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Biomedical subjects

D F Parker

Publications and source records attributed to D F Parker.

16 recordsLinked to original sources
PubMed2005

Existence and stability of accelerating solitons in sliding-frequency filter systems.

Sliding-frequency filter systems are known to admit two families of accelerating solitons: high-amplitude and low-amplitude families. Such equilibrium solutions are computed here, for a wide range of filter strengths, as self-similar solutions having Airy function asymptotics. In a limited parameter region, the profile possesses a secondary small hump. The high-amplitude solitons are found to be stable over a region of parameter space which is here determined by the Evans function method, adjusted to Airy function asymptotics. The loss of stability is due to a Hopf bifurcation.

Journal Article↗
PubMed2003

Stability of screening solitons in photorefractive media.

Normal mode stability of both rectilinear and self-bending photorefractive screening solitons is considered. In each case, the Evans function procedure is used to investigate stability and to search for internal modes. For the rectilinear case, a standard Evans function procedure is applied. However, in the self-bending case the asymptotic form of the eigenvalue problem is a system of Airy equations, instead of the usual system of constant coefficient differential equations. To overcome this difference, a modified version of the Evans function method, using Airy functions rather than exponentials, is implemented and applied. The results confirm stability and give an internal mode pattern in good agreement with full numerical integration.

Journal Article↗
PubMed2002

Accelerating solitons for sliding-frequency filter systems.

The sliding-frequency filter equation is shown to have similarity solutions which travel with steady profile but with constant acceleration. Over a wide range of the gain, filter strength and sliding-rate parameters, the pulse envelope is very well approximated by a sech profile. However, when the sliding rate is large, the chirp differs greatly from the usually assumed linear variation of frequency through the pulse. The amplitude and chirp are found for small and moderate sliding rate by a perturbation analysis and, for larger sliding rates, by solving a nonlinear eigenvalue problem for a nonautonomous differential equation.

Journal Article↗
PubMed1993

Muscle performance and gross motor function of children with spastic cerebral palsy.

The purpose of this study was to determine whether, and to what extent, performance on a measure of motor function (Gross Motor Function Measure, GMFM) was related to the physiological fitness of children with cerebral palsy (CP). Two elements of physiological function were measured: aerobic power and anaerobic power of the arms and legs. 15 boys and eight girls aged between seven and 13.9 years with spastic CP participated in the study. There was a good relationship between the standing and walking, running and jumping sub-sections and the total score of the GMFM on one hand, and anaerobic capacity of the legs on the other. However, the relationships for the arms were limited, indicating that the GMFM is not a suitable tool for providing information about aerobic fitness in children with CP, or about anaerobic power of the arms.

Adolescent↗
PubMed1992

Anaerobic endurance and peak muscle power in children with spastic cerebral palsy.

The aim of this study was to provide information on anaerobic muscle endurance (mean power) and peak muscle power in children with spastic cerebral palsy. We measured peak power and mean power of the upper and lower limbs in 29 boys and 20 girls, aged from 6 to 14 years, by means of the Wingate Anaerobic Test. In addition, the physical components (physical capacity, upper limb, and lower limb) of a system used for evaluating function in the physically disabled were assessed. Of the 49 subjects, 46 and 37 successfully completed the arm and leg Wingate Anaerobic Test, respectively. Compared with norms for age and gender (healthy, nonathletic children), peak and mean power in the patients, even when corrected for body weight, were distinctly subnormal. The performance of subjects with quadriplegia was 3 to 4 SDs below the mean for controls. Twenty-five of diplegic and hemiplegic subjects had values below 2 SDs. When the data were analyzed according to the severity of the cerebral palsy, with the use of the physical capacity, upper limb, and lower limb score, those children with moderate to severe cerebral palsy had values for mean and peak power of the arm and leg 3 to 4 SDs below the normal mean. Values for children with only mild cerebral palsy also fell below the mean, but the data were more scattered, especially for the leg. The lower muscle performance may reflect both quantitative and qualitative differences in the upper- and lower-limb muscles, due to altered innervation and, in the more severely affected children, disuse.

Adolescent↗
PubMed1989

Physiological changes in skeletal muscle as a result of strength training.

The picture of training that emerges is of a process that can be divided into a number of phases. In the first phase there is a rapid improvement in the ability to perform the training exercise such as lifting weights which is the result of a learning process in which the correct sequence of muscle contractions is laid down as a motor pattern in the central nervous system. This phase is associated with little or no increase in the size or strength of individual muscles. The learning process appears to be very specific in that lifting weights makes better weight lifters but not better sprinters. The second phase is an increase in the strength of individual muscles which occurs without a matching increase in the anatomical cross-section. The mechanism for this is not clear but could be a result of increased neural activation or some change in the fibre arrangement or connective tissue content. The third phase starts at a point where scientific studies usually end, at about 12 weeks when non-athletic subjects are beginning to tire of the repeated training and testing. After this point, if training continues, there is probably a slow but steady increase in both size and strength of the exercised muscles. The stimulus for these changes remains enigmatic but almost certainly involves high forces in the muscle, probably to induce some form of damage that promotes division of satellite cells and their incorporation into existing muscle fibres. Our information on the effect of long-term training comes primarily from observations on elite athletes whose physique may well be the result of genetic endowment or the use or abuse of drugs. For the athlete or patient hoping to increase muscle size by weight training the best combination of intensity, frequency and type of exercise still remains a matter of individual choice rather than a scientific certainty.

Humans↗
PubMed1988

Changes in strength and cross sectional area of the elbow flexors as a result of isometric strength training.

Changes in strength and size of the elbow flexor muscles have been compared during six weeks of isometric strength training in six male and six female subjects. Isometric training of one arm resulted in a significant increase in isometric force (14.5 +/- 5.1%, mean +/- SD, n = 12). No differences were seen in the response of male and female subjects. The extent of the change was similar to that reported for training studies of other muscles, thus refuting the suggestion that the elbow flexors may be especially amenable to training. Biceps and brachialis cross-sectional area (CSA) was measured from mid-upper arm X-ray computerized tomography before and after training. Muscles increased in area (5.4 +/- 3.8%) but this was smaller than, and not correlated with, the increase in strength. The main change in the first six weeks of strength training was therefore an increase in the force generated per unit cross-sectional area of muscle. The arrangement of fibres in the biceps is nearly parallel to the action of the muscle and it is argued that the increase in force per unit cross-sectional area is unlikely to be due to changes in the pennation of the muscle fibres as has been suggested for other muscles.

Adult↗
PubMed1988

The Association for Clinical Pastoral Education.

ACPE has developed over a sixty year period. If has undergone several major changes through the years. The changes have challenged members to move into new organizational structures, face issues of inclusiveness with openness, and develop new centers in a variety of settings. COMISS is viewed as another new challenge and opportunity.

Humans↗
PubMed1987

Appropriateness of antibiotic therapy in long-term care facilities.

The objective of this study was to examine the appropriateness of antibiotic therapy in nursing homes. Information was abstracted from infection control reports and patients' charts for a three-month period at two nursing homes in Portland, Oregon. A panel of two board-certified infectious disease specialists and one hospital pharmacist reviewed the information and rated the appropriateness of each prescription using a previously developed scale. Among the 120 infections, treatment was rated as appropriate in 49 percent, as inappropriate in 42 percent, and as unjustified in 9 percent. Cephalosporins received the lowest percent of appropriate ratings (27 percent). The primary reason for an inappropriate rating was that a more effective drug was recommended for empiric therapy of gram-negative bacillary infections. These bacteria are often resistant to oral antibiotics. There were no significant differences in appropriateness by type of organism, infection site, or clinical outcome. Physician education and the development of systems and guidelines for optimal management in this population are appropriate actions for the future.

Aged↗
PubMed1987

Cardiopulmonary resuscitation in long-term care facilities: a survey of do-not-resuscitate orders in nursing homes.

Growing public debate regarding no cardiopulmonary resuscitation (no-CPR) policies in acute care hospitals, together with recent changes in the patient population of long-term care facilities, has led nursing homes to examine their need for resuscitation policies. To determine current cardiopulmonary resuscitation policies and procedures in nursing homes, medical directors and directors of nursing service in long-term care facilities in Portland, Oregon, were surveyed. Seventy-five percent responded; of these, only 41% reported having a resuscitation policy. Of those with no policy, 70% thought one was needed. Most nursing homes reported that resuscitation was infrequently discussed with patients and families. When a no-CPR determination was made, it was usually documented in the patient's chart. Training in basic life support was required for registered nurses in two thirds of the facilities. Few homes had equipment necessary for advanced life support. It is recommended that: a) nursing homes develop cardiopulmonary resuscitation policies; b) resuscitation orders be made part of the medical record; and c) nursing home personnel increase their ability to perform basic life support.

Aged↗
PubMedDate not supplied

The effect of resident involvement on community hospital charges.

Attempts to explain the high cost of care in teaching hospitals have yielded conflicting results. This study was conducted to compare hospital charges and lengths of stay for two groups of patients: one cared for by a resident team and the other cared for by attending physicians. The study was conducted at a university-affiliated hospital in Portland, Oregon. An initial group of 5,451 admissions was examined, considering type of doctor (resident or attending), severity of illness, and patient demographic characteristics. A regression analysis revealed that total charges were similar in the two groups, but only 14% of the variance in log total charges was explained. A subgroup of 1,058 admissions in the eight most common diagnosis-related groups (DRGs) was further evaluated. In this analysis total charges for the resident patient group were 52% higher than charges for the patient group cared for by attending physicians. Forty-one per cent of the variance was explained, with type of doctor and severity of illness accounting for 5% and 10%, respectively. Further examination of one DRG indicated that additional factors not included in previous studies, such as extent of preadmission evaluation, ethical factors influencing treatment options, and patient expectations for care, may be important determinants of hospital charges. This study demonstrates that the high cost of resident care is not fully explained by currently available measures.

Diagnosis-Related Groups↗
PubMedDate not supplied

A cross-sectional survey of upper and lower limb strength in boys and girls during childhood and adolescence.

Changes in height and weight during childhood and adolescence are well documented, yet there is comparatively little comprehensive information about muscular development during this time. In a cross-sectional survey standing height, body weight and isometric strength of the elbow flexor and quadriceps muscles have been measured in 267 boys and 284 girls aged from 5 to 17 years. All the children were from private London schools. The mean heights and weights for each age group were between the 50th and 75th centiles for British children. The strength of both muscle groups in the boys and girls rose steadily in each age group from 8 to 12 years, after which there was a rapid increase in strength of both the quadriceps and elbow flexors in boys which continued even when growth in height and body weight had virtually ceased. In the pre-adolescent phase of growth, muscle strength of the elbow flexors and quadriceps increased as a function of height squared and cubed respectively, suggesting that stretch as a result of elongation of the long bones, and for the quadriceps, loading, may be the primary stimuli during this phase. In the postpubertal phase some other stimulus, such as a direct action of hormones on the muscle, must be responsible for the continued increase in strength in the boys.

Adolescent↗