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Biomedical subjects

G Stark

Publications and source records attributed to G Stark.

At least 19 recordsLinked to original sources
PubMed2006

Investigation of suspected laboratory cross-contamination: interpretation of single smear-negative, positive cultures for Mycobacterium tuberculosis.

Restriction fragment length polymorphism (RFLP) analysis can be used to assess genetic relatedness of Mycobacterium tuberculosis isolates. This study reports a collaborative investigation of false-positive cultures for M. tuberculosis, suspected when the DNA fingerprint from an index case matched an epidemiologically improbable source case. RFLP analysis matched fingerprints in ten of 16 cases of suspected laboratory contamination to four separate smear-positive sources that were processed on the same day in the same laboratory. All single smear-negative, positive cultures processed on the same day as smear-positive specimens should be reviewed on a case-by-case basis to identify possible false-positive cultures.

Adult↗
PubMed2005

Oscillator strength and linewidth measurements of dipole-allowed transitions in 14N2 between 93.5 and 99.5 nm.

Line oscillator strengths in 16 electric dipole-allowed bands of 14N2 in the 93.5-99.5 nm (106,950-100,500 cm(-1)) region have been measured at an instrumental resolution of 6.5 x 10(-4) nm (0.7 cm(-1)). The transitions terminate on vibrational levels of the 3psigma 1Sigma u (+), 3ppi 1Pi u, and 3ssigma 1Pi u Rydberg states and of the b' 1Sigma u (+) and b 1Pi u valence states. The J dependences of band f values derived from the experimental line f values are reported as polynomials in J'(J'+1) and are extrapolated to J'=0 in order to facilitate comparisons with results of coupled-Schrodinger-equation calculations that do not take into account rotational interactions. Most bands in this study reveal a marked J dependence of the f values and/or display anomalous P-, Q- and R-branch intensity patterns. These patterns should help inform future spectroscopic models that incorporate rotational effects, and these are critical for the construction of realistic atmospheric radiative transfer models. Linewidth measurements are reported for four bands. Information provided by the J dependences of the experimental linewidths should be of use in the development of a more complete understanding of the predissociation mechanisms in N2.

Journal Article↗
PubMed2005

Rotational effects in the band oscillator strengths and predissociation linewidths for the lowest 1Pi u-X 1Sigmag+ transitions of N2.

A coupled-channel Schrodinger equation (CSE) model of N2 photodissociation, which includes the effects of all interactions between the b, c, and o 1Pi u and the C and C' 3Pi u states, is employed to study the effects of rotation on the lowest-upsilon 1Pi u-X 1Sigmag+(upsilon,0) band oscillator strengths and 1Pi u predissociation linewidths. Significant rotational dependences are found which are in excellent agreement with recent experimental results, where comparisons are possible. New extreme-ultraviolet (EUV) photoabsorption spectra of the key b 1Pi u<--X 1Sigmag +(3,0) transition of N2 are also presented and analyzed, revealing a b(upsilon=3) predissociation linewidth peaking near J=11. This behavior can be reproduced only if the triplet structure of the C state is included explicitly in the CSE-model calculations, with a spin-orbit constant A approximately 15 cm(-1) for the diffuse C(upsilon=9) level which accidentally predissociates b(upsilon=3). The complex rotational behavior of the b-X(3,0) and other bands may be an important component in the modeling of EUV transmission through nitrogen-rich planetary atmospheres.

Journal Article↗
PubMed2005

Functional consequences of oxidative membrane damage.

The interaction of reactive oxygen species with biological membranes is known to produce a great variety of different functional modifications. Part of these modifications may be classified as direct effects. They are due to direct interaction of the reactive species with the molecular machinery under study with a subsequent chemical and functional modification of these molecules. An important part of the observed functional modifications are, however, indirect effects. They are the consequence of an oxidative modification of the environment of biological macromolecules. Lipid peroxidation-via its generation of chemically reactive products-contributes to the loss of cellular functions through the inactivation of membrane enzymes and even of cytoplasmic (i.e., water soluble) proteins. Oxidation of membrane lipids may, however, also increase the efficiency of membrane functions. This was observed for a series of transport systems. Lipid peroxidation was accompanied by activation of certain types of ion channels and ion carriers. The effect is due to an increase of the polarity of the membrane interior by accumulation of polar oxidation products. The concomitant change of the dielectric constant, which may be detected via the increase of the membrane capacitance, facilitates the opening of membrane channels and lowers the inner membrane barrier for the movement of ions across the membrane. The predominant effect, however, at least at a greater extent of lipid peroxidation, is the inhibition of membrane functions. The strong increase of the leak conductance contributes to the depolarization of the membrane potential, it destroys the barrier properties of the membrane and it may finally lead, via an increase of cytoplasmic Ca(2+) concentration, to cell death. The conclusions were derived from experiments performed with different systems: model systems in planar lipid membranes, native ion channels either reconstituted in lipid membranes or investigated in their natural environment by the patch-clamp method, and two important ion pumps, the Na/K-ATPase and the sarcoplasmic reticulum (SR) Ca-ATPase.

Animals↗
PubMed2004

Photodynamic inactivation of the Na,K-ATPase occurs via different pathways.

The photodynamic, i.e., the light-induced, inactivation of the Na,K-ATPase in the presence of the sensitizer rose bengal was studied under different conditions. The shape of inactivation curves of the enzyme activity was analyzed as well as partial reactions of the pump cycle. Both experimental approaches showed the existence of two different time constants of inactivation of the ion pump, which reflect two pathways of a photodynamic modification. This is supported by the following observations: (1) The amplitude of the initial fast decay of enzyme activity was enhanced in the presence of D2O and reduced in the presence of the singlet oxygen scavenger imidazole. (Similar results were found for the SR Ca-ATPase.) (2) Contrary to the fast enzyme inactivation the slow process shows an inverse dose-rate behavior. (3) Inactivation of the partial reactions of Na+ -binding and of K+-binding to the membrane domain of the Na,K-ATPase showed only a single time constant, which corresponded to the slower time constant of enzyme inactivation. In the presence of high concentrations of singlet oxygen the fast time constant dominated the inactivation of the ATP-induced partial reaction for which the cytoplasmic domains of the enzyme play an important role. The data support the conclusion that fast inactivation is due to modification of the cytoplasmic domains and slow inactivation due to modifications of the membrane domain of the ion pumps.

Animals↗
PubMed2004

The evaluation of the no-independent vasodilatative effect of iloprost in isolated perfused Guinea pig hind limbs.

AIM: In critical limb ischemia vasodilatators play an important role in the treatment of the disease. Considering that the endothelium is seriously damaged in these patients, we wanted to evaluate if the vasodilatative effect of iloprost does or does not depend on the endothelium by using the model of the isolated perfused guinea pig hind limb. METHODS: A catheter was inserted via the distal aorta and common iliac artery. After stabilization, iloprost was administered at a dosage of 0.1 microM. In a subsequent series of experiments precontraction of the peripheral vascular bed was achieved with 40 mM KCl followed by 0.1 microM iloprost. In a 3rd series of experiments L-NAME (100 microM) was administered after the equilibration period for 30 minutes, followed by 0.1 microM iloprost. In the 4th series of experiments, after the administration of L-NAME (100 microM), KCl (40 mM) was administered to precontract the vascular bed and iloprost 0.1 microM was added. RESULTS: The administration of iloprost alone and after addition of KCL induced a significant decrease in vascular resistance(-49.6+/-14.1% [x+/-SEM, n=7]). The addition of L-NAME did not affect vascular resistance. The consecutive addition of iloprost reduced vascular resistance significantly (-4.2+/-0.7% [x+/-SEM, n=7]). After addition of L-NAME 100 microM and precontraction with KCl 40 mM, iloprost once again significantly reduced peripheral vascular resistance (-51.5+/-14.4% [x+/-SEM, n=6]). Reduction of peripheral vascular resistance by iloprost was comparable to that without L-NAME. CONCLUSION: Our data show that iloprost at a dosage of 0.1 microM achieves a significant reduction in peripheral vascular resistance and that the vasodilatative effect of iloprost is independent of NO. Iloprost therefore seems to be an ideal vasodilatative drug for the treatment of patients with impaired endothelial function.

Animals↗
PubMed2002

Aborted sudden death in a patient with a structurally normal heart: the Brugada syndrome.

We report a 37-year-old man with documented aborted sudden death. After resuscitation, the patient showed no structural heart disease but the ECG showed a right bundle-branch block with a descending ST segment elevation in leads V(1) and V(2). After transient normalization of the ECG, the administration of ajmaline led to spontaneous development of the distinct descending ST segment elevation in the right precordial leads and therefore to the diagnosis of Brugada syndrome. The incidence of sudden cardiac death among these patients is high. The only treatment is an implantable cardioverter-defibrillator (ICD). The Brugada syndrome should therefore be borne in mind in the differential diagnosis of sudden death.

Adult↗
PubMed2002

Pygeum africanum for benign prostatic hyperplasia.

BACKGROUND: Benign prostatic hyperplasia (BPH), nonmalignant enlargement of the prostate, can lead to obstructive and irritative lower urinary tract symptoms (LUTS). The pharmacologic use of plants and herbs (phytotherapy) for the treatment of LUTS associated with BPH has been growing steadily. The extract of the African prune tree, Pygeum africanum, is one of the several phytotherapeutic agents available for the treatment of BPH. OBJECTIVES: To investigate the evidence whether extracts of Pygeum africanum (1) are more effective than placebo in the treatment of Benign Prostatic Hyperplasia (BPH), (2) are as effective as standard pharmacologic BPH treatments, and (3) have less side effects compared to standard BPH drugs. SEARCH STRATEGY: Trials were searched in computerized general and specialized databases (MEDLINE (1966-2000), EMBASE, Cochrane Library, Phytodok), by checking bibliographies, and by contacting relevant manufacturers and researchers. SELECTION CRITERIA: Trials were eligible if they (1) were randomized (2) included men with BPH (3) compared preparations of Pygeum africanum (alone or in combination) with placebo or other BPH medications (4) included clinical outcomes such as urologic symptom scales, symptoms, or urodynamic measurements. Eligibility was assessed by at least two independent observers. DATA COLLECTION AND ANALYSIS: Information on patients, interventions, and outcomes were extracted by at least two independent reviewers using a standard form. The main outcome measure for comparing the effectiveness of Pygeum africanum with placebo and standard BPH medications was the change in urologic symptoms scale scores. Secondary outcomes included change in urologic symptoms including nocturia and urodynamic measures (peak and mean urine flow, prostate size). The main outcome measure for adverse effects was the number of men reporting adverse effects. MAIN RESULTS: A total of 18 randomized controlled trials involving 1562 men met inclusion criteria and were analyzed. Only one of the studies reported a method of treatment allocation concealment, though 17 were double-blinded. There were no studies comparing Pygeum africanum to standard pharmacologic interventions such as alpha-adrenergic blockers or 5-alpha reductase inhibitors. The mean study duration was 64 days (range, 30-122 days). Many studies did not report results in a method that permitted meta-analysis. Compared to men receiving placebo, Pygeum africanum provided a moderately large improvement in the combined outcome of urologic symptoms and flow measures as assessed by an effect size defined by the difference of the mean change for each outcome divided by the pooled standard deviation for each outcome (-0.8 SD [95% confidence interval (CI), -1.4, -0.3 (n=6 studies)]). Men using Pygeum africanum were more than twice as likely to report an improvement in overall symptoms (RR=2.1, 95% CI = 1.4, 3.1). Nocturia was reduced by 19%, residual urine volume by 24% and peak urine flow was increased by 23%. Adverse effects due to Pygeum Africanum were mild and comparable to placebo. The overall dropout rate was 12% and was similar between Pygeum Africanum (13%), placebo (11%) and other controls (8%). REVIEWER'S CONCLUSIONS: A standardized preparation of Pygeum africanum may be a useful treatment option for men with lower urinary symptoms consistent with benign prostatic hyperplasia. However, the reviewed studies were small in size, were of short duration, used varied doses and preparations and rarely reported outcomes using standardized validated measures of efficacy. Additional placebo-controlled trials are needed as well as studies that compare Pygeum africanum to active controls that have been convincingly demonstrated to have beneficial effects on lower urinary tract symptoms related to BPH. These trials should be of sufficient size and duration to detect important differences in clinically relevant endpoints and use standardized urologic symptom scale scores.

Humans↗
PubMed2002

Genetic evaluation of the common variant of the endothelial nitric oxide synthase (Glu(298)-><Asp) in patients with thromboangiitis obliterans.

BACKGROUND: Nitric oxide is synthesized by endothelial nitric oxide synthase and plays a key role in adequate endothelial function. An important effect is the reduction of free radicals caused by cigarette smoking, which is the only established risk factor for thromboangiitis obliterans (TAO). In patients with TAO a genetic defect of endothelial nitric oxide synthase may therefore result in deteriorated endothelial function. The aim of our study was to evaluate whether a genetic defect of the common variant of endothelial nitric oxide synthase (Glu(298)-->Asp) can be found in a higher degree in patients with TAO compared to healthy controls. METHODS: We enrolled 42 patients with TAO and 149 healthy subjects. RESULTS: Nineteen patients (45.2%) showed homozygosity for Glu(298) versus 76 (51%) in the control group. The heterozygous status for Glu(298)-->Asp was found among 18 patients (42.9%) compared to 61 (40.9%) members of the control group, which was a nearly equal distribution. Homozygosity for the mutant Asp(298) was slightly elevated in the patient group with 11.9 versus 8.1% in the control group. Allele frequency for Asp(298) was 0.333. CONCLUSIONS: Our data do not show elevated homozygosity for the common variant Glu(298)-->Asp in patients with TAO compared to healthy controls. The limitation of our evaluation is the small number of patients, which is a general problem when evaluating patients with TAO, as this is not a common disease.

Aspartic Acid↗
PubMed2001

Hypothenar hammer syndrome caused by posttraumatic aneurysm of the ulnar artery.

The so-called hypothenar hammer syndrome is a rare entity caused by lesions of the ulnar artery secondary to repetitive trauma to the hypothenar eminence, typically found in persons working with vibrating tools. Its clinical symptoms are pain, stiffness and whitening of the smitten fingers, sometimes in combination with Raynaud's syndrome. Angiographic evaluation of the smitten forearm and hand reveals occlusions, kinking, vasospasm and stenoses of the arteries in the hand and fingers. An aneurysm of the ulnar artery causing the hypothenar hammer syndrome is an even more rare morphological finding. The difficult aspect of treating a hypothenar hammer syndrome is to reopen the occluded vessels. Eventually, circulation deteriorates and skin lesions of the fingers may occur. The advantage of an isolated aneurysm of the ulnar artery is that normal circulation can be restored by vascular surgery, for example, with a vessel interponate. Surgical removal of the isolated aneurysm helps to prevent microembolism to the distal arteries and consequent deterioration of peripheral circulation. We report a young patient who presented with clinical symptoms of the hypothenar hammer syndrome and an aneurysm of the distal ulnar artery, diagnosed by magnetic resonance angiography. The only likely cause of the aneurysm was a bicycle accident some months prior to the occurrence of the aneurysm. The patient underwent vascular surgery and has been free of symptoms during six months of follow-up. A control magnetic resonance angiography performed one month after surgery revealed a normal vascular morphology.

Adolescent↗
PubMed2001

Lower respiratory tract infections in Inuit infants on Baffin Island.

BACKGROUND: It has long been suspected that Canadian Inuit children suffer from frequent severe lower respiratory tract infections (LRTIs), but the causes and risk factors have not been documented. This study assessed the infectious causes and other epidemiologic factors that may contribute to the severity of LRTI in young Inuit children on Baffin Island. METHODS: A prospective case study was carried out at the Baffin Regional Hospital in Iqaluit, Nunavut, of infants less than 6 months of age, who were admitted to hospital between October 1997 and June 1998 with a diagnosis of LRTI. Immunofluorescent antibody testing was used to identify respiratory viruses, and enzyme immunoassay (EIA) and polymerase chain reaction (PCR) were used to test for Chlamydia trachomatis. Demographic and risk factor data were obtained through a questionnaire. RESULTS: The annualized incidence rate of admission to hospital for bronchiolitis at Baffin Regional Hospital was 484 per 1000 infants who were less than 6 months of age; 12% of the infants were intubated. Probable pathogens were identified for 18 of the 27 cases considered in our study. A single agent was identified for 14 infants: 8 had respiratory syncytial virus, 2 adenovirus, 1 rhinovirus, 1 influenza A, 1 parainfluenza 3 and 1 had cytomegalovirus. For 4 infants, 2 infectious agents were identified: these were enterovirus and Bordetella pertussis, adenovirus and enterovirus, cytomegalovirus and respiratory syncytial virus, and respiratory syncytial virus and adenovirus. C. trachomatis was not identified by either EIA or PCR. All infants were exposed to maternal smoking in utero, second-hand smoke at home and generally lived in crowded conditions. INTERPRETATION: Inuit infants in the Baffin Region suffer from an extremely high rate of hospital admissions for LRTI. The high frequency and severity of these infections calls for serious public health attention.

Air Pollution, Indoor↗
PubMed2001

Photomodification of the electrical properties of the plasma membrane: a comparison between 6 different membrane-active photosensitizers.

The present study deals with photomodification of the electrical properties of the plasma membrane of an epithelial cell line (opossum kidney (OK) cells). The effect of photofrin II (previously investigated) is compared with that of 5 other membrane-active sensitizers: sulfonated Zn-phthalocyanine, merocyanine 540, rose bengal, methylene blue and protoporphyrin IX (an endogenous sensitizer induced by addition of its biosynthetic precursor 5-aminolaevulinic acid). The study was performed in order to investigate whether photomodification of the ion transport properties of the plasma membrane by membrane-active sensitizers is a general and early event in cellular photosensitization. The changes in the electrical properties were monitored by application of the whole-cell and the inside-out configuration of the patch-clamp technique. Illumination in the presence of the compounds (apart from merocyanine 540) gave rise to similar changes of the electrical properties of the membrane: depolarization of the membrane potential, inactivation of a large-conductance, Ca2+-dependent K+-channel (maxi-KCa), and a strong increase of the leak conductance of the membrane. This similarity indicates the general character of the functional photomodifications by membrane-active sensitizers previously reported for photofrin II.

Aminolevulinic Acid↗
PubMed2001

Cystic adventitial degeneration of the popliteal artery-the diagnostic value of duplex sonography.

Cystical adventitial degeneration of the popliteal artery is a disorder which is difficult to diagnose, due to the similarity of the symptoms of people presenting with peripheral arterial occlusive disease (PAOD) or popliteal entrapment syndrome. The only thing that differs from patients suffering from PAOD is the lack of typical risk factors for arteriosclerosis. Typical diagnostic procedures like conventional angiography or magnetic resonance Imaging angiography can be negative, too and therefore misleading. The only which is crucial in the diagnosis of cystic adventitial degeneration of the popliteal artery is to know the morphological background of this disorder, namely that it is a cyst of the adventitia of the artery which leads to a dynamic exercise-dependent flow inhibition. We present a 57-year old white male who had a week's history of intermittent claudication in his left calf. He was lacking of typical risk factors for arteriosclerosis and on first examination all pulses in both lower extremities were palpable and Doppler index on both legs was >1. Only duplexsonography revealed a cystic formation impressing the left popliteal artery in the hight of the rift in the popliteal joint.

Arterial Occlusive Diseases↗
PubMed2001

Antiarrhythmic effects of adenosine on ischemia-induced ventricular fibrillation.

PURPOSE: The antiarrhythmic efficacy of adenosine during states of AV-nodal reentrant tachycardias is well known and clinically established. Adenosine is also able to reduce ventricular arrhythmias when applied before coronary ligation in rats. Hypoxia or ischemia leads to an increased production of adenosine by cardiac myocytes. The purpose of this study was to evaluate if adenosine also has a direct antiarrhythmic effect on ischemia-induced ventricular fibrillation. MATERIALS AND METHODS: In this study, the antiarrhythmic effects of adenosine on ventricular fibrillation during global (low flow) ischemia were evaluated in isolated guinea pig hearts perfused by the method of Langendorff. RESULTS: Adenosine showed a dose-dependent prolongation of the peak to peak interval of the ventricular ECG signal during ventricular fibrillation until ventricular flutter or tachycardia occurred at a concentration of 2 mmol/L. At a concentration of 20 mmol/L, adenosine converted ventricular fibrillation into ventricular tachycardia with intermittent periods of asystole. This conversion of ventricular fibrillation to asystole was antagonised by 200 micromol/L theophylline. CONCLUSION: Adenosine appears to have an antiarrhythmogenic effect both in supraventricular and ventricular rhythm disturbances. During myocardial infarction, where huge amounts of adenosine are present in ischemic regions, asystole may respond to adenosine antagonists.

Adenosine↗