Development of a Pressure Sensing System for a Left Ventricular Assist Device

Open Access
Author:
Fritz, Bryan
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Drs Gerson Rosenberg/Eric Paterson, Thesis Advisor
  • Gerson Rosenberg, Thesis Advisor
  • Eric Paterson, Thesis Advisor
Keywords:
  • inlet pressure
  • blood pressure
  • non-invasive
  • LVAD
Abstract:
Heart failure is defined as the failure of the heart to effectively pump blood throughout the body. The condition, caused by a variety of diseases and ailments, will claim the life of as many as 300,000 patients this year alone. Today, a relatively common treatment includes implantation of a left ventricular assist device (LVAD) to help the patient’s heart move blood throughout the circulatory system. A continuous flow left ventricular assist device modeled after a Tesla pump has been designed by Advanced Bionics, Inc. and The Pennsylvania State University. When a continuous flow device is employed, care must be taken to not create low pressures or suction in the left ventricle that can produce an obstruction to the inlet cannula or trigger malignant arrhythmias. Design of an inexpensive, semi-conductor strain gage inlet pressure sensor to detect suction has been completed. The transducer can be incorporated into the lumen of the titanium inlet connector of the VAD. Analytical analysis and finite element modeling of the sensing region was completed. Sensitivity, step-response, temperature dependence and hysteresis tests have been performed on prototype units. All sensors were able to withstand the maximum expected strain of 25 ìin/in at 250 mmHg internal pressure. Average sensitivity for the prototype devices was 0.52 ±0.24 µV/mmHg with 0.5 V excitation (n=5 units). Step response time for a 0 to 90 mmHg step change averaged 22 milliseconds (n=5 units). Hysteresis was measured by applying and holding 75mmHg internal pressure for 4 hours, followed by a zero pressure measurement, and ranged from -15 mmHg to 4.1 mmHg (n=3 units). The cause of hysteresis is currently being investigated. Offset (zero pressure) drift varied between 180 and -140 mmHg over a four week period. (n=2 units). Span drift ranged from 18 to -21 µV/°C (n=5 units). Gain drift ranged from -7.4 to 4.9 µV/°C (n=5 units). Improved temperature compensation is currently being developed.