Ultrasonic energy. Effects on vascular function and integrity

Low Intensity Ultrasound as an Antidote to Taxane/Paclitaxel-induced Cytotoxicity

The taxane family of compounds, including Taxol/paclitaxel and Taxotere/docetaxel, are surprisingly successful drugs used in combination or alone for the treatment of most major solid tumors, especially metastatic cancer. The drugs are commonly used in regimen with other agents (often platinum drugs) as frontline treatment, or used as a single agent in a dose dense regimen for recurrent cancer. The major side effects of taxanes are peripheral neuropathy, alopecia, and neutropenia, which are grave burden for patients and limit the full potential of the taxane drugs. Especially in the current treatment protocol for peripheral neuropathy, taxane dosage is reduced once the symptoms present, resulting in the loss of full or optimal cancer killing activity.

Substantial efforts have been made to address the problem of cytotoxic side effects of taxanes, though strategies remain very limited. Following administration of the taxane compound by infusion, taxane binds to cellular microtubules and is sequestered within the cells for several days. Taxane stabilizes and interferes with microtubule function, leading to ultimate death of cancer cells, but also damages hair follicles, peripheral neurons, and hemopoietic stem cells. Currently, cryo-treatment is practiced to limit exposure and side effects of the drug during infusion, though the effectiveness is uncertain or limited.

A recent laboratory finding may provide a new strategy to counter taxane cytotoxicity, that a brief exposure to low density ultrasound waves was sufficient to eliminate paclitaxel cytotoxicity cells in culture by transiently breaking microtubule filaments, which were then relocated to lysosomes for disposal. Thus, ultrasonic force to break rigid microtubules is an effective solution to counter taxane cytotoxicity. The discovery and concept of low intensity ultrasound as an antidote may have the potential to provide a practical strategy to counter paclitaxel-induced peripheral neuropathy and alopecia that resulted from chemotherapy.

Taxanes are a class of important drugs used in chemotherapy to treat several major cancers. This article reviews a new laboratory discovery that ultrasound can be used as an antidote for the peripheral cytotoxicity of taxane drugs and discusses the potential development and application of low intensity ultrasound to prevent side effects in chemotherapeutic treatment of cancer patients.

Reducing the Guidewire Friction for Endovascular Interventional Surgery by Radial Micro-Vibration

Guidewires for endovascular interventional surgery are inevitably affected by high frictional resistance because of direct contact with the vascular wall, which greatly reduces the operation efficiency and safety. This article presents a method of applying radial ultrasonic microvibration at the proximal end of a conventional passive guidewire to reduce the frictional resistance. The proposed method theoretically reduced the frictional resistance by reducing the friction coefficient, actual contact area, and the net friction time between the guidewire and vascular wall. The effectiveness of the proposed method was experimentally demonstrated in designed simulations of the blood vessel environment, where the influences of the vibration amplitude on the drag reduction effect were considered. The results indicated that vibrating the guidewire at the resonant frequency with the designed device clearly reduced the drag with a maximum frictional reduction rate of 85.19%. At the resonant frequency, the change in frictional resistance showed a linear negative correlation with the applied vibration amplitude. The proposed method offers a new approach to improving the efficiency and safety of vascular interventional surgery.

Exposure to low intensity ultrasound removes paclitaxel cytotoxicity in breast and ovarian cancer cells

BACKGROUND

Paclitaxel (Taxol) is a microtubule-stabilizing drug used to treat several solid tumors, including ovarian, breast, non-small cell lung, and pancreatic cancers. The current treatment of ovarian cancer is chemotherapy using paclitaxel in combination with carboplatin as a frontline agent, and paclitaxel is also used in salvage treatment as a second line drug with a dose intensive regimen following recurrence. More recently, a dose dense approach for paclitaxel has been used to treat metastatic breast cancer with success. Paclitaxel binds to beta tubulin with high affinity and stabilizes microtubule bundles. As a consequence of targeting microtubules, paclitaxel kills cancer cells through inhibition of mitosis, causing mitotic catastrophes, and by additional, not yet well defined non-mitotic mechanism(s).

RESULTS

In exploring methods to modulate activity of paclitaxel in causing cancer cell death, we unexpectedly found that a brief exposure of paclitaxel-treated cells in culture to low intensity ultrasound waves prevented the paclitaxel-induced cytotoxicity and death of the cancer cells. The treatment with ultrasound shock waves was found to transiently disrupt the microtubule cytoskeleton and to eliminate paclitaxel-induced rigid microtubule bundles. When cellular microtubules were labelled with a fluorescent paclitaxel analog, exposure to ultrasound waves led to the disassembly of the labeled microtubules and localization of the signals to perinuclear compartments, which were determined to be lysosomes.

CONCLUSIONS

We suggest that ultrasound disrupts the paclitaxel-induced rigid microtubule cytoskeleton, generating paclitaxel bound fragments that undergo degradation. A new microtubule network forms from tubulins that are not bound by paclitaxel. Hence, ultrasound shock waves are able to abolish paclitaxel impact on microtubules. Thus, our results demonstrate that a brief exposure to low intensity ultrasound can reduce and/or eliminate cytotoxicity associated with paclitaxel treatment of cancer cells in cultures.

Time- and Dose-Dependent Effects of Pulsed Ultrasound on Dermal Repair in Diabetic Mice

Chronic wounds, including diabetic, leg and pressure ulcers, impose a significant health care burden worldwide. Some evidence indicates that ultrasound can enhance soft tissue repair. However, therapeutic responses vary among individuals, thereby limiting clinical translation. Here, effects of pulsed ultrasound on dermal wound healing were assessed using a murine model of chronic, diabetic wounds. An ultrasound exposure system was developed to provide daily ultrasound exposures to full-thickness, excisional wounds in genetically diabetic mice. Wounds were exposed to 1 MHz ultrasound (2 ms pulse, 100 Hz pulse repetition frequency, 0-0.4 MPa) for 2 or 3 wk. Granulation tissue thickness and wound re-epithelialization increased as a function of increasing ultrasound pressure amplitude. At 2 wk after injury, significant increases in granulation tissue thickness and epithelial ingrowth were observed in response to 1 MHz pulsed ultrasound at 0.4 MPa. Wounds exposed to 0.4 MPa ultrasound for 3 wk were characterized by collagen-dense, revascularized granulation tissue with a fully restored, mature epithelium. Of note, only half of wounds exposed to 0.4 MPa ultrasound showed significant granulation tissue deposition after 2 wk of treatment. Thus, the db⁺/db⁺ mouse model may help to identify biological variables that influence individual responses to pulsed ultrasound and accelerate clinical translation.

Ultrasound therapy for treatment of lower extremity intermittent claudication

BACKGROUND

While often thought of as a diagnostic tool, ultrasound (US) can also potentially be used as a therapeutic modality. US applies mechanical stress on endothelial cells and induces nitric oxide synthase, which regulates the secretion of nitric oxide, a potent vasodilator. In animal ischemic models, US has been shown to improve hindlimb, myocardial, and cerebral perfusion. We performed a pilot trial of US therapy in the lower extremities of human subjects with intermittent claudication.

METHODS

10 subjects (5 male, 5 female, mean age 69.7 ± 10.3) with intermittent claudication were recruited. Both legs were placed in a specially designed boot with a water interface between US transducers and the legs. Subjects underwent pulsed US therapy at 250 kHz frequency for 30 min for three treatments a week for six weeks. Pre and post treatment ankle:brachial index (ABI), 6-min walk (6 MW), Walking Impairment Questionnaire (WIQ), and Short Form 36 (SF36) were performed. Pre and post-treatment results were compared with paired t-test.

RESULTS

Six minute walking distance at baseline was 352 ± 70 m, after one treatment session 353 ± 70 m (p = 0.99), and at completion 372 ± 71 m (p = 0.015). There was a trend toward improved ABI after 6 weeks of treatment (0.53 ± 0.17 vs 0.64 ± 0.12, p = 0.083). After six weeks, significant improvements were noted in overall WIQ score (2.00 ± 1.48 vs 2.63 ± 1.38, p = 0.0001), WIQ (distance) 2.07 ± 1.54 vs 2.73 ± 1.42 (p = 0.036), and WIQ (stair) 2.00 ± 1.67 vs 2.62 ± 1.24, p = 0.034, with a trend in WIQ (speed), 1.89 ± 1.26 vs 2.46 ± 1.43, p = 0.069. In the SF-36, significant improvements were noted in the domains of physical functioning (44.0 ± 41.6 vs 50.5 ± 41.1, p = 0.009) and role limitations - physical (35.0 ± 48.3 vs 60.0 ± 49.6, p = 0.006) after six weeks.

CONCLUSIONS

Therapeutic US is a potential noninvasive treatment for intermittent claudication. Pilot study patients noted significant improvements in 6 MW and WIQ results after 6 weeks of treatment. A nonsignificant improvement in ABI was noted. Further research will be needed to clarify optimal treatment frequency and duration.

Low-Frequency (20 kHz) Ultrasonic Modulation of Drug Action

We tested the effect of low-frequency ultrasound (LUS, 20 kHz, 4 W/cm²) on the function of rat mesentery and human pulmonary arteries with wire myography. The vessels were induced to contract with either noradrenaline or physiologic saline solution (PSS) with a high potassium concentration (KPSS) and then incubated with capsaicin (2.1 × 10^-7 M, TRPV1 [transient receptor potential vanilloid 1] activator), dopamine (1 × 10^-4 M, dopamine and α₂-receptor activator), or fenoldopam (dopamine_A1 receptor agonist, 1 × 10^-4 M) with and without glibenclamide (1 μM, KATP [adenosine triphosphate {sensitive potassium channel (ATP)}-sensitive potassium channel] inhibitor and α₂-receptor modulator), and insonated. Vessels were incubated in Ca²⁺-free PSS and induced to contract with added extracellular Ca²⁺ and noradrenaline. Pulmonary arteries were induced to contract with KPSS and dopamine. Then the vessels were insonated. LUS inhibited the influx of external Ca²⁺, inhibited the dopamine-induced vasoconstriction in the KPSS (glibenclamide reversible), reduced the capsaicin-induced vasorelaxation, increased the gentamicin-induced vasorelaxation and increased the dopamine-induced contraction in the KPSS in human pulmonary arteries.

Therapeutic Ultrasound Increases Myocardial Blood Flow in Ischemic Myocardium and Cardiac Endothelial Cells: Results of In Vivo and In Vitro Experiments

BACKGROUND

Therapeutic ultrasound can reduce infarct size in a model of coronary thrombosis even when sonothrombolysis is ineffective. The aim of this study was to test the hypothesis that ultrasound-induced cardioprotection is mediated by molecules released from the vascular endothelium that increase myocardial blood flow (MBF) and also have direct tissue-salvaging effects.

METHODS

In vivo and in vitro experiments were performed using a 1.05-MHz transducer. For the in vivo experiments 10 control and 10 ultrasound-treated dogs undergoing occlusion of the left anterior descending coronary artery were studied. MBF was measured using myocardial contrast echocardiography. For the in vitro experiments, primary mouse cardiac endothelial cells were exposed to ultrasound at baseline or following oxygen-glucose deprivation and endothelial nitric oxide synthase phosphorylation as well as adenosine and the eicosanoids epoxyeicosatrienoic acids, dihydroxyeicosatrienoic acids, and hydroxyl-eicosatetraenoic acids were measured.

RESULTS

In vivo, ultrasound treatment caused higher MBF (20 ± 10 vs 10 ± 8, P = .03) and higher wall thickening (3 ± 3% vs 1 ± 0.4%, P = .01) in the collateral-derived border zone compared with control. Epicardial MBF in the left anterior descending coronary artery bed also tended to be higher (17 ± 17 vs 5 ± 4, P = .05) in ultrasound-treated versus control animals; however, endocardial MBF in this region was similar to that in controls (13 ± 14 vs 14 ± 7). In vitro, phosphorylated endothelial nitric oxide synthase and adenosine increased (by 129 ± 11% and 286 ± 63%, respectively, P < .01) with ultrasound compared with unstimulated cells. Similar results were obtained with epoxyeicosatrienoic acids. After oxygen-glucose deprivation, phosphorylated endothelial nitric oxide synthase decreased and was restored with application of ultrasound. Similar changes were noted with epoxyeicosatrienoic acids. Cell viability decreased with oxygen-glucose deprivation and returned to near baseline with ultrasound.

CONCLUSIONS

Ultrasound increases MBF in ischemic tissue in vivo. This effect is likely mediated by the release of a plethora of coronary vasodilators during ultrasound treatment that also have direct tissue-salvaging effects. Therapeutic ultrasound, therefore, has potential for treatment of acute and chronic myocardial ischemia independent of its effect on thrombolysis.

In-vitro assessment of the thrombolytic efficacy of therapeutic ultrasound

BACKGROUND

Ultrasound is mainly used as a diagnostic tool. Several studies demonstrated that therapeutic ultrasound (TUS) can enhance thrombolysis, but the optimal mechanical parameters to achieve this biological effect are still unknown.

METHODS

We assembled 46 blood clots in a closed in-vitro circulatory model. Clots were randomly divided into 7 groups, control group and six TUS groups of three frequencies (0.3, 0.5, 0.7 MHz) and six intensities (0.75, 1.5, 3, 237.7, 475, 950 W/cm²). Treatment was composed of 12 repetitions, 5 min US application and 3 min pause, lasting 93 min in total. Clots' weight and flow rate were measured before and after the treatment.

RESULTS

Mean initial clot weight (0.318 ± 0.129 g) and flow (0.53 ± 0.31 ml/min) were comparable among the experimental groups. We found a final clot weights reduction (0.15 ± 0.05, 0.16 ± 0.06, 0.09 ± 0.07, 0.21 ± 0.09, 0.17 ± 0.09, 0.17 ± 0.07 and 0.18 ± 0.02 g in groups 1 through 6, respectively) and a flow increase (30.61 ± 19.76, 52.1 ± 25.44, 28.78 ± 8.15, 43.93 ± 20.03, 40.86 ± 18.25 and 45.10 ± 22.20 ml/min in groups 1-6, respectively) in all TUS groups. Clot weight change (%) and flow increase reveals that the TUS profile f = 0.5 MHz I = 1.5 W/cm² was most efficacious. In the control group, clot weight change was +6.3% of baseline and flow increase of 4.4% of baseline, whereas -75.4% of baseline and 209.3% of baseline in the f = 0.5 MHz I = 1.5 W/cm² profile were noted, respectively.

CONCLUSIONS

Our study proved that TUS at low frequency (0.5 MHz) is most effective, whereas changing the intensity of TUS has only a minor effect on clot lysis magnitude.

Endoluminal Atherosclerotic Plaque Debulking Using Enzymatic and Ultrasonic Energy

BACKGROUND

Current procedures to treat severe atherosclerosis are traumatic to the arterial wall and often result in restenosis due to neointimal hyperplasia. We developed a novel therapy using a specially designed double occlusion balloon catheter, ultrasonic wire, and enzymatic digestion solution to atraumatically debulk atherosclerotic plaques.

MATERIALS AND METHODS

A combination of different enzymes, chemicals, and treatment conditions were evaluated for its effect at reducing atherosclerotic plaque harvested from human carotid artery endarterectomies ex vivo. The optimized digestion solution was examined in harvested intact human superficial femoral arteries in situ. A conventional Yorkshire/Landrace and a genetically modified Yucatan minipig homozygous for a nonfunctional LDLR mutation were used to evaluate the endovascular therapy in nonatherosclerotic and atherosclerotic environments in vivo.

RESULTS

Ex vivo, the technology successfully digested human carotid artery plaques by 75%. In situ, the therapy successfully reduced plaque area in harvested superficial femoral arteries by 46%. In vivo, the endovascular therapy was technically feasible and demonstrated initial safety with no thrombosis, dissection, or aneurysmal dilatation in a nonatherosclerotic porcine model. In an atherosclerotic porcine model, the therapy demonstrated initial efficacy by successfully reducing atherosclerotic plaque while preserving the arterial wall with an intact internal elastic lamina.

CONCLUSIONS

Using human plaque, human artery, and a normal and atherosclerotic pig model, we demonstrated that delivery of our therapy to the vasculature is technically feasible, appears safe, and shows initial efficacy. Our percutaneous plaque debulking method is a unique and promising therapy for the treatment of atherosclerosis and warrants further study.

Osteogenic commitment and differentiation of human mesenchymal stem cells by low-intensity pulsed ultrasound stimulation

Low-intensity pulsed ultrasound (LIPUS) as an adjuvant therapy in in vitro and in vivo bone engineering has proven to be extremely useful. The present study aimed at investigating the effect of 30 mW/cm² LIPUS stimulation on commercially available human mesenchymal stem cells (hMSCs) cultured in basal or osteogenic medium at different experimental time points (7, 14, 21 days). The hypothesis was that LIPUS would improve the osteogenic differentiation of hMSC and guarantying the maintenance of osteogenic committed fraction, as demonstrated by cell vitality and proteomic analysis. LIPUS stimulation (a) regulated the balance between osteoblast commitment and differentiation by specific networks (activations of RhoA/ROCK signaling and upregulation of Ribosome constituent/Protein metabolic process, Glycolysis/Gluconeogenesis, RNA metabolic process/Splicing and Tubulins); (b) allowed the maintenance of a few percentage of osteoblast precursors (21 days CD73+/CD90+: 6%; OCT-3/4+/NANOG+/SOX2+: 10%); (c) induced the activation of osteogenic specific pathways shown by gene expression (early: ALPL, COL1A1, late: RUNX2, BGLAP, MAPK1/6) and related protein release (COL1a1, OPN, OC), in particular in the presence of osteogenic soluble factors able to mimic bone microenvironment. To summarize, LIPUS might be able to improve the osteogenic commitment of hMSCs in vitro, and, at the same time, enhance their osteogenic differentiation.

Radiosensitizing Pancreatic Cancer Xenografts by an Implantable Micro-Oxygen Generator

Over the past decades, little progress has been made to improve the extremely low survival rates in pancreatic cancer patients. Extreme hypoxia observed in pancreatic tumors contributes to the aggressive and metastatic characteristics of this tumor and can reduce the effectiveness of conventional radiation therapy and chemotherapy. In an attempt to reduce hypoxia-induced obstacles to effective radiation treatment, we used a novel device, the implantable micro-oxygen generator (IMOG), for in situ tumor oxygenation. After subcutaneous implantation of human pancreatic xenograft tumors in athymic rats, the IMOG was wirelessly powered by ultrasonic waves, producing 30 μA of direct current (at 2.5 V), which was then utilized to electrolyze water and produce oxygen within the tumor. Significant oxygen production by the IMOG was observed and corroborated using the NeoFox oxygen sensor dynamically. To test the radiosensitization effect of the newly generated oxygen, the human pancreatic xenograft tumors were subcutaneously implanted in nude mice with either a functional or inactivated IMOG device. The tumors in the mice were then exposed to ultrasonic power for 10 min, followed by a single fraction of 5 Gy radiation, and tumor growth was monitored thereafter. The 5 Gy irradiated tumors containing the functional IMOG exhibited tumor growth inhibition equivalent to that of 7 Gy irradiated tumors that did not contain an IMOG. Our study confirmed that an activated IMOG is able to produce sufficient oxygen to radiosensitize pancreatic tumors, enhancing response to single-dose radiation therapy.

Dutch randomized trial comparing standard catheter-directed thrombolysis and ultrasound-accelerated thrombolysis for arterial thromboembolic infrainguinal disease (DUET)

PURPOSE

To report the results of the Dutch randomized trial comparing standard catheter-directed and ultrasound-accelerated thrombolysis (UST) for the treatment of arterial thromboembolic occlusions.

METHODS

The DUET study ( controlled-trials.com ; identifier ISRCTN72676102) was designed to assess whether UST can reduce therapy time significantly compared with standard thrombolysis (ST). Sixty patients (44 men; mean age 64 years) with recently (7-49 days) thrombosed infrainguinal native arteries or bypass grafts causing acute limb ischemia (Rutherford category I or IIa) were randomized to ST (n = 32) or UST (n = 28). The primary outcome was the duration of thrombolysis needed for uninterrupted flow (> 95% thrombus lysis), with outflow through at least 1 below-the-knee artery. Continuous data are presented as means ± standard deviations.

RESULTS

Thrombolysis was significantly faster in the UST group (17.7 ± 2.0 hours) than in the ST group (29.5 ± 3.2 hours, p = 0.009) and required significantly fewer units of urokinase (2.8 ± 1.6 × 10(6) IU in the ST group vs. 1.8 ± 1.0 × 10(6) IU in the UST group, p = 0.01) for uninterrupted flow. Technical success was achieved in 27 (84%) patients in the ST group vs. 21 (75%) patients in the UST group (p = 0.52). The combined 30-day death and severe adverse event rate was 19% in the ST group and 29% in the UST group (p = 0.54). The 30-day patency rate was 82% in the ST group as compared with 71% in the UST group (p = 0.35).

CONCLUSION

Thrombolysis time was significantly reduced by UST as compared with ST in patients with recently thrombosed infrainguinal native arteries or bypass grafts.

External ultrasound for carotid atherosclerotic plaque treatment

OBJECTIVES

The purpose of this study was to evaluate the efficacy of external ultrasound in the treatment of carotid atherosclerotic plaques.

METHODS

In the prospective study, 357 patients with 363 carotid atherosclerotic plaques were divided into an ultrasound treatment group and a control group. For 30 days, conventional medical treatment was conducted on 54 plaques in the control group, whereas irradiation therapy in addition to conventional medical treatment was conducted on 309 plaques in the ultrasound group. Carotid sonography was conducted before and after treatment, and the maximum plaque thickness and area were measured in a longitudinal section.

RESULTS

No patients withdrew from the treatment because of related side effects. After treatment, the maximum thickness and area of 79.94% of the plaques in the ultrasound group were reduced, whereas in the control group, the thickness and area of 18.52% were reduced. The mean changes in plaque thickness and area ± SD in the ultrasound and control groups were 0.22 ± 0.19 mm (7.61% ± 5.67%) versus 0.02 ± 0.05 mm (0.74% ± 1.64%) and 0.047 ± 0.039 cm(2) (13.28% ± 9.8%) versus 0.0044 ± 0.0102 cm(2) (1.1% ± 2.46%), respectively. Changes in both plaque thickness and area in the ultrasound group were significantly greater than those in the control group (P< .0001). Furthermore, the plaque echo type was another prognostic factor affecting efficacy (P < .05).

CONCLUSIONS

External ultrasound treatment is safe and effective for carotid atherosclerotic plaques and is worthy of further research and applications. The efficacy in anechoic/hypoechoic plaques is significantly higher than that in mixed echoic and calcified echoic plaques.

Exploratory analysis of estimated acoustic peak rarefaction pressure, recanalization, and outcome in the transcranial ultrasound in clinical sonothrombolysis trial

PURPOSE

Acoustic peak rarefaction pressure (APRP) is the main factor that influences ultrasound-enhanced thrombolysis. We sought to determine whether recanalization rate and functional outcomes in the Transcranial Ultrasound in Clinical SONothrombolysis (TUCSON) trial could be predicted by estimated in vivo APRP.

METHODS

We developed an acoustic attenuation model to estimate the in vivo APRP at the arterial occlusion site in each subject of the TUCSON trial with CT scans eligible for measurements. Variables included temporal bone thickness, depth of arterial occlusion site, and average attenuation of skin and brain tissues. Recanalization was defined as partial or complete using the Thrombolysis in Brain Infarction flow grades. Functional independence was assessed at 3 months using the modified Rankin Scale score (mRS, 0-1).

RESULTS

APRP was calculated in 20 acute ischemic stroke patients treated with sonothrombolysis (mean age, 64 ± 15 years, 65% men; median NIHSS score, 13; IQR, 6-17). The mean APRP was 30.2 ± 15.5 kPa (range, 8-68 kPa). Patients with persisting occlusion had nonsignificantly lower APRP than patients with partial or complete recanalization (25.2 ± 8.0 versus 32.3 ± 17.7 kPa; p = 0.228). Patients who were functionally independent at 3 months had nonsignificantly higher APRP than patients with worse outcome (35.1 ± 19.5 versus 25.9 ± 11.2 kPa; p = 0.217).

CONCLUSIONS

Our exploratory analysis suggests a potentially important role of successful energy delivery to augment thrombolysis with 2-MHz ultrasound in acute ischemic stroke patients.

Taboos and opportunities in sonothrombolysis for stroke

Systemic thrombolysis with tissue plasminogen activator (tPA) is the only approved treatment for acute ischaemic stroke that improves functional outcome if given up to 4.5 h from symptom onset. At least half of treated patients have unfavourable outcomes long-term though, emphasising the need to amplify the only approved acute stroke therapy. Ultrasound targeting of an intra-arterial occlusive clot and delivering mechanical pressure to its surrounding fluids (referred to as sonothrombolysis) accelerates the thrombolytic effect of tPA. Higher recanalisation rates produce a trend towards better functional outcomes that could be safely achieved with the combination of 2 MHz frequency ultrasound and systemic tPA. To further accelerate the clot-dissolving effect of ultrasound, a variety of frequencies and intensities as well as other adjuvant treatment elements are being studied. However, literature reports argue efficacy and safety of these novel approaches doubting promptly translation into the clinical practice. This review will summarise our current knowledge about potentially harmful (taboos) directions and what we think are promising avenues for these future stroke therapies. We also give a prospect for novel technologies such as operator-independent devices that aim to further spread the use of sonothrombolysis for stroke.

Increased susceptibility of arterial tissue to wire perforation with the application of high-frequency mechanical vibrations

High-frequency mechanical vibrations (20-50 kHz), delivered via small diameter flexible wire waveguides represent a minimally invasive technology for the treatment of chronic total occlusions and in other tissue ablation applications. Tissue disruption is reported to be caused by repetitive mechanical contact and cavitation. This work focuses on the effects of vibrating wire waveguides in contact with arterial tissue. An apparatus with clinically relevant parameters was used, characterized as operating at 22.5 kHz and delivering amplitudes of vibration of 17.8-34.3 μm (acoustic intensity, I(SATA): 1.03-3.83 W/cm(2)) via 1.0-mm diameter waveguides. Inertial cavitation (in water at 37 °C) was determined to occur above amplitudes of vibration greater than 31.4 μm (I(SATA) = 3.21 W/cm(2)). The energized waveguides were advanced through tissue samples (porcine aorta) and the force profiles were measured for a range of acoustic intensities. The results show that the tissue perforation initiation force, perforation initiation energy, and total energy required to perforate the tissue reduces with increasing acoustic intensity. No significant reduction in perforation force or energy was observed in the inertial cavitation region. Multistage perforation was evident through the force profile and histological examination of the tissue samples post wire waveguide perforation.

Combined low-frequency ultrasound and streptokinase intravascular destruction of arterial thrombi in vivo

To prevent a distal embolization in the course of ultrasound (US) angioplasty, we combined US thrombus disruption in peripheral artery in vivo with simultaneous administration of streptokinase (SK). Acute thrombosis was induced in the femoral arteries of 23 dogs. Two hours after thrombus formation, thrombus destruction was performed using US (36 kHz) and by a combined US+SK (75,000 U/kg) administration. The results showed that thrombi were disrupted completely by 1.5 ± 0.5 min US. A combined US+SK action resulted in activation of fibrinolysis, as indicated by the increase in the content of fibrinogen and fibrin degradation products and D-dimers by a factor of 1.5-2.0 after 120 min from start of treatment compared with the SK lysis. The duration of clot destruction did not change; the distal embolization was not indicated; platelet aggregation activity dropped after thrombus destruction. In summary, intravascular thrombus destruction by a combined US and SK action in vivo is accompanied by enhancing the enzymatic fibrinolysis and lowering the platelet aggregation activity that assists in preventing the distal embolization of the resulting clot debris.

Ultrasound-induced contraction of the carotid artery in vitro

Ultrasound is known to produce a range of nonlethal responses in cells and tissues. Frequencies in the kilohertz ultrasound range have been shown to produce relaxation in large arteries. The present work explores the effects of insonation at MHz frequencies, representative of those used diagnostically and therapeutically, in an in vitro preparation of the carotid artery. Fresh 12.7 mm wide rings of equine common carotid artery obtained from the abattoir were mounted in a purpose-made myograph. They were immersed in a bath of Krebs-Ringer buffer at 37 degrees C and were positioned at the focus of an ultrasound beam from a weakly focused 3.2 MHz source. Continuous wave insonation produced contraction. The tension increased rapidly over the first 2 min, followed by a slower increase for the duration of the exposure up to 15 min. At a power of 145 mW a maximum contractile stress of 0.04 +/- 0.03 mN/mm(2) (mean +/- SD, n = 77) was measured, which was approximately 4% of the maximum wall stress generated by noradrenaline (0.1 mM). The magnitude of the response was weakly dependent on power in the range 72-145 mW and was not significantly different for pulsed and continuous wave stimulation where time averaged power was constant. The response was unaffected by mechanical removal of the endothelium. The ultrasound beam generated insufficient radiation force to produce a measurable effect and streaming at the vessel surface was very small compared with flow rates known to produce physiologic effects. The temperature rise at the beam focus was approximately 0.3 degrees C and we hypothesise that this contributes to the observed response, probably through changes in ion channel activity in smooth muscle cell membranes. (E-mail: e.martin@exeter.ac.uk).

Ultrasound thrombolysis

Ultrasound energy for thrombolysis dates back to 1976. Trubestein et al. demonstrated first in vitro that a rigid wire delivery low frequency ultrasound energy could disrupt clot. These investigators also showed that this system had potential for peripheral arterial clot dissolution in vivo in animal studies [G. Trubestein, C. Engel, F. Etzel, Clinical Science 51 (1976) 697s-698s]. Subsequently, four basic approaches to ultrasonic thrombolysis have been pursued--two without pharmacological agents: (1) catheter-delivered external transducer ultrasound, (2) transcutaneous-delivered HIFU external ultrasound without drug delivery and ultrasound in conjunction with thrombolytic drugs and/or microbubbles or other agents, (3) Catheter-delivered transducer-tipped ultrasound with local drug delivery, and (4) transcutaneous-delivered low frequency ultrasound with concomitant systemic (intravenous) drug delivery for site specific ultrasound augmentation. This article reviews recent data on therapeutic ultrasound for thrombolysis in vitro, in vivo, in animal studies, as well as in human clinical trials.

Nitric oxide generation directly responds to ultrasound exposure

Recently, several reports have been published on ultrasonic vascular dilation produced with relatively low-frequency ultrasound. It has been speculated that nitric oxide (NO) is an important factor for this ultrasonic vascular dilation. However, a quantitative relationship between the ultrasound intensity and NO generation was not clarified in these reports. We investigated the quantity of NO generated by various ultrasonic intensities by means of real-time measurement of NO concentration in the adductor muscles of the thigh of New Zealand white rabbits exposed to a continuous-wave ultrasound (490 kHz). In the quantitative relationship between NO generation and ultrasonic intensity, the percent increase in NO concentration was 1.25% +/- 1.25%, 10.6% +/- 2.9% and 20.1% +/- 3.5%, with the maximum muscle temperature increase 0.5 +/- 0.2 degrees C, 0.7 +/- 0.2 degrees C, and 0.8 +/- 0.3 degrees C at the ultrasonic intensity (SPTA) of 0.21, 0.35 and 0.48 W/cm(2), respectively. The effect of ultrasound on NO generation was intensity-dependent with a progressive increase from 0.21 W/cm(2) to 0.48 W/cm(2) without significant thermal effect. Ultrasonic NO generation was partially reduced by NOS inhibitor of L-NMMA, clarifying that ultrasound can activate both NOS-dependent and NOS-independent NO generation. These new findings provided scientific basis for ultrasonic vasodilatation and support the potentiality of a new ultrasonic technology for the treatment and prevention of the ischemic tissue based on the new concept of NO generated angiogenesis. (E-mail: furuhata@jikei.ac.jp).

Ultrasound at 27 kHz increases tissue expression and activity of nitric oxide synthases in acute limb ischemia in rabbits

Transcutaneous low-frequency ultrasound (US) preserves myocardial and skeletal muscle viability by increasing tissue perfusion through an undefined nitric oxide (NO)-dependent mechanism. We have examined whether US increases tissue expression and activity of the three nitric oxide synthase (NOS) isoforms: endothelial (eNOS), neuronal (nNOS) and inducible (iNOS). The two femoral arteries of four New Zealand rabbits were ligated for a total of 120 min. After 60 min of ligation, transcutaneous low-frequency US (27 kHz, 0.13 W/cm2) was applied for 60 min to one thigh, while the contra-lateral artery served as a control (total ischemia time=120 min). Calcium-dependent (cNOS) and -independent (ciNOS) NOS activity, and concentration of total eNOS, ser-1177 phosphorylated eNOS (P-eNOS), nNOS and iNOS were then determined in the gracilis muscle. Compared with the control, US application significantly increased cNOS activity [3.34+/-0.28 versus 3.87+/-0.10x1000 counts per minute (cpm), respectively, p=0.031] and ciNOS activity (1.99+/-0.09 versus 3.26+/-0.68 cpm, respectively, p<0.001). Western immunoblotting revealed a significant increase in protein content of both iNOS (184.5+/-1.08%; p<0.0001) and P-eNOS (381.5+/-2.47%; p<0.001), with only a small increase in total eNOS and nNOS expression. In conclusion, application of transcutaneous low-frequency US to ischemic muscular tissue significantly increases both cNOS and ciNOS activity by increasing eNOS phosphorylation and iNOS expression, respectively.

Mechanisms by which low-intensity ultrasound improve tolerance to ischemia-reperfusion injury

Recent studies show that low-intensity ultrasound (US) increases endothelial nitric oxide (NO) levels in different models both in vitro and in vivo. Ischemia-reperfusion (I/R) injury is characterized by endothelial cell dysfunction, mainly as a result of altered shear stress responses associated with vasoconstriction, reduced capillary perfusion and excessive oxidative stress. This review provides an overview of the microvascular effects of low-intensity US and suggests that US exposure can be a method to provide tolerance to I/R damage. The hamster cheek pouch, extensively used in studies of I/R-induced injury, has been characterized in terms of changes of arteriolar diameter, flow and shear stress. The low-intensity US exposure reduces vasoconstriction and leukocyte adhesion and increases capillary perfusion during postischemic reperfusion. These effects may be the result of enhanced fluctuations in shear stress exerted by the flowing blood on the vessel wall. The fluctuations in turn are due to mechanical perturbations arising from the difference in acoustical impedance between the endothelial cells and the vessel content. We believe that periodic pulses of US may also cause a sustained reduction of oxidative stress and an enhanced endothelial NO level by increasing oscillatory shear stress during postischemic reperfusion. Low-intensity US exposure may represent a safe and novel important therapeutic target for patients with acute coronary syndromes and for treatment of chronic myocardial ischemia.

Noninvasive low-frequency ultrasound energy causes vasodilation in humans

OBJECTIVES

We evaluated the potential vasodilator effects of transcutaneous low-frequency ultrasound (US) in human brachial arteries.

BACKGROUND

Recent data show that transthoracic low-frequency US energy results in canine coronary artery vasodilation.

METHODS

Brachial artery diameters were measured before and after low-frequency US (29 kHz, 1.4 W/cm2) exposure using US imaging with a linear-array transducer. We assessed the time course of diameter changes after US in 20 subjects. In 10 of 20 subjects, brachial artery flow-mediated vasodilation (FMD) was measured to compare the effect of US to a standard method of evaluating endothelial function.

RESULTS

Significant vasodilation was seen after 2 min of US compared with baseline values. At 5 min of US, the brachial artery diameter increased by 4.1%. In addition, the arteries continued to dilate after US exposure. At 3 min after US there was a 5.4%, and at 5 min after US a 6.0% increase in vessel diameter (p < 0.001). These diameters returned to baseline dimensions about 20 min after stopping US. Ultrasound-mediated vasodilation and percentage FMD showed good correlation (r = 0.87; p < 0.001).

CONCLUSIONS

This is the first study to demonstrate that noninvasive transcutaneous low-frequency US energy dilates human brachial arteries. This arterial vasodilator effect has a rapid onset (within 2 min), lasts about 20 min, and is similar in magnitude to that of FMD. The vasodilator effect of US may have diagnostic and therapeutic potential in patients with or at risk for vascular disease.

Ultrasound energy improves myocardial perfusion in the presence of coronary occlusion

OBJECTIVES

We evaluated whether ultrasound improves myocardial tissue perfusion in 14 animals with coronary artery occlusion.

BACKGROUND

A recent study demonstrated that low-frequency ultrasound improves tissue perfusion in the rabbit ischemic limb, but there are no data on ultrasound enhancement of myocardial perfusion.

METHODS

Fourteen animals (9 dogs, 5 pigs) underwent thoracotomy and occlusion of a diagonal branch of the left anterior descending coronary artery. Myocardial tissue perfusion units (TPUs) and pH were measured before coronary occlusion, after occlusion, and after direct exposure of the ischemic myocardium in the presence of fixed occlusion to low-frequency ultrasound (27 kHz).

RESULTS

The TPU decreased from 100.9 +/- 13 at baseline to 71.1 +/- 13 (p < 0.01) after 60 min occlusion but rose by 19.7% to 85.1 +/- 8 (p < 0.01) after ultrasound exposure for 60 min. After 60-min coronary occlusion, myocardial pH fell from 7.43 +/- 14 to 7.05 +/- 0.15 (p < 0.01) but then improved to normal (7.46 +/- 0.32) after ultrasound for 60 min. Administration of L-Nomega-nitro-arginine methyl esther (L-NAME), an inhibitor of nitric oxide synthase, before ultrasound exposure, blocked improvement in myocardial tissue perfusion and pH by ultrasound. Quantitative histomorphology showed a significant increase in the capillary area of myocardium exposed to ultrasound versus non-exposed myocardium (16.2 +/- 7.9 vs. 8.2 +/- 2.1, p < 0.02).

CONCLUSIONS

Low-frequency, low-intensity ultrasound improves myocardial tissue perfusion and pH in the presence of a fixed coronary artery occlusion.

Low-intensity ultrasound increases endothelial cell nitric oxide synthase activity and nitric oxide synthesis

Low-intensity ultrasound (US) increases tissue perfusion in ischemic muscle through a nitric oxide (NO)-dependent mechanism. We have developed a model to expose endothelial cells to well-characterized acoustic fields in vitro and investigate the physical and biological mechanisms involved. Human umbilical vein endothelial cells (HUVEC) or bovine aortic endothelial cells (BAEC) were grown in tissue culture plates suspended in a temperature-controlled water bath and exposed to US. Exposure to 27 kHz continuous wave US at 0.25 W cm(-2) for 10 min increased HUVEC media NO by 102 +/- 19% (P < 0.05) and BAEC by 117 +/- 23% (P < 0.01). Endothelial cell NO synthase activity increased by 27 +/- 24% in HUVEC and by 32 +/- 16% in BAEC (P < 0.05 for each). The cell response was rapid with a significant increase in NO synthesis by 10 s and a maximum increase after exposure for 1 min. By 30 min post-exposure NO synthesis declined to baseline, indicating that the response was transient. Unexpectedly, pulsing at a 10% duty cycle resulted in a 46% increase in NO synthesis over the response seen with continuous wave US, resulting in an increase of 147 +/- 18%. Cells responded to very low intensity US, with a significant increase at 0.075 W cm(-2) (P < 0.01) and a maximum response at 0.125 W cm(-2). US caused minor reversible changes in cell morphology but did not alter proliferative capacity, indicating absence of injury. We conclude that exposure of endothelial cells to low-intensity, low-frequency US increases NO synthase activity and NO production, which could be used to induce vasodilatation experimentally or therapeutically.

Effects of diagnostic cardiac ultrasound on oxygen free radical production and microvascular perfusion during ischemia reperfusion

Diagnostic ultrasound (US) is reported to increase intracellular oxidative stress in vitro. Increased oxidative stress mediated ischemia-reperfusion injury in the microcirculation. To examine the effects of US in hamster cheek pouch microcirculation during baseline and ischemia and reperfusion (I/R), I/R injury was provoked in the cheek pouch under "sham" (transducer off, group 1) and active US irradiation (group 2) at baseline (15 min) and at the beginning (15 min) of the reperfusion after ischemia (30 min). US transmission was delivered in the harmonic mode (2.5 MHz) with 1.3 mechanical index (MI) and 2.0 peak negative pressure. Microvascular damage was evaluated by measuring arterial diameter, red blood cell velocity, wall shear stress, permeability, perfused capillary length and adherent leukocytes in venules. Lipid peroxides were determined in the systemic blood. US increased permeability (baseline: 0.04 +/- 0.02; after US 0.30 +/- 0.04, p < 0.01) and slightly decreased capillary perfusion by 7% during baseline (p < 0.01). Arteriolar diameter (35 +/- 7 microm vs. 20 +/- 5 microm, p < 0.05), RBC velocity (2.8 +/- 0.4 mm s(-1) vs. 0.75 +/- 0.05 mm s(-1), p < 0.05) and shear stress ( 0.76 +/- 0.09 Pa vs. 0.36 +/- 0.05 Pa, p < 0.05) decreased significantly after reperfusion. These parameters increased by 40, 64 and 33%, respectively after US. Leukocyte adhesion decreased by 31 % (p < 0.05) after US and lipid peroxides decreased by 26% and 51% during baseline and 15 min of reperfusion after US, respectively. In conclusion, diagnostic US increased microvascular permeability during baseline and reperfusion. Moreover, US enhanced wall shear stress and reduced oxidative stress during postischemic reperfusion; thus, increasing capillary perfusion.

Nitric oxide and prostacyclin in ultrasonic vasodilatation of the canine internal mammary artery

BACKGROUND

Investigators recently demonstrated increased free blood flow from radial artery free grafts harvested using ultrasonic technology. We investigated the mechanism underlying this phenomenon.

METHODS

Canine internal mammary artery segments (with and without intact endothelium) were precontracted with norepinephrine and sonicated 3 seconds in organ chambers with ultrasonic coagulating shears (Harmonic Scalpel; Ethicon Endo-Surgery, Cincinnati, OH) functioning at level 2. Vessel tension was continuously measured to examine vasoactivity in response to sonication alone (control) or with N(ù)-Nitro-l-arginine (l-NNA) and indomethacin added to the chamber medium individually or in combination. Tissue heating, acoustic pressure, and endothelial damage as detected by scanning electron micrography were also assessed.

RESULTS

In vitro sonication with the Harmonic Scalpel induced predominately endothelium-dependent internal mammary artery vasorelaxation but a small endothelium-independent contribution was also observed. Early vasorelaxation (1 minute after stimulus) was maximally inhibited by l-NNA alone and in combination with indomethacin. Relaxation during this period was insignificantly affected by indomethacin alone. Only the combination of l-NNA and indomethacin maximally inhibited late vasorelaxation (5 minutes after stimulus), whereas inhibitory effects of l-NNA diminished during this time period. Indomethacin inhibited relaxation substantially during this phase, although significantly less than did l-NNA alone. The Harmonic Scalpel minimally heated the tissue surface (0.3 +/- 0.03 degrees C) and did not disrupt endothelial cell integrity while operating at 50 mW/cm(2) intensity (acoustic pressure 40 kPa).

CONCLUSIONS

Sonication induces vasorelaxation almost completely by time-dependent endothelial nitric oxide and prostacyclin release, which appears unrelated to tissue heating or endothelial architectural disruption.

Coronary vasodilation by noninvasive transcutaneous ultrasound: an in vivo canine study

OBJECTIVES

We evaluated the coronary vasodilatory effects of transcutaneous low-frequency (27-kHz) ultrasound (USD).

BACKGROUND

Ultrasound has been shown to affect vascular function.

METHODS

Ultrasound energy was administered transcutaneously to 12 dogs. Coronary arterial dimensions were assessed using intravascular coronary ultrasound (IVUS) and quantitative coronary angiography (QCA).

RESULTS

The IVUS mid-left anterior descending (LAD) luminal area was 6.77 +/- 1.27 mm(2) at baseline. After 30 s of ultrasound, this area increased by 9% (7.40 +/- 1.44 mm(2), p < 0.05), after 3 min by 19% (8.05 +/- 1.72 mm(2), p < 0.05) and after 5 min increased by 21% (8.16 +/- 1.29 mm(2), p < 0.05). The mean coronary diameter (2.69 +/- 0.33 mm) at baseline (QCA of three segments of LAD and three segments of left circumflex coronary artery) increased by 19.3% (3.21 +/- 0.28 mm) after 5 min of USD exposure. After a 90-min observation period there was a return to baseline values (p = NS). Intracoronary nitroglycerin (NTG) administered to five dogs revealed a similar magnitude of vasodilation as USD.

CONCLUSIONS

Noninvasive, transthoracic low-frequency USD energy results in coronary artery vasodilation within seconds of exposure. The vasodilation is reversible and is similar in magnitude to that induced by NTG. Further evaluation is needed to assess its potential applications in humans.

Pre-exposure effects of 1 and 3 MHz therapeutic ultrasound on ConA activated spleenocytes

This study was performed to evaluate the pre-exposure effects of ultrasound (1 MHz or 3 MHz) on ConA activated spleenocyte proliferation and cytokine production. Cells were treated for 10 min at various intensities, rested for 1h and stimulated with the T cell activator ConA. The cells were then analyzed for the effects of non-thermal ultrasound on cell growth and the presence of IL-2, IL-4 and IFN-g. The data show that pre-exposure of spleenocytes had no significant effects on the proliferation of ConA activated spleenocytes at either 1 or 3 MHz (10 min at 0.1 or 0.5 W/cm(2)). Significant increases in IL-2 were observed in both 1 and 3 MHz pre-treated and ConA activated spleenocytes. Cells pre-treated with 1 MHz and stimulated with ConA showed a significant increase in IL-4 and IFN-g. Conversely, cells pre-treated with 3 MHz and stimulated with ConA show a significant decrease in IL-4 and IFN-g. Interleuken-4 is known to increase the growth of mast cells, inhibit macrophage activation and increases the activity of the T cell subpopulation, T(H2). Interferon-gamma is known to stimulate production of collagen in fibroblasts, enhance debridement activity of macrophage and inhibit activity of the T cell subpopulation, T(H2).

Ultrasound angioplasty: an update review

The use of therapeutic ultrasound to treat atherosclerosis and thrombosis has been appreciated for decades. However, it was only the explosive growth of angioplasty in the 1980s that brought real momentum to the development of therapeutic catheter ultrasound. The idea behind this technique was that ultrasound, by its bioselectivity, might provide a solution to some of the shortcomings of balloon angioplasty. In the late 1980s, two groups, headed by Rosenschein and Siegel, began serious work to address the technical challenge of developing a catheter that would provide efficient external ultrasound energy to the lesion. Current catheters from both groups consist of a solid metal probe which is connected to a piezoelectric transducer. In the distal segment, the wire is specially designed to increase energy delivery. Initial in vitro studies concentrated on understanding the mechanisms of ablation and the effects of mechanical vibration, thermal phenomena and cavitation. Clinical studies of ultrasound ablation were initially performed in peripheral vessels. Later, after safety had been assured, clinical studies involving the coronary arteries began to take place. In this article we aim to update the reader about the experimental and limited clinical experience in this novel technique for treating different kinds of arterial obstruction.

Direct ultrasound application had no effect on cardiac hemodynamic performance in a baseline isolated rat heart model

Therapeutic ultrasound (US) has been used for more than 3 decades to promote tissue healing in cases of tissue injury and muscle soreness. It was previously suggested that US may have vasorelaxatory and inotropic properties. However, the direct effect of therapeutic US in a whole heart model has not yet been investigated. Our hypothesis was that application of US might enhance cardiac function. The Langendorf model was modified in a special manner to allow application of US to the heart. Using this model, 20 male rats were equally divided into two groups. Group 1: the hearts were perfused for 15 min, to obtain baseline measurements, and then they were perfused for another 15 min in a special bath full of perfusate. Group 2: after 15 min of baseline measurements, continuous US of 1 MHz 2 W/cm(2) was applied for another 15 min. The parameters that were measured at 5-min intervals were: left ventricular pressure P(max), first derivative of the rise and fall in left ventricular pressure (dP/dt(max), dP/dt(min)), and pressure-time integral. There was no significant difference between the two groups in all parameters at baseline and during US application. P(max) and dP/dt(max) remained constant. After 15 min of US propagation, P(max) was 98% +/- 3 from baseline level vs. 98% +/- 7 in the control group, and dP/dt(max) was 98% +/- 3 vs. 99% +/- 9 in the control. In dP/dt(min), a gradual decline after 15 min of perfusion was measured. In the US- treated group, it declined to 80% +/- 10 vs. 83% +/- 5 in the controls. In conclusion, US radiation at the dose specified does not improve healthy isolated heart hemodynamic performance. We established a model that may be used for further investigation.

Efeito do ultrasom terapêutico nas anastomoses colônicas. Estudo experimental em ratos

Objetivou-se conhecer a influência do ultra-som na cicatrização colônica em ratos e avaliar os fios de aço e náilon na vigência desta terapia. Utilizou-se 64 ratos machos Wistar divididos em protocolos. Protocolo 1 com 32 ratos submetidos a anastomose colônica com fio de náilon divididos em 2 grupos C (controle), e T (terapêutico). O grupo T realizou a terapia com ultra-som de alta freqüência, na região dorsal. O subgrupo sacrificado no 3o dia, recebeu ultra-som no 1o e 2o dias pós-operatório. E o no 7o, terapia no 4o, 5o e 6o P.O. No Protocolo 2 anastomoses com aço, subdivididos da mesma forma. E no Protocolo 3 comparou-se os grupos T do náilon e aço. Avaliou-se pressão de ruptura à insuflação (PRI) e estudo histológico. Resultados: Protocolo 1 no 3o dia a PRI foi maior no grupo T (p=0,001) e no 7o dia não houve diferença (p=0,0950). No Protocolo 2 no 3o dia não houve diferença na PRI (p=0,3060) e no 7o dia a PRI foi maior no C (p=0,0010). No Protocolo 3 no 3o dia a PRI foi maior no NáilonT (p=0,0010) e no 7o dia não houve diferença (p=0,3100). Concluiu-se que o ultra-som não influencia a cicatrização de anastomoses feitas com náilon e não compromete a viabilidade das feitas com aço.

Ultrasound inhibits the adhesion and migration of smooth muscle cells in vitro

This study investigated in vitro the effect of therapeutic ultrasound (ULS) on smooth muscle cell (SMC) function as adhesion, migration and proliferation. Experiments were conducted on aortic SMC in culture. The LD50 was established (1.5 W for 15 s at a frequency of 20 kHz) and used as standard dose in all experiments. Control SMC and viable sonicated SMC were compared in each experiment. Migratory capacity decreased 2.4-fold after sonication and stayed reduced for up to 24 h. Adhesion capacity decreased 5.5-fold after ULS. The proliferative capacity was similar to that of nonsonicated SMC. Sonication was accompanied by the disorganization of alpha-SM actin fibers and diminished distribution of vinculin; tyrosinated alpha tubulin and vimentin appeared unaffected. These changes might be responsible for the observed inhibition of SMC adhesion and migration. Sonicated cells exhibited less lamellipodia, membrane collapse and bleb formation. The signal transduction cascade, which involves activation of the phospholipase-C pathway, was unaffected by ULS.

Ultrasonic coronary angioplasty during coronary artery bypass grafting

This preliminary study in 20 patients demonstrated that ultrasonic coronary angioplasty in the setting of bypass grafting is feasible, safe, and able to recanalize atherosclerotic vessels. Shorter monorail probes were superior to longer probes without guidewires in terms of success of vessel recanalization; >95% of particle debris was <25 microm in size.

Catheter-delivered ultrasound potentiates in vitro thrombolysis

PURPOSE

To develop a catheter-directed method to enhance urokinase- mediated thrombolysis with use of ultrasound.

MATERIALS AND METHODS

A prototype catheter was constructed by using a 9-F piezoelectric crystal capable of producing 640-kHz pulsed ultrasound energy. Clots formed in vitro from whole blood were trace-labeled with iodine-125 fibrinogen, and the release of radiolabeled fibrin degradation products was measured in the presence of urokinase, ultrasound, or a combination of urokinase and ultrasound.

RESULTS

By 30 minutes, clot lysis was more complete with urokinase plus ultrasound (78.7% +/- 5.3 [mean +/- SD]) than with ultrasound alone (19.3% +/- 10.0) or urokinase alone (47.9% +/- 10.0) (P < .001 for ultrasound and urokinase vs either alone). The time to 50% clot lysis was shortened by 46% on average with the application of urokinase and ultrasound compared with urokinase alone (P < .03).

CONCLUSIONS

Catheter-based ultrasound enhances enzymatic thrombolysis in vitro and may be a practical means to reduce the dose of enzyme and the time needed to achieve clot lysis in vivo.

Safety of coronary ultrasound angioplasty: effects of sonication on intact canine coronary arteries

The purpose of this work was to examine in vivo the safety of sonication in the coronary arteries in a live animal model. In intact dogs (n = 8), balloon dilatation was performed on the proximal left anterior descending artery (LAD) followed by sonication to the left circumflex artery (LCX) in power levels found to be optimal for thrombus ablation. Post-dilatation and post-ultrasound coronary angiography, echocardiography, histopathology, CK-MB, indices of hemolysis, and coagulation were compared. Sonication did not induce changes in the ECG or blood pressure. Coronary angiography revealed no adverse side effects or change in arterial diameter (2.3 +/- 0.7 vs. 2.4 +/- 0.3 mm). Echocardiography showed transient opacification of the myocardium. Histopathology revealed a comparable minimal degree of endothelial denudation. After sonication there were no changes in the level of CK-MB (312 +/- 168 vs. 283 +/- 207 IU), hemoglobin (11.3 +/- 0.9 vs. 12.7 +/- 1.1 gr%), haptoglobin (479 +/- 136 vs. 451 +/- 121 mg/dL), fibrinogen (142 +/- 18 vs. 165 +/- 28 mg%), partial thromboplastin time (17.3 +/- 3.2 vs. 17.6 +/- 3.4 sec), prothrombin time (13.3 +/- 7.8 vs. 11.5 +/- 2.9 sec), and degree of platelet aggregation (55 +/- 17 vs. 62 +/- 8%). Thus, the data suggest that transluminal coronary sonication exerts no overt adverse effects in vivo.

High intensity, low frequency catheter-delivered ultrasound dissolution of occlusive coronary artery thrombi: an in vitro and in vivo study

OBJECTIVES

This study assessed the efficacy of a new high intensity, low frequency therapeutic coronary ultrasound catheter for thrombus dissolution in vitro and in vivo in canine coronary arteries.

BACKGROUND

Therapeutic ultrasound has been shown to dissolve thrombi in vitro and in peripheral arteries in vivo. There have been no previous studies on in vivo coronary thrombus dissolution by ultrasound.

METHODS

In vitro, we exposed 1- to 4-h old human blood clots for 3 min to pulsed-wave ultrasound. Clot dissolution under various conditions was evaluated. In vivo occlusive coronary thrombi were induced in 18 dogs.

RESULTS

In vitro irrigation alone (10 ml/min of normal saline solution) and ultrasound alone each contributed to a reduction of clot weight by 47.1 +/- 11.4 mg and 84.6 +/- 25.6 mg, respectively, after 3 min (p < 0.001). Ultrasound plus irrigation resulted in a reduction of clot weight by 216.5 +/- 31.5 mg after 3 min (p < 0.001). The magnitude of clot dissolution was considerably amplified when ultrasound energy was combined with irrigation, probably because of cavitational effects. In vivo, in three dogs mechanical passage of the unactivated probe failed to recanalize the artery, and the arteries remained thrombotically occluded. After passage of the activated ultrasound probe, angiography revealed widely patent coronary arteries in 13 of 15 dogs and partial recanalization with filling defects indicative of residual thrombus in 2 of 15 dogs. Three of 15 coronary arteries were histologically free of residual thrombi. Mural thrombi extending to < or = 10% of the vessel circumference were seen in 10 of 15 dogs. Residual thrombi > or = 50% of the vessel circumference were found in two cases. There was no histologic evidence of ultrasound-mediated vessel damage.

CONCLUSIONS

Catheter-delivered therapeutic ultrasound effectively dissolves clots in vitro and in canine coronary arteries in vivo. Thus, therapeutic catheter-delivered ultrasound has the potential to serve as an adjunct or alternative treatment for thrombus-mediated coronary ischemic syndromes or myocardial infarction.

Clinical trial of percutaneous peripheral ultrasound angioplasty

OBJECTIVES

The purpose of this study was to present follow-up data as well as short-term results on a larger clinical series of patients undergoing ultrasound angioplasty.

BACKGROUND

Previous pilot studies have demonstrated the feasibility of peripheral arterial ultrasound angioplasty.

METHODS

We performed percutaneous ultrasound angioplasty on 50 arterial lesions in 45 patients. Our ultrasound ablation system had a frequency of 19.5 kHz. A fixed-wire probe with 2- or 3-mm ball tips and a 3-mm over-the-wire probe were used to treat 40 femoral, 7 popliteal and 3 tibioperoneal lesions. Seventeen (34%) of the lesions were calcific. Thirty (86%) of 35 occluded segments, 0.5 to 28 cm long (mean 6.2 +/- 5.7), were recanalized.

RESULTS

In the 45 patent arteries, the stenosis decreased from 94 +/- 10% to 55 +/- 23% after ultrasound angioplasty and to 12 +/- 8% after balloon angioplasty. Mechanical arterial dissections (n = 4) and perforations (n = 4) without clinical consequence occurred only with the fixed non-over-the-wire probes. No evidence of embolism or vasospasm was detected; in fact, vasodilation occurred. There were no clinical manifestations of acute reocclusion. At 24 h, ankle-brachial indexes increased by 0.23 +/- 0.21 (range -0.27 to 0.72). Six- to 12-month clinical and ankle-brachial index follow-up data for 35 patients treated with ultrasound and adjunctive balloon angioplasty were indicative of restenosis in 7 patients (20%).

CONCLUSIONS

Our findings indicate that percutaneous peripheral ultrasound angioplasty 1) is useful for recanalization of fibrous, calcific and thrombotic arterial occlusions; 2) reduces arterial stenoses; and 3) has clinical and ankle-brachial index data indicative of a restenosis rate of 20% at 6 to 12 months in a small cohort of patients. A larger randomized series of patients will need to be studied to assess the impact of ultrasound ablation on restenosis.

Effects of ultrasound energy on total peripheral artery occlusions: initial angiographic and angioscopic results

Ultrasonic energy has been shown to ablate atherosclerotic plaques and arterial and venous thrombi. We used an ultrasonic angioplasty device developed by our group in ten patients with totally occluded femoral artery during surgical bypass. Ultrasonic angioplasty was performed with a 130-cm long and 0.8-cm diameter titanium probe with a 2- or 2.5-mm titanium ball-tip. In one patient, angioplasty could not be performed. Angiographic and angioscopic examination were performed before and after angioplasty in nine patients. Before ultrasound recanalization, angioscopic examination showed that the proximal end of the occlusion was formed by atheromatous material in 3 cases, red thrombus in 3 cases, amd white thrombus in 3 cases. After ultrasound recanalization, angioscopy showed residual stenosis at the site of entry in only one case. In three other cases, the artery was free of residual stenosis without persistent clot. In the five other patients, a residual stenosis was present beyond the proximal occlusion point with some fibrin mesh and small clots. At angiography, flow was restored in 4 cases; in 4 patients flow rate of entry was slow in the distal segment; and in 1 patient, the distal arterial bed could not be opacified. Altogether, ultrasonic angioplasty was able to recanalize a complete occlusion in nine out of ten patients, with partial or complete dissolution of clots and with no complication. At its present stage of development, adjunctive balloon angioplasty would be needed in most cases to obtain unrestricted flow and unsignificant residual stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of fibrinolysis in vitro by ultrasound

The effect of ultrasound on the rate of fibrinolysis has been investigated using an in vitro system. Plasma or blood clots containing a trace label of 125I fibrin were suspended in plasma containing plasminogen activator and intermittently exposed to continuous wave 1-MHz ultrasound at intensities up to 8 W/cm2. Plasma clot lysis at 1 h with 1 microgram/ml recombinant tissue plasminogen activator (rt-PA) was 12.8 +/- 1.2% without ultrasound and was significantly (P = 0.0001) increased by exposure to ultrasound with greater lysis at 1 W/cm2 (18.0 +/- 1.4%), 2 W/cm2 (19.3 +/- 0.7%), 4 W/cm2 (22.8 +/- 1.8%), and 8 W/cm2 (58.7 +/- 7.1%). Significant increases in lysis were also seen with urokinase at ultrasound intensities of 2 W/cm2 and above. Exposure of clots to ultrasound in the absence of plasminogen activator did not increase lysis. Ultrasound exposure resulted in a marked reduction in the rt-PA concentration required to achieve an equivalent degree of lysis to that seen without ultrasound. For example, 15% lysis occurred in 1 h at 1 microgram/ml rt-PA without ultrasound or with 0.2 microgram/ml with ultrasound, a five-fold reduction in concentration. Ultrasound at 1 W/cm2 and above also potentiated lysis of retracted whole blood clots mediated by rt-PA or urokinase. The maximum temperature increase of plasma clots exposed to 4 W/cm2 ultrasound was only 1.7 degrees C, which could not explain the enhancement of fibrinolysis. Ultrasound exposure did not cause mechanical fragmentation of the clot into sedimentable fragments, nor did it alter the sizes of plasmic derivatives as demonstrated by SDS polyacrylamide gel electrophoresis. We conclude that ultrasound at 1 MHz potentiates enzymatic fibrinolysis by a nonthermal mechanism at energies that can potentially be applied and tolerated in vivo to accelerate therapeutic fibrinolysis.

Clinical demonstration that catheter-delivered ultrasound energy reverses arterial vasoconstriction

OBJECTIVES

This study was designed to describe the clinical effects of ultrasound energy on guide-wire-induced arterial vasoconstriction.

BACKGROUND

We have previously shown that ultrasound energy (20 kHz) delivered by a wire probe produces dose-dependent, endothelium-independent smooth muscle relaxation capable of reversing both receptor-mediated and voltage-dependent vasoconstriction in vitro.

METHODS

A high intensity, low frequency ultrasound catheter system was used to recanalize total occlusions in the superficial femoral arteries of two patients. After recanalization, the proximal residual stenoses were each less than 15%. However, distal arterial vasospasm was found angiographically in a popliteal artery of one patient and in an anterior tibial artery of another. Subsequently, the ultrasound catheter probe was advanced to the sites of arterial vasospasm (diffuse in one, focal in one).

RESULTS

After 30 and 90 s, respectively, of exposure to ultrasound energy with a frequency of 19.5 kHz, peak tip amplitude of 111 microns and power output at the transducer of 25 W, the vasospasm resolved in each arterial segment.

CONCLUSIONS

Our findings are the first reported clinical cases documenting that catheter-delivered low frequency, high intensity ultrasound induces arterial vasodilation at the site of vasoconstriction. These biologic effects appear to be relatively unique for an angioplasty device and may have potential clinical importance.

Ultrasound recanalization of diseased arteries. From experimental studies to clinical application

At present, percutaneous peripheral ultrasound angioplasty should be considered in those patients with symptoms of claudication or resting limb ischemia. With the development of an over-the-wire system, we treat patients with suprageniculate or infrageniculate lesions. It is expected that the over-the-wire probe will allow application of ultrasound angioplasty not only to lesions below the knee but to contralateral vascular occlusions as well. An intraoperative device for plaque ablation and arterial recanalization is in development for use in less accessible sites such as the coronary arteries. Experimental studies have shown that catheter-delivered therapeutic ultrasound recanalizes complete occlusions, reduces stenoses, dissolves thrombus, vasodilates, and enhances arterial distensibility. The potential clinical applications of therapeutic ultrasound include recanalizing total arterial occlusions, dissolving thrombi, facilitating balloon angioplasty by increasing arterial compliance, and as a stand-alone angioplasty device.