Effects of 15% oxygen on breathing patterns and oxygenation in infants.
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Aerospace Medicine↗
Biomedical subjects
A D Milner
Publications and source records attributed to A D Milner.
Grasping spatial relationships: failure to demonstrate allocentric visual coding in a patient with visual form agnosia.
The cortical visual mechanisms involved in processing spatial relationships remain subject to debate. According to one current view, the "dorsal stream" of visual areas, emanating from primary visual cortex and culminating in the posterior parietal cortex, mediates this aspect of visual processing. More recently, others have argued that while the dorsal stream provides egocentric coding of visual location for motor control, the separate "ventral" stream is needed for allocentric spatial coding. We have assessed the visual form agnosic patient DF, whose lesion mainly affects the ventral stream, on a prehension task requiring allocentric spatial coding. She was presented with transparent circular disks. Each disk had circular holes cut in it. DF was asked to reach out and grasp the disk by placing her fingers through the holes. The disks either had three holes (for forefinger, middle finger, and thumb) or two holes (for forefinger and thumb). The distance between the forefinger and thumb holes, and the orientation of the line formed by them, were independently varied. DF was quite unable to adjust her grip aperture or her hand orientation in the three-hole task. Although she was able to orient her hand appropriately for the two-hole disks, she still remained unable to adjust her grip aperture to the distance between the holes. These findings are consistent with the idea that allocentric processing of spatial information requires a functioning ventral stream, even when the information is being used to guide a motor response.
Agnosia↗
Perception and action in depth.
Little is known about distance processing in patients with posterior brain damage. Although many investigators have claimed that distance estimates are normal or abnormal in some of these patients, many of these observations were made informally and the examiners often asked for relative, and not absolute, distance estimates. The present investigation served two purposes. First, we wanted to contrast the use of distance information in peripersonal space for perceptual report as opposed to visuomotor control in our visual form agnosic patient, DF. Second, we wanted to see to what extent her abilities to process distance cues were dependent on binocular vision, in light of Milner et al.'s (1991) observations of preserved stereopsis in DF, and Dijkerman et al.'s (1996) and Marotta et al.'s (1997) observations that her visual guidance of grasping may be particularly dependent on binocular vision of the target. We hypothesized that DF's visuomotor responses would show normal sensitivity to target distance, while her perceptual estimates would not. In the first experiment, we required DF and two age- and sex-matched control subjects to reach out and grasp black cubes placed at varying distances, or to estimate the distance of the cubes from the hand starting position without making a reaching movement. In the second experiment, we required DF and two age-matched control subjects to point as rapidly and accurately as possible to small LED targets which differed in spatial location, under binocular and monocular conditions. The results showed that, relative to the control subjects, DF's grasping movements produced normal peak velocity-distance scaling-when she reached for blocks which varied in depth or pointed to LED targets which were presented at different distances in depth. In contrast, in the cube experiment, her verbal estimates of object distance were poorly scaled, although they improved slightly under the binocular conditions. The results are discussed in terms of current theories of processing streams in extrastriate visual cortex and the distinction between categorical and coordinate spatial processing.
Agnosia↗
The perception and prehension of objects oriented in the depth plane. II. Dissociated orientation functions in normal subjects.
Normal human subjects were tested for their ability to discriminate the orientation of a square plaque tilted in depth, using two different tasks: a grasping task and a perceptual matching task. Both tasks were given under separate monocular and binocular conditions. Accuracy of performance was measured by use of an opto-electronic motion analysis system, which computed the hand orientation (specifically, a line joining the tips of the thumb and index finger) as the hand either approached the target during grasping or was used to match the target. In all cases there was a very strong statistical coupling between hand orientation and target orientation, irrespective of viewing conditions. However, the matching data differed from the grasping data in showing a consistent curvature in the hand-target relationship, whereby the rate of change of hand orientation as a function of object orientation was smaller for oblique orientations than for those near the horizontal or vertical. The results are interpreted as reflecting the operation of two different mechanisms for analysing orientation in depth: a visuomotor system (assumed to be located primarily in the dorsal cortical visual stream) and a perceptual system (assumed to be located in the ventral stream). It may be that the requirements of visuomotor control dictate a primary need for absolute orientation coding, whereas those of perception dictate a need for more categorical coding.
Adult↗
Visual size processing in spatial neglect.
Evidence from the use of the landmark task and from two size-matching tasks shows that many patients with left-sided neglect systematically under-perceive visual extent in leftward parts of space. This perceptual distortion of size serves to explain the occurrence of rightward line-bisection errors in most neglect patients. One possibility is that attentional biases of a chronic nature might underlie these perceptual changes seen in neglect patients. But contrary to this idea, we have found that attentional cueing in the landmark task causes changes in neglect patients exactly opposite to those seen in healthy subjects. The distortions of size perception seen in neglect could instead be caused by a high-level alteration of visual processing rather than by an attentional bias. In order to explore which visual stream of cortical processing might be compromised in such a disorder, we have begun to examine neglect patients on visuomotor as well as perceptual tasks. We have found clear evidence in one patient for intact grip scaling for object size in the neglected half of space, despite gross perceptual underestimations of the same objects. This result suggests that neglect can occur without major disruption of the dorsal stream, and may result instead from damage to a cortical system whose predominant visual input comes from the ventral stream.
Attention↗
Resuscitation at birth.
UNLABELLED: It is only in recent years that the techniques used for resuscitation at birth have come under critical review and there have been very few controlled trials to assess their efficacy. Recent studies have indicated that the large majority of asphyxiated term babies can be resuscitated using air rather than 100% oxygen, possibly reducing damage from oxygen free radicals during re-perfusion. Physiological studies have shown that inflation pressures of 25-30 cm H2O maintained for up to 1 s, only result in approximately 40% of the mean inspiratory volume achieved by babies who breathed spontaneously at birth. These spontaneous inflation volumes can be matched either by maintaining the first inflation for 3 s, or by using pressures of up to 50 cm H2O for 300 ms, a pattern adopted by spontaneously breathing babies. Bag and mask systems are even less effective, often depending on the Head paradoxical reflex to stimulate respiration rather than producing adequate tidal exchange. Face mask T-piece devices provide more effective ventilatory exchange and are easier to use. CONCLUSION: Although the pattern of ventilatory support in current use often leads to successful resuscitation of asphyxiated babies at birth, more physiological and randomised controlled studies are needed to refine techniques in order to limit babies' exposure to potentially damaging hypoxia to the minimum.
Air↗
A possible role for the Hering-Breuer deflation reflex in apnea of prematurity.
BACKGROUND: The vagally mediated Hering-Breuer deflation reflex terminates expiration and initiates inspiration when lung volume is reduced to less than functional residual capacity. The effects of prematurity on this reflex are not known. STUDY DESIGN: Fifteen term and 20 preterm nonventilated infants were studied. Lung deflation was achieved by chest compression using an inflatable jacket. Relative changes in expiratory time and inspiratory time on chest compression were calculated from airflow recordings. Esophageal pressure changes in the term infants and chest wall movements in the preterm infants were also measured. RESULTS: The term infants had a mean prolongation of inspiratory time on squeezing of 15% versus a 24% shortening in the preterm infants (p < 0.001). The term infants had a mean shortening of expiratory time on squeezing of 35% versus 18% in the preterm infants (p < 0.001). Fifteen of the 20 preterm infants demonstrated a tendency to have short apneas (2 to 5 seconds) on squeezing, 88% of which were central in origin. In these infants shortening of inspiratory time was greater than that seen in the preterm infants not having apneas (p < 0.05). CONCLUSIONS: Preterm infants responded to a rapid reduction in lung volume with a shortened inspiratory effort and a tendency to have central apneas. This may be due to an immaturity in part of the reflex arc responsible for transmitting the Hering-Breuer deflation reflex.
Apnea↗
Phase analysis in high-frequency oscillation.
UNLABELLED: In an oscillating system driven by a sine wave pump, the resonance frequency of the respiratory system can be determined using phase analysis. At resonance frequency, when elastance and inertance cancel out, flow becomes in-phase with resistance. In premature infants with respiratory distress syndrome, owing to surfactant deficiency, localized areas of hyperinflation and collapse develop, resulting in complex changes in overall pulmonary mechanics. We investigated the effect of measuring resonance frequency of the respiratory system by phase analysis at different points of the respiratory cycle: end of inspiration, end of expiration, mid-inspiration and mid-expiration. Ten ventilated premature infants with respiratory distress syndrome were studied, gestational age ranged from 24 to 30 weeks (mean 27.6 weeks) and birth weight ranged from 0.7 to 1.505 kg (mean 0.984 kg). RESULTS: The resonance frequency was consistently higher when measured at the end of inspiration compared with the end of expiration. The expected trend of phase variation, that is, negative below the resonance frequency and positive above, was most consistently found when analysis was done at the end of inspiration. CONCLUSIONS: These findings were most likely a result of the complexity of pulmonary mechanics in the surfactant-deficient lungs, rendering the single compartment model we based our theory on inadequate. However, phase analysis performed at the end of inspiration seemed to produce the most reliable and consistent results.
Biomedical Engineering↗
Central fixations are inadequately controlled by instructions alone: implications for studying cerebral asymmetry.
A fundamental concern when using visual presentations to study cerebral asymmetry is to ensure that stimuli are presented with the same degree of retinal eccentricity from a central fixation point in either visual field. However, a widely used procedure intended to control fixation location merely instructs participants to fixate appropriately without any other means of ensuring that central fixations actually occur. We assessed the validity of assuming that instructions alone ensure central fixation by using the traditional RVF advantage for words and either (a) only instruction to fixate centrally, or (b) eye-tracking device that ensured central fixation on every trial. Experiments 1 and 2 found that when only instructions were given, the vast majority of fixations were not central, and more occurred to the right of centre than to the left. Moreover, the prevalence of non-central fixations was otherwise disguised by the finding that both fixation procedures produced similar RVF advantages in overt performance. The impact of typical non-central fixations on performance was revealed by systematically manipulating fixation location in Experiment 3, where deviations in fixation of only 0.25 degrees from centre had a reliable impact on visual field effects. Implications of these findings for studies of cerebral asymmetry are discussed.
Adult↗
Volume delivery during high frequency oscillation.
AIM: To examine the delivered volume during "high volume strategy" high frequency oscillation, used as rescue treatment in preterm infants; and to identify factors, other than frequency and oscillatory amplitude, influencing the magnitude of volume delivery. METHOD: Twenty infants (median gestational age 29 weeks) were studied on 45 occasions. Two oscillator types were used (SensorMedics and SLE). Delivered volume was measured under clinical conditions with the arterial blood gases within a predetermined range. A specially calibrated pneumotachograph system was used. RESULTS: Overall, the median delivered volume was 2.4 ml/kg (range 1.0 to 3.6 ml/kg); on 32 occasions the delivered volume was greater than 2.0 ml/kg and on seven greater than 3.0 ml/kg. The delivered volume related significantly to disease severity; there was an inverse correlaton between delivered volume and both the oxygenation index (OI) (r = -0.51) and AaDO2 (r = -0.54). CONCLUSION: Delivered volume during HFO may, in certain infants, exceed the anatomical dead space, permitting some direct alveolar ventilation.
High-Frequency Ventilation↗
Vision without knowledge.
A brain-damaged patient (D.F.) with visual form agnosia is described and discussed. D.F. has a profound inability to recognize objects, places and people, in large part because of her inability to make perceptual discriminations of size, shape or orientation, despite having good visual acuity. Yet she is able to perform skilled actions that depend on that very same size, shape and orientation information that is missing from her perceptual awareness. It is suggested that her intact vision can best be understood within the framework of a dual processing model, according to which there are two cortical processing streams operating on different coding principles, for perception and for action, respectively. These may be expected to have different degrees of dependence on top-down information. One possibility is that D.F.'s lack of explicit awareness of the visual cues that guide her behaviour may result from her having to rely on a processing system which is not knowledge-based in a broad sense. Conversely, it may be that the perceptual system can provide conscious awareness of its products in normal individuals by virtue of the fact that it does interact with a stored base of visual knowledge.
Adult↗
Copying without perceiving: motor imagery in visual form agnosia.
Patient DF has severely impaired visual contour perception, despite being able to use that same visual information to guide her motor actions. We report that DF has developed a strategy to overcome some of her perceptual deficits. DF was first asked to copy single lines set at different orientations. She performed surprisingly accurately, although her responses were slow. When questioned, DF reported imagining tracing the line with her finger before copying the line on paper, although she was still unable to discriminate perceptually between different line orientations. We found that time restraints, or the requirement to perform secondary concurrent tasks, severely disrupted DF's orientation copying ability. We conclude that DF can use pure motor imagery to compensate for some of her perceptual difficulties.
Agnosia↗
Determination of gas-trapping during high frequency oscillatory ventilation.
OBJECTIVE: To determine the effect of frequency and percent inspiratory time on tidal volume and gas-trapping during high-frequency oscillatory ventilation (HFOV). SUBJECTS: Nine preterm infants with respiratory distress syndrome tested in the first 48 h of life. METHODS: Tidal volumes and the presence of gas-trapping were measured by respiratory jacket plethysmography at frequencies of 10, 14, and 17.8 Hz and at inspiratory times of 30%, 50% and 70%, using a commercially available high frequency oscillator.74 RESULTS: Mean (SD) tidal volumes were 2.40 (1.06) ml/kg at 10 Hz, 2.52 (1.07) ml/kg at 14 Hz and fell significantly to 1.96 (0.92) at 17.8 Hz (p < 0.05). Tidal volumes at 50% inspiratory time were significantly greater than at 30% inspiratory time [2.81 (1.42) ml/kg and 2.32 (1.18) ml/kg, respectively] but fell to baseline levels at 70% inspiratory time. There was no significant gas-trapping with increases in either frequency or percent inspiratory time. CONCLUSIONS: Gas-trapping is not a significant problem during HFOV in premature infants. Changes in tidal volume with increases in frequency and percent inspiratory time are similar to that seen in animal models.
High-Frequency Ventilation↗
Respiratory status and allergy nine to 10 years after acute bronchiolitis.
In order to evaluate further the relationship between acute bronchiolitis in infancy and subsequent respiratory problems, children prospectively followed up from the time of their admission to hospital were reviewed along with a group of matched controls recruited at the previous five and a half year assessment. Sixty one index children and 47 controls took part. The groups were well matched for age, height, parental smoking, and social class. Although the prevalence of respiratory symptoms had fallen when related to the previous review, there remained an excess of coughing (48 and 17% in index and control children respectively; odds ratio 4.02) and wheezing (34 and 13% in index and control children respectively; odds ratio 3.59). Bronchodilator therapy was used by 33% of index children compared with 3% of controls. Lung function tests revealed no significant differences in the measurements of lung growth-for example, forced vital capacity, functional residual capacity, and total lung capacity-but the index children had significant reductions in measurements of airways obstruction-for example, forced expiratory volume in one second, maximum expiratory flow at 75, 50 and 25% of vital capacity, and airways resistance. Family history and personal skin tests showed no excess of atopy in the index group. This study supports the claim that the excess respiratory symptoms after acute bronchiolitis are not due to familial or personal susceptibility to atopy.
Acute Disease↗
Adrenal function and high dose inhaled corticosteroids for asthma.
OBJECTIVE: To investigate effects on adrenal function of fluticasone, a recently released inhaled steroid preparation with lower systemic bioavailability than beclomethasone dipropionate. METHODS: 34 children on high doses (400-909 micrograms/m2/d) of inhaled beclomethasone dipropionate or budesonide were recruited into a double blind, crossover study investigating the effects on adrenal function of beclomethasone and fluticasone propionate, given using a standard spacer (Volumatic). The 24 hour excretion rates of total cortisol and cortisol metabolites were determined at baseline (after a two week run in), after six weeks treatment with an equal dose of beclomethasone, and after six weeks of treatment with half the dose of fluticasone, both given through a spacer device. RESULTS: The comparison of effects between fluticasone and beclomethasone during treatment periods, although favouring fluticasone in all measured variables, reached significance only after correction for urinary creatinine excretion (tetrahydrocortisol and 5 alpha-tetrahydrocortisol geometric means: 424 v 341 micrograms/m2/d). The baseline data showed adrenal suppression in the children taking beclomethasone (total cortisol geometric means: 975 v 1542 micrograms/d) and a dose related suppression in the children taking budesonide. Suppressed adrenal function in the children who were taking beclomethasone at baseline subsequently improved with fluticasone and beclomethasone during treatment periods. CONCLUSIONS: Fluticasone is less likely to suppress adrenal function than beclomethasone at therapeutically equivalent doses. The baseline data also support the claim that spacer devices should be used for the administration of high doses of inhaled topical steroids.
Administration, Topical↗
The role of corticosteroids in bronchiolitis and croup.
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Adrenal Cortex Hormones↗
Pulmonary hypoplasia presenting as persistent tachypnoea in the first few months of life.
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Female↗
The influence of sleeping position on functional residual capacity and effective pulmonary blood flow in healthy neonates.
Variation in body position has been shown to affect respiratory function in adults and neonates with and without respiratory illness. At present it remains unclear why respiratory function should be affected by different body positions. We hypothesized that the effect of body weight on the relatively compliant chest wall of the newborn infant in the prone position would cause a reduction in functional residual capacity (FRC) and a compensatory improvement in ventilation/perfusion matching as measured by effective pulmonary blood flow. To evaluate this, a paired crossover study was performed on 12 normal newborn infants. The inert gas (argon) rebreathing method adapted for neonates was used to measure FRC. Simultaneously effective pulmonary blood flow (Qpeff) was determined using Freon 22 and a mass spectrometer with computerized analysis. The babies were studied in three different positions in random order: prone, supine and right lateral decubitus. The means (95% confidence intervals) of the three groups of FRC were 23.8 (19.2 to 28.4), 23.8 (20.2 to 27.5), and 24.3 (19.5 to 29.2) ml/kg, respectively (P = 0.59) and for Qpeff were 104 (91 to 116), 108 (95 to 122), 109 (97 to 122) ml/ kg-min, respectively (P = 0.11). Thus no significant differences were demonstrated. In nine of the babies, a repeat supine measurement was taken at the end of the study to assess repeatability of the method. In these nine babies alone the results were 22.7 (19.1 to 26.3) and 22.1 (18.6 to 25.6) ml/kg for FRC, and 102 (89 to 116) and 98 (90 to 107) ml/kg-min for Qpeff. The coefficients of repeatability were 4.7 ml/kg for FRC (21%) and 30 ml/kg-min for Qpeff (30%).
Argon↗