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Biomedical subjects

A D Milner

Publications and source records attributed to A D Milner.

At least 19 recordsLinked to original sources
PubMed1992

Response to tube breathing in preterm infants with apnea.

In order to analyze the effects of maturity and apnea frequency on the respiratory control of preterm infants, we studied their responses to tube breathing using tubes equivalent to two anatomical dead spaces. Ventilation during tube breathing was expressed as a percentage above baseline and compared to an "expected" value calculated from the volume of the added tube. Twenty-seven preterm infants (median birthweight, 1.14 kg.; and gestational age, 29 weeks) were studied on 86 occasions. The percentage of "expected" ventilation increased with post-conceptional age (r = 0.48, slope = 3.12, P less than 0.0005), from a mean of 73% at 26 weeks up to 104% at 36 weeks. Using multiple regression analysis, neither postnatal age nor apnea frequency had any effect once allowance had been made for post-conceptional age. Although the respiratory adaptation of the most immature infants was poor, this study suggests that infants with apnea show no gross deficit in respiratory control, compared to those without apnea.

Apnea↗
PubMed1992

Response to external obstruction in preterm infants with apnea.

A proportion of preterm infants respond to an external airway obstruction by becoming apneic. We have studied 23 infants (median birthweight, 1.14 kg; gestation, 29 weeks) on 80 occasions, to determine the time course of the response and its relationship with spontaneous apnea occurrence. Upper airway flow was measured with a face mask and pneumotachograph, and a tap was turned intermittently to produce an occlusion. A total of 380 occlusions were analyzed. The infants became apneic during the obstruction on 72 occasions (19%), and after the obstruction on 122 occasions (32%). Both of these events were significantly more common than immediately prior to the obstruction, when apnea occurred on 29 occasions (8%). Of the apneas following occlusion 57% were central in type. The point in the respiratory cycle at which obstruction occurred had no effect on the production of apnea. An obstruction score was calculated for each study. This was the mean of the number of apneas during and after each obstruction, expressed as a percentage of the number of obstructions per study. This score was positively correlated with the number of spontaneous apneas recorded. Obstruction score rose from a mean of 20% during days 0-14, to 34% during days 15-28, and thereafter it declined. This pattern may be relevant to the time course of apnea in susceptible infants.

Airway Obstruction↗
PubMed1992

Is thoraco-abdominal phase relationship an indicator of sleep state?

The phase relationship between ribcage and abdominal movement in 1440 breaths from 12 infants (mean age 3.2 days) showed statistically significant differences between sleep states as judged by physiological criteria. The mean phase difference (+/- 1 SD) was 20 (+/- 16)% in active sleep, 9 (+/- 17)% in indeterminate sleep and 3 (+/- 5)% in quiet sleep (P less than 0.0005). However, the wide scatter within sleep states meant that even the mean value from 50 breaths was not specific enough to delineate sleep state.

Abdomen↗
PubMed1992

Dynamic lung inflation during high frequency oscillation in neonates.

The effects of high frequency oscillation (HFO) on dynamic lung inflation were examined in 22 neonates ventilated for respiratory disease. HFO was combined with conventional ventilation and a series of frequencies from 2-25 Hz was tested. Dynamic lung inflation was measured using a jacket plethysmograph which was converted to a measure of alveolar pressure using the compliance of the respiratory system obtained during conventional ventilation. The results showed an increase in dynamic lung inflation with frequency such that volume increased by 0.4 ml for each increase of 10 Hz. Alveolar pressure increased by 1.2 cm H2O for each increase of 10 Hz. Dynamic lung inflation also increased with increased volumes of oscillation.

High-Frequency Ventilation↗
PubMed1992

The effects of mid-trimester amniocentesis on lung function in the neonatal period.

Lung function tests were carried out on 39 healthy full term babies born after pregnancies subjected to mid-trimester amniocentesis. The results were compared to 42 babies born after normal pregnancies. There were no significant differences in gestational age, birth weight, thoracic gas volume or crying vital capacity. Babies subjected to amniocentesis had a significantly lower dynamic compliance (6.96 ml/cm H2O vs. 8.60 ml/cm H2O) and tended to have higher resistance compared to controls (52.8 cm H2O/l/s vs. 37.3 cm H2O/l/s). This provides further evidence that mid-trimester amniocentesis does have an adverse effect on lung growth and development.

Adolescent↗
PubMed1992

To halve and to halve not: an analysis of line bisection judgements in normal subjects.

Normal adults were tested in a series of three experiments to examine the influences of spatial location and cueing upon line bisection judgements. Judgements in all three experiments were strongly influenced by cueing with a letter at one or other end of the line. The spatial location of the line (in left, central or right body space) also had a minor effect in Experiments 1 and 2, where evidence was additionally found for a small constant error when lines were presented centrally. It is argued from the results of Experiments 2 and 3, where no explicit bisection response was required, that perceptual/attentional factors, rather than an orienting bias, play the major role in mediating the cueing effect. It is concluded that there is a substantial attentional effect upon judgements of extent, whereby paying less attention decreases perceived relative line length. However the constant error and the effect of spatial location, whilst mainly perceptual in nature, may also be partly determined by premotor orienting biases caused by differential hemispheric activation.

Adult↗
PubMed1992

Measurement of tidal lung volumes in neonates during high-frequency oscillation.

High-frequency oscillation (HFO) has been used clinically to ventilate infants with respiratory distress. However, there are problems in monitoring the effects on the respiratory system and in particular in measuring the volumes delivered; this is important information in terms of safety and mechanisms of action of HFO. We have validated two sizes of respiratory jacket for measuring oscillatory volume changes of 0.25-5 ml at frequencies of 2-25 Hz, the volume delivered from a purpose-built oscillator having first been validated. Different combinations of volume and frequencies were then oscillated into each jacket, while it was being worn by a well preterm baby. Studies were performed with each jacket on five babies with weights between 0.82 and 1.86 kg. The results showed that at any given frequency there was a linear relationship between the pressure oscillations measured from a side port of the jacket and the delivered volume. Both jackets showed the same pattern of frequency response, overreading at less than 10 Hz and underreading at 10-25 Hz. When appropriately calibrated, the respiratory jacket can be used as a non-invasive method of measuring volumes delivered by HFO.

Calibration↗
PubMed1992

Separate visual pathways for perception and action.

Accumulating neuropsychological, electrophysiological and behavioural evidence suggests that the neural substrates of visual perception may be quite distinct from those underlying the visual control of actions. In other words, the set of object descriptions that permit identification and recognition may be computed independently of the set of descriptions that allow an observer to shape the hand appropriately to pick up an object. We propose that the ventral stream of projections from the striate cortex to the inferotemporal cortex plays the major role in the perceptual identification of objects, while the dorsal stream projecting from the striate cortex to the posterior parietal region mediates the required sensorimotor transformations for visually guided actions directed at such objects.

Animals↗
PubMed1992

Respiratory support using patient triggered ventilation in the neonatal period.

There are now a number of purpose built patient triggered ventilators for use in the newborn. These ventilators are triggered either by air flow or airway pressure changes, their triggering devices all have very high sensitivity and short systems delay. They all have the advantage that they perform well without inadvertent positive end expiratory pressure at the fast ventilator rates frequently triggered by immature infants. Despite all these improvements in both ventilator and trigger performance, PTV is still frequently unsuccessful in the most immature infants. We must conclude that the nature of the extremely preterm infant's respiratory efforts in the acute stage of respiratory illness may mean that PTV is unlikely to provide the optimal mode of respiratory support for this group of patients. Short term studies have suggested that those infants with relatively mild respiratory distress syndrome showed the greatest improvement in blood gases. These results suggest that PTV may have its most efficacious role during weaning and in the larger, more mature baby who is 'fighting the ventilator'.

Humans↗
PubMed1992

Inhaled budesonide for chronic wheezing under 18 months of age.

The role of budesonide in controlling chest symptoms in infants was assessed. It was administered from a metered dose inhaler into a large volume spacer (Nebuhaler) with attached Laerdal mask. Twenty nine infants were recruited into a double blind crossover trial. Five defaulted. The remaining 24 (mean age 11 months) were assessed for the tolerance of the device, adverse effects, treatment failures, parental opinion, and daily symptom and treatment records. Twenty tolerated the modified Nebuhaler. One developed meningitis on placebo. Two experienced exacerbations on placebo. Eleven of 18 parents whose children completed the maximum treatment preferred budesonide to placebo and one preferred placebo. Mean symptom scores on budesonide were better than on placebo for the 15 children with complete symptom records. Fewer bronchodilator doses were used while taking budesonide. Our findings indicate that budesonide given in this way is an effective treatment for infants who may need prophylaxis for their wheezing.

Administration, Inhalation↗
PubMed1992

Respiratory status and allergy after bronchiolitis.

As part of a long term prospective study, 73 children who had been admitted to hospital with viral bronchiolitis as infants, were reviewed 5.5 years later and compared with a carefully matched control group. In the postbronchiolitis group, there was a highly significant increase in respiratory symptoms including wheezing (42.5% v 15.0%, relative risk = 2.8). Although atopy in the family was not significantly increased in the index group, personal atopy was more prevalent. However, personal atopy was not significantly more prevalent in the symptomatic postbronchiolitis, compared with those who were symptom free, and so did not account for the high prevalence of postbronchiolitis wheezing in this cohort. In addition, in a stepwise logistic regressional model, bronchiolitis remained a significant predictor of wheezing after adjusting for potential confounding variables, including atopy. Bronchial responsiveness to histamine was significantly increased in the index group. However, no significant relationship of positive tests to wheezing could be demonstrated, and a high rate of positive responses was noted in the controls.

Bronchiolitis, Viral↗
PubMed1992

Upper airway patency during apnoea of prematurity.

Twenty four preterm infants (median birth weight 1120 g and gestation 29 weeks) were studied on 83 occasions by measuring upper airway airflow. Airway patency was detected by the transmission of cardiac impulse up the airway and airway closure by its absence. A total of 309 apnoeas of at least five seconds' duration were recorded. One hundred and eighty (58.0%) were central, 109 (35.5%) mixed, and 20 (6.5%) obstructive. Airway closure was noted in 47% of apparently central apnoeas. Airway closure occurred as apnoea lengthened; the airway remained patent in 38% of apnoeas of 5-9 seconds, 17% of those 10-14 seconds, and 11% of those 15-19 seconds' duration. Airway closure occurred in every apnoea of greater than or equal to 20 seconds. As a consequence, closed apnoeas were longer than open apnoeas (mean 9.7 v 6.6 seconds). In 72% of mixed apnoeas, airway closure was recorded during the central element and this usually preceded obstructive breaths. In 20% of mixed apnoeas and 15.5% of the total group the airways closed, having previously been patent. This occurred after a mean of 3.5 seconds (range 1-17). Mixed apnoea produced a significantly greater drop in arterial oxygen saturation than central apnoea, but only because of the greater duration of mixed apnoea. Airway closure occurs in both central and mixed apnoea and appears to be important in the pathophysiology of mixed apnoea. Central and mixed apnoea are part of a continuum of airway closure and not separate entities.

Apnea↗
PubMed1992

Drug delivery from holding chambers with attached facemask.

There is much interest in the use of holding chambers with an attached facemask to deliver aerosols from metered dose inhalers to infants. In order to study the influence of various design factors on the dose inhaled at different tidal volumes, a model was constructed in which a Starling ventilator was used to generate an inspiratory/expiratory cycle across a filter. Sodium cromoglycate was administered via a Nebuhaler and mask, Aerochamber and mask, and a coffee cup using tidal volumes of 25, 50, and 150 ml and the dose deposited upon the filter after six breaths was assayed using an ultraviolet spectrophotometric method. At the lowest tidal volume the high aerosol concentration in the smaller chamber enhanced drug delivery while at the highest tidal volume delivery was greatest from the larger chamber reflecting the larger dose available. Multiple breaths ensured that the dose inhaled per kilogram from each chamber was relatively large and also permitted significant drug delivery despite the introduction of a relatively large dead space between valve and filter. The dose delivered was increased by increasing the dose introduced into the chamber though not proportionately. These devices appear likely to deliver significant quantities of aerosol to infants, though drug delivery may be enhanced by the use of an appropriate valve.

Aerosols↗
PubMed1992

Drug delivery from jet nebulisers.

Maximising the rate of drug delivered in particles small enough to reach the lower respiratory tract from jet nebulisers may allow treatment times to be reduced and thus improve the acceptability of this form of treatment, particularly in very young patients. The role of various technical factors such as driving gas flow (DGF) in determining the rate of drug delivery was studied by constructing a model to simulate the respiratory pattern of individuals with different tidal volumes using a Starling ventilator and filter. Sodium cromoglycate was nebulised under a variety of operating conditions and the dose deposited on the filter was assayed. Tidal volumes of 50 and 400 ml were used at a frequency of 32 breaths per minute. Increasing the DGF from 4 to 8 l/minute produced a 264% increase in the rate of drug output but only a 32% increase in aerosol concentration. The mass of drug contained within droplets less than 5 microns increased from 26.8% to 70.8% of the total. The resultant increase in rate of drug delivery to the filter was 34% for a tidal volume of 50 ml and 79% for a tidal volume of 400 ml though the dose contained within droplets less than 5 microns increased by 4-fold at 50 ml tidal volume and by more than 5-fold at the higher tidal volume. Halving the solution concentration halved the rate of drug delivery. Increasing the tidal volume 8-fold from 50 to 400 ml resulted in an increase in the rate of drug deposition upon the filter of only 2.2 to 3-fold depending upon the DGF so that substantially more drug per ml inhaled was delivered at the lower tidal volume. These results are explained by considering factors that influence the rate of drug delivery. At low tidal volumes the rate of drug delivery at a given respiratory rate is dependent on the tidal volume and aerosol concentration. At high tidal volumes it is dependent upon aerosol concentration and volume of available aerosol and is essentially independent of tidal volume.

Aerosols↗
PubMed1992

New aerosol delivery system for neonatal ventilator circuits.

There is mounting evidence that a variety of drugs delivered as aerosols are likely to be of benefit in neonatal units. To avoid many of the problems associated with the use of jet nebulisers in ventilator circuits, a chamber was designed to be used in conjunction with a metered dose inhaler (MDI). The dimensions (4 cm x 11 cm) were chosen in an attempt to maximise drug delivery. In vitro studies were subsequently performed in order to determine the optimum operating conditions. Sodium cromoglycate delivered via this system was collected on a filter placed between the tip of an endotracheal tube and a model lung. The dose delivered was determined by means of an ultraviolet spectrophotometric assay. Using a Draeger Babylog 8000 ventilator it was found that drug delivery as maximised by actuating the device just before the inspiratory cycle when the chamber was placed adjacent to the endotracheal tube and by using a long (one second) inspiratory time. Under these conditions 1.5-2% of the original dose was deposited upon the filter at tidal volumes of 11-22 ml. When considered in terms of body weight this is many times the equivalent dose delivered to adults from an MDI. Effective drug delivery to the filter was confirmed using a radiolabelled aerosol. Radiolabelled studies delivering aerosol to the lungs of intubated rabbits demonstrated that deposition aerosol was distributed uniformly between lobes when corrected for the weight of each lobe. In conclusion, the device appears likely to deliver significant, reproducible quantities of drug to the lower respiratory tract while being simple to use.

Aerosols↗