Page 52 - JSOM Spring 2018

intended for out-of-hospital control of bleeding. The design The flow volume was sampled as collected in each test over
consisted of a pair of related experiments using water as simu- a time period. The flow rate was calculated in units of mL/s
lated blood flow through a tube. The control group was com- [Equation (1)]. Mean values were also expressed as a percent-
posed of tests with freely flowing water without compression, age of control mean values.
and this control group was used for both experiments. Data
were collected in March and April 2016. Volume Sampled
Flow Rate = (1)
Sampling Time
Experiment 1 Setup:
Flow Changes by Degrees of Compression Normal Flow: Constitution of the
Control Group With No Compression of the Tube
The model setup included a water tank, a line of tubes, and Control group data were gathered in a state of no external
a basin to collect the water (Figure 1). The tank was atop the compression of the wall to represent normal flow. Time was
setup and connected to a line through which the water flowed; measured with use of a stopwatch, and volume was measured
a section of the line contained the collapsible tube, at which by using a 1000mL beaker marked in 50mL increments. The
point testing was done. The tank allowed a 1.37m vertical col- flow rate was averaged from six samples timed to collect water
umn of water to flow via gravity. The head of static pressure volumes at the 750mL mark.
was calculated to be 100mmHg, a realistic mean arterial pres-
sure, driving a steady volumetric flow through the tube. Measuring the Cross-sectional Area of a Lumen in a Tube
Before the collapsible tube was inserted into the line of tubing,
FIGURE 1 Experimental setup.
each area of lumen was measured. The cross-sectional area of
the lumen of the tube was calculated optically by using soft-
ware (ImageJ; https://imagej.nih.gov/ij/) for both processing of
the digital images and analysis of the measurement data. For
example, the tube with no compression had an end-on view of
the tube showing the circular lumen in cross section (Figure 2).
A wall outline was digitally overlaid on the image of the lumen
and luminal area was then measured with use of the software.
Ten measurements of area were averaged for each cross section.
Again, in the example of the control group, the cross section
2
was a circle with a radius (r) of 5mm and an area of 79mm by
both measurement and geometric calculations (π × r ).
2
FIGURE 2 Collapsible tube compressed between two pipes.

The water tank is at the top, and a line of tubing goes down from the
tank to a collapsible tube at the bottom, where it is laid flat over a
black box. The tank has a valve with a handle, which is used to open
and close the tubing to allow and stop flow via gravity. The black tube is shown end-on in outline of its cross section in the
center of the diagram to represent an artery wall that is compressed
from above and below. The gray pipes are also seen end-on in circular
The collapsible tube was designed to mechanically mimic an cross sections above and below the tube. The shape of the tube lumen
arterial wall. The tube (Remedy Simulation Group; www is similar to that produced in compression by a uniform gradient of
transmural pressure such as by a circumferentially applied tourniquet
.remedysim.com) was made of silicone. The silicone was soft, or blood pressure cuff.
and reinforcement was added during fabrication to lessen the
risk of tears and to simulate the properties of an artery. Such Constitution of the Study Group in Experiment 1
a cylindrical tube (150mm length, 1mm wall thickness, 10mm With Degrees of Compression of the Tube
lumen [inner opening] diameter) allows fluid flow to be radi- For the first experiment, methods were similar to those used
ally symmetric about the center axis. The wall was mechani- for the control group, but the study group was tested with
cally unsupported by external structures. The collapsible tube compression. The study group was a set of six tests made at
was laid horizontally to keep the pressure head constant over each of six degrees of compression applied compared to the
the length of the tube. The rest of the setup was vertical. control group with no compression.

48 | JSOM Volume 18, Edition 1/Spring 2018