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Biomedical subjects

J Stocks

Publications and source records attributed to J Stocks.

At least 19 recordsLinked to original sources
PubMed1997

Lung development and early origins of childhood respiratory illness.

In the last two decades, 5 cohort studies have been initiated to examine the association of infant respiratory function with genetic and environmental risk factors, as well as with subsequent lower respiratory illness in early childhood. While the current complexity of respiratory function tests in this age group precludes study samples with sufficient power to examine more complex issues, information from these studies has provided an exciting adjunct to that available from the longer cohort studies. Premorbid alterations in airway function or lung development increase the risk of wheezing lower respiratory illnesses during the preschool years and the risk of impaired airway function at 5-6 years of age. In addition, gender differences in airway function and the response to maternal smoking have been observed. Larger collaborative population-based studies are needed to explore the environmental, genetic and immunological mechanisms responsible, but will depend on the development of less invasive tests of airway function appropriate for use in healthy infants.

Adolescent↗
PubMed1997

Urinary antimony in infancy.

OBJECTIVE: To determine whether antimony may be detected in the urine during infancy and early childhood and its association with passive exposure to tobacco smoke, as assessed by urinary cotinine. DESIGN: Analysis of spare aliquots of urine collected from infants participating in studies of respiratory function and passive smoking. Urinary antimony was assayed using inductively coupled plasma mass spectroscopy in 201 urine specimens collected at different ages throughout the first two years of life from 122 term and 26 preterm infants. Urinary cotinine was measured using gas liquid chromatography. MAIN OUTCOME MEASURE: Urinary antimony concentrations. RESULTS: Absolute antimony concentrations varied widely between infants, being below the laboratory detection limit of 0.02 microgram/l in 7% of samples, below 0.5 microgram/l in 90.5%, and above the reference value of 1 microgram/l reported for non-occupationally exposed UK populations in 4%. Creatinine standardised antimony values were unrelated to postnatal age or urinary cotinine concentrations and were highest in urine collected from preterm infants within 24 hours of birth (geometric mean (95% confidence interval): 2.3 ng/mg (1.5 to 3.4)). CONCLUSIONS: Although antimony is present at very low concentrations in urine during infancy and early childhood, the relevance to health is uncertain. The higher levels found in preterm infants may reflect prematurity or fetal assimilation of antimony. Tobacco is unlikely to be an important source of environmental exposure to antimony during infancy and early childhood.

Aging↗
PubMed1997

Infant respiratory function after RSV-proven bronchiolitis.

The mechanisms underlying the increased risk of wheezing in early childhood following acute bronchiolitis in infancy remain unclear. Previous studies have reported significant abnormalities in infant respiratory function after clinical recovery from bronchiolitis, but are difficult to interpret because of the frequent omission of a concurrent comparison group. Respiratory function was compared within pairs of previously healthy full-term caucasian infants admitted with a first episode of acute bronchiolitis to an inner London hospital, and age- and sex-matched control infants without prior wheezing, asthma, or lower respiratory illness who were recruited from local general practices. Respiratory function was measured in 29 control and 29 asymptomatic index infants, with measurements in the latter done at a median interval of 36 wk (range: 16 to 49 wk) after admission, when 16 (55%) had experienced subsequent wheezing. Index infants tended to be autumn-born and of shorter gestation than control infants, to have younger mothers, and to have been exposed to tobacco smoke. There were no statistically significant differences in plethysmographic FRC, initial inspiratory airway resistance (Raw), or respiratory system compliance (mean [index minus control] within-pair difference [95% confidence interval]: -11 ml [-29, 7 ml]; -0.2 kPa/L/s [-0.7, 0.4 kPa/L/s]; -8 ml/kPa [-21, 4 ml/kPa], respectively), but respiratory rate and time to peak tidal flow as a proportion of total expiratory time (tPTEF:tE) were significantly diminished in index as compared with control infants (-4.0 breaths/min [-7.6, -0.4 breaths/min], versus -0.035 [-0.066, -0.005], respectively). These findings suggest a better prognosis for infant lung function after acute bronchiolitis than reported previously. Longitudinal studies are needed to clarify whether subclinical alterations in airway function precede acute bronchiolitis.

Acute Disease↗
PubMed1996

A new microtransducer catheter for measuring esophageal pressure in infants.

Measurement of esophageal pressure, as a reflection of pleural pressure, is essential for assessment of dynamic lung mechanics in neonates and infants. Conventionally, an esophageal balloon or a fluid-filled catheter is used, but considerable skill is required to obtain accurate results. Both devices have problems, and failure to achieve valid occlusion tests have been reported, particularly in small infants with lung disease. Recently, a flexible #3 French gauge (FG) microtransducer catheter (MTC, Dräger Netherlands) has become available for medical monitoring. We have assessed the accuracy and feasibility of using this device for measuring lung mechanics in 51 spontaneously breathing infants and small children aged 1 day to 24 months (weight 1.35 to 12.0 kg), 9 of whom were healthy neonates, the remainder suffering from a variety of cardio-respiratory diseases, and in 18 sick ventilated infants (weight 0.6 to 4.0 kg). Positioning of the catheter was well tolerated by all infants. The ratio of esophageal to airway opening pressure changes (delta Pes:delta Pao) ranged from 0.94 to 1.09 [mean (SD) 1.013 (0.03)] for the spontaneously breathing infants and from 0.98 to 1.06 [mean (SD) 1.003 (0.02)] In the ventilated infants with no significant difference in this ratio between the two groups (p = 0.16). This new generation of catheter tip pressure transducers may provide a simpler and more reliable tool for assessing transpulmonary pressure changes in infants than has previously been available.

Catheterization↗
PubMed1996

Delayed maturation of Hering-Breuer inflation reflex activity in preterm infants.

We have previously shown that the strength of the Hering-Breuer inflation reflex (HBIR) diminishes between 2 and 12 mo of age in full-term babies. The purpose of this study was to determine whether the onset of this decline had commenced by 3 to 4 mo of age in healthy full-term infants and whether preterm delivery influences the pattern of maturation. Serial measurements of HBIR activity using the end-inspiratory occlusion technique were made in 25 preterm and 27 full-term infants at matched postnatal and postconceptional ages during the first 6 mo of life. Although similar levels of reflex activity were observed at birth (mean +/- SD of 101.2% +/- 42.4% in preterm, and 101.0% +/- 33.9% in full-term infants), by 40 wk postconceptional age (PCA) (i.e., term equivalent) HBIR activity (mean +/- SD) had increased to 121.7% +/- 51.2% in preterm infants, which was significantly greater than that in full-term infants of similar PCA (95% CI of difference: 0.2; 41.2%). By 15 wk postnatal age (PNA), HBIR activity had decreased to 68.8% +/- 26.6% in full-term infants, but remained significantly higher in those delivered prematurely (87.8% +/- 32.7%). However, when measurements were repeated at approximately 4 mo after the expected rather than actual date of delivery, these differences were no longer evident (95% CI difference preterm-full-term: -21.2; 3.8%). This study suggests that important transitions in respiratory control mechanisms occur between 8 and 15 wk PNA in full-term infants and that these changes are delayed in preterm infants.

Aging↗
PubMed1995

In vitro assessment of infant pulmonary function equipment.

Commercially available automated pulmonary monitors are used increasingly in neonatal intensive care units. However, detailed information regarding the static and dynamic accuracy of these monitors is rarely available. Collaboration between scientists, clinicians, and manufacturers is essential to establish improved technical standards and protocols for testing of equipment and for the development of more reliable neonatal pulmonary monitors. The aim of this study was to develop a protocol for the in vitro assessment of commercial infant pulmonary function equipment which could be applied within the laboratory to provide rapid feedback to the manufacturer. A recently released neonatal pulmonary monitor, the Bicore CP100 (software version 3.3), was selected for the development of this protocol. The deadspace and resistance of the measuring device were determined. The flow and airway pressure measuring systems were evaluated alone and connected to a tracheal tube for both static accuracy and frequency response. The pressure-volume relationship of the esophageal balloon was determined and its static accuracy and frequency response were assessed. The algorithms for on-line calculations were checked and their correct application confirmed by examination of an ASCII data print out. Finally, the pulmonary monitor was tested during intermittent positive pressure ventilation of a neonatal lung model of known compliance and resistance.

Algorithms↗
PubMed1995

The single breath test in neonates: does pressurization of the pneumotachograph make a difference?

The single breath test for the measurement of respiratory system resistance and compliance in newborns consists of an end inspiratory occlusion which is subsequently released, allowing expiration to proceed through a pneumotachograph (PNT). The measured flow is then integrated to give volume. The simplicity of the test is one of the major reasons for its popularity. However, some investigators have cautioned against the use of an occlusion distal to the PNT because pressurization of the PNT may introduce artifacts in the flow measurement. Despite this caution, many commercial systems use a pressurized PNT. This study investigated the errors that would result from pressurization of the PNT by providing a step function of flow to two infant PNTs, a Fleisch #0 and a Hans Rudolph 4500, in the unpressurized and pressurized state. In each case there was an initial rapid rise of the flow signal, followed by some overshoot and oscillations that rapidly died out. The overshoot and oscillations for the Hans Rudolph PNT were greater when pressurized whereas pressurization had little effect on the Fleisch PNT. Unpressurized, the two were similar. In either case, the artifact introduced by pressurization of the PNT died out so quickly that it would have little effect on any measurement in an infant.

Airway Obstruction↗
PubMed1995

A critical assessment of uncalibrated respiratory inductance plethysmography (Respitrace) for the measurement of tidal breathing parameters in newborns and infants.

We have compared results obtained with an uncalibrated respiratory inductance plethysmograph (RIP) with those of a face mask and pneumotachograph (PNT) for the computerized measurement of the time to reach peak tidal expiratory flow as a ratio of total expiratory time (tPTEF:tE). Simultaneous measurements were made in 32 healthy neonates aged 0-3 weeks, 35 healthy infants aged 5-82 weeks, and 28 infants aged 15-94 weeks with physician diagnosed recurrent wheeze. The group mean (+/- SD) values of tPTEF:TE determined using a PNT were 0.455 (+/- 0.129), 0.263 (+/- 0.077), and 0.232 (+/- 0.089) for the neonates, healthy infants and infants with recurrent wheeze respectively. RIP gave mean (+/- SD) values that were 0.055 (+/- 0.044) and 0.025 (+/- 0.104) lower than the PNT in healthy neonates and infants with recurrent wheeze respectively; RIP values were 0.002 (+/- 0.073) higher in the healthy infants over 4 weeks of age than measurements by PNT. Although the difference between the two measurements was not related to the thoracoabdominal phase angle, as measured from Lissajous figures, examination of the RIP ribcage and abdominal signals revealed that many healthy subjects, while appearing clinically in phase, had ribcage and abdominal signals that differed markedly from each other in terms of convexity/concavity during early expiration. This may explain the lack of agreement between the two methods. We conclude that uncalibrated RIP should be used with caution for the determination of tPTEF:tE, even in subjects whose ribcage and abdomen appear to move synchronously. The measurement of tPTEF:tE did not differentiate between the healthy infants and infants with recurrent wheezing.

Data Interpretation, Statistical↗
PubMed1995

Effect of neck rotation on the timing and pattern of infant tidal breathing.

While neck flexion and extension are known to influence the patency of the upper airway, far less information is available regarding the effects of neck rotation. The effect of neck rotation on respiratory rate (RR), expiratory time (tE), and phase angle (phi) was assessed in 17 healthy infants aged between 1 and 4 months. An inclinometer was used to measure neck rotation and uncalibrated Respiratory inductive Plethysmography to measure the dependent variables while the infants were in natural, quiet sleep. Baseline measurements were made with the head positioned centrally (0 degree rotation); further measurement positions included 30 degrees, 60 degrees, 90 degrees rotation, and repeat measurement at 0 degree (0r degree) in randomized order. Mean RR, tE, and phi were determined for each infant in each position. Using the paired t-test, RR at 0 degree rotation was significantly higher than that at 0r degree rotation (mean difference, 5 bpm; 95% CI, 2.1, 8.1; P = 0.0023); mean tE at 0 degree rotation was significantly shorter than at 0r degree rotation (mean difference, -0.18s; 95% CI, -0.27, -0.07; P = 0.002); whereas phi remained similar (mean difference, 10 degrees; 95% CI, -2.2, 22.3; P = 0.10. These changes probably reflect the slowing of metabolism that occurs after the onset of quiet sleep, and they emphasize the importance of randomization. Measurements at 0r degree were randomized and hence were most likely to reflect the true basal condition of the infant with the head in a neutral position. Consequently, these data, rather than those collected at 0 degree at the onset of quiet sleep, were used for comparisons with all subsequent positional changes. When comparing the positions whose order was randomized, neck rotation did not significantly affect RR (P = 0.445), tE (P = 0.272), or phi (P = 0.169). However, two infants demonstrated marked changes in respiratory pattern with decreases in RR and increases in tE at 90 degrees rotation, suggesting that some infants may be susceptible to obstruction in this position.

Humans↗
PubMed1995

Oxygen saturation in children in the postoperative period.

Some adult patients have periods of significant oxygen desaturation after surgery but, other than for immediately after surgery in the recovery room, few data are available in children. We monitored overnight paired preoperative and postoperative oxygen saturations in 19 children, and overnight postoperative saturations in 50 additional children to determine whether children have periods of desaturation in the postoperative period. The children underwent surgery usually associated with moderate to severe postoperative pain, and were treated with epidural, intravenous, or intramuscular opioids. In the group of 19 children mean (SD) preoperative oxygen saturation was 96.6% +/- 1.3%, and the mean postoperative saturation was 95.7% +/- 1.2%. The average change was 0.88% +/- 1.52%. The 95% confidence interval of the paired difference was 0.13% to 1.6%. There was no significant difference in the percent of monitored time that the patients spent with an oxygen saturation less than 95%, 90%, 85%, or 80%. In the 50 children monitored only in the postoperative period, mean (SD) saturation was 97.8% +/- 1.9%. The data show that, in contrast to some reports in adults, this group of children did not have multiple episodes of clinically significant oxygen desaturation in the postoperative period.

Adolescent↗
PubMed1995

Comparison of single-breath and plethysmographic measurements of resistance in infancy.

Single-breath technique (SBT) measurements of total respiratory resistance (Rrs) were compared with plethysmographic measurements of airway resistance (Raw) in healthy infants < or = 13 wk of age (Group 1; n = 49) and > 13 wk of age (Group 2; n = 37) and in infants > 13 wk of age with prior wheeze (Group 3; n = 49). A significantly higher percentage of Rrs (19%) than of Raw (2%) measurements were technically unsatisfactory, alinearity of the flow-volume curve accounting for 54% of Rrs failures. Although both Rrs and Raw were significantly higher in Group 3 infants, between-subject variability was wide in all groups. Rrs was significantly higher than initial expiratory (IE) Raw in all groups. Mean difference Rrs-IE Raw (95% CI) values were 1.98 (1.51, 2.48), 1.29 (0.96, 1.62), and 1.97 (1.56, 2.38) kPa.L-1.s for Groups 1, 2, and 3, respectively. Significant but smaller differences were seen for end-expiratory (EE) Raw in Groups 1 and 2 but not in Group 3. Mean difference Rrs-EE Raw (95% CI) values were 0.68 (0.11, 1.26), 0.55 (0.19, 0.92), and 0.31 (-0.06, 0.69) kPa.L-1.s for Groups 1, 2, and 3, respectively. Despite wide between-subject variability in Rrs and a relatively high failure rate, the SBT is simple to use, and it may be applicable to epidemiologic studies. However, clinical applications in individual infants may be limited by failure to detect the dynamic changes in resistance throughout the breath evident from plethysmographic studies.

Airway Resistance↗