Startseite Artificial blood circulatory and special Ultrasound Doppler probes for detecting and sizing gaseous embolism
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Artificial blood circulatory and special Ultrasound Doppler probes for detecting and sizing gaseous embolism

  • Philipp Stark EMAIL logo , Christoph Kalkbrenner , Patrick Braß und Rainer Brucher
Veröffentlicht/Copyright: 30. September 2016
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Current Directions in Biomedical Engineering
Aus der Zeitschrift Current Directions in Biomedical Engineering Band 2 Heft 1

Abstract

This paper presents a special designed artificial blood circulatory (ABC) for studying gaseous embolism based on detection of gaseous emboli and their sizing using ultrasound (US) spectral Doppler. Blood mimicking fluid (BMF) was used in the circulatory to get valid results without using human blood. The additional necessary degassing circulatory shows a promising effect of decontaminating the BMF from air bubbles. This offers the base for detecting and sizing microemboli using special algorithms and finally leads to reliable calculations of dangerous embolism and its air volume. Standard US probes at an integrated tissue model and a new 8-MHz central catheter ultrasound (CCUS) probe inside a superior vena cava model (SVCM) are used and deliver the Doppler spectrogram as input for automatic emboli detection and further signal analysis. First results using the newly developed 8-MHz CCUS probe inside the SVCM and its Doppler spectrogram characteristics show promising results but need more detailed studies.

Keywords: air bubble contamination; air embolism; artificial blood circulatory; central venous catheter; doppler ultrasound; embolus detection; microemboli

1 Introduction

In up to 80% of all brain surgeries in sitting position gaseous emboli occur [1]. The air which is sucked into the venous blood stream by hydrostatic effects can reach the arterial bloodstream via the patent foramen ovale (PFO) which occurs in up to 35% of people [2]. Such collected air volumes up to 2–3 ml in the cerebral blood circulatory can be a lethal amount as well as 0.5–1.0 ml of air in the vena pulmonalis can lead to myocardial infarction [3]. The ability to detect, to characterize and to size intraoperative occurring emboli and at last their aspiration via catheter may have a great potential for patients safety. Two methods of automatic detection and discrimination between solid and gaseous microemboli based on transcranial Doppler ultrasound (TCD) have shown success, the dual-frequency technique [4], [5] and the frequency modulation method [6], [7]. These methods however use Doppler probes outside the body and are only able to detect emboli and cannot offer any treatments by removing gaseous emboli by aspiration.

The aim of this study was to assess by in vitro studies the specially designed ABC as well as the first ultrasound Doppler central venous catheter system that was specially developed for the automatic detection of intraoperative emboli inside the superior vena cava.

2 Material and methods

2.1 Development of the artificial blood circulatory

The developed artificial blood circulatory (ABC) is designed to represent the human blood circulatory including a SVCM for the in vitro experiments. The ABC consists of two parts, the large main blood circulatory and an additional small degassing circulatory (see Figure 1). The whole ABC holds up to 1.2 liter of blood mimicking fluid (BMF). The ABC is driven by the membrane pump (SUK-0220, SHURflo). To generate different flow profiles with a flow up to 2.4 l/min a control unit by hard- and software was build up using Labview.

Figure 1 Artificial blood circulatory: Main circulatory with tissue phantom and the Vena Cava model (red arrows), additional degassing circulatory with implemented gear pump for low pressure degassing (green arrows).
Figure 1

Artificial blood circulatory: Main circulatory with tissue phantom and the Vena Cava model (red arrows), additional degassing circulatory with implemented gear pump for low pressure degassing (green arrows).

The BMF recipe was taken from EN 61685:2001 D.3.3 (see Table 1). This BMF shows the same properties as blood with a hematocrit value of 42% to 48% (see Table 2).

Table 1

Components of BMF in weight % of pure components

Water83.86%
Glycerol10.06%
Dextran (molecular weight 150 kDa)3.36%
Orgasol-particel 5 μm1.82%
Synperonic N.0.09%
Table 2

BMF properties

c1548 m/s
ρ1037 kg/m3
Z1.61 ⋅ 1066 kg/(m2 s)
ν4,0 mPa s

The SVCM consists of an inlet, outlet and was designed for a laminar flow with a Reynolds number of Re = 122.37 <<Rekrit = 2320 as stated in [8] to avoid warping of the velocity profile. The SVCM was manufactured out of polycarbonate which has a similar acoustic impedance as blood vessel walls.

It is of the utmost importance for the results of the experiments and the development of algorithms that the BMF is not contaminated with microbubbles. Analyzing the echogenity of air embolism on its enhancement in Doppler spectrogram would result in false estimations if the BMF is contaminated by microbubbles. To decontaminate the fluid the degassing circulatory was added to the ABC. It consists of a choke and a special gear pump (Fresenius Medical Care) (see Figure 2). The degassing process is done by generating a low pressure. Low pressure conglomerates the dissolved gas and forms larger bubbles which rise up to the surface of the fluid in the venous reservoir and disappear out of the main circulatory.

Figure 2 Central catheter ultrasound probe (CCUS): Intravascular positioning recording passing air embolus by radial insonation. Therapeutical air aspiration located on the top end of the catheter.
Figure 2

Central catheter ultrasound probe (CCUS): Intravascular positioning recording passing air embolus by radial insonation. Therapeutical air aspiration located on the top end of the catheter.

The injection of the gaseous emboli is done manually using calibrated high precision microliter syringes (Carl Roth) with a grading down to 0.1 μl.

The BMF is monitored via three US probes. The 2-MHz TCD-probe and 8-MHz hand-held probe, are used as control recordings and as a reference for the distal integrated 8-MHz CCUS probe (MTB Medizintechnik Basler AG), which has to be optimized in future experiments. The two references probes are located right after the injection spot on top of the US tissue model (MiniSim Trainer, Life-Tech, Inc.) insonating via a 45° angle. The 8-MHz catheter probe is positioned via a medical port into the SVCM and has a radial insonation. The audio signals from the US reference probes are processed by our own system (FHU LabDop) and its corresponding software for spectral Doppler. The signals of the 8-MHz catheter probe is processed by the DWL Doppler-BoxX and its corresponding QL software offering a spectral and a Power-M-Mode Doppler.

To monitor the ABC in respect to the volume rate a flowmeter (B.I.O-TECH e.K.) as well as specially designed pressure and temperature sensors are integrated into the circulatory to register the physical effects on the injected gaseous embolism. For data acquisition a module (NI USB-6008, National Instruments) and Labview software was integrated. Both pumps are controlled via this module. The main pump resembles the heart and offers a continuous or a pulsatile flow profile. The pulsatile flow can be varied on three parameters: heartrate, overall flow ejection and the duration of the systole.

3 Results

3.1 2/8-MHz reference ultrasound probes

Figure 3 shows the pulsatile flow profile. Multiple air bubble events are detected by the 2-MHz Spectral Doppler instrumentation analyzing the enhancement of the short-term events in the Doppler spectrogram caused by resonance effects. In opposite the signals recorded by the 8-MHz Doppler show no events. Here the effect of low pass filtering of the insonated 8-MHz US suppress the expected enhancement.

Figure 3 2-MHz (left) and 8-MHz (right) Doppler spectrogram showing pulsatile flow profile enhancements caused by air bubble injection.
Figure 3

2-MHz (left) and 8-MHz (right) Doppler spectrogram showing pulsatile flow profile enhancements caused by air bubble injection.

3.2 8-MHz ultrasound catheter probe

Figure 4 shows air bubble events, detected by the intravascular positioned 8-MHz CCUS probe recording the enhancements of the bubbles due to higher embolus/blood ratios within the SVCM compared to 8-MHz reference recording in tissue model. The 8-MHz CCUS Doppler records a characteristic spectrogram during passing embolus. Here the bottom part of the spectrogram shows towards flow to the US probe. The mid part close to the zero line shows no Doppler effect. The top part of the spectrogram shows the flow away from the probe. Therefore the event of passing by of the air bubbles shows time sequentially the according Doppler shift frequencies.

Figure 4 8-MHz CCUS probe spectral Doppler recording of passing bubbles during pulsatile flow profile.
Figure 4

8-MHz CCUS probe spectral Doppler recording of passing bubbles during pulsatile flow profile.

3.3 Degassing

Figure 5A shows a 2-MHz spectrogram of the BMF before degassing. In the Doppler spectrogram events of microbubbles are present in parallel to the normal background flow profile. These gas bubbles originate either from former experiments or the natural dissolved gas in the liquid. The simultaneous positive and negative Doppler effects during microbubbles events are due to overload and reduced channel separation.

Figure 5 2-MHz-spectrogram showing flow profile (A) before degassing. Circulatory is contaminated due to microbubbles from former experiments or due to natural dissolved gas, (B) during degassing with a typical strong enhancement due to the large number of microbubbles like contrast agents, (C) after degassing shows single sporadic microbubble event (red arrow).
Figure 5

2-MHz-spectrogram showing flow profile (A) before degassing. Circulatory is contaminated due to microbubbles from former experiments or due to natural dissolved gas, (B) during degassing with a typical strong enhancement due to the large number of microbubbles like contrast agents, (C) after degassing shows single sporadic microbubble event (red arrow).

Figure 5B shows a 2-MHz-spectrogram during degassing signal of the BMF. Compared to the pre-degassing-condition an overall enhanced signal can be observed. Here the whole system is flooded with microbubbles like during injection of contrast agent.

Figure 5C shows the 2-MHz-spectrogram after one hour of degassing and a couple of minutes of settling time to get rid of the last bubbles. Afterwards the Dopper spectrogram shows only neglect able events gas bubbles in the ABC.

4 Discussion and conclusion

Air bubble event detected by the 8-MHz CCUS probe (see Figure 4) shows time sequentially an enhancement at Doppler shifted frequencies according the variation of the Doppler effect due to insonation angle. This time delay of enhancement in forward and backward Doppler shift frequencies is a characteristic for all detected air bubble events recorded by the CCUS probe. In opposite an artefact shows simultaneous enhancement in the upper and lower part of the spectrogram (see Figure 6). Therefore an air bubble can be distinguished from an artefact based on these different characteristics.

Figure 6 8-MHz CCUS probe spectrogram with enhancements due to air bubble events (red arrows) and an artefact (yellow arrows).
Figure 6

8-MHz CCUS probe spectrogram with enhancements due to air bubble events (red arrows) and an artefact (yellow arrows).

During the degassing process the whole ABC system is flooded with microbubbles (see Figure 5b). This is due to the procedure in the degassing circulatory connected in parallel to the main circulatory. To decontaminate the BMF a pressure difference is generated via the gear pump and a choke on the inlet of the degassing circulatory. Since the degassing circulatory and the ABC work simultaneously the generated bubbles spread into the main circulatory. The signal is almost free of embolic events after one hour of degassing followed by a settling time of a few minutes (see Figure 5C). During the settling phase all the generated bubbles are trapped in fluidic filters (100 μm) and the venous reservoir. Based on this tremendous reduction of microembolic events the analysis of enhancements leads to reliably results for detection and size estimation of the overall volume of the detected microbubbles.

Based on these first results the ABC is a very promising design for in vitro studies using the newly designed 8-MHz CCUS probe and its optimization. The ABC is able to degas contaminated fluids in an easy way in an acceptable short amount of time. It also allows to operate in continuous and pulsatile flow profiles. The variation of pulsatile flow profile offers the setting to all natural blood flow characteristics and to study the requirements for reliable air bubble detection and their volume calculation. The newly designed 8-MHz CCUS probe shows promising results and characteristics for automatic detection of embolic events. Therefore further future experiments using this SVCM might lead to the improvement of the central venous catheter ultrasound probe including finally automatic triggered aspiration of air embolism in respect to its application of therapy.

Acknowledgement

The authors would like to thank Compumedics Germany GmbH for their hardware, assistance and support.

Author’s Statement

Research funding: This study is part of the project entitled “EmboKath” in cooperation with Compumedics Germany GmbH supported by the Arbeitsgemeinschaft industrieller Forschungsvereinigungen AiF (KF2186206KJ4). Conflict of interest: Authors state no conflict of interest. Material and methods: Informed consent: Informed consent has been obtained from all individuals included in this study. Ethical approval: The research related to human use complies with all the relevant national regulations, institutional policies and was performed in accordance with the tenets of the Helsinki Declaration, and has been approved by the authors’ institutional review board or equivalent committee.

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Published Online: 2016-9-30
Published in Print: 2016-9-1

©2016 Philipp Stark et al., licensee De Gruyter.

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

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https://doi.org/10.1515/cdbme-2016-0062
Schlagwörter für diesen Artikel
air bubble contamination; air embolism; artificial blood circulatory; central venous catheter; doppler ultrasound; embolus detection; microemboli
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BY-NC-ND 4.0

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  70. Climate retainment in carbon dioxide incubators
  71. Multiple factors influencing OR ventilation system effectiveness
  72. Evaluation of an app-based stress protocol
  73. Medication process in Styrian hospitals
  74. Control tower to surgical theater
  75. Development of a skull phantom for the assessment of implant X-ray visibility
  76. Surgical navigation with QR codes
  77. Investigation of the pressure gradient of embolic protection devices
  78. Computer assistance in femoral derotation osteotomy: a bottom-up approach
  79. Automatic depth scanning system for 3D infrared thermography
  80. A service for monitoring the quality of intraoperative cone beam CT images
  81. Resectoscope with an easy to use twist mechanism for improved handling
  82. In vitro simulation of distribution processes following intramuscular injection
  83. Adjusting inkjet printhead parameters to deposit drugs into micro-sized reservoirs
  84. A flexible standalone system with integrated sensor feedback for multi-pad electrode FES of the hand
  85. Smart control for functional electrical stimulation with optimal pulse intensity
  86. Tactile display on the remaining hand for unilateral hand amputees
  87. Effects of sustained electrical stimulation on spasticity assessed by the pendulum test
  88. An improved tracking framework for ultrasound probe localization in image-guided radiosurgery
  89. Improvement of a subviral particle tracker by the use of a LAP-Kalman-algorithm
  90. Learning discriminative classification models for grading anal intraepithelial neoplasia
  91. Regularization of EIT reconstruction based on multi-scales wavelet transforms
  92. Assessing MRI susceptibility artefact through an indicator of image distortion
  93. EyeGuidance – a computer controlled system to guide eye movements
  94. A framework for feedback-based segmentation of 3D image stacks
  95. Doppler optical coherence tomography as a promising tool for detecting fluid in the human middle ear
  96. 3D Local in vivo Environment (LivE) imaging for single cell protein analysis of bone tissue
  97. Inside-Out access strategy using new trans-vascular catheter approach
  98. US/MRI fusion with new optical tracking and marker approach for interventional procedures inside the MRI suite
  99. Impact of different registration methods in MEG source analysis
  100. 3D segmentation of thyroid ultrasound images using active contours
  101. Designing a compact MRI motion phantom
  102. Cerebral cortex classification by conditional random fields applied to intraoperative thermal imaging
  103. Classification of indirect immunofluorescence images using thresholded local binary count features
  104. Analysis of muscle fatigue conditions using time-frequency images and GLCM features
  105. Numerical evaluation of image parameters of ETR-1
  106. Fabrication of a compliant phantom of the human aortic arch for use in Particle Image Velocimetry (PIV) experimentation
  107. Effect of the number of electrodes on the reconstructed lung shape in electrical impedance tomography
  108. Hardware dependencies of GPU-accelerated beamformer performances for microwave breast cancer detection
  109. Computer assisted assessment of progressing osteoradionecrosis of the jaw for clinical diagnosis and treatment
  110. Evaluation of reconstruction parameters of electrical impedance tomography on aorta detection during saline bolus injection
  111. Evaluation of open-source software for the lung segmentation
  112. Automatic determination of lung features of CF patients in CT scans
  113. Image analysis of self-organized multicellular patterns
  114. Effect of key parameters on synthesis of superparamagnetic nanoparticles (SPIONs)
  115. Radiopacity assessment of neurovascular implants
  116. Development of a desiccant based dielectric for monitoring humidity conditions in miniaturized hermetic implantable packages
  117. Development of an artifact-free aneurysm clip
  118. Enhancing the regeneration of bone defects by alkalizing the peri-implant zone – an in vitro approach
  119. Rapid prototyping of replica knee implants for in vitro testing
  120. Protecting ultra- and hyperhydrophilic implant surfaces in dry state from loss of wettability
  121. Advanced wettability analysis of implant surfaces
  122. Patient-specific hip prostheses designed by surgeons
  123. Plasma treatment on novel carbon fiber reinforced PEEK cages to enhance bioactivity
  124. Wear of a total intervertebral disc prosthesis
  125. Digital health and digital biomarkers – enabling value chains on health data
  126. Usability in the lifecycle of medical software development
  127. Influence of different test gases in a non-destructive 100% quality control system for medical devices
  128. Device development guided by user satisfaction survey on auricular vagus nerve stimulation
  129. Empirical assessment of the time course of innovation in biomedical engineering: first results of a comparative approach
  130. Effect of left atrial hypertrophy on P-wave morphology in a computational model
  131. Simulation of intracardiac electrograms around acute ablation lesions
  132. Parametrization of activation based cardiac electrophysiology models using bidomain model simulations
  133. Assessment of nasal resistance using computational fluid dynamics
  134. Resistance in a non-linear autoregressive model of pulmonary mechanics
  135. Inspiratory and expiratory elastance in a non-linear autoregressive model of pulmonary mechanics
  136. Determination of regional lung function in cystic fibrosis using electrical impedance tomography
  137. Development of parietal bone surrogates for parietal graft lift training
  138. Numerical simulation of mechanically stimulated bone remodelling
  139. Conversion of engineering stresses to Cauchy stresses in tensile and compression tests of thermoplastic polymers
  140. Numerical examinations of simplified spondylodesis models concerning energy absorption in magnetic resonance imaging
  141. Principle study on the signal connection at transabdominal fetal pulse oximetry
  142. Influence of Siluron® insertion on model drug distribution in the simulated vitreous body
  143. Evaluating different approaches to identify a three parameter gas exchange model
  144. Effects of fibrosis on the extracellular potential based on 3D reconstructions from histological sections of heart tissue
  145. From imaging to hemodynamics – how reconstruction kernels influence the blood flow predictions in intracranial aneurysms
  146. Flow optimised design of a novel point-of-care diagnostic device for the detection of disease specific biomarkers
  147. Improved FPGA controlled artificial vascular system for plethysmographic measurements
  148. Minimally spaced electrode positions for multi-functional chest sensors: ECG and respiratory signal estimation
  149. Automated detection of alveolar arches for nasoalveolar molding in cleft lip and palate treatment
  150. Control scheme selection in human-machine- interfaces by analysis of activity signals
  151. Event-based sampling for reducing communication load in realtime human motion analysis by wireless inertial sensor networks
  152. Automatic pairing of inertial sensors to lower limb segments – a plug-and-play approach
  153. Contactless respiratory monitoring system for magnetic resonance imaging applications using a laser range sensor
  154. Interactive monitoring system for visual respiratory biofeedback
  155. Development of a low-cost senor based aid for visually impaired people
  156. Patient assistive system for the shoulder joint
  157. A passive beating heart setup for interventional cardiology training
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Heruntergeladen am 26.9.2025 von https://www.degruyterbrill.com/document/doi/10.1515/cdbme-2016-0062/html
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