Conflicting scientific views on the health risks of low-level ionising radiation.
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Humans↗
Biomedical subjects
R H Clarke
Publications and source records attributed to R H Clarke.
First and subsequent pregnancies after tubal microsurgery: evaluation of the fertility index.
OBJECTIVE: To determine the number of children born after a tubal microsurgical operation and to evaluate the fertility index, a long-term measure of reproductive potential. DESIGN: A case series involving a follow-up questionnaire. SETTING: A tertiary care university hospital. PATIENT(S): Three hundred twelve women undergoing microsurgery for tubal disease. INTERVENTIONS: A range of open microsurgical procedures including reversal of sterilizations. MAIN OUTCOME MEASURE(S): Cumulative pregnancy rates to the first and second normal pregnancies and calculation of the fertility index. RESULT(S): The 2-year cumulative pregnancy rates (probability +/- SE) for a first normal pregnancy for proximal disease, distal disease, tubal reanastomoses, and tubal adhesions were 0.51 +/- 0.05, 0.29 +/- 0.06, 0.47 +/- 0.06, and 0.30 +/- 0.07, respectively. Of the 288 (92%) women responding to the questionnaire, 142 women had at least one child. Of the 100 women who wanted a second child, 68 succeeded, the proportions being similar in each surgery category. The fertility index described restoration of normal fertility in 30%, 12%, 34%, and 23% for women with proximal disease, distal disease, anastomotic procedures, and adhesion disease, respectively. CONCLUSION(S): The fertility index is a useful measure of long-term reproductive potential. The high recurrent pregnancy rate emphasizes the value of microsurgery in restoring normal fertility to some women.
Adult↗
ICRP recommendations applicable to the mining and minerals processing industries and to natural sources. International Commission on Radiological Protection.
The current views of the International Commission on Radiological Protection on exposure to natural radiation are presented in the new recommendations (ICRP Publication 60) where the concepts of practice and intervention are both used to establish mechanisms of control. The history of the present recommendations is reviewed, and the latest guidance on the control of 222Rn at home and at work (ICRP Publication 65) is outlined. The new model of the respiratory tract, which has been adopted by ICRP, is discussed in the context of its predictions of the doses from radon and from particulate natural radionuclides. Consideration is given finally to criteria for the restoration of sites previously contaminated by natural radionuclides.
Air Pollution, Indoor↗
Implementation of the 1990 recommendations of ICRP in the countries of the European Community.
The International Commission on Radiological Protection (ICRP) has published new Recommendations in ICRP Publication 60. These 1990 Recommendations provide a System of Radiological Protection that takes account of the most recent information on the effects on health of exposure to ionising radiation and trends in the setting of safety standards. Within the European Community the Recommendations of the ICRP are implemented through a Euratom Directive which is binding on member states, a draft of which has been accepted by the Article 31 Group and must eventually be ratified by the Council of Ministers. It is expected that the new directive will broadly endorse the principles of protection given in the 1990 Recommendations together with the dose limits for both workers and members of the public. There are likely to be some modifications to the 1990 Recommendations that are mainly related to their practical application. As it will be some time before the directive is incorporated into national regulations, a number of member states have taken independent initiatives. The development of dose constraints for occupational, medical and public exposure is being seen by national organisations in many countries as a significant new approach to improving standards of radiation protection.
European Union↗
Percutaneous delivery of low-level laser energy reverses histamine-induced spasm in atherosclerotic Yucatan microswine.
BACKGROUND: Previous in vitro experiments performed in our laboratory have shown that low-level laser energy may produce prompt reduction in isometric tension of vascular smooth muscle. The present study was designed to extend these previous in vitro findings to an in vivo model and thereby investigate the hypothesis that laser light delivered percutaneously in vivo could successfully reverse arterial spasm. METHODS AND RESULTS: Spasm defined as greater than 50% reversible reduction in luminal diameter persisting for greater than or equal to 5 minutes was successfully provoked by injection of histamine (100-400 micrograms/kg) in 13 arteries among 10 atherosclerotic Yucatan microswine; the magnitude of histamine-induced vasoconstriction was then documented angiographically by repeated injections of contrast media for as long as 30 minutes (controls). After return of angiographic luminal diameter to baseline, spasm was reproduced with a second injection of histamine into the same artery. Representative wavelengths generated by ultraviolet (UV), visible, and infrared lasers were then delivered percutaneously via conventional fiberoptics to the site of spasm, and angiographic assessment was repeated for as long as 30 minutes (treatment trial). In three arteries treated with UV (351 nm) light from an excimer laser, angiographic luminal diameter narrowing decreased from 100% to 23.9%, 50.0% to 9.3%, and 76.0% to 42.3%, respectively. The magnitude of laser-induced increase in luminal diameter was 50.2 +/- 22.7%, which was significantly greater than the magnitude of relaxation observed spontaneously during the control trials (10.9 +/- 9.8%, p = 0.02). Visible light from a helium-neon (632 nm) laser accomplished complete reversal of histamine-induced spasm in two of four arteries; in the remaining two arteries, luminal diameter narrowing percentages were reduced from 57.0% to 20.0% and from 76.5% to 30.8%, respectively. The magnitude of helium-neon laser-induced relaxation (55.8 +/- 17.9%) was again significantly greater than that observed during the control trials (0.9 +/- 1.9%, p = 0.01). Finally, infrared irradiation from a diode-pumped neodymium:yttrium aluminum garnet (1,064 nm) laser decreased histamine-induced luminal diameter narrowing in three arteries from 100% to 21.4%, 56.0% to 8.7%, and 68.3% to 35.3%, respectively. The magnitude of infrared laser-induced improvement in luminal diameter narrowing was 53.0 +/- 23.3%, which was significantly greater than that observed during the control trials (12.9 +/- 10.7%, p = 0.01). In three additional arteries, fiberoptic sham trials (without laser irradiation) failed to produce relaxation of histamine-induced spasm. CONCLUSIONS: These findings document for the first time that light-induced relaxation of vascular smooth muscle, previously documented in vitro, may be reproduced in vivo.
Animals↗
Analysis of photoproducts, free radicals, and particulate debris generated during in vivo argon laser myoplasty.
Catheter-guided laser myoplasty in a closed ventricle has been advocated for the treatment of hypertrophic cardiomyopathy, ablation of arrhythmogenic foci, and transmyocardial laser revascularization of ungraftable regions of ischemic myocardium. The purpose of this study was to evaluate the nature of particulate debris and photoproducts generated in vivo. Accordingly, cardiopulmonary bypass was established in four dogs without active cooling and an apical left ventricular vent was placed. In two dogs, a laser catheter was inserted into the cardioplegia-arrested left ventricle through the left atrial appendage and across the mitral valve. In the other two dogs the laser catheter was inserted into a perfused, fibrillating left ventricle retrograde across the aortic valve. Myocardial ablation of the ventricular septum was performed using continuous argon-ion laser irradiation (8-10 watts, 4-11 minutes) and blood samples were drawn through the ventricular vent. The final ablation in each dog was done during a separate ventricular flush with a chemical "spin trap" capable of detecting free radicals. Analysis of ventricular effluent revealed levels of carboxyhemoglobin and hydrogen cyanide which were well below accepted clinical toxic limits. Microparticulate debris (2-300 femtoliter) was not detected. Evidence of trace free radical generation was suggested in one of four dogs. In conclusion, closed ventricular argon laser myoplasty did not generate clinically significant levels of the toxic photoproducts we measured, or microparticulate debris. These in vivo findings suggest that the clinical application of catheter-based laser myoplasty will not be limited by the generation of these toxic photoproducts or microembolic debris.
Animals↗
Angiographic contrast media interference with laser-induced fluorescence excitation and detection in atherosclerotic human coronary arteries.
Laser-induced fluorescence has been used in conjunction with angiography for laser angioplasty guidance. The effect of radiopaque contrast media on the excitation and detection of arterial fluorescence has not been previously reported. Accordingly, fluorescence emission spectra from human coronary artery necropsy specimens (n = 7) during excitation with pulsed excimer laser excitation (308 nm) was examined before and after the addition of three different contrast media, sodium and meglumine diatrizoate, sodium and meglumine ioxaglate, and iopamidol. A decrease in overall fluorescence intensity was observed at all wavelengths for each contrast agent examined. The decrease in intensity of fluorescence emission was more marked at wavelengths less than 410 nm than at wavelengths above 425 nm. Similar effects were observed for contrast media diluted with whole blood. Absorption spectra for all three contrast media demonstrated absorption in the ultraviolet centered around 240 nm. We conclude that preferential absorption in the ultraviolet range by contrast media interferes with the excitation and detection of laser-induced fluorescence; use of visible light excitation may obviate interference with laser-induced fluorescence analysis of plaque.
Angioplasty, Laser↗
Radiation detriment: its quantification and use in setting standards.
At the end of 1990 the International Commission on Radiological Protection adopted new recommendations for the control of exposure to ionizing radiation. The main reasons for the revision of existing standards were first, the new estimates of the risks associated with exposure and second, the need to develop a conceptual framework that covered not only occupational exposures but also radon in homes and the consequences of accidents. This paper addresses these issues and shows how the definition of radiation detriment is used to set new standards in a System of Radiological Protection.
Humans↗
Risks from ionizing radiation.
For the public in the United Kingdom--and the United States--natural radon is a far greater radiation hazard than are emissions from nuclear installations.
Environmental Exposure↗
Correlation of fluorescence emission with the plaque content and intimal thickness of atherosclerotic coronary arteries.
The use of fluorescence emission for guidance during laser angioplasty may be limited by the complexity of the emission from the broad range of atherosclerotic plaques normally encountered in disease coronary arteries. Fatty, fibrous, and calcific plaque content as well as maximal intimal thickness were measured and correlated with fluorescence intensity ratios from the emission spectra for a broad cross-section of atherosclerotic plaques from human necropsy specimens. Multiple and stepwise regression analysis was used to analyze intensity ratios of 13 wavelengths between 390 and 600 nm corresponding to regions of observed spectral structure. The level of correlation of the intensity ratios with fatty and calcific plaque content was found to be dependent on the complexity of the atherosclerotic lesion. The fluorescence emission was found to correlate well with both fibrous plaque content and intimal thickness, allowing the differentiation between normal and atherosclerotic samples. In conclusion, plaque characteristics can be assessed by fluorescence emission, although the successful implementation of spectroscopic guidance is dependent on the level of prediction error which may vary with tissue type.
Arteries↗
Vascular spasm complicates continuous wave but not pulsed laser irradiation.
Preliminary clinical experience with laser angioplasty has suggested that arterial spasm may complicate attempts to employ laser light to accomplish vascular recanalization. The present study was designed to investigate the role of energy profile on the development of arterial spasm during laser angioplasty. Laser irradiation was delivered percutaneously in vivo to New Zealand white rabbits and to Yucatan microswine with or without atherosclerotic lesions induced by a combination of balloon endothelial denudation and atherogenic diet. Continuous wave (CW) laser irradiation from an argon ion gas laser (wavelength 488 to 514 nm) was applied to 23 arteries, while 16 arteries were irradiated using a pulsed xenon chloride (308 nm) or xenon fluoride (351 nm) excimer laser. Arterial spasm, defined as greater than 50% reduction in luminal diameter narrowing, complicated delivery of laser light to 17 (74%) of the 23 arteries irradiated with the CW argon laser. Spasm was consistently observed at powers greater than 2 W, at cumulative exposures greater than 200 seconds, and at total energy greater than 200 joules. Spasm was typically diffuse (including the length of the vessel) and protracted (lasting up to 120 minutes). Intra-arterial nitroglycerin (up to 300 micrograms) produced only temporary and incomplete resolution of laser-induced spasm. In contrast, spasm was never observed in any of the 16 arteries in which laser angioplasty was performed using a pulsed laser (0.95 to 6.37 joules/cm2, 10 to 50 Hz, 48 to 370 seconds). Thus CW but not pulsed laser angioplasty may be complicated by arterial spasm.(ABSTRACT TRUNCATED AT 250 WORDS)
Angiography↗
Laser-induced thermal occlusion of berry aneurysms: initial experimental results.
An intravascular laser-catheter technique was used to occlude 12 experimental berry aneurysms, ranging in size from 4 X 3 mm to 8 X 6 mm (length X width), while the patency of adjacent arteries was preserved. A small steel cap on the end of an optical fiber was fluoroscopically positioned within the aneurysm. The cap was rapidly heated by the optical transmission of laser energy. This produced a thermal tissue reaction within the aneurysm, resulting in its occlusion. After treatment, the steel cap was detached atraumatically from the fiber and left as a permanent implant within the occluded aneurysm. This method has an advantage over the use of a bare-ended intravascular optical fiber because the steel cap provides a uniform distribution of thermal energy, thereby reducing the risk of unexpected perforation during treatment. The radiologic and histologic results of using this laser-catheter system were evaluated 1-21 weeks after treatment.
Animals↗
Pulsed ultraviolet laser irradiation produces endothelium-independent relaxation of vascular smooth muscle.
Recent studies have shown that continuous wave laser irradiation induces contraction of vascular smooth muscle, except at powers far below the threshold for tissue ablation. To determine the corresponding effects of pulsed laser irradiation on vascular smooth muscle tone, vascular rings of rabbit thoracic aorta were mounted isometrically with 1 g tension in Krebs-bicarbonate buffer and irradiated with 308 or 351 nm from an excimer laser through a 400-microns optical fiber. A total of 250 exposures were performed with 1-6.5 mJ/pulse (fluence = 0.8-5.5 J/cm2), 10-50 Hz, and cumulative exposures of 10-120 seconds. Excimer laser irradiation in combinations of pulse energy (PE), repetition rate (RR), and cumulative exposure below, at, or above threshold for tissue ablation consistently produced relaxation unassociated with contraction in each of the 250 exposures. For the total 250 exposures, the magnitude of relaxation (reduction in recorded tension, Rmax) was 55 +/- 4% (mean +/- SEM) of maximum vasomotor reactivity recorded in the specimen in response to administration of serotonin. Rmax varied directly with both PE and RR. When PE was increased from 1 to 5 mJ/pulse (n = 13), Rmax increased from 57 +/- 19% to 80 +/- 19% (p less than 0.0001); when RR was increased from 10 to 50 Hz (n = 10), Rmax increased from 27 +/- 8 to 46 +/- 8 (p less than 0.0001). Rmax varied independently of endothelial integrity (assessed anatomically and pharmacologically) and wavelength (308 vs. 351 nm). Simultaneously recorded tissue-temperature profiles disclosed that during pulsed laser irradiation, tissue temperature rise did not exceed 5 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Spectroscopic characterization of cardiovascular tissue.
We present results of a series of laser spectroscopic measurements on in vitro samples of cardiovascular tissue. These include laser Raman scattering, Fourier transform infrared, plasma emission and fluorescence, and electron paramagnetic resonance spectroscopy. The results of these spectroscopic measurements are discussed in terms of their implications for the field of laser angioplasty.
Cardiovascular Diseases↗
Percutaneous, in vivo excimer laser angioplasty: results in two experimental animal models.
Pulsed ultraviolet light from an excimer laser was successfully transmitted via conventional fused silica optical fibers and used to accomplish recanalization of stenotic or totally occluded arteries in an intact, flowing blood field of two atherosclerotic animal models. The fibers, 300-600 micron in diameter, were delivered percutaneously in wire-guided multilumen catheters and then used to transmit wavelengths of 308 or 351 nm from excimer lasers with pulse durations of 12 nsec or less. Lesions from 70-100% diameter narrowing, and 0.6 to 5.5 cm in length were successfully recanalized (less than 50% residual diameter narrowing) in eight animals, using 3-4 J/cm2/pulse, 10-50 Hz, and 48-370-sec cumulative exposure. Necropsy examination in six of the eight animals disclosed no signs of thermal injury. Perforations were observed in four of eight animals. Thus, while use of an excimer laser power source did not obviate vascular perforation as a complication of laser angioplasty, these preliminary results indicate that energies of pulsed ultraviolet light sufficient to ablate atherosclerotic plaque can be both transmitted via conventional fused silica optical fibers and used successfully within an intact, flowing blood field. It may therefore be possible to use pulsed ultraviolet light from an excimer laser to accomplish percutaneous ablation of atherosclerotic arterial obstructions in humans.
Angiography↗
Mechanism of laser ablation in an absorbing fluid field.
Selection of a laser source for intravascular applications has frequently been predicated upon assumptions involving transmissibility in blood of the wavelength of light emitted by a given laser. Standard absorption curves for ultraviolet radiation in blood and infrared radiation in water would suggest that transmission of ultraviolet radiation through a blood field and infrared radiation through any aqueous fluid field would be insufficient for tissue ablation. The present series of experiments was undertaken to determine whether these theoretical predictions would in fact obviate the use of these wavelengths in a blood field. Specimens of normal human myocardium and/or polyvinylchloride were submerged under blood and water and irradiated with ultraviolet radiation (351 nm) delivered as a focused beam and via an optical fiber and infrared radiation (10,600 nm) delivered as a focused beam. Ablation of myocardium was successfully accomplished with a focused beam of both ultraviolet and infrared radiation under as much as 5 mm of blood and with ultraviolet radiation via an optical fiber with the fiber tip up to 3 mm distant from the tissue specimen. High-speed cine recordings of ablation carried out using a focused beam of laser radiation demonstrated that formation of a dynamic optical cavity is the basis for successful pulsed ultraviolet and infrared laser transanguineous tissue ablation. These results thus demonstrate that prediction of wavelength transmission through fluid media based on optical properties of a static fluid does not predict ability to accomplish ablation under dynamic circumstances of laser irradiation.
Blood↗
Focal occlusion of the rabbit carotid artery by endovascular laser therapy.
Laser energy was fiberoptically transmitted into the carotid artery of a series of rabbits to induce an acute focal arterial occlusion. Temporary interruption of blood flow during the treatment was necessary to achieve an occlusion. The arterial occlusive effects of three wavebands of laser energy were compared and the violet band proved the most effective when using 0.3-0.5 Joules/second for 25-30 seconds. There was always the risk of vascular perforation during treatment when laser energy emission was from a bare-tipped optical fiber.
Animals↗