Laser angioplasty with a metal laser probe (‘hot tip’): Probe temperature in blood

In vitro experiments to determine the physical characteristics of a metal laser probe for laser angioplasty are described. The probe was filmed in stationary saline and plasma. The temperature of the probe was measured with thermocouples in air, stationary saline, whole blood, diluted packed cells (40%) and plasma. In the latter three media an envelope of denatured blood elements was found on the probe. This envelope entrapped a vapour layer which acts as an effective insulator, allowing the probe temperature to reach 600°C within 3 s of application of 10 W from an neodymium-YAG laser. Our observations suggest that the transfer of heat from the metal to the tissue will depend both on the formation and destruction of this thermally insulating envelope, which may well protect the arterial wall from heat injury during laser angioplasty.     

Effect of CO2 and blood media on laser probe temperature

Blood may limit laser ablation of arterial plaque by decreasing thermal energy transfer from metal-capped probes to arterial occlusions. Since a gas is a good insulator of heat, CO2 may be a better medium for laser recanalization. To study this possibility, a metal-capped fiber was positioned in a segment of blood-filled polyethylene tubing and activated with an argon laser. Probe temperatures were measured in blood and as the blood was displaced by flowing CO2 gas. Probe temperatures were higher at all powers studied in CO2 gas than in blood. Maximum probe temperatures averaged 518 +/- 24 degrees C after CO2 infusion versus 320 +/- 7 degrees C in blood, (P less than 0.0001). Blood aggregate formation was noted on the probe surface in blood but not in CO2 medium. Thus CO2 gas may be a preferable medium for laser recanalization, since higher probe temperatures are achieved, and the probe surface remains free of insulating blood coagulate.     

Laser thermal angioplasty probe ("hot tip") temperature: effects of flow

The temperature developed by the laser thermal ("hot tip") probe during arterial recanalisation is primarily dependent on the rate of energy delivery and the rate of dissipation to the surrounding medium. While higher probe tip temperatures enhance the efficacy of atheroma ablation, so too is the incidence of adverse effects increased. We studied the temperature developed in the probe tip in an artificial circulation using both saline and blood. In saline the peak probe temperatures were limited to 100 degrees C (boiling point), falling with each increment in flow. Small discrepancies in probes at different times and may be due to malalignment of the optical fibre-metal cap coupling, temperature measurement inaccuracy, tip insulation, or generator output instability. In blood, charring and clot formation insulated the tip raising the temperature (up to 700 degrees C within 5 seconds at 10 W) but also retarded dissipation of heat to the surroundings. The degree of clot and char formation was critical in determining subsequent thermal responses in any particular probe. The unknown rate and quantity of char buildup and changing blood flow during in vivo angioplasty are likely to be important obstacles to developing a reliable thermal feedback control system.     

Sapphire and metal tip recanalisation: Implications for safety

The characteristics of two modified fiber tips, the metal laser probe and the rounded sapphire contact probe, were examined in vitro and in vivo with respect to some of the risks of laser angioplasty.Both probes have an atraumatic, blunt shape. The laser beam profile of the sapphire contact probe looses its focussing properties in water. In vitro, we found a large temperature gradient from the front to the rim of the probe. Ablative temperatures were reached at the tip whereas the temperature of the metal connector near the rim of the sapphire crystal rose only 30 °C in blood when 15 W Nd-YAG was applied for 1 s. In contrast, the metal laser probe reached temperatures over 500 °C in an in vitro tissue/blood environment when 10 W was applied for 5 s. The metal probe ablated both in the forward and the radial direction. In a rabbit model there was a large variation in temperature of the metal in vivo (70 – 320 °C). The highest temperatures were associated with acute complications. However, in spite of transmural coagulation necrosis the artery wall remained functionally intact during a follow up period of up to 56 days.     

The effect of plaque composition on laser recanalization

Laser recanalization using metal-capped laser fibers and continuous-wave laser energy occurs by thermal ablation of atherosclerotic plaque. Different types of plaque respond differently to laser energy and plaque composition may be an important determinant of the success of laser recanalization. To investigate this hypothesis, 16 patients with symptomatic arterial occlusions in the mid and distal superficial femoral artery underwent B-mode ultrasound arterial imaging prior to attempted argon laser recanalization. The composition of the occlusions was classified as soft (echogenicity less than the adjacent arterial wall), dense (echogenicity equal to the adjacent arterial wall), or calcified (echoreflective). Recanalization was successful in 100% (8/8) of patients with soft occlusions versus 38% (3/8) with dense or calcified occlusions (P = 0.01). Thus, plaque composition as assessed by B-mode ultrasound imaging appears to be an important predictor of the success or failure of arterial recanalization using a thermal laser probe.     

Influence of probe motion on laser probe temperature in circulating blood

The purpose of this study was to evaluate the effect of probe motion on laser probe temperature in various blood flow conditions. Laser probe temperatures were measured in an in vitro blood circulation model consisting of 3.2 nm-diameter plastic tubes. A 2.0 mm-diameter metal probe attached to a 300 microns optical quartz fiber was coupled to an argon laser. Continuous wave 4 watts and 8 watts of laser power were delivered to the fiber tip corresponding to a 6.7 +/- 0.5 and 13.2 +/- 0.7 watts power setting at the laser generator. The laser probe was either moved with constant velocity or kept stationary. A thermocouple inserted in the lateral portion of the probe was used to record probe temperatures. Probe temperature changes were found with the variation of laser power, probe velocity, blood flow, and duration of laser exposure. Probe motion significantly reduced probe temperatures. After 10 seconds of 4 watts laser power the probe temperature in stagnant blood decreased from 303 +/- 18 degrees C to 113 +/- 17 degrees C (63%) by moving the probe with a velocity of 5 cm/sec. Blood flow rates of 170 ml/min further decreased the probe temperature from 113 +/- 17 degrees C to 50 +/- 8 degrees C (56%). At 8 watts of laser power a probe temperature reduction from 591 +/- 25 degrees C to 534 +/- 36 degrees C (10%) due to 5 cm/sec probe velocity was noted. Probe temperatures were reduced to 130 +/- 30 degrees C (78%) under the combined influence of 5 cm/sec probe velocity and 170 ml/min blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)     

Excimer laser (308 nm) recanalisation of in-stent restenosis: thermal considerations

. Excimer laser recanalisation of in-stent restenosis may be a viable modality for improving coronary patency. However, the presence of arterial stents modifies the thermal properties of the irradiated area and may alter temperature patterns generated during ablation. The goal of this study was to evaluate, in vitro, temperature changes during excimer laser ablation of stented vessels and compare them with those obtained from unstented (control) vessels. Six different stent types (AVE Microstent-II, AVE-GFX, ACS Multi-link, JJ Palmaz-Schatz, JJ Crown, and NIR) were deployed in freshly excised porcine coronary vessels. Three control unstented samples were also measured. Blood or saline was infused through the vessels, while the tissue environment was kept at ∼37°C. A 308 nm excimer laser (Spectranetics, CVX300) with an eccentric 2.0 mm laser catheter (Spectranetics, EII) delivered two trains of 200 pulses each, 10 s apart, at 60 mJ/mm², and 40 Hz, simulating maximum clinical exposure. The catheter was positioned midway in the stent, first coaxially parallel to the vessel wall, and then at an angle against the stent and vessel wall. Temperature measurements (n=168 for blood, n=96 for saline) were performed with a ∼210 μm diameter, fast-response thermocouple with 0.1°C resolution. The probe was positioned to within ∼250 μm from the inner surface of the vessels. Tissue temperature was measured at the catheter tip and at the distal and proximal edges of the stents. Maximum recorded temperatures for coaxial and angular alignment, did not exceed 42.2°C (∼6°C above baseline) and 54.2°C (∼18.1°C above baseline) respectively, for all stents types tested, controls, and all probe locations. Both stented and unstented vessels exhibited comparable temperature gradients. The observed maximum temperatures, obtained under extreme lasing conditions, indicated that 308 nm ablation, in the presence of stents under blood or saline infusion, produces clinically acceptable temperatures.     

Carbon dioxide gas as a perfusion medium for the sapphire probe in laser ablation of human atheromatous plaques: comparison study with saline

The effectiveness of CO2 gas as a perfusion medium was compared to that of saline in laser ablation of human atheromatous plaque. In an experimental circulation-occlusion model using flowing whole blood, human cadaveric arterial samples were irradiated by a sapphire probe with the Nd-YAG laser. The following experiments were performed: 1) lasing without perfusion, 2) lasing with saline perfusion of the probe, and 3) lasing with CO2 perfusion. Different perfusion flow rates of saline and CO2 were used. Results showed that the mean ablation area was 1.6-fold larger with CO2 than with saline perfusion (P less than 0.05, Student's t test). The mean lateral injury at the site adjacent to the ablation crater and at the area directly facing the probe was not significantly different with either perfusion medium. The larger ablation area with CO2 was probably due to the fact that CO2 is a good insulator for maintaining a higher probe temperature and keeps the probe free of blood debris. In conclusion, our results show that CO2 perfusion facilitates more effective laser ablation of atheromatous plaque than saline perfusion by the sapphire probe with the continuous wave Nd-YAG laser.     

"Hot tip": another method of laser vascular recanalization

This study is a preliminary report evaluating the use of laser radiation to heat a metal-capped fiber for arterial recanalization. The method was compared to the currently used bare-ended fiber for recanalization of occluded vessels. The model used was a human coronary artery xenograft transplanted in the femoral artery of the dog. At 4 weeks following the transplantation, laser recanalization was attempted using the heated metal probe ("hot tip") in five arteries and the bare fiber in another five arteries. Results: 1) Angiography demonstrated recanalization in all five arteries treated with the "hot tip" and three of the five arteries treated with the bare fiber. 2) Only one perforation occurred with the "hot tip," whereas three perforations occurred with the bare fiber. 3) The larger metal cap was capable of creating a wider channel in the occluded arterial segment. Although the trend favored the heated metal cap in terms of recanalization and less perforation than the bare fiber, the total number of experiments were not adequate to demonstrate statistical significance. Microscopic examination of the vessels recanalized by either technique was similar. Characteristic charring at the recanalization site was seen regardless of the technique used. These observations suggest that the effect of direct laser radiation on plaques is predominantly a thermal effect. Although these results would suggest utilization of a metal-capped fiber for vascular recanalization, more studies need to be done to confirm these preliminary findings.     

“Hot tip”: Another method of laser vascular recanalization

This study is a preliminary report evaluating the use of laser radiation to heat a metal-capped fiber for arterial recanalization. The method was compared to the currently used bare-ended fiber for recanalization of occluded vessels. The model used was a human coronary artery xenograft transplanted in the femoral artery of the dog. At 4 weeks following the transplantation, laser recanalization was attempted using the heated metal probe (“hot tip”) in five arteries and the bare fiber in another five arteries. Results: 1) Angiography demonstrated recanalization in all five arteries treated with the “hot tip” and three of the five arteries treated with the bare fiber. 2) Only one perforation occurred with the “hot tip,” whereas three perforations occurred with the bare fiber. 3) The larger metal cap was capable of creating a wider channel in the occluded arterial segment. Although the trend favored the heated metal cap in terms of recanalization and less perforation than the bare fiber, the total number of experiments were not adequate to demonstrate statistical significance. Microscopic examination of the vessels recanalized by either technique was similar. Characteristic charring at the recanalization site was seen regardless of the technique used. These observations suggest that the effect of direct laser radiation on plaques is predominantly a thermal effect. Although these results would suggest utilization of a metal-capped fiber for vascular recanalization, more studies need to be done to confirm these preliminary findings.     

Percutaneous recanalization of arteries: Status and prospects of laser angioplasty with modified fibre tips

Percutaneous balloon dilatation of arterial stenoses is a firmly established non-surgical treatment of ischaemic disease. The number of percutaneous transluminal coronary angioplasties performed per year in the USA approaches the number of coronary artery bypass graft operations. A great number of novel percutaneous recanalization schemes address the major problems of balloon angioplasty: failure to cross the stenosis (occlusion), failure to dilate effectively (15–20%), acute complications (5%) and re-stenosis within six months (30–40%). Laser energy can effectively evaporate atheromatous plaque, but delivery by an unmodified bare fibre creates only a small channel and carries a high risk of vessel-wall perforation in the coronary arteries. It appears impossible to maintain an axial position in small, tortuous and moving arteries with multiple side-branches. Coronary lesions are anatomically and structurally heterogeneous. Reduction of the perforation risk is being approached by four strategies: (a) optimization of the power source; (b) enhancement of laser-light absorption by plaque relative to artery wall; (c) improvement of plaque recognition; and (d) modification of the delivery system, which is discussed in detail. Recanalization of occluded femoropopliteal arteries with the 2.0-mm metal laser probe has proved to be safe and effective in more than 100 patients. The 2.2-mm rounded sapphire contact probe has been used with success in the peripheral arteries of over 30 patients. The recanalization mechanism of both probes is not yet fully understood. Closed-chest attempts at recanalization of coronary arteries by the 1.7-mm metal laser probe have been reported in 13 patients, with success in the majority. There were no complications requiring emergency surgery. The possible occurrence of embolism or spasm in three cases warrants a cautious approach to application of the metal laser probe in the coronary catheterization room. The primary benefit of laser recanalization with modified fibre tips is the possible transformation of a candidate for surgery into a candidate for balloon angioplasty. It remains to be established whether prior laser debulking of the atheroma will reduce the incidence of acute complications of balloon dilatation and will reduce restenosis in the subsequent year. In the past two years an avalanche of laser and non-laser recanalization schemes have been developed. In peripheral arteries, early results of most methods have shown an acceptably low incidence of acute perforations or other complications. The human arterial wall can take a heavy beating, both mechanically and thermally. In the next decade, catheter intervention techniques will progressively contribute to the treatment of peripheral and coronary artery disease.     

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.     

Experimental studies on argon laser angioplasty

To evaluate the safety and efficacy of recanalization of the occlusive arterial diseases by Argon laser, we investigated the effects of the laser irradiation using bare-ended probe (BEP) and metal-tip probe (MTP) on human cadaveric aorta and canine femoral arteries with thrombotic occlusion. In case of the BEP, the incidence of perforation of the arterial wall was high as compared with the MTP. However, laser angioplasty with angioscopic guidance could reduce the perforation rate, and made it possible to observe the new channel recanalized by laser. In case of the MTP, it was confirmed that the smaller MTP showed higher tip temperature and was more effective on plaques under the same laser energy. Optimal laser energy for single ablation was from 15J to 25J in case of 2.0mm tip and from 30J to 40J in case of 2.5mm tip. Application of the MTP equipped with thermal feedback control system could avoid the excessive thermal damage in comparison with the conventional MTP. It was considered that optimal temperature of the MTP equipped with thermal feedback control system ranged between 200 degrees C and 300 degrees C. It was concluded that laser angioplasty would be a useful treatment for the occlusive diseases of the peripheral arteries.     

Sapphire probe laser ablation of human arteries with CO2 gas and saline perfusion: The effect of flow rate,lasing power and lasing time

To evaluate flow rate dependence of CO₂ gas and saline perfusion for sapphire probe ablation, all together 204 human arterial specimens of atheroma and normal vessel were irradiated with Nd-YAG laser, in an experimental circulation-occlusion model within 37°C flowing whole blood. During lasing procedures, various flow rates of CO₂ gas (0.2–2.01 min⁻¹) and saline (2.0–20.0 ml min⁻¹), and various lasing powers (7, 12 and 17 W) and lasing time (1–20 s) were used. Histological changes of all specimens irradiated were microscopically examined. The results showed that the laser ablation area enlarged with increasing CO₂ flow rates and decreasing saline flow rates. Relative ablation efficiency on atheromatous plaque, in comparison to those on normal vessel wall and surrounding tissue site, increased slightly with increasing lasing power and lasing time. In this experimental setting, the mode of action of the sapphire probe ablation on human arterial atheroma seems to be more satisfactory with CO₂ gas perfusion than with saline perfusion.     

Argon laser angioplasty with a laser probe

A preliminary basic study of argon laser angioplasty with the use of a specially designed probe is presented. Arterial specimens were harvested from 10 amputated lower extremities. The studies included the evaluation of coaxial laser angioplasty in 10 partially or totally occluded arteries; the observation of the effect of perpendicularly applied laser energy on 35 thrombi, 54 soft and 10 hard atherosclerotic, and 51 normal arterial walls; the comparison of laser energy requirements for coaxial vessel lumen enlargement or recanalization vs. perpendicular penetration in 10 occluded, hard atherosclerotic arteries; and the spectrographic analysis of calcium density gradient in two specimens. The results showed that the power required for vessel lumen enlargement was 10 +/- 6 J/mm of atherosclerotic vessel (mean +/- standard deviation). The probe followed the original arterial lumen, did not perforate the vessel wall, and created a smooth, enlarged path. The power required to penetrate perpendicularly to a similar depth for thrombi, soft and hard atherosclerotic plaques, and normal arterial walls was 15 +/- 4, 30 +/- 15, 65 +/- 32, and 246 +/- 123 J/mm, respectively. In the hard calcified specimens, laser energy required for coaxial lumen enlargement or recanalization was significantly less than that for perpendicular penetration (p less than 0.05), which correlated with the calcium density map indicating an increase from inside to outside.     

Perineural injection to nerve root and radicular blood flow: a clinical study during spinal surgery

BACKGROUND AND OBJECTIVE: To investigate the effects of the perineural injection of lidocaine or corticosteroids on radicular blood flow during spinal surgery. METHODS: After lumbar discectomy, a probe for laser Doppler flowmetry was placed directly on the 4th or 5th lumbar nerve root. Thirty patients undergoing lumbar discectomy were randomly assigned to one of three groups. Each group received one of three protocols for a perineural injection to the nerve root: 1.0 mL 0.9% saline in group A, 1.0 mL 1% lidocaine in group B or 1.0 mL dexamethasone (4 mg) in group C. Measurements included radicular blood flow, mean arterial pressure, haemoglobin concentration, percutaneous oxygen saturation and end-tidal carbon dioxide tension. Radicular blood flow was measured by laser Doppler flowmetry before the injection and 15 min after these injections. The three groups were similar with respect to mean arterial pressure, haemoglobin concentration, percutaneous oxygen saturation and end-tidal carbon dioxide tension. RESULTS: Radicular blood flow did not change after the injection in any of the groups. CONCLUSIONS: The results suggest that the perineural injection of 1% lidocaine or dexamethasone does not affect radicular blood flow during lumbar discectomy.     

In vitro validation of the Affinity NT oxygenator arterial outlet temperatures

During cardiopulmonary bypass, the rates of cooling and rewarming and the maximum temperatures attained are implicated in patient morbidity. Thus, accurate oxygenator arterial outlet temperature measurements are needed. The purpose of this study was to determine the accuracy of the arterial outlet temperature probe on the "Affinity NT" membrane oxygenator in measuring perfusate temperatures. An in vitro circuit was used. Crystalloid solution was recirculated through an Affinity NT membrane oxygenator and, to simulate the patient, a second oxygenator. Water was recirculated through the heat exchanger of the second oxygenator via a reservoir. A myocardial temperature probe was inserted in-line 4 cm distal to the Affinity NT oxygenator arterial outlet temperature probe and was considered to measure the actual temperature of the perfusate. Temperatures were simultaneously recorded from the in-line probe, arterial outlet probe, and reservoir every second. Twenty-seven trials were run using random combinations of three Affinity NT oxygenators and three in-line probes. Each trial entailed cooling an initially normothermic reservoir to 28 degrees C and then rewarming it to normothermia again. The arterial outlet temperature probe on the Affinity NT membrane oxygenator underestimated the perfusate temperatures during early rewarming (bias of 0.72 degrees C; precision of +/-1.15 degrees C) and late rewarming (bias of 0.52 degrees C; precision of +/-0.97 degrees C). An overestimation of the perfusate temperatures occurred during early cooling (bias of -0.57 degrees C; precision of +/-1.37 degrees C). Only during the late cooling phase was the arterial outlet temperature probe accurate (bias of -0.02 degrees C; precision of +/-0.3 degrees C). The perfusionist should be aware of the temperature probe monitoring characteristics of the oxygenator to safely perfuse the patient.     

Design and evaluation of a fiberoptic fluorescence guided laser recanalization system

Current angioplasty techniques for recanalization of totally occluded arteries are limited by the inability to cross the occlusion and by the risk of perforation. A fiberoptic fluorescence guided laser recanalization system was developed and evaluated in vitro for recanalization of 17 human femoral or tibial totally occluded arterial segments (length 1.9-6.8 cm, diameter 2.5-6.0 mm). A 400 or 600 micron silica fiber was coupled to a helium-cadmium laser (lambda = 325 nm) for fluorescence excitation and to a holmium: YAG laser (lambda = 2.1 micron) for tissue ablation. Fluorescence was recorded during recanalization after every other holmium laser pulse. During recanalization, each arterial segment was bent 30-90 degrees with respect to the fiber to simulate arterial tortuosity. Ablation continued with fiber advancement as long as the fluorescence confirmed that the target tissue was atherosclerotic. Arterial spectra were classified as normal or atherosclerotic by an on-line computerized fluorescence classification algorithm (sensitivity 93%, specificity 95%). Normal fluorescence necessitated redirection of the fiber greater than 30 times per segment to continue recanalization. Fifteen of 17 totally occluded arteries had multiple recanalization channels created following total energy delivery of 40-1,016 Joules per segment with no angiographic or histologic evidence of laser perforation. Two heavily calcified arterial occlusions were not recanalized due to inhibition of holmium: YAG laser ablation by the recording of normal fluorescence spectra. Therefore, this fluorescence guided laser recanalization system appears safe and effective for recanalization of totally occluded arteries and merits in vivo evaluation. However, the lower sensitivity of fluorescence detection of heavily calcified plaques may limit the efficacy (but not safety) of fluorescence guided recanalization of heavily calcified occlusions.     

Use of the Cobra catheter for targeted temperature management during cardiopulmonary bypass in swine

BACKGROUND: The purpose of this investigation was to determine whether temperatures of the aortic arch and descending aortic circulations could be controlled independently during cardiopulmonary bypass with a cannula possessing an endoaortic baffle (Cobra; Cardeon, Cupertino, Calif). METHODS: After Institutional Animal Care and Use Committee approval, 12 pigs weighing 60 kg were started on bypass through a sternotomy. A dual-lumen endoaortic cannula with a deployable baffle was used for arterial cannulation. Bypass was initiated at 37 degrees C, and control measurements were obtained. The baffle was then inflated with saline solution, segmenting blood flow along the greater and lesser curvatures of the aortic arch. Parallel heat exchangers were used to independently control temperature of the arch and descending aortic perfusates. Cerebral and systemic temperatures were recorded continuously. RESULTS: During cardiopulmonary bypass, mean flow and arterial pressure were maintained at 2.4 to 2.6 L x min(-1) x m(-2) and 60 to 70 mm Hg, respectively. With aortic flow distributed by the baffle, a 5 degrees C temperature differential between brain (30 degrees C) and body (35 degrees C) was established in a mean of 5 +/- 2 minutes. Mean brain and corporeal temperatures of 27 degrees C and 35 degrees C were then maintained over 60 minutes. Relative to control, internal jugular and inferior vena cava oxygen saturations increased during targeted temperature control with the device. CONCLUSIONS: The Cobra cannula allows for independent control of brain and body temperature while providing satisfactory hemodynamics. Application of this temperature management strategy may offer cerebral protection and the advantages of warm systemic bypass temperature.     

Blood flow,pressure and compliance in the male human bladder

PURPOSE: The regulation of human bladder blood flow during filling is poorly understood. We characterized changes in bladder blood flow with filling and examined the relationship of bladder compliance and blood flow. MATERIALS AND METHODS: A total of 17 awake male patients underwent saline cystometry followed by cystoscopy while under local anesthesia, during which a laser Doppler flow probe was placed into the posterior bladder wall detrusor. Systemic blood pressure, bladder blood flow and intravesical pressure were measured with the bladder empty and filled to 25%, 50%, 75% and 100% of awake maximum cystometric capacity as well as immediately after bladder drainage. RESULTS: Mean bladder blood flow was lowest in the empty bladder and increased with bladder filling. A mean peak flow plus or minus standard error of 7.6 +/- 1.1 ml. per minute per 100 gm. tissue was observed at volumes greater than 75% but less than 100% of maximum cystometric capacity. At 100% maximum cystometric capacity mean intravesical pressure increased by 73% from 25.2 to 43.5 cm. water and bladder blood flow decreased by 36%. Rapid bladder drainage was associated with a rebound in mean bladder blood flow to approximately 1.6 times baseline. Bladder compliance calculated for the whole filling curve positively correlated with bladder blood flow (p = 0.025), that is low compliance was associated with low blood flow. CONCLUSIONS: Human bladder blood flow tends to increase with increasing volume and pressure, and depends largely on local regulation. At capacity bladder blood flow is significantly decreased. Immediately after bladder drainage there is a rebound in blood flow, allowing reperfusion to occur. Decreased bladder blood flow and decreased bladder wall compliance correlated strongly, suggesting that ischemia may lead to structural changes in the bladder wall.