Pulmonary Capillary Hemorrhage Research Articles

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

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. 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. 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. 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.

The vulnerable air-tissue interface: Summary of ultrasound related bioeffects on lung and their implications for the use of different imaging modes and applications beyond

Introduction: Lung tissue is sensitive to mechanical stress. Animal studies showed induction of pulmonary capillary hemorrhage (PCH) in lung in the diagnostic regime at intensities. Therefore, this work summarizes novel findings regarding the interaction of ultrasound at the alveolar epithelium-gas interface. Method: Literature research related to ultrasound bio-effects on lung was carried out. Furthermore, recent studies reporting thresholds of PCH induction depending on imaging mode and duration will be discussed. Results: Ventilated lung tissue is more vulnerable to mechanical forces than solid tissue. From peak negative pressure below 1.5 MPa the likelihood of PCH induction increases with exposure time. Such PCH is asymptomatic but can falsify the diagnostic outcome. The causes remain still unknown but is not related to cavitation or thermal effects. The extent of PCH in lung is depending of physiological beside acoustic parameters. The extend of PCH is, therefore, not entirely predictable. In addition, observational studies on humans could not confirm the findings as investigated on pathological level on animal models. Conclusion: The vulnerability of lung should become aware in the lung ultrasound community. Current recommendations for output limitations given by AIUM and EFSUMB should be followed and only increased for diagnostics needs.

Frame Rate Exposimetry for Pulmonary Capillary Hemorrhage During Lung Ultrasound.

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). A Philips iE33 machine with L15-7io probe was used to scan anesthetized rats in a warmed water bath. B mode was applied at 9MHz with settings of 34, 61 and 118 fps. After 2minutes 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. 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. 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.

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.

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

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. 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. 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). 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.

Experimental Measurements of Ultrasound Attenuation in Human Chest Wall and Assessment of the Mechanical Index for Lung Ultrasound

Knowledge of the acoustic attenuation characteristics of the chest wall is necessary to estimate the acoustic exposure at the pleural surface during lung ultrasound and is useful in the prediction of bio-effects (e.g., pulmonary capillary hemorrhage) and the development of safe, effective lung imaging. Currently, this property is not well characterized in humans. The aim of this work was to characterize ultrasonic attenuation in human chest wall such that the ultrasound exposures of the lung can be estimated for clinically relevant conditions. In this study, we experimentally measured ultrasound transmitted through the intercostal tissue of 15 human cadaver chest wall samples relative to ultrasound transmitted through saline to determine attenuation coefficients for each sample. A GE Vivid 7 diagnostic ultrasound machine (GE Vingmed, Horten, Norway) and 3 S and 5 S phased array probes were used at center frequencies from 1.6 to 5 MHz. The chest wall samples varied in thickness from 2.3–5.5 cm with a median thickness of 3.8 cm. The frequency-normalized attenuation coefficient was approximately 1.44 dB/cm/MHz based on a linear best fit through all attenuation measurements. Attenuation characteristics varied appreciably between samples, and the sample-averaged linear attenuation coefficient was 1.43 ± 0.32 (mean ± standard deviation) dB/cm/MHz. This attenuation is higher than that previously measured in mammalian chest wall samples (1.1–1.3 dB/cm/MHz for mice and rats) and is much greater than that used by the mechanical index (0.3 dB/cm/MHz). Mechanical index values calculated using saline values de-rated by 0.3 dB/cm/MHz were up to 1.2 MPa/MHz1/2 greater than those calculated using the measured through-tissue ultrasound waves. We conclude that the mechanical index overestimates exposures for lung ultrasound and thus may not be an appropriate dosimetry metric for pulmonary ultrasound.

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.

Acoustic Fountains and Atomization at Liquid Surfaces Excited by Diagnostic Ultrasound

Pulmonary capillary hemorrhage (PCH) has been found in mammalian lungs exposed to diagnostic ultrasound (DUS), although the mechanism is poorly understood. This work investigates acoustic atomization and fountains at liquid-air interfaces subjected to DUS, which has been suggested as a possible PCH damage mechanism. Primarily using a SuperSonic Imagine Aixplorer DUS machine (SuperSonic Imagine, Aix-en-Provence, France), blood and water surfaces were excited in vitro by DUS and recorded with a high-speed camera. The surface was driven by B-mode, color Doppler, pulsed Doppler, and shear wave elastography imaging modes with center frequencies from 5.0–7.2 MHz and mechanical indexes (MI) up to 1.7. Fountains and atomization were only observed for SWE, for MI as low as 1.0. A comparison of the SWE waveforms with the surface dynamics suggests that fountains and atomization were driven by push-pulses and depended on pulse duration and intensity. However, we conclude that atomization and fountaining are unlikely primary mechanisms behind all DUS-induced PCH because neither phenomenon occurred for traditional diagnostic imaging modes.

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

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. 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. 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). 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.

A review of pulmonary injury by diagnostic ultrasound

Diagnostic ultrasound (DUS) induction of pulmonary capillary hemorrhage (PCH) presents a unique clinical safety issue. Pulmonary DUS has become routine in clinical and point-of-care settings worldwide for diagnosis of edema, effusion, pneumonia, etc. Our experiments in rats have shown that DUS-induced PCH increased rapidly above exposure thresholds, which depended on specific conditions. Using a linear array at 6.6 MHz, peak rarefactional pressure amplitude thresholds were 1.5 MPa for B mode, 1.1 MPa for Angio Doppler, 1.1 MPa for M mode, and 0.6 MPa for pulsed Doppler. Thresholds were nearly constant from 1.5 MHz to 12 MHz, suggesting involvement of a frequency-independent mechanism, such as radiation pressure. Physiological conditions were found to be as important as physical exposure parameters. Infusion of saline reduced the effect. Xylazine in the normal ketamine/xylazine anesthesia enhanced PCH relative to ketamine only, and the clinical sedative dexmedetomidine also lowered thresholds. Rats with positive-pressure ventilation had DUS-induced PCH inhibited by only + 4 cm H2O, or enhanced by only -4 cm H2O end expiratory pressure acting on the blood-air barrier. With subsequent studies and better understanding of this phenomenon, DUS-induced PCH will be avoidable by use of sub-threshold output by sonographers using DUS machines with output control. Diagnostic ultrasound (DUS) induction of pulmonary capillary hemorrhage (PCH) presents a unique clinical safety issue. Pulmonary DUS has become routine in clinical and point-of-care settings worldwide for diagnosis of edema, effusion, pneumonia, etc. Our experiments in rats have shown that DUS-induced PCH increased rapidly above exposure thresholds, which depended on specific conditions. Using a linear array at 6.6 MHz, peak rarefactional pressure amplitude thresholds were 1.5 MPa for B mode, 1.1 MPa for Angio Doppler, 1.1 MPa for M mode, and 0.6 MPa for pulsed Doppler. Thresholds were nearly constant from 1.5 MHz to 12 MHz, suggesting involvement of a frequency-independent mechanism, such as radiation pressure. Physiological conditions were found to be as important as physical exposure parameters. Infusion of saline reduced the effect. Xylazine in the normal ketamine/xylazine anesthesia enhanced PCH relative to ketamine only, and the clinical sedative dexmedetomidine also lowered thresholds. Rats with po...

Observation of acoustic fountain generation by diagnostic ultrasound shear wave elastography

High-intensity focused ultrasound has been shown to drive fountains and atomization at liquid-gas and tissue-gas interfaces. Though these phenomena are not well studied for diagnostic ultrasound, they have been hypothesized to play a role in diagnostic ultrasound-induced pulmonary capillary hemorrhage (PCH). We demonstrate that push pulses used in diagnostic shear wave elastography (SWE) also cause fountaining and atomization at water-air and blood-air interfaces. A focused ultrasound transducer (SSI SL15-4), was aimed upward, through water, at an air interface. An SWE pulse sequence, including four push pulses (amplitude ≤ 8.6 MPa, pulse duration ≅ 650 ms, and center frequency ≅ 5.0 MHz), was initiated. The interface was photographed at 20k fps and four successive fountains were observed. Fountains heights up to 12 and 11 mm were observed for water and blood respectively and ejected water droplets traveled up to 30 cm above the surface. The spacing of the four fountains was measured to be the same as the spacing of four PCH areas observed on rat lungs exposed to the same pulse sequence. Concurrent studies should reveal the relative efficacy of PCH induction from SWE and normal pulse echo and Doppler imaging.

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.

The Safety of Pulmonary Ultrasonography in the Neonatal Intensive Care Unit

IntroductionDue to specific anatomy of children are more vulnerable to the carcinogenic effects of ionizing radiation from chest X-rays. Lung ultrasound (LUS) is a validated procedure which can easily be used in diagnosing pathologies of the neonatal lung. However, experimental studies have shown that low frequency ultrasound may induce pulmonary capillary hemorrhage (PCH).Aim of the studyTo evaluate the potential relationship between lung ultrasound and pulmonary hemorrhage in very low birth weight infants.Patients and methodsWe analysed the medical records of very low birth weight infants admitted to our neonatal tertiary centre between 2008 and 2011 (group 1), when CXR was the main procedure used to evaluate the respiratory system, and between 2013 and 2016 (group 2), when LUS became a routine procedure, replacing the chest X-ray.Results297 infants were enrolled in the first group and 286 in the second group, respectively. There was no difference in the frequency of pulmonary hemorrhages between the two groups (p=1). In the first group there was only one episode of PCH and in the second group no PCH was seen. Statistically significant differences were seen in a number of patients with pulmonary hemorrhage risk factors: surfactant administration (p<0.001), mechanical ventilation (p=0.0003), and hemodynamically significant patent ductus arteriosus (p=0.025).ConclusionsRoutine lung ultrasound appears to be safe in very low birth weight infants; there were no episodes of pulmonary hemorrhage.

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

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. 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. 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). These results show PCH dependence on the specific intravenous infusion fluid and illustrate the complex importance of physiologic parameters for US-induced PCH.

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.

The Influence of Ventilation on Pulmonary Capillary Hemorrhage Induced by Diagnostic Ultrasound

The Influence of Ventilation on Pulmonary Capillary Hemorrhage Induced by Diagnostic Ultrasound

Semiparametric profile likelihood estimation for continuous outcomes with excess zeros in a random-threshold damage-resistance model.

Continuous outcome data with a proportion of observations equal to zero (often referred to as semicontinuous data) arise frequently in biomedical studies. Typical approaches involve two-part models, with one part a logistic model for the probability of observing a zero and some parametric continuous distribution for modeling the positive part of the data. We propose a semiparametric model based on a biological system with competing damage manifestation and resistance processes. This allows us to derive a closed-form profile likelihood based on the retro-hazard function, leading to a flexible procedure for modeling continuous data with a point mass at zero. A simulation study is presented to examine the properties of the method in finite samples. We apply the method to a data set consisting of pulmonary capillary hemorrhage area in lab rats subjected to diagnostic ultrasound. Copyright © 2017 John Wiley & Sons, Ltd.

The interaction of pulsed ultrasound with mammalian lung

The impedance difference for a water-air interface yields virtually complete reflection for ultrasound, which coincidentally delivers an acoustical radiation surface pressure (ARSP). ARSP may be a physical mechanism for pulmonary capillary hemorrhage induced by diagnostic ultrasound. Fundamental tissue parameters in biomedical acoustics are the density ρ, speed of sound c, and the resulting acoustical impedance z=ρc. Many tissues are similar to water (z = 1,628 krayl), but not lung. The gas content of lung imparts an extreme heterogeneity with air having z = 0.424 krayl. If the lung surface is modeled simply as a water-air interface, then the ARSP is maximal. During a diagnostic ultrasound pulse, ARSP can be comparable to the pulmonary capillary blood pressure, thus adding stress to capillaries. However, the bulk properties of the lung are different from air. One of the few reports on acoustical properties of lung was by Floyd Dunn (JASA 1986;80:1248). Consideration of these bulk properties of lung tissue yields a much higher z ≈ 336 krayl at 2.8 MHz, and indicates substantial transmission of ultrasound through the pleura (O’Brien et al. JASA 2000;108:1290). This model suggests a reduced ARSP, and the potential involvement of additional mechanisms for capillary injury within the pulmonary interior.