Search PubMed⌕ Search

Biomedical subjects

A D Milner

Publications and source records attributed to A D Milner.

At least 91 records · Page 5Linked to original sources
PubMed1994

Nitric oxide.

Although persistent pulmonary hypertension of the newborn (PPHN) has been considered to be a relatively rare condition, there is increasing evidence that pulmonary vasoconstriction is a common finding in moderate and severe respiratory distress syndrome. High pressure, high rate ventilation may overcome this problem but it is associated with an unacceptably high incidence of pneumothorax and chronic lung disease. Vasodilators including tolazoline, prostacyclin and nitroprusside have a nonspecific effect, often producing systemic as well as pulmonary hypotension. Nitric oxide (NO) offers an exciting alternative therapy. NO is produced by the conversion of arginine to citrulline by NO synthase in the vascular endothelial cells. The NO then diffuses through to the underlying smooth muscle leading to relaxation. It then combines with haemoglobin to form small quantities of methaemoglobin, preventing spread of its effect elsewhere. The main potential toxic effect is due to the rapid conversion of NO to nitrogen dioxide in the presence of oxygen. Animal studies have shown that concentrations of NO up to 100 ppm are safe and also effective in relieving vasoconstriction induced by hypoxia, thromboxane analogues and infusions of group B haemolytic streptococcus. Preliminary studies on adults with respiratory distress syndrome have been encouraging showing reductions in pulmonary artery pressure and improvements in oxygenation without any changes in systemic blood pressure. Two small studies indicate that NO therapy is both effective and safe when given to full term babies with PPHN. Further data are urgently needed to find optimal concentrations so that multicentre studies can be carried out.

Animals↗
PubMed1994

Spatial bias in visually-guided reaching and bisection following right cerebral stroke.

Groups of patients with left or right unilateral cerebral stroke were tested for their ability to reach either toward a single visual target or midway between 2 targets. The tasks were performed both in free vision and in conditions preventing visual feedback from the hand. It was found that only the right CVA patients were inaccurate in reaching, and only when visual feedback was absent. This effect of right hemisphere lesions took the form of a rightward bias, present throughout the trajectory of the hand during the reach. It was present regardless of the hand used in reaching and whichever of the two tasks was performed, and was of a similar magnitude irrespective of target location. It is suggested that this rightward bias might reflect the 'premotor' effects that have been proposed to contribute to line-bisection errors in certain patients with visuospatial neglect.

Aged↗
PubMed1994

Is tapping jet nebulisers worthwhile?

An in vitro system was used to study the effect of tapping a jet nebuliser on the dose delivered to patients. Using a 2 ml fill, effective drug delivery had ceased by 3 minutes but a further 38% was delivered to the filter by 5 minutes if the chamber was tapped.

Cromolyn Sodium↗
PubMed1994

Analysis of cells obtained by bronchial lavage of infants with respiratory syncytial virus infection.

To study the cellular infiltrate that occurs within the airways of infants with respiratory syncytial virus bronchiolitis, samples of airways secretions were obtained by bronchial lavage from the lower respiratory tract of infants ventilated for this condition and from the upper airway of non-intubated infants with this disorder using nasopharyngeal aspirates. Cytospin samples were prepared so that differential cell counts could be performed on the cells obtained and alkaline phosphatase-antialkaline phosphatase immunocytochemical analysis of lymphocyte subsets was carried out using a panel of monoclonal antibodies, which included anti-CD3, anti-CD4, anti-CD8, anti-CD19, and anti-TcR gamma delta. Results from the lower and upper airways were similar. Large numbers of inflammatory cells were obtained, of which neutrophils accounted for a median of 93% in the upper airway and 76% in the lower airway. The numbers of CD8 positive cells detected were small and consistently less than CD4 positive cells, median CD4:CD8 ratios being 22.5:1 and 15:1 for the lower and upper airways. CD19 positive cells were rarely observed and no gamma delta positive lymphocytes were detected. These results indicate that neutrophils probably play a major part in causing symptoms in these infants. They do not support the concept that excessive lymphocyte mediated cytotoxic activity is principally responsible for the pathology in respiratory syncytial virus bronchiolitis.

Acute Disease↗
PubMed1994

The performance of a new valveless ventilator at rates of up to 250 bpm.

The efficacy of a new ventilator, incorporating a valveless pneumatic exhalation circuit, at rates of up to 250 bpm was first assessed in the laboratory. Using this ventilator the effect of fast rate ventilation on blood gases of infants with acute respiratory distress was then examined. Infants were studied at three rates: 60, 125 and 250 bpm. Peak inflating and positive end expiratory pressure, inspiratory: expiratory ratio and inspired oxygen were kept constant. The laboratory study demonstrated that as ventilator rate was increased the delivered volume fell, but even at 250 bpm the delivered volume was 7 ml. In the clinical study, oxygenation at 250 bpm was not significantly different from that at 60 bpm, but significantly lower than at 125 pbm. Carbon dioxide levels were significantly lower at 250 bpm that at 60 bpm, but did not differ significantly from that at 125 bpm. We conclude increasing ventilator rate from 125 to 250 bpm is not advantageous for infants ventilated for acute respiratory distress.

Case-Control Studies↗
PubMed1993

The effect of frequency and mean airway pressure on volume delivery during high-frequency oscillation.

The performance of a commercially available oscillator (SensorMedics 3100) at different frequencies was assessed. A frequency response curve of a pneumotachograph system was constructed and this was used to measure the volume delivered by the oscillator to a lung model. The volume delivered by a constant diaphragm displacement was demonstrated to be inversely proportional to the frequency, but unaffected by increasing mean airway pressure from 15 to 25 cm H2O. The volume delivered during high frequency oscillation (HFO) was then assessed in 8 infants, median gestational age 29 weeks. The infants were studied at two frequencies, 10 and 15 Hz, both of which were used at two levels of mean airway pressure (MAP): 2 and 5 cm H2O above the MAP level previously used during conventional ventilation. The delivered volume was not significantly different at the two MAP levels, but was significantly greater at 10 than 15 Hz at both MAP levels (P < 0.03); at MAP +2 cm H2O above baseline the reduction in delivered volume was from a median of 1.54 mL/kg (range, 0.88-3.12) at 10 Hz to 1.18 mL/kg (range, 0.65-4.5) at 15 Hz. These results suggest that higher frequencies would require an increase in the oscillator displacement if effective gas exchange is to be maintained.

Blood Gas Analysis↗
PubMed1993

Response to added dead space in ventilated preterm neonates and outcome of trial of extubation.

The ventilatory response to an added external dead space was assessed in preterm babies, recovering from respiratory distress syndrome, immediately prior to extubation. All babies were ready for extubation as defined by routine clinical criteria. Baseline measurements of respiratory rate, tidal volume, and minute ventilation were made over a 2 min period using a computerized system consisting of a pneumotachometer connected directly to the proximal end of the endotracheal tube. The measurements were repeated after addition of an external dead space equivalent to 2 anatomical dead spaces (4.4 mL/kg body weight). Thirty-four babies were studied on 40 occasions. Twenty-four infants (60%) were successfully extubated and 16 (40%) required reintubation. Infants in the success and failure groups were matched for gestation at birth, postconceptional age and weight at the time of study, maximum ventilatory requirements, and treatment with methylxanthines. The added external dead space resulted in an increase in minute ventilation in 38 out of the 40 studies. Extubation success and failure groups were compared by expressing the minute ventilation after addition of the external dead space as a percentage of the baseline minute ventilation (%MV1). Successful extubation was associated with a higher median %MV1 compared with babies who failed extubation (156; range, 89.3 to 230; compared to 131; range, 75.2 to 165; P = 0.006). This test may be useful in deciding which babies could be successfully extubated.

Humans↗
PubMed1993

The effect of instrumental dead space on measurement of breathing pattern and pulmonary mechanics in the newborn.

The effect of the instrumental dead space on breathing pattern and the values of pulmonary mechanics was evaluated because of concern about the relatively large dead space of 26 mL in a commercially available system. Sixty-three healthy newborn infants were studied with a system as commercially supplied, and with the dead space eliminated using a 2 L/min biased flow. This led to a significant reduction in mean (+/- SD) values of respiratory rate from 56.8 (+/- 11.7) to 48.2 (+/- 11.7) breath/min (P < 0.0001), tidal volume from 5.2 (+/- 1.3) to 4.9 (+/- 0.9) mL/kg (P < 0.05), minute volume from 284 (+/- 68) to 220 (+/- 63) mL/min/kg (P < 0.0001), and work of breathing from 13.7 (+/- 6.6) to 11.8 (+/- 7.6) g.cm/kg (P < 0.02). There was a significant increase in dynamic lung compliance from 5.2 (+/- 1.5) to 5.6 (+/- 1.2) mL/cm H2O (P < 0.01) but no difference for total pulmonary resistance 39.6 (+/- 22.8) and 38.8 (+/- 22.2) cm H2O/L/sec. This shows that the instrumental dead space prevents measurement of the basal breathing patterns and alters the values of pulmonary mechanics. It is, therefore, important to use equipment with low dead space or make efforts to remove it by using a biased flow system such as we describe when measuring breathing patterns and pulmonary mechanics in the newborn.

Female↗
PubMed1993

Line bisection errors in visual neglect: misguided action or size distortion?

The rightward line bisection errors made by patients with visuospatial neglect can be explained as due to a spatially misdirected response, which would be predicted on either of two accounts. An alternative view, however, is that such patients actually misperceive the left half of a horizontal line as being shorter than the right half. We have tested this possibility directly in three neglect patients, by giving them prebisected lines: they were found to judge a central transection mark as lying nearer to the left end of the lines. We were also able to test one of the patients on a series of size comparisons using computer-generated patterns. She was found to judge horizontal lines as shorter in the left half of visual space than in the right. This was also true for comparisons of the areas of nonsense figures. However she did not make such constant errors when comparing the lengths of vertical lines. It is suggested that an attentional deficit in left hemispace may result in the underestimation of horizontal extent. This would act in combination with misdirected reaching to determine the magnitude of line bisection errors.

Aged↗
PubMed1993

An assessment of a new breath actuated inhaler device in acutely wheezy children.

A randomised double blind, two period cross over study was designed to compare the ability of 51 hospitalised asthmatics with acute exacerbations to use each of two inhalers. The inhalers compared were a new breath actuated metered dose inhaler, the Autohaler inhalation device, and a dry powder device, the Rotahaler. Preassessment data included the measurement of peak inspiratory flow rate (PIFR), peak expiratory flow rate (PEFR), pulse rate, and oxygen saturation. Therapeutic response to each inhaler was compared by measurement of PEFR, oxygen saturation, and pulse rate. PIFR was sufficient in all children to fire the Autohaler, including the youngest. No significant difference was found between the two inhalers as assessed by PEFR. However the Autohaler inhalation device could be actuated 99/100 times successfully compared with 74 for the Rotahaler. There was a consistent, but clinically insignificant, increase in pulse rate after use of the Rotahaler compared with the Autohaler. All 11 patients under 6 years of age failed to empty the Rotahaler but five of these patients received a significant benefit from using the Autohaler compared with after the Rotahaler. A significant drop in oxygen saturation was observed 15 minutes after use of either inhaler. This may at times reach levels of clinical importance.

Acute Disease↗
PubMed1993

Site of upper airway obstruction in infants following an acute life-threatening event.

Twenty-five patients were screened following an acute life-threatening event for the presence of obstructive and mixed apnea. Simultaneous cardiorespiratory monitoring with fiberoptic laryngoscopy was performed to identify the site of upper airway obstruction during these episodes. In 3 of these subjects, who had been born prematurely, obstruction was observed at the laryngeal level, with the arytenoid masses and aryepiglottic folds closing over across the vocal cords. Such closure was also observed during periodic breathing, which was found to be prominent in 4 of the infants studied. The possible role of laryngeal reflexes as a mechanism for these events is discussed.

Acute Disease↗
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↗