Lung Ultrasound Induction of Pulmonary Capillary Hemorrhage in Rats With Consideration of Exposimetric Relationships to Previous Similar Observations in Neonatal Swine.

OBJECTIVE: Lung ultrasound (LUS) has become an essential clinical tool for pulmonary evaluation. LUS has been found to induce pulmonary capillary hemorrhage (PCH) in animal models, posing a safety issue. The induction of PCH was investigated in rats, and exposimetry parameters were compared with those of a previous neonatal swine study. METHODS: Female rats were anesthetized and scanned in a warmed water bath with the 3Sc, C1-5 and L4-12t probes from a GE Venue R1 point-of-care ultrasound machine. Acoustic outputs (AOs) of sham, 10%, 25%, 50% or 100% were applied for 5-min exposures with the scan plane aligned with an intercostal space. Hydrophone measurements were used to estimate the in situ mechanical index (MIIS) at the lung surface. Lung samples were scored for PCH area, and PCH volumes were estimated. RESULTS: At 100% AO, the PCH areas were 73 ± 19 mm2 for the 3.3 MHz 3Sc probe (4 cm lung depth), 49 ± 20 mm2 (3.5 cm lung depth) or 96 ± 14 mm2 (2 cm lung depth) for the 3.0 MHz C1-5 probe and 7.8 ± 2.9 mm2 for the 7 MHz L4-12t (1.2 cm lung depth). Estimated volumes ranged from 378 ± 97 mm3 for the C1-5 at 2 cm to 1.3 ± 1.5 mm3 for the L4-12t. MIIS thresholds for PCH were 0.62, 0.56 and 0.48 for the 3Sc, C1-5 and L4-12t, respectively. CONCLUSION: Comparison between this study and previous similar research in neonatal swine revealed the importance of chest wall attenuation. Neonatal patients may be most susceptible to LUS PCH because of thin chest walls.

Frame Rate Exposimetry for Pulmonary Capillary Hemorrhage During Lung Ultrasound.

OBJECTIVES: Lung ultrasound (LUS) is a powerful and accessible clinical tool for pulmonary diagnosis, but risk of pulmonary capillary hemorrhage (PCH) presents a safety issue. The dependence of PCH in a rat model of LUS was evaluated for image frames-per-second (fps) and associated on-screen Mechanical Index (MIOS ) and Thermal Index (TI). METHODS: A Philips iE33 machine with L15-7io probe was used to scan anesthetized rats in a warmed water bath. B mode was applied at 9 MHz with settings of 34, 61 and 118 fps. After 2 minutes of exposure at an MIOS setting, samples were obtained for assessment of PCH areas on the lung surface. Ultrasound parameters were measured to determine the in situ MIIS at the lung surface. RESULTS: The PCH trend counter-intuitively decreased with increasing fps, with areas of 19.5 mm2 for 34 fps (MIOS  = 1.0, TI = 0.8, 4080 images), 9.6 mm2 at 61 fps (MIOS  = 1.0, TI = 0.5, 7320 images) and 7.5 mm2 at 118 fps (MIOS  = 1.1, TI = 0.4, 14,160 images). The PCH was not significantly different for 34 fps (TI = 0.5, MIOS  = 0.8) (10.7 mm2 ), compared to 61 and 118 fps, above, indicating some value for the TI as a predictive indicator of PCH. MIIS thresholds were 0.42, 0.46, and 0.49 for 34, 61 and 118 fps, respectively. CONCLUSIONS: The increase in PCH at low fps was associated with delivering more relatively high amplitude grazing pulse exposures during slower image scans. No significant PCH was found for the MIOS setting of 0.5, corresponding to in MIIS values of 0.35-0.39.

Lung Ultrasound Induction of Pulmonary Capillary Hemorrhage in Neonatal Swine.

This study investigated induction of pulmonary capillary hemorrhage (PCH) in neonatal pigs (piglets) using three different machines: a GE Venue R1 point-of-care system with C1-5 and L4-12t probes, a GE Vivid 7 Dimension with a 7L probe and a SuperSonic Imagine machine with an SL15-4 probe and shear wave elastography (SWE). Female piglets were anesthetized, and each was mounted vertically in a warm bath for scanning at two or three intercostal spaces. After aiming at an innocuous output, the power was raised for a test exposure. Hydrophone measurements were used to calculate in situ values of mechanical index (MIIS). Inflated lungs were removed and scored for PCH area. For the C1-5 probe at 50% and 100% acoustical output (AO), a PCH threshold of 0.53 MIIS was obtained by linear regression (r2 = 0.42). The L4-12t probe did not induce PCH, but the 7L probe induced zones of PCH in the scan planes. The Venue R1 automated B-line tool applied with the C1-5 probe did not detect PCH induced by the C1-5 probe as B-line counts. However, when PCH induced by C1-5 and 7L exposures were subsequently scanned with the L4-12t probe using the automated tool, B-lines were counted in association with the PCH. The SWE induced PCH at push-pulse positions for 3, 30 and 300 s of SWE with PCH accumulating at 0.33 mm2/s and an exponential rise to a maximum of 18.4 mm2 (r2 = 0.61). This study demonstrated the induction of PCH by LUS of piglets, and supports the safety recommendation for use of MIs <0.4 in neonatal LUS.

Bio-based poly (γ-glutamic acid)-gelatin double-network hydrogel with high strength for wound healing.

Building bio-based hydrogels with high strength and biocompatibility is still a challenge. Herein, we successfully constructed a hybrid double-network (DN) full biological hydrogel with excellent mechanical properties and biocompatibility by introducing a physically cross-linked gelatin (GEL) network in a covalently cross-linked poly (γ-glutamic acid) (γ-PGA) network. The γ-PGA-GEL DN hydrogel demonstrated ultra-high compression performance (38 MPa), which was better than all currently reported γ-PGA-based hydrogels, and its tensile performance (0.27 MPa) was also satisfactory. Due to the unique multi-crosslinked DN structure, the γ-PGA-GEL DN hydrogel had better recovery and healing properties than those of the γ-PGA single-network (SN) hydrogel. In addition, the γ-PGA-GEL DN hydrogel exhibited good transparency, swelling and degradability. In vitro cell experiments demonstrated that the γ-PGA-GEL DN hydrogel was beneficial to cell adhesion and proliferation. The evaluation of the full-thickness skin defects model in rats exhibited that the γ-PGA-GEL DN hydrogel could significantly accelerate wound healing. These results indicated that the γ-PGA-GEL DN hydrogel was an ideal candidate material for wound dressing.

The Influence of Xylazine and Clonidine on Lung Ultrasound-Induced Pulmonary Capillary Hemorrhage in Spontaneously Hypertensive Rats.

Induction of pulmonary capillary hemorrhage (PCH) by lung ultrasound (LUS) depends not only on physical exposure parameters but also on physiologic conditions and drug treatment. We studied the influence of xylazine and clonidine on LUS-induced PCH in spontaneously hypertensive and normotensive rats using diagnostic B-mode ultrasound at 7.3 MHz. Using ketamine anesthesia, rats receiving saline, xylazine, or clonidine treatment were tested with different pulse peak rarefactional pressure amplitudes in 5 min exposures. Results with xylazine or clonidine in spontaneously hypertensive rats were not significantly different at the three exposure pulse peak rarefactional pressure amplitudes, and thresholds were lower (2.2 MPa) than with saline (2.6 MPa). Variations in LUS PCH were not correlated with mean systemic blood pressure. Similar to previous findings for dexmedetomidine, the clinical drug clonidine tended to increase susceptibility to LUS PCH.

Bio-based poly (γ-glutamic acid) hydrogels reinforced with bacterial cellulose nanofibers exhibiting superior mechanical properties and cytocompatibility.

Natural polymer hydrogels are expected to be promising biomaterial because of its excellent biocompatibility and biodegradability, but they are soft and easily broken. Herein, the poly (γ-glutamic acid) (γ-PGA)/bacterial cellulose (BC) composite hydrogels with excellent mechanical properties were constructed by introducing bacterial cellulose. The γ-PGA/BC composite hydrogels were obtained by the covalent cross-linking of γ-PGA in the BC nanofibers suspensions. The γ-PGA/BC composite hydrogels exhibited excellent strength and toughness due to the more effective energy dissipation of hydrogen bonds network among BC nanofibers and γ-PGA hydrogel matrix and BC also acts as an enhancer. The compressive fracture strength and toughness of the γ-PGA/BC composite hydrogels could reach up to 5.72 MPa and 0.42 MJ/m3 respectively. Additionally, the tensile strength of γ-PGA/BC composite hydrogels were improved 8.16 times compared with γ-PGA single network hydrogels. More significantly, BC could disperse evenly in the γ-PGA hydrogels because of the hydrophilic nature of γ-PGA and BC nanofillers, which led to good interface compatibility. The result of cytotoxicity tests indicated that γ-PGA/BC composite hydrogels present excellent cytocompatibility, which suggested that the γ-PGA/BC composite hydrogels could serve as promising materials for many biomaterial related applications.

The Impact of Hemorrhagic Shock on Lung Ultrasound-Induced Pulmonary Capillary Hemorrhage.

OBJECTIVES: Lung ultrasound (LUS) exposure can induce pulmonary capillary hemorrhage (PCH), depending on biological and physical exposure parameters. This study was designed to investigate the variation in the LUS induction of PCH due to hemorrhagic shock, which itself can engender pulmonary injury. METHODS: Male rats were anesthetized with isoflurane in air. Shock was induced by withdrawal of 40% of the blood volume and assessed by the blood pressure detected by a femoral artery catheter and by blood glucose tests. B-mode ultrasound was delivered at 7.3 MHz with a low output (-20 dB) for aiming and with the maximal output (0 dB) for exposure. Pulmonary capillary hemorrhage was quantified by an assessment of comet tail artifacts in the LUS images and by measurement of PCH areas on the surface of fresh lung samples. RESULTS: Tests without shock or catheterization surgery gave results for PCH similar to those of previous studies using different methods. Exposure before hemorrhagic shock gave a mean PCH area ± SE of 24.8 ± 9.2 mm2 on the ultrasound scan plane, whereas exposure after shock gave 0 PCH (P < .001; n = 7). CONCLUSIONS: The presence of hemorrhagic shock significantly reduces the occurrence of LUS-induced PCH.

Variation of Diagnostic Ultrasound-Induced Pulmonary Capillary Hemorrhage with Fraction of Inspired Oxygen.

Pulmonary capillary hemorrhage induction by diagnostic ultrasound (DUS-PCH) was investigated with respect to the influence of the fraction of inspired oxygen (FiO2). Sprague-Dawley rats were anesthetized with Telazol only (TO) or Telazol plus xylazine (TX), which can enhance DUS-PCH. A linear array probe (10 L, GE Vivid 7 Dimension) was used in B-mode at 7.5 MHz to expose the right lung. FiO2 at 10%, 20%, 60% and 100% was delivered through a nose cone. On the ultrasound images, the PCH effect was observed as growing comet tail (B-line) artifacts and as subpleural consolidated segments at higher FiO2. PCH for TO with 20% and 60% FiO2 were significantly greater (p < 0.05) than for the 10% FiO2. PCHs with TX at 10% and 20% FiO2 were significantly greater (p < 0.02) than those for TO anesthesia. Added xylazine and high percentages of FiO2 reduced PCH thresholds, but xylazine and high percentages of FiO2 together did not lower the PCH threshold further. The lowest threshold observed, 1.4 MPa, corresponded to an in situ mechanical index of 0.5.

Pulmonary Capillary Hemorrhage Induced by Super Sonic Shear Wave Elastography in Rats.

The occurrence of the pulmonary capillary hemorrhage (PCH) bioeffect of diagnostic ultrasound in rats was investigated for a SuperSonic Imagine shear wave elastography system (Aixplorer, Supersonic Imagine, Aix-en-Provence, France). The elastography imaging repeated at 1 Hz and consisted of widely spaced B-mode image pulses, supersonic push (SSP) pulses and shear wave imaging (SWI) pulses. Groups of rats anesthetized with ketamine and xylazine, or with ketamine only, were imaged on their right side in a warm water bath for one frame, 30 s and 300 s. The image focus and region of interest were adjusted to give exposure only with the background B-mode imaging, or primarily with the SSP and SWI pulses. A sham group had only low power aiming scans. The lungs were removed 5 min after exposure and evaluated for PCH area and volume. The B mode was notably ineffective and produced significant PCH only at the maximum 0 dB output. The SSP pulses together with the SWI pulses produced significant PCH for 300 s, 30 s and even single image exposures. Peak rarefactional pressure amplitude PCH thresholds for 300 s exposure were the same with or without the B-mode pulses at 1.5 MPa (in situ mechanical index, MIIS = 0.67). A 30 s duration resulted in a slightly increased threshold of 1.7 MPa (MIIS = 0.76). The omission of xylazine from the anesthetic, which reduces the sensitivity of rat lung to PCH occurrence, resulted in an increased threshold of 2.1 MPa (MIIS = 0.94). The unique SSP pulses were much more effective than the B mode, but thresholds were comparable to previous results with other diagnostic ultrasound modes on other systems.

Ginsenoside Rb1 regulates prefrontal cortical GABAergic transmission in MPTP-treated mice.

Parkinson's disease (PD) is a common neurodegenerative disease, featured by motor deficits and non-motor symptoms such as cognitive impairment, and malfunction of gamma-aminobutyric acid (GABA) mediated inhibitory transmission plays an important role in PD pathogenesis. The ginsenoside Rb1 molecule, a major constituent of the extract from the Ginseng root, has been demonstrated to ameliorate motor deficits and prevent dopaminergic neuron death in PD. However, whether Rb1 can regulate GABAergic transmission in PD-associated deficits and its underlying mechanisms are still unclear. In this study, we explored the effects of Rb1 on the GABAergic synaptic transmission in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. We demonstrated that Rb1 can bind with GABAARα1 and increase its expression in the SH-SY5Y cells and in the prefrontal cortex (PFC) of MPTP model in vitro and in vivo. Furthermore, Rb1 can promote prefrontal cortical GABA level and GABAergic transmission in MPTP-treated mice. We also revealed that Rb1 may suppress presynaptic GABABR1 to enhance GABA release and GABAA receptor-mediated inhibitory transmission. In addition, Rb1 attenuated MPTP-induced dysfunctional gait dynamic and cognitive impairment, and this neuroprotective mechanism possibly involved regulating prefrontal cortical GABAergic transmission. Thus, Rb1 may serve as a potential drug candidate for the treatment of PD.

Capillary Hemorrhage Induced by Contrast-Enhanced Diagnostic Ultrasound in Rat Intestine.

Contrast-enhanced diagnostic ultrasound (CEDUS) can lead to microvascular injury and petechial hemorrhage by the cavitational mechanism of ultrasonic bioeffects. Capillary hemorrhage has been noted in the heart and kidney, which are common targets of CEDUS examination. CEDUS has also become useful for monitoring intestinal inflammation. In the 1990s, the risk of intestinal microvascular hemorrhage was investigated both for incidental exposure by lithotripter shockwaves and for contrast agent microbubbles acting as cavitation nuclei with laboratory pulsed ultrasound systems. This study was initiated to update the risk assessment for intestine exposed to diagnostic imaging simulating CEDUS. The abdomens of anesthetized rats were scanned by a 1.6 MHz phased array probe during infusion of microbubble suspensions simulating Definity ultrasound contrast agent. Dual image frames were triggered intermittently, and the output power was varied to assess the exposure response. Petechiae counts in small intestine mucosa and muscle layers increased with increasing trigger interval from 2 s to 10 s, indicative of a slow refill after microbubble destruction. The counts increased with increasing output above a threshold of 1.4 MPa peak rarefactional pressure amplitude. Petechiae were also seen in Peyer's patches, and occult blood was detected in many affected segments of intestine. These results are consistent with early laboratory pulsed-ultrasound results.

Pulmonary Capillary Hemorrhage Induced by Acoustic Radiation Force Impulse Shear Wave Elastography in Ventilated Rats.

OBJECTIVES: Diagnostic ultrasound (DUS) imaging can induce pulmonary capillary hemorrhage (PCH), possibly related to the ultrasonic radiation surface pressure arising from reflection at the lung blood-air interfaces. Acoustic radiation force impulse (ARFI) elastography is a relatively new DUS mode with high-energy "push pulses" used to move tissue and generate shear waves. The objective of this study was to characterize PCH induced by the ARFI elastographic mode for comparison with other previously tested DUS modes. METHODS: Pulmonary capillary hemorrhage induction was examined for ARFI elastographic frames with 5.7-MHz push pulses (Acuson S3000; Siemens Medical Solutions, Mountain View, CA), which had a derated PRPA of 2.6 MPa. Groups of rats with tracheal tube placement had no ventilation (spontaneous breathing), intermittent positive pressure ventilation (IPPV), or IPPV plus 8 cm H2 O of positive end-expiratory pressure (PEEP). Exposure was to 1 or 20 manually triggered image frame acquisitions. The PCH area was measured on the lung surface. RESULTS: All 20-frame exposure groups, and even the single-frame group, had significant PCH relative to shams. Single-frame exposures produced significantly less PCH (P = .002) than 20-frame exposures in rats with a tracheal tube only (spontaneous breathing). The PEEP inhibited the PCH and produced about half of the PCH area induced for IPPV without PEEP (P = .014). CONCLUSIONS: The PCH results were comparable with those from a previous study using B-mode or color Doppler exposure for 5 minutes; however, these modes delivered many more pulses for continuous imaging frames, suggesting that the ARFI elastographic frames were individually much more effective.

Hepatocyte Injury Induced by Contrast-Enhanced Diagnostic Ultrasound.

OBJECTIVES: Contrast-enhanced diagnostic ultrasound (US) has a potential to induce localized biological effects. The potential for contrast-enhanced diagnostic US bioeffects in liver were researched, with guidance from a report by Yang et al (Ultrasonics 2012; 52:1065-1071). METHODS: Contact and standoff scanning was performed for 10 minutes with a diagnostic US phased array at 1.6 MHz during bolus injection or infusion of a contrast agent at a high dose. The impact of the imaging on rat liver was investigated by measuring enzyme release, microvascular leakage, and staining of injured hepatocytes. RESULTS: The results showed liver enzyme release at 30 minutes, indicating liver injury, and elevated extraction of Evans blue dye, indicating microvascular leakage. In addition, Evans blue and trypan blue vital-staining methods revealed scattered stained cells within the US scan plane. For the Evans blue method, fluorescent cell counts in frozen sections were greatest for standoff exposure with contrast infusion. The count decreased strongly with depth for bolus injection, which was probably reflective of the high attenuation noted for this agent delivery method. CONCLUSIONS: The results qualitatively confirmed the report by Yang et al and additionally showed hepatocyte vital staining. Research is needed to determine the threshold for the effects and the contrast agent dose response.

Influence of Microbubble Size and Pulse Amplitude on Hepatocyte Injury Induced by Contrast-Enhanced Diagnostic Ultrasound.

Recent research has found that contrast-enhanced diagnostic ultrasound (CEDUS) has the potential to induce localized injury in the liver, with clearly observable effects for contrast agent doses higher than the recommended dose and maximal mechanical index values. This study was undertaken to assess effects with intermittent exposure at lower contrast doses of infusion and at reduced output to determine thresholds. In addition, microbubble (MB) suspensions with enhanced content of larger MBs were tested. Exposure from a phased array probe (GE Vivid 7 Dimension, GE Vingmed Ultrasound, Horten, Norway) was applied at 1.6 MHz and 1-s intermittent frame trigger for 10 min with infusion of MB suspension with normal (1.8 µm), medium (3.1 µm) and large (5.3 µm) mean MB diameters. The bio-effect endpoint was the count of hepatocytes stained with Evans blue dye in frozen sections. For the normal MBs, the count increased for clinically relevant infusion dosages, but leveled off above 20 µL/kg/min. The evidence of injury declined with time from 30 min to 4 h and was lacking at 24 h. The exposure thresholds in terms of peak rarefactional pressure amplitude, divided by the square root of frequency (in situ mechanical index) were 1.7, 1.3 and 1.2 for the normal-, medium- and large-sized MB suspensions. The enhanced efficacy for larger MBs lends support to the two-criterion model for cavitational microvascular injury during CEDUS. Overall, CEDUS in liver appears to have markedly less potential for induction of tissue injury than has been reported in other tissues, which indicates a satisfactory safety profile for CEDUS using recommended parameters in normal liver.

Pulmonary Capillary Hemorrhage Induced by Diagnostic Ultrasound in Ventilated Rats.

Pulmonary capillary hemorrhage (PCH) can be induced by diagnostic ultrasound-a potential safety issue. Anesthetized rats were intubated for intermittent positive-pressure ventilation (IPPV) with 0 end-expiratory pressure, +4 cm H2O end-expiratory pressure (PEEP) and -4 cm H2O end-expiratory pressure (NEEP). Rats were imaged at 7.6 MHz with a Philips HDI 5000 ultrasound machine. The output was low (mechanical index [MI] = 0.22) for aiming and then was raised for 5 min in 20 different exposure groups with n = 8. Peak rarefactional pressure amplitudes were measured in water and de-rated for chest attenuation. The PCH areas were measured on the lung surface. At 2.2 MPa, PCH was 9.3 ± 6.6 mm2 for IPPV, 1.6 ± 3.2 mm2 for PEEP (p <0.001) and 26.8 ± 6.4 mm2 for NEEP (p <0.001). Thresholds were 1.3 MPa for IPPV, 2.1 MPa for PEEP and 1.0 MPa for NEEP. The small ventilator pressures subtracted or added to trans-capillary stress generated by diagnostic ultrasound pulses, virtually eliminating PCH for PEEP but enhancing PCH for NEEP.

Biomedical Potential of Ultrafine Ag Nanoparticles Coated on Poly (Gamma-Glutamic Acid) Hydrogel with Special Reference to Wound Healing.

In wound care management, the prevention of wound infection and the retention of an appropriate level of moisture are two major challenges. Therefore, designing an excellent antibacterial hydrogel with a suitable water-adsorbing capacity is very important to improve the development of wound dressings. In this paper, a novel silver nanoparticles/poly (gamma-glutamic acid) (γ-PGA) composite dressing was prepared for biomedical applications. The promoted wound-healing ability of the hydrogels were systematically evaluated with the aim of attaining a novel and effective wound dressing. A diffusion study showed that hydrogels can continuously release antibacterial factors (Ag). Hydrogels contain a high percentage of water, providing an ideal moist environment for tissue regeneration, while also preventing contraction of the wound. Moreover, an in vivo, wound-healing model evaluation of artificial wounds in mice indicated that silver/γ-PGA hydrogels could significantly promote wound healing. Histological examination revealed that hydrogels can successfully help to reconstruct intact epidermis and collagen deposition during 14 days of impaired wound healing. Overall, this research could shed new light on the design of antibacterial silver/γ-PGA hydrogels with potential applications in wound dressing.

Ultrasonic Cavitation-Enabled Treatment for Therapy of Hypertrophic Cardiomyopathy: Proof of Principle.

Ultrasound myocardial cavitation-enabled treatment was applied to the SS-16BN rat model of hypertrophic cardiomyopathy for proof of the principle underlying myocardial reduction therapy. A focused ultrasound transducer was targeted using 10-MHz imaging (10 S, GE Vivid 7) to the left ventricular wall of anesthetized rats in a warmed water bath. Pulse bursts of 4-MPa peak rarefactional pressure amplitude were intermittently triggered 1:8 heartbeats during a 10-min infusion of a microbubble suspension. Methylprednisolone was given to reduce initial inflammation, and Losartan was given to reduce fibrosis in the healing tissue. At 28 d post therapy, myocardial cavitation-enabled treatment significantly reduced the targeted wall thickness by 16.2% (p <0.01) relative to shams, with myocardial strain rate and endocardial displacement reduced by 34% and 29%, respectively, which are sufficient for therapeutic treatment. Premature electrocardiogram complexes and plasma troponin measurements were found to identify optimal and suboptimal treatment cohorts and would aid in achieving the desired impact. With clinical translation, myocardial cavitation-enabled treatment should fill the need for a new non-invasive hypertrophic cardiomyopathy therapy option.

Pulmonary Capillary Hemorrhage Induced by Different Imaging Modes of Diagnostic Ultrasound.

The induction of pulmonary capillary hemorrhage (PCH) is a well-established non-thermal biological effect of pulsed ultrasound in animal models. Typically, research has been done using laboratory pulsed ultrasound systems with a fixed beam and, recently, by B-mode diagnostic ultrasound. In this study, a GE Vivid 7 Dimension ultrasound machine with 10 L linear array probe was used at 6.6 MHz to explore the relative PCH efficacy of B-mode imaging, M-mode (fixed beam), color angio mode Doppler imaging and pulsed Doppler mode (fixed beam). Anesthetized rats were scanned in a warmed water bath, and thresholds were determined by scanning at different power steps, 2 dB apart, in different groups of six rats. Exposures were performed for 5 min, except for a 15-s M-mode group. Peak rarefactional pressure amplitude thresholds were 1.5 MPa for B-mode and 1.1 MPa for angio Doppler mode. For the non-scanned modes, thresholds were 1.1 MPa for M-mode and 0.6 MPa for pulsed Doppler mode with its relatively high duty cycle (7.7 × 10-3 vs. 0.27 × 10-3 for M-mode). Reducing the duration of M-mode to 15 s (from 300 s) did not significantly reduce PCH (area, volume or depth) for some power settings, but the threshold was increased to 1.4 MPa. Pulmonary sonographers should be aware of this unique adverse bio-effect of diagnostic ultrasound and should consider reduced on-screen mechanical index settings for potentially vulnerable patients.

Does Intravenous Infusion Influence Diagnostic Ultrasound-Induced Pulmonary Capillary Hemorrhage?

OBJECTIVES: Pulmonary diagnostic ultrasound (US) can induce pulmonary capillary hemorrhage (PCH) in mammals. This singular biological effect of diagnostic US imaging was discovered more than 25 years ago but remains poorly understood. Our objective here was to investigate rapid infusion of intravenous fluids as a possible stressor for capillaries, which might enhance pulmonary diagnostic US-induced PCH. METHODS: Rats were anesthetized with Telazol (Zoetis, Inc, Kalamazoo, MI), which yielded relatively low pulmonary diagnostic US-induced PCH, or Telazol and xylazine, which yielded relatively high pulmonary diagnostic US-induced PCH. Groups of rats were not infused or infused either with normal saline, 10% mannitol, or 5% albumin. Rats were scanned in a warmed water bath with B-mode US for 5 minutes with a 7.6-MHz linear array set to different mechanical index values to obtain exposure response information. Pulmonary capillary hemorrhage was observed as comet tail artifacts in the image and measured on the lung surface. RESULTS: For Telazol anesthesia, all of the PCH results were very low, with no significant differences at the maximum output with an in situ peak rarefactional pressure amplitude of 2.1 MPa (on-screen mechanical index, 0.9). The addition of xylazine to the Telazol anesthetic significantly enhanced the PCH (P < .001) without infusion and likewise for the mannitol and albumin infusion. Saline infusion eliminated this enhancement, with significantly reduced PCH for Telazol-plus-xylazine anesthesia (P < .001); however, both mannitol and albumin infusion resulted in significantly more PCH than saline infusion (P < .01). CONCLUSIONS: These results show PCH dependence on the specific intravenous infusion fluid and illustrate the complex importance of physiologic parameters for US-induced PCH.

The Dependence of Glomerular Capillary Hemorrhage Induced by Contrast Enhanced Diagnostic Ultrasound on Microbubble Diameter.

A recently proposed two-criterion model for cavitational bioeffects in tissue with microbubbles (MBs) was tested. The glomerular capillary hemorrhage bioeffect was observed in rat kidney for contrast agent MB suspensions with mean diameters of 1.6, 3.1 and 5.5 µm. A diagnostic ultrasound machine was used at 3.6 MHz and 5.5 MHz for intermittent scans at power settings 2 dB apart. Petechial hemorrhage counts scored on the surface of the kidneys, and glomeruli were scored in histology. Thresholds for the petechial hemorrhage measurements were the same for the large and medium MB suspensions but substantially higher for the small MBs. For the histology, the medium MBs gave a higher threshold than the large MBs at 5.5 MHz. The pressure amplitude thresholds are in approximate agreement with theory, and the optimum MB size counterintuitively increased for increasing ultrasound frequency, as predicted. The two-criterion model of MB-associated capillary hemorrhage is supported.