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Biomedical subjects

P Summers

Publications and source records attributed to P Summers.

At least 19 recordsLinked to original sources
PubMed2006

Relevance of postmortem radiology to the diagnosis of fatal cerebral gas embolism from compressed air diving.

AIMS: To test the hypothesis that artefact caused by postmortem off-gassing is at least partly responsible for the presence of gas within the vascular system and tissues of the cadaver following death associated with compressed air diving. METHODS: Controlled experiment sacrificing sheep after a period of simulated diving in a hyperbaric chamber and carrying out sequential postmortem computed tomography (CT) on the cadavers. RESULTS: All the subject sheep developed significant quantities of gas in the vascular system within 24 hours, as demonstrated by CT and necropsy, while the control animals did not. CONCLUSIONS: The presence of gas in the vascular system of human cadavers following diving associated fatalities is to be expected, and is not necessarily connected with gas embolism following pulmonary barotrauma, as has previously been claimed.

Animals↗
PubMed2006

A preliminary study of the effects of trigger timing on diffusion tensor imaging of the human spinal cord.

BACKGROUND AND PURPOSE: Diffusion tensor and diffusion-weighted spinal cord imaging remain relatively unexplored techniques despite demonstrations that such images can be obtained and may yield clinically relevant findings. In this study, we examined the temporal dynamics of spinal cord motion and their impact on diffusion tensor image quality. METHODS: Four healthy volunteers underwent phase contrast-based velocity mapping and segmented echo-planar diffusion tensor scans of the cervical spinal cord. Regions of interest in the cord were used to identify the temporal patterns of motion. The delay of data acquisition after the cardiac trigger was varied to correspond to either quiescence or motion of the cord. RESULTS: The cervical spinal cord consistently displayed maximal velocities in the range of 0.5 cm/s and accelerations of up to 25 cm/s(2). In both these respects, the cervical cord values were greater than those of the medulla. Despite this pronounced motion, approximately 40% of the cardiac cycle can be described as relatively calm, with absolute velocities and accelerations less than 20% of the maximum values. Confining image acquisition to this window reduced ghosting artifacts and increased the consistency with which the dominant direction of diffusion was along the rostral-caudal axis in both gray and white matter of the spine. Preliminary clinical application and fiber tracking in pathologic cases was feasible, and alterations of the diffusion properties by multiple sclerosis lesions, tumor, and syringomyelia were seen. CONCLUSIONS: Acquiring DTI data during the quiescent phase of spinal cord motion can reduce ghosting artifacts and improve fiber tracking.

Adult↗
PubMed2005

Cortical organization of sensory corrections in visuomotor skill acquisition.

During sensorimotor skill acquisition, early learning of the required neuromuscular pattern and sensorimotor mappings is followed by an intermediate stage of gradually increasing consistency and efficiency of execution, which gives way, with persistent practice, to the later stages of automatization. It has been suggested that the intermediate stage is distinguished by refinements in the background sensory corrections that support, stabilize and smoothen the fine motor adjustments required by the new coordination. While the later stages of motor refinement are thought to be sub-cortically organized, the neurophysiology of the proposed sensory learning component in the intermediate stage is not well understood. During explicit learning of a visually cued finger-tap sequence, the present research used fMRI to isolate those cortical activations that were significant in the immediate post-learning phase, but were not also observed during the corresponding pre-learning phase. Such exclusively post-learning activation occurred significantly more in visual and somatosensory association areas, than in primary somatosensory or primary and secondary motor areas. These results show that the intermediate stage of skill acquisition has a significant sensory learning component, and that the process has observable cortical correlates.

Cerebral Cortex↗
PubMed2002

Limb volume reduction after physical treatment by compression and/or massage in a rodent model of peripheral lymphedema.

Lack of a standardized experimental counterpart of peripheral lymphedema (LE) in a small animal has hampered research into treatment of this debilitating condition. We recently refined a rodent model consisting of radical unilateral lymphatic/nodal groin excision in conjunction with a circumferential integumental gap, followed by regional irradiation of the groin to reproduce stable unilateral hindlimb LE (1). In the current study, Wistar-Fuzzy rats with established right hindlimb LE, were subdivided into five groups and subjected to one of the following daily physical regimens over a 5-day period: pneumatic compression pumping at 30 torr (PCP); low-stretch multi-layered compressive bandaging using Coban (CB); manual lymphedema drainage (MLD) or a light massage consisting of stationary circular motions using the fingertips; combined physiotherapy (CPT consisting of MLD + CB); and a no treatment or control group (CTRL). Hindlimb and LE volumes were serially measured before and after treatment. Whereas CTRL showed progressive worsening of hindlimb swelling, PCP, CB, CPT and MLD each produced similar and substantial edema reduction over the 5 day interval, PCP, CB and CPT induced vacillating edema reduction which, however, exceeded rebound swelling on a daily basis. MLD, on the other hand, showed a steady gradual daily decline in LE volume.

Animals↗
PubMed2001

SPAMM, cine phase contrast imaging and fast spin-echo T2-weighted imaging in the study of intracranial cerebrospinal fluid (CSF) flow.

AIM: To compare the qualitative assessment of cerebrospinal fluid (CSF) flow using a SPAMM (spatial modulation of magnetization) technique with cine phase contrast images (cine PC) and fast spin echo (FSE) T2-weighted images. MATERIALS AND METHODS: SPAMM, PC and T2-weighted sequences were performed on 22 occasions in 19 patients. Eleven of the studies were performed following a neuroendoscopic third ventriculostomy (NTV), and in these cases, the success of the NTV was determined by clinical follow-up. Two observers used consensus to grade the presence of CSF flow at nine different sites for each study. RESULTS: At 14 of the 178 matched sites, which could be assessed by both SPAMM and cine PC, SPAMM CSF flow grade was higher than that of cine PC. At a further 14/178 matched sites, the cine PC grade was higher than that of SPAMM. There was definite CSF flow at 113/182 (62%) of all the cine PC sites assessed, and 110/181 (61%) of all SPAMM sites assessed whilst 108/198 (54%) of FSE T2-weighted image sites demonstrated flow voids. Cine PC grades were higher than SPAMM at the cerebral aqueduct (P < 0.05, Wilcoxon sign rank test). Definite CSF flow within the anterior third ventricle was present in 4/5 (SPAMM) and 3/5 (cine PC) successful NTVs, 0/2 (SPAMM and cine PC) unsuccessful NTVs and 1/10 (SPAMM and cine PC) patients without NTV. CONCLUSION: SPAMM provides a comparable assessment of intracranial CSF flow to that of cine phase contrast imaging at all CSF sites except the cerebral aqueduct.

Adolescent↗
PubMed1998

Visualization of the human larynx: a three-dimensional computer modeling tool.

The larynx is a complex compact organ. A detailed understanding of the anatomical relationships of its various structures is critical to the various workers in the field. To facilitate this goal, a 3-D model of the human larynx has been developed using multiple thin section MRI and CT images taken through a cadaver larynx. A databank of individual laryngeal structures ('units') has been built up. A software package has then been utilized which allows for representation of any of the stored 'units'. In this manner, elements of the larynx can be viewed from any direction, with the larynx static or in motion. Similarities and differences from current CD-ROM packages of the larynx are discussed.

Computer Simulation↗
PubMed1998

Parental divorce during early adolescence in Caucasian families: the role of family process variables in predicting the long-term consequences for early adult psychosocial adjustment.

The relationship between parental divorce occurring during adolescence and young adult psychosocial adjustment was examined, as was the role of family process variables in clarifying this relationship. Participants were young Caucasian adults from divorced (n = 119) and married (n = 123) families. Assessments were conducted during adolescence and 6 years later during early adulthood. Young adults from married families reported more secure romantic attachments than those from divorced families; however, differences were not evident in other domains of psychosocial adjustment after demographic variables were controlled. Three family process variables (parent-adolescent relationship, interparental conflict, and maternal depressive symptoms) were examined as potential mediators and moderators of the association between parental divorce and young adult adjustment. No evidence supporting mediation or moderation was found; however, the parent-adolescent and parent-young adult relationships, particularly when the identified parent was the father, emerged as significant predictors of young adult psychosocial adjustment.

Adolescent↗
PubMed1997

Family members' uncertainty about parental chronic illness: the relationship of hemophilia and HIV infection to child functioning.

Examined the relationships among parental and child uncertainty about fathers' illnesses and child internalizing problems. Participants included 65 families in which the father had hemophilia, approximately one half of the fathers also were HIV infected. Within each family, respondents included the father, the mother and one child. Outcome variables included both self- and parent-reported child internalizing behaviors. Results indicated that family members' illness uncertainty was intercorrelated, that child uncertainty about the father's illness predicted both anxiety and depressive symptoms in the child, and that mother's uncertainty predicted child-reported anxiety beyond the child's uncertainty.

Adolescent↗
PubMed1997

The role of parental and extrafamilial social support in the psychosocial adjustment of children with a chronically ill father.

The relationships among illness stress, perceived support, and child psychosocial adjustment were examined for children living with a chronically ill father. Participants included fathers, mothers, and one child from 53 families in which the father had hemophilia and, in some cases, was HIV seropositive. Objective indicators of severity of illness and subjective measures of the physical and psychological impact of illness were used as sources of children's stress. Results indicated that the impact of illness, but not the severity of illness itself, related to child psychosocial adjustment. Main effects were observed for parental support on child- and parent-reported internalizing problems and stress-buffering effects were obtained for parental support and extrafamilial support on parent-reported internalizing problems. Parental support also demonstrated a stress-buffering effect for child-reported depression. Assessment and intervention implications for behavioral clinicians and researchers are discussed.

Adaptation, Psychological↗
PubMed1996

Evaluation of three-dimensional ultrasonography and magnetic resonance imaging in assessment of congenital heart anomalies in fetal cardiac specimens.

In this observational study, multiplanar three-dimensional ultrasound images were reconstructed from tomographic views obtained by scanning seven cadavaric fetal hearts with various congenital heart defects. Comparisons were made with multiplanar three-dimensional magnetic resonance imaging (MRI) of the hearts. Good-quality echocardiographic images were obtained in all but one of the fetal hearts. Multiplanar as well as three-dimensional reconstructions were possible and allowed accurate assessment of complex cardiac defects. Overall, the MRI projections had better image quality and revealed more structural details than the sonographic views, although both imaging modes showed the same cardiac anatomical abnormalities. Our initial results demonstrate that simultaneous multiplanar display of cross-sectional echocardiographic views can be performed to provide three-dimensional images of the fetal heart, demonstrating structural cardiac malformation. However, the clinical application of three-dimensional fetal echocardiography is at present limited by the time required for image data acquisition and the need for accurate temporal and positional gating in the living fetus.

Autopsy↗
PubMed1996

Effects of elevated circulating IGF-1 on the extracellular matrix in "high-growth" C57BL/6J mice.

Collagen biosynthesis was analyzed in C57BL/6J mice homozygous for the high-growth locus. Plasma levels of insulin-like growth factor-1 (IGF-1) were significantly elevated in high-growth mice at all ages studied (3 wk-6 mo); IGF-binding proteins were also elevated. Skin biopsies were obtained from mice aged 3, 6, and 9 wk under halothane anesthesia. Mice were killed at 6 mo of age. Collagen, expressed per weight of tissue, was significantly increased in all tissues from high-growth mice, as was collagen cross-linking, expressed as moles of cross-link per mole of collagen. Expression of types I and III collagen, lysyl oxidase, and lysyl hydroxylase was increased in all tissues analyzed. There was a preferential increase in type III expression relative to type I expression. Rate and extent of accumulation of collagen in granulation tissue were measured in polyvinyl alcohol sponges implanted subcutaneously; collagen accumulation was significantly greater in the high-growth mice. These results suggest that 1) elevated circulating IGF-1 may increase collagen deposition both in normal tissue as well as in granulation tissue by increasing collagen gene expression, 2) IGF-1 may increase collagen cross-linking by stimulating expression of lysyl oxidase, and 3) the preferential increase in dihydroxylated cross-links observed in high-growth mice may be due to the stimulation of lysyl hydroxylase expression by IGF-1. In summary, elevated levels of IGF-1 appear to affect collagen both quantitatively and qualitatively, primarily through their effects on gene expression of collagen and of those enzymes responsible for posttranslational modifications of collagen.

Animals↗
PubMed1994

A variable pitch oxygen saturation indicator designed for use in the magnetic resonance environment.

Many commercially available pulse oximeters have a variable pitch blood oxygen saturation indicator, which emits a 'beep' between 175 Hz and 675 Hz with each heart beat. The frequency of this beep is dependent on the blood oxygenation measured by the oximeter, higher frequencies corresponding to higher blood saturation percentages. This is a useful feature for an anaesthetist, rapidly communicating potentially life-threatening situations in an easily detectable manner. Most available oximeters with an audio output feature are vulnerable to the effects of magnetic resonance scanning. In this article an add-on module is described for generating a beep to indicate the blood oxygen saturation which has been specifically designed to operate in the MR environment.

Algorithms↗
PubMed1991

Research into HIV and AIDS between 1981 and 1990: the epidemic curve.

The main features of research into HIV and AIDS between 1981 and 1990 were examined using a database of medical, nursing and dental journals [compact disc read-only memory (CD-ROM) version of the Medline database (Silver Platter Information Services, London, UK)]. More than 30,000 papers on HIV and AIDS were indexed by Medline between 1981 and 1990. Of these, only 3% were concerned with African populations although a quarter of AIDS cases worldwide were reported from African countries during the decade. The number of papers on HIV/AIDS increased from 24 in 1982 to an estimated 8300 in 1990. Between 1983 and 1988 the number of indexed papers on HIV/AIDS increased at around 50-60% per year; between 1988 and 1989, however, the rate of growth fell to 6%. The percentage of papers discussing the aetiology of AIDS fell from 25 to 3% between 1983 and 1990. During the same period, papers concerned with HIV increased from 2 to 37% of the HIV/AIDS total. Research into drug therapy also accounted for an increasing proportion of indexed papers during the decade. The percentage of papers dealing with prevention and control rose to 18% in 1988, but had declined to 12% by 1990. Priorities for the 1990s should include a renewed interest in aetiology and a sustained emphasis on prevention. Furthermore, countries that have so far been neglected should be granted priority in future research.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Plasma vitamins A and E and hydrogen peroxide-induced in vitro erythrocyte haemolysis in common marmosets (Callithrix jacchus).

Plasma total lipid, cholesterol, all-trans retinol (vitamin A) and alpha-tocopherol (vitamin E) concentrations, and the susceptibility of erythrocytes to hydrogen peroxide-induced haemolysis in vitro were investigated in healthy laboratory-bred common marmosets (Callithrix jacchus). The concentrations of alpha-tocopherol and total cholesterol were similar to those of control human subjects. The mean lipid concentration was higher (P less than 0.025) and the retinol concentration lower (P less than 0.001) in the marmosets. The susceptibility of the erythrocytes of the marmosets to hydrogen peroxide-induced haemolysis was high, both in absolute value and relative to the controls. Changes in phospholipid and fatty acid composition might have rendered the red cells susceptible to oxidative stress.

Adult↗
PubMed1990

N-3 and N-6 phosphoglyceride fatty acids in relation to in vitro erythrocyte haemolysis induced by hydrogen peroxide in captive common marmosets (Callithrix jacchus).

1. Hydrogen peroxide-induced haemolysis (HPIH) was studied in the red blood cells of the common marmoset monkey (Callithrix jacchus) in relation to the composition of the membrane fatty acids. HPIH (%) was surprisingly high (mean 41% +/- 34; median 33.4%) and significantly different (P less than 0.001) from the corresponding value in healthy human subjects (mean 0.98% +/- 0.6; median 1.3%). 2. It was negatively correlated with 18:2n-6 (r = -0.76, P less than 0.001), 18:2n-6/20:4n-6 (r = -0.70, P less than 0.005) and 18:2n-6/22:6n-3 (r = -0.44, P less than 0.025) in the ethanolamine phosphoglycerides of the erythrocytes. 3. A shift in the n-6/n-3 balance in favour of the n-3 in the fatty acid composition of the membrane may have predisposed the red blood cells to haemolysis. 4. An increase in 22:6n-3, and a decrease of 20:4n-6 and 18:2n-6, may have been the result of feeding a diet containing fish products rich in long chain n-3 fatty acids.

Animals↗
PubMed1989

Biosynthesis of collagen crosslinks. II. In vivo labelling and stability of lung collagen in rats.

Rat lung collagen was labelled in vivo by a single intraperitoneal injection of [3H]lysine at several key timepoints in lung development: days 11 (alveolar proliferation), 26 (start of equilibrated growth), 42 (end of equilibrated growth), and 100 (adult lung structure present). The rates of deposition of labelled hydroxylysine and the difunctional, Schiff base-derived crosslinks hydroxylysinonorleucine (HLNL) and dihydroxylysinonorleucine (DHLNL) were quantified. We also measured total lung content of the trifunctional, mature crosslink hydroxypyridinium (OHP) in these same animals. While the relative rates of accumulation of labelled collagen [3H]hydroxylysine differed by a factor of about 6 at the different times of injection of labelled precursor, quantitative and qualitative patterns of collagen crosslinking were very similar at all of the lung developmental stages studied. Furthermore, there was little or no breakdown of the lung collagen pool as defined by the presence of labelled crosslinks; changes in lung DHLNL content could be completely accounted for by its maturation to OHP, regardless of the age of the rats when injected with the radioactive precursor. We conclude that mature, crosslinked collagen in the lungs of rats, which is obligatorily an extracellular pool, is not being degraded at a measurable rate. Therefore, studies of others that have shown apparent high rates of breakdown of newly synthesized collagen in lungs of whole animals using different methods are probably not reflective of the metabolic fate of total lung collagen, and may indicate that degradation of normal lung collagen occurs predominantly or exclusively intracellularly.

Animals↗