Dramatic slowing of compositional relaxations in the approach to the glass transition for a bimodal colloidal suspension.

Molecular dynamics simulation was used to study a model colloidal suspension with two species of slightly different sized colloidal particles in an explicit solvent. In this work we calculated the four interdiffusion coefficients for the ternary system, which were then used to calculate the decay coefficients D_{±} of the two independent diffusive modes. We found that the slower D_{-} decay mode, which is associated with the system's ability to undergo compositional changes, was responsible for the long-time decay in the intermediate scattering function. We also found that a decrease in D_{-} to negligible values at a packing fraction of Φ_{g}=0.592 resulted in an extreme slow-down in the long-time decay of the intermediate scattering function often associated with the glass transition. Above Φ_{g}, the system formed a long-lived metastable state that did not relax to its equilibrium crystal state within the simulation time window. We concluded that the inhibition of crystallization was caused by the inability of the quenched fluid to undergo the compositional changes needed for the formation of the equilibrium crystal.

Dynamics of a model colloidal suspension from dilute to freezing.

Molecular dynamics simulation was used to study a model colloidal suspension at a range of packing fractions from the dilute limit up to the freezing point. This study builds on previous work by the authors which modeled the colloidal particles with a hard core surrounded by a Weeks-Chandler-Anderson potential with modified interaction parameters, and included an explicit solvent. In this work, we study dynamical properties of the model by first calculating the velocity autocorrelation function, the self-diffusion coefficient, and the mutual diffusion coefficient. We also perform detailed calculations of the colloidal particle intermediate scattering function to study the change in dynamics leading up to the freezing point, and to determine whether the current model can be used to interpret light scattering experiments. We then perform a multiexponential analysis on the intermediate scattering function results and find that the data are fitted well by the sum of two exponentials, which is in line with previous analysis of experimental colloidal suspensions. The amplitudes and decay coefficients of the two modes are determined over a large range of wave vectors at packing fractions leading up to the freezing point. We found that the maximum wave vector at which macroscopic diffusive behavior was observed decreased as the packing fraction increased, and a simple extrapolation shows the maximum wave vector going to zero at the melting point. Lastly, the ratio of the two decay coefficients is compared to the scaling law proposed by Segrè and Pusey [Phys. Rev. Lett. 77, 771 (1996)PRLTAO0031-900710.1103/PhysRevLett.77.771]. It was found that the ratio was not constant, but instead was wave vector dependent.

Natriuretic peptides in septic patients.

The natriuretic peptide family is comprised of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), dendroaspis natriuretic peptide - DNP and urodilatin. They play a role in the diagnosis of several diseases, especially those involving the cardiovascular system. Sepsis is a complex condition that can lead to multiorgan failure, shock and death. The number of people developing sepsis is still increasing (approximately 750,000 cases of sepsis occur annually in the USA). Both ANP and pro-ANP have attracted interest as new markers for sepsis. Reports indicate that ANP or BNP levels are elevated in septic patients. However, many mechanisms are still unexplained. This situation is complicated by the fact that contradictory results have been published. There are several reasons for this controversy including differences in the techniques used to assay natriuretic peptides. Nevertheless, natriuretic peptides might eventually prove useful for the diagnosis and/or the treatment of septic patients.

Relation of exhaled nitric oxide levels to development of bronchopulmonary dysplasia.

OBJECTIVE: To test the hypothesis that exhaled nitric oxide levels on day 28 and changes in exhaled nitric oxide levels in the neonatal period would differ according to whether infants developed bronchopulmonary dysplasia (BPD) and its severity. DESIGN: Prospective observational study. SETTING: Tertiary neonatal intensive care unit. PATIENTS: 80 infants (median gestational age 28, range 24-32 weeks), 46 of whom developed BPD. INTERVENTIONS: Exhaled nitric oxide measurements were attempted on days 3, 5, 7, 14, 21 and 28. MAIN OUTCOME MEASURES: BPD (oxygen dependency at 28 days), mild BPD (oxygen dependent at 28 days, but not 36 weeks postmenstrual age (PMA)); moderate BPD (oxygen dependent at 36 weeks PMA) and severe BPD (respiratory support dependent at 36 weeks PMA). RESULTS: On day 28, exhaled nitric oxide levels were higher in infants with BPD compared to those without BPD (p<0.001) and there was a linear trend in exhaled nitric oxide results as BPD severity increased (p = 0.006). No significances in the change in exhaled nitric oxide levels over the neonatal period were found between the four groups. CONCLUSION: Exhaled nitric oxide levels are raised in infants with established BPD, particularly in those developing moderate or severe BPD, and may reflect ongoing inflammation.

Work of breathing during SIMV with and without pressure support.

OBJECTIVE: In a randomised trial, pressure support with synchronised intermittent mandatory ventilation (SIMV) compared to SIMV alone was associated with a significant reduction in supplementary oxygen duration. The hypothesis that the addition of pressure support to SIMV compared to SIMV alone would reduce the work of breathing was examined. DESIGN: Prospective study. SETTING: Perinatal service. PATIENTS: 20 infants, with a mean gestational age of 31 weeks, being weaned from mechanical ventilation were studied. INTERVENTIONS: 1 h periods of SIMV and SIMV with pressure support at 50% of the difference between the peak inflating pressure and positive end expiratory pressures. MAIN OUTCOME MEASURES: The work of breathing was assessed by measurement of the transdiaphragmatic pressure time product (PTPdi). RESULTS: The mean PTPdi on SIMV plus pressure support was 112 cm H(2)Oxs/min, approximately 20% lower than that on SIMV alone (141 cm H(2)Oxs/min) (p<0.001). CONCLUSION: The addition of pressure support to SIMV reduces the work of breathing in infants being weaned from the ventilator.

Sleeping position, oxygenation and lung function in prematurely born infants studied post term.

OBJECTIVE: To determine the effect of sleeping position on the lung function of prematurely born infants when post term, whether any effect was similar to that before discharge from the neonatal unit, and if it differed according to bronchopulmonary (BPD) status. DESIGN: Prospective study. SETTING: Tertiary neonatal unit. PATIENTS: Twenty infants, median gestational age 30 weeks (range 25-32); 10 had BPD. INTERVENTIONS: Before neonatal unit discharge (median age 36 weeks postmenstrual age (PMA)) and when post term, infants were studied prone and supine, each position maintained for 3 h. MAIN OUTCOME MEASURES: Oxygen saturation was monitored continuously and, at the end of each 3 h period, functional residual capacity (FRC) and compliance (CRS) and resistance (RRS) of the respiratory system were measured. RESULTS: At a median of 36 weeks PMA and 6 weeks later (post term), respectively, oxygen saturation (98% vs 96%, p = 0.001; 98% vs 97%, p = 0.011), FRC (26 vs 24 ml/kg, p<0.0001; 35 vs 31 ml/kg, p = 0.001) and CRS (3.0 vs 2.4 ml/cm H(2)O, p = 0.034; 3.7 vs 2.5 ml/cm H(2)O, p = 0.015) were higher in the prone than the supine position. In the prone position, both BPD and non-BPD infants had significantly greater FRCs on both occasions and oxygen saturation at 36 weeks PMA, but oxygen saturation was significantly better post term only in non-BPD infants. Twelve infants had superior oxygen saturation and 17 superior FRCs in the prone compared with the supine position at both 36 weeks PMA and post term. CONCLUSIONS: These results suggest that lung function impairment does not explain why prematurely born infants are at increased risk of sudden infant death syndrome in the prone compared with the supine position.

Congenital syphilis as a differential diagnosis of non-accidental injury.

A two-month-old infant presented with swelling and tenderness of his right forearm. Initially, non-accidental injury was suspected but X-ray appearances were typical of congenital syphilis, which was confirmed on serological testing.

Nonfatal congenital alveolar dysplasia due to abnormalities of NO synthase isoforms.

Congenital alveolar dysplasia (CAD) is a rare disorder thought to represent alveolar growth arrest at the canalicular stage of development. An infant with CAD diagnosed on lung biopsy is reported, her respiratory problems resolved spontaneously and she was doing well at follow-up. The infant additionally suffered from systemic hypertension and hypertrophic pyloric stenosis. In conclusion, we speculate that the association of CAD with systemic hypertension and hypertrophic pyloric stenosis might be explained by abnormalities of isoforms of nitric oxide synthase (NOS) resulting in congenital deformities involving smooth muscles.

Dampened ventilatory response to added dead space in newborns of smoking mothers.

BACKGROUND: Term newborns can compensate fully for an imposed dead space (tube breathing) by increasing their minute ventilation. OBJECTIVE: To test the hypothesis that infants of smoking mothers would have an impaired response to tube breathing. DESIGN: Prospective study. SETTING: Perinatal service. PATIENTS: Fourteen infants of smoking and 24 infants of non-smoking mothers (median postnatal age 37 (11-85) hours and 26 (10-120) hours respectively) were studied. INTERVENTIONS: Breath by breath minute volume was measured at baseline and when a dead space of 4.4 ml/kg was incorporated into the breathing circuit. MAIN OUTCOME MEASURES: The maximum minute ventilation during tube breathing was determined and the time constant of the response calculated. RESULTS: The time constant of the infants of smoking mothers was longer than that of the infants of non-smoking mothers (median (range) 37.3 (22.2-70.2) v 26.2 (13.8-51.0) seconds, p = 0.016). Regression analysis showed that maternal smoking status was related to the time constant independently of birth weight, gestational or postnatal age, or sex (p = 0.018). CONCLUSIONS: Intrauterine exposure to smoking is associated with a dampened response to tube breathing.

Evaluation of soil gas sampling and analysis techniques at a former petrochemical plant site.

Methods for soil gas sampling and analysis are evaluated as part of a research study on soil vapour intrusion into buildings, conducted at a former petro-chemical plant site ("Chatterton site"). The evaluation process was designed to provide information on reliability and selection of appropriate methods for soil gas sampling and analysis, and was based on a literature review of data and methods, and experiments completed as part of the research study. The broader context of this work is that soil gas characterization is increasingly being used for input into risk assessment of contaminated sites, particularly when evaluating the potential intrusion of soil vapour into buildings. There are only a limited number of research studies and protocols addressing soil gas sampling and analysis. There is significant variability in soil gas probe design and sample collection and analysis methods used by practitioners. The experimental studies conducted to evaluate soil gas methods address the permeation or leakage of gases from Tedlar bags, time-dependent sorption of volatile organic compound (VOC)-vapours onto probe surfaces and sampling devices, and analytical and quality control issues for light gas and VOC analyses. Through this work, common techniques for soil gas collection and analysis are described together with implications for data quality arising from the different methods used. Some of the potential pitfalls that can affect soil gas testing are identified, and recommendations and guidance for improved protocols are provided.

Exhaled nitric oxide in chronically ventilated preterm infants.

Exhaled nitric oxide (eNO) levels were measured in eight ventilated infants, mean gestational age 25.8 (SD 1.7) weeks and postnatal age 55 (SD 39) days, before and after three days of dexamethasone treatment. The eNO levels fell from a mean of 6.5 (SD 3.4) to 4.2 (SD 2.6) parts per billion (p = 0.031) and the mean supplementary oxygen levels from 62% to 45% (p = 0.0078).

Effect of posture on respiratory function and drive in preterm infants prior to discharge.

Our objective was to determine the effect of posture on respiratory function and drive in prematurely born infants immediately prior to discharge. Twenty infants (6 oxygen-dependent), median gestational age 29 weeks (range, 25-32), were studied at a median postconceptional age (PCA) of 36 weeks (range, 33-39). On 2 successive days, infants were studied both supine and prone; each posture was maintained for 3 hr. The order on each day in which postures were studied was randomized between infants. At the end of each 3-hr period, tidal volume (Vt), inspiratory (Ti) and expiratory (Te) time, respiratory rate, and minute ventilation were measured. In addition, respiratory drive was assessed by measuring the pressure generated in the first 100 msec of an imposed airway occlusion (P(0.1)), and respiratory muscle strength was assessed by recording the maximum inspiratory pressure (Pimax) generated against an occlusion which was maintained for at least five breaths. Overall, tidal volume was higher (P < 0.05), but respiratory rate (P < 0.05), P(0.1) (P < 0.05), and Pimax (P < 0.05) were lower in the prone compared to the supine position. There were no significant differences in Ti or Te between the two postures. In oxygen-dependent infants only, minute volume was higher in the prone position (P < 0.05). In conclusion, posture-related differences in respiratory function are present in prematurely born infants studied prior to neonatal unit discharge.

Characterisation of the Hering-Breuer deflation reflex in the human neonate.

Human infants have been observed making inspiratory efforts in response to chest compression. These may be a manifestation of the Hering-Breuer deflation reflex. We sought to stimulate the reflex in 33 term infants by rapidly reducing lung volume using an inflatable jacket. The effect of altering the timing, magnitude or rate of application of the lung deflation on the strength of the inspiratory response was investigated. Inspiratory effort was quantified by measuring (1) the rate of fall in oesophageal pressure on inspiration; and (2) the mean inspiratory flow (MIF) in response to lung deflation. Variables which significantly affected (1) and resulted in increased inspiratory effort were, in order of importance: larger rises in oesophageal pressure on chest compression (38%) (percentage of variance explained), greater reductions in lung volume below functional residual capacity (FRC) (26%), faster rates of lung deflation (19%) and slower respiratory rates (11%). Increased inspiratory efforts, as assessed by response (2), were generated by greater reductions in FRC (23%), larger rises in oesophageal pressure (11%) and faster rates of lung deflation (10%). Increasing deflation pressures eventually resulted in a plateau in both measures of inspiratory response. These results were consistent with the Hering-Breuer deflation reflex being activated which could have a role in protecting the FRC of the newborn infant.

Investigation of prolonged neonatal jaundice.

UNLABELLED: Jaundice persisting beyond 14 d of age (prolonged jaundice) can be a sign of serious underlying liver disease. Protocols for investigating prolonged jaundice vary in complexity and the yield from screening has not been assessed. In order to address these issues, we carried out a prospective study of term infants referred to our neonatal unit with prolonged jaundice over an 18 mo period. Infants were examined by a paediatrician and had the following investigations: a total and conjugated serum bilirubin, liver function tests, full blood count, packed cell volume, group and Coombs' test, thyroid function tests, glucose-6-phosphate dehydrogenase levels and urine for culture. One-hundred-and-fifty-four infants were referred with prolonged jaundice out of 7,139 live births during the study period. Nine infants were referred to other paediatric specialties. One infant had a conjugated hyperbilirubinaemia, giving an incidence of conjugated hyperbilirubinaemia of 0.14 per 1,000 live births. Diagnoses included: giant cell hepatitis (n = 1), hepatoblastoma (n = 1), trisomy 9p (n = 1), urinary tract infections (n = 2), glucose-6-phosphate dehydrogenase deficiency (n = 3) and failure to regain birthweight (n = 1). CONCLUSIONS: In conclusion, a large number of infants referred to hospital for prolonged jaundice screening had detectable problems. The number of investigations may safely be reduced to: a total and conjugated bilirubin, packed cell volume, glucose-6-phosphate dehydrogenase level (where appropriate), a urine for culture and inspection of a recent stool sample for bile pigmentation. Clinical examination by a paediatrician has a vital role in the screening process.

Rib abnormalities arising before and after birth.

UNLABELLED: Rib abnormalities detected in the neonatal period are usually thought to be part of a skeletal disorder. There are, however, many causes which include metabolic bone disease, infection and trauma. Rib abnormalities are also found in general disorders such as chromosomal abnormalities or hypothyroidism. CONCLUSION: A thorough examination of the neonatal chest radiograph must include the review of the skeletal parts, which can often be revealing.