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Biomedical subjects

P Walker

Publications and source records attributed to P Walker.

At least 307 records · Page 17Linked to original sources

Neurologic profiles of infants and children after perinatal stroke.

Twenty-nine children with a single, unilateral cerebral infarct acquired pre- or perinatally were examined subsequently for an average of 43 months. No consistent pre- or perinatal events were identified to explain the occurrence of the stroke. The children acquired motor milestones at nearly expected times, even in the presence of hemiparesis. In children older than 2 years of age, I.Q. scores all were within the normal range. More than one-half of the children experienced seizures at some time during the follow-up period. Good intellectual and functional motor outcome can be expected in children with isolated perinatal stroke.

Cerebral Infarction↗

Pathology of the liver, kidney and gonad of flounder (Platichthys flesus) from a UK estuary impacted by endocrine disrupting chemicals.

The Mersey estuary is highly contaminated with xenobiotics compared to the nearby Dee estuary. Male flounder, a migratory flatfish caught in the Mersey frequently contains high blood concentrations of the oestrogen controlled, female protein vitellogenin, suggesting that Mersey flounder have been exposed to endocrine disrupting contaminants. Males caught from the Dee contain lower blood vitellogenin levels. Preliminary histopathological examination of 410 flounder from both estuaries, focuses on the liver, kidney and gonads. Hepatic tubular vacuolation, foci of cellular alteration, and hepatocellular tumours were seen. Renal and gonadal pathology included the presence of two Mersey fish with enlarged and abnormal glomeruli, three phenotypic male Mersey flounder with unilateral intersex gonads and one male with bilateral, abnormal ovarian follicular components in the testis. These initial results provide pathological evidence of xenobiotic exposure in flounder sampled from both estuaries. Preliminary findings from flounder sampled from Millport, an offshore site in Southwest Scotland, showed no histopathological evidence of xenobiotic exposure.

Animals↗

[Spectroscopy of phosphorus in nuclear magnetic resonance. General review of clinical applications to the study of human skeletal muscle].

Phosphorus nuclear magnetic resonance spectroscopy enables the energy metabolism of skeletal muscles to be studied non-invasively in vivo. Relative concentrations of phosphocreatine (PCr), inorganic phosphate (iP), monophosphoric sugars (mP) and ATP, as well as intracellular pH values, are directly accessible through the spectra. The striated muscle is continuously studied at rest, during exercise and during recovery. Exercise-induced changes in pH and mP provide indirect information on glycogenolysis and glycolysis. The speed of PCr resynthesis during post-exercise recovery and the PCr/iP ratio values at rest excellently reflect mitochondrial oxidative phosphorylations. Phosphorus NMR spectroscopy therefore is of interest not only to study the impact, through hypoxia, on muscle energy metabolism of such pathologies as cardiac or respiratory failure, or to study various acquired metabolic muscular diseases, but also and above all, to detect and locate muscular enzyme deficiencies involving glycogenolysis, glycolysis or mitochondrial metabolism, thereby pointing to the diagnosis of congenital, and mainly metabolic, myopathies.

Energy Metabolism↗

The use of image processing in the investigation of artificial heart valve flow.

A circulation model enlarged ten times with a likewise enlarged model of the artificial heartvalve leads to a very slow motion of the fluid. Many methods of flow visualization can therefore be applied. The particle method has been chosen as the most appropriate for further processing. The flow is videotaped, two consecutive frames are selected and with the help of image processing the vector field, the streamlines and the velocity profiles are computed and drawn.

Blood Flow Velocity↗

Relationship between increased peak oxygen uptake and modifications in skeletal muscle metabolism following rehabilitation after myocardial infarction.

PURPOSE: Rehabilitation after myocardial infarction produces an increased peak oxygen uptake (VO2peak). This study investigates the relationship between the modifications in skeletal muscle metabolism and the modification in VO2peak induced by a standard program of physical training following a myocardial infarction. METHODS: Seventeen patients (14 male, 3 female) were studied by phosphorus 31(31P) magnetic resonance spectroscopy after the acute phase of a myocardial infarction and after 2 months of rehabilitation. Changes in calf muscle pH, phosphocreatine, and inorganic phosphates were measured at rest and during a plantar flexion-type incremental workload protocol. Calf muscle pH, phosphocreatine/(phosphocreatine + inorganic phosphates), and inorganic phosphates/phosphocreatine ratios were compared at the highest identical workload attained in both studies. The VO2peak (mL/kg/min) was determined during a cycle stress test. RESULTS: At the highest identical workload attained in both tests, the ratio phosphocreatine/(phosphocreatine + inorganic phosphates) was significantly higher (0.48 +/- 0.15 to 0.57 +/- 0.18: P < .001), and the ratio inorganic phosphates/phosphocreatine was lower (1.38 +/- 1.14 to 0.99 +/- 0.87: P < .01). After rehabilitation, no difference was observed for the pH at stress (6.83 +/- 0.16 to 6.91 +/- 0.14: not significant [NS]). The increase in the VO2peak was significant after rehabilitation (24 +/- 9 to 29 +/- 11 mL/kg/min: P < .001). The VO2peak improvement induced by the physical training was correlated with the increase in the phosphocreatine/(phosphocreatine + inorganic phosphates) (r = 0.818, P < .001). CONCLUSIONS: The reduction in phosphocreatine depletion indicated that the oxidative capacity of the skeletal muscle was improved during the rehabilitation. The good correlation between the indexes of skeletal muscle metabolism and VO2peak suggests the peripheral effect of training.

Adaptation, Physiological↗

Effects of low-frequency electrical stimulation of quadriceps and calf muscles in patients with chronic heart failure.

PURPOSE: The aim of this preliminary study was to evaluate the effects of low-frequency electrical stimulation of quadriceps and calf muscles on global exercise capacities, skeletal muscle metabolism, calf muscle volume, and cardiac output in patients with chronic heart failure. METHODS: Fourteen patients with chronic heart failure (mean age of 56.4 years +/- 9.1 SD; mean radionuclide left ventricular ejection fraction of 22.3% +/- 8.8 SD) underwent 5 weeks (1 hour per day, 5 days per week) of low-frequency electrical stimulation of quadriceps and calf muscles. RESULTS: Low-frequency electrical stimulation was well tolerated. Exercise capacity and the calf muscles volumes increased significantly after rehabilitation in comparison with prior rehabilitation (the peak oxygen consumption increased from 17.2 mL/(kgmin) +/- 5.3 SD to 19.6 mL/(kgmin) +/- 5.9 SD; the anaerobic threshold increased from 12.3 mL/(kgmin) +/- 3.2 SD to 15.2 mL/(kgmin) +/- 3.3 SD; the 6-minute walking test increased from 419 m +/- 122 SD to 459 m +/- 114.3 SD; the gastrocnemius volume increased from 259.4 cm3 +/- 58 SD to 273.4 cm3 +/- 74 SD, and the soleus volume increased from 319 cm3 +/- 42.9 SD to 338 cm3 +/- 52.5 SD). The New York Heart Association class was improved after rehabilitation. The P-31 nuclear magnetic resonance spectroscopy of gastrocnemius muscle data were not significantly modified after rehabilitation, thereby inferring that no significant improvement of the muscle metabolism occurred. These data reinforce the hypothesis of an increased muscle mass during stimulation. It is noteworthy that the electrical stimulation did not increase cardiac output at any stage; an enormous asset in favor of this mode of rehabilitation. CONCLUSION: These results suggest that low-frequency muscular electrical stimulation is well tolerated, induces an increased exercise capacity in patients with chronic heart failure, without an undesirable increase in cardiac output.

Cardiac Output↗

In vitro structural properties of braided tendon grafts.

In an effort to increase strength in hamstring tendon grafts for anterior cruciate ligament reconstruction, braiding or weaving of the tendons has been suggested. The purpose of this study was to examine the biomechanical properties of two braiding techniques compared with a four-stranded tendon graft using a sheep model. Digital extensor tendons from 5 adult sheep were harvested in 28 matched pairs and randomly allocated to French plait or four-stranded weave. The grafts were tested in a hydraulic testing machine with the tendons secured in brass grips frozen with liquid carbon dioxide. The tendons were preconditioned to a distraction of 1 mm for 10 cycles followed by testing to failure at 50 mm/sec, with a data acquisition rate of 1,000 Hz. The stiffness, ultimate load to failure, and the mode of failure were recorded. All braided samples failed at the midsubstance, while the four-stranded controls failed at the grip interface. There was a significant reduction in strength and stiffness of the braided samples compared with the controls. This study demonstrated that braiding decreases the strength and stiffness of a four-stranded tendon graft by up to 54% and 85%, respectively. This finding is supported by the work of Hearle et al. (1969), who demonstrated that the decrease in strength of fiber bundles is equal to the square of the cosine of the twist angle. The twist angle in our samples was approximately 45 degrees, which equates to a decrease in strength of 50%.

Analysis of Variance↗

Biomechanical performance of Bankart repairs in a human cadaveric shoulder model.

The objective of this study was to develop a method to evaluate the biomechanical performance of Bankart repairs in a human cadaveric shoulder in a clinically relevant orientation. Twenty fresh-frozen human cadaveric shoulder girdles were used to compare the biomechanical performance of intact anteroinferior capsulolabral complexes with the biomechanical performance of three Bankart lesion reconstruction techniques. Repairs were performed on surgically created Bankart lesions. Evaluations were performed with the shoulders in glenohumeral abduction and external rotation. The repair techniques employed interosseous sutures, Mitek GII suture anchors, or Acufex T-Fix devices. The suture material used in all repairs was No. 2 Ti-Cron. The biomechanical performance of the three reconstruction techniques did not differ, but each was significantly inferior compared with that of the intact shoulder samples. The interosseous repairs failed by suture pullout through soft tissue. Repairs in the Mitek GII group failed by pullout of the suture anchors, suture breakage, or pullout of the suture through soft tissue. Repairs in the T-Fix group failed by pullout of the suture through soft tissue or failure of the polymer portion of the T-Fix suture.

Biomechanical Phenomena↗

Collaborating with congregations: opportunities for financial services in the inner city.

In all economies, financial systems perform a basic set of functions, which include the need to pool resources, to save and borrow, to make payments, and to collect information. And yet, in rich and poor communities, the ways in which those needs are met differ greatly. In part, this is because traditional financial service firms have found it too expensive to serve poor neighborhoods. But it is possible to work with less traditional institutions to meet those needs. According to the authors, inner cities face two core impediments to financial services: lack of economies of scale and lack of good information. An inner-city investor with $500, for instance, does not warrant much attention from financial service firms. But 20,000 parishioners investing $500 apiece can collectively wield $10 million. By partnering with strong social organizations such as churches, financial institutions can benefit both themselves and investors. A lack of good information concerning credit histories--a common problem in poor communities--also makes low-income customers much less appealing to financial institutions. Churches can help close such information gaps by vouching for parishioners' reliability. There are certainly problems that come with mixing business and religion, as the authors concede. Ethical issues, trust issues, and issues of experience all come to mind. But understanding that functions need to dictate the structure of the financial service sector may be the first step toward achieving inner-city prosperity.

Capital Financing↗

Participation of the complement system in ischemia/reperfusion injury.

Reperfusion of ischemic skeletal muscle is associated with an early infiltration of WBC, a process mediated by locally generated chemotactic factors. We present evidence that selective activation of the alternative complement cascade occurs in response to skeletal muscle ischemia/reperfusion injury. Complement activation may result in the generation of peptides which are chemotactic for neutrophils, and the formation of molecular complexes which injure cell membranes.

Animals↗