What's New At Transonic
Surgical Protocol Booklets Posted on transonic.com
Whether you are a cardiothoracic surgeon, vascular surgeon, cerebrovascular or transplant surgeon, you can now have ready access of all of Transonic’s Surgical Flow Protocols. The protocols for each discipline have been compiled into booklet form and are posted at transonic.com/resources under the appropriate discipline.
New Hemodialysis Video:
Save and Access, Save a Life!
Throwback HD Video:
Travel back in time with us to the humble beginnings of a great science and technology to see Dr. Nikolai Krivitski, PhD, DSc, from Transonic, Ithaca, NY, explain his then brand new and cutting edge technology which soon went on to revolutionize vascular access surveillance.
Study Using 0.7mm Microvascular Flowprobe Reports Prediction of Thrombosis Formation in 1 mm Diameter Anastomoses
In a landmark study published in the Journal of Plastic Reconstructive Surgery, researchers from New York City’s Columbia University and Jesús Usón Minimally Invasive Surgery Center, Cáceres, Spain report their findings after using Transonic’s new 0.7mm Microvascular Flowprobe to study the patency of femoral vessels following anastomosis in rats.
Such a tool that can accurately predict the patency of an anastomosis intraoperatively will enable a surgeon to detect and correct flow restrictions while a patient is still in the operating room. Therefore, the researchers used a rat model to establish a minimal cutoff flow value for postoperative blood flow that would reliably predict sustained vessel patency at 24 hours postoperatively.
For the study, surgical end-to-end anastomoses were performed on fifty-six Sprague-Dawley rat femoral arteries. Diameters of the femoral arteries ranged from 0.6 to 1.2 mm. A 0.7 mm Microvascular Flowprobe was used to measure flow directly in these tiny vessels. To assess the patency of the vessels, postoperative volume blood flow measurements were taken at twenty-minute intervals up to one hour, and then again at twenty-four hours.
They found that 47 of the 56 total anastomoses created were patent twenty-four hours after surgery. Sixteen percent or nine of the anastomoses had thrombosed within twenty-four hours.
Moreover, using receiver operating characteristic curve analysis, they established that the optimal cutoff value for immediate postoperative flow for predicting thrombosis within twenty-four hours of a microvascular anastomosis is 0.21 mL/min.
From their study the researchers concluded that, at twenty minutes postoperatively, blood flow greater than 0.30 mL/min is highly suggestive of patency, and flow less than 0.21 mL/min is highly suggestive of failure. Therefore, in order to predict long-term postoperative vascular patency, the authors recommend a minimal cutoff flow value of 0.30 mL/min for vessels ranging from 0.6 to 1.2 mm in diameter.
Shaughness G, Blackburn C, BallestÌn A, Akelina Y, Ascherman JA, “Predicting Thrombosis Formation in 1-mm-Diameter Arterial Anastomoses with Transit-Time Ultrasound Technology,” Plast Reconstr Surg. 2017; 139(6): 1400-1405. (Transonic Reference # 11200A)
Transonic Clamp-on Tubing Flowsensors Used to Test 3-D Printed Mock Pulmonary Circulation Model1
Eisenmenger's syndrome is defined as the process in which a long-standing left-to-right cardiac shunt caused by a congenital heart defect (typically by a ventricular septal defect, atrial septal defect, or less commonly, patent ductus arteriosus) causes pulmonary hypertension and eventual reversal of the shunt into a cyanotic right-to-left shunt. Because of the advent of fetal screening with echocardiography early in life, the incidence of heart defects progressing to Eisenmenger's has decreased.
Researchers from six United Kingdom institutions2 collaborated to use a 3-D printer to construct an anatomical mock circulatory system model to study pulmonary hemodynamics. Their groundbreaking endeavor, reported in the July issue of Artificial Organs is entitled “A Mock Circulatory System Incorporating a Compliant 3-D Printed Anatomical Model to Investigate Pulmonary Hemodynamics.”
The publication describes using a 3-D printer to mold a block of latex into an anatomically-correct pulmonary arterial mock circulatory model that could be used to test in vitro clinically relevant scenarios such as pulmonary hypertension (PAH), unilateral PA stenosis, a flow split after repair of transposition of the great arteries (TGA) and Eisenmenger’s syndrome. The group constructed their model from actual patient data.
Central to testing the feasibility of their model were measurements of pulsatile flow and pressure. As water was pumped through the model from its inlet, A Transonic 9PXL perivascular ultrasound probe calibrated over a range of flows (0–6 L/min) was applied to Tygon tubing to measure volume flow at the model’s inlet and all seven outlets. A high fidelity pressure wire, threaded through a 9F catheter sheath into the model through one of its outlets, measured pressure. The model was tested under physiological pulsatile flow conditions that simulated healthy and pathological conditions. Results were analyzed using wave intensity analysis (WIA).
In order to test non-invasive measurements with the model, a clinical magnetic resonance scanner was used. The compliance chamber, pulmonary arterial model and reservoir were located in the bed of the scanner along with the MR-compatible flowsensors and pressure wire. The pump and data acquisition devices were placed in the MRI control room.
The researchers report that the model tested successfully both and and out of the MRI environment. An increased in mean pressure was recorded in the main pulmonary artery, the simulated the clinical range for pulmonary arterial hypertension. Noting the ease and low cost of producing rapid prototyping molds, and the model’s versatility for invasive and noninvasive measurements, they anticipate that the model will be useful for further investigation of a host of pulmonary hemodynamic scenarios.
1 Knoops PGM, Biglino G, Hughes AD, Parker KH, Xu L, Schievano S, Torii R, “A Mock Circulatory System Incorporating a Compliant 3D-Printed Anatomical Model to Investigate Pulmonary Hemodynamics,” Artif Organs. 2017 Jul;41(7):637-646. (Transonic Reference # EC1121A)
2 UCL Institute of Child Health, London, UK; Great Ormond Street Hospital for Children, NHS Trust, London, UK; Department of Mechanical Engineering, University College London, London, UK; Bristol Heart Institute, School of Clinical Sciences, University of Bristol, Bristol, UK; UCL Institute of Cardiovascular Science, London, UK; Department of Bioengineering, Imperial College London, London, UK.
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Transonic Flowmeters Used in Development of Extra-Uterine Womb
Image source: E.A. PARTRIDGE ET AL/NATURE COMMUNICATIONS 2017
More than one-tenth of all babies, or about 15 million babies worldwide each year, are born prematurely. Many of these babies die. Over a third of infant deaths and half of cerebral palsy diagnoses in the United States are attributed to premature birth and frequently, the underdevelopment of their lungs. Despite advances in neonatal intensive care that have increased the limits of viability, survivors of premature birth before 28 weeks often deal with chronic lung disease and other complications from immature organs.
Bronchopulmonary dysplasia — an arrest in lung development secondary to premature transition from liquid to gas ventilation — is the most common and challenging problem facing extremely premature infants.
In an effort to create a more physiological approach to support these infants, researchers at Children’s Hospital of Philadelphia (CHOP) created an extra-uterine womb.
How it Works
Researchers delivered premature lambs and placed them into a sterile bag filled with electrolyte fluid. Then, tubes carrying oxygenated blood were plugged into the lamb’s umbilical cord. This allows the lamb’s heart to pump blood at volumes and pressure comparable to what a placenta would provide. The fluid inside the artificial womb helps the lamb’s lungs develop as they would while still in utero.
In order for the extra-uterine womb to be used on human infants, the babies would have to be born surgically and placed into the fluid incubator. This presents an issue, says lead researcher Alan Flake, because up to 50 percent of extremely premature infants are born vaginally. Also, delicate fetal surgery would need to be performed to connect the baby’s umbilical cord to the ventilator while he or she is still attached to his or her mother.
However, Flake and his team estimate that once these and other issues are corrected, the device may be ready for human trials in as little as five years.
Transonic Flowsensors Used
According to the report published in Nature Communications, “Connections were established as an arterial-venous extracorporeal oxygenation circuit, with the carotid artery or umbilical arteries providing inflow to the oxygenator (CA/JV or UA/UV) connected to the oxygenator inflow port and the jugular vein or umbilical vein (CA/JV or UA/UV) providing outflow from the oxygenator and connected to the oxygenator outflow port.”
Researchers used Transonic’s HXL Tubing Flowsensor to continuously measure circuit flow. Researchers also used the HXL Tubing Flowsensor to monitor the level of fluid volume in the artificial amniotic sac.
“It was such a thrill to scroll through the news and see Transonic Flowmeters being used in this groundbreaking research on the development of an extra-uterine womb to support premature fetal development,” said Margo Sosa, Senior Research Product Manager at Transonic. “As a company whose roots began in research over 30 years ago, Transonic has tremendous pride in seeing our products used to support the type of truly revolutionary science that Dr. Flake and his team at CHOP are working on. Being able to be even a small part of something like this is the kind of kick that makes us excited to get up and go to work every morning!”
EG4 Brings Transit-time Ultrasound Volume Blood Flow Measurements to Telemetry
Ever since the development of transit-time flow measurement over 30 years ago, researchers have been asking for a telemetry option. However, the power and processing needs of the technology were prohibitive for such a small-scale endeavor. For years, researchers had to make do with skin buttons and tethers or backpacks for chronic studies. Now, for the first time, gold standard transit-time ultrasound Flowprobes are incorporated into a telemetry system, the EndoGear4.
EndoGear4 incorporate a transit-time ultrasound flowprobe for volume blood flow measurements in addition to pressure, ECG and temperature measurements, providing a complete hemodynamic profile for cardiovascular studies. With an implant sized slightly larger than a quarter, the EG4 is suitable for rats and small animals, 250g and larger. EndoGear4 implants are user-configurable and can include up to two channels of Pressure/ECG and two same-size volume Flowprobes.
When to Use Pen-tip Doppler and Transonic Transit- Time Ultrasound during Cerebrovascular Surgery
Dr. Fady Charbel’s Flow-Assisted Surgical Technique (F.A.S.T) protocols rely on transit-time ultrasound’s direct measurements of volume flow in mL/min to verify flow preservation or flow augmentation during cerebrovascular surgery.
Transit-time ultrasound flow measurements:
- Inform surgical decisions by helping the surgeon achieve optimal clip placement to completely isolate an aneurysm, AVM or dural fistula while confirming that flow is preserved in parent vessels and distal branches;
- Provide immediate assessment of residual and collateral flow reserve during temporary clipping;
- Confirm that a flow preservation or flow augmentation bypass is working before the patient leaves the OR, or by alerting the surgeon to dangerous, flow-limiting conditions.
Can’t a pen-tip Doppler also assess flow preservation?
A pen-tip Doppler probe measures directional intensity, not flow. When a pen-tip Doppler is placed against the wall of an exposed vessel during surgery, it registers how fast particles are moving, not how much blood is moving as do Transonic’s transit-time ultrasound Flowprobes.
Doppler readings are unreliable because high velocities can occur despite low flows. Doppler measurements cannot distinguish between normal diameter flows and flows at a Grade IV stenosis (see figure on next page).
Transit-time ultrasound Flowprobes will identify Grade V (occlusive or near-occlusive) stenoses, and residual flow within an aneurysm if clip placement is incomplete. Moreover, pen-tip Doppler, with its subjective swoosh-swoosh sound representation of flow velocity, does not quantify flow reliably so it is impossible to compare absolute pre- and post-clip flow values to determine if flow has been compromised.
When is a pen-tip Doppler of value during surgery?
The pen-tip Doppler does has value in certain surgical protocols. For instance: if a surgeon does not clip an aneurysm completely, and the bulb of the of aneurysm is still receiving arterial flow, blood will still be swirling within the bulb and a pen-tip Doppler will reveal this swirling blood. For other Transonic flow-assisted surgical protocols, the surgeon needs to measure an accurate rate of flow (mL/min). A Pen-tip Doppler cannot do this.
Flow velocity has little value in identifying a stenosis unless one can use a pen-tip Doppler to scan flow velocity across a length of the vessel. If the Doppler probe is held at one site where there is low flow velocity, it can be indicating that the probe is not being held above a flow constriction. If the probe is moved further along the vessel where the flow velocity is high, it can be indicating that there must be a narrowing of the vessel or stenosis at that point. In this way a pen-tip Doppler probe can be useful in locating the site of a stenosis.
Transonic Flow Capability Integral in Development of Mechanical Circulatory Support Devices
The fist-sized human heart is an incredible pump. To be exact it is two pumps separated by a wall down the middle and encased in a single sheath of muscle. The right side sends blood gently to the lungs, while the left side pump propels five quarts of oxygen-rich blood per minute throughout the body. Although the two pumps exert significantly different forces, their synchronous beat ensures smooth and continuous blood flow. If blood flow is blocked or fails, the heart fails as well. Its action must be augmented to sustain life. Mechanical circulatory support is one strategy used to help a damaged heart pump blood through the body.
The need for mechanical circulatory support devices for heart failure is daunting. Of an estimated 5.7 million Americans with heart failure, nearly one million have end-stage heart failure and are no longer responsive to maximal medical therapy. Although the ideal goal for these patients is to receive a heart transplant, only 2-4% will actually receive a new heart. In the interim, many of these patients depend on a variety of mechanical circulatory support devices to improve their cardiac outflow, hemodynamics, and tissue perfusion.
As mechanical support devices have evolved the past quarter century, one critical measurement has been at the forefront of their development — flow. Transonic flow measurements have been used to test virtually all devices in mock circulatory models on the bench and in vivo.
Transonic Clamp-on Tubing Sensors Measure Delivered Blood Flow
Thrombosis is one dreaded complication of left ventricular assist devices. However, with the unmatched accuracy of Transonic H-XL-Series Clamp-on Tubing Sensors, true blood flow through the circuit can be known at all times. By comparing actual delivered blood flow to the flow reading on the pump, flow limiting causes can be detected and corrected on the spot. Kinks and circuit blockages can be detected and corrected before catastrophic circuit failures with dire consequences can occur.
VAD Implantation Surgery Aided by Blood Flow Measurements
Surgery to implant a mechanical circulatory assist device such as a pVAD or LVAD is precise and precarious. Cannulas must be placed in major arteries, and the heart. Bleeding is a frequent complication, and flow can also be compromised at any moment. Measuring aortic or pulmonary artery flow intraoperatively with a Transonic Perivascular COnfidence Flowprobe keeps a cardiac surgeon appraised of the function of the heart throughout the surgery.
Heart Failure Forestalled by Blood Flow Measurements
Management of acute right heart failure following implantation of an VAD for left ventricular circulatory support, requires a reliable estimation of left ventricular preload and contractility. A Transonic® Flowprobe on a VAD’s outflow line will measure a progressive decline in outflow. Coupled with a loss of pulsatility and other indicators such as lower pressure and/or acute renal failure, early measures can be undertaken to restore flow before acute right heart failure ensues.
Three-Year Randomized Controlled Trial Finds that Surveillance Reduces Rate of Thromboses and Costs
“I love this machine!” exclaimed Dr. Inés Aragoncillo when a slide displaying the Transonic Hemodialysis Monitor, was shown at the recent American Association of Nephrology (ASN) convention in Chicago. Dr. Aragoncillo was presenting the findings of her three-year RCT in which she and her colleagues studied the addition of ultrasound Doppler and ultrasound dilution (Transonic) surveillance to classic vascular access monitoring in their hemodialysis patients.
The Spanish clinicians conducted the controlled, multicenter, trial because the hemodialysis literature was not clear about whether surveillance, based on vascular access blood flow, actually enhanced the function and longevity of arteriovenous fistulas (AVFs). They wanted to know definitively whether measurement of flow could reduce thrombosis, increase thrombosis-free and secondary patency in arteriovenous fistulas, and reduce vascular access-associated costs.
The results of the study entitled, “Adding access blood flow surveillance reduces thrombosis and improves arteriovenous fistula patency: a randomized controlled trial,” is now published in the July 2017 issue of the Journal of Vascular Access. Two hundred and seven patients, drawn from nine Madrid hospitals, were included in the study. They were randomized into two groups: one with 103 patients had classic monitoring of their AVFs every three months augmented by vascular access flow measurements with Doppler ultrasound and Transonic ultrasound dilution technologies; a second control group with 104 patients did not have flow surveillance added their quarterly AVF monitoring.
At the end of the three years, the Transonic surveillance group displayed significantly fewer thromboses compared to the control group: (0.025 versus 0.086 thrombosis/patient/year). They also showed a significant improvement in their thrombosis-free patency rate and in their secondary patency rate compared to the control group. No differences were seen in the non-assisted primary patency rate between the two groups.
There was a greater need for infection-prone central venous catheters and more hospital admissions in the control group compared to the surveillance group. Moreover, vascular access-related costs were considerably lower (42%) in the surveillance group than in the control group.
From their study, the clinicians concluded that flow-based surveillance combining Doppler ultrasound and ultrasound dilution reduces the frequency of thrombosis, is cost effective, and improves thrombosis free and secondary patency in autologous arteriovenous fistulas.
Aragoncillo I et al, ”Adding access blood flow surveillance reduces thrombosis and improves arteriovenous fistula patency: a randomized controlled trial,” J Vasc Access. 2017; 18(4): 352-358. (Transonic Reference # HD11190AH)
Tessitore N et al, “Can blood flow surveillance and pre-emptive repair of subclinical stenosis prolong the useful life of arteriovenous fistulae? A randomized controlled study,” Nephrol Dial Transplant 2004; 19: 2325-2333. (Transonic Reference # HD407AH)