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Biomedical subjects

A D Milner

Publications and source records attributed to A D Milner.

At least 127 records · Page 7Linked to original sources
PubMed1991

A neurological dissociation between perceiving objects and grasping them.

Studies of the visual capacity of neurological patients have provided evidence for a dissociation between the perceptual report of a visual stimulus and the ability to direct spatially accurate movements toward that stimulus. Some patients with damage to the parietal lobe, for example, are unable to reach accurately towards visual targets that they unequivocally report seeing. Conversely, some patients with extensive damage to primary visual cortex can make accurate pointing movements or saccades toward a stimulus presented in their 'blind' scotoma. But in investigations of visuomotor control in patients with visual disorders, little consideration has been given to complex acts such as manual prehension. Grasping a three-dimensional object requires knowledge not only of the object's spatial location, but also of its form, orientation and size. We have examined a patient with a profound disorder in the perception of such object qualities. Our quantitative analyses demonstrate strikingly accurate guidance of hand and finger movements directed at the very objects whose qualities she fails to perceive. These data suggest that the neural substrates for the visual perception of object qualities such as shape, orientation and size are distinct from those underlying the use of those qualities in the control of manual skills.

Adult↗
PubMed1991

Combined conventional ventilation with high frequency oscillation in neonates.

Combined high frequency oscillation (HFO) with conventional ventilation was used on a group of 12 ventilator dependent neonates in order to investigate the frequency response of the respiratory system to HFO. Pressure oscillations were measured at the airway opening with a transducer and volume oscillations at the chest wall using a calibrated respiratory jacket. Pressure oscillations increased with increasing frequency but the oscillating volumes showed a variable pattern with maximum oscillating volumes of up to 4 ml/kg. Three babies showed no change in volume between 2-25 Hz, 3 babies showed increasing volumes up to 25 Hz and the remainder showed a maximum volume (or resonant frequency) at 15-20 Hz. Oscillating volumes were higher when the conventional ventilator was in the expiratory phase. The differences in frequency response were unrelated to severity of lung disease, birth weight, age at testing, or size of the endotracheal (ET) tube. Local factors in the ET tube and large airways may account for some of the observed differences.

Combined Modality Therapy↗
PubMed1991

Unexpected side-effects of inhaled steroids: a case report.

An asthmatic child is presented who developed a cushingoid appearance with evidence of adrenal suppression and growth impairment while on low dose inhaled topical steroids. When the inhaled steroids were replaced by inhaled sodium cromoglycate his adrenal function recovered while his appearance and growth returned to normal. This report indicates that there are some children who are at risk of developing side-effects on doses of inhaled topical steroids normally considered to be entirely safe.

Administration, Inhalation↗
PubMed1991

Perception and action in 'visual form agnosia'.

A single case study of a patient with 'visual form agnosia' is presented. A severe visual recognition deficit was accompanied by impairments in discriminating shape, reflectance, and orientation, although visual acuity and colour vision, along with tactile recognition and intelligence, were largely preserved. Neuropsychological and behavioural investigations have indicated that the patient is able to utilize visual pattern information surprisingly well for the control of hand movements during reaching, and can even read many whole words, despite being unable to make simple discriminative judgements of shape or orientation. She seems to have no awareness of shape primitives through Gestalt grouping by similarity, continuity or symmetry. It is proposed that many of these perceptual disorders might be the combined result of (1) a selective loss of the cortical elaboration of the magnocellular visual processing stream, and (2) a selective output disconnection from a central processor of visual boundaries and shape primitives in the occipital cortex.

Adult↗
PubMed1991

Endotracheal resuscitation of neonates using a rebreathing bag.

Thirty asphyxiated neonates were resuscitated endotracheally with an anaesthetic rebreathing bag. The system was not limited either by pressure or by volume and chest movement was used as the criterion for adequate inflation. Inflation pressure and flow were recorded during resuscitation, and flow was integrated to obtain volume. Median mean pressure over the first 10 inflations was 40 cm H2O and this dropped during later resuscitation to 29 cm H2O. The volume delivered did not change significantly, so volume divided by pressure increased from a median of 0.18 to 0.35 ml/kg/cm H2O. Fourteen infants formed part of their functional residual capacity with artificial ventilation and five with spontaneous breaths. Eleven infants showed no evidence of functional residual capacity formation. In the 22 preterm infants there was a strong association between absence of functional residual capacity formation and later hyaline membrane disease that required ventilation. We suggest that pressures of more than than 30 cm H2O may be helpful during initial resuscitation and that there should be further study of devices using positive end expiratory pressure for resuscitation of preterm infants.

Anesthesia, Closed-Circuit↗
PubMed1991

Apnoea, bradycardia, and oxygen saturation in preterm infants.

To analyse the effects of apnoea and bradycardia on the oxygen saturation (SaO2) of preterm infants and to make recommendations for apnoea alarm limits, polygraphic recordings were made on 89 occasions of 27 preterm infants; 1029 apnoeic episodes were analysed. Reduction in SaO2 was positively correlated with duration of apnoea, but the scatter of results was such that reductions in SaO2 of up to 40% occurred with apnoeas of less than 10 seconds duration. The median initial SaO2 was significantly lower in those episodes that resulted in bradycardia (92% compared with 95%), and there was also a significantly greater reduction in median SaO2 (9% compared with 5%). This study illustrates the difficulty of setting alarm limits for the detection of apnoea. We suggest that rather than simply detecting apnoea it is more appropriate to monitor heart rate and SaO2 in infants with recurrent apnoea.

Apnea↗
PubMed1991

Site of upper airway obstruction in preterm infants with problematical apnoea.

Airway obstruction is an important factor predisposing to the development of apnoea in preterm infants. An ultrafine fibreoptic scope was used to examine the upper airway of 12 preterm infants with recurrent problematical apnoea. Continuous visualisation of the airway was possible and recorded on to videotape together with simultaneous cardiorespiratory monitoring to detect apnoeic episodes in 12 infants studied. In seven infants obstruction was observed at laryngeal level with the arytenoid masses and aryepiglottic folds closing across the vocal cords. This was not only observed in obstructive apnoea but also during mixed apnoea in periods where no respiratory effort was detectable and again in apparently pure central apnoea. The findings confirm the larynx as an anatomical site of upper airway obstruction. They agree with other indirect methods of assessing airway patency that obstruction has an important role in the pathophysiology of apnoea of prematurity.

Airway Obstruction↗
PubMed1991

Nebulised water as a bronchoconstricting challenge in infancy.

The pulmonary response to inhalation challenge with nebulised distilled water was measured in 100 sedated infants with a history of wheeze. Lung function was measured by total body plethysmography. Satisfactory results were obtained in 88 infants. Fifty one were considered to have responded by developing a greater than 20% decrease in specific conductance (sGaw) after nebulised water. Thirty two of these infants had previously been challenged with nebulised saline before but only one showed a greater than 20% decrease in sGaw after saline. Twenty infants who developed signs of bronchoconstriction after challenge with nebulised water were rechallenged 20 minutes later. After the initial challenge a fall in sGaw of greater than 20% was found in 19 of the 20. After a second challenge with nebulised water only 15 (75%) showed a 20% or greater decrease in sGaw. Nine of the 20 infants remained sedated and were rechallenged for a third time. Eight showed a greater than 20% decrease in sGaw. This study indicates that approximately 60% of infants with a history of wheeze will bronchoconstrict in response to inhaled nebulised water and that up to 75% show no evidence of a subsequent refractory period to inhaled water challenge.

Administration, Inhalation↗
PubMed1990

Auditory orienting and detection in rats following lesions of the superior colliculus.

Rats were trained to run towards a lighted target following either bilateral lesions of the superior colliculus (SC) or control lesions of the overlying cortex. At 4 months post-surgery, the animals were tested for the disruptive effects of an auditory tone. An increase in running times was found in both groups, attributable to frequent freezing reactions in all animals. However, only the control rats made orienting reactions to the tones. It is argued that the freezing responses show that the SC lesions did not impair sensory detection; consequently, the orienting failure cannot be attributed to a sensory deficit.

Animals↗
PubMed1990

Dynamic responses to tube breathing during the first 10 days of life.

To assess whether there is a maturation of the response to tube breathing during the first 10 days of life, we have measured the dynamic ventilatory responses of nine term infants (34 studies) to added tubes equivalent to two anatomical dead spaces. Such a method allows an assessment of the baby's ability to increase dead space ventilation in response to an added stress. There was a significant improvement with age over the first 10 days in the babies' ability to reach "expected" values of minute ventilation when the tubes were added (P = 0.003). The rates at which 63% and maximum adaptation were achieved also increased significantly with age (P less than 0.005). The rate to 63% adaptation appeared to be faster in active compared with quiet sleep (P less than 0.05). The dynamic responses to tube breathing improve over the first 10 days of life. This is likely to be due to a maturation of peripheral chemoreceptor control, although improving lung mechanics may also be important.

Aging↗
PubMed1990

What are the mechanisms producing increased ventilation in dead space studies in neonates?

In 21 studies on 15 infants an additional dead space tube produced a significant rise in end-tidal PCO2 and fall in end-tidal PO2, associated with a rise in minute ventilation (228 +/- 77 mL/kg/min at zero, 348 +/- 85 mL/kg/min at one, and 437 +/- 128 mL/kg/min at two anatomical dead spaces). The differences between end-inspiratory and end-expiratory PCO2 and PO2 did not change significantly, suggesting an increase in dead space, but not in alveolar ventilation. In a further 9 babies the rise in ventilation was unchanged when measurements were repeated in 30% oxygen (361 +/- 65 vs. 340 +/- 54 mL/kg/min at one anatomical dead space). Studies on 8 babies, with the added tube ventilated by a fan, showed that a mean 28% of the rise in minute ventilation was due to increased resistance. Although the response to tube breathing in neonates is complex, carbon dioxide appears to be the major factor producing increased ventilation.

Carbon Dioxide↗
PubMed1990

The effect of changes in inspiratory time on neonatal triggered ventilation.

Nine preterm infants with hyaline membrane disease were studied using a ventilator triggered from abdominal movement. It was possible to alter respiratory rate over a short space of time by adjustments of the inspiratory time setting. There was a marked inverse relationship between inspiratory time and both ventilator and baby's respiratory rate--mean baby respiratory rate was 62 breaths/min at an inspiratory time of 0.2 s and 45 breaths/min at 0.8 s. This drop was statistically significant (P less than 0.005). Mean tidal volume changed little over this range. This interaction meant that mean minute ventilation was optimal at inspiratory times of 0.2 to 0.4 s, being 269 and 258 ml/kg per minute, respectively, but at 0.8 s fell to 213 ml/kg per minute (P less than 0.05).

Female↗
PubMed1990

Combined impedance and inductance for the detection of apnoea of prematurity.

To compare two methods of detecting central apnoea, 27 preterm infants (median birth weight 1.14 kg, gestation 29 weeks) were studied on 89 occasions, using combined thoracic impedance and abdominal respiratory inductive plethysmography. During 353 h recording time, 946 apnoeic episodes were noted. In 651 of these, there was agreement between impedance and inductance traces, but apnoea appeared longer in 106 episodes on impedance, and in 189 on inductance. If a single system had been used 27 would have been missed by inductance and 112 by impedance (P less than 0.05). Failure of impedance monitoring was mainly due to technical reasons, especially cardiac artefact, and to movement. The use of a dual system of impedance and inductance offers improved detection of central apnoea, particularly for research purposes.

Apnea↗
PubMed1990

Kinematic analysis of limb movements in neuropsychological research: subtle deficits and recovery of function.

In this brief review, we argue that a detailed analysis of the spatial and temporal characteristics of visually guided limb movements can provide important insights into the nature of neuropsychological deficits and the functional organization of the brain. In particular, we will show how kinematic analysis of a simple aiming movement can reveal differences that might not be apparent clinically in the behaviour of patients with unilateral brain lesions. We will argue that the subtle but distinctive deficits that follow damage to the left or right hemisphere can be related to the clinical syndromes of manual apraxia and hemispatial neglect, respectively. The fact that these deficits are apparent only with kinematic analysis demonstrates the potential of these techniques for evaluating recovery of function.

Attention↗
PubMed1990

Age-matching improves the results of renal transplantation with older donors.

Whilst HLA matching is routine for renal transplantation, the possible benefits of matching donor and recipient age have not been previously examined. In this study we examined the simultaneous effect of donor to recipient age difference on the graft survival of 141 consecutive first cadaver transplant recipients treated by cyclosporin immunosuppression. Multivariate regression analysis, taking into account other variables of moderately matched recipients (i.e. dialysis time and type, donor/recipient sex, local/imported kidneys, recent sensitivity, total ischaemic time, preoperative transfusions), indicated that age-difference was the single most important variable (P less than 0.05). Individually there was no significant effect of recipient age, whilst older donors (aged greater than 50 years) were associated with significantly worse graft survival than those younger (P less than 0.01). When dealing with donors aged greater than or equal to 50 years the corresponding recipient 1-year graft was improved when the donor was no more than 5 years older than the transplant recipient. Donor age to recipient age difference is a potentially important selection criterion in renal transplantation.

Adolescent↗