Provident associations and medical fees.
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Fees, Medical↗
Biomedical subjects
P K Davis
Publications and source records attributed to P K Davis.
Anoxia-induced changes in extracellular K+ and pH in mammalian central white matter.
In gray matter (GM), anoxia induces prominent extracellular ionic changes that are important in understanding the pathophysiology of this insult. White matter (WM) is also injured by anoxia but the accompanying changes in extracellular ions have not been studied. To provide such information, the time course and magnitude of anoxia-induced changes in extracellular K+ concentration ([K+]o) and extracellular pH (pHo) were measured in the isolated rat optic nerve, a representative central WM tract, using ion-selective microelectrodes. Anoxia produced less extreme changes in [K+]o and pHo in WM than are known to occur in GM; in WM during anoxia, the average maximum [K+]o was 14 +/- 2.9 mM (bath [K+]o = 3 mM) and the average maximum acid shift was 0.31 +/- 0.07 pH unit. The extracellular space volume rapidly decreased by approximately 20% during anoxia. Excitability of the rat optic nerve, monitored as the amplitude of the supramaximal compound action potential, was lost in close temporal association with the increase in [K+]o. Increasing the bath glucose concentration from 10 to 20 mM resulted in a much larger acid shift during anoxia (0.58 +/- 0.08 pH unit) and a smaller average increase in [K]o (9.2 +/- 2.6 mM). The increased extracellular glucose concentration presumably provided more substrate for anaerobic metabolism, resulting in more extracellular lactate accumulation (although not directly measured) and a greater acid shift. Enhanced anaerobic metabolism during anoxia would provide energy for operation of ion pumps, including the sodium pump, that would result in smaller changes in [K+]o. These effects were probably responsible for the observation that the optic nerve showed significantly less damage after 60 min of anoxia in the presence of 20 mM glucose compared to 10 mM glucose. Under normoxic conditions, increasing bath K+ concentration to 30 mM (i.e., well beyond the level shown to occur with anoxia) for 60 min caused abrupt loss of excitability during the period of application but minimal change in the amplitude of the compound action potential following the period of exposure. The anoxia-induced increase in [K+]o, therefore, was not itself directly responsible for irreversible loss of optic nerve function. These observations indicate that major qualitative differences exist between mammalian GM and WM with regard to anoxia-induced extracellular ionic changes.
Action Potentials↗
Promoting stimulus control with textual prompts and performance feedback for persons with mild disabilities.
We assessed whether written task analyses would serve as textual prompts for performing functional tasks by persons with mild disabilities. Several variables that could influence the effectiveness of textual prompts to promote stimulus control were examined across four groups. A consistent finding was that written specific task analyses combined with end-of-trial performance feedback were effective for promoting the acquisition and generalization of several tasks. Performance transferred immediately to natural discriminative stimuli when the written task analyses and feedback were withdrawn for most tasks and participants. For 2 participants, transfer of stimulus control was accomplished by prompt fading, using individualized written task analyses either with or without performance feedback (Group 1). When feedback was not provided, the effectiveness of written specific task analyses was inconsistent across groups. In contrast to the controlling effects of written specific task analyses, written generic task analyses, which specified only major task outcomes, when combined with performance feedback (Group 1) did not control responding. Overall, this research demonstrated the effectiveness of written specific task analyses and performance feedback to promote stimulus control for persons with mild disabilities.
Activities of Daily Living↗
Intravascular plastic catheters. How they potentiate tumor necrosis factor release and exacerbate complications associated with sepsis.
We tested the hypothesis that long-term intravascular cannulation exacerbates the harmful effects of an infectious challenge. Four groups of rats were initially studied: rats without intravascular catheters or infection (group 1), rats without catheters with a polymicrobial infection (group 2), rats with catheters but no infection (group 3), and rats with catheters and infection (group 4). Infected animals had an increased mortality and generated a significantly increased tumor necrosis factor response compared with noninfected animals. Animals with catheters and infection generated far less cardiac output than animals from the other three groups. No histologic changes differentiated the four groups. Therefore, the presence of a sterile intravascular catheter significantly increases cardiac dysfunction and mortality rates in rats with chronic bacteremia. These results suggest that intravascular plastic catheters potentiate the destructive cascade of events produced by the host in response to bacteremia.
Abscess↗
Complications and long-term results following abdominoplasty: a retrospective study.
A 6-year retrospective series of 133 abdominoplasties was studied and type and incidence of complications are presented. From this series a group of 34 patients was re-examined between 4 and 10 1/2 years postoperatively and conclusions were made from this long-term follow-up. A high incidence of injury to the lateral cutaneous nerve of the thigh was recorded. A blood transfusion was required in 19% of the cases, the average hospitalisation was 12.4 days and the complication rate ranged between 24% in those who did not attend review and 65% in those who were re-examined. Objectively judged, 55% of the patients had excellent or good results, but subjective patient satisfaction was nearly 90%.
Abdominal Muscles↗
Pain and forehead expansion.
Tissue expansion of the forehead by intermittent bolus injection in three patients was noted to be extremely painful. This stimulated a prospective study in four patients whose discomfort was found to be related to a sharp rise in intraluminal pressure after bolus inflation. Tolerable infusion volumes were small (mean 6.25 cc) and associated with high pain scores (mean 7/10). Adequate expansion was protracted (mean 45 1/2 days) and was limited by pain. To eliminate the sharp rises in pressure associated with expansion by bolus injection, a syringe pump was used in two further inpatients. Adequate expansion was both quicker (mean 8.5 days) and less painful (mean pain score 2.6/10).
Aged↗
Cumulative and interspersal task sequencing in self-paced training for persons with mild handicaps.
The effectiveness of cumulative and interspersal task sequencing of self-paced instruction was evaluated. Young adults with mild disabilities were taught savings account, bill paying, and money order skills. A self-paced workbook, with its content sequenced in either a cumulative or interspersal format, was used to provide instruction. Ten participants were randomly assigned to each of the two sequencing conditions. Results showed that both task-sequencing methods produced statistically significant and comparable improvements in performance. Gains maintained on 1-week and 1-month follow-ups. Cumulative and interspersal sequencing appear to be equally suitable for teaching complex monetary skills in a self-paced format.
Activities of Daily Living↗
Anoxic injury of mammalian central white matter: decreased susceptibility in myelin-deficient optic nerve.
The rat optic nerve, a typical central nervous system white matter tract, rapidly loses excitability when it is exposed to anoxia and is irreversibly damaged by prolonged anoxia. Neonatal optic nerve is extremely resistant to anoxia-induced dysfunction and injury; the adult pattern of response to anoxia appears between 10 and 20 days postnatal, that is, during the period of oligodendroglial proliferation and myelination. To test the hypothesis that myelination, or associated events, confer anoxic susceptibility on developing white matter, we analyzed the effects of anoxia on the myelin-deficient (md) strain of rat. Acutely isolated optic nerves from 19- to 21-day-old md rats and control optic nerves from unaffected male littermates were maintained in vitro at 37 degrees C, and exposed to a standard 60-minute period of anoxia. The supramaximal compound action potential was recorded and amplitude of the compound action potential, expressed as % of amplitude before anoxic exposure, was determined. The compound action potential was nearly abolished within 3 to 6 minutes after onset of anoxia in control optic nerves, while optic nerves from md rats displayed a slower decrease in compound action potential amplitude during anoxia, with a distinct action potential present even after 60 minutes of anoxia. Optic nerves from md rats showed significantly greater recovery of compound action potential (71 +/- 25%) than did control optic nerves (33 +/- 21%; p less than 0.02) after 60 minutes of anoxia. These findings support the hypothesis that myelination, or changes associated with it, may be important in the development of anoxic susceptibility in central white matter.
Action Potentials↗
Role of extracellular calcium in anoxic injury of mammalian central white matter.
White matter (WM) of the mammalian brain is susceptible to anoxic injury, but little is known about the pathophysiology of this process. We studied the mechanisms of anoxic injury in WM using the isolated rat optic nerve, a typical central nervous system WM tract. Optic nerve function, measured as the area under the compound action potential, rapidly failed when exposed to anoxia and recovered to 28.5% of control after a standard 60-min period of anoxia. Irreversible anoxic injury was critically dependent on the molar concentration of extracellular calcium [( Ca2+]o); maintaining the tissue in Ca2(+)-free solution throughout the anoxic period resulted in 100% compound action potential recovery. Increasing perfusion [Ca2+] during anoxia from zero to 4 mM resulted in progressively less recovery. As the introduction of the Ca2(+)-free solution was progressively delayed with respect to the onset of anoxia, a graded decrease in recovery of function was observed, suggesting that in WM the deleterious effects of Ca2+ accumulate slowly during anoxia. At the time of reoxygenation, an additional stepwise increase in injury was observed that was also Ca2(+)-dependent. Mammalian WM, which is relatively resistant to anoxic injury compared with gray matter, is damaged by anoxia in a manner that appears to depend on the gradual accumulation of Ca2+ in a cytoplasmic compartment.
Action Potentials↗
Anoxic injury of CNS white matter: protective effect of ketamine.
Gray and white matter of the mammalian CNS are both damaged by anoxia. Anoxic injury in gray matter is mediated in part by excessive accumulation of excitotoxins like glutamate. Drugs such as ketamine, a dissociative anesthetic known to block glutamate (NMDA) receptors, reduce hypoxic neuronal injury in gray matter. In this study we used the isolated rat optic nerve preparation to determine if ketamine influences recovery after anoxia in a nonsynaptic system, ie, CNS white matter. Optic nerves from adult rats were exposed to a standard 60-minute period of anoxia. Ketamine (1 mM) improved recovery of the compound action potential (CAP) after anoxia. Since glutamate and aspartate (up to 10 mM) had no effect on CAP amplitude in the optic nerve, the effect of ketamine is probably not mediated by NMDA receptor blockade. These observations indicate that ketamine is able to protect CNS white matter, as well as gray matter, from anoxic injury.
Action Potentials↗
A personalized system of instruction for teaching checking account skills to adults with mild disabilities.
This study evaluated the efficacy of a personalized system of instruction to teach checking account skills to persons with mild disabilities. Using a self-paced manual, 8 participants in two groups were taught to write checks, complete deposit slips, and reconcile monthly bank statements. Four participants were assessed for generalization from the classroom to community sites and demonstrated nearly perfect performance. A multiple probe design showed that acquisition occurred sequentially for each skill only after training using the self-paced manual. Follow-up sessions demonstrated that participants maintained the checking account skills. The results provide evidence of the effectiveness and adaptability of a personalized system of instruction for teaching complex monetary skills to persons with mild disabilities.
Adolescent↗
Current status of permanent total artificial hearts.
Pneumatic total artificial heats, although demonstrating utility as temporary mechanical circulatory support devices, have not demonstrated a great deal of promise as permanent cardiac replacements. The increasing number of patients who would be candidates for total heart replacement suggests a large role for a permanent implantable total artificial heart. To that end, the Pennsylvania State University is developing an electric motor-driven total artificial heart; the results with implants in calves are encouraging. In this device, a roller-screw mechanism is used to translate the rotation of a brushless direct-current motor into rectilinear motion of a pusher-plate assembly, which in turn empties the blood sacs. The total artificial heart of the future will function under automatic control without percutaneous leads, and this should provide the patient with a nearly normal life-style. Although further experimental efforts are necessary to prepare the device for clinical trials, the technology to provide a safe and reliable electric blood-pump system is at hand.
Animals↗
Mortality of coronary artery bypass grafting before and after the advent of angioplasty.
In an effort to determine whether the population of patients undergoing isolated coronary artery bypass grafting and the outcome of these operations have changed, we analyzed the records of two patient populations from our institution. Interventional cardiology techniques (angioplasty, thrombolysis) were not used at our institution before 1982. The records of 736 patients (group 1) who underwent isolated coronary artery bypass grafting from January 1975 to July 1981 were reviewed and compared with a group of 603 patients (group 2) who underwent operation from July 1985 to December 1987. The techniques of operation and myocardial preservation were virtually identical during the two periods. During the group 2 analysis period, 343 angioplasty procedures were performed. The patients in group 2 were significantly older, had increased preoperative New York Heart Association classification, had sustained more previous myocardial infarctions, and had more associated morbid medical conditions. There was a threefold increase in patients seen for reoperative revascularization procedures and a fourfold increase in emergency operations. Overall mortality, although not significantly different, did increase slightly from 2.69% in group 1 to 3.83% in group 2. Mortality after elective procedures remained essentially unchanged (2.05% for group 1 and 1.90% for group 2).
Aged↗
Toward an implantable artificial heart. Experimental and clinical experience at The Pennsylvania State University.
The number of patients who would be candidates for replacement of their failing native heart with an artificial device increases every year. A multidisciplinary group at The Pennsylvania State University is working toward the development of a reliable, totally implantable artificial heart. Initial work resulted in a pneumatic total artificial heart that has performed well in animal implants and has been used clinically in three patients as a temporary bridge to cardiac transplantation. Although pneumatic total artificial hearts have demonstrated utility as temporary mechanical circulatory support devices, attempts at permanent implantation by other groups have been fraught with complications. Because of the suboptimal performance of the pneumatic devices used for permanent implantation, the authors' groups at Penn State is developing n electric motor-driven total artificial heart with encouraging results in calf implants. This artificial heart of the future will use a transcutaneous energy transmission system that will obviate the need for percutaneous lines. Thus, the patient will be provided with as near a normal life-style as possible. At present the technology is at hand to implant an electric blood pump system that should provide a reasonable life-style and function reliably with minimal care. Ongoing cooperative experimental efforts will help to provide the answers necessary to make this system ready for clinical use.
Animals↗
Systemic response to intralesional steroid therapy.
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Adult↗
Training self-advocacy skills to adults with mild handicaps.
We developed and empirically evaluated an instructional program to teach self-advocacy skills to eight young adults with mild handicaps. Participants were taught to discriminate whether or not possible violations of legal rights occurred in socially validated scenarios and, if so, to role-play how to redress rights violations. Experimental control was demonstrated with a multiple probe design across four general legal rights categories for the discrimination component of training, and a multiple probe across groups of subjects for the redressing legal rights component of training. Participants' behavior was probed in simulations and deceptions of legal rights violations in natural settings. There were marked increases in dependent measures after instruction. Difficulties in assessing generalization and maintenance of low-rate behaviors and suggestions for future research are presented.
Adult↗
Postoperative necrotizing fasciitis in children.
Necrotizing fasciitis is a rapidly progressive soft tissue infection, involving the skin, subcutaneous tissue, and superficial fascia. It is a rare but life-threatening complication in the postoperative patient. In the last 7 years, we have treated four children in whom necrotizing fasciitis developed after appendectomy for ruptured appendix, bilateral inguinal herniorrhaphy, or gastrostomy closure. These four patients and seven well-described children from the literature with necrotizing fasciitis following surgery form the basis of this review. The ages ranged from six days to 15 years (mean 4.5 years). There were eight boys and three girls. There were five clean, five clean-contaminated, and one contaminated surgical procedures. No patient had evidence of malignancy or diabetes. Two of our four patients had evidence of failure to thrive. Only one patient had an intraabdominal abscess. In ten, the infection started in the abdominal wall; in one, the infection started in the chest wall. In our four patients, three had neutropenia and fever, four had tachycardia, and two had wound crepitation and radiographic evidence of subcutaneous gas. Cultures of all ten wounds were positive for bacteria; six were positive for more than one organism. Blood culture results were positive in five of five patients who died and in only two of five patients who survived. All survivors had wide surgical debridement and were treated with broad-spectrum antibiotics. The mortality rate was 45% in the whole series.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent↗