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Biomedical subjects

L C Johnson

Publications and source records attributed to L C Johnson.

At least 19 recordsLinked to original sources
PubMed2002

Sustained stabilization of the resistive-wall mode by plasma rotation in the DIII-D tokamak.

Values of the normalized plasma pressure up to twice the free-boundary stability limit predicted by ideal magnetohydrodynamic (MHD) theory have been sustained in the DIII-D tokamak. Long-wavelength modes are stabilized by the resistive wall and rapid plasma toroidal rotation. High rotation speed is maintained by minimization of nonaxisymmetric magnetic fields, overcoming a long-standing impediment [E. J. Strait, Phys. Rev. Lett. 74, 2483 (1995)]]. The ideal-MHD pressure limit calculated with an ideal wall is observed as the operational limit to the normalized plasma pressure.

Journal Article↗
PubMed2002

Proportional assist ventilation as an aid to exercise training in severe chronic obstructive pulmonary disease.

BACKGROUND: The effects of providing ventilatory assistance to patients with severe chronic obstructive pulmonary disease (COPD) during a high intensity outpatient cycle exercise programme were examined. METHODS: Nineteen patients (17 men) with severe COPD (mean (SD) forced expiratory volume in 1 second (FEV(1)) 27 (7)% predicted) underwent a 6 week supervised outpatient cycle exercise programme. Ten patients were randomised to exercise with ventilatory assistance using proportional assist ventilation (PAV) and nine (two women) to exercise unaided. Before and after training patients performed a maximal symptom limited incremental cycle test to determine peak work rate (Wpeak) followed by a constant work rate (CWR) test at 70% of Wpeak achieved in the baseline incremental test. Minute ventilation (VE), heart rate, and arterialised venous plasma lactate concentration [La(+)] were measured before and after each test. RESULTS: Mean training intensity (Wt/Wpeak) at 6 weeks was 15.2% (95% CI 3.2 to 27.1) higher in the group that used ventilatory assistance (p=0.016). Peak work rate after training was 18.4% (95% CI 6.4 to 30.5) higher (p=0.005) in the assisted group (p=0.09). [La(+)] at an identical workload after training was reduced by 30% (95% CI 16 to 44) in the assisted group (p=0.002 compared with baseline) and by 11% (95% CI -7 to 31) (p=0.08 compared with baseline) in the unassisted group (mean difference 18.4% (95% CI 3.3 to 40), p=0.09). A significant inverse relationship was found between reduction in plasma lactate concentration (DeltaL) at an equivalent workload after training during the CWR test and Wt/Wpeak achieved during the last week of training (r=-0.7, p=0.0006). CONCLUSIONS: PAV enables a higher intensity of training in patients with severe COPD, leading to greater improvements in maximum exercise capacity with evidence of true physiological adaptation.

Aged↗
PubMed2002

Inspiratory muscle maximum relaxation rate measured from submaximal sniff nasal pressure in patients with severe COPD.

BACKGROUND: Slowing of the inspiratory muscle maximum relaxation rate (MRR) is a useful index of severe inspiratory muscle loading and potential fatigue and has been measured from the oesophageal pressure during sniffs in patients with chronic obstructive pulmonary disease (COPD). The purpose of this study was to investigate whether it is possible to measure MRR and detect slowing using sniff nasal pressure in patients with COPD and to investigate the relationship between sniff oesophageal and sniff nasal MRR. METHODS: Eight patients with severe COPD (mean FEV1 0.7 l; 26% predicted) were studied. Each subject performed submaximal sniff manoeuvres before and after walking to a state of severe dyspnoea on a treadmill. Oesophageal and gastric pressures were measured using balloon tipped catheters and nasal pressure was measured using an individually modelled nasal cast. MRR (% pressure fall/10 ms) was determined for each sniff and any change following exercise was reported as percentage of baseline to allow comparison of sniff nasal and oesophageal MRR. RESULTS: At rest the mean (SE) sniff Poes MRR was 7.1 (0.3) and the mean Pnasal MRR was 8.6 (0.1). At 1 minute following exercise there was a mean decrease in sniff Poes MRR of 33.7% (range 20.7-53.4%) and a mean decrease in sniff Pnasal MRR of 28.2% (range 8.1-52.8%). The degree of slowing and time course of recovery was similar, with both returning to baseline values within 5-10 minutes. A separate analysis of the sniff pressures using only the nasal pressure traces demonstrated a similar pattern of slowing and recovery. CONCLUSIONS: It is possible to detect slowing of the inspiratory muscles non-invasively using sniff nasal pressures in patients with COPD. This could be a useful technique with which to measure severe and potentially fatiguing inspiratory muscle loading, both in clinical settings and during exercise studies.

Aged↗
PubMed2001

Outcomes of a leadership intervention for a metropolitan fire department.

Poor leadership can contribute to job dissatisfaction and employees' "burnout." Perceived lack of leadership skills is also a source of stress for supervisors. This study evaluated the efficacy of a brief multicomponent leadership intervention provided for fire service supervisors in an urban fire department. Ratings by 51 line firefighters and 8 first-line supervisors documented improvements in their immediate supervisors' performance at 3 mo. postintervention. Self-reports by line firefighters also showed improvements in perceptions of their ability to attain career goals, which were sustained at 9 mo. postintervention. There were also improvements on certain stress related symptoms indices reported by the sample of firefighter supervisors at both the 3-mo. and 9-mo. follow-ups. No significant changes on any of these measures, obtained at comparable time points, were observed in a (nonequivalent) control sample of firefighters and their first-line supervisors in an "untreated" urban fire department.

Adult↗
PubMed2001

The community/privacy trade-off in supportive housing: consumer/survivor preferences.

Supportive housing for psychiatric consumers/survivors can range in form from dispersed apartments to group homes. This research asked: What form is more supportive, apartments or housing with common spaces? Is it privacy and normalcy or community and peer support that promote well-being? The literature is divided. This study convened a charrette for supportive housing residents to express their views. Some 20 supportive housing residents formed two teams, with one team producing a housing design based on the principle of privacy and the other team producing one based on the principle of community. Despite their differing terms of reference, the teams developed similar designs. The results reinforced the importance of both private and common spaces in supportive housing.

Adult↗
PubMed2000

Bone tumor dynamics: an orthopedic pathology perspective.

The diagnosis and classification of primary bone tumors remains as much a challenge today as it has for the last 80 plus years. Although pathology is invariably equated with the image of a diagnostic microscope, the vast majority of diagnoses are made grossly with the unaided eye, as are the tissue specimens selected for microscopic "confirmation." Radiologic studies, particularly plain radiographs, remain the gold standard in gross pathologic diagnosis of the skeleton. Today, confirmation and final classification continue as the pathologist's domain, but perhaps not for long, considering the evolving ancillary imaging techniques and progressive sophistication of magnetic resonance (MR) imaging. The bone tumor cases collected and compiled by Ernest Codman, M.D. during the second through fourth decades of this century formed the basis of the first tumor registry. The Codman Bone Sarcoma Registry demonstrated among other things the importance of radiographic/pathologic correlation, underscoring the reliability of a bone tumor's location, margin (host bone/tumor interface), periosteal reaction, and matrix patterns as an accurate guide to classification and likely future biologic behavior. "A General Theory of Bone Tumors," written by Lent C. Johnson nearly 50 years ago and published in the Bulletin of The New York Academy of Medicine (February 1953, second series, vol. 29, no. 2, pp. 164-171), provided a conceptual cellular approach to the understanding bone tumor dynamics reinforcing radiologic/pathologic correlation as a reliable diagnostic tool. At the time of Dr. Lent C. Johnson's death (1910-1998), he was literally working on an updated version of his original article, the latter of which is being reprinted as the core of this illustrated revision. Our continued experience with bone tumors over the past five decades has only served to validate, on a daily basis, the fundamental principles outlined in Johnson's original article. In like fashion, it is important to keep in mind that terminology and nomenclature has also evolved since 1953, despite a continued inability to achieve complete consensus.

Bone Neoplasms↗
PubMed1999

PTSD among bereaved parents following the violent deaths of their 12- to 28-year-old children: a longitudinal prospective analysis.

This study examined the prevalence of posttraumatic stress disorder (PTSD) among parents bereaved by the violent deaths of their 12- to 28-year-old children. A community-based sample of 171 bereaved mothers and 90 fathers was recruited by a review of Medical Examiner records and followed for 2 years. Four important findings emerged: Both parents' gender and children's causes of death significantly affected the prevalence of PTSD symptoms. Twice as many mothers and fathers whose children were murdered met PTSD caseness (full diagnostic) criteria compared with accident and suicide bereavement. Symptoms in the reexperiencing domain were the most commonly reported. PTSD symptoms persisted over time, with 21% of the mothers and 14% of the fathers who provided longitudinal data still meeting caseness criteria 2 years after the deaths. Parents who met caseness criteria for PTSD, compared with those who did not, were significantly different on multiple study variables. Both theoretical and clinical implications for the findings are discussed.

Adaptation, Psychological↗
PubMed1999

Changes in parents' mental distress after the violent death of an adolescent or young adult child: a longitudinal prospective analysis.

This study examined changes in bereaved parents' mental distress following the violent deaths of their 12- to 28-year-old children. A community-based sample of 171 bereaved mothers and 90 fathers was recruited by a review of medical examiner records. Data were collected 4, 12, and 24 months post-death. Repeated measures analysis of variance showed significant reductions in 8 of 10 measures of mental distress among mothers and 4 of 10 for fathers, with the most change for both genders occurring between 4 and 12 months post-death. During the 2nd year of bereavement, mothers' symptoms continued to decline, whereas fathers, who started out with less distress than mothers, reported slight increases in 5 of 10 symptom domains. Nonetheless, 2 years after the deaths, mothers' mental distress scores were up to 5 times higher than those of "typical" U.S. women and fathers' scores were up to 4 times higher than "typical" U.S. men. Of the 7 intervening variables examined, higher scores on self-esteem and self-efficacy predicted lower distress for both mothers and fathers 4, 12, and 24 months post-death. Repressive coping was predictive of distress among fathers. It was concluded that violent death bereavement has sustained, distressing consequences on parents of children who die as a result of accidents, homicides, and suicide.

Adaptation, Psychological↗
PubMed1999

Diaphragm electromyogram measured with unilateral magnetic stimulation.

The purpose of this study was to establish the phrenic nerve conduction time (PNCT) for magnetic stimulation and further assess the relatively new technique of anterior unilateral magnetic stimulation (UMS) of the phrenic nerves in evaluating the diaphragm electromyogram (EMG). An oesophageal electrode was used to record the diaphragm compound muscle action potential (CMAP) elicited by supramaximal percutaneous electrical phrenic nerve stimulation (ES) and UMS from eight normal subjects. The oesophageal electrode used for recording the CMAP was positioned at the level of the hiatus and 3 cm below. The diaphragm CMAP was also recorded from chest wall surface electrodes in five subjects. All of the phrenic nerves could be maximally stimulated with UMS. A clear plateau of the amplitude of the CMAP was achieved for the right and left phrenic nerves. The mean amplitudes of the CMAP recorded from the oesophageal electrode were, for the right side, 0.74+/-0.29 mV (mean+SD) for ES and 0.76+/-0.30 mV for UMS with maximal power output, and for the left side 0.88+/-0.33 mV for ES and 0.80+/-0.24 mV for UMS. PNCT measured by the oesophageal electrode with ES and UMS with maximal output were, for the right side, 7.0+/-0.8 ms and 6.9+/-0.8 ms, respectively, and for the left side 7.8+/-1.2 ms and 7.7+/-1.3 ms, respectively. However, the CMAP recorded from chest wall surface electrodes with UMS was unsuitable for the measurement of PNCT. The results suggest that unilateral magnetic stimulation of the phrenic nerves combined with an oesophageal electrode can be used to assess diaphragmatic electrical activity and measure the phrenic nerve conduction time.

Action Potentials↗
PubMed1998

Diaphragm EMG measured by cervical magnetic and electrical phrenic nerve stimulation.

The purpose of the study was to compare electrical stimulation (ES) and cervical magnetic stimulation (CMS) of the phrenic nerves for the measurement of the diaphragm compound muscle action potential (CMAP) and phrenic nerve conduction time. A specially designed esophageal catheter with three pairs of electrodes was used, with control of electrode positioning in 10 normal subjects. Pair A and pair B were close to the diaphragm (pair A lower than pair B); pair C was positioned 10 cm above the diaphragm to detect the electromyogram from extradiaphragmatic muscles. Electromyograms were also recorded from upper and lower chest wall surface electrodes. The shape of the CMAP measured with CMS (CMS-CMAP) usually differed from that of the CMAP measured with ES (ES-CMAP). Moreover, the latency of the CMS-CMAP from pair B (5.3 +/- 0.4 ms) was significantly shorter than that from pair A (7.1 +/- 0.7 ms). The amplitude of the CMS-CMAP (1.00 +/- 0.15 mV) was much higher than that of ES-CMAP (0.26 +/- 0.15 mV) when recorded from pair C. Good-quality CMS-CMAPs could be recorded in some subjects from an electrode positioned very low in the esophagus. The differences between ES-CMAP and CMS-CMAP recorded either from esophageal or chest wall electrodes make CMS unreliable for the measurement of phrenic nerve conduction time.

Action Potentials↗
PubMed1997

G-protein(S), G alpha q/G alpha 11, in the olfactory neuroepithelium of the channel catfish (Ictalurus punctatus) is altered by the herbicide, dichlobenil.

The immunohistochemical localization of G alpha q/G alpha 11 was studied in the olfactory neuroepithelium of the channel catfish. Antigenicity in the rosette was found at the apical surfaces of cells, within the apical neck regions of some cells, and within the area of the basal nerve tracts. Specific labeling was eliminated by preincubation of the G alpha q/G alpha 11 antibodies with the cognate peptide. Catfish, exposed to a 20 ppm dose of the herbicide, dichlobenil, displayed a reduction in G alpha q/G alpha 11 antigenicity. Proteins were extracted from olfactory tissues and solubilized. Using SDS-PAGE and Western blotting, bands corresponding in apparent molecular weight to a 38 kD protein were found. These data demonstrate that the herbicide may be a potent nasal olfactory toxicant in aquatic situations.

Animals↗
PubMed1997

Hepatitis-B-virus resistance to lamivudine given for recurrent infection after orthotopic liver transplantation.

BACKGROUND: Orthotopic liver transplantation for end-stage hepatitis-B-virus (HBV) infection is commonly complicated by recurrence of HBV. Lamivudine, a cytosine nucleoside analogue, has been shown to suppress HBV infection. We report the development of resistance to lamivudine in three patients who underwent transplantation for end-stage liver disease secondary to hepatitis B. METHODS: Two of the patients received lamivudine for recurrent HBV infection after transplantation, whereas the third patient began treatment 1 month before transplantation in an attempt to prevent HBV recurrence after transplantation. The three patients initially responded well to treatment, but viral recurrence occurred after 9-10 months of treatment in all patients. HBV DNA was amplified from serum and sequenced through a conserved polymerase domain-the tyrosine, methionine, aspartate, aspartate (YMDD) locus. We assessed the susceptibility of HBV to lamivudine by infecting primary human hepatocytes with serum taken before the start of treatment and after recurrence in varying concentrations of lamivudine. FINDINGS: DNA sequencing showed a common mutation within the YMDD locus of the HBV polymerase gene in all patients during lamivudine treatment. In hepatocyte cultures infected with pretreatment serum, HBV DNA concentrations were reduced to less than 6% of those in control cultures by addition of lamivudine in concentrations as low as 0.03 mumol/L. By contrast, in cultures treated with serum taken after recurrence, HBV DNA concentrations did not fall below 20% of control values, even with lamivudine at 30 mumol/L. INTERPRETATION: Resistance to lamivudine has been reported in HIV patients with mutations in the YMDD locus of the polymerase gene. Our findings indicate a common mechanism of lamivudine resistance for HIV and HBV that involves similar point mutations in homologous domains of the viral polymerases.

Antiviral Agents↗
PubMed1997

Clinical process cost analysis.

BACKGROUND: New systems of reimbursement are exerting enormous pressure on clinicians and hospitals to reduce costs. Using cheaper supplies or reducing the length of stay may be a satisfactory short-term solution, but the best strategy for long-term success is radical reduction of costs by reengineering the processes of care. However, few clinicians or institutions know the actual costs of medical care; nor do they understand, in detail, the activities involved in the delivery of care. Finally, there is no accepted method for linking the two. METHODS: Clinical process cost analysis begins with the construction of a detailed flow diagram incorporating each activity in the process of care. The cost of each activity is then calculated, and the two are linked. This technique was applied to Diagnosis Related Group 75 to analyze the real costs of the operative treatment of lung cancer at one institution. RESULTS: Total costs varied between $6,400 and $7,700. The major driver of costs was personnel time, which accounted for 55% of the total. Forty percent of the total cost was incurred in the operating room. The cost of care decreased progressively during hospitalization. CONCLUSIONS: Clinical process cost analysis provides detailed information about the costs and processes of care. The insights thus obtained may be used to reduce costs by reengineering the process.

Cost Control↗
PubMed1997

Clinical process cost analysis: a promising tool for clinical improvement.

In today's environment, health care organizations are expected to provide the best possible care at the lowest possible cost. Neither aspect can be considered independently, but correlating the two with traditional systems of cost analysis is very difficult. This article presents a new method for linking costs to the process of care that also promises to be a powerful tool for clinical improvement and redesign.

Accounting↗
PubMed1997

The importance of the pharmacist's expanding role on the diabetes team: reinforcing nutritional guidelines for improved glycemic control.

The role of the pharmacist on the diabetes care team is expanding due to the increasing number of patients diagnosed with diabetes, limited health care dollars, and the education related to and required for patients by managed care organizations and insurance companies. In the past, training of patients in diabetes self-management skills has been inadequate, and this continues to be the case. Clinical pharmacists, in cooperation with physicians, have increased opportunities to provide education about medications and may include instructions for patients regarding the interaction of food consumed with changes in blood glucose levels. Because of monthly refills on prescribed medications, a patient's interaction with the pharmacist in the setting of a commercial pharmacy is more frequent than with any other member of the diabetes team. This contact offers an ideal educational opportunity. The action and efficacy of medications that affect the pancreas, hepatic glucose production, the utilization of glucose by muscle cells, and the absorption of glucose from the intestines are influenced directly by the meal plan. Nutritional guidelines, meal planning for the Type I and Type II patient, use of the exchange system, carbohydrate counting, artificial sweeteners, alcoholic beverages, and suggestions for guiding patients to establish eating habits that lead to improved diabetes control are important issues for every member of the diabetes team to address. The reinforcement of dietary principles may occur in the educational setting of the hospital or the clinic or within the commercial pharmacy setting. When the team presents accurate and current information, continuity of care and improved patient understanding are achieved.

Blood Glucose↗
PubMed1996

Reliability, construct validity, and subscale norms of the Brief Symptom Inventory when administered to bereaved parents.

The Brief Symptom Inventory (BSI) was administered to parents (N = 260; 171 mothers and 89 fathers) whose adolescent and young adult children died unexpectedly and violently by accident, homicide, or suicide. Summary statistics and reliability coefficients (Cronbach's alpha) for the nine subscales and the Global Severity Index were calculated. A comparison of means and standard deviations confirmed the expectation that this sample is dramatically different from the normative American community standard. Raw scores for the subscales were transformed into standardized T scores and critical values for a screening heuristic presented. An attempt to obtain construct validity using factor analysis suggested that a five-factor solution provided a description of this population of bereaved parents that is more insightful than the nine standard subscales of the BSI. Implications for both clinicians and future research are discussed.

Adult↗
PubMed1994

Effect of continuous heat exposure on sleep during partial sleep deprivation.

This study examined the effects of continuous heat exposure on sleep structure during a partial sleep-deprivation regime. The experimental protocol was divided into three periods. After a baseline period (5 days and nights at 20 degrees C), the sleep of the subjects was restricted to the second half of the night (3 a.m.-7 a.m.) for four consecutive nights. The restricted-sleep period was followed by two recovery days and nights. During the deprivation and recovery periods, the ambient temperature was 20 degrees C for six of the 12 subjects and 35 degrees C for the others. Sleep, esophageal and mean skin temperatures were continuously recorded. At 20 degrees C, the expected effect of sleep debt was apparent. There were significant reductions in time spent awake and in latencies for sleep and stage 4 sleep. The duration of stage 4 sleep significantly increased during the four successive restricted-sleep nights, whereas esophageal temperature significantly decreased over the successive days. When heat was added, esophageal temperature decrease was weakened, and the significant increase in stage 4 duration seen at 20 degrees C was not found. The findings suggest that the heat load imposed in our experimental condition has a suppressive effect on sleep stage 4 increase, which is induced by sleep restriction. The hypothesis that an increase in this sleep stage serves as a mechanism for energy conservation should be also considered.

Adult↗