Originally Published EMDM January 2006
Engineering Insight
Piezoceramic Sensor Is Lifeblood of Haemodynamic Status Monitor
Fixed on the end of a minimally invasive probe, the ceramic measures blood flow during surgical procedures
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The CardioQ haemodynamic status monitor from Deltex Medical reportedly can reduce the length of postsurgical hospital stays by as much as 40%. |
Oesophageal Doppler probes are used in conjunction with haemodynamic status monitors to determine the volume of blood circulating in a patient’s body during a surgical procedure. One such monitor, developed by Deltex Medical (Chichester, W Sussex, UK), that uses this technology reportedly has been shown in clinical studies to reduce the length of patients’ hospital stays by 25 to 40%. In developing the CardioQ monitor, Deltex Medical enlisted the help of Morgan Electro Ceramics (MEC; Southampton, Hants, UK) to design and manufacture a piezoceramic element for its probe.
Deltex Medical became aware of MEC because of its work in the development of innovative medical devices such as fetal heart monitors. The two companies worked together to determine an appropriate material for the application.
“The sensor uses time-of-flight measurement of a travelling ultrasound wave to measure blood flow,” explains MEC general manager Tony Beswick. Consequently, a high-performance and reliable material was required. MEC recommended its PZT5H piezoceramic, citing the material’s mechanical and electrical properties, specifically its high dielectric constant and sensitivity.
The ceramic is attached to the end of the probe, which measures approximately 5 mm diam. In order to meet the size requirements of a minimally invasive device, the sensor’s transmitter and receiver combination is fabricated from a single piezoceramic piece with wrap-around electrodes.
Housed in a nontoxic, latex-free silicone rubber sleeve, the device is inserted into the patient’s oesophagus, either orally or via the nose. Once the probe is in position, it transmits a signal that rebounds off blood flowing in the descending aorta. The transmission is received by another piezoelectric ceramic, which converts the ultrasonic pulses back into an electrical signal, which is digitized and shown as a real-time waveform on the CardioQ display.
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A piezoceramic sensor designed and manufactured by Morgan Electro Ceramics is fixed on the end of a disposable probe that measures blood flow by means of time-of-flight measurement. |
“Virtually every patient undergoing surgery suffers from hypovolaemia, which is akin to severe dehydration,” explains Andy Mears, operations director at Deltex Medical. “This is because of the combined effects of preoperative fasting, the impact of anaesthetic agents, and trauma from the surgery itself. Insufficient amounts of oxygen may be delivered to the vital organs, which can cause medical complications including peripheral and major organ failure,” he adds. The introduction of fluids and drugs, guided by the CardioQ device, optimizes the amount of circulatory blood volume and reduces postoperative complications. Therefore, patients can recover faster and return home earlier, says the company.
“MEC manufactures the PZT ceramic and assembles the probe components,” Mears explains. “This has enabled a more efficient manufacturing process and allowed Deltex to optimize the supply chain. We worked closely with MEC throughout the development of the product,” adds Mears. “The company’s extensive knowledge of ceramics was a great benefit to us.”
Other applications of ceramic in medical devices include ultrasonic imaging and high-frequency wave transmitters used in surgical cutting procedures such as cataract removal.
MEC has a comprehensive range of piezoelectric and dielectric materials that are typically used in transducers, sensors, actuators, and high-voltage and radio-frequency capacitors. It is part of the Morgan Technical Ceramics Group, which has manufacturing locations throughout Europe, North America, and Asia. The firm prioritizes research and development, innovative design, and application engineering.
Copyright ©2006 European Medical Device Manufacturer
