Modified Fiber Tips for Laser Angioplasty: Mechanisms of Action

Laser angioplasty with modified fiber tips has become a common procedure for the recanalization of totally occluded peripheral arteries. We evaluated the contribution of optical, thermal, and mechanical effects to the mechanism of recanalization of various probes, theoretically and experimentally. Temperature behavior and tissue penetration were measured in relation to axial force exerted by metal laser probes, and optical contact probes coupled to continuous-wave and pulsed Nd:YAG lasers. Modified fiber tips only penetrated tissue when the contact surface of the probe exceeded a temperature threshold of about 225°C in the fatty tissue model used. Metal laser probes had to be insulated from a liquid environment to attain this temperature. Optical probes needed to have an absorbing layer of carbonized tissue particles to attain this temperature. Tissue penetration by modified fiber tips was force dependent, especially with optical probes. Since the diameter of the probe was larger than the ablative laser beam, the atraumatic probe had to distend soft tissues mechanically. Because the metal laser probes delivered their energy in all directions, undesired heating in the radial direction has to be reduced by motion. The recanalization mechanism of modified fiber tips will depend on the properties of the obstruction. Sometimes the probes will recanalize the obstruction without the use of laser energy (Dotter effect). Moderate heating of the tissue by either direct absorption of light, or by heat conduction from the heated surface of the probe, may help to remodel the obstruction. Tissue temperatures around 100°C will vaporize the water compound, and temperatures higher than 225°C will ablate the solid compounds of the tissue creating a channel. The present unsteerable probes will not penetrate heavily calcified obstructions. Calcific deposits may deflect the probe into the wall with the risk of perforation.     

Feasibility of assessing regional myocardial uptake of 18F-fluorodeoxyglucose using single photon emission computed tomography

Differentiation between viable myocardium and scar tissue insegments with abnormal contraction has important consequencesin the clinical management of patients with coronary arterydisease. Positron emission tomography (PET) can identify viabletissue using ¹⁸F-fluorodeoxyglucose (FDG). However, applicationof PET for daily routine is limited. In this study, FDG uptakewas visualized with single photon emission computed tomography(SPECT) and compared with regional perfusion assessed with thallium-201(²⁰¹Tl) SPECT. The scintigraphic findings were related to regionalregional wall motion determined with two-dimensional echocardiography.Patients (n = 9) with wall motion abnormalities underwent FDGSPECT and resting ²⁰¹Tl SPECT. To control the metabolic statuspatients were studied with a hyperinsulinaemic euglycemic clampduring FDG SPECT. Analysis of reconstructed data was performedvisually and semiquantitatively using circumferential profiles.High-quality images were obtained. Eight ²⁰¹Tl defects showedconcordantly decreased FDG uptake (metabolism-perfusion matches)indicating scarred tissue, whereas six regions of hypoperfusiondemonstrated a relatively increased FDG uptake (mismatches),suggesting viable myocardium. Semiquantitative analysis confirmedvisual findings. Mean ²⁰¹Tl and FDG activities were not significantlydifferent in matching defects. In mismatches the mean FDG activitywas 81 ± 11% vs 64 ± 9% mean ²⁰¹Tl activity (P<0.0001).In four of six segments with increased FDG uptake, two-dimensionalecho revealed hypokinesia. Seven of eight regions with a matchingdefect in contrast were akinetic. Thus, in the areas with amismatch contractility was preserved. We conclude that FDG uptakecan be visualized with SPECT. Furthermore, our preliminary observationssuggest that this approach can identify viable tissue.     

Measurement of IgE antibodies against purified grass pollen allergens (Lol p 1, 2, 3 and 5) during immunotherapy

Background IgE titres tend to rise early after the start of immunotherapy, followed by a decline to pre-immunotherapy levels or lower. Objectives We were interested to ktiow whether the early increase in IgE antibodies includes new specificities of IgE, and whether these responses persist. Methods Sera of 64 patients undergoing grass pollen immunotherapy were tested for IgE against four purified grass pollen allergens: Lol p 1. 2, 3, and 5. At least two serum samples were taken, one before the start of therapy and one between 5 and 18 months after the first immunization (mean: 10 months). Results The mean IgE responses to Lol p 1, 2 and 3 showed a moderate but not significant increase. In contrast, the mean IgE response to Lol p 5 showed a significant decrease of >30%. IgE against total Lolium perenne pollen extract moderately increased (>20%), showing that a RAST for total pollen is not always indicative for the development of IgE against its major allergens. For >40% of the patients it was found that IgE against one or more of the four allergens increased, while IgE against the remaining allergen(s) decreased. Eor 10 sera the ratio of IgE titres against at least two allergens changed by at least a factor of 5. The changes in specific IgE also included conversions from negative (< 0.1 RU) to positive (0.6 to 5.0 RU) for five patients. For two patients, the induction of these ‘new’ IgE antibodies against major allergens was shown to result in a response that was persistent over several years. Conclusion Although active induction of new IgE specificities by immunotherapy was not really proven, the observations in this study indicate that monitoring of IgE against purified (major) allergens is necessary to evaluate changes in specific IgE in a reliable way.     

A Reassessment of the HL—A System in Khoisan Populations of South West Africa

Work supported in part by the South African Institute for Medical Research, the Chris Barnard Fund and a grant from the U.K. Medical Research Council. Also the J. A. Cohen Institute for Radiopathology and Radiation Protection (IRS), the National Institute of Health (Contract PH 43-65-992), the Dutch Organisation for Health Research (TNO), the Dutch Foundation for Medical Research (FUNGO) and the Dutch Organisation for the Advancement of Pure Research (ZWO).