Effects of Cavitation from Extracorporeal Shock Wave Combined with Sulfur Hexafluoride Microbubble on Myocardial Ultrastructure in Rats

BACKGROUND

In the present study, the effects of extracorporeal cardiac shock waves combined with different concentrations of sulfur hexafluoride ultrasound microbubbles on myocardial ultrastructure in rats were observed.

METHODS

Thirty-six rats were randomly divided into 6 groups: control group (N), extracorporeal cardiac shock wave group, and combined group, i.e., extracorporeal cardiac shock wave combined with different concentrations of sulfur hexafluoride microbubble (0.225 mL/kg/min, 0.45 mL/kg/min, 0.9 mL/kg/min, 1.8 mL/kg/min). The combination of extracorporeal cardiac shock wave combined with sulfur hexafluoride microbubbles of different concentrations had no significant effect on hemodynamic indexes and left ventricular function in rats.

RESULTS

There were significant differences in cardiac troponin I (cTnI) and nitricoxide among different groups. Histopathology showed that inflammatory cells infiltrated in the shock wave+microbubble 0.9 and shock wave+microbubble 1.8 groups. The myocardial ultrastructural injury score of shock wave+microbubble1.8 group was significantly higher than that of the N group, shock wave group, shock wave+microbubble 0.225 group, and shock wave+microbubble 0.45 group. The score of shock wave+microbubble 0.9 group was higher than that of the control group (P=.009). Western blot results showed that the expression of vascular endothelial growth factor and endothelial nitricoxide synthase (eNOS) protein in the rats treated with extracorporeal cardiac shock wave combined with sulfur hexafluoride microbubbles of different concentrations was higher than that in the N group and shock wave group, with shock wave+microbubble 0.45 group having the strongest expression.

CONCLUSION

Myocardial ultrastructure damage occurs when high concentrations of sulfur hexafluoride microbubbles are present, but a proper concentration of sulfur hexafluoride microbubbles could promote the cavitation effect of extracorporeal cardiac shock waves. Thus combination therapy may become a new paradigm in coronary heart disease, especially contributing to the treatment of refractory angina. Combination therapy may change coronary heart disease treatment, especially for refractory angina.

Contrast-enhanced Ultrasound (CEUS) vs contrast-enhanced computed tomography for multilocular cystic renal neoplasm of low malignant potential: A retrospective analysis for diagnostic performance study

Multilocular cystic renal neoplasm of low malignant potential (MCRNLMP) might be benefited from nephron-sparing surgery. Contrast-enhanced computed tomography is used for the diagnosis of MCRNLMP but contrast-enhanced ultrasound has lack of nephrotoxicity and several advantages over contrast-enhanced computed tomography and contrast-enhanced magnetic resonance. The purpose of the study was to compare diagnostic parameters of preoperative contrast-enhanced ultrasound against contrast-enhanced computed tomography for the detection of MCRNLMP in patients who faced curative surgery for complex cystic renal mass.Data regarding contrast-enhanced ultrasound, contrast-enhanced computed tomography, and clinicopathological results of 219 patients who underwent curative surgery for complex cystic renal mass (Bosniak classification III or IV) were retrospectively collected and analyzed. Bosniak classification for imaging modality and the 2016 WHO criteria for clinic pathology were used for detection of MCRNLMP.Contrast-enhanced ultrasound, contrast-enhanced computed tomography, and clinicopathology were detected 68, 66, and 67 as a MCRNLMP respectively. Contrast-enhanced ultrasound and contrast-enhanced computed tomography had 30.37% and 29.27% sensitivities for the detection of MCRNLMP. While 60% and 50% specificities respectively. Bosniak classification III (P = .045) and lower mean Hounsfield unit (P = .049) were associated with the prevalence of MCRNLMP. Contrast-enhanced computed tomography was detected 6 and 7, while contrast-enhanced ultrasound detected 3 and 2 complex cystic renal mass as false positive and false negative MCRNLMP respectively. A contrast-enhanced ultrasound had 0.011 to 1.0 diagnostic confidence and contrast-enhanced computed tomography had 0.045 to 0.983 diagnostic confidence for decision making of nephron-sparing surgeries.Contrast-enhanced ultrasound may have better visualization of MCRNLMP than contrast-enhanced computed tomography.Level of Evidence: III.

[Use of contrast-enhanced ultrasound for assessment of the state of femoropopliteal bypass graft anastomoses]

Analysed herein is the experience of the first eight ultrasonographic studies of peripheral arteries with dynamic contrast enhancement using sulphur hexafluoride («SonoVue») carried out in patients after previously performed femoropopliteal bypass grafting with a synthetic prosthesis (in seven cases the distal anastomosis of the bypass graft was located below the fissure of the knee joint and in one case - above the fissure of the knee joint). Contrast-enhanced ultrasonography was performed averagely 12.5±4.0 months after the operation, according to the technique recommended by the manufacturer of the contrast agent. It was demonstrated that control ultrasonic scanning of lower-limb arteries using contrast enhancement in the remote period after bypass operations proved more informative in relation to detection of stenoses of the distal anastomosis of the femoropopliteal bypass graft, trifurcation of the popliteal artery and near-ostium segments of tibial arteries than a study with no contrast medium.

Effects of RNA interference combined with ultrasonic irradiation and SonoVue microbubbles on expression of STAT3 gene in keratinocytes of psoriatic lesions

The most effective sequence of small interfering RNA (siRNA) silencing STAT3 of psoriatic keratinocytes (KCs) was screened out, and the effects of the most effective siRNA combined with ultrasonic irradiation and SonoVue microbubbles on the expression of STAT3 of KCs and the dose- and time-response were investigated. Three chemically-synthetic siRNAs targeting STAT3 carried by Lipofectamine 3000 were transfected into KCs, and the effects on STAT3 expression were detected, then the most effective siRNA was selected for the subsequent experiments. The negative controls of siRNA (siRNA-NC) labeled with Cy3 carried by Lipofectamine 3000 combined with ultrasonic irradiation and SonoVue microbubbles were transfected into KCs, then the optimal parameters of ultrasonic irradiation were determined. The most effective siRNA carried by Li-pofectamine 3000 combined with ultrasonic irradiation at the optimal parameters and SonoVue microbubbles was transfected into KCs, and the dose- and time-response of RNA interference was determined. The effect of RNA interference by the most effective siRNA at the optimal time and dose carried by Lipofectamine 3000 combined with ultrasonic irradiation and SonoVue microbubbles (LUS group) was compared with that only carried by Li-pofectamine 3000 (L group). The results showed that siRNA-3 achieved the highest silencing efficacy. 0.5 W/cm2 and 30 s were selected as the parameters of ultrasonic irradiation. The siRNA-3 carried by Lipofectamine 3000 combined with ultrasonic irradiation and SonoVue microbubbles could effectively knock down the STAT3 expression at mRNA and protein levels in dose- and time-dependent manners determined at 100 nmol/L with maximum downregulation on mRNA at 48 h, and on protein at 72 h after transfection. The LUS group achieved the highest silencing efficacy. It was concluded that siRNA-3 carried by Lipofectamine 3000 combined with ultrasonic irradiation and SonoVue microbubbles could effectively knock down the STAT3 expression in psoriatic KCs, and the optimized transfection condition and the sequence of siRNA-3 could serve for further research on gene therapy of psoriasis.

Streaming flow from ultrasound contrast agents by acoustic waves in a blood vessel model

To elucidate the effects of streaming flow on ultrasound contrast agent (UCA)-assisted drug delivery, streaming velocity fields from sonicated UCA microbubbles were measured using particle image velocimetry (PIV) in a blood vessel model. At the beginning of ultrasound sonication, the UCA bubbles formed clusters and translated in the direction of the ultrasound field. Bubble cluster formation and translation were faster with 2.25MHz sonication, a frequency close to the resonance frequency of the UCA. Translation of bubble clusters induced streaming jet flow that impinged on the vessel wall, forming symmetric vortices. The maximum streaming velocity was about 60mm/s at 2.25MHz and decreased to 15mm/s at 1.0MHz for the same acoustic pressure amplitude. The effect of the ultrasound frequency on wall shear stress was more noticeable. Maximum wall shear stress decreased from 0.84 to 0.1Pa as the ultrasound frequency decreased from 2.25 to 1.0MHz. The maximum spatial gradient of the wall shear stress also decreased from 1.0 to 0.1Pa/mm. This study showed that streaming flow was induced by bubble cluster formation and translation and was stronger upon sonication by an acoustic wave with a frequency near the UCA resonance frequency. Therefore, the secondary radiant force, which is much stronger at the resonance frequency, should play an important role in UCA-assisted drug delivery.

Combined effect of ultrasound/SonoVue microbubble on CD4(+)CD25(+) regulatory T cells viability and optimized parameters for its transfection

The purpose of this study was to investigate the combined effect of ultrasound and SonoVue microbubble on CD4(+)CD25(+) regulatory T cells (Tregs) viability and to explore the appropriate parameters for Tregs transfection. Tregs were separated from peripheral venous blood of patients with hepatocellular carcinoma and seeded in 96-well plates. The optimal ultrasound exposure time and optimal SonoVue microbubble concentration for Tregs were measured by mechanical index (MI) of 1.2 or 1.4, exposure time of 0, 30, 60, 90, 120, 150, 180s, and 0, 10, 20, 30, 40, 50μL/100μL microbubble per well, respectively. In addition, the combined effect of ultrasound and microbubble on Tregs viability was evaluated according to the following parameters: MI 1.2/1.4+exposure time of 120, 150, 180s+0, 10, 20, 30, 40, 50μL/100μL microbubble per well. Tregs viability investigations were performed in order to explore the optimal transfection condition. The efficiency of plasmid transfer was determined by detection of luciferase activity on the microscopic examinations. The proliferation of Tregs could be promoted by ultrasound exposures, while being decreased with the increasing concentration of microbubbles. Under the current experimental conditions, the optimal ultrasound parameters were MI=1.4 and exposure time=150/180s. The optimal microbubble concentration was 10μL/100μL. Compared with treatment with ultrasound or microbubbles alone, the transfection efficiency of Tregs improved 50% by combining ultrasound and microbubble. The results indicate that both ultrasound and microbubble could affect the Tregs proliferation and the optimal Treg transfection rate was obtained by treating with 10% microbubbles and ultrasound exposure for 150/180s under ultrasound MI of 1.4.

Lens subluxation after plasmin and SF6 injections in rabbit eyes

Purpose

To investigate the rate of lens subluxation following plasmin and/or SF₆ injections in eyes, and whether a subsequent elevated level of vascular endothelial growth factor (VEGF) and vitreous tap would aggravate subluxation.

Methods

Four groups of rabbits were used. Group 1 received an intravitreal injection (IVI) of plasmin and SF₆ in the right eye; group 2 received an IVI of plasmin in the right eye; group 3 received an IVI of SF₆ in the right eye; and group 4 received an IVI of balanced salt solution in the right eye. After treatment, IVIs of VEGF were given and vitreous tap was performed three times, followed by clinical observation of lens subluxation and scanning electronic microscope evaluation of the zonular fibers.

Results

After IVIs of plasmin and SF₆, and VEGF and vitreous tap had been performed one to three times, lens subluxation was noted in 0%, 43%, 71%, 71%, and 86% of the eyes in group 1. After IVIs of plasmin, VEGF, and vitreous tap had been performed one to three times, lens subluxation was noted in 11%, 22%, 44%, 44%, and 67% of the eyes in group 2. The eyes in group 3 and 4 did not show signs of lens subluxation after VEGF IVIs and vitreous tap. Histology confirmed zonular fiber damage in the eyes treated with plasmin.

Conclusions

The incidence of lens subluxation increased following plasmin injections in the eyes, and this was aggravated by the subsequent high VEGF level in the eyes and vitreous tapping. Zonular fibers were disrupted following plasmin treatment. These effects should be kept in mind when using plasmin enzymes in patients with vitreoretinal abnormalities.

Contrast-enhanced ultrasonographic findings of hepatic paragonimiasis

AIM: To investigate the features of hepatic paragonimiasis on contrast-enhanced ultrasound (CEUS) imaging.

METHODS: Fifteen patients with hepatic paragonimiasis who were admitted to our hospital between March 2008 and August 2012 were enrolled to this study. The conventional ultrasound and CEUS examinations were performed with a Philips IU22 scanner with a 1-5-MHz convex transducer. After conventional ultrasound scanning was completed, the CEUS study was performed. Pulse inversion harmonic imaging was used for CEUS. A bolus injection of 2.4 mL of a sulfur hexafluoride-filled microbubble contrast agent (SonoVue) was administered. CEUS features were retrospectively reviewed and correlated with pathological findings.

RESULTS: In total, 16 lesions were detected on CEUS. The mean size of the lesions was 4.4 ± 1.6 cm (range, 1.7-6.6 cm). Subcapsular location was found in 12 lesions (75%). All the lesions were hypoechoic. Six lesions (37.5%) were of mixed content, seven (43.8%) were solid with small cystic areas, and the other three (18.8%) were completely solid. Ten lesions (62.5%) were rim enhanced with irregular tract-like nonenhanced internal areas. Transient wedge-shaped hyperenhancement of the surrounding liver parenchyma was seen in seven lesions (43.8%). Areas with hyper- or iso-enhancement in the arterial phase showed contrast wash-out and appeared hypoenhanced in the late phase. The main pathological findings included: (1) coagulative or liquefactive necrosis within the lesion, infiltration of a large number of eosinophils with the formation of chronic eosinophilic abscesses and sporadic distribution of Charcot-Leyden crystals; and (2) hyperplasia of granulomatous and fibrous tissue around the lesion.

CONCLUSION: Subcapsular location, hypoechogenicity, rim enhancement and tract-like nonenhanced areas could be seen as the main CEUS features of hepatic paragonimiasis.

The value of time-intensity curves obtained after microbubble contrast agent injection to discriminate responders from non-responders to anti-inflammatory medication among patients with Crohn's disease

OBJECTIVE

To assess the value of time-intensity curves obtained after sulphur hefluoride-filled microbubble contrast agent injection to discriminate responders from non-responders among patients with Crohn's disease (CD).

METHODS

Forty-three patients (29 male and 14 female; mean age ± SD, 48.5 ± 17.17 years) with initial diagnosis of active CD were recruited. In each patient, the therapeutic outcome was assessed after 12 weeks from the beginning of pharmacologic treatment. The terminal ileal loop was scanned after sulphur hexafluoride-filled microbubble injection, and the digital cine-clip registered during the first-pass dynamic enhancement was quantified in gray-scale levels. The percentage of maximal enhancement, time to peak enhancement, and area under the time-intensity curve in responders vs. non-responders were compared by Mann-Whitney U non-parametric test.

RESULTS

Responders (n = 25 patients) vs. non-responders (n = 18) differed in the area under the time-intensity curve (621.58 ± 374.53 vs. 1,199.64 ± 386.39 P < 0.05), while they did not differ in percentage of maximal enhancement (41.26 ± 15.22 vs. 43.17 ± 4.41, P = 0.25) and time to peak enhancement (11.31 ± 3.06 vs. 10.12 ± 3.47, P = 0.15).

CONCLUSIONS

The area under the time-intensity curve obtained after microbubble injection was the only parameter to discriminate responders from non-responders among patients with CD during pharmacologic treatment.

KEY POINTS

• Dynamic ultrasound using microbubble contrast agents can help assess inflammatory bowel disease • Time-intensity curves can assess therapeutic outcome in Crohn's disease (CD) • The area under the time-intensity curve differentiates responders from non-responders during pharmacological treatment.

The impact of ultrasound contrast medium administration on the right ventricle in patients with heart failure

BACKGROUND

The purpose of the present study was to examine the effect of SonoVue™ on right ventricular (RV) dimensions and contractility in patients with heart failure.

PATIENTS AND METHODS

Twenty-four patients were divided into two groups. Group A consisted of 15 patients with heart failure and group B (control) of nine patients without heart disease. SonoVue was administered at low (2 ml) and high (4 ml) doses in both groups separately, in a random order. RV dimensions, contractility, peak systolic pressure gradient from tricuspid regurgitation (TRPG) and the time to maximal RV end-diastolic dimension (EDD), as well as the time for RV-EDD to return to the baseline value (recovery), were calculated in every cardiac cycle starting before the administration of SonoVue (baseline) until the recovery of RV-EDD.

RESULTS

Low-(group A, p<0.001 and group B, p<0.05) and high-dose (group A, p<0.0001 and group B, p<0.01) contrast infusion increased the RV-EDD compared to baseline values. TRPG increased significantly (p<0.05) in both groups, under low-as well as high-dose. In group A, high-dose compared to low-dose produced a significant delay in the time duration to max RV-EDD (p<0.05) and in the time to RV-EDD recovery (p<0.0001).

CONCLUSION

The administration of SonoVue in patients with heart failure was followed by an acute, transient, dose-dependent increase in RV-EDD and TRPG, without any effect on RV contractility.

Investigation of microbubble response to long pulses used in ultrasound-enhanced drug delivery

In current drug delivery approaches, microbubbles and drugs can be co-administered while ultrasound is applied. The mechanism of microbubble interaction with ultrasound, the drug and the cells is not fully understood. The aim of this study was to investigate microbubble response to long ultrasonic pulses used in drug delivery approaches. Two different in vitro set-ups were considered: with the microbubbles diluted in an enclosure and with the microbubbles flowing in a capillary tube. Acoustic streaming, which influences the observed bubble response, was observed in "typical" drug delivery conditions in the first set-up. With the capillary set-up, streaming effects were avoided and accurate bubble responses were recorded. The diffraction pattern of the source greatly influences the bubble response and in different locations of the field different bubble responses are observed. At low nondestructive pressures, microbubbles can oscillate for thousands of cycles repeatedly. At high acoustic pressures (at 1 MHz), most bubble activity disappeared within about 100 μs despite the length of the pulse, mainly due to violent bubble destruction and subsequent accelerated diffusion.

Sonophoresis using ultrasound contrast agents for transdermal drug delivery: an in vivo experimental study

Sonophoresis temporally increases skin permeability such that various medications can be delivered noninvasively. Previous sonophoresis studies have suggested that cavitation plays an important role in enhancing transdermal drug delivery (TDD). In this study, the feasibility of controlled cavitation using ultrasound contrast agents (UCAs) at high frequency was explored through in vivo experiments in a rat model. Two commercially available UCAs, SonoVue® and Definity®, were used at 2.47 MHz and 1.12 MHz, respectively. Fluorescein isothiocyanate (FITC)-dextran with 0.1% UCA was used as the drug to be delivered through the skin. Ultrasound with a 10 ms pulse and a 1% duty cycle at 1 MPa acoustic pressure for 30 min was applied in all sonication sessions. The efficacy of sonophoresis with UCAs was quantitatively analyzed using an optical imaging system that was used to count photons emitted from fluorescein. The results showed that the proposed sonophoresis method significantly improved drug penetration compared with the traditional sonophoresis method with 4 kD, 20 kD and 150 kD FITC-dextrans at 1.12 MHz, and with 4 kD and 20 kD FITC-dextrans at 2.47 MHz. Sonophoresis for TDD was performed more effectively with the aid of UCAs. Sonophoresis with UCAs has excellent potential for broad applications in drug delivery for diseases requiring the chronic administration of medications such as diabetes.

The targeted gene (KDRP-CD/TK) therapy of breast cancer mediated by SonoVue and ultrasound irradiation in vitro

Suicide gene therapy has become an effective therapy for breast cancer, and ultrasound targeted microbubble destruction (UTMD) has become a popular topic in the gene therapy field. In this study, MCF-7 cells with the KDR promoter and LSl74T cells without the KDR promoter were transfected with the recombinant plasmid pEGFP-KDRP-CD/TK using UTMD. The recombinant plasmid pEGFP-KDRP-CD/TK was transfected into MCF-7 and LS174T cells successfully with no significant difference in transfection efficiency (p>0.05). By RT-PCR, the CD/TK fusion gene was shown to be expressed in MCF-7 cells but not expressed in LS174T cells. In a cytotoxicity experiment, transgenic MCF-7 cells were sensitive to the prodrugs 5-FC and GCV. When both 5-FC and GCV were administered, the rate of cellular inhibition was significantly greater than that achieved when only one of the prodrugs was administered (p<0.001). Moreover, the inhibition rates achieved administering 5-FC, GCV and both 5-FC and GCV were all significantly greater than the gene transfection rate of 21.92±3.64% (p<0.001). However, transgenic LS174T cells were not sensitive to any prodrug. These results demonstrated that UTMD is a safe, effective and targeted gene delivery system. Also, the KDR promoter can drive expression of the CD/TK double suicide gene target in MCF-7 cells, and the targeted killing effect of the KDRP-CD/TK gene on MCF-7 cells in vitro has good synergy with expression of the CD/TK fusion gene.

The effect of contrast medium SonoVue® on the electric charge density of blood cells

The effect of contrast medium SonoVue® on the electric charge density of blood cells (erythrocytes and thrombocytes) was measured using a microelectrophoretic method. We examined the effect of adsorbed H⁺ and OH⁻ ions on the surface charge of erythrocytes or thrombocytes. Surface charge density values were determined from electrophoretic mobility measurements of blood cells performed at various pH levels. The interaction between solution ions and the erythrocyte's or thrombocyte's surface was described by a four-component equilibrium model. The agreement between the experimental and theoretical charge variation curves of the erythrocytes and thrombocytes was good at pH 2-9. The deviation observed at a higher pH may be caused by disregarding interactions between the functional groups of blood cells.

Influence of needle gauge on in vivo ultrasound and microbubble-mediated gene transfection

Ultrasound and microbubble-mediated gene transfection are potential tools for safe, site-selective gene therapy. However, preclinical trials have demonstrated a low transfection efficiency that has hindered the progression of the technique to clinical application. In this paper it is shown that simple changes to the method of intravenous injection can lead to an increase in transfection efficiency when using 6-MHz diagnostic ultrasound and the ultrasound contrast agent, SonoVue. By using needles of progressively smaller gauge, i.e., larger internal diameter (ID), from 29 G (ID 0.184 mm) to 25 G (ID 0.31 mm), the transfection of a luciferase plasmid (pGL4.13) was significantly increased threefold in heart-targeted female CD1 mice. In vitro work indicated that the concentration and size distribution of SonoVue were affected by increasing needle gauge. These results suggest that the process of systemic delivery alters the bubble population and adversely affects transfection. This is exacerbated by using high-gauge needles. These findings demonstrate that the needle with the largest possible ID should be used for systemic delivery of microbubbles and genetic material.

Effect of SonoVue on the synovial membrane in rabbit knees

OBJECTIVES

The purpose of this study was to evaluate the effect of intra-articular injection of SonoVue (sulfur hexafluoride with a phospholipid shell; Bracco SpA, Milan, Italy) on the synovial membrane in an animal model.

METHODS

Twenty-one New Zealand White rabbits (42 knees) were used in this study. We injected the knees with normal saline (saline group; n = 21) and SonoVue (SonoVue group; n = 21). A histologic examination of the knees was performed out at 3 and 12 hours and 3, 7, 15, 30, and 45 days after injection. Four histologic parameters (synovial hyperplasia, synovial stroma, vascular dilatation, and inflammatory infiltrates) were graded separately.

RESULTS

We found no significant differences in this study for synovial hyperplasia, vascular dilatation, or inflammatory infiltrates between the saline and SonoVue groups. A significant difference was only observed for synovial stroma (P < .05), and most of the histologic changes were mild in the saline group and moderate in the SonoVue group. The histologic changes observed in this study are considered transitory and reversible.

CONCLUSIONS

The results suggest that intra-articular injection of SonoVue is a safe procedure.

[Effects of high intensity focused ultrasound with SonoVue on blood vessels pathological examinations]

The injury of tumor blood vessels will break up the nutrition supply for the tumor. In this paper, we investigated the effects exerted by high intensity focused ultrasound (HIFU) combined with ultrasound microbubble agent on blood vessels. Ultrasound diagnosis was used to find the goat hepatic blood vessels each being approximately 3mm in diameter. HIFU was focused on the blood vessels. The acoustic power was 250W; HIFU irradiating Mode was line scan (the length of the line: 10 mm; speed: 3 mm/s; irradiating time: 30s). In the experimental group, 0.03 ml/kg SonoVue was injected into the goat before HIFU irradiation,while normal saline was given to the control group. The goats were killed at 24h after HIFU irradiation, then goat liver tissues and blood vessels of target area were taken out. HE staining and Victoria's blue and Ponceau's staining of tissue section showed that the endothelial cells of blood vessels dropped off and became necrosed, and the continuity of blood vessels was interrupted. HIFU combined with SonoVue will damage large blood vessels on HIFU focus, but there is no evident discrepancy between the group with SonoVue and the group without SonoVue.

Delivery of TFPI-2 using ultrasound with a microbubble agent (SonoVue) inhibits intimal hyperplasia after balloon injury in a rabbit carotid artery model

Here we report a new, simple and efficient method by using ultrasound and a microbubble agent (SonoVue) for delivering a gene to balloon-injured carotid arteries for restenosis prophylaxis. The tissue factor pathway inhibitor-2 (TFPI-2) has been shown to inhibit the postinjury intimae hyperplasia in atherosclerotic vessels. New Zealand white rabbits were divided into 4 groups with 14 in each, a treatment control for balloon injury, a gene vehicle control, a gene delivery of TFPI-2 without using ultrasound and a gene delivery of TFPI-2 using ultrasound. After four weeks, the injured artery neointimal proliferation was significantly lower in the TFPI-2 group with ultrasound than the control groups (p < 0.01) according to the measurement of the mean luminal diameters by B-mode ultrasonography. The ratio of intimal/media area and the stenosis rate in the gene delivery facilitated by ultrasound were significantly lower than those of the nonultrasound gene delivering method (p < 0.01).

Synergistic effects of sonoporation and taurolidin/TRAIL on apoptosis in human fibrosarcoma

Sonodynamic therapy, in combination with ultrasound contrast agents, proved to enhance the uptake of chemotherapeutics in malignant cells. HT1080 fibrosarcoma cells were treated in vitro with a combination of ultrasound SonoVue™-microbubbles and taurolidine (TRD) plus tumor necrosis factor related apoptosis inducing ligand (TRAIL). Apoptosis was measured by TdT-mediated dUTP-biotin nick end labelling (TUNEL) assay and fluorescence activated cell sorting (FACS) analysis. Gene expression was analysed by RNA-microarray. The apoptotic effects of TRD and TRAIL on human fibrosarcoma are enhanced by sonodynamic therapy and additional application of contrast agents, such as SonoVue™ by 25%. A broad change in the expression of genes related to apoptotic pathways is observed when ultrasound and microbubbles act synchronously in combination with the chemotherapeutics (e.g. BIRC3, NFKBIA and TNFAIP3). Some of these genes have already been proven to play a role in programmed cell death in human fibrosarcoma (HSPA1A/HSPA1B, APAF1, PAWR, SOCS2) or were associated with sonication induced apoptosis (CD44). Further studies are needed to explore the options of sonodynamic therapy on soft tissue sarcoma and its molecular mechanisms.

Effects of ultrasound-induced inertial cavitation on enzymatic thrombolysis

Cavitation induced by ultrasound enhances enzymatic fibrinolysis by increasing the transport of reactants. However, the effects of cavitation need to be fully understood before sonothrombolysis can be applied clinically. In order to understand the underlying mechanisms, we examined the effects of combining ultrasound, microbubbles and thrombolytic enzymes on thrombolysis. First, we evaluated the relations between inertial cavitation and the reduction in the weight of a blood clot. Inertial cavitation was varied by changing the amplitude and duration of the transmitted acoustic wave as well as the concentration of microbubbles used to induce cavitation. Second, we studied the combined effects of streptokinase and inertial cavitation on thrombolysis. The results show that inertial cavitation increases the weight reduction of a blood clot by up to 33.9%. With linear regression fitting, the measured differential inertial cavitation dose and the weight reduction had a correlation coefficient of 0.66. Microscopically, enzymatic thrombolysis effects manifest as multiple large cavities within the clot that are uniformly distributed on the side exposed to ultrasound. This suggests that inertial cavitation plays an important role in producing cavities, while microjetting of the microbubbles induces pits on the clot surface. These observations preliminarily demonstrate the clinical potential of sonothrombolysis. The use of the differential inertial cavitation dose as an indicator of blood clot weight loss for controlled sonothrombolysis is also possible and will be further explored.

Gas-filled microbubbles--a novel susceptibility contrast agent for brain and liver MRI

Gas-filled microbubbles have the potential to become a unique intravascular MR contrast agent due to their magnetic susceptibility effect, biocompatibility and localized manipulation via ultrasound cavitation. However, in vivo demonstration of microbubble susceptibility effect is limited so far and microbubble susceptibility effect is relatively weak when compared with other intravascular MR susceptibility contrast agents. In this study, two types of microbubbles, custom-made albumin-coated microbubbles (AMBs) and a commercially available lipid-based clinical ultrasound contrast agent (SonoVue), were investigated with in vivo dynamic brain and liver MRI in Sprague-Dawley rats at 7 Tesla. Transverse relaxation rate enhancements (DeltaR2*) maps were computed for brain and liver, yielding results similar to those obtained with a common MR blood pool contrast agent. These results indicate that gas-filled microbubbles can serve as an intravascular MR contrast agent at high field. Enhancement of microbubble susceptibility effect by entrapping monocrystalline iron oxide nanoparticles (MIONs) into microbubbles was also investigated at 7 T in vitro. This is the first experimental demonstration of microbubble susceptibility enhancement for MRI application. This study indicates that gas-filled microbubble susceptibility effect can be substantially increased using iron oxides nanoparticles. With such approach, microbubbles can potentially be visualized with higher sensitivity and lower concentrations by MRI. Such capability has the potential to lead to real-time MRI guidance in various microbubble-based drug delivery and therapeutic applications.

Ultrasound and microbubble-induced intra- and intercellular bioeffects in primary endothelial cells

Recent developments in the field of ultrasound (US) contrast agents have demonstrated that these encapsulated microbubbles can not only be used for diagnostic imaging but may also be employed as therapeutic carriers for localized, targeted drug or gene delivery. The exact mechanisms behind increased uptake of therapeutic compounds by US-exposed microbubbles are still not fully understood. Therefore, we studied the effects of stably oscillating SonoVue microbubbles on relevant parameters of cellular and intercellular permeability, i.e., reactive oxygen species (ROS) homeostasis, calcium permeability, F-actin cytoskeleton, monolayer integrity and cell viability using live-cell fluorescence microscopy. US was applied at 1-MHz, 0.1MPa peak-negative pressure, 0.2% duty cycle and 20Hz pulse repetition frequency to primary endothelial cells. We demonstrated increased membrane permeability for calcium ions, with an important role for H(2)O(2). Catalase, an extracellular H(2)O(2) scavenger, significantly blocked the influx of calcium ions. Further changes in ROS homeostasis involved an increase in intracellular H(2)O(2) levels, protein nitrosylation and a decrease in total endogenous glutathione levels. In addition, an increase in the number of F-actin stress fibers and F-actin cytoskeletal rearrangement were observed. Furthermore, US-exposed microbubbles significantly affected endothelial monolayer integrity, but importantly, disrupted cell-cell interactions were restored within 30min. Finally, cell viability was not affected. In conclusion, these data provide more insight in the interactions between US, microbubbles and endothelial cells, which is important for understanding the mechanisms behind US and microbubble-enhanced uptake of drugs or genes.

Low-intensity ultrasound-exposed microbubbles provoke local hyperpolarization of the cell membrane via activation of BK(Ca) channels

Ultrasound (US) contrast agents have gained wide interest in gene therapy as many researchers reported increased membrane permeability and transfection efficiency by sonoporation in the presence of US contrast agents. We recently demonstrated an increase in cell membrane permeability for Ca2+ in rat cardiomyoblast (H9c2) cells insonified in the presence of microbubbles. In the present study, we specifically investigated whether US-exposed microbubbles have an effect on the cell membrane potential and whether Ca2+-dependent potassium (BK(Ca)) channels are involved. We particularly focused on local events where the microbubble was in contact with the cell membrane. H9c2 cells were cultured on US transparent membranes. US exposure consisted of bursts with a frequency of 1 MHz with a peak-to-peak pressure of 0.1 or 0.5 MPa. Pulse repetition frequency was set to 20 Hz, with a duty cycle of 0.2%. Cells were insonified during 30 s in the presence of Sonovue(trade mark) microbubbles. The membrane potential was monitored during US exposure using the fluorescent dye di-4-aminonaphtylethenylpyridinium (di-4-ANEPPS). The experiments were repeated in the presence of iberiotoxin (100 nM), a specific inhibitor of BK(Ca) channels. Surprisingly, despite the previously reported Ca(2+) influx, we found patches of hyperpolarization of the cell membrane, as reflected by local increases in di-4-ANEPPS mean intensity of fluorescence (MIF) to 118.6 +/- 2.5% (p < 0.001, n = 267) at 0.1 MPa and 125.7 +/- 5.9% (p < 0.001, n = 161) at 0.5 MPa at t = 74 s, respectively, compared with "no US" (100.3 +/- 3.4%, n = 52). This hyperpolarization was caused by the activation of BK(Ca) channels, as iberiotoxin completely prevented hyperpolarization. (MIF(t74) = 100.6 +/- 1.4%; p < 0.001, n = 267) and 0.5 MPa (MIF(t74) = 88.8 +/- 2.0%; p< 0.001, n = 193), compared with 0.1 and 0.5 MPa microbubbles without iberiotoxin. In conclusion, US-exposed microbubbles elicit a Ca2+ influx, which leads to activation of BK(Ca) channels and a subsequent, local hyperpolarization of the cell membrane. This local hyperpolarization of the cell membrane may facilitate uptake of macromolecules through endocytosis and macropinocytosis. (E-mail: ljm.juffermans@vumc.nl).

Assessment of the sulfur hexafluoride (SF6) tracer technique for measuring enteric methane emissions from cattle

A commonly used method of measuring enteric methane (CH4) emissions from ruminants is the SF6 tracer technique that measures respired and eructated CH4. However, within the animal, a small proportion of CH4 is produced post-ruminally and some of this may escape through the rectum. The comparison of emissions using a chamber technique that measures all enteric CH4 losses, and the SF6 tracer technique, could give some insight into the magnitude of post-ruminal emission. The objective of our study was to assess the precision and accuracy of the SF6 tracer technique against a chamber technique for cattle fed a range of diets. Using a repeated-measures design, eight beef heifers were offered a high grain or high forage diet for ad libitum or restricted (65% of ad libitum) feed intake to vary the site of digestion within the gastrointestinal tract (n = 24). The SF6 tracer technique underestimated CH4 emissions on average by 4% relative to the chamber technique. This difference was not significant (P > 0.05) and suggests low post-ruminal CH4 emissions. There was a trend for greater accuracy and precision of the SF6 tracer technique when used with cattle fed a high forage diet at a restricted level of intake. The high forage diet corresponds to the conditions of cattle grazing pasture, suggesting the SF6 tracer technique is most reliable for the grazing system.

Increase in capillary perfusion following low-intensity ultrasound and microbubbles during postischemic reperfusion

OBJECTIVES

We postulated that the increase in shear stress caused by microbubbles in the presence of low-intensity ultrasound increases vasodilation in ischemia/reperfusion.

DESIGN

Prospective, randomized, and blinded experimental study.

SETTING

Research laboratory.

SUBJECTS

Forty hamsters were subjected to ischemia/reperfusion and observed by intravital microscopy.

INTERVENTIONS

Ultrasound (2.5 MHz, 1.3 mechanical index, 2.0 peak pressure) was applied to the hamster cheek pouch in ischemia/reperfusion with and without microbubbles (Levovist or Sono Vue) at baseline (15 mins) and at the beginning (15 mins) of reperfusion after ischemia (30 mins).

MEASUREMENTS AND MAIN RESULTS

Arterial diameter (A2-A3, 38.5 +/- 5.3 microm; A4,15.0 +/- 7.0 microm), red blood cell velocity, wall shear stress, permeability, perfused capillary length, and adherent leukocytes in venules were evaluated. Lipid peroxides were also determined in the systemic blood. Ultrasound and microbubbles in reperfusion significantly increased the diameter (A2-A3 Sono Vue, 33%; Levovist, 53% vs. ischemia/reperfusion, p < .05; A4, Sono Vue, 93%; Levovist, 104% vs. ischemia/reperfusion, p < .05), red blood cell velocity, flow, and shear stress in both A4 and A2-A3 arterioles. Shear stress was significantly higher with Levovist (A2-A3, 105%; A4, 185%) and Sono Vue (A2, 108%; A4, 140% vs. ischemia/reperfusion, p < .05) than ultrasound alone in arterioles. With ischemia/reperfusion, perfused capillary length was reduced significantly, whereas it increased with Levovist and Sono Vue (43%, 41% vs. ischemia/reperfusion p < .05). Lipid peroxides increased early during reperfusion and remained at increased levels throughout reperfusion. Lipid peroxides were unchanged after ultrasound alone or ultrasound with Sono Vue or Levovist during ischemia/reperfusion. With ultrasound there was a significant increase in vascular permeability vs. ischemia/reperfusion. Treatment with Sono Vue (-36%) and Levovist (-57%) decreased permeability vs. ischemia/reperfusion in reperfusion (p < .001). Ischemia/reperfusion had significantly increased leukocyte adhesion. Ultrasound alone (-39%) or with Sono Vue (-64%) and Levovist (-57%) caused smaller increases in leukocyte adhesion than ischemia/reperfusion (p < .05).

CONCLUSIONS

Ultrasound and microbubbles equilibrate microvascular shear stress, thus avoiding the failure of capillary perfusion in postischemic reperfusion.

Tissue Doppler imaging does not show infraclinical alteration of myocardial function after contrast echocardiography

BACKGROUND

It has been previously suggested that simultaneous exposure of hearts to contrast and ultrasound can damage the myocardium and produce a transient decrease of the contractility in animals. Tissue Doppler imaging (TDI) is a useful tool to quantify the myocardial function with very high temporal resolution.

AIM OF THE STUDY

The aim of the study was to test whether contrast echocardiography (CE) can cause alteration of the myocardial function by using tissue Doppler analysis.

METHODS

Twenty-eight healthy patients (mean age: 44 +/- 22) underwent baseline echocardiography before and after 5 min of continuous intravenous infusion of Sonovue from the apical views, using an intermediate mechanical index (MI = 1). High frame rate images were acquired in tissue Doppler mode. Data were averaged over 3 cardiac cycles and analysed off-line before and after CE.

RESULTS

There were no significant changes, before and after CE, in the peak systolic velocity (basal septum (BS): 6.2 +/- 2.2 vs 6.4 +/- 2.6; basal lateral (BL): 6.2 +/- 3.1 vs 6.4 +/- 3.3 cm/s), in the peak diastolic E velocity (BS: 5.4+/-1.8 vs 5.3+/-1.7; BL: 7.3+/-2.4 vs 7.7 +/- 3.2 cm/s), in the peak diastolic A velocity (BS: 6.3 +/- 1.9 vs 6.9 +/- 2.4; BL: 6.1 +/- 3.5 vs 6.2 +/- 2.5 cm/s), in the peak systolic strain (BS: 16 +/- 7 vs 17 +/- 7; BL: 12.6 +/- 5 vs 12.9 +/- 5%) and in peak systolic strain rate (BS: 1.3+/-0.6 vs 1.4+/-0.6; BL: 1.2+/-0.5 vs 1.21+/-0.51 1/sec).

CONCLUSIONS

Our data suggest that CE does not cause alterations in the myocardial function as assessed by tissue Doppler imaging. CE, even with high MI settings, usually used for left ventricular opacification, can be safely performed.

Micromanipulation of endothelial cells: ultrasound-microbubble-cell interaction

Ultrasound (US) in combination with contrast microbubbles has been shown to alter the permeability of cell membranes without affecting cell viability. This permeabilisation feature is used to design new drug delivery systems using US and contrast agents. The underlying mechanisms are still unknown. One hypothesis is that oscillating microbubbles cause cell deformation resulting in enhanced cell membrane permeability. This technical note reveals the interaction between oscillating microbubbles and endothelial cells under a microscope recorded with a fast framing camera at 10 million frames per second. A microbubble expansion of 100% resulted a 2.3-mum displacement of the cell membrane. During the insonification, changes of approximately 15% in the cross-sectional distance of the endothelial cells were observed due to microbubble vibrations. In conclusion, the use of such a camera makes it possible to reveal the mechanisms of interactions between ultrasound, microbubbles and cells.

Effect of 60 degrees head-down tilt on peripheral gas mixing in the human lung

The phase III slope of sulfur hexafluoride (SF6) in a single-breath washout (SBW) is greater than that of helium (He) under normal gravity (i.e., 1G), thus resulting in a positive SF6-He slope difference. In microgravity (microG), SF6-He slope difference is smaller because of a greater fall in the phase III slope of SF6 than He. We sought to determine whether increasing thoracic fluid volume using 60 degrees head-down tilt (HDT) in 1G would produce a similar effect to microG on phase III slopes of SF6 and He. Single-breath vital capacity (SBW) and multiple-breath washout (MBW) tests were performed before, during, and 60 min after 1 h of HDT. Compared with baseline (SF6 1.050 +/- 0.182%/l, He 0.670 +/- 0.172%/l), the SBW phase III slopes for both SF6 and He tended to decrease during HDT, reaching nadir at 30 min (SF6 0.609 +/- 0.211%/l, He 0.248 +/- 0.138%/l; P = 0.08 and P = 0.06, respectively). In contrast to microG, the magnitude of the phase III slope decrease was similar for both SF6 and He; therefore, no change in SF6-He slope difference was observed. MBW analysis revealed a decrease in normalized phase III slopes at all time points during HDT, for both SF6 (P < 0.01) and He (P < 0.01). This decrease was due to changes in the acinar, and not the conductive, component of the normalized phase III slope. These findings support the notion that changes in thoracic fluid volume alter ventilation distribution in the lung periphery but also demonstrate that the effect during HDT does not wholly mimic that observed in microG.

Ultrasound contrast agents can influence the respiratory burst activity of human neutrophil granulocytes

Activated leucocytes can bind and, subsequently, phagocytose microbubbles that are used as ultrasound (US) contrast agents. The purpose of this study was to investigate whether or not microbubbles can influence the inflammatory response of human neutrophil granulocytes. Granulocytes isolated from healthy volunteers were activated with various stimuli, for example, the bacterial peptide N-formyl-methyonyl-leucyl-phenylalanine (fMLP), the calcium ionophore A23187, the protein kinase C activator phorbol myristate acetate (PMA) and the cytokine tumor necrosis factor alpha (TNF-alpha), and incubated with albumin or phospholipid microbubbles. Neutrophil respiratory burst activity and elastase release were quantified. Albumin (Optison) and phospholipid (SonoVue) contrast agents induced an extensive oxidative response of human granulocytes to all the stimuli used, and these effects could be significantly impaired by preincubation of the cells with cytochalasin B. Left heart contrast agents used for contrast-enhanced US assessment can activate human neutrophil granulocytes, inducing an extensive respiratory burst to secondary stimuli. The potential clinical relevance of this effect needs to be elucidated.

Effect of sulfur hexafluoride gas on antibacterial activity of antibiotics in vitro against agents causing endophthalmitis

BACKGROUND

We conducted a study to evaluate the effect of sulfur hexafluoride gas (SF(6)) on the antibacterial activity of antibiotics in vitro against Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa, which are common endophthalmitis-causing agents.

METHODS

In this experimental study, antibiotic susceptibility tests were prepared according to the National Committee for Clinical Laboratory Standards macrobroth dilution method. Müller-Hinton broth was the test medium. Standard P. aeruginosa (ATCC 27853), S. epidermidis (ATCC 12228) and S. aureus (ATCC 29213) strains were studied. For P. aeruginosa ceftazidime, ofloxacin and tobramycin dilutions, and for S. epidermidis and S. aureus, cefazolin, ofloxacin and tobramycin dilutions were prepared identically in two sets of tubes. One set of tubes, into which pure SF(6) was injected, was defined as the SF(6) group. The other set of tubes, into which no SF(6) was injected, was taken as the control group. To determine the minimal bactericidal concentrations of the antibiotics, subcultures were made onto Müller-Hinton agar, and the colonies were counted after 18 h of incubation at 37 degrees C.

RESULTS

The minimal inhibitory concentrations of the antibiotics in the SF(6) group were found to be identical with those of the control group. However, the minimal bactericidal concentrations of the antibiotics were found to be at least two dilutions lower in the SF(6) group than in the control group, except for the minimal bactericidal concentration of cefazolin for S. aureus, which was found to be one dilution lower in the SF(6) group.

CONCLUSION

SF(6) was found to potentiate the in vitro antibacterial activity of ofloxacin and tobramycin against S. aureus, S. epidermidis and P. aeruginosa, ceftazidime against P. aeruginosa, and cefazolin against S. epidermidis. Experimental animal studies are required to determine the role of SF(6) in the management of endophthalmitis.

Helium and sulfur hexafluoride bolus washin in short-term microgravity

We performed single-breath washout (SBW) tests in which He and sulfur hexafluoride (SF6) were inspired throughout the vital capacity inspirations or were inhaled as discrete boluses at different points in the inspiration. Tests were performed in normal gravity (1 G) and in up to 27 s of microgravity (microG) during parabolic flight. The phase III slope of the SBW could be accurately reconstructed from individual bolus tests when allowance for airways closure was made. Bolus tests showed that most of the SBW phase III slope results from events during inspiration at lung volumes below closing capacity and near total lung capacity, as does the SF6-He phase III slope difference. Similarly, the difference between 1 G and microG in phase III slopes for both gases was entirely accounted for by gravity-dependent events at high and low lung volumes. Phase IV height was always larger for SF6 than for He, suggesting at least some airway closure in close proximity to airways that remain open at residual volume. These results help explain previous studies in microG, which show large changes in gas mixing in vital capacity maneuvers but only small effects in tidal volume breaths.

Detection of perfusion defects during coronary occlusion and myocardial reperfusion after thrombolysis by intravenous administration of the echo-enhancing agent BR1

The purpose of this study was to detect myocardial perfusion defects as a result of coronary occlusion and myocardial reperfusion after thrombolysis with intravenous (i.v.) administration of the echo contrast agent BR1 (Bracco Research, Switzerland), which consists of microbubbles (median diameter 2.5 microm) containing sulfur exafluoride in a phospholipidic shell. To generate a coronary thrombosis, a copper coil was advanced into the left circumflex coronary artery in eight anesthetized dogs with opened chest cavities. Coronary occlusion occurred 18 +/- 10 minutes after the insertion of the coil and was documented both by an electromagnetic flow meter (as zero blood flow) and by radiolabeled microspheres (as myocardial perfusion defect). After 2 hours of occlusion, streptokinase was infused i.v.; reperfusion was documented by both the flow-meter and microspheres. Left ventricular cavity enhancement was apparent after all contrast injections. Peak cavity intensity did not increase with dose and was not affected by signal processing (suggesting signal saturation), whereas the duration of contrast effect significantly increased with the dose (from 26 +/- 16 to 147 +/- 74 seconds). Myocardial contrast intensity also increased after contrast (from 15 +/- 12 to 21 +/- 18 gray level/pixel, p < 0.001). Contrast echo detected myocardial perfusion defects (corresponding to 17% +/- 11% of LV cross-sectional area) in all the injections performed during coronary occlusion and detected myocardial reperfusion with a sensitivity of 50% versus microspheres. The extent of perfusion defects by contrast echo showed a good correlation with microspheres (r = 0.73). Myocardial reperfusion was not detected by changes in heart rate, aortic pressure, pulmonary arterial pressure, cardiac output, left ventricular fractional area change, or wall-motion score index. Hemodynamic parameters were not affected by contrast injections. Thus, the i.v. administration of BR1 allows us to accurately detect myocardial perfusion defects during coronary occlusion and, to a lesser extent, myocardial reperfusion after thrombolysis.

Cardiogenic oscillation phase relationships during single-breath tests performed in microgravity

We studied the phase relationships of the cardiogenic oscillations in the phase III portion of single-breath washouts (SBW) in normal gravity (1 G) and in sustained microgravity (microG). The SBW consisted of a vital capacity inspiration of 5% He-1.25% sulfurhexafluoride-balance O2, preceded at residual volume by a 150-ml Ar bolus. Pairs of gas signals, all of which still showed cardiogenic oscillations, were cross-correlated, and their phase difference was expressed as an angle. Phase relationships between inspired gases (e.g., He) and resident gas (n2) showed no change from 1 G (211 +/- 9 degrees) to microG (163 +/- 7 degrees). Ar bolus and He were unaltered between 1 G (173 +/- 15 degrees) and microG (211 +/- 25 degrees), showing that airway closure in microG remains in regions of high specific ventilation and suggesting that airway closure results from lung regions reaching low regional volume near residual volume. In contrast, CO2 reversed phase with He between 1 G (332 +/- 6 degrees) and microG (263 +/- 27 degrees), strongly suggesting that, in microG, areas of high ventilation are associated with high ventilation-perfusion ratio (VA/Q). This widening of the range of VA/Q in microG may explain previous measurements (G.K. Prisk, A.R. Elliott, H.J.B. Guy, J.M. Kosonen, and J.B. West J. Appl. Physiol. 79: 1290-1298, 1995) of an overall unaltered range of VA/Q in microG, despite more homogeneous distributions of both ventilation and perfusion.

Paradoxical helium and sulfur hexafluoride single-breath washouts in short-term vs. sustained microgravity

During single-breath washouts in normal gravity (1 G), the phase III slope of sulfur hexafluoride (SF6) is steeper than that of helium (He). Two mechanisms can account for this: 1) the higher diffusivity of He enhances its homogeneous distribution; and 2) the lower diffusivity of SF6 results in a more peripheral location of the diffusion front, where airway asymmetry is larger. These mechanisms were thought to be gravity independent. However, we showed during the Spacelab Life Sciences-2 spaceflight that in sustained microgravity (microG) the SF6-to-He slope difference is abolished. We repeated the protocol during short periods (27 s) of microG (parabolic flights). The subjects performed a vital-capacity inspiration and expiration of a gas containing 5% He-1.25% SF6-balance O2. As in sustained microG, the phase III slopes of He and SF6 decreased. However, during short-term microG, the SF6-to-He slope difference increased from 0.17 +/- 0.03%/l in 1 G to 0.29 +/- 0.06%/l in microG, respectively. This is contrary to sustained microG, in which the SF6-to-He slope difference decreased from 0.25 +/- 0.03%/l in 1 G to -0.01 +/- 0.06%/l in microG. The increase in phase III slope difference in short-term microG was caused by a larger decrease of He phase III slope compared with that in sustained microG. This suggests that changes in peripheral gas mixing seen in sustained microG are mainly due to alterations in the diffusive-convective inhomogeneity of He that require > 27 s of microG to occur. Changes in pulmonary blood volume distribution or cardiogenic mixing may explain the differences between the results found in short-term and sustained microG.

Blood oxygen saturation measured in the presence of a mixture of cyclopropane, sulfur hexafluoride, and ethane

Some anesthetic gases interfere with the determination of blood O2 values. We evaluated, for its potential for such interference, a gas mixture containing (v/v) approximately 70% ethane, 20% sulfur hexafluoride, and 10% cyclopropane, as is currently used in trace amounts to determine ventilation-perfusion (v/Q) ratios. Normal human blood samples were first tonometered with control gas mixtures containing (v/v): (1) 20.9% O2, 0.04% CO2; (2) 16.0% O2, 4.0% CO2; and (3) 9.9% O2, 7.8% CO2. A large quantity (20.9%) of the v/Q mixture was blended experimentally into the control mixture and the tonometry repeated. The entire experiment was then repeated substituting pure N2 for the v/Q mixture as a dilution control. O2 values were determined by three methods: (1) a polarographic electrode, ABL-300 (ABL); (2) a spectrophotometric method, Co-Oximeter (COOX); and (3) a galvanic cell, Lex-O2-Con (LEX). The v/Q gas mixture lowered significantly all measured LEX values by 2.5-3.6 saturation percent (sat%), but showed no effect, dilution or otherwise, on the O2 values determined by the COOX and ABL methods. The N2 dilution lowered the LEX values by an average of only 0.9 sat%; the ABL and the COOX were approximately 0.6 sat% lower. We therefore suggest that, if any of these O2 measurement methods are used in the presence of the v/Q mixture, baseline O2 values should be determined both before and after injection of the mixture into the bloodstream, prior to performing other experimental manipulations. The difference between the two values, if any, can then be used to interpret subsequent results.

Effect of SF6-O2 (80/20) breathing on air bubbles in rat tissues

We studied the effect of SF6-O2 breathing on air bubbles injected into skeletal muscle, rat-tail tendon, the anterior chamber of the eye, and spinal white matter. Decompression-induced nitrogen bubbles in adipose tissue were studied during breathing of SF6-O2 (80/20). The results of SF6-O2 breathing are compared with previous experiments using heliox (80/20) as the breathing medium. Bubbles studied in skeletal muscle, eye chamber, and spinal white matter were found to behave in a two-phased manner during SF6-O2 (80/20) breathing. All bubbles would initially decrease rapidly in size for a period of 10-80 min (depending on the tissue). Subsequently, the bubbles stabilized and decreased in size with a shrinking rate near zero. In spinal white matter, very small bubbles decreased size with a shrinking rate near zero. In spinal white matter, very small bubbles could disappear before development of the slow phase. All bubbles in tendon shrank at a rather constant rate during SF6-O2 (80/20) breathing until they disappeared. During SF6-O2 (80/20) breathing, all bubbles in adipose tissue shrank and disappeared at least as fast as during heliox (80/20) breathing. Just before disappearance of the bubbles the shrinking rate slowed. Comparison of the effects of SF6-O2 (80/20) and heliox (80/20) breathing suggests that countercurrent gas exchange is at work in some tissues.

CO2 binding by Baralyme in three different carrier gases

The absorptive properties of Baralyme and Sodasorb for CO2 in a container were studied by measuring the lifetime T0.5 of the unit, i.e., the time until the exit concentration of CO2 reaches 0.5%. The container size, the inlet gas flow rate, and the inlet CO2 concentration were varied. The experiments were repeated with either He, N2, or SF6 as the inert gas to evaluate the effect of increased gas density due to hyperbaric conditions on scrubber performance. It was found that T0.5 is best described by an exponential function of the type b (ttr)a, where ttr is the transit time of the gas through the container. The exponent a equals about 1.5 and varies relatively little. The constant b, however, is strongly dependent on inert gas density and on CO2 concentration in the inlet gas; it is independent of container size and gas flow rate. In addition, the amount of absorber reaching up to time T0.5 was measured in all conditions. It is strongly dependent on CO2 concentration; however, surprisingly it is nearly independent of inert gas properties. These results are compared with a mathematical model of scrubber behavior that is based on the chemical reaction rate of an imaginary absorber. The model neglects possible effects of CO2 diffusion in the gas phase, of ash formation, and of heat produced by the reaction. Differences between our experimental data and the model are analyzed as a function of these effects. The results give some simple predictive equations for the lifetime and the amount of absorber reacting.

Relative narcotic potency and mode of action of sulfur hexafluoride and nitrogen in humans

Impairments of psychomotor, perceptual, and cognitive abilities were determined in nine male subjects exposed to inhaled SF6 partial pressures of 0, 52, 104, and 156 kPa and to inhaled N2 partial pressures of 103, 575, 825, and 1,075 kPa. Also data from a previous study with inhaled N2O partial pressures of 0, 13, 26, and 39 kPa were included. With the highest gas concentrations, performances were reduced by 41-57%. Effective doses for a 20% performance impairment were 830, 97, and 21.5 kPa for N2, SF6, and N2O, respectively, yielding relative narcotic potencies of 1.0:8.5:39. The order of narcotic potencies is the same as for the lipid solubility of the three gases. In contrast, the order of increasing tendency for hydrate formation (decreasing hydrate dissociation pressure) for the three gases is N2, N2O, and SF6. Thus, mild to moderate inert gas narcosis in humans shows the same positive relationship to lipid solubility as was shown in previous animal models that utilized much deeper levels of anesthesia.

Pressure changes in the eye due to an injection of inert gases: a theoretical model

In the repair of retinal tears and detachments, the vitreous humor is often completely replaced with a temporary mixture of gases, one of which is not normally found in the bloodstream. The resulting bubble can then support the healing retina. There is diffusion of gases, however, from the bubble into the bloodstream and vice versa. This alters the intraocular pressure, with possible adverse consequences, as the intraocular pressure must be maintained within a certain range for the procedure to be successful. A simple model has been developed to predict the evolution of intraocular pressure over time, given a certain initial mixture of injected gases. This model could be useful in determining what mixture to use to support effectively and safely a healing retina.

Comparisons among external resistive loading, drug-induced bronchospasm, and dense gas breathing in cats: roles of vagal and spinal afferents

In anesthetized cats, breathing spontaneously, increase in lung resistance (RL) was induced by either external resistive loads (ERL) or internal loading produced by dense gas breathing (sulfur hexafluoride, SF6) or serotonin (5-HT)-induced bronchoconstriction. The 3 test agents were used in each animal. Arterial blood gases were maintained in the normal range. Ventilatory and cardiovascular responses were studied in 3 groups of animals: intact, vagotomized, or spinalized at C8 level, a condition that preserved diaphragmatic afferents. In intact or spinal animals, ERL as well as SF6 inhalation lengthened the inspiratory and/or the expiratory periods, whereas 5-HT injections elicited rapid shallow breathing. The changes in ventilatory timing with either type of load were not observed in vagotomized cats. In all animals, ERL breathing or 5-HT injections increased the moving-time average of diaphragmatic EMG measured at constant time (Edi 0.1 and 0.5 secs), but this was not observed during SF6 inhalation, a condition in which the magnitude of RL increase was less than in the 2 other situations. The changes in systemic arterial blood pressure and/or cardiac frequency were mostly associated with 5 HT-induced bronchoconstriction. They persisted in spinalized cats, but were not observed or reversed in vagotomized ones. These observations demonstrate that vagal afferents play a major role in the changes in ventilatory timing and cardiovascular function in response to both external or internal moderate resistive loading. The existence of Edi changes in the 3 groups of cats suggests also that diaphragmatic afferents, preserved in both situations, are involved in this response.

Effects of sulphur hexafluoride on psychomotor performance

The narcotic influence of sulphur hexafluoride on mental and psychomotor performance has been studied in 9 subjects at normal atmospheric pressure. Control experiments were performed with air and with nitrous oxide. Psychomotor, perceptual and cognitive abilities were assessed using a computerized test battery. Subjects were exposed to air and six different normoxic gas mixtures: 13, 26, and 39% N2O, and 39, 59, and 79% SF6. Significant performance impairments were found with 13% N2O and gradual further impairment with 26, and 39% N2O. During exposure to 39, 59, and 79% SF6 over-all performance was impaired by 5, 10, and 18%, respectively. Impairment was significant with 59 and 79% SF6. The results indicate that the relative narcotic potency of SF6: N2O is about 1:4 in humans. It is concluded that a normoxic SF6-O2 mixture can be inhaled for lung function studies without any harmful effects and that the short-lasting narcotic effect, although detectable with a test battery, would not impair the ability of the subject to perform simple breathing procedures.

Increased breathing gas density enhances cardiac workload

The effect of increased breathing gas density on the left ventricular pressure (LVP), cardiac contractility (dP/dt), heart rate (HR), intrapleural pressure (P(ip)) and respiratory frequency (RF) was evaluated in pentobarbital-anaesthetized rats (n = 8) and cats (n = 6). Catheters were placed in the left cardiac ventricle via the right carotid artery to measure the LVP, in the oesophagus for indirect measurements of P(ip) and RF, and into the aorta from the right femoral artery for arterial pressure measurements. The RF fell significantly within the first 30 s and had reached a stable value 2 min after gas shift in both rats and cats. Concomitant with the RF fall, the depth of inspiration and intrapleural pressure differences in both rats and cats increased. The acid-base balance remained at control levels in both animal groups. LVP and dP/dt started to increase during the first half-minute, and reached their maximum values 2-5 min after the introduction of normoxic sulphur hexafluoride. A linear relationship between the enhanced dP/dt and the P(ip) increase was found. The HR remained unchanged in both cats and rats. These findings indicate that the breathing gas density might influence the cardiac contractility found during hyperbaric exposure, and that a gas density of five times that of air at 1 bar does not influence the diffusion of O2 and CO2 in the lung. The O2 consumption of the heart in cats and rats was calculated to rise by 25% and 30% respectively in the dense breathing gas atmosphere.

Postpneumonectomy space control with SF6

Four cases of patients whose postpneumonectomy spaces had been controlled with SF6 were examined at autopsy, which showed that the spaces were entirely covered with thickening parietal pleura and that the mediastinum had moderate elasticity. Histologically, fibrotic changes with minimum inflammation patterns were seen in the pleura. We consider that mediastinal elasticity becomes a factor in improving pulmonary function and the above observations confirmed that SF6 prevents the proliferative reaction of postpneumonectomy spaces without any toxicity.

The ocular effects of gases when injected into the anterior chamber of rabbit eyes

We studied the toxic effects of sulfur hexafluoride and perfluoropropane in comparison with air, balanced salt solution, hyaluronate sodium, and aqueous humor in a rabbit model. Sixty normal pigmented rabbits were studied during a period of 4 weeks. The variables studied were slit-lamp biomicroscopic examination of the anterior segment, intraocular pressure as measured by pneumotonometry, corneal thickness and endothelial cell count as measured by specular microscopy, lens opacity by Scheimpflug photography, and light and transmission electron microscopy. All three gases were more toxic to the cornea and lens than were balanced salt solution, hyaluronate, and aqueous humor. However, 15% perfluoropropane and 50% sulfur hexafluoride were no more toxic to the eye than air was. Therefore, this study suggests that nonexpansile mixtures of perfluoropropane and sulfur hexafluoride may be beneficial and relatively safe in re-forming persistently flat anterior chambers in situations where the use of air is being considered.

Respiratory frequency and distribution of cardiac output in rats breathing gas with different densities

The effect of increased and reduced breathing-gas density on cardiac output (CO) and organ blood flow was studied with radiolabelled microspheres on pentobarbital anaesthetized rats using normoxic sulphurhexafluoride (SF6) and normoxic helium (He). The mean arterial pressure (MAP), heart rate (HR), and CO remained unchanged during exposure to any gas composition. The respiratory frequency (RF) was reduced from 98 +/- 6 (mean +/- SE) to 85 +/- 3 min-1 (p less than 0.01) in the dense breathing-gas, while the RF increased from 96 +/- 6 to 108 +/- 4 (p less than 0.01) in the He-O2 atmosphere. The arterial acid-base chemistry was mainly unaltered in any situation, indicating almost unchanged alveolar ventilation. Since the cerebral blood flow increased (30%, p less than 0.01), we suggest that SF6 gas is not a truly inert gas; blood flow to the eyes was also increased (30%, p less than 0.01). Though the pumping action of the heart (MAP X HR) remained constant, the blood flow to the left ventricular myocardium was increased (28%, p less than 0.01) by the elevated gas density. Reduced breathing-gas density increased the myocardial blood flow in the right ventricle (20%, p less than 0.02) suggesting a constrictive effect of He on the pulmonary arteries. Except for reduced renal blood flow, no blood flow changes were observed in any organ in this situation.

Mechanisms of gas loss from normal and hyperinflated excised guinea pig lungs

Increased pulmonary gas trapping was produced by in vivo inhalation exposures of guinea pigs to bronchoconstrictive aerosols. Both normal (filtered air-exposed) and hyperinflated excised lungs lost about 20% of their initial volume by 4 h; gas loss was more rapid during the first 60 min (early period) than the following 180 min (late period). During both periods, absolute rates of gas loss were positively correlated (P less than 0.001) with initial excised lung gas volumes (ELGVs). Tracheal foam movement was observed in most of the hyperinflated lungs, but only during the early period. Occlusion of the trachea reduced gas loss during the early period, but not the late. Gas volumes increased in lungs of animals exposed to SF6:O2 (tracheas tied), and decreased most rapidly in lungs of animals exposed to He:O2 (tracheas tied). Our results suggest that a major part of the early gas loss from excised guinea pig lungs occurs via the trachea and may be influenced by airway foam or menisci formation. After 60 min, airways may be closed and gas loss may occur via transpleural diffusion.

Breathing He-O2 shifts the lung pressure-volume curve of the dog

To determine whether breathing a mixture of 80% He-20% O2 affects the lung pressure-volume (PV) curve, eight anesthetized paralyzed dogs were studied in a volume-displacement plethysmograph. Static PV curves on air were compared with PV curves obtained after equilibration with He-O2. The He-O2 PV curves were significantly shifted upward by an average of 5% total lung capacity. There was no change in compliance, indicating that the shift was due to lung expansion rather than a change in elasticity. Pretreatment of the dogs with cyclooxygenase inhibitors abolished the PV shift with He-O2. Four dogs had PV curves recorded on air and a mixture of O2, SF6, and Ne, a gas mixture with the same density as air but with 45% greater viscosity. The PV curve shift was even greater than observed with He-O2 and could again be virtually abolished with a cyclooxygenase inhibitor. These results suggest that breathing a high-viscosity gas mixture results in alveolar duct dilatation due to the release of a prostaglandin bronchodilator. This may need to be taken into account in the analysis of flow augmentation with He-O2.

Nasal conductance and effective airway diameter

1. Transnasal pressure (delta p) in Pa and gas flow in cm3 s-1 were measured in men breathing gases of different density, assuming flow through each nostril (f) to be half the measured total flow. Measurements were also made in children with allergic rhinitis before and after nasal antigen challenge. 2. Flow always showed evidence of turbulence when transnasal pressure exceeded 40-80 Pa breathing air and Reynolds number exceeded 2400 (1800 in the presence of nasal obstruction). 3. Changes in effective mean nasal airway diameter (D) after nasal challenge can be determined at points of similar pressure from the relation log (D2/D1) = 0.368 log (f2/f1) when flow is turbulent. 4. Absolute estimates of airway diameter in cm can be obtained from the relation 4.75 log D = 1.75 log f--log delta p+log L--4.756 breathing air when flow is turbulent (since the relation between pressure and flow approximates to that found in a long cylinder) and these estimates are only marginally affected by differing assumptions about nasal airway length (L). 5. Because pressure and flow are non-linearly related, and changing nasal dimensions have a profound effect on the flow at which turbulence occurs, it is suggested that measures of nasal conductance at delta p greater than or equal to 0.1 kPa are preferable to the more conventional measures of nasal resistance at a specified flow rate.

Changes in acid-base balance of chick embryos exposed to a He or SF6 atmosphere

On day 16 of the chick embryo, a catheter was implanted in the allantoic vein carrying arterialized blood, and a syringe was attached to the blunt end of the shell connecting to the air cell. This technique allowed for repetitive sampling and analysis of air cell gas and arterialized blood when these eggs were exposed to a He-O2 or SF6-O2 atmosphere. Exposure to He-O2 reduced the arterial CO2 tension(PaCO2) from 36 to 17 Torr and increased pH by 0.17 units; exposure to SF6-O2 increased PaCO2 from 37 to 62 Torr and reduced the pH by 0.14 units. These responses were brought about by changes in the gas conductance of the shell, resulting in a diffusive hypocapnia and respiratory alkalosis in He-O2 and a diffusive hypercapnia and respiratory acidosis in SF6-O2. During a 4-h exposure to these foreign gases the observed pH changes were smaller than predicted because of marked shifts of HCO3- into the blood (SF6-O2) or out of the blood (He-O2).