In-Vivo and Postmortem Biomechanics of Abdominal Organs Under Compressive Loads: Experimental Approach in a Laparoscopic Surgery Setup

Brown, J.D. (2003) In-Vivo and Postmortem Biomechanics of Abdominal Organs Under Compressive Loads: Experimental Approach in a Laparoscopic Surgery Setup. Doctoral thesis, University of Washington.

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In order to provide realistic haptic (touch) feedback, simulators must incorporate accurate computational models of the in-vivo mechanical behavior of soft tissues. It is important to test tissues in surgically relevant ranges of applied force, duration, and deformation. In order to determine these ranges, a system known as the Blue DRAGON has been created that can track the motions of and the forces applied to surgical tools during live procedures. Thirty-one surgeons of varying skill were recorded performing three different surgical tasks. The mean force applied to the tool handles during tissue grasps was 8.52 N ± 2.77 N. Ninety-five percent of the handle angle frequency content was below 1.98 Hz ± 0.98 Hz. Average grasp time was 2.29 s ± 1.65 s, and 95 of all grasps observed were held for less than 8.86 s ± 7.06 s. The average maximum grasp time performed by surgeons during these tasks was 13.37 s ± 11.42 s. <p> Using these values as design parameters, a computer-controlled, motorized endoscopic grasper (MEG) has been designed to obtain biomechanical properties of soft tissues in-vivo. The MEG uses a geared DC motor to drive a Babcock grasper using a cable-and-pulley mechanism. The motor is capable of producing the equivalent of 26.5 N of grasping force (470 kPa) by the end effector jaws. Two strain gage force-sensing beams are mounted in the partial pulley to accurately measure applied force. Computer-control is provided using a proportional-derivative position controller to command cyclic (up to 3 Hz) or step loadings. The MEG can be hand-held, weighs about 0.7 kg, and can be inserted into the body through standard endoscopic ports. The MEG has been calibrated and validated on linear springs with known stiffness. <p> The MEG has been used to test 7 different porcine abdominal organs in-vivo and through 24 hours postmortem. Elastic and relaxation properties have been recorded and analyzed. Constitutive force-deformation relations have been fit to the elastic data, and stress relaxation functions have been fit to the stress-time data recorded during relaxation tests. An understanding of how the tissue properties and model parameters are influenced by time postmortem and loading condition has been obtained.

Item Type: Thesis (Doctoral)
Subjects: Z Other
Divisions: Department of Electrical Engineering
Depositing User: Andrew Haddock
Date Deposited: 13 Jul 2015 23:31
Last Modified: 13 Jul 2015 23:31

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