Material reduces time patients stay in hospitals

Edited by the Engineeringtalk editorial team Feb 28, 2006

Piezoceramic material with high dielectric constant and sensitivity uses time of flight measurement of travelling ultrasound wave to measure the blood flow for haemodynamic status monitor.

Morgan Electro Ceramics has been working with Deltex Medical in developing its oesophageal doppler probes, which are used with the Cardioq haemodynamic status monitor.

A disposable ultrasound probe is used to determine the amount of blood being pumped around the body (circulating blood volume) of patients during operations.

Oesophageal doppler technology can reduce the length of hospital stay by 25 to 40% across a range of surgical specialities.

West Sussex-based Deltex Medical has made critical care devices for over 20 years and was looking for a partner who could design and manufacture the piezoceramic sensor that incorporates a transmitter and receiver for the Cardioq ultrasonic probe.

Morgan was known because of its work developing medical devices such as foetal heart monitors so the two worked together to establish which material would be best suited to the application.

"We worked closely with Morgan throughout the development of the product," said Andy Mears, Operations Director, Deltex Medical.

"The company's extensive knowledge of ceramics was a great benefit to us." Morgan recommended its PZT5H piezoceramic material for its mechanical and electrical properties, specifically its high dielectric constant and sensitivity.

"The sensor uses time of flight measurement of the travelling ultrasound wave to measure the blood flow," said Tony Beswick, General Manager at Morgan.

The ceramic is fixed on the end of the probe, which has a diameter of about 5mm, and is sleeved in a non-toxic, latex-free silicone rubber.

It is inserted into the patient's oesophagus either orally or via the nose and once in position the transmitted signal rebounds off blood flowing in the descending aorta.

The signal is received by another piezoelectric ceramic, which converts the ultrasonic pulses back into an electrical signal.

To produce a minimally invasive device the transmitter-receiver combination is made from a single piece of piezoceramic with wrap-around electrodes.

The received signal is then digitised and displayed into a real time waveform on the Cardioq display.

"Virtually every patient undergoing surgery suffers from hypovolaemia (akin to severe dehydration)," said Mears.

"This is because of the combined effects of pre-operative starvation, the impact of the anaesthetic agents and trauma from the surgery itself".

"This leads to insufficient amounts of oxygen being delivered to the vital organs which can cause medical complications including peripheral and major organ failure".

Using fluids and drugs, guided by the Cardioq, to optimise the amount of circulating blood volume reduces post operative complications allowing patients to make a faster more complete recovery and return home earlier.

"Morgan manufactures the PZT ceramic and assembles the probe components on site," said Mears.

"This has enabled a more efficient manufacturing process and allowed us to optimise the supply chain".

Other applications of ceramic in medical devices include ultrasonic imaging and high power transmitters of high frequency waves that assist with surgical cutting procedures such as cataract removal.