Poster R8 - Advancements in Pediatric Cardiac Surgery: Implantable Doppler Ultrasound for Real-Time Blood Flow Monitoring

Introduction: During pediatric cardiac surgery for heart defects, monitoring cardiac output is critical as it influences the heart’s pumping efficiency and organ function. Traditional direct measurements are invasive, offering only momentary insights during procedures in cardiac catheterization labs. Implantable catheters provide ongoing monitoring but are limited to high-risk patients due to their complex management requirements.

In routine practice, physicians use indirect metrics like urine output, body temperature, blood pressure, and serum lactate levels to assess cardiac output. However, these methods can delay recognizing inadequate cardiac function. With around 900,000 cardiac surgeries annually in the U.S., there's a pressing need for non-invasive, continuous cardiac output measurement directly at the bedside. The necessity for accurate, quantitative blood flow measurement is also critical in other surgical contexts. For example, transplant surgery demands precise blood supply management to prevent organ loss. Plastic surgeons, during free tissue flap procedures, depend on subjective evaluations like capillary bleeding, tissue color, and temperature, lacking a method for objective blood flow assessment. Similarly, surgeries involving kidney, liver, and pancreas transplants require careful vascular anastomosis to prevent iatrogenic stenosis that can compromise organ function or lead to failure. Immediate correction of these vascular issues during surgery is crucial. Moreover, in peripheral vascular surgeries—where approximately 150,000 operations are conducted annually in the U.S.—early detection of inadequate post-operative blood flow is vital for improving patient outcomes. These surgeries often involve peripheral vessels, abdominal organ transplants, and free flap closures.

Materials and

Methods: We have created a flexible, ultrathin ultrasound flow probe for pediatric cardiac output measurement, addressing the limitations of current probe sizes. The design incorporates continuous-wave (CW) Doppler technology, with dual transducers to manage the challenges associated with unknown Doppler angles and to accurately measure blood flow velocity. The fabrication process for the probe involves creating graphene electrodes through laser induction on a polyimide substrate, followed by the deposition and poling of a PVDF layer to enhance its piezoelectric properties. After fabrication, the device undergoes rigorous testing for its acoustic performance and mechanical stability to ensure compliance with medical standards. Additionally, our work includes developing a pediatric heart and blood flow phantom model using commercially available pumps and tubing to simulate the unique anatomical features of pediatric patients. This model facilitates controlled testing and refinement of the Doppler sensor against standard clinical pumps, ensuring accuracy and reliability. The final component of our work involves testing the newly developed flexible Doppler ultrasound flow probe with the phantom model to assess its in vitro performance. Detailed comparisons of the Doppler spectra and flow velocity measurements against known standards are conducted to evaluate the device’s accuracy, precision, and repeatability. This comprehensive approach is designed to revolutionize pediatric cardiac care by providing precise, real-time data on cardiac output, enhancing treatment and recovery outcomes.

Results, Conclusions, and Discussions: Our research has led to three major innovations in pediatric cardiac care technology. The primary innovation is the development of a novel flexible Doppler ultrasound sensor made from graphene and polyvinylidene fluoride (PVDF). This sensor's flexibility allows it to be sutured onto blood vessels of various diameters during cardiac surgery and designed for easy postoperative removal without additional surgery, significantly advancing cardiac output measurement technology.

The second major innovation is the quantification of blood flow with high precision using Vector Doppler signal processing. This method improves the accuracy of flow velocity estimates, making it robust against slight variations in the insonation angle, crucial for monitoring dynamic changes in cardiac output during surgery.

The third innovation is the creation of a realistic pediatric heart and blood flow phantom model. This model provides a standardized tool for research and training, enhancing the testing and validation of our Doppler ultrasound device under controlled conditions that simulate real pediatric cardiac scenarios.

In testing, our flexible Doppler ultrasound device demonstrated high performance in measuring blood flow velocity, with our Vector Doppler approach confirming its precision and reliability. Comparative testing with clinical pumps like the Berlin Heart and CentriMag further validated the device's consistency and accuracy across a range of flow conditions. These results were corroborated by rigorous statistical analysis and a systematic evaluation of the device's repeatability and precision in a simulated clinical environment.

In conclusion, our interdisciplinary approach has successfully developed a flexible, implantable Doppler ultrasound device that promises to transform pediatric cardiac care by providing precise, real-time monitoring of cardiac output. The integration of advanced materials like graphene and PVDF, along with innovative signal processing techniques, establishes a new standard in the functionality and applicability of ultrasound technology in medical settings. This work not only furthers the understanding of dynamic blood flow in pediatric patients but also sets the groundwork for future innovations in medical device development.

Acknowledgements (Optional):