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Biomedical subjects

Janet Stocks

Publications and source records attributed to Janet Stocks.

32 records · Page 2Linked to original sources
PubMed2004

Respiratory physiotherapy vs. suction: the effects on respiratory function in ventilated infants and children.

OBJECTIVE: To assess and compare the effects of physiotherapy and suction on expired tidal volume (V(TE)), respiratory compliance (C(rs)), resistance (R(rs)) and arterial blood gases. DESIGN: Randomised cross-over study comparing outcomes after both treatments on the same day. SETTING: Intensive tertiary care units, Great Ormond Street Hospital, London. PATIENTS: One hundred children on full ventilatory support requiring physiotherapy. Paired measurements were obtained in 90 participants, and 7 others were excluded because of tracheal tube leak. INTERVENTIONS: Respiratory physiotherapy and suction. MEASUREMENTS AND RESULTS: Physiotherapy lasted longer and required more saline and catheters per treatment. There were no significant group changes in V(TE) or C(rs) after either treatment, but a tendency for R(rs )to fall following physiotherapy which reached significance in patients on volume-preset ventilation. There were also small but statistically significant reductions in HCO(3)(-), base excess and SaO(2) after physiotherapy. V(TE) and C(rs) increased and R(rs) decreased in excess of their 95% limits of agreement for normal variability in approximately twice as many subjects following physiotherapy than suction, these differences being significant for V(TE) and approaching significance for C(rs) and R(rs). CONCLUSIONS: Physiotherapy appeared to have an advantage in reducing R(rs )in some patients, but also produced changes in derived blood gas parameters. Within individuals, physiotherapy treatments were also more likely to produce improvements in V(TE), C(rs) and R(rs) than suction. Further research should identify sensitive patient selection criteria and assess longer-term effects of such treatments.

Child↗
PubMed2004

Quality control for spirometry in preschool children with and without lung disease.

The reliability of spirometry is dependent on strict quality control. We examined whether quality control criteria recommended for adults could be applied to children aged 2-5 years. Forty-two children with cystic fibrosis and 37 healthy children attempted spirometry during their first visit to our laboratory. Whereas 59 children (75%) were able to produce a technically satisfactory forced expiration lasting 0.5 second, only 46 (58%) could produce an expiration lasting 1 second, with the youngest children having the most difficulty. Start of test criteria for adults were inappropriate for this age group, with only 16 of 59 children producing a volume of back extrapolation as a proportion of forced vital capacity of less than 5%, whereas all but 4 could produce a volume of back extrapolation of 80 ml or less. More than 90% of children were able to produce a second forced vital capacity and a second forced expired volume in 0.75 second within 10% of their highest. Errors in the spirometry software resulted in inaccurate reporting of expiratory duration and inappropriate timed expired volumes in some children. We describe recommendations for modified start of test and repeatability criteria for this age group, and for improvements in software to facilitate better quality control.

Case-Control Studies↗
PubMed2004

The evolution of airway function in early childhood following clinical diagnosis of cystic fibrosis.

This study aimed to investigate the evolution of airway function in infants newly diagnosed with cystic fibrosis (CF). FEV(0.5) was measured soon after diagnosis (median age of 28 weeks) and 6 months later in subjects with CF and on two occasions 6 months apart (median ages of 7.4 and 33.7 weeks) in healthy infants, using the raised-volume technique. Repeated measurements were successful in 34 CF and 32 healthy subjects. After adjustment for age, length, sex, and exposure to maternal smoking, mean FEV(0.5) was significantly lower in infants with CF both shortly after diagnosis and at the second test, with no significant difference in rate of increase in FEV(0.5) with growth between the two groups. When compared with published reference data, FEV(0.5) was reduced by an average of two z scores on both test occasions in those with CF, with 72% of individuals having an FEV(0.5) of less than 1.64 z-scores (i.e., less than the fifth percentile) on one or both test occasions. On longitudinal analysis, subjects with CF experienced a mean (95% confidence interval) reduction in FEV(0.5) of 20% (11, 28). Airway function is diminished soon after diagnosis in infants with CF and does not catch up during infancy and early childhood. These findings have important implications for early interventions in CF.

Body Height↗
PubMed2003

Progressive decline in plethysmographic lung volumes in infants: physiology or technology?

During the last 30 years, there has been an unexplained trend toward declining values for plethysmographic assessments of lung volume at functional residual capacity (FRC) in infants. The aim of this study was to compare data collected from healthy infants using contemporary equipment with published reference data and to explore reasons for discrepancies. Lung volumes were measured in 32 healthy infants (age, 4-93 weeks; weight, 3.9-12.4 kg) using a new, commercially available infant plethysmograph. Mean (SD) FRC was 19.6 (3.4) ml/kg (within subject coefficient of variation 3.4 [2.3%]), which was on average 7.0 [3.5] ml/kg and 2.3 [1.2] SD (Z) scores lower than the recently collated reference data from an American Thoracic Society task force. A total of 66% of these healthy infants had a FRC that was below the predicted normal range. Comparison of equipment, software, and protocols with those from previous reports revealed the importance of minimization of dead space and of adequate subtraction of all compressible occluded volume when calculating FRC in infants. These findings emphasize the need to establish reference data for lung function tests in infants that are appropriate for the equipment and protocols in current use.

Age Factors↗
PubMed2003

The effect of parental smoking on lung function and development during infancy.

While the adverse effects of parental smoking on respiratory health during childhood are well recognized, its potential impact on early lung development is less clear. This review summarizes current evidence on the effect of parental smoking on lung function during infancy. It is difficult to separate the effects of pre- and postnatal exposure, since the majority of mothers who smoke in pregnancy (currently around 30% worldwide) continue to do so thereafter. Nevertheless, measurements undertaken prior to any postnatal exposure have consistently demonstrated significant changes in tidal flow patterns in infants whose mothers smoked in pregnancy. While there is, as yet, no convincing evidence from studies in human infants that smoking during pregnancy is associated with increased airway responsiveness at birth, many studies have demonstrated a reduction in forced expiratory flows (on average by 20%) in infants exposed to parental smoking. While maternal smoking during pregnancy remains the most significant source of such exposure and is likely to be responsible for diminished airway function in early life, continuing postnatal tobacco smoke exposure will increase the risk of respiratory infections, the combination of both being responsible for the two- to fourfold increased risk of wheezing illnesses observed during the first year of life in infants whose parents smoke. These findings emphasize the need to keep infants in a smoke-free environment both before and after birth, not least because of growing awareness that airway function in later life is largely determined by that during foetal development and early infancy.

Airway Resistance↗
PubMed2002

Relative ability of full and partial forced expiratory maneuvers to identify diminished airway function in infants with cystic fibrosis.

The tidal and raised volume rapid thoracoabdominal compression techniques are increasingly used to detect diminished airway function in infancy. The aim of this study was to assess the relative ability of parameters measured by these techniques to identify diminished airway function in infants newly diagnosed with cystic fibrosis (CF) with and without clinical evidence of prior lower respiratory illness. A cross-sectional, prospective study design was used in which maximal flow at functional residual capacity (VmaxFRC) from the tidal technique and FVC, FEV0.5, FEF75, and FEF25-75 from the raised volume technique were measured in 47 infants with CF and 187 healthy infants of similar body size, sex distribution, ethnic group, and exposure to maternal smoking. Multiple linear regression was used to assess group differences and to calculate SD scores for each parameter for the infants with CF. Airway function was also compared with clinical assessments of respiratory status made by pediatric pulmonologists. FEV0.5 was significantly diminished in 13 infants with CF, of whom 4 had been identified by clinicians as having normal respiratory status. Only one infant with CF had a VmaxFRC below the estimated normal range. Airway function is diminished in infants with CF irrespective of prior lower respiratory illness and in those whose respiratory status is considered normal by pediatric pulmonologists. In infants with CF, the raised volume technique identified diminished airway function more frequently than the tidal technique.

Age Factors↗
PubMed2002

Sex-specific prediction equations for Vmax(FRC) in infancy: a multicenter collaborative study.

Measurements of maximal flow at functional residual capacity (Vmax(FRC)) from partial forced expiratory maneuvers remain the most popular method for assessing small airway function in infants and young children. However, the lack of appropriate reference data that are both applicable outside the centers that developed them and reflect the normal variability between healthy subjects has limited interpretation of Vmax(FRC) results in both clinical practice and research. To address this problem, we collated Vmax(FRC) data from 459 healthy infants (226 boys) tested on 654 occasions during the first 20 months of life from three collaborating centers. Multiple linear regression analysis indicated that sex, age, and length were important predictors of Vmax (FRC), which was, on average, 20% higher in girls than in boys during the first 9 months of life. (Vmax(FRC))0.5 (ml x second(-1)) = 4.22 + 0.00210 x length2 (cm) for boys (RSD = 3.01; R2 = 0.48), and -1.23 + 0.242 x length for girls (RSD = 2.72; R2 = 0.49). Alternative models incorporating both age and length z scores are also described. Failure to use sex-specific prediction equations for Vmax(FRC) may preclude detection of clinically significant changes in girls and lead to false reports of diminished airway function in boys. Appropriate use of z scores, which indicate a "normal" range (z scores of 0 +/- 2) for Vmax(FRC), during infancy should also improve interpretation of both clinical and research studies.

Body Constitution↗
PubMed2002

Effect of airway inflation pressure on forced expiratory maneuvers from raised lung volume in infants.

The raised lung volume technique is increasingly used to measure forced expiratory maneuvers in infants. However, there is no consensus regarding the optimal airway inflation pressure (P(inf)) required for such maneuvers, or the influence of small changes in P(inf) within and between infants. The aim of this study was to assess the effect of small differences (0.2-0.3 kPa) in P(inf) on forced vital capacity (FVC), forced expired volume in 0.5 sec (FEV(0.5)), and forced expired flow at 75% of vital capacity (FEF(75)), all derived from the raised volume rapid thoraco-abdominal compression (RVRTC) technique. Randomized paired forced expiratory maneuvers were obtained in 32 healthy infants ( 3.9-39.3 weeks old, 3.8-9.9 kg) with the safety pressure relief valve for P(inf) set to 2.7 kPa or 3.0 kPa (27 or 30 cm H(2)0). When mean (SD) P(inf) was increased by 8.4 (2.8)%, there was a significant (P < 0.01) increase in mean (SD) FVC, FEV(0.5), and FEF(75) by 5.8 (5.7)%, 6.1 (6)%, and 8.3 (16.2)%, respectively. In conclusion, relatively small differences in P(inf) will result in significant differences in FVC, FEV(0.5), and FEF(75) by RVRTC technique. Precision in setting and reporting the applied P(inf) is therefore essential, particularly if data are to be compared between centers.

Female↗
PubMed2002

Influence of jacket tightness and pressure on raised lung volume forced expiratory maneuvers in infants.

While the use of the raised volume rapid thoraco-abdominal compression (RVRTC) technique has been shown to provide new insights into airway and pulmonary pathophysiology in infants, and appears to resemble the spirometric techniques used in older subjects, there is as yet no consensus regarding measurement procedures, which are known to vary considerably between laboratories (Gappa [1999] Pediatr Pulmonol 28:391-393). The aims of this study were to assess the effects of tightness of jacket fit, the efficiency with which pressure is transmitted from the jacket to the intrathoracic airways, and the effect of jacket pressure on parameters derived from the RVRTC technique. Paired forced expiratory maneuvers were performed in 20 infants with the jacket snugly or loosely wrapped around the infant's torso, and in a further 21 infants using "optimal" or a higher jacket pressure (P(j)) (1-2 kPa above "optimal" P(j)). When either a loosened jacket or a higher than "optimal" P(j) was used, forced expired flow at low lung volumes (FEF(75)) was significantly reduced by, on average, 8% and 7%, respectively. There were, however, minimal changes in forced vital capacity (FVC) or forced expired volume in 0.4 sec (FEV(0.4)). The observed changes may have been due to the increased pressure transmitted to the intrathoracic structures under these experimental conditions, and emphasize the need to assess optimal jacket pressure within each infant when using the RVRTC technique. In addition, when using a loosened jacket or a higher than "optimal" P(j), chest wall and upper airway reflexes such as glottic closure, peripheral airway closure, and negative flow dependence were more evident.

Confidence Intervals↗
PubMed2002

Development of airway function in infancy after preterm delivery.

OBJECTIVE: To assess airway function at 1 year and compare this with similar measurements made shortly after birth in preterm infants without clinical neonatal respiratory disease. STUDY DESIGN: Infants born at </=36 weeks' gestational age were eligible if they required no neonatal ventilatory support and were otherwise healthy. Paired measurements of maximal expiratory flow at functional residual capacity (V'(maxFRC)) were obtained ~3 weeks after birth in 24 preterm infants (gestational age [mean +/- SD], 33.2 +/- 2.2 weeks) and repeated at a corrected postnatal age (mean +/- SD) of 57.0 +/- 12.2 weeks. V'(maxFRC) values were expressed as Z scores by means of sex-specific prediction equations. RESULTS: V'(maxFRC) was within normal range for all infants shortly after birth (mean +/- SD Z score: -0.06 +/- 0.92). By 1 year, Z scores had reduced significantly [mean (95% CI) 2nd-1st test: -1.94 (-2.27, -1.60)]. V'(maxFRC )Z scores at 3 weeks were highly correlated with those at 1 year of age (Spearman correlation coefficient 0.64). CONCLUSIONS: Airway function during the first year shows considerable tracking. Even in the absence of neonatal respiratory disease, preterm delivery is associated with altered airway development during early infancy.

Body Height↗
PubMed2002

Accuracy of displayed values of tidal volume in the pediatric intensive care unit.

OBJECTIVES: To assess the accuracy of the expired tidal volumes (VT(E)) displayed by one of the most frequently used ventilators that measures exhaled volume at the expiratory valve. DESIGN: Prospective study. SETTING: The intensive care units of a pediatric tertiary referral center in London, UK. PATIENTS: A total of 56 intubated children aged between 3 wks and 16.6 yrs who were clinically stable and ventilated with a Servo 300 ventilator. INTERVENTIONS: The CO2SMO Plus respiratory monitor, which measures flow at the airway opening, was validated using calibrated syringes and appropriate tracheal tubes and connections. Simultaneous in vivo recordings of VT(E) from the Servo 300 and CO2SMO Plus were compared before (displayed Servo VT(E)) and after (effective Servo VT(E)) compensating for ventilator circuit compliance. MEASUREMENTS AND MAIN RESULTS: The in vitro accuracy of the CO2SMO Plus was within +/-5% over a wide range of volumes and measurement conditions. The displayed Servo 300 VT(E) overestimated the true VT(E) by between 2% and 91%. The magnitude of error varied within and between children, according to pressure change (peak inspiratory pressure minus positive end-expiratory pressure), VT(E), and circuit size. Mean (sd) error was 32% (20%) in 40 children with displayed Servo VT(E) of <160 mL and 18% (6%) in 16 subjects with displayed Servo VT(E) of >/=160 mL. After correcting for gas compression, effective VT(E) from the Servo 300 underestimated the true VT(E) by up to 64% in the smallest infants but continued to overestimate by as much as 29% in older children. CONCLUSIONS: The accuracy of tidal volume values is crucially dependent on the site of measurement. Unless measured at the airway opening, displayed values are an inconsistent and misleading indicator of the true volumes delivered.

Adolescent↗