children completed lung function tests. At 9 years of age, the Wide Range Assessment of Memory and Learning (WRAML) and Kaufman Brief Intelligence Test (K-BIT) were administered. Linear regression was used to assess the relationship between cognition and lung function.

RESULTS

The sample of 165 children included 53% girls and 52% Hispanic. Mean (+/- standard deviation) forced expiratory volume in 1 second (FEV (1)) was 1.26 +/- 0.2 L; mean forced vital capacity (FVC) was 1.37 +/- 0.2 L. In multivariate regression, a 1% increase from expected FEV(1) was associated with increases in the matrices and composite subscales of the K-BIT (p < .05), and in the verbal and learning subscales of the WRAML (p < .10). FVC was associated with increases in the composite and matrices subscale of the KBIT and in the visual and learning subscales of the WRAML (all p < .05).

CONCLUSION

Increased lung function was associated with increased cognitive development among children after adjusting for tobacco exposure, birthweight, and peak blood lead. Lung and cognitive function may operate under common regulatory processes and thus have shared vulnerabilities to a host of environmental factors during development.

Hemolytic anemia presenting with idiopathic intracranial hypertension

We report on an 8-year-old girl with hemolytic anemia because of infection with parvovirus B19 and increased intracranial pressure. She presented acutely with headache, vomiting, and mild scleral and mucosal icterus. Upon evaluation, the patient exhibited profound hemolytic anemia, papilledema, and increased intracranial pressure. The patient was treated with intravenous immunoglobulin, prednisone, and packed red blood cells. Concurrent with an improvement of her anemia, she experienced a gradual resolution of her headache, vomiting, and optic-disc swelling. Signs of idiopathic intracranial hypertension may occur as a consequence of severe anemia, and are reversible upon correction of the underlying hematologic disorder.

Gene expression in mouse brain following chronic hypoxia: role of sarcospan in glial cell death

Hypoxia is a hallmark of respiratory, neurological, or hematological diseases as well as life at high altitude. For example, chronic constant hypoxia (CCH) occurs in chronic lung diseases or at high altitude, whereas chronic intermittent hypoxia (CIH) occurs in diseases such as sleep apnea or sickle cell disease. Despite the fact that such conditions are frequent, the cellular and molecular mechanisms underlying the effect of hypoxia, whether constant or intermittent, are not well understood. In this study, we first determined the effect of CCH and CIH on global gene expression in different regions of mouse brain using microarrays and then investigated the biological role of genes of interest. We found that: 1) in the cortical region, the expression level of 80 genes was significantly altered by CIH (16 up- and 64 downregulated), and this number increased to 137 genes following CCH (34 up- and 103 downregulated); 2) a similar number of gene alterations was identified in the hippocampal area, and the majority of the changes in this region were upregulations; 3) two genes (Sspn and Ttc27) were downregulated in both brain regions and following both treatments; and 4) RNA interference-mediated knockdown of Sspn increased cell death in hypoxia in a cell culture system. We conclude that CIH or CCH induced significant and distinguishable alterations in gene expression in cortex and hippocampus and that Sspn seems to play a critical role in inducing cell death under hypoxic conditions.

Therapy Insight: stroke risk and its management in patients with sickle cell disease

Children with sickle cell disease, a chronic hemolytic anemia, present with a wide variety of neurological syndromes, including ischemic and hemorrhagic stroke, transient ischemic attacks, 'soft neurological signs', seizures, headache, coma, visual loss, altered mental status, cognitive difficulties, and covert or 'silent' infarction. Those with ischemic stroke usually have stenosis or occlusion of the distal internal carotid and proximal middle cerebral arteries. Indefinite transfusion prevents recurrence in most patients who have had a stroke, and can prevent first stroke in those with high transcranial Doppler velocities. High white cell count, low hemoglobin and oxyhemoglobin desaturation predict neurological complications. Other risk factors for overt ischemic stroke include hypertension, previous transient ischemic attack, covert infarction and chest crisis. For hemorrhagic stroke, aneurysms are common in adults but not children, who often present with hypertension after transfusion or corticosteroids. Seizures are particularly common in patients with cerebrovascular disease and covert infarction; the latter is also associated with hyposplenism and infrequent pain. Factors associated with cognitive difficulties include thrombocytosis, infarction, large-vessel disease, and perfusion abnormality on neuroimaging. As well as investigating the role of genes and the possibility that hydroxyurea or blood pressure control reduce neurological complications, we should explore the modifiable effects of poor nutrition, chronic infection, hemolysis and oxyhemoglobin desaturation on stroke risk.