Abstracts - Conference Planning and Management - Iowa State ...

An Experimental Study of Pulsed Micro Flows Pertinent to Continuous
Subcutaneous Insulin Infusion Therapy
Bin Wang 1 , Ayodeji Demuren 2 , Eric Gyuricsko 3 and Hui Hu 1
1. Aerospace Engineering Dept., Iowa State University, Ames, Iowa Email:huhui@iastate.edu
2. Mechanical Engineering Dept., Old Dominion University, Norfolk, VA
3. Children's Hospital of the King's Daughters, Eastern Virginia Medical School, Norfolk, VA
Introduction
Continuous subcutaneous insulin infusion (CSII) therapy, also known as insulin pump therapy, has become an important
advancement in diabetes therapy to improve the quality of life for millions of diabetes patients. Insulin delivery failures
caused by the precipitations of insulin within micro-sized CSII tubing systems have been reported in recent years. It has also
been conjectured that the flow of insulin through an insulin infusion set may be reduced or inhibited by air bubbles entrained
into the capillary CSII tubing system during the typical three- to five-day operation between refills. Currently, most
solutions to insulin occlusion related problems are based on clinical trials. It is of great value to elucidate underlying physics
of insulin infusion process, from the pump action to the catheter delivery, and from a fluid dynamics perspective, in order to
provide a better guidance for troubleshooting.
In the present study, an experimental investigation was conducted to quantify the transient behavior of the unsteady
micro-flow driven by an insulin pump commonly used in CSII therapy to elucidate the underlying physics for a better
understanding of the microphysical process associated with the insulin delivery. A microscopic Particle Image Velocimetry
(-PIV) system was used to provide detailed flow velocity field measurements inside a 300μm×300μm microchannel to
characterize the transient behavior of the micro-flow upon the pulsed excitation of the insulin pump. The effects of the air
bubbles entrained into the micro-sized tubing system on the insulin delivery process are also assessed based the detailed -
PIV measurements.
Experimental Setup and μ-PIV Measurements
Fig. 1 shows the schematic of the experimental setup used in the present study. A Medtronic MiniMed Paradigm 512 insulin
pump was used to drive the flow passing through a standard Paradigm Quick-Set infusion set (inner diameter=356m) at
the flow rate of 2.0 U/H (~20 L per hour). A transparent microchannel (L×W×H: 38mm×300m×300m) was used to be
a part of the tubing system for -PIV measurements. For simplicity, DI water premixed with ~1m FluoSpheres® beads
was used as the working fluid in the present study.
For the -PIV measurements, a double-pulsed Nd:YAG laser at the second harmonic wavelength (532nm)
was used to provide illumination for the micro-PIV measurements. The repetition rate of the laser pulses was 10 Hz. A highresolution
12-bit CCD camera mounted on an inverted microscope with a 10X objective lens (NA=0.4) was used to acquire
PIV images. The timing of the CCD camera and the pulsed laser illumination was controlled via a Digital Delay Generator.
After micro-PIV images were acquired, instantaneous flow velocity vectors were obtained by using a frame to frame crosscorrelation
technique. The measurement uncertainty level for the measurements of the instantaneous velocity vectors was
estimated to be within 2.0%.
Experimental Results and Discussions
Fig. 2 shows a frame of the typical -PIV measurement results obtained when the insulin pump operated in basal mode at
the flow rate of 2.0 U/H. Based on time sequences of the instantaneous -PIV measurement results as that shown in Fig. 2,
the time variation of the flow velocity inside the CSII tubing system in response to the pulsed action of the insulin pump can
be derived, which is given in Fig. 3. As expected from the basal rate setting (2.0 U/H) and the minimum controllable dose
(0.1 U) of the pump, the period of the pulsed operation cycle of the insulin pump was found to be 180s. It can be seen
clearly that the fluid would creep slowly through the CSII tubing system most of the time during each pump operation cycle;
all of a sudden a flood would be generated upon the pulsed action of the insulin pump. While the time-averaged flow
velocity at the centerline of the channel was only found to be about 0.098 mm/s as indicated by the red dash line in Fig. 3,
the instantaneous maximum flow velocity inside the microchannel can be as high as 26.4mm/s, which is two orders of
magnitude higher than the time-averaged flow velocity. The zoom-in view of the flow velocity history right before and after
the pump operation pulse reveals clearly that the duration of the pump operation was as short as about 0.25 seconds. The
subsequent decay process of the flow velocity inside the CSII tubing system can be fitted reasonably well by an exponential
function.
Society of Engineering Science ▪ 47 th Annual Technical Meeting 46