Biomedical subjects

C Borst

Publications and source records attributed to C Borst.

At least 109 records · Page 6Linked to original sources

PubMed1992

Effect of balloon angioplasty on femoral artery evaluated with intravascular ultrasound imaging.

BACKGROUND: Intravascular ultrasound was used to assess the immediate effect of balloon angioplasty on the superficial femoral artery. METHODS AND RESULTS: In 16 consecutive patients, corresponding ultrasonic cross sections (n = 72) before and after balloon angioplasty were qualitatively and quantitatively analyzed. The qualitative data were compared with angiographic findings. Before intervention, the angiographically demonstrated obstructive lesions were confirmed by intravascular ultrasound. Ultrasound enabled discrimination between soft (n = 43) and hard (n = 29) lesions, as well as between eccentric (n = 57) and concentric (n = 15) lesions. After balloon angioplasty, the presence of a dissection assessed angiographically in 14 patients was confirmed by intravascular ultrasound. Additional morphological information provided by ultrasound included plaque rupture in 14 patients and internal lamina rupture in six patients. Quantitative ultrasound data revealed an increase in free lumen area from 9.7 +/- 4.7 to 18.3 +/- 7.0 mm2 (p less than or equal to 0.01), an increase in minimal lumen diameter from 2.8 +/- 0.7 to 3.6 +/- 1.2 mm (p less than or equal to 0.01), and an increase in media-bounded area from 21.7 +/- 5.4 to 28.3 +/- 5.8 mm2 (p less than or equal to 0.01). The lesion area for the majority of cases (n = 32) remained unchanged (13.0 +/- 4.9 mm2 versus 12.9 +/- 4.6 mm2), or the lesion disappeared partially (from 9.1 +/- 0.9 to 4.3 +/- 1.4 mm2, n = 4, p less than or equal to 0.01) or totally (from 10.1 +/- 4.2 to 0 mm2, n = 6). Stretching of the arterial wall was further evidenced by medial thinning from 0.55 +/- 0.19 to 0.34 +/- 0.11 mm (p less than or equal to 0.01). CONCLUSIONS: Luminal enlargement by balloon dilatation is achieved primarily by overstretching the arterial wall, with the lesion volume remaining practically unchanged. Overstretching is accompanied almost always by dissection and plaque rupture and occasionally by an internal lamina rupture.

Aged↗

PubMed1992

Mid-infrared pulsed laser ablation of the arterial wall. Mechanical origin of "acoustic" wall damage and its effect on wall healing.

Pulsed mid-infrared lasers are an alternative to excimer lasers for transluminal angioplasty. The mid-infrared lasers, however, were reported to produce "acoustic" wall damage that might impair the immediate and long-term results. To study the immediate and long-term effects on the arterial wall, 184 craters (1 mm diameter and 1 mm depth) were produced perpendicular to the intimal lining in the thoracic aortas of pigs. Three types of craters were evaluated: Ho-YSGG laser-induced (lambda = 2.09 microns, 2 pulses of 500 microseconds, 0.50 joule/pulse, 50 gm force), mechanically drilled, and "acoustic" craters. "Acoustic" craters were produced by two laser pulses delivered into a saline-filled metal fiber cap, which was placed in a mechanically drilled crater. The metal cap was provided with four outlets for water vapor and isolated "acoustic" from optical and thermal laser effects. The pigs survived 3, 14, and 28 days. Arterial wall damage, medial necrosis, and wall healing were assessed microscopically. At 3 days, laser and "acoustic" craters were accompanied by large tissue ruptures (2.7 +/- 0.9 mm and 2.9 +/- 0.8 mm, respectively, mean +/- standard deviation). These were attributed to large vapor bubbles expanding within the tissue. A zone of medial necrosis was observed adjacent to the laser craters (0.43 +/- 0.15 mm) and to the "acoustic" craters (0.17 +/- 0.14 mm). Neither ruptures nor necrosis was observed with the mechanical craters. At 2 and 4 weeks, the necrotic areas were repopulated with smooth muscle cells and all craters were adequately filled with smooth muscle cells, without any sign of an exaggerated proliferative response. We conclude that within the arterial wall, Ho-YSGG ablation was accompanied by the rapid expansion of a water vapor bubble. The formation of the relatively large vapor bubble is inherent to the use of a mid-infrared laser. The risk of creating dissections clinically, when delivering Ho-YSGG laser pulses, remains to be determined. The present study provided no indication that the arterial wall fissures might affect the restenosis rate unfavorably by promoting myointimal proliferation.

Angioplasty, Laser↗

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↗

PubMed1991

Imaging of post-mortem coronary arteries by 30 MHz intravascular ultrasound.

Intravascular ultrasound cross-sectional imaging of the atherosclerotic artery may be employed to guide plaque ablation by spark erosion, atherectomy, laser irradiation or other means. To assess whether in the coronary artery the echolucent zone of the three-layered ultrasound appearance of muscular arteries might be a reliable boundary to halt transluminal ablative angioplasty, epicardial coronary arteries were scanned under pressure over a distance of 4-8 cm at 1 mm intervals. A 5.2F catheter with a 30 MHz transducer rotating at 600 RPM was used. In 419 images from four post-mortem hearts, aged at death 22, 31, 56 and 82 years, the presence of a distinct echolucent zone was scored as percentage of the wall circumference. The median scores were 0%, 0%, 10% and 75%, respectively. In the three youngest hearts, the three-layered appearance was largely absent. In the 82 year old heart, in contrast, the three-layered appearance could generally be identified. Within subjects, the presence of an echolucent zone was variable in location. Qualitatively, neither abundant medial elastin tissue nor a reduced medial thickness could explain the absence of an echolucent zone when the ultrasound image was compared to the corresponding microscopic section. The results show that in the 82 year old heart, 30 MHz intravascular ultrasound discrimination of coronary wall layers would be adequate to guide transluminal plaque ablation. In the younger hearts, guided ablation would fail due to the limited presence of a distinct echolucent zone as an ultrasound landmark of the media. Whether the presence or absence of an echolucent zone is related to age remains to be determined.

Adult↗

PubMed1991

Percutaneous coronary and peripheral angioscopy with saline solution and carbon dioxide gas in porcine and canine arteries.

To obtain a clear view with angioscopy, blood must be displaced. Carbon dioxide (CO2) gas has proved to be a safe intraarterial contrast agent, and it may have advantages over saline solution as an infusion medium for angioscopy. This study compared the use of CO2 gas and saline solution in the femoral artery, in the presence and absence of a proximal occlusion, in nine pigs and six dogs. The applicability of CO2 gas in the coronary arteries was also evaluated. In total 185 angioscopy procedures were evaluated. With proximal occlusion, angioscopy with CO2 gas was successful in all 28 peripheral procedures, whereas with saline solution only 65% of the procedures resulted in a clear view (p less than 0.005). Without proximal occlusion, angioscopy was successful with CO2 gas and saline solution in 61% and 3% of procedures, respectively (p less than 0.0001). Cardiovascular parameters and blood gases showed minor changes after administration of CO2 gas. During coronary angioscopy with CO2 gas, mechanical heart failure occurred in all instances, which was lethal in 12 animals. None of the animals died as a result of saline angioscopy. In conclusion, CO2 gas is a safe medium for angioscopy in the peripheral arteries and in general offers a better view than saline solution. In contrast to saline solution, without proximal balloon occlusion CO2 gas provided a clear view in 61% of the peripheral procedures. In the coronary arteries, however, CO2 angioscopy was generally fatal in both animal models.

Animals↗

PubMed1991

Modulation of ouabain binding in beating ventricular myocardium from guinea-pigs: effects of lidocaine and monensin.

To further elucidate the interdependence between digitalis sensitivity and the cellular Na+ load, the influence of two Na+ load modifying drugs, monensin and lidocaine, on the concentration-dependence of ouabain binding and ouabain effects was studied in beating ventricular strips from guinea-pig heart. Monensin (3 x 10(-6)M), a Na+ ionophore known to elevate Na+ influx, enhanced 3H-ouabain binding (by approximately 40%) as well as the ouabain effect at non-toxic ouabain concentrations, and it shifted the threshold for toxicity towards threefold lower ouabain concentrations. Lidocaine (2 x 10(-4)M), a Na+ channel blocker, lowered ouabain binding by about one third, and it extended the ouabain concentration range tolerated without toxicity by a factor of three. In the concentrations used, neither compound exerted any direct effect on ouabain binding studied in isolated cardiac membranes. The binding data obtained in the muscle strips were well fitted by a mathematical model which quantifies the dependence of ouabain binding on the underlying (Na+ +K+)-ATPase activity. These findings provide evidence for an indirect drug-induced modulation of ouabain binding via the interference with the cellular Na+ load.

Animals↗

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

Epicardial cryosurgery as used in ablation of accessory atrioventricular pathways: effect on valvular function in the dog.

Epicardial cryosurgery for ablation of atrioventricular accessory pathways has surgical advantages. However, it is applied directly to the valve base. To assess the risk of valve impairment, 10 anaesthetized dogs were subjected to standardized epicardial cryosurgery of the right atrioventricular junction. Two of these underwent sham procedure (dissection only). Valve function was assessed by colour Doppler echocardiography preoperatively and at 2 days, 1 week, 2 weeks and 10 weeks postoperatively. Three out of the eight animals subjected to cryosurgery developed moderate (grade 2/4) tricuspid insufficiency, which appeared at 1 week postoperatively, following regression of congestive oedema. Two out of the three cases of TI were associated with leaflet prolapse. No tricuspid insufficiency was seen in the sham-operated animals. At the end of each interval two animals were killed for histological examination. Histological examinations showed that cryolesions extended a maximum of 3 mm into the valve leaflet. The tricuspid insufficiency is attributed to the extensive scarring (including chondroid metaplasia), which causes retraction and restricted motion of the annulus. It is concluded that cryolesions may impair atrioventricular valve function. Patients undergoing cryosurgery should be monitored postoperatively by echocardiography for atrioventricular valve insufficiency.

Animals↗

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

Loss of blood platelet adhesion after heating native and cultured human subendothelium to 100 degrees Celcius.

STUDY OBJECTIVE: Balloon angioplasty produces mechanical vessel wall injury that leads to substantial blood platelet deposition at the angioplasty site. The aim of the study was to determine whether thermal angioplasty might, by contrast, reduce platelet adhesion by denaturation of subendothelial adhesive proteins. DESIGN: Native and cultured human subendothelium was briefly heated to greater than or equal to 100 degrees C by laser irradiation or to 50-100 degrees C by immersion in preheated phosphate buffered saline (PBS). Subsequently, the subendothelium was exposed for 5 min to flowing human blood at a shear rate of 1300 s-1. Blood platelet adhesion to the subendothelium was determined quantitatively. EXPERIMENTAL MATERIAL: Human umbilical arteries were used and the subendothelial matrix derived from cultured umbilical vein endothelial cells. MEASUREMENTS AND RESULTS: After heating arterial subendothelium by laser irradiation to greater than or equal to 100 degrees C, zero platelet adhesion was found v 36(SD 2)% adhesion to the non-heated surface (p less than 0.001). After laser heating of the subendothelial matrix to greater than or equal to 100 degrees C, platelet adhesion was absent in 10/10 experiments (p less than 0.01). After heating the matrix to 100 degrees C by immersion in PBS, platelet adhesion was reduced to 5(5)% v 31(7)% at 37 degrees C (p less than 0.001). CONCLUSIONS: These in vitro results, if extrapolated to catheter interventions, suggest that thermal injury to the vessel wall by laser angioplasty or other thermal angioplasty methods may provide a basic and clinically relevant advantage over mechanical angioplasty modalities, because of a potentially reduced risk of complications related to platelet adhesion.

Angioplasty, Balloon, Coronary↗

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↗

PubMed1989

Laser ablation and the need for intra-arterial imaging.

In 48 patients with severe claudication due to a total obstruction of the femoropopliteal artery, percutaneous recanalization was attempted with a 2.2 mm diameter rounded sapphire contact probe in conjunction with a continuous wave Nd:YAG laser. In eight patients the contact probe laser catheter took a subintimal course that could not be redressed. Laser recanalization needs high-resolution diagnostic information on the complex anatomy of the obstruction. Intra-arterial ultrasound imaging may provide the necessary information to evaluate, monitor or guide novel angioplasty techniques. The design of an ultrasound catheter which combines high-resolution diagnostic imaging with steerability, flexibility and controlled ablation is now the major engineering challenge in interventional cardiology.

Angioplasty, Balloon↗

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↗

PubMed1987

31P NMR study of intracellular pH during the calcium paradox.

Reperfusion of an isolated mammalian heart with a calcium-containing solution after a brief calcium-free perfusion results in irreversible cell damage: the calcium paradox. It has been suggested that acidification of the cytosol, as a result of hydrolysis of ATP and accumulation of calcium by mitochondria, is an important factor in the development of the calcium paradox. Phosphorus nuclear magnetic resonance (31P NMR) spectroscopy was used to investigate the course of intracellular pH during the calcium paradox in isolated rabbit heart at 37 degrees C. Intracellular pH was measured from the chemical shift of the intracellular inorganic phosphate (Pi) peak. During control perfusion and the subsequent calcium-free period intracellular pH amounted to 7.1. After induction of the calcium paradox by readmitting calcium to the perfusion fluid, intracellular pH amounted to 7.0. It is concluded that acidification of the cytosol does not play a causal role in the development of the calcium paradox.

Animals↗

PubMed1987

Proarrhythmic effects of ventricular electrical catheter ablation in dogs.

Electrical catheter ablation of arrhythmogenic sites is a new therapy for ventricular tachycardia that is still being investigated. Recent studies have shown, however, that the procedure itself can provoke serious ventricular arrhythmias. The incidence, course and mechanism of these arrhythmias were studied in 10 beagles treated with a single R wave-synchronized cathodal shock delivered to the endocardial ventricular wall (5 dogs left ventricular, 5 dogs right ventricular). Shocks were delivered at 30 (four dogs), 80 (two dogs) or 250 J (four dogs). Each dog underwent programmed electrical stimulation at or near the ablation site before, within 1 hour after and 1 week after the shock. Holter electrocardiographic monitoring (24 hours) was performed during day 1 and 7 after the shock in all the dogs, and extended Holter monitoring was done during the first 5 days in four dogs. All dogs survived for 1 week. Within 10 minutes after the shock, a sustained ventricular tachycardia was recorded in nine dogs; deterioration into ventricular fibrillation occurred in two dogs. In nine dogs, 60 to 169 monomorphic ventricular tachycardia episodes (mean 101) occurred on day 1 and 0 to 11 (mean 3) occurred on day 7; Holter monitoring failed for technical reasons in one dog. Extended Holter monitoring showed a marked decline in the incidence of tachycardia during the first 3 days. Early activation during ventricular tachycardia was always derived at or near the ablation site, and the QRS configuration during pre- and postablation pacing at this site was identical to the tachycardia configuration. Ventricular tachycardia was never inducible with programmed stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗