title: Evaluation of a Prototype Hybrid Vacuum Pump to Provide Vacuum-Assisted Suspension for Above-Knee Prostheses.
abstract: Vacuum-assisted suspension (VAS) of prosthetic sockets utilizes a pump to evacuate air from between the prosthetic liner and socket, and are available as mechanical or electric systems. This technical note describes a hybrid pump that benefits from the advantages of mechanical and electric systems, and evaluates a prototype as proof-of-concept. Cyclical bench testing of the hybrid pump mechanical system was performed using a materials testing system to assess the relationship between compression cycles and vacuum pressure. Phase 1 in vivo testing of the hybrid pump was performed by an able-bodied individual using prosthesis simulator boots walking on a treadmill, and phase 2 involved an above-knee prosthesis user walking with the hybrid pump and a commercial electric pump for comparison. Bench testing of 300 compression cycles produced a maximum vacuum of 24 in-Hg. In vivo testing demonstrated that the hybrid pump continued to pull vacuum during walking, and as opposed to the commercial electric pump, did not require reactivation of the electric system during phase 2 testing. The novelty of the hybrid pump is that while the electric system provides rapid, initial vacuum suspension, the mechanical system provides continuous air evacuation while walking to maintain suspension without reactivation of the electric system, thereby allowing battery power to be reserved for monitoring vacuum levels.
authors.affiliation: Jesse Brown VA Medical Center, Northwestern University Prosthetics-Orthotics Center, 680 North Lake Shore Drive, Suite 1100, Chicago, IL 60611 e-mail:  matthew-major@northwestern.edu.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Major
authors.affiliation: Scheck and Siress Orthotics and Prosthetics, Northwestern University Prosthetics-Orthotics Center, 680 North Lake Shore Drive, Suite 1100, Chicago, IL 60611 e-mail:  ryan.caldwell@northwestern.edu.
authors.forename: Ryan
authors.initials: R
authors.lastname: Caldwell
authors.affiliation: Northwestern University Prosthetics-Orthotics Center, 680 North Lake Shore Drive, Suite 1100, Chicago, IL 60611 e-mail:  s-fatone@northwestern.edu.
authors.forename: Stefania
authors.initials: S
authors.lastname: Fatone
keywords: prosthesis; socket; suspension; vacuum