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Background:
Background:
During spaceflights, exposure to microgravity results in headwards shift of blood and cerebrospinal fluids. This phenomenon increases intracranial pressure and in prolonged spaceflight, which ultimately increases the risk of developing SANS. Symptoms of SANS or Spaceflight-Associated Neuro-Ocular Syndrome include damages to the ocular nerve, refractive changes in the eye, deterioration of body muscle, and impediments in neuromotor control.
Ongoing research solutions has shown the effectiveness of an LBNP device in countering headwards fluid shifts. An LBNP (lower body negative pressure) device generates weight bearing and gravitational blood pressures through negative pressure applied on the lower body and is used by astronauts in prolonged spaceflights to reduce discomforts relating to high intracranial pressures.
Objectives:
Objectives:
The project objective was to improve the current prototype, ensuring a solid pressure chamber will generate 20 - 25 mmHg of pressure without the use of external power sources. Reinforcements should be considered to prevent chamber collapse under pressure. For testing purposes, the goal is to maintain the negative pressure for more than 10 minutes. Finally, the prototype must work in supine position to best stimulate microgravity conditions for testing on earth.
Primary Requirements:
Chamber must generate around 20 to 25 mm Hg of negative pressure
Maintains negative pressure for at least 15 minutes for testing purposes
Must work in supine position to mimic microgravity conditions for on earth testings
Secondary Requirements:
Fully self generative
Chamber does not collapse
User comfortability
Wow Solution:
Maintains pressure for at least 30 minutes
Final Design:
Final Design:
The final design as seen in figure 1 features a 42 inch neoprene chamber bounded by a top and bottom plate made of stainless steel. The chamber is solid and airtight and works as an controlled volume. Negative pressure is generated when the user inside pushes on the bottom plate thus expanding the chamber. A neoprene waist seal encloses the lower body of the user inside the device and prevents air leakage when negative pressure is generated. The range of negative pressure generated is dependent on the rate at which the user expands the chamber.
Figure 1: Final Chamber Body Design
Key components for the design includes:
Reinforcement Rings
Reinforcement rings primarily functions to provide additional structural support to the neoprene chamber and to help prevent chamber collapse. Five 304L stainless steel rings are evenly fitted inside the chamber and stitched into place. The reinforced chamber is able to withstand up to 30 mmHg. Figure 2, 3 shows the FEA of the neoprene chamber collapse with and without the added reinforcement rings.
Figure 2: FEA of Chamber Without Reinforcement Rings
Figure 3: FEA of Chamber With Reinforcement Rings
Waist Seal
The waist seal is a critical component that prevents air leakage and pressure loss. The current seal uses neoprene fabric imbedded with a waist belt that can be fastened onto the user's waaist and works similarly to a corset. Foam pieces are added to the belt to form a tighter fit and waist size can accomodate up to 44 inches. Figure 4 shows the different iterations of the neoprene waist seal.
Figure 4: Old (left) and New (right) Prototype Waist Seal
Foot Straps
User comfortability is another critical part of the design process. Figure 5 shows the implementation of foot straps securely installed onto the bottom plate so that the user is able to more easily retract the chamber. Handles and shoulder straps are also installed to provide greater control of the whole device.
Figure 5: Foot Strap
Negative Pressure Results:
From the ultrasound images taken by Ryan Kassel using the LBNP chamber in figure 6, internal jugular vein cross section can be observed under different scenarios. The upright condition represents normal blood gradients within the user in regular gravity conditions and the supine condition represents blood gradients in microgravity conditions. Comparing the jugular vein size between the supine and the LBNP conditions, it is observed that the device is effective at decreasing the jugular vein size around 28.9 ~ 42%.
Figure 6: Internal Jugular Vein Cross Section under different scenarios
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