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Biomedical subjects

S B Johnson

Publications and source records attributed to S B Johnson.

At least 55 records · Page 3Linked to original sources
PubMed1998

Testing neonate-infant membrane oxygenators with the University of Texas neonatal pulsatile cardiopulmonary bypass system in vitro.

Neurologic complications are already well documented after cardiopulmonary bypass (CPB) procedures in neonates and infants. Physiologic pulsatile flow CPB systems may be the alternative to the currently used steady-flow CPB circuits. In addition to the pulsatile pump, a membrane oxygenator should be chosen carefully, because only a few membrane oxygenators are suitable for physiologic pulsatile flow. We have tested four different types of neonate-infant membrane oxygenators for physiologic pulsatility with The University of Texas neonate-infant pulsatile CPB system in vitro. Evaluation criteria were based on mean ejection time, extracorporeal circuit (ECC) pressure, and upstroke of dp/dt. The results suggested that the Capiox 308 hollow-fibre membrane oxygenator produced the best physiologic pulsatile waveform according to the ejection time, ECC pressure, and the upstroke of dp/dt. The Minimax Plus and Masterflo Infant hollow-fibre membrane oxygenators also produced adequate pulsatile flow. Only the Variable Prime Cobe Membrane Lung (VPCML) Plus flat-sheet membrane oxygenator failed to reach the criteria for physiologic pulsatility. Depending on the oxygenator used, the lowest priming volume of the infant CPB circuit was 415 ml and the highest 520 ml.

Brain Diseases↗
PubMed1998

Empirically supported psychosocial interventions for children: an overview.

Discusses issues related to the identification of psychosocial interventions for children that have demonstrated efficacy. Recent debate concerning differences between clinical trials research and clinical practice is summarized, including the tradeoff between interpretability (internal validity) and generalizability (external validity) of outcome studies. This article serves as an introduction to the special issue containing articles that have as their focus the identification of empirically supported psychosocial interventions for children as part of a task force. The article provides an overview of the history, agenda, and methodology used by the task force to define and identify specific empirically supported interventions for children with specific disorders. Whereas a number of well-established or probably efficacious interventions are identified within the series, more work directed at closing the gap between research and practice is needed.

Adolescent↗
PubMed1998

Offering a randomized trial of intensive therapy for IDDM to adolescents. Reasons for refusal, patient characteristics, and recruiter effects.

OBJECTIVE: To identify reasons adolescents refuse to participate in a randomized trial of intensive therapy (IT) for IDDM, to describe the patient characteristics of those who consent and those who refuse to participate, and to examine recruiter effects on trial participation rates. RESEARCH DESIGN AND METHODS: A total of 99 adolescents, age 11-18 years, were provided with the results of the Diabetes Control and Complications Trial and approached for possible study participation by two nurse recruiters. Adolescents refusing the trial were administered a semi-structured interview to describe reasons for study refusal; responses were recorded and later coded into categories. Patient characteristics of consenters and refusers were collected and compared. The differential enrollment rates of the two nurse recruiters were also compared. RESULTS: A total of 56 patients (approximately 57%) agreed to participate; 43 refused. The four most common reasons for study refusal were 1) increased clinic visits (42%), 2) increased insulin injections (30%), 3) increased frequency of self-monitoring of blood glucose (SMBG) (28%), and 4) transportation difficulties (19%). Concerns about randomization to an unwanted treatment condition and fears of hypoglycemia or weight gain were rarely cited. Consenters and refusers did not differ in demographic characteristics, disease status, or family composition. Large differences were found between the two nurse recruiters: one experienced a 60% refusal rate, while the other experienced a 27% refusal rate. CONCLUSIONS: Issues of convenience (increased clinic visits, transportation difficulties) and concerns about the demands of IT (increased injections and SMBG) were the predominant reasons for trial refusal. Patient characteristics did not differentiate consenters from refusers. However, recruiters differed greatly in study refusal rates, suggesting that provider behavior may be an important but understudied aspect of adolescent acceptance of randomized trials in general and IT in particular.

Adolescent↗
PubMed1998

Resource utilization in traumatic brain injury: the role of magnetic resonance imaging.

Cerebral CT scanning is routine in the acute evaluation of traumatic brain injury (TBI) patients. MRI has been reported to identify cerebral lesions better than CT scan. The purpose of this study was to determine whether MRI influenced the acute diagnosis and management of TBI patients. A retrospective medical records review was performed on all TBI patients undergoing cerebral CT scan and MRI admitted to a regional trauma center during a 2-year period. Patient data collected included demography, extent of TBI, CT scan and MRI use, and therapeutic interventions. Forty TBI patients (initial Glascow Coma Scale, 8.8+/-0.7) underwent 79 CT scans and 40 MRIs. Time to initial CT scan was 6.3+/-4.3 hours and time to MRI was 2.9+/-3.1 days. Nine patients (22.5%) had injuries on CT scan but not on MRI, most commonly skull fractures or small subarachnoid hemorrhages. Twenty-four patients (60%) had injuries on MRI but not on CT scan, most commonly corpus callosum shear injuries. There were two cases of child abuse and both had injuries of varying ages identified by MRI, but not CT. All injuries requiring a therapeutic intervention or change in management were identified by CT scan. Magnetic resonance angiography identified one patient with a traumatic internal carotid artery thrombosis. The performance of MRI resulted in additional charges of $75,640 or $3,152/patient identified with a new lesion. Although MRI identifies lesions not evident on CT scan, MRI does not alter management plans and is of limited value in the acute management of TBI. MRI may be of medicolegal benefit in cases of child abuse.

Adult↗
PubMed1998

Conceptual graph grammar--a simple formalism for sublanguage.

There are a wide variety of computer applications that deal with various aspects of medical language: concept representation, controlled vocabulary, natural language processing, and information retrieval. While technical and theoretical methods appear to differ, all approaches investigate different aspects of the same phenomenon: medical sublanguage. This paper surveys the properties of medical sublanguage from a formal perspective, based on detailed analyses cited in the literature. A review of several computer systems based on sublanguage approaches shows some of the difficulties in addressing the interaction between the syntactic and semantic aspects of sublanguage. A formalism called Conceptual Graph Grammar is presented that attempts to combine both syntax and semantics into a single notation by extending standard Conceptual Graph notation. Examples from the domain of pathology diagnoses are provided to illustrate the use of this formalism in medical language analysis. The strengths and weaknesses of the approach are then considered. Conceptual Graph Grammar is an attempt to synthesize the common properties of different approaches to sublanguage into a single formalism, and to begin to define a common foundation for language-related research in medical informatics.

Computer Graphics↗
PubMed1997

Beta-adrenergic augmentation of flecainide-induced conduction slowing in canine Purkinje fibers.

BACKGROUND: This study was undertaken to test the hypothesis that beta-adrenergic stimulation in the setting of membrane depolarization will potentiate flecainide-induced conduction slowing. METHODS AND RESULTS: To elucidate the potential mechanism for the flecainide proarrhythmia observed in CAST, the voltage dependence of beta-adrenergic modulation of impulse propagation in eight flecainide-superfused canine Purkinje fibers was examined with a dual-microelectrode technique. At physiological membrane potentials (Vm) ([K+]o=5.4 micromol), 1 micromol flecainide decreased Vmax from 698+/-55 to 610+/-72 V/s (P=.003) and squared conduction velocity (theta2) from 2.11+/-1.1 to 1.72+/-0.9 (m/s)2 (P=.001). With K+ depolarization to Vm=-70 mV, flecainide further reduced Vmax from 306+/-101 to 245+/-65 V/s and theta2 from 1.12+/-0.4 to 0.99+/-0.6 (m/s)2, producing a 2.0-mV hyperpolarizing shift of apparent Na+ channel availability curves derived from theta2. The addition of 1 micromol isoproterenol to flecainide-superfused fibers at physiological Vm increased theta2 by 8% to 1.84+/-0.6 (m/s)2 (P<.01) without altering Vmax. At -70 mV, the addition of isoproterenol magnified the flecainide-induced reduction of Vmax an additional 24% to 185+/-52 V/s (P<.01) and theta2 by 17% to 0.82+/-0.5 (m/s)2 (P=.04), producing an additional 1.8-mV (P=.002) and 1.9-mV (P=.002) hyperpolarizing shift in the apparent Na+ channel inactivation curves generated from Vmax and theta2, respectively. At physiological Vm, the action potential duration (APD95) was reduced from 307+/-35 to 269+/-27 ms (P<.001) by flecainide and subsequently to 217+/-4 ms (P<.001) with isoproterenol addition. With 12 mmol/L K+, APD95 decreased from 198+/-23 to 182+/-17 ms (P=.005) with flecainide and to 164+/-10 ms (P=.004) with isoproterenol. CONCLUSIONS: At depolarized Vm, isoproterenol amplified the flecainide-induced reduction of Vmax and theta2, suggesting a further adrenergic-mediated reduction of Na+ current. Consequently, the synergy between catecholamines and flecainide at depolarized Vm and the shortened APD95 could facilitate arrhythmogenesis in the presence of underlying ischemia.

Action Potentials↗
PubMed1997

Dual-inflow great vessel aneurysm: delayed presentation after penetrating trauma.

Aneurysms constitute uncommon sequelae of injuries to the thoracic outlet. Most such aneurysms are secondary to blunt trauma and usually involve the great vessels at their take-off from the aortic arch. Penetrating injuries are more often identified in the more distal vessels and only very rarely present as pseudoaneurysms. Reported here is a single case of a chronic posttraumatic pseudoaneurysm arising from both the right common carotid artery and the right subclavian artery. The workup and surgical approach provide practical lessons, complemented with illustrations that aid in the understanding of the case. It is an unusual case because of the dual-inflow nature of the aneurysm.

Aneurysm, False↗
PubMed1997

Impact of volume loading and load reduction on ventricular refractoriness and conduction properties in canine congestive heart failure.

OBJECTIVES: This investigations was undertaken to examine the alteration of electrophysiologic properties, including refractoriness, strength-interval relations and conduction, with the development of heart failure and to characterize the impact of volume loading on these indexes in the cardiomyopathic setting. METHODS: Electrophysiologic properties in eight dogs with pacing-induced dilated cardiomyopathy were compared with those in six control dogs before and after rapid infusion of 800 ml of intravenous saline. RESULTS: The right ventricular (RV) and left ventricular (LV) effective refractory period (ERP) and absolute refractory period (ARP) were significantly longer in dogs with pacing-induced cardiomyopathy than in control dogs: RV ERP 181 +/- 11 ms versus 138 +/- 7 ms (mean +/- SD) (p < 0.0001) and anterior LV ERP 177 +/- 13 ms versus 128 +/- 11 ms (p < 0.0001), respectively; ARP 159 +/- 14 ms versus 114 +/- 7 ms (p < 0.0001) at the RV site and 153 +/- 12 versus 117 +/- 5 ms (p < 0.0001) at the anterior LV site. After volume loading in cardiomyopathic animals, posterior and anterior LV ERPs became prolonged to 178 +/- 5 ms (p = 0.004) and 189 +/- 14 ms (p = 0.065), respectively, shifting the strength-interval relation in the direction of longer S1S2 coupling intervals. Anterior LV monophasic action potential durations at 90% repolarization also became prolonged from 192 +/- 10 ms to 222 +/- 23 ms (p < 0.012) with volume loading. These findings were not altered by subsequent sodium nitroprusside. Local conduction times parallel and perpendicular to fiber orientation were not altered by development of cardiomyopathy or volume alterations. CONCLUSIONS: The development of dilated cardiomyopathy results in significant prolongation of refractoriness and repolarization that is increased further by volume augmentation but is not reversed by pharmacologic load reduction. Although these abnormalities may contribute to the environment needed for a non-reentrant, triggered or stretch-mediated arrhythmogenic process in cardiomyopathic states, additional studies will be required to demonstrate such a focal mechanism conclusively.

Action Potentials↗
PubMed1997

Efficacy of prehospital surgical cricothyrotomy in trauma patients.

OBJECTIVE: The use of surgical cricothyrotomy (SC) in the prehospital setting is controversial, and the need to teach this procedure to paramedics and intermediate emergency medical technicians remains unclear. The purpose of this study is to define the efficacy, complication rate, and overall survival after SC performed in the prehospital setting. METHODS: In our region, emergency medical technicians receive training in this technique using an animal model with bi-annual updates required. We retrospectively reviewed data in our regional trauma register (15,686 injured patients) for the years 1991-1995. RESULTS: Prehospital emergency airway intubation was required in 376 patients, 56 of whom received SC. The primary indications for SC were facial fractures and deformities (32%) and blood in the airway (30%). In 79% of the patients requiring SC, attempted orotracheal intubation prior to SC was unsuccessful, with a mean of 1.9 attempts per patient. SC was judged to provide an adequate airway in the field in 89% of attempts. Complications at the scene included six failed attempts, one case of excessive bleeding, and one adverse patient reaction (agitation). When patients arrived at the trauma center, the SC was judged to be acceptable in 64%, whereas 16% were functioning with some question of adequacy and required airway manipulation (most commonly a mainstem bronchial intubation). Overall survival to hospital discharge was 27%; however, survival to emergency department discharge (an indicator of emergency airway adequacy) was 62%. Using TRISS methodology, there were five unexpected survivors and six unexpected deaths. Only three patients were discharged with a "good neurologic recovery." CONCLUSION: (1) Prehospital SC can be performed effectively with few complications after training on animal models (2) Good neurologic outcome is rare after the use of this procedure. (3) Although it is effective, clear indications must be developed and followed for the prehospital use of SC.

Adult↗
PubMed1997

Mechanism of lethal proarrhythmia observed in the Cardiac Arrhythmia Suppression Trial: role of adrenergic modulation of drug binding.

A variety of recent in vivo studies have sought to clarify the mechanism underlying the proarrhythmic response of flecainide in the Cardiac Arrhythmia Suppression Trial (CAST). Increased inducibility of relatively stable ventricular arrhythmias in subacute and chronic postinfarction models has been universally observed. The arrhythmogenesis has been explained in part by drug induced modulation of anisotropic conduction in persistently ischemic tissue, increased durations of vulnerable windows, enhanced generation of unidirectional block with the introduction of extrastimuli, variability of repolarization within the ventricular wall, and the creation of stable reentrant circuits with narrow central zones of propagation. While these data explain arrhythmogenesis in general, malignant ventricular arrhythmia capable of producing the excess sudden or arrhythmic death mortality in the CAST trial have not been universally observed, nor have the proported beneficial effects of beta-blockade seen in the CAST trial and other studies been explained. Additional studies examining the adrenergic modulation of flecainide binding have shown reversal of flecainide effects in normal tissue, but paradoxical amplification of flecainide induced conduction slowing in depolarized tissue. This variable effect in normal versus abnormal tissue produces significant dispersions of conduction with an expected increased propensity for conduction failure in response to ectopy, increased liminal length for impulse propagation, enhanced vulnerability to premature extrastimuli, and completed reentrant circuits in regions of depressed membrane potentials. This, along with the decrease in action potential duration and accompanying refractoriness in the setting of adrenergic modulation may favor more malignant double wavelet or unstable ventricular arrhythmias.

Animals↗
PubMed1997

Improved separation and immunodetection of rat cytochrome P450 4A forms in liver and kidney.

In the study of tissues that contain several forms of one cytochrome P450 subfamily, it is useful to develop immunoblotting techniques so that the various individual members of the family can be distinguished. This paper describes improvements in the immunoblotting technique to distinguish members of the rat cytochrome P450 4A subfamily, 4A1, 4A2, and 4A3, as they are present in Sprague-Dawley rat liver microsomes. This procedure was used to investigate differences in the cytochrome P450 4A forms observed under various conditions such as: untreated versus peroxisome proliferator treated rats, Sprague-Dawley versus Fischer 344 male versus female rats, and liver versus kidney microsomes. In liver microsomes of male Sprague-Dawley rats, forms 4A1, 4A2, and 4A3 were induced by the peroxisome proliferators, clofibrate, di-(2-ethylhexyl) phthalate, dehydroepiandrosterone, aspirin, and ibuprofen. Expression of the 4A forms shows strain specificity. A comparison of the cytochrome P450 4A forms in male Sprague-Dawley and Fischer 344 rats treated with peroxisome proliferators demonstrated that three distinct protein bands are visible on immunoblots of liver microsomes of Sprague-Dawley rats, whereas only two distinct protein bands are detectable in liver microsomes of Fischer 344 rats. The two protein bands in liver microsomes of male Fischer 344 rats migrate in positions corresponding to the 4A2 and 4A3 bands in male Sprague-Dawley rats. There did not appear to be a protein band corresponding to the 4A1 band of Sprague-Dawley rats. Expression of the 4A forms also shows gender specificity. In liver microsomes of female Sprague-Dawley rats, expression of the P450 4A2 form was not observed after treatment with a peroxisome proliferator. Expression of the 4A forms also shows tissue specificity. In kidney, 4A2 is the major protein band in male Sprague-Dawley rats with minor amounts of the 4A3 protein, whereas two prominent protein bands (4A2 and 4A3) are seen in male Fischer 344 rats.

Animals↗
PubMed1997

Generic database design for patient management information.

Patient management information tracks general facts about the location of the patient and the providers assigned to care for the patient. The Clinical Data Repository at Columbia Presbyterian Medical Center employs a generic schema to record patient management events. The schema is extremely simple, yet can support several different views of patient information, as required by different applications: a longitudinal view of patient visits, including both inpatient and outpatient encounters; a visit-oriented view, to record facts related to a current encounter; a location-based view to provide a census of a nursing ward; and a provider-based view to give a list of the patients currently being cared for by a given clinician. All of these views can be supported in a highly efficient manner by the use of appropriate indexes.

Databases as Topic↗
PubMed1996

Design of a clinical event monitor.

The issues and implementation of a clinical event monitor are described. An event monitor generates messages for providers, patients, and organizations based on clinical events and patient data. For example, an order for a medication might trigger the generation of a warning about a drug interaction. A model based on the active database literature has as its main components an event (which triggers a rule to fire), a condition (which tests whether an action ought to be performed), and an action (often the generation of a message). The details of implementing such a monitor are described, using as an example the Columbia-Presbyterian Medical Center clinical event monitor, which is based on the Arden Syntax for Medical Logic Modules.

Artificial Intelligence↗
PubMed1996

Essential fatty acid deficiency and predisposition to lung disease in cystic fibrosis.

UNLABELLED: Essential fatty acid (EFA) deficiency is a predisposing factor for pulmonary infection with Staphylococcus aureus and Pseudomonas aeruginosa, the two major pathogenic microorganisms in cystic fibrosis (CF). OBJECTIVE: The goal of this study was to investigate the essential fatty acid status of CF patients from infancy to 20 years old. MATERIALS AND METHODS: Plasma fatty acid profiles for phospholipid (PL) were determined for cord (n = 6), 4 months (n = 40), 16 months (n = 25), 3 y (n = 8), 5-10 y (n = 10), and 10-20 y (n = 10) aged CF patients and compared to their respective control; cord (n = 22), 1-36 months (n = 38) and adult (n = 100). Significance was established by Student's t-test (p < 0.05). RESULTS: The plasma PL fatty acid profile for all CF patients, except cord, revealed consistent deficiency in omega 3 and omega 6 EFAs. These deficiencies were most marked at infancy and more pronounced for patients with meconium ileus. CONCLUSIONS AND RELEVANCE: EFA deficiency may contribute to the predisposition of CF infants to develop respiratory disease and to the excess cytotoxic activity found in bronchoalveolar lavage fluid at 2 months of age in the majority of screened infants.

Adult↗
PubMed1996

Integrating data from natural language processing into a clinical information system.

Demographic data extracted from discharge summaries by natural language processing was compared to data gathered by a conventional hospital admitting system. Discrepancies in data were noted in names, age, sex, race, and ethnicity. Some differences are attributable to errors in collection: interaction with patient, dictation, transcription, and data entry. Very few differences were due to errors in natural language processing. Other differences can be used to critique existing data, or to enhance data with more detailed information. Discrepancies in data as elementary as patient demographics raise the issue of resolving conflicts when neither source of data is known to be more reliable. Clinical repositories can represent conflicting data from multiple sources, but clinical information systems must bear the cost of increased complexity in the application programs that will use the data.

Evaluation Studies as Topic↗
PubMed1995

Unlocking clinical data from narrative reports: a study of natural language processing.

OBJECTIVE: To evaluate the automated detection of clinical conditions described in narrative reports. DESIGN: Automated methods and human experts detected the presence or absence of six clinical conditions in 200 admission chest radiograph reports. STUDY SUBJECTS: A computerized, general-purpose natural language processor; 6 internists; 6 radiologists; 6 lay persons; and 3 other computer methods. MAIN OUTCOME MEASURES: Intersubject disagreement was quantified by "distance" (the average number of clinical conditions per report on which two subjects disagreed) and by sensitivity and specificity with respect to the physicians. RESULTS: Using a majority vote, physicians detected 101 conditions in the 200 reports (0.51 per report); the most common condition was acute bacterial pneumonia (prevalence, 0.14), and the least common was chronic obstructive pulmonary disease (prevalence, 0.03). Pairs of physicians disagreed on the presence of at least 1 condition for an average of 20% of reports. The average intersubject distance among physicians was 0.24 (95% Cl, 0.19 to 0.29) out of a maximum possible distance of 6. No physician had a significantly greater distance than the average. The average distance of the natural language processor from the physicians was 0.26 (Cl, 0.21 to 0.32; not significantly greater than the average among physicians). Lay persons and alternative computer methods had significantly greater distance from the physicians (all > 0.5). The natural language processor had a sensitivity of 81% (Cl, 73% to 87%) and a specificity of 98% (Cl, 97% to 99%); physicians had an average sensitivity of 85% and an average specificity of 98%. CONCLUSIONS: Physicians disagreed on the interpretation of narrative reports, but this was not caused by outlier physicians or a consistent difference in the way internists and radiologists read reports. The natural language processor was not distinguishable from the physicians and was superior to all other comparison subjects. Although the domain of this study was restricted (six clinical conditions in chest radiographs), natural language processing seems to have the potential to extract clinical information from narrative reports in a manner that will support automated decision-support and clinical research.

Humans↗
PubMed1995

Transesophageal echocardiography in the diagnosis of traumatic rupture of the aorta.

BACKGROUND: Rupture of the aorta is a major cause of death after motor vehicle accidents. Survival depends on early diagnosis, and emergency aortography is the standard imaging method. Although transesophageal echocardiography is noninvasive and can provide high-resolution images of the aorta, information about its value in patients with trauma is limited. We conducted this study to assess prospectively the value of transesophageal echocardiography in the emergency evaluation of patients at risk for aortic injury. METHODS: Transesophageal echocardiography of the aorta was attempted in 101 patients admitted to the emergency room with a diagnosis of possible traumatic rupture of the aorta. Echocardiography and aortography personnel were notified simultaneously of the arrival of the patient, and the two tests were performed sequentially by operators who were blinded to the results of the other test. The sensitivity and specificity of transesophageal echocardiography were calculated on the basis of the results of aortography of the arch, surgery, or autopsy. RESULTS: Transesophageal echocardiography was attempted in 101 patients. The study was successfully performed in 93 patients but could not be completed in 8 because of lack of cooperation on the part of the patient (7 patients) or maxillofacial trauma (1 patient). Despite a high injury-severity score (mean, 29.6), transesophageal echocardiography was performed without complications, and within a mean (+/- SD) of 29 +/- 12 minutes. Eleven of the 93 studies (12 percent) demonstrated rupture of the aorta near the isthmus. The findings were confirmed in 10 of the 11 patients by aortography (9 patients), surgery (9 patients), or autopsy (1 patient), yielding a sensitivity of 100 percent and specificity of 98 percent for the detection of injury to the aorta. There was one false positive echocardiogram. CONCLUSIONS: Transesophageal echocardiography is a highly sensitive and specific method of detecting injury to the thoracic aorta. This technique can be used safely and quickly in critically injured patients with suspected traumatic rupture of the aorta and compares favorably with arch aortography.

Acute Disease↗