Economic costs associated with moderate and late preterm birth: a prospective population-based study

OBJECTIVE

We sought to determine the economic costs associated with moderate and late preterm birth.

DESIGN

An economic study was nested within a prospective cohort study.

SAMPLE

Infants born between 32(+0) and 36(+6)  weeks of gestation in the East Midlands of England. A sample of infants born at ≥37 weeks of gestation acted as controls.

METHODS

Data on resource use, estimated from a National Health Service (NHS) and personal social services perspective, and separately from a societal perspective, were collected between birth and 24 months corrected age (or death), and valued in pounds sterling, at 2010-11 prices. Descriptive statistics and multivariable analyses were used to estimate the relationship between gestational age at birth and economic costs.

MAIN OUTCOME MEASURES

Cumulative resource use and economic costs over the first two years of life.

RESULTS

Of all eligible births, 1146 (83%) preterm and 1258 (79%) term infants were recruited. Mean (standard error) total societal costs from birth to 24 months were £12 037 (£1114) and £5823 (£1232) for children born moderately preterm (32(+0) -33(+6)  weeks of gestation) and late preterm (34(+0) -36(+6)  weeks of gestation), respectively, compared with £2056 (£132) for children born at term. The mean societal cost difference between moderate and late preterm and term infants was £4657 (bootstrap 95% confidence interval, 95% CI £2513-6803; P < 0.001). Multivariable regressions revealed that, after controlling for clinical and sociodemographic characteristics, moderate and late preterm birth increased societal costs by £7583 (£874) and £1963 (£337), respectively, compared with birth at full term.

CONCLUSIONS

Moderate and late preterm birth is associated with significantly increased economic costs over the first 2 years of life. Our economic estimates can be used to inform budgetary and service planning by clinical decision-makers, and economic evaluations of interventions aimed at preventing moderate and late preterm birth or alleviating its adverse consequences.

TWEETABLE ABSTRACT

Moderate and late preterm birth is associated with increased economic costs over the first 2 years of life.

Experiences with maternal and perinatal death reviews in the UK--the MBRRACE-UK programme

Established in 1952, the programme of surveillance and Confidential Enquiries into Maternal Deaths in the UK is the longest running such programme worldwide. Although more recently instituted, surveillance and confidential enquiries into perinatal deaths are also now well established nationally. Recent changes to funding and commissioning of the Enquiries have enabled both a reinvigoration of the processes and improvements to the methodology with an increased frequency of future reporting. Close engagement with stakeholders and a regulator requirement for doctors to participate have both supported the impetus for involvement of all professionals leading to greater potential for improved quality of care for women and babies.

Neonatal intensive care outcomes and resource utilisation of infants born <26 weeks in the former Trent region: 2001-2003 compared with 1991-1993

OBJECTIVES

To provide survival data and rates of severe disability at 2 years of corrected age in infants born prior to 26 weeks' gestation in 2001-2003 and to compare these outcomes with an earlier cohort from 1991 to 1993.

DESIGN

Population-based prospective cohort study.

SETTING

Former Trent region of UK covering a population of approximately five million and around 55 000 births per annum.

PARTICIPANTS

The authors identified a 3-year cohort of infants born before 26 weeks' gestation between 1 January 2001 and 31 December 2003 from The Neonatal Survey (TNS). Questionnaires based on the Oxford minimum dataset were completed.

MAIN OUTCOME MEASURES

Survival, service use and disability levels were compared between the 2001- 2003 cohort and the cohort from 1991 to 1993.

RESULTS

In 2001-2003, 0%, 18% and 35% of live born babies were alive at 2 years without any evidence of severe disability at 23, 24 and 25 weeks' gestation, respectively. Overall, of those children admitted to neonatal care, the proportion with no evidence of severe disability at 2 years corrected age improved from 14.5% in 1991-1993 to 26.5% in 2001-2003. There was an increase in the proportion of children with at least one severe disability, out of total admissions to neonatal unit (8% vs 17%) and of those assessed at 2 years (35% vs 39%).

CONCLUSIONS

This study has shown an improvement in survival to discharge in babies admitted for neonatal care. However, this improved survival has been associated with an increase in the proportion of children with at least one severe disability at a corrected age of 2 years.

Predicting neonatal mortality among very preterm infants: a comparison of three versions of the CRIB score

OBJECTIVE

To validate Clinical Risk Index for Babies (CRIB) and CRIB II mortality prediction scores in a UK population of infants born at </=32 weeks' gestation, and investigate CRIB II calculated without admission temperature.

METHODS

Infants born at 22-32 weeks' gestation to mothers resident in a UK region in 2005-2006 admitted for neonatal care were identified. Predictive probabilities for mortality were calculated using CRIB, CRIB II and CRIB II without admission temperature (CRIB II((-T))) using published algorithms and after recalibration. Predictive performance was investigated overall and for groups defined by gestation and admission temperature and summarised by area under receiver-operating curve, Cox's regression, Brier scores and Spiegelhalter's z-scores.

RESULTS

3268 infants were included: 317 (9.7%) died before discharge. Using published algorithms each score showed excellent discrimination (area under the curve = 0.92). The total number of deaths was predicted well for CRIB (324.4) but for both versions of CRIB II the number of deaths was underpredicted (255.2 and 216.6). All scores performed poorly for subgroups. After recalibration CRIB II displayed excellent predictive characteristics overall (Spiegelhalter's z-score p = 0.52) and in the gestation groups (p = 0.44 and 0.57) but not for the temperature groups (p = 0.026 and 0.97). CRIB II((-T)) displayed excellent predictive characteristics for all groups: overall p = 0.53; gestation groups p = 0.64 and 0.42; temperature groups p = 0.42 and 0.66.

CONCLUSIONS

The published algorithm for CRIB II was poorly calibrated but simple linear recalibration provided good results. The CRIB II score without admission temperature showed good predictive characteristics once recalibrated and this version of the score should be used when benchmarking mortality in neonatal intensive care units.

Toxic additives in medication for preterm infants

BACKGROUND

Little is known about exposure of preterm infants to excipients during routine clinical care.

OBJECTIVE

To document excipient exposure in vulnerable preterm babies in a single centre, taking into account chronic lung disease (CLD) as a marker of illness severity.

DESIGN

Excipient exposure after treatment with eight oral liquid medications was determined by retrospectively analysing the drug charts of infants admitted to a neonatal unit.

SETTING

The Leicester Neonatal Service.

PARTICIPANTS

38 infants born between June 2005 and July 2006 who were less than 30 weeks' gestation and 1500 g in weight at birth and managed in Leicester to discharge.

RESULTS

The 38 infants represented 53% of the eligible target group; 7/38 infants had CLD. During their in-patient stay, infants were exposed to over 20 excipients including ethanol and propylene glycol, chemicals associated with neurotoxicity. Infants with CLD were exposed to higher concentrations of these toxins. Infants were also exposed to high concentrations of sorbitol, with some infants being exposed to concentrations in excess of recommended guidelines for maximum exposure in adults.

CONCLUSIONS

Preterm infants are commonly exposed to excipients, some of which are potentially toxic. Strategies aimed at reducing excipient load in preterm infants are urgently required.

Antenatal umbilical Doppler abnormalities: an independent risk factor for early onset neonatal necrotizing enterocolitis in premature infants

BACKGROUND

Necrotizing enterocolitis (NEC) is the most common gastrointestinal (GI) emergency seen in neonatal units. Many factors have been considered as potentially important aetiologically, including gut ischaemia, sepsis and feeding. However, evidence remains equivocal.

OBJECTIVE

This study investigated whether preterm babies born to mothers with abnormal antenatal umbilical Dopplers (absent or reversed end diastolic flow--AREDF), that is exposed to antenatal gut ischaemia, are at an identical risk of developing NEC early in life, compared to babies born to mothers with normal Dopplers.

METHODS

All preterm (<or=32+6 week gestation) babies with no congenital anomaly, born to mothers resident in the county of Leicestershire in United Kingdom in 2001 and 2002 were identified using the Trent Neonatal Survey (TNS). Clinical data including the presence and severity of any NEC were extracted from the notes.

RESULTS

Two hundred forty-three preterm babies who met the criteria were identified during the period. Babies in whom umbilical Dopplers were not available and babies that died in the first 48 h were excluded. Complete data was thus available for 206 of these babies. A strong relation between AREDF and subsequent development of NEC was noted in these babies (OR: 5.88, 95% CI: 2.41 to 14.34, p<0.0001). This association still held after adjustment for gestational age at birth (OR: 7.64, 95% CI: 2.96 to 19.70, p<0.0001) and after adjustment for birthweight for gestational age z-score (OR: 6.72, 95% CI: 2.23 to 20.25, p=0.0007).

CONCLUSIONS

This study, based on a neonatal cohort, indicates that AREDF is an important independent risk factor for the production of NEC.

Natural image statistics and efficient coding

Natural images contain characteristic statistical regularities that set them apart from purely random images. Understanding what these regularities are can enable natural images to be coded more efficiently. In this paper, we describe some of the forms of structure that are contained in natural images, and we show how these are related to the response properties of neurons at early stages of the visual system. Many of the important forms of structure require higher-order (i.e. more than linear, pairwise) statistics to characterize, which makes models based on linear Hebbian learning, or principal components analysis, inappropriate for finding efficient codes for natural images. We suggest that a good objective for an efficient coding of natural scenes is to maximize the sparseness of the representation, and we show that a network that learns sparse codes of natural scenes succeeds in developing localized, oriented, bandpass receptive fields similar to those in the mammalian striate cortex.

Socioeconomic inequalities in very preterm birth rates

AIMS

To investigate the extent of socioeconomic inequalities in the incidence of very preterm birth over the past decade.

METHODS

Ecological study of all 549 618 births in the former Trent health region, UK, from 1 January 1994 to 31 December 2003. All singleton births of 22(+0) to 32(+6) weeks gestation (7 185 births) were identified from population surveys of neonatal services and stillbirths. Poisson regression was used to calculate incidence of very preterm birth (22-32 weeks) and extremely preterm birth (22-28 weeks) by year of birth and decile of deprivation (child poverty section of the Index of Multiple Deprivation).

RESULTS

Incidence of very preterm singleton birth rose from 11.9 per 1000 births in 1994 to 13.7 per 1000 births in 2003. Those from the most deprived decile were at nearly twice the risk of very preterm birth compared with those from the least deprived decile, with 16.4 per 1000 births in the most deprived decile compared with 8.5 per 1000 births in the least deprived decile (incidence rate ratio 1.94; 95% CI (1.73 to 2.17)). This deprivation gap remained unchanged throughout the 10-year period. The magnitude of socio-economic inequalities was the same for extremely preterm births (22-28 weeks incidence rate ratio 1.94; 95% CI (1.62 to 2.32)).

CONCLUSIONS

This large, unique dataset of very preterm births shows wide socio-economic inequalities that persist over time. These findings are likely to have consequences on the burden of long-term morbidity. Our research can assist future healthcare planning, the monitoring of socio-economic inequalities and the targeting of interventions in order to reduce this persistent deprivation gap.

Follow up of infants following discharge from the neonatal unit: structure and process

Reviewing high risk infants after discharge to provide ongoing clinical care and to monitor later outcomes is an important role for neonatologists and paediatricians. Clinical need is the primary reason for such follow up but the process does provide additional opportunities, for example collecting information on later outcomes is vital for health care commissioning, and to determine the longer term effects of new medical treatments. Parents welcome the early identification of any problems in their infant and the opportunity for early intervention may improve outcomes in some circumstances. However, depending on the model adopted, follow up can be costly and this expenditure must be justified by considering the benefits obtained.

Developmental outcome in newborn infants treated for acute respiratory failure with extracorporeal membrane oxygenation: present experience

OBJECTIVE

To describe the later health status of newborn infants who received extracorporeal membrane oxygenation (ECMO) for acute respiratory failure in the era after the UK ECMO trial.

DESIGN

Prospective follow up study of newborn infants who received ECMO at a single centre between January 1997 and January 2001.

SETTING

Departments of ECMO and Paediatric Intensive Care, University Hospitals of Leicester.

PATIENTS

All babies who received ECMO within 14 days of birth.

INTERVENTIONS

Neurodevelopment screening using the schedule for growing skills-II (SGS-II) assessment tool.

MAIN OUTCOME MEASURES

Survival at 12 months of age by disease and functional development at follow up.

RESULTS

A total of 145 neonates received ECMO for treatment of respiratory failure. Of these, 108 (75%) were alive at 1 year of age. There were no deaths in children treated for respiratory failure secondary to meconium aspiration syndrome (73/145). Ninety three (86% of survivors) infants attended a follow up visit at 11-19 months postnatal age. Eighty two were classed as normal, seven as having "impairment", and four as having "severe disability".

CONCLUSIONS

Most newborn infants with acute respiratory failure treated with ECMO will have a normal neurodevelopment screening assessment at 11-19 months of postnatal age. There is no evidence to suggest that changes in neonatal practice since the UK ECMO trial have led to changes in outcome of infants undergoing ECMO therapy.

Neonatal disease severity scoring systems

Illness severity scores have become widely used in neonatal intensive care. Primarily this has been to adjust the mortality observed in a particular hospital or population for the morbidity of their infants, and hence allow standardised comparisons to be performed. However, although risk correction has become relatively commonplace in relation to audit and research involving groups of infants, the use of such scores in giving prognostic information to parents, about their baby, has been much more limited. The strengths and weaknesses of the existing methods of disease severity correction in the newborn are presented in this review.

Contour integration and cortical processing

Our understanding of visual processing in general, and contour integration in particular, has undergone great change over the last 10 years. There is now an accumulation of psychophysical and neurophysiological evidence that the outputs of cells with conjoint orientation preference and spatial position are integrated in the process of explication of rudimentary contours. Recent neuroanatomical and neurophysiological results suggest that this process takes place at the cortical level V1. The code for contour integration may be a temporal one in that it may only manifest itself in the latter part of the spike train as a result of feedback and lateral interactions. Here we review some of the properties of contour integration from a psychophysical perspective and we speculate on their underlying neurophysiological substrate.

The potential impact on costs and staffing of introducing clinical networks and British Association of Perinatal Medicine standards to the delivery of neonatal care

OBJECTIVE

To produce models to estimate the impact of introducing clinical networks and the 2001 BAPM standards to the delivery of neonatal care.

DESIGN

Prospective observational study using a geographically defined population and data collected by questionnaire on staffing levels and cot availability.

SETTING

Trent Health Region UK.

SUBJECTS

All infants born to Trent resident mothers at or before 32 weeks gestation between 1 January 1998 and 31 December 1999. Staffing numbers and cot availability for neonatal care in 2001.

METHODS

A modelling exercise was carried out using information for all neonatal admissions for Trent resident infants. Three models were investigated: (a). the current care provision; (b). a network where three lead centres provided the intensive care for the region and the remaining units provided either high dependency or special care alone; (c). a network where six lead centres provided the intensive care for the region and the remaining units provided either high dependency or special care alone. Overall costings, staffing levels, and cot requirements were calculated for each model. Data on staffing levels and cot availability were used to calculate current care provision costings.

RESULTS

The current cost of running the service is approximately pound 33.35 million, although a proportion of nursing posts are currently unfilled. Estimates for the introduction of a three centre model meeting BAPM 2001 standards range from pound 37.31 to pound 43.40 million. Equivalent figures for the six centre model were: pound 36.32 to pound 42.62 million. Approximately 370 and 230 babies a year would be involved in transfer in the three and six centre models respectively. This is in contrast with 374 and 368 urgent transfers that actually took place in 1998 and 1999 respectively.

CONCLUSION

The costs associated with the introduction of managed clinical networks and meeting BAPM standards of care are not excessive, especially when considered against the likely implementation timetable of perhaps 7-10 years. Attracting and retaining sufficient staff will pose the major challenge.

Repeatability of cellular constituents and cytokine concentration in fluid obtained by non-bronchoscopic bronchoalveolar lavage of infants receiving extracorporeal oxygenation

BACKGROUND

Since few studies have assessed the repeatability of non-bronchoscopic bronchoalveolar lavage (NB-BAL), we compared cellular counts and cytokine concentrations in fluid obtained by standardised NB-BAL from each side of 20 intubated infants receiving extracorporeal membrane oxygenation (ECMO).

METHODS

Total cell counts were obtained from 95 paired lavages and 77 pairs were suitable for differential counts and measurement of cytokine concentrations.

RESULTS

Moderate correlation was noted between the two sides for most cell types including total cell counts and percentages of neutrophils and macrophages (R=0.70-0.84) and for cytokine concentrations (IL-8 R=0.78, IL-6 R=0.75, TNF-alpha R=0.64, all p< or =0.001). Using Bland-Altman analysis the mean difference between the two sides approached zero for cellular constituents (total cell counts mean difference 1.7, limits of agreement -187.5 to +190.9 x 10(4)/ml; percentage neutrophils -3.9%, -41.5% to +33.6%; percentage macrophages 3.9%, -33.8% to +41.6%) but tended to be greater on the right for logarithmically transformed cytokine measurements (IL-8: left/right ratio 0.74, limits of agreement 0.12 to 5.45, IL-6: 0.93, 0.09 to 5.87, and TNF-alpha: 0.93, 0.27 to 3.16). Using linear regression with random effects to assess the variability, only the infant's age appeared to influence the cellular results but, for cytokines, only the volume retrieved affected the variability. The magnitude of the measurements, the underlying disease, the operator's experience, days on ECMO, or survival did not affect the variability.

CONCLUSION

Measurements obtained by NB-BAL need to be interpreted with caution and strongly suggest that normalisation for the dilutional effects of saline is essential.

UK collaborative randomised trial of neonatal extracorporeal membrane oxygenation: follow-up to age 4 years

Extracorporeal membrane oxygenation (ECMO) is a supportive intensive-care technique used for babies with acute respiratory failure. We examined morbidity at age 4 years in surviving children recruited to the UK Collaborative ECMO Trial, and provide long-term data on ECMO support compared with contemporary conventional care. The neonatal ECMO policy resulted in improved survival and a favourable outcome. We therefore advocate the safety and efficacy of this intervention.

Local contrast in natural images: normalisation and coding efficiency

The visual system employs a gain control mechanism in the cortical coding of contrast whereby the response of each cell is normalised by the integrated activity of neighbouring cells. While restricted in space, the normalisation pool is broadly tuned for spatial frequency and orientation, so that a cell's response is adapted by stimuli which fall outside its 'classical' receptive field. Various functions have been attributed to divisive gain control: in this paper we consider whether this output nonlinearity serves to increase the information carrying capacity of the neural code. 46 natural scenes were analysed with the use of oriented, frequency-tuned filters whose bandwidths were chosen to match those of mammalian striate cortical cells. The images were logarithmically transformed so that the filters responded to a luminance ratio or contrast. In the first study, the response of each filter was calibrated relative to its response to a grating stimulus, and local image contrast was expressed in terms of the familiar Michelson metric. We found that the distribution of contrasts in natural images is highly kurtotic, peaking at low values and having a long exponential tail. There is considerable variability in local contrast, both within and between images. In the second study we compared the distribution of response activity before and after implementing contrast normalisation, and noted two major changes. Response variability, both within and between scenes, is reduced by normalisation, and the entropy of the response distribution is increased after normalisation, indicating a more efficient transfer of information.

Sensitivity to contrast histogram differences in synthetic wavelet-textures

Recent research on texture synthesis suggests that characterisation of those properties of textures to which human observers are sensitive may be provided by the histograms of the coefficients of a wavelet decomposition. In this study we examined the properties of wavelet histograms that affect texture discrimination by measuring observer sensitivity to differences in the wavelet histograms of synthetic textures. The textures, generated via Gabor micropattern synthesis, were broadband, with amplitude spectra that are characteristic of natural images, i.e. 1/f. We measured texture-difference thresholds for three moments of the wavelet histograms -- variance, skew and kurtosis -- by manipulating the contrast, phase, and density, of the Gabor elements used to construct the textures. Observers discriminated more efficiently between textures that had differences in kurtosis, than between textures that had differences in either variance or skew. Performance was compared to two model observers; one used the pixel-luminance histogram, the other used the histogram of the output of wavelet-filters. The results support the idea that the visual system is relatively sensitive to the kurtosis, or 4th moment, of the wavelet histogram of textures. We argue that higher than 4th-order moments will, in practice, become increasingly difficult for the visual system to represent because the lack of a perfect match between the elements and the receptive fields effectively blurs the response histogram, thereby attenuating higher moments.

The roles of polarity and symmetry in the perceptual grouping of contour fragments

We describe two experiments that investigate the roles of polarity and symmetry in the perceptual grouping of contour fragments. Observers viewed, for one second on each presentation, arrays of oriented, spatial-frequency band-pass, elements, in which a subset of the elements was aligned along a twisting curve. In each of five conditions we measured observers' ability to detect aligned combinations of even- and odd-symmetric elements, of the same and different polarities, against a background of 'noise' elements. As with previous experiments we found that the 'path' could be reliably detected, even when the elements of the path were oriented at angles of up to +/- 60 deg relative to each other. Detection of the path was still possible when the polarity of path elements alternated. However, the probability of detection of the path was raised significantly when the path elements were all of the same polarity. Perceptual grouping of even-symmetric elements was no different to perceptual grouping of odd-symmetric elements. The results provide evidence, that in achieving integration of contour fragments, the visual system uses a process that is to some degree phase selective. We use the results to describe how the visual system may resolve natural contours when they occur against backgrounds that vary over a wide range of intensities. The data presented here have been published in conference-abstract form (Hayes et al., 1993; Field et al., 1997).

Concentration of nitric oxide products in bronchoalveolar fluid obtained from infants who develop chronic lung disease of prematurity

AIMS

To determine if nitric oxide (NO) products (nitrate and nitrite) are increased in bronchoalveolar lavage (BAL) fluid obtained from infants who develop chronic lung disease of prematurity (CLD).

METHODS

One hundred and thirty six serial bronchoalveolar lavages were performed on 37 ventilated infants (12 with CLD, 18 with respiratory distress syndrome (RDS), and seven control infants) who did not receive inhaled NO.

RESULTS

During the first week of life nitrate concentration was between 25-31 micromol/l in all three groups. Thereafter, the concentration of BAL fluid nitrate decreased to 14 micromol/l and 5.5 micromol/l, respectively in the RDS and control groups by 14 days of age. In contrast, nitrate in the CLD infants remained constant until 28 days of age (31.3 micromol/l at day 14; p<0.05). In all BAL fluid samples the mean concentration of nitrite was <1.2 micromol/l throughout the first 28 days with no significant differences noted among the three groups.

CONCLUSION

The similar concentration of BAL fluid nitrate in all groups during the first week of life suggest that NO may be important in the adaptation of the pulmonary circulation after birth. However, persistence of nitrate in the BAL fluid of infants with CLD during the second week may reflect pulmonary maladaptation, or, more likely, persisting pulmonary inflammation.

Prediction of survival for preterm births by weight and gestational age: retrospective population based study

OBJECTIVE

To produce current data on survival of preterm infants.

DESIGN

Retrospective population based study.

SETTING

Trent health region.

SUBJECTS

All European and Asian live births, stillbirths, and late fetal losses from 22 to 32 weeks' gestation, excluding those with major congenital malformations, in women resident in the Trent health region between 1 January 1994 and 31 December 1997.

MAIN OUTCOME MEASURES

Birth weight and gestational age specific survival for both European and Asian infants (a) known to be alive at the onset of labour, and (b) admitted for neonatal care.

RESULTS

738 deaths occurred in 3760 infants born between 22 and 32 weeks' gestation during the study period, giving an overall survival rate of 80.4%. The survival rate for the 3489 (92.8%) infants admitted for neonatal care was 86.6%. For European infants known to be alive at the onset of labour, significant variations in gestation specific survival by birth weight emerged from 24 weeks' gestation: survival ranged from 9% (95% confidence interval 7% to 13%) for infants of birth weight 250-499 g to 21% (16% to 28%) for those of 1000-1249 g. At 27 weeks' gestation, survival ranged from 55% (49% to 61%) for infants of birth weight 500-749 g (below the 10th centile) to 80% (76% to 85%) for those of 1250-1499 g. Infants who were large for dates (>/=27 weeks' gestation) had a slightly reduced, but not significant, predicted survival. Similar survival rates were observed for Asian infants. The odds ratio for the survival of infants from a multiple birth compared with singleton infants was 1.4 (1.1 to 1.8). Survival graphs for infants admitted for neonatal care are presented by sex.

CONCLUSION

Easy to use birth weight and gestational age specific predicted survival graphs for preterm infants facilitate decision making for clinicians and parents. It is important that these graphs are representative, are produced for a geographically defined population, and are not biased towards the outcomes of particular centres. Such graphs, produced in two stages, allow for the changing pattern of survival of infants from the start of the intrapartum period to immediately after admission for neonatal care.

Health status of a population of infants born before 26 weeks gestation derived from routine data collected between 21 and 27 months post-delivery

This retrospective study was designed: (a) to determine the extent to which routine data sources in the UK can provide data relating to the later health status of selected groups of infants; and (b) to use such an approach to describe the outcome of a geographically defined population of infants born before 26 weeks gestation. All infants of less than 26 weeks gestation admitted for neonatal intensive care during the period 1/1/91 and 31/12/93 whose mother's address at the time of birth was within the boundaries of the Trent Health Region were included. Health status was assessed against a previously described simple scheme and using information from existing sources only. During the 3-year period 249 infants of less than 26 weeks gestation were admitted for intensive care. Of these 66 (26.5%) survived to be discharged from the neonatal service. A further seven infants died before the age of 2 years. Of the remaining 59 four were lost to follow up (three could not be traced; one was living abroad). Of the 55 infants reviewed, 36 demonstrated no features, pre-defined in the classification scheme, of severe disability. However, only 30 children appeared to be considered entirely normal.

CONCLUSION

Infants born before 26 weeks gestation and admitted for neonatal intensive care had, approximately, a 12% chance of normal survival to 2 years. A slightly smaller proportion of infants survived with significant disability. Existing routine data sources could be adapted to provide useful public health information about the outcome of 'high risk' groups of infants.

Synthetic lethality of yeast slt mutations with U2 small nuclear RNA mutations suggests functional interactions between U2 and U5 snRNPs that are important for both steps of pre-mRNA splicing

A genetic screen was devised to identify Saccharomyces cerevisiae splicing factors that are important for the function of the 5' end of U2 snRNA. Six slt (stands for synthetic lethality with U2) mutants were isolated on the basis of synthetic lethality with a U2 snRNA mutation that perturbs the U2-U6 snRNA helix II interaction. SLT11 encodes a new splicing factor and SLT22 encodes a new RNA-dependent ATPase RNA helicase (D. Xu, S. Nouraini, D. Field, S. J. Tang, and J. D. Friesen, Nature 381:709-713, 1996). The remaining four slt mutations are new alleles of previously identified splicing genes: slt15, previously identified as prp17 (slt15/prp17-100), slt16/smd3-1, slt17/slu7-100, and slt21/prp8-21. slt11-1 and slt22-1 are synthetically lethal with mutations in the 3' end of U6 snRNA, a region that affects U2-U6 snRNA helix II; however, slt17/slu7-100 and slt21/prp8-21 are not. This difference suggests that the latter two factors are unlikely to be involved in interactions with U2-U6 snRNA helix II but rather are specific to interactions with U2 snRNA. Pairwise synthetic lethality was observed among slt11-1 (which affects the first step of splicing) and several second-step factors, including slt15/prp17-100, slt17/slu7-100, and prp16-1. Mutations in loop 1 of U5 snRNA, a region that is implicated in the alignment of the two exons, are synthetically lethal with slu4/prp17-2 and slu7-1 (D. Frank, B. Patterson, and C. Guthrie, Mol. Cell. Biol. 12:5179-5205, 1992), as well as with slt11-1, slt15/prp17-100, slt17/slu7-100, and slt21/prp8-21. These same U5 snRNA mutations also interact genetically with certain U2 snRNA mutations that lie in the helix I and helix II regions of the U2-U6 snRNA structure. Our results suggest interactions among U2 snRNA, U5 snRNA, and Slt protein factors that may be responsible for coupling and coordination of the two reactions of pre-mRNA splicing.

The role of "contrast enhancement" in the detection and appearance of visual contours

We test the proposition that the appearance and detection of visual contours is based on an increase in the perceived contrast of contour elements. First we show that detection of contours is quite possible in the presence of very high levels of variability in contrast. Second we show that inclusion in a contour does not induce Gabor patches to appear to be of higher contrast than patches outside of a contour. These results suggest that, contrary to a number of current models, contrast or its assumed physiological correlate (the mean firing rate of early cortical neurons) is not the determining information for identifying the contour.

Sparse coding with an overcomplete basis set: a strategy employed by V1?

The spatial receptive fields of simple cells in mammalian striate cortex have been reasonably well described physiologically and can be characterized as being localized, oriented, and bandpass, comparable with the basis functions of wavelet transforms. Previously, we have shown that these receptive field properties may be accounted for in terms of a strategy for producing a sparse distribution of output activity in response to natural images. Here, in addition to describing this work in a more expansive fashion, we examine the neurobiological implications of sparse coding. Of particular interest is the case when the code is overcomplete--i.e., when the number of code elements is greater than the effective dimensionality of the input space. Because the basis functions are non-orthogonal and not linearly independent of each other, sparsifying the code will recruit only those basis functions necessary for representing a given input, and so the input-output function will deviate from being purely linear. These deviations from linearity provide a potential explanation for the weak forms of non-linearity observed in the response properties of cortical simple cells, and they further make predictions about the expected interactions among units in response to naturalistic stimuli.

Visual sensitivity, blur and the sources of variability in the amplitude spectra of natural scenes

A number of researchers have suggested that in order to understand the response properties of cells in the visual pathway, we must consider the statistical structure of the natural environment. In this paper, we focus on one aspect of that structure, namely, the correlational structure which is described by the amplitude or power spectra of natural scenes. We propose that the principle insight one gains from considering the image spectra is in understanding the relative sensitivity of cells tuned to different spatial frequencies. This study employs a model in which the peak sensitivity is constant as a function of frequency with linear bandwith increasing (i.e., approximately constant in octaves). In such a model, the "response magnitude" (i.e., vector length) of cells increases as a function of their optimal (or central) spatial frequency out to about 20 cyc/deg. The result is a code in which the response to natural scenes, whose amplitude spectra typically fall as 1/f, is roughly constant out to 20 cyc/deg. An important consideration in evaluating this model of sensitivity is the fact that natural scenes show considerable variability in their amplitude spectra, with individual scenes showing falloffs which are often steeper or shallower than 1/f. Using a new measure of image structure (the "rectified contrast spectrum" or "RCS") on a set of calibrated natural images, it is shown that a large part of the variability in the spectra is due to differences in the sparseness of local structure at different scales. That is, an image which is "in focus" will have structure (e.g., edges) which has roughly the same magnitude across scale. That is, the loss of high frequency energy in some images is due to the reduction of the number of regions that contain structure rather than the amplitude of that structure. An "in focus" image will have structure (e.g., edges) across scale that have roughly equal magnitude but may vary in the area covered by structure. The slope of the RCS was found to provide a reasonable prediction of physical blur across a variety of scenes in spite of the variability in their amplitude spectra. It was also found to produce a good prediction of perceived blur as judged by human subjects.

Contour integration in strabismic amblyopia: the sufficiency of an explanation based on positional uncertainty

Contour integration was measured in a group of strabismic amblyopes to determine if an explanation based solely on positional uncertainty was sufficient to explain performance. The task involved the detection of paths composed of micropatterns with correlated carrier orientations embedded in a field of similar micropatterns of random position and orientation (Field et al. Contour integration by the human visual system; Evidence for a local "association field". Vision Research, 33, 173-193, 1993). The intrinsic positional uncertainty for each amblyopic eye was measured with the same stimulus and it was found that in 10 out of our 11 amblyopic subjects, the reduced performance of the amblyopic eye could be modelled by the normal eye with an equivalent amount of positional uncertainty added to the stimulus. We conclude that the rules by which cellular outputs are combined, at least as reflected by this task, are normal in amblyopia.

Uncalibrated distortions vs undersampling

In a recent paper of ours [Hess & Field (1993). Vision Research, 33, 2663-2670], we claim that there was a predictable relationship between position errors and contrast errors for an undersampled system. In this paper we re-state our main points. We feel that the response to that paper by Levi and Klein in the accompanying article does not require us to produce changes in our original position. We believe that the data support the notion that the principal causes of the positional errors in the normal periphery and the in the amblyopic visual system are due to uncalibrated distortions in the local signs of visual neurons. We believe that undersampling plays a major role in producing positional errors only in the far periphery at, or very near, the acuity limit. We maintain that our initial studies provide strong evidence that undersampling is insufficient as an explanation for the positional errors in the periphery of normals (Hess & Field, 1993) or the central field of amblyopes [Hess & Field (1994). Vision Research, 34, 3397-3406.

Emergence of simple-cell receptive field properties by learning a sparse code for natural images

The receptive fields of simple cells in mammalian primary visual cortex can be characterized as being spatially localized, oriented and bandpass (selective to structure at different spatial scales), comparable to the basis functions of wavelet transforms. One approach to understanding such response properties of visual neurons has been to consider their relationship to the statistical structure of natural images in terms of efficient coding. Along these lines, a number of studies have attempted to train unsupervised learning algorithms on natural images in the hope of developing receptive fields with similar properties, but none has succeeded in producing a full set that spans the image space and contains all three of the above properties. Here we investigate the proposal that a coding strategy that maximizes sparseness is sufficient to account for these properties. We show that a learning algorithm that attempts to find sparse linear codes for natural scenes will develop a complete family of localized, oriented, bandpass receptive fields, similar to those found in the primary visual cortex. The resulting sparse image code provides a more efficient representation for later stages of processing because it possesses a higher degree of statistical independence among its outputs.

Impact of extremely immature infants on neonatal services

The impact of very immature infants on neonatal services was examined within the United Kingdom. The Trent Health Region was used as a geographically defined population. Data were obtained on all infants weighing less than 1501 g at birth and all infants born before 32 weeks gestation between 1991-93. Information relating to length of stay, duration of ventilation, and survival was documented. Only one of 49 infants born before 24 weeks gestation survived. However, 75% of this group were ventilated. Most of the remaining infants died before 48 hours of age. A similar pattern was also seen in infants of 24 and 25 weeks gestation. Infants under 24 weeks gestation comprised 1.5% of all ventilated infants and consumed 2.14% of the total neonatal ventilator days for the region. It is concluded that the United Kingdom operates a conservative policy towards infants born before 24 weeks gestation and as a result resources expended on them are limited.

Functionally redundant interactions between U2 and U6 spliceosomal snRNAs

Base-pairing between U2 and U6 snRNAs to form intermolecular helix II has been demonstrated previously as a requirement for pre-mRNA splicing in mammalian cells. In contrast, deletion and substitution mutation experiments in yeast have indicated that helix II is not essential; instead, other regions of U2 and U6 have been proposed to pair, forming a helix called Ib. To investigate the importance of U2/U6 helices in yeast, we have systematically mutagenized the regions proposed to form helices II and Ib. Allele-specific suppression of certain U6 mutations by complementary substitutions in U2 show that helix II indeed form in yeast but that it is essential only in the presence of additional mutations that disrupt U2 stem I and the proposed helix Ib. Similarly, the proposed helix Ib is essential only when helix II is disrupted. These observations provide an explanation for apparently conflicting data in yeast and mammalian experimental systems, and identify synergistic or functionally redundant interactions between U2 and U6 snRNAs.

Chronic lung disease following neonatal ventilation. II. Changing incidence in a geographically defined population

The objective of this study was to examine the change in incidence of chronic lung disease following neonatal ventilation in a geographically defined population. Prospective data were collected over two 1-year periods (1987-1988 and 1990-1991) in the Trent Health Region, England. All infants were < or = 32 weeks gestation and/or < or = 1500g birthweight, born to mothers normally resident in the Trent Health Region. The principal outcome measures were mortality rate, presence of chronic lung disease, days of ventilation, and oxygen used by each infant. The proportion of low gestation, low birthweight babies was 1.5% in each period, made up of 897 and 925 babies from 61,050 and 63,350 births, respectively. There was a significant fall in mortality in infants of 750-1500g birthweight. However, the incidence of chronic lung disease (using either of two definitions) rose significantly between the two periods, with a corresponding large rise in the amount of respiratory care required. The contribution of various antenatal factors previously thought to be related to the development of chronic lung disease was examined. Birthweight and gestation were shown to be of overwhelming significance. We concluded that improvements in neonatal care, including the introduction of surfactant therapy, improved survival for some infants at the expense of an increased incidence of chronic lung disease. Clearly the hoped-for cost saving following the introduction of surfactant therapy has not occurred.

Chronic lung disease following neonatal ventilation. I. incidence in two geographically defined populations

The objective of this study was to compare the incidence of chronic lung disease following neonatal ventilation in two geographically defined populations. Prospective data collection was carried out over a 1 year period from March 11, 1990 to February 28, 1991 in the Trent Health Region (England) and in British Columbia, Canada. All infants < or = 32 weeks gestation and/or < or = 1500 g birthweight born to mothers normally resident in either the Trent Health Region or British Columbia were included. The main outcome measures were mortality rate, presence of chronic lung disease, days of ventilation, and oxygen used by each infant. The proportion of shortened gestation, low birthweight babies was 1.5% in Trent and 1.2% in British Columbia (957 of 63,350 births in Trent and 526 of 45,333 births in British Columbia). There were no significant differences in mean birthweight or gestation between the two cohorts, but there was a trend towards lower mortality for infants 750-1500 g birthweight in British Columbia. The incidence of chronic lung disease (using either of two definitions) was significantly higher in British Columbia, with a corresponding greater amount of respiratory care required. This occurred despite higher use of antenatal steroids and surfactant therapy in the British Columbia group. We conclude that there are important clinical and resource implications resulting from the number of ventilator and oxygen days used by the preterm population in terms of planning of neonatal services. The role of individual treatment modalities in producing differences in the incidence of chronic lung disease warrants further study in the setting of a geographically defined population.

Circulatory effects of ventilator rate and end-expiratory pressure in unparalysed preterm infants

Impairment of cerebrovascular autoregulation may be important in the pathogenesis of ischaemic brain injury in preterm infants. A previous study in ventilated preterm infants paralysed with pancuronium showed that changes in cerebral blood flow velocity (CBFV) were related to concomitant changes in arterial blood pressure. In a similar study in unparalysed infants, changes in CBFV in response to changes in ventilator rate or end-expiratory pressure were independent of associated changes in the arterial blood pressure. These results emphasize the importance of avoiding large swings in blood pressure in paralysed infants. Whether alternative paralysing agents have similar effects warrants further study.

Contour integration across depth

In order to investigate the extent of the local connections subserving contour integration across depth, we measured performance for detecting the continuity of a path of Gabor elements distributed in depth and embedded in a three-dimensional field of random background elements. The results show that performance cannot be explained in terms of monocular performance and that contour information is not limited to single disparity planes. Path detection does indeed involve the integration of information across different, very disparate depth planes. The rules which emerge are in general similar to that already described in the two-dimensional case in as far as orientation and disparity are important. Unlike the two-dimensional case, three-dimensional integration operates over relatively large three-dimensional distances.

What's constant in contrast constancy? The effects of scaling on the perceived contrast of bandpass patterns

"Contrast constancy" refers to the ability to perceive objects as maintaining a constant contrast independent of size or distance. When tested with high contrast sinusoidal gratings, contrast constancy has been shown to hold for a wide range of spatial frequencies, suggesting that sensitivity is constant across the spectrum at suprathreshold. In this study, we show that contrast constancy also holds for relatively broadband patterns. We describe how the frequency spectra of such functions change as the patterns scale in size. In particular, we emphasize how these changes in the spectra depend on whether the functions are localized (coherent phase) or spatially distributed (incoherent phase). In Fourier terms, the scaling properties depend on the phase spectra of the patterns. Contrast constancy is shown to hold for both localized Gabor patches (coherent phase spectra) and bandpass noise patterns (incoherent phase spectra). Constancy holds over a wide range of suprathreshold contrasts; in fact, matching is quite accurate as soon as the pattern is suprathreshold. These results are explained with a model in which mechanism bandwidths increase with frequency (constant in octaves) and peak spectral sensitivity is equal across frequency out to around 16 c/deg. In the case of the Gabor stimuli, perceived contrast is assumed to be mediated by a mechanism centered on the patch. For the bandpass noise, contrast is determined by the average response of units distributed across the stimulus. This model can account for the matching data without assuming that the contrast-response gain of the underlying channels changes with spatial frequency. Neither does the model assume "response pooling". In addition to explaining the experimental results, the model also predicts that perceived contrast will be approximately constant across scale for scenes whose spectra fall as 1/f, as is typical of natural scenes.

Is the spatial deficit in strabismic amblyopia due to loss of cells or an uncalibrated disarray of cells?

We examine two competing explanations for the spatial localization deficit in human strabismic amblyopia, namely neural undersampling and uncalibrated neural disarray. An undersampling hypothesis would predict an associated deficit for contrast discrimination for which we find no evidence in strabismic amblyopia. A neural disarray hypothesis would predict an associated deficit in the degree to which stimuli appear spatially distorted. We find evidence for such a deficit in strabismic amblyopia. We propose that the spatial deficit in strabismic amblyopia is due to a filter-based distortion which is unable to be re-calibrated by higher visual centres.

Excessive rates of asphyxia-anecdote or fact?

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The epidemiology of neonatal respiratory disease

The epidemiology of many conditions affecting the newborn infant is influenced by the health of the mother, prematurity and the effects of medical and obstetric management. In this review we have considered the role of each of these factors in seven respiratory conditions presenting in the newborn infant.

Neonatal extra corporeal membrane oxygenation (ECMO)

Extra corporeal membrane oxygenation (ECMO) is a novel, but invasive, form of life support developed from cardio pulmonary by pass technology. The technique has been used successfully in mature infants with severe respiratory failure since 1975. Where persistent pulmonary hypertension is a complicating problem the improved oxygenation resulting from the use of ECMO has a therapeutic role. Controversy exists, however, with regard to whether ECMO offers any advantage over more conventional life support in terms of improved survival. Descriptive data relating to cost and morbidity suggest no disadvantage from the use of ECMO. It is hoped that the current U.K. collaborative trial will clarify whether ECMO should be considered standard therapy for severe respiratory failure occurring in mature infants.

Contour integration by the human visual system: evidence for a local "association field"

The Gestalt law of "good continuation" has been used to describe a variety of phenomena demonstrating the importance of continuity in human perception. In this study, we consider how continuity may be represented by a visual system that filters spatial data using arrays of cells selective for orientation and spatial frequency. Many structures (e.g. fractal contours) show a form of redundancy which is well represented by the continuity of features as they vary across space and frequency. We suggest that it is possible to take advantage of the redundancy in continuous, but non-aligned features by associating the outputs of filters with similar tuning. Five experiments were performed, to determine the rules that govern the perception of continuity. Observers were presented with arrays of oriented, band-pass elements (Gabor patches) in which a subset of the elements was aligned along a "jagged" path. Using a forced-choice procedure, observers were found to be capable of identifying the path within a field of randomly-oriented elements even when the spacing between the elements was considerably larger than the size of any of the individual elements. Furthermore, when the elements were oriented at angles up to +/- 60 deg relative to one another, the path was reliably identified. Alignment of the elements along the path was found to play a large role in the ability to detect the path. Small variations in the alignment or aligning the elements orthogonally (i.e. "side-to-side" as opposed to "end-to-end") significantly reduced the observer's ability to detect the presence of a path. The results are discussed in terms of an "association field" which integrates information across neighboring filters tuned to similar orientations. We suggest that some of the processes involved in texture segregation may have a similar explanation.

UK experience in neonatal extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is a life support technique capable of supporting pulmonary, cardiac, or cardiopulmonary function. It has proved most successful in neonatal respiratory failure. We report the initial UK experience with a survival rate of 80% in 15 neonates (gestations 36-41 weeks, birth weights 2690-3990 g) whose condition exceeded American criteria for ECMO treatment for a prolonged period before referral. Ages at referral varied from 11 to 240 hours and the duration of bypass required varied from 30 to 240 hours respectively.