Efficiency and safety of optically modified fiber tips for laser angioplasty.

To evaluate the safety and efficiency of optically modified fiber tips, craters were created in human cadaver atherosclerotic arterial walls using sapphire contact probes and lensed fibers connected to a continuous wave neodymium yttrium aluminum garnet (Nd-YAG) laser. Laser energy was emitted at a constant level of 50 J. The sapphire contact probe catheter consisted of a round 2.2 mm diameter synthetic sapphire attached to an 8F catheter into which a 0.2 mm diameter optical fiber was inserted with the distal tip maintained at 3 mm from the sapphire. The lensed fiber catheter consisted of a 0.2 mm optical fiber at the end of which a 1 mm diameter lens was made. The fiber was inserted into a 5F low profile balloon catheter with the lens maintained 3 mm beyond the catheter tip. During laser emissions the catheter tips were maintained in a stationary position in contact with tissue targets immersed in blood at an angle of 90 degrees. The diameter of holes at the entry and exit of craters, the depth of craters and thermal injury to adjacent tissue (rim of carbonization and vacuolization) were measured with microscopy. The volume of tissue removed was derived from these values. Controlled effect index was determined as the ratio of diameter of holes and the extent of thermal injury. Efficiency was determined as the ratio of volume of tissue removed and the energy required to vaporize tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental angioplasty: circumferential distribution of laser thermal energy with a laser probe.

A new laser probe that converts argon laser energy to heat in a metallic cap on a fiberoptic fiber was compared with a bare argon laser fiberoptic catheter system for the dissolution of atherosclerotic obstructions under fluoroscopic guidance in 24 atherosclerotic rabbits. Twelve animals were randomly assigned to receive treatment with either a bare fiberoptic system or a laser probe coupled to an argon laser. Both fibers had similar outer (0.9 mm) and core (400 mu) diameters. Pulses of 1 watt for 1 second's duration were delivered from the tip of the fiberoptic system, while pulses of 6 watts for 2 seconds' duration were delivered to the laser probe. The results of angiography indicated that widening of luminal stenosis was seen in only 2 of 12 animals treated with the fiberoptic system compared with 8 of 12 animals treated with the laser probe. Perforation of the vessel wall occurred more frequently with the fiberoptic fiber (9 of 12 animals) as compared with the laser probe (1 of 12 animals). Histologic examination of direct laser radiation with the fiberoptic fiber revealed a small localized laser defect along one side of the vessel wall associated with charring, a gradient of thermal injury and considerable thrombus formation. In contrast, those vessels treated with the laser probe showed histologic evidence of thermal injury distributed evenly around the entire luminal circumference. This was associated with minimal charring, a gradient of thermal injury and thinner, flatter thrombus formation. Carbonization of the metallic tip and adherence of atherosclerotic debris with secondary vessel tearing were potential adverse effects of the laser probe.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrasonic assessment of skin and wounds with the scanning laser acoustic microscope.

The aim of the present study was to test the hypothesis that ultrasonic propagation properties in skin and wound tissue would correlate with material properties such as collagen content, water content, and tensile strength of those tissues. Both ultrasonic speed and ultrasonic attenuation coefficient were directly correlated with tissue collagen content, [r = 0.80 and r = 0.56, respectively (p less than 0.001)]. In addition, ultrasonic speed and attenuation coefficient were inversely correlated with tissue water content, [r = -0.57 and r = -0.73, respectively (p less than 0.001)]. Tensile strength also correlated very significantly with ultrasonic speed (r = 0.90, p less than 0.001), and significantly with attenuation coefficient (r = 0.58, p less than 0.001). The results demonstrate the feasibility of using ultrasound for noninvasively determining the material properties of biologic tissues including healing cutaneous wounds.

Low-energy, Q-switched ruby laser iridotomies in Macaca mulatta.

Laser iridotomies have been pursued as a means of performing anterior segments surgery as a virtually noninvasive procedure. An ideal single laser pulse technique has been elusive. In this study, iridotomies in rhesus monkeys were produced with a single exposure to a Q-switched ruby laser pulse. The iridotomy formation was accompanied by acoustic wave generation, bubble formation, and explosive tissue disruption, evidence of a nonlinear laser-iris interaction. The average energies at which these iridotomies were produced ranged between 18 and 48 mJ, some of the lowest energies reported for a laser iridotomy. Corneal changes were observed both at the epithelium and at the endothelium in some, but not all, of the eyes exposed. The epithelial changes morphologically resembled nonlinear damage reported for transparent solids. Damage to physical materials has been attributed to stimulated Brillouin scattering, a mechanism that may also play a role at the cornea. Consideration of such phenomena should be a part of the clinical evaluation prior to exposure of a cornea to high-power laser pulses. Although the endothelial change was more difficult to analyze, a shock-wave effect could not be discounted.

Argon laser trabeculotomies in primates: evaluation by histological and perfusion studies.

The continuous argon laser beam has been applied to the trabeculum at the anterior chamber angle of one eye of nine primates. The treatment was evaluated by light and scanning electron microscopy and constant rate infusion studies at different intervals following the laser treatment. This histological studies revealed coagulative necrosis, with trabeculotomies extending into Schlemm's canal in the immediate postoperative period. However, complete closure of the laser-induced trabeculotomies by healing was observed within 1 to 3 weeks following the treatment. Outflow facility data as measured by the perfusion studies revealed somewhat increased values of the treated eye during the early 2 weeks after laser treatment. On longer follow-up, no significant outflow differences were measured between the treated and untreated eyes.

Argon endolaser.

We developed an endolaser probe that is capable of delivering argon laser light for photocoagulation of retinal breaks or vascular fronds. Energy is transmitted through a fiberoptic cord from a console outside of the surgical area to an endolaser probe inside the operating suite. The probe can be fired into fluid- or gas-filled media. With the use of this system, panretinal photocoagulation can be performed rapidly and conveniently during a vitrectomy procedure. We have also successfully managed posterior retinal tears and bleeding fibrovascular fronds with this system.

Laser photocoagulation with biomicroscopic scleral indentation.

The treatment of peripheral retinal tears by laser photocoagulation is an accepted technique. One of its limitations is its difficulty in use near the ora serrata. The inability to treat the anterior border of a rentinal tear may allow the tear to progress to clinical retinal detachment despite treatment of the tear's posterior and lateral borders. The use of a scleral indentation funnel at the time of laser photocoagulation permits the sealing of all margins of the break. This technique increases the number of retinal tears that can be treated by the laser, and it may improve the rate of success of photocoagulation of peripheral retinal tears.

Intraocular photocoagulation with the argon-krypton laser.

We have developed an intraocular laser coagulator using a low-loss single-fiber probe system connected to an argon-krypton laser. Coagulation can be accomplished at distances of 3 mm or greater from the retina, permitting easy control of lesion size, location, and intensity. The probe can be fired rapidly without overheating and can also be fired into air without damage to the tip.

Slit-lamp fundus microscopy without contact lens and with laser attachment.

Gullstrand's fundus microscopy is adapted for slit-lamp microscopy without a contact lens, equipped by a wide-aperture argon laser beam. The z axis magnification of the image is used to advantage for vitrectomy. The mobility of the device permits vitrectomy on a fixed eye.

Dual delivery system for argon laser photocoagulation. Improved techniques of the binocular indirect argon laser photocoagulator.

A dual delivery system provided alternate delivery of the laser beam to the slit lamp and binocular ophthalmoscope. Ophthalmologists may choose between the two systems in accordance with the nature and location of the fundus lesion. A pilot study comparing the rate of laser hit between the slit-lamp photocoagulator and the binocular indirect argon laser photocoagulator (BIALP) showed that accuracy was better with the slit lamp and BIALP when they were operated in the sitting position than with the BIALP operated in the standing position. A photo-electric safety switch was attached to the blocking filter of the BIALP to protect operator's and patient's eyes. The improved machine and techniques increased the efficiency and safety of argon laser photocoagulation. Postoperative use of the BIALP was of particular value. Laser photocoagulation in children's eyes became possible for the first time with the BIALP.

Clinical photocoagulation with the organic dye laser. A preliminary communication.

Clinical research utilizing the yellow, orange, and red wavelengths of the liquid organic dye laser has demonstrated that this laser may be successfully used for photocoagulation of certain ophthalmic defects. The advantage of the dye laser as a photocoagulation source is its capability to produce monochromatic wavelengths at relatively high output powers through a large range of the visible spectrum. Therefore, a target tissue can be coagulated with minimal transmittal of laser energy through the ocular media, by the selection of a wavelength that would be most highly absorbed by that tissue. The dye laser, as a system that permits transspectral photocoagulation, should prove valuable in the treatment of ocular disease.

Repair of small blood vessels with the neodymium-YAG laser: a preliminary report.

A technique for repair of incisions in small blood vessels (diameter, 0.3 to 1.0 mm) in the rat is described using a Neodymium-YAG laser. It is possible to seal the incision without the use of sutures and to preserve the lumen of the vessel. The advantages of this technique over electrocoagulation and microsuture techniques are pointed out. Although the work is in preliminary stages, the technique is considered to be relatively safe, and the potential use of the application in human surgery is indicated. The possible complications of this technique are pointed out.

Measurement in vitro of pulsatile arterial diameter using a helium-neon laser.

A noncontacting in vitro measurement of pulsatile arterial diameter using a scanning optical micrometer is described. The major component of this system is a He-Ne laser whose beam scans the pulsating artery to be measured. The laser micrometer was integrated into a pulsatile perfusion apparatus that imposed various hemodynamic conditions on excised canine vessels. The laser system reliably tracked the pulsating arterial diameter at a particular longitudinal site as well as at various increments in the presence of an experimentally created stenosis. The He-Ne laser measured the radial motion of canine arteries and various vascular substitutes anastomosed in an end-to-end fashion. From these novel measurements, calculations were made of arterial compliance and bending stress, two biomechanical parameters that are implicated as potential causes of anastomotic intimal hyperplasia and graft failure. Although this device is inherently limited to in vitro use, it is a potentially useful instrument for vascular physiology and biophysics.

Effects of thermal knives on wound healing.

Tissue response to injury caused by the electrosurgical scalpel, the hemostatic Shaw scalpel, the CO2 laser, and a standard steel scalpel have been compared. Subcutaneous incisions in pigs were evaluated histologically at 1, 4, 7, 14, and 22 days postincision. The least damage was produced by the standard steel scalpel at all time periods. Epithelial migration started on day 1 for the standard steel scalpel, on day 4 for the Shaw scalpel, and only on day 7 for the electrosurgical scalpel and laser knives. Lateral thermal necrotic zones were found for all three thermal knives. Tensile testing showed no significant differences in the early postincision tissue strength. By day 14 wounds made with the standard steel scalpel were stronger than those made with the Shaw and electrosurgical scalpel. These findings indicate that thermal injury delays the wound healing process.

Endoscopic argon-ion laser phototherapy of bleeding gastric lesions.

An argon-ion laser, coupled to a flexible fiberoptic endoscope, was used to photocoagulate experimentally produced bleeding gastric ulcers in dogs. Argon-ion laser phototherapy rapidly and effectively achieved hemostasis in all bleeding ulcers. Bleeding arteries up to 2 mm in diameter were photocoagulated. Intact normal gastric mucosa was exposed to laser energy for varying periods of time to determine if transmural photothermal injury occurred. Exposure for greater than 15 seconds at 1.0 w of throughput power caused microscopical evidence of transmural injury. Healed, laser-treated ulcers could not be differentiated from nontreated control ulcers or normal stomach one month after injury. The Beer law and the heattransfer factors relating to soft tissues are discussed. The coupled argon-ion laser-endoscope may be a safe tool to treat self-limited superficial bleeding gastric lesions.

Urethroscopic recanalization of urethral stenosis using argon laser.

A technique is presented for urethroscopic treatment of urethral stricture by Argon-Laser. A 23-watt Argon Laser is used as energy source. The radiation energy is applied into the urethra by means of a quartz fiber laser conductor. The flexible laser conductor can be inserted into the urethra through the opening of a standard urethroscope with water-inflow. It is necessary when withdrawing the urethroscope circularly to remove the entire stricture area down to the wall of the corpus cavernosum urethra, so that a totally smooth transition is created between the urethral sections proximal and distal to the stricture. The results of treatment were documented by infusion urethrography and uroflowmetric examination. The maximum flow rate (m) of 5.5 ml. before the treatment increased to 21.2 ml. after the operation. Among a total of 40 patients reconstriction occurred in 6 cases necessitating a renewal laser evaporization. These patients were treated in an early period of our urethroscopic laser recanalization. In these cases the stricture ring was not removed completely down to the wall of the corpus cavernosum urethra.

Influence of ADP, blood flow velocity, and vessel diameter on the laser-induced thrombus formation.

The laser-induced thrombus model in rat mesenteric arterioles and venules represents a reliable and reproducible in vivo method. It is suitable for basic investigations concerning factors involved in thrombus formation as well as for testing antithrombotic effects of drugs. The laser-induced thrombus formation depends significantly on the presence of ADP, as ADP-utilizing enzymes inhibit thrombosis in the animal model. The instrumental test set-up consists of a 4 W Argon laser (Spectra Physics, Mountain View, CA, USA), a ray adaptation and adjusting device (BTG, Munich, FRG), a microscope (ICM 405, Zeiss, Oberkochen, FRG), and a video system (Sony, Japan). RBC velocity data were recorded with the help of a modified dual-slit technique (acc. to Wayland and Johnson). Results were expressed as number of laser injuries necessary to produce a defined thrombus (minimum size: 1/4 of the vessel diameter) under constant conditions (effective capacity: 30 mW, exposure time: 1/5 sec). The number of laser lesions necessary to induce a defined thrombus decreased with an increase in arteriole diameter (10 to 20 micron) but increased again in larger arterioles and small arteries (greater than 25 micron). On the arteriolar side there are significant correlation coefficients between vessel diameter and RBC velocity (r = 0.69), vessel diameter and No. of laser injuries (r = 0.70), and RBC velocity and No. of laser injuries (r = 0.71). Due to relative low flow conditions in the venules, the number of laser injuries required to induce a defined thrombus does not significantly depend on the vessel diameter.

Carbon dioxide laser scleral dissection and filtering procedure for glaucoma.

A comparison of eye bank eyes using continuous wave or rapid superpulsed carbon dioxide laser energy indicated that rapid superpulsed was the superior modality for scleral dissection, because there is less charring and puckering of tissue. The results of filtering procedures in five glaucomatous eyes by using rapid superpulsed carbon dioxide energy to perform the scleral dissection revealed the possible advantages of performing the procedure this way might be: (1) the technical ease by which the microdissection is performed under direct microscopic observation with the absence of blood or instruments in the field; (2) the safety factor of never having penetrated into the anterior chamber with a sharp instrument; (3) the possible advantage of the inhibition of healing at the wound margin because of coagulation of tissue at the wound edge by the laser beam; and (4) the bacteriocidal effect of thermal cutting.

The argon "contact" laser scalpel: technical considerations.

The authors describe the use of a new contact argon laser scalpel designed specifically for hand-controlled cutting and hemostasis. This instrument delivers energy precisely to targeted tissue and produces minimal damage to adjacent healthy structures. Potential clinical applications are discussed.