James B. Laudenslager

Laser ablation of human atherosclerotic plaque without adjacent tissue injury

Seventy samples of human cadaver atherosclerotic aorta were irradiated in vitro using a 308 nm xenon chloride excimer laser. Energy per pulse, pulse duration and frequency were varied. For comparison, 60 segments were also irradiated with an argon ion and an Nd:YAG (neodymium:yttrium aluminum garnet) laser operated in the continuous mode. Tissue was fixed in formalin, sectioned and examined microscopically. The Nd:YAG and argon ion-irradiated tissue exhibited a central crater with irregular edges and concentric zones of thermal and blast injury. In contrast, the excimer laser-irradiated tissue had narrow deep incisions with minimal or no thermal injury. These preliminary experiments indicate that the excimer laser vaporizes tissue in a manner different from that of the continuous wave Nd:YAG or argon ion laser. The sharp incision margins and minimal damage to adjacent normal tissue suggest that the excimer laser is more desirable for general surgical and intravascular uses than are the conventionally used medical lasers.

Near thermal energy charge transfer reactions of rare gas ions with diatomic and simple polyatomic molecules: The importance of Franck‐Condon factors and energy resonance on the magnitude of the rate constants

Charge transfer rate constants for reactions of He+, Ne+, Ar+, Kr+, and Xe+ with N2, O2, CO, NO, CO2, N2O, and CH4 were measured using an ion cyclotron resonance spectrometer. The absolute values of the rate constants were within the upper limit predicted from the Gioumousis‐Stevenson orbiting theory for ion‐molecule reactions. The magnitudes for the charge transfer rate constants are discussed with respect to (1) the availability of an energy level of the molecular ion resonant with the recombination energy of the rare gas ion, and (2) the value of the Franck‐Condon factor connecting this energy level of the molecular ion with the molecular neutral.

Pulsed ultraviolet lasers and the potential for safe laser angioplasty.

Endoscopic laser ablation of atheroma using continuous wave lasers is limited by imprecise control of thermal ablation, resulting in a crater that expands in width and depth, with thermal damage to adjacent normal tissue. We compared the gross and histologic effects of pulsed 308 mm excimer irradiation to continuous-wave Nd:YAG and Argon Ion laser irradiation, and pulsed 1,060 nm, 532 nm, 355 nm, and 266 nm laser irradiation in 205 atherosclerotic aortic segments. In contrast to the continuous-wave Nd: YAG, Argon Ion, and pulsed 1,060 nm, 532 nm, and 355 nm laser irradiation, which produced gross and histologic evidence of uncontrolled ablation, the 308 nm and 266 nm pulsed lasers induced incisions that conformed precisely to the beam configuration without gross evidence of thermal injury. The incision edges from these two lasers were histologically smooth and comparable to a scalpel incision. Our histologic findings suggest that rapid, precise endoscopic ablation of vascular and nonvascular tissue can be performed at these shorter pulsed wavelengths with very high precision with relatively little damage or risk to adjacent tissue.

Percutaneous excimer laser coronary angioplasty: Results in the first consecutive 3,000 patients

OBJECTIVES We report the comprehensive results of the first consecutive 3,000 patients treated in an excimer laser coronary angioplasty registry. BACKGROUND Excimer laser coronary angioplasty involves the use of a pulsed, 308-nm ultraviolet laser transmitted by optical fibers to reduce coronary stenoses. Preliminary reports have described safety and efficacy profiles in small numbers of patients. METHODS Patients were enrolled in a prospective, nonrandomized manner. The catheters used were 1.3, 1.6, 2.0, 2.2 and 2.4 mm in diameter, at energy densities up to 70 mJ/mm2. Procedures were performed by standard angioplasty technique with conventional guide catheters. RESULTS Seventy-five percent of patients were male, 68% were in Canadian Cardiovascular Society functional class III or IV and the cohort included 3,592 lesions. Procedural success (final stenosis < or = 50% without in-hospital Q wave myocardial infarction, coronary artery bypass surgery or death) was 90% and did not differ between the first 2,000 and the last 1,000 patients treated. There was no significant difference in success or complication rates with respect to lesion length, nor were there differences between selected complex and simple lesions. Complications included in-hospital bypass surgery (3.8%), Q wave myocardial infarction (2.1%) and death (0.5%). Coronary artery perforation occurred in 1.2% of patients (1% of lesions) but significantly decreased to 0.4% in the last 1,000 patients (0.3% of lesions). Angiographic dissection occurred in 13% of lesions, transient occlusion in 3.4% and sustained occlusion in 3.1%. Comprehensive lesion morphologic data collected in the latter portion of the study showed the procedure predominantly limited to American College of Cardiology-American Heart Association type B2 and C lesions, with no significant difference in short-term outcome between groups. CONCLUSIONS Excimer laser angioplasty can be safely and effectively applied, even in a variety of complex lesions not well suited for percutaneous transluminal coronary angioplasty. These types may include aorto-ostial, long lesions, total occlusions crossable with a wire, diffuse disease and vein grafts. Most recent data show a trend for the selection of predominantly complex lesions and a reduction in the incidence of perforation. This procedure may broaden the therapeutic window for the interventional treatment of selected complex coronary artery disease.Objectives. We report the comprehensive results of the first consecutive 3,000 patients treated in an excimer laser coronary angioplasty registry. Background. Excimer laser coronary angioplasty involves the use of a pulsed, 308-nm ultraviolet laser transmitted by optical fibers to reduce coronary stenoses. Preliminary reports have described safety and efficacy profiles in small numbers of patients. Methods. Patients were enrolled in a prospective, nonrandomized manner. The catheters used were 1.3, 1.6, 2.0, 2.2 and 2.4 mm in diameter, at energy densities up to 70 mJ/mm2. Procedures were performed by standard angioplasty technique with conventional guide catheters. Results. Seventy-five percent of patients were male, 68% were in Canadian Cardiovascular Society functional class III or IV and the cohort included 3,592 lesions. Procedural success (final stenosis ≤50% without in-hospital Q wave myocardial infarction, coronary artery bypass surgery or death) was 90% and did not differ between the first 2,000 and the last 1,000 patients treated. There was no significant difference in success or complication rates with respect to lesion length, nor were there differences between selected complex and simple lesions. Complications included in-hospital bypass surgery (3.8%), Q wave myocardial infarction (2.1%) and death (0.5%). Coronary artery perforation occurred in 1.2% of patients (1% of lesions) but significantly decreased to 0.4% in the last 1,000 patients (0.3% of lesions). Angiographic dissection occurred in 13% of lesions, transient occlusion in 3.4% and sustained occlusion in 3.1%. Comprehensive lesion morphologic data collected in the latter portion of the study showed the procedure predominantly limited to American College of Cardiology-American Heart Association type B2 and C lesions, with no significant difference in short-term outcome between groups. Conclusions. Excimer laser angioplasty can be safely and effectively applied, even in a variety of complex lesions not well suited for percutaneous transluminal coronary angioplasty. These types may include aorto-ostial, long lesions, total occlusions crossable with a wire, diffuse disease and vein grafts. Most recent data show a trend for the selection of predominantly complex lesions and a reduction in the incidence of perforation. This procedure may broaden the therapeutic window for the interventional treatment of selected complex coronary artery disease.

Radiative lifetimes and electronic quenching rate constants for single-photon-excited rotational levels of no (A2Σ+, ν′ = 0)☆

Abstract A narrow-band, frequency-doubled, tunable dye laser has been used to excite fluorescence from the A2Σ+, ν′ = 0 state of NO. Collision-free lifetimes were measured for 21 different K′ levels giving a mean radiative lifetime τ = 217 ± 4 ns. Electronic quenching rate constants of NO (A2Σ+, ν′ = 0) were measured for O2, N2, H2O, CO2 and Ar. No dependence of the quenching-rate constant on the initially excited rotational level was observed.

Radiative lifetimes and quenching rate coefficients for directly excited rotational levels of OH (A 2Σ+,v′=0)

A narrow bandwidth pulsed dye laser has been used to excite OH X 2Πi radicals to the A 2Σ+ state by pumping in the (0,0) vibrational band around 308 nm. The radiative lifetimes of specific (K′,J′) rotational levels in v′ = 0 were measured at low pressures ⩽1 mTorr which gave a mean lifetime τ0=0.721±0.009 μs (2σ). Electronic quenching rate constants for important atmospheric species N2, O2, H2O, and also for H2 were measured for a range of initially excited rotational levels. A strong dependence of this rate constant on the initially excited level was found for N2, and less markedly for O2, with the rate constant tending to increase for the lowest rotational levels K′⩽3. The implications of these measurements of radiative and quenching rates for state selected rotational levels of OH A, v′=0 to the laser‐induced fluorescence detection of atmospheric OH are discussed.

Effect of hematoporphyrin derivative and photodynamic therapy on atherosclerotic rabbits

This study was performed to demonstrate selective uptake of hematoporphyrin derivative (HPD) within actively developing atheroma, to localize the site of uptake of HPD within the atheroma, and to determine the potential for photodynamic therapy (PDT) of atherosclerosis in the rabbit model. Fifteen rabbits were rendered atherosclerotic. Five rabbits received neither HPD nor PDT and 2 rabbits received HPD, 10 mg/kg intravenously, without subsequent irradiation. Eight other rabbits received 5 to 20 mg of HPD intravenously and subsequent intravascular 636-nm laser radiation to either the thoracic aorta or the aortic arch. A total of 32 to 288 J of laser energy was delivered through a 300-mu quartz fiber. All rabbits that received in vivo HPD had red fluorescence of their aortas when placed under ultraviolet light. The pattern of fluorescence corresponded precisely to the pattern of atheroma. In segments that received PDT, light microscopic examination revealed an accumulation of smooth muscle cells at the intimal surface. Fluorescence microscopy revealed a diminishing concentration gradient of HPD from intimal surface layers towards the media. Assessment of treated thoracic aortic segments revealed quantitative and qualitative differences compared with control segments. In the arch-treated segments, however, no changes were seen. It is concluded that HPD localizes within rabbit atheroma, can be detected by fluorescence and is deposited in a diminishing concentration gradient from lumen toward media. Irradiation with 636-nm light may induce qualitative and quantitative changes in atheroma.

Product distributions for some thermal energy charge transfer reactions of rare gas ions

Ion cyclotron resonance methods were used to measure the product distributions for thermal energy charge transfer reactions of He+, Ne+, and Ar+ ions with N2, O2, CO, NO, CO2, and N2O. Except for the He+–N2 reaction, no molecular ions were formed by thermal energy charge transfer from He+ and Ne+ with these target molecules. The propensity for dissociative ionization channels in these highly exothermic charge transfer reactions at thermal energies contrasts with the propensity for formation of parent molecular ions observed in photoionization experiments and in high energy charge transfer processes. This difference is explained in terms of more stringent requirements for energy resonance and favorable Franck–Condon factors at thermal ion velocities.

Ultranarrow linewidth, magnetically switched, long pulse, xenon chloride laser

A spectral linewidth of <7×10−4 A and diffraction‐limited beam divergence has been obtained from a long pulse, electric discharge xenon chloride laser with intracavity Fabry–Perot etalons. A gain duration of 100 ns provided for multipass operation of the etalons, significantly improving both contrast and finesse. The electrical discharge circuit required to produce this long gain duration was comprised of a pulse forming network, saturable inductor magnetic switch, and a tapered, constant impedance, interface transmission line.

Single longitudinal mode operation of an XeCl laser

Single longitudinal mode output from a directly tuned, long pulse, magnetically switched XeCl laser is reported for the first time. Mode control was achieved using spatial aperatures and intracavity etalons. The narrow bandwidth laser output was diffraction limited with an optical pulse width of 30 ns, which would yield a transform limited bandwidth of 30 MHz.