Page 53 - JSOM Spring 2018

Measurements of luminal areas were expressed as a per cent- FIGURE 3 Flow rate results as a function of area reduction of the lumen.
age—the luminal area for a test divided by the luminal area of
the control group. The control group had an area of 100%.
Tests with compression had reduced areas, which were a sur-
rogate of the degree of compression. Area reductions were 0%
(control), 74%, 81%, 91%, 94%, and 97%; the lumen was
0% closed in the control group in that normal flow had a fully
open vessel with no compression and no area reduction.

Statistical Analysis of Experiment 1:
Effect of Degree of Compression on Flow Rate.
To associate flow rate by compression, a one-way analysis of
variance (ANOVA; Minitab 17.2.1; https://www.minitab.com/ The experimental data points (gray circles with black outlines) have
en-us/products/minitab/) was used. Tukey’s method was used a best-fit line (dashed curve). Two data points overlap partly. For this
one vessel as tested, for flow to be more than halved (>50% reduced),
to determine whether differences were statistically significant. the luminal area had to be reduced by 94% or greater. Of note, a lu-
Significance for results was set at a value of p < .05. men closed by 97% reduced flow by 95%.
FIGURE 4 Collapsible tube.
Results of Experiment 1
In experiment 1, mean flow rate was measured as a function
of the mean area reduction (Table 1). The greater the area was
reduced, the greater the flow was reduced. However, the as-
sociation was parabolic and not linear. The curved association
between area reduction and flow rate began without area re-
duction (no compression in that the lumen is fully open) and
moved to an area reduction of 75% (compressed to become
75% closed), as flow rate decreased steadily but not steeply.
Thereafter, with further reductions in area, flow rate decreased
more steeply to become nearly straight down near 95% (Fig-
ure 3). For this one vessel as tested, when flow was reduced
by 59% and 95%, the lumen was closed 94% and 97%, re-
spectively. Only large (>50%) reductions in area led to large
(>50%) reductions in flow; smaller reductions in area led to
smaller reductions in flow. Flow nearly stopped only when the
vessel was almost fully closed.
TABLE 1 Resulting Changes in Flow Rate by Changes in Area
Area Reduction
Reduction of Lumen
Number Mean Flow Mean in Mean Compared With
of Flow Rate (mL/s, Flow Rate Flow Rate No Compression
Tests mean ± SE) (%) (%) (%)
6 63 ± 1 100 0 0
6 48 ± 1 76 24 68
6 46 ± 1 73 27 74
6 38 ± 0.3 60 40 81
6 37 ± 0.2 59 41 85 The collapsible tube (red tube at top) was buckled under the com-
pressing pipes (at far left top, a yellow pipe opening is seen clamped
6 26 ± 0.2 41 59 94 between two gray metal presses), but that degree of buckling contin-
6 3 ± 0.04 5 95 97 ued downstream as collapse of the tube to the right beyond the end of
SE is the standard error, a calculated measure of variability. Area re- the two compressing pipes (another pipe is hidden behind the collaps-
ible tube) until the tube connected to the yellow drainage tubing (at
duction is an effect caused by compression of the artery lumen.
right). Turbulent flow within the tube downstream of the compression
was visible as a flutter of the wall and felt when the external wall was
By design, the wall was buckled inward where compression lightly touched.
was applied. However, during each test, that degree of buck-
ling also continued downstream in the tube despite there being (Figure 5), representing a range of values for first-aid interven-
no downstream compression. Buckling ended where the tube tions to control bleeding.
connected to the rigid drainage tubing (Figure 4).
Mean flow rate was associated by length in a one-way ANOVA
Experiment 2: which was used both among the three lengths and also among
Flow Changes by Changes in Length of Compression the control group with the three lengths. Tukey’s method was
In experiment 2, the setup differed in two ways. The lengths used to determine if differences were significant.
of compression varied but the luminal area was constant at
26% (the lumen was 26% open compared with the area in the The mean flow rate for the compressed lumens significantly
control group; that is, there was a 74% area reduction). The decreased by 32% compared with the uncompressed con-
lengths of compression used were 5mm, 20mm, and 70mm trol group (p < .05). For the three lengths of compression,

Collapsible Tube Model of Bleeding Control | 49