Applications for implantable SAW pressure sensors 6 th April 2004 Applications for implantable SAW pressure sensors Chris McLeod 1 Robert Dickinson 2 Aimen Sabkha 1 Chris Toumazou 2

Applications for implantable SAW pressure sensors 6 th April 2004 Goal Implant a sensor element yielding localised pressure measurement for long-term monitoring of patients in the hospital or at home with minimal risk.

Applications for implantable SAW pressure sensors 6 th April 2004 Applications in Clinical Care Where implantation could accompany an existing intervention or replace catheterisation: Cardiovascular system : Intra-cardiac post transplant or post valve replacement Chronic heart disease Arterial grafts Aneurism repair Hypertension Neurological system : Intra-cranial pressure Gastro-Intestinal system : Bladder pressure

Applications for implantable SAW pressure sensors 6 th April 2004 Some Contributions to Market Size UK Figures Implanted heart valves (mechanical or biological) c. 6,500 paImplanted heart valves (mechanical or biological) c. 6,500 pa Heart or Heart&Lung Transplants c. 400 paHeart or Heart&Lung Transplants c. 400 pa Heart assist devices (implanted variety) n/aHeart assist devices (implanted variety) n/a Major cardiac intervention where implanting would marginally alter the risk. Benefits: Local pressure measurement in one or more chambers. Continuous and instantaneous measurement. Continuous and instantaneous measurement. No further intervention (catheterisation) No further intervention (catheterisation)

Applications for implantable SAW pressure sensors 6 th April 2004 Some Contributions to Market Size UK Figures Abdominal Aortic Aneurism (High mortality 8,500 deaths/year (England & Wales)(High mortality 8,500 deaths/year (England & Wales) High volume (15,000 year (England & Wales)High volume (15,000 year (England & Wales) Small increase in RiskSmall increase in Risk

Applications for implantable SAW pressure sensors 6 th April 2004 Some Contributions to Market Size UK Figures Hypertension High total number: c. 1 millionHigh total number: c. 1 million Risk assessment by classification: Grade 1,2,3Risk assessment by classification: Grade 1,2,3 (Systolic >140, 160, 180 and Diastolic >90, 100, 110)

Applications for implantable SAW pressure sensors 6 th April 2004 Some Contributions to Market Size: Hypertension & Risk WHO/ISH 1 Stratification of Risk to Quantify Prognosis Other Risk Factors and Blood Pressure Disease History Grade 1Grade 2Grade 3 I No other risk factorsLow Medium High II 1-2 risk factorsMediumMediumHigh III >/= 3 risk factors or TOD or ACCHighHighHigh Factors: Age, Smoking, Cholesterol >61mmol/L, Family history, Obesity. ACC, associated clinical condition; TOD, target organ damage 1 International Society of Hypertension

Applications for implantable SAW pressure sensors 6 th April 2004

Applications for implantable SAW pressure sensors 6 th April 2004 SAW Wireless Passive Remote Sensor SAW Sensor Unit SAW Sensor Unit Local Readout (Interrogation Unit) Local Readout (Interrogation Unit) Transmitter/Receiver held in close vicinity of implanted sensor. Could be worn. Transmitter/Receiver held in close vicinity of implanted sensor. Could be worn. Remote Readout Remote Readout Logs data from local readout via wire/Bluetooth/GSM network to a physician on duty in the hospital. Logs data from local readout via wire/Bluetooth/GSM network to a physician on duty in the hospital.

Applications for implantable SAW pressure sensors 6 th April 2004 SAW Sensor Features Structure: Piezoelectric substrate + InterDigitated Transducers (IDT’s)Structure: Piezoelectric substrate + InterDigitated Transducers (IDT’s) Propagation: SAW waves excited using IDT’s due to piezoelectric property of substrate; electrical to mechanical energy conversion and vice versa.Propagation: SAW waves excited using IDT’s due to piezoelectric property of substrate; electrical to mechanical energy conversion and vice versa. RF input pulse-> SAW -> RF retransmittedRF input pulse-> SAW -> RF retransmitted

Applications for implantable SAW pressure sensors 6 th April 2004 Features for Long Term Use Frequency Range in UseFrequency Range in Use Industrial Scientific Medical (ISM) band, which requires no licence. Industrial Scientific Medical (ISM) band, which requires no licence. Power RequirementPower Requirement Passive; no battery; infinite life. Passive; no battery; infinite life. There is a maximum allowed radiated power, but it is adequate. There is a maximum allowed radiated power, but it is adequate. Range & AccuracyRange & Accuracy Measurable range (0-250mm Hg), with an accuracy of approx. 1%. Measurable range (0-250mm Hg), with an accuracy of approx. 1%. Biocompatibility & SafetyBiocompatibility & Safety Made from inert silicon and hermetically encapsulated. Made from inert silicon and hermetically encapsulated. Extremely stable and do not suffer from drift. Extremely stable and do not suffer from drift. No battery; no replacement; no leaking chemicals. No battery; no replacement; no leaking chemicals.

Applications for implantable SAW pressure sensors 6 th April 2004 Different Designs of SAW Sensors SAW Resonators SAW Reflective Delay Lines

Applications for implantable SAW pressure sensors 6 th April 2004 Advantages of implantation Single intervention –v- multiple catheterisations (cost)Single intervention –v- multiple catheterisations (cost) Single intervention – greatly reduced infection riskSingle intervention – greatly reduced infection risk Continuous monitoring possible over years; cf Holter ECGContinuous monitoring possible over years; cf Holter ECG Alarm Alarm Control Control Confirmed monitoring siteConfirmed monitoring site No interference with normal physiologyNo interference with normal physiology

Applications for implantable SAW pressure sensors 6 th April 2004 Development programme Proof of Principle : Use existing SAW pressure sensors + readersProof of Principle : Use existing SAW pressure sensors + readers Bench-testing : Simulated implants immersed in saline – communication optimisation and physiological pressure range sensitivity and accuracy.Bench-testing : Simulated implants immersed in saline – communication optimisation and physiological pressure range sensitivity and accuracy. Animal testing : Biocompatability, fixing, thrombogenesis.Animal testing : Biocompatability, fixing, thrombogenesis. Approvals : Manufacturing process (BS 9002/IEC) and MHRA / FDAApprovals : Manufacturing process (BS 9002/IEC) and MHRA / FDA Human clinical testing : Trials : Integrated with arterial graftsHuman clinical testing : Trials : Integrated with arterial grafts Intra-cardiac : single, then multiple Intra-cardiac : single, then multiple Reader development for remote monitoring : Bluetooth/GSM-linked.Reader development for remote monitoring : Bluetooth/GSM-linked.

Applications for implantable SAW pressure sensors 6 th April 2004 Alternative /Competing Technologies MEMS devices: Pressure-dependent Capacitance Pressure-dependent Inductance CardioMEMS Inc. Atlanta GA USA