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Clinical Lower Body Negative Pressure Chamber
Clinical Lower Body Negative Pressure Chamber
A Non-Invasive Medical Device for Lowering Intracranial Pressure
Sponsored by: Dr. Lonnie Petersen, Dr. Allen Hargens, Dr. Jeffery Steinberg
Lower Body Negative Pressure Chamber
Background
Lower body negative pressure chambers (LBNPC) are being tested as a non invasive method to reduce intracranial pressure after a traumatic brain injury. By reducing air pressure around the lower body to just -30mmHg, the brain will see a dramatic drop in pressure and can reduce the need for drugs or instances of craniotomies. LBNPC's have been in use since the 1980's for research purposes and were first used with MRI's to simulate brain pressure of an upright person while lying flat for scans. Further research is needed to test the effectiveness of LBNP on persons with high intracranial pressure (ICP) due to injury. If injured patient trials are successful this device may be used in hospitals to lower ICP non-invasively.
An existing LBNP design for use on healthy patients
Objectives
Prototype LBNP devices exist but they are bulky, hard to control pressure, and are nearly impossible to put an incapacitated person into. The objective of this project is to create a chamber for use in a hospital setting that can be assembled around a patient on a hospital bed, easily stored, sanitized, and is comfortable for a patient over long periods of use.
Design, build an test an LBNP that can sustain a pressure of -4 kPa for several hours
Pressure must be adjustable in increments of 0.5 kPa from 0 to -4 kPa
Easily sanitized
Safe
Portable
Easy to operate
Compatible with existing ICU hospital beds
Deliverables
Functional prototype of a portable LBNP chamber
LBNP fabric shell with pressure transducer and vacuum connection
Bill of Materials
CAD Files
Design Blueprints
User Manual
Design
Our design will be portable and easy to bring to a patient in a hospital bed. A lighter polycarbonate internal structure will support an airtight fabric shell that can be placed under the patient without removing the patient from the bed. The airtight shell will have an upper transparent dome to make monitoring the patient easier. Removal can be done quickly by unzipping the shell and lifting off the internal frame.
The internal frame is made entirely of polycarbonate and nylon keeping it light weight and MRI compatible. The support structure poles (Nylon Rods) rest in cutouts in the polycarbonate allowing for easy assembly on top of a patient. This design also reduces the number of small and complicated components which are difficult to sanitize.
Full Assembly
The effectiveness of the LBNP will be measured by a flow meter and an electronic pressure transducer. Both relay information through an arduino to an LCD readout for live monitoring of conditions inside the LBNP. The pressure sensor is a PX26-005GV atmospheric differential pressure sensor, and the flow meter is a PC fan with an internal hall effect sensor, mounted between two 3D printed adapters for a connection inline with the vacuum system.
Performance Results
To test the LBNP, the maximum pressure obtainable along with the corresponding flow rate were desired, as well as the flow rate at a set pressure of -4 kPa. To test both of these conditions, the neoprene seal was rolled up like a dry bag and clamped shut with a standard C clamp. First the vacuum was run at full power with no restriction with a ball valve. LBNP conditions stabilized at a gauge pressure of -4.8 kPa with a flow of 0.01 cubic meters per second. Next the ball valve was opened to allow some air to bypass the LBNP until the pressure stabilized at a gauge pressure of -4 kPa. The leaked air flow through the LBNP remained close enough to not register any change. The maximum pressure reached was higher than stated in the functional requirements, and the air leakage was above the minimum calculated to eliminate excess heat and humidity from inside the LBNP.
Results of pressure testing
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