Page 51 - JSOM Spring 2018

Laboratory Model of a Collapsible Tube

to Develop Bleeding Control Interventions

Effects of Compression on Flow

Lanny V. Griffin, PhD ; John F. Kragh Jr, MD *; Michael A. Dubick, PhD 2
1
2

ABSTRACT
Background: To develop knowledge of mechanical control of tubes, steady flow, rheology, pressure, biomedical engineer-
bleeding in first aid, a laboratory model was set up to simu- ing; models, theoretical
late flow through a blood vessel. A collapsible tube was used
to mimic an artery in two experiments to determine (1) the
extent of volumetric flow reduction caused by increases in Introduction
the degree of compression of the vessel and (2) the extent of
flow reduction caused by increases in the length of compres- Limb-wound bleeding is often controllable in caregiving
sion. Methods: Water was used in vertical tubing. Gravity ap- through the compression of blood vessels above the wound.
1
plied a pressure gradient of about 100mmHg to cause flow. For example, a limb tourniquet can compress the underlying
A silicone tube (10mm-diameter lumen [the inner opening], skin and the arteries. Tubular vessels such as arteries generally
1mm-thick wall, 150mm length) was used. Tests of no com- run longitudinally in the limbs, and a circumferential tourni-
pression of the external wall constituted the control group for quet reliably compresses them. Collapsible tubes have consis-
2
both experiments. For all groups, flow volume was sampled tent mechanical traits, and their study has become a maturing
over a period of time, and six samples were averaged. In both field of biomechanical engineering called collapsible tube sci-
experiments, the study group consisted of tests with compres- ence. In this science, if the internal opening of a tube, such as
3
sion that was measured as the reduced area of the luminal cross the lumen of an artery, is caused to become small enough, fluid
section. In the first experiment, six groups with luminal area flow—that is, blood flow—through the obstructed area can be
reductions of 0% (control), 74%, 81%, 91%, 94%, and 97% reduced or stopped. 4
were tested. In the second experiment at 74% luminal area re-
duction, the three lengths of compression were 5mm, 20mm, Although collapsible tube science is advancing, its application
and 70mm. The measured data were compared with calculated to control bleeding in first aid is not one of its developed top-
data by applying established mathematical equations. Results: ics. Furthermore, such science is infrequently applied to clini-
In the first experiment, flow decreased with decreasing area cal medicine because it is a specialized field of engineering and
due to luminal compression, but the association was a para- thus is neither routinely applied to medicine nor commonly
bolic curve such that 94% or greater reduction in luminal area present in medical books. This awareness gap presents an
5,6
was required to reduce flow by greater than 50%. A reduction opportunity for both developing knowledge and improving
in luminal area of 97% reduced flow by 95%. In the second awareness of hemorrhage control. It is hoped that a developed
experiment, mean flow rates were not significantly different line of research will eventually improve understanding of how
among the three lengths of compression. Measured data and to optimally stop the bleeding. In this respect, the first attempt
calculated data were in good agreement. Conclusions: Com- we made was at simple interventions suitable for use by per-
pared with an uncompressed vessel, volumetric flow of water sons without training in first aid to compress large arteries.
through a single, unsupported collapsible tube in steady, non- The purpose of the present study is to determine the reduction
pulsatile conditions with compression applied to its external in flow caused by increasing degrees of compression on the
wall to produce a reduction in luminal area of 97% reduced lumen and by increasing lengths of compression.
flow by 95%. Flow was affected by the degree of compression
but not by the length of compression.
Methods
Keywords: first aid/therapy, tourniquet; hemorrhage, preven- This study was conducted according to the guidelines of a proto-
tion and control, bleeding control; biomechanics, collapsible col that involved experimentation that compared interventions
*Address correspondence to 3698 Chambers Pass, Joint Base San Antonio Fort Sam Houston, TX 78234-7767; or john.f.kragh.civ@mail.mil
1 LTC Griffin is a professor of biomedical engineering at California Polytechnic State University, San Luis Obispo, CA, and an engineer in the US
Army Reserves. Drs Kragh and Dubick are at the US Army Institute of Surgical Research, where Dr Kragh is a researcher of bleeding control and
2
Dr Dubick is a resuscitation researcher and the manager of the Damage Control Resuscitation task area. Dr Kragh also is an associate professor
in the Department of Surgery, Uniformed Services University of the Health Sciences, Bethesda, MD.
47