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Biomedical subjects

R M Verdaasdonk

Publications and source records attributed to R M Verdaasdonk.

29 records · Page 2Linked to original sources
PubMed1992

Nd:YAG laser-assisted angioplasty in femoropopliteal artery occlusions: "hot" versus "cold" recanalization with transparent contact probe.

Percutaneous recanalization of femoropopliteal artery occlusions (1-21 cm; median, 8 cm) was attempted in 50 patients. A 2.2-mm-diameter contact probe catheter connected to a continuous-wave neodymium yttrium aluminum garnet (Nd:YAG) laser was used. The laser was activated (15 W, 1-second pulses) only if too much resistance was met. Balloon angioplasty was performed after successful traversal of the occlusion. Primary success was achieved in 40 of 50 patients (80%). In 20 cases, recanalization was achieved mechanically (cold group). In the other 20 cases, recanalization was achieved with the help of laser irradiation (hot group: 15-405 J; median, 90 J). Except for the length of the obstruction (longer in the cold group), the two groups did not differ in baseline characteristics. Neither the length of the occlusion nor the duration of symptoms correlated with failure or success or with the delivered laser energy. Cold and hot groups did not differ with regard to functional improvement and angiographic patency at 3 and 12 months (94% +/- 4). Thus, brief laser activation doubled the cold primary success rate, but the major action of the laser contact probe is mechanical remodeling of the obstruction.

Adult↗
PubMed1992

End-to-side anastomosis of small vessels using an Nd:YAG laser with a hemispherical contact probe. Technical note.

A new technique is described which enables the surgeon to perform an end-to-side anastomosis between arteries with little (less than 2 minutes) or no occlusion of the recipient artery. The technique was developed in rabbits, but has recently been successfully used in a patient in whom an anastomosis between the superficial temporal artery and a proximal branch of the middle cerebral artery was created.

Aged↗
PubMed1991

Noncontact tissue ablation by holmium:YSGG laser pulses in blood.

To assess the feasibility of intra-arterial tissue ablation by Holmium:YSGG laser pulses (2.1 microns) in a noncontact mode, the transmission of the laser pulses through saline and blood was measured. The temporal interaction between the 500 microseconds laser pulse and saline at the fiber tip was investigated with time-resolved flash photography. The penetration depth in blood, and saline depended on the fiber output energy. In blood at 37 degrees C, the penetration depth varied from 1.2 to 2.1 mm for intensities of 3.1 to 12.4 J/mm2 per pulse, respectively, whereas its theoretical value for water is 0.33 mm, which is based on the measured absorption coefficient of 3.0 +/- 0.1/mm. The large penetration depth was due to the development of a transparent vapour cavity around the fiber tip. In saline, its maximum length was 4.7 mm. Its maximum width was 2.8 mm. The lifetime of the cavity was 450 microseconds. In blood, ablation of porcine aorta was feasible at a distance of 3 mm. Large fissures observed in adjacent tissue are likely to be caused by the expansion of the vapour cavity. We conclude that, due to a "Moses effect in the microsecond region," Holmium:YSGG tissue ablation is possible through at least 2.7 mm of blood.

Animals↗
PubMed1991

Mechanism of CW Nd:YAG laser recanalization with modified fiber tips: influence of temperature and axial force on tissue penetration in vitro.

Modified fiber tips are used for laser angioplasty of totally occluded peripheral arteries. It has not been established, however, to what extent the mechanism of action of various laser probes is optical, thermal, or mechanical. We examined transparant contact probes (hemispherical contact probes and ball-shaped fibers) and metal laser probes, coupled to a continuous-wave Nd-YAG laser. By using homogeneous thick porcine fatty tissue samples submerged in blood plasma, tissue penetration was measured in relation to the temperature of the probe and the axial force exerted on the tissue. By using 15 W, 1 s laser pulses, the surface of transparent contact probes had to be first contaminated by carbonized tissue particles to achieve tissue penetration. Penetration increased from 1 to 10 mm per pulse when axial force increased from 20 to 100 g. Metal probes had to be sufficiently insulated from the liquid environment by water vapour entrapped in a denatured protein layer to exceed the threshold temperature of 225 degrees C for tissue penetration. When axial force increased from 20 to 80 g at 10 W continuous exposure, the velocity of tissue penetration increased in the range from 1 to 4 mm/s. Tissue penetration by modified fiber tips is attributed to both remodeling and vaporization of tissue. With transparent contact probes, tissue is heated partly by direct light absorption and partly by a hot probe surface. Axially directed force is necessary to displace lateral non-ablated tissue and to overcome mechanical resistance. We conclude that mechanical dilation due to axial catherization force (Dotter effect) contributes substantially to tissue penetration by transparent contact probes.

Angioplasty, Laser↗
PubMed1991

Temperature along the surface of modified fiber tips for Nd:YAG laser angioplasty.

For laser angioplasty probes, the thermal properties of the probes will primarily determine their mechanism of action. We examined the absorption, temperature increase, and probe degradation of transparent contact probes (hemispherical contact probe and ball-shaped fibers) and metal laser probes coupled to a continuous-wave Nd-YAG laser. Temperature was recorded by means of thermocouples and the measurements were corrected for direct light absorption by the thermocouple. During 15 W, 1 s exposure, the peak temperature rise of the hemispherical contact probe in contact with tissue dropped from approximately 1,000 degrees C at the front end to below 45 degrees C (95% drop) at the lateral side. In contrast, during continuous exposure the peak temperature rise of metal laser probes in contact with tissue dropped from 560 degrees C at the front end to near 400 degrees C (30% drop) at the 5.5 mm proximal rear end. During exposure in blood or tissue, the transparent contact probes became contaminated. Their absorption increased from 5 to 33% and the probe deteriorated. Repeated use of metal laser probes in blood resulted in a higher temperature at the rear than at the front end due to backburing of the fiber. Owing to the large temperature drop along the surface of transparent contact probes, the area of thermal destruction is limited to the tissue in front of the probe, whereas along the entire surface of metal laser probes the tissue will be affected. The large difference between these temperature distributions should be respected during clinical application of the transparent contact probe and the metal laser probe.

Absorption↗
PubMed1990

Early and late arterial healing response to catheter-induced laser, thermal, and mechanical wall damage in the rabbit.

Pulsed lasers are being promoted for laser angioplasty because of their capacity to ablate obstructions without producing adjacent thermal tissue injury. The implicit assumption that thermal injury to the artery is to be avoided was tested. Thermal lesions were produced in the iliac arteries and aorta of normal rabbits by a) electrical spark erosion, b) the metal laser probe, and c) continuous wave neodymium-yttrium aluminum garnet (Nd-YAG) laser energy through the sapphire contact probe. High-energy doses were used to induce substantial damage without perforating the vessel wall. Thermal lesions (n = 77) were compared with mechanical lesions (n = 22) induced by oversized balloon dilation. Medial necrosis was induced by all four injury methods. Provided no extravascular contrast was observed after the injury, all damaged segments were patent after 1 to 56 days. The progression of healing with myointimal proliferation was remarkably similar for all injuries. At 56 days, the neointima measured up to 370 microns. In conclusion, provided no perforation with contrast extravasation occurred, the normal rabbit artery recovered well from transmural thermal injury. The wall healing response is largely nonspecific.

Angioplasty, Balloon↗
PubMed1990

Explosive onset of continuous wave laser tissue ablation.

The phenomena at the onset of and during tissue ablation using continuous wave lasers were studied. Aortic and myocardial bovine tissues were exposed in air and in water to Nd-YAG (10 to 60 W) and argon (3.5 W) laser light. The transmitted light was measured, the surface of the tissue was filmed and the tissue was processed for histology. Three distinct phases were observed. Phase A was tissue denaturation. Phase B started with explosive vaporisation ('popcorn') in conjunction with a drop of about 50% in light transmission due to enhanced reflection and scattering. The 'popcorn' is possibly associated with a layered structure of the tissue. Phase C started with carbonisation of the tissue beginning in the centre and expanding in a cyclic fashion while the tissue was vaporised leaving a crater. Forward light transmission did not decrease. Thin layers of carbon (20 microns) and vacuoles (30 microns) suggested a large temperature gradient along the tissue ablation front. The ablation velocity was constant (r greater than 0.92) and tissue dependent. Reported models on laser tissue ablation need to be extended to include explosive vaporisation ('popcorn') at the onset and cyclic carbonisation during steady-state crater formation.

Animals↗
PubMed1990

In vitro comparison of radiofrequency-heated and laser-heated metal probes for angioplasty.

The effects of a metal probe catheter on tissue using radiofrequency (RF) as its energy source is evaluated. The energy dissipation and the temperature increase of this probe was compared with a laser-heated probe. After 15 seconds, the temperature rise of the RF-heated probe at a maximum power setting was 68 degrees C in water and 106 degrees C in plasma. In contrast, the temperature rise of the Nd:YAG laser-heated probe after 10 seconds, 10 watt (W), was 80 degrees C in water and 595 degrees C in plasma. Calorimetric experiments showed that in a 7 to 30 W range of the power setting for the RF generator, only 3.5 to 4.5 W was dissipated at the RF catheter tip. Using axial forces equivalent to 100 g in fatty tissue, the penetration velocity of the RF-heated probe was 0.015 mm/s, with a temperature rise of the tip of 180 degrees C; whereas the velocity of the laser-heated probe was 3.4 mm/s with a temperature rise of the tip of 300 degrees C. These in vitro results suggest that during clinical application, tissue in contact with the front surface of the RF-heated angioplasty probe will be remodeled, whereas with the laser-heated probe tissue will be vaporized circumferentially. The RF-heated probe's risk of vessel wall perforation is probably small.

Electrocoagulation↗
PubMed1989

[Percutaneous recanalization of occluded upper leg arteries using laser treatment].

Percutaneous transluminal laser recanalization was attempted in 21 patients with occluded superficial femoral arteries and 'life style limiting claudication'. Primary success was achieved in 20 (95%) of these total occlusions. In 7/21 no laser energy was required. At one month only 1 patient had claudication and the mean Doppler ankle/arm systolic pressure ratio had increased by 0.36 +/- 0.19 (p less than 0.001) at rest and 0.47 +/- 0.34 (p less than 0.001) after exercise. Complications directly attributable to the procedure were: perforation (1), peripheral embolic episodes (2), haematoma (1), transient vasospasm (2). All complications could be treated non-surgically. These preliminary data suggest that laser recanalization of relatively short occlusions of the superficial femoral artery, followed by balloon dilatation, may be accomplished with satisfactory acute and short-term results, but not without risk.

Aged↗
PubMed1988

Nd-YAG laser energy distribution in an artificial obstruction: influence of lasing parameters in a model of laser angioplasty.

A Nd-YAG laser (1064 nm) coupled to a silica fiber (0.6 mm core diameter) was used to create defects in a model of arterial vascular obstruction. We employed transparent agar doped with black ink as atheromatous material and studied the size and shape of defects created by various lasing parameter settings. By adding calcium sulphate to the agar its scattering properties were enhanced. The created defects correspond to a temperature boundary. The optical properties of the agar greatly influenced the size and shape of the created defects. In the agar with enhanced scattering properties, the created defects showed an unfavourable penetration width-depth ratio. Maximum width of penetration always exceeded the fiber diameter. This may contribute to an increased risk of vessel wall perforation in small vessels and, if the fiber is positioned close to the vessel wall, even when a coaxial position is maintained. With increasing cumulative energy, both maximum depth and width of penetration leveled off in both agars. The results suggest that agar can be used to obtain empirically the lasing parameters that will minimize the risk of vessel wall perforation by an axially positioned fiber. The agar model needs further study to determine its limitations, but agar seems to be a useful substitute for atheroma in the study of laser catheter angioplasty.

Agar↗