Introduction: Because all aspects of human physiology are affected by microgravity, an integrated countermeasure approach is warranted. The aim of this proposal is to finalize and further validate our prototype of an intravehicular mobile countermeasure suit, which consists of lower body negative pressure (LBNP) trousers and vest to reproduce the effects of gravitational stress during spaceflight. This mobile “Gravity Suit” aims to be: 1) Comfortable enough to allow for use for several hours per day, which entails monitoring and some form of regulation of the internal environment (temperature and humidity); 2) Not interfere with everyday in-flight activities, which entails being slim enough to allow for movement around the station and to be mobile and un-tethered, i.e., to have a mobile battery-operated vacuum system; 3) be flexible enough to be combined with some forms of exercise and movement, which entails ability to flex the knee and hip to at least 90 degrees.
Background: LBNP was used as early as the Apollo program through Skylab and Mir (Hoffler et al. 1977, Iwasaki et al. 2007). Currently the Russian LBNP device (“Chibis”) is available on International Space Station (ISS). Several indications point to beneficial multi-system effects. To make LBNP feasible as a countermeasure, we created a wearable, untethered, mobile, and flexible device.
Aim: To test that the suit induces caudal fluid shift as know from “classic rigid LBNP” devices (Petersen et al. 2019) and in addition to that it provides mechanical loading of the body which could potentially be beneficial for the musculoskeletal system.
Materials and Methods: We have designed and built a wearable LBNP device consisting of a set of trousers that can be pressurized with a seal created at the iliac crest and attached “boots” that support ground reaction forces. The mechanical loads are carried to the shoulders by means of the attached vest to provide mechanical loading to the entire axial length of the body. Negative pressure is generated by a portable vacuum powered by a rechargeable battery. Following Institutional Review Board (IRB) approval 8 healthy subjects were included in initial testing. Mechanical loading was quantified as ground reaction forces (GRF) under the sole of each foot using force sensors (Tekscan, USA) and on the shoulders under the vest. Caudal fluid shift was assessed from the reductions in internal jugular venous cross-sectional area (IJVa) using ultrasounds (treason t3200, treason, USA). Continuous cardiovascular profile was recorded using the volume-clamp method from a finger cuff (Nexfin, BMeye, The Netherlands) and presented as 1 min average following 5 minutes of rest at each condition. Range of motion was recorded as maximum comfortable angle of flexion of the hip and knees from the normal position. Incremental LBNP from 0 to 40 mmHg at increments of 10 mmHg were applied while subjects were resting in a suspended supine position. Following completion of the incremental protocol, LBNP was set at 20 mmHg and range of motion at this level was recorded.
Results: Relative to normal body weight (BW) when standing upright, increments of 10 mmHg LBNP from 0 to 40 mmHg whilst supine generated incremental axial mechanical loading of the body with around 35 mmHg generating close to one bodyweight. Caudal fluid displacement was indicated by the significant reduction of IVJa while cardiovascular parameters were well maintained (P > 0.05) with the exception of stroke volume (SV) which decreased at 40 mmHg, and which was accompanied by a non-significant increase in heart rate (HR). Mean arterial blood pressure (MAP) was maintained throughout the incremental LBNP protocol. Range of motion across the hip and knee joints was measured and confirmed to reach 90 degrees.
Discussion: LBNP is a potential countermeasure to reverse the cranial fluid shift associated with weightlessness. In the first year of this omnibus project, we have demonstrated that a caudal fluid shift and mechanical loading can be achieved using a wearable mobile LBNP suit.
Limitations: An important limitation is the restricted dimensions of the suit which only allowed for inclusion of subjects with a limited waist-, hip-, and leg-circumference and length of the legs. Ongoing efforts are directed toward including subjects of varying size and further investigating the effects of LBNP in combination with GRF.
Hoffler WG, Johnson P, Nicogossian AE, et al Vectorcardiographic Results From Skylab Medical Experiment M092: Lower Body Negative Presure. In: Biomedical results from Skylab. Scientific and Technical Information Office, National Aeronautics and Space Administration, Washington, D.C., pp 313–323, 1977
Iwasaki K,Levine BD, Zhang R, Zuckerman JH, Pawelczyk JA, Diedrich A, Ertl AC, Cox JF, Cooke WH, Giller CA, Ray CA, Lane LD, Buckey JC Jr, Baisch FJ, Eckberg DL, Robertson D, Biaggioni I, Blomqvist CG. Human cerebral autoregulation before, during and after spaceflight J Physiol. 579:799-810. 2007
Petersen LG, Lawley JS, Lilja-Cyron A, Petersen JCG, Howden EJ, Sarma S, Cornwell WK, Zhang R, Whitworth LA, Williams MA, Juhler M, Levine BD. Lower Body Negative Pressure To Safely Reduce Intracranial Pressure. J Phys 597:237-248, 2019.
Abstracts for Journals and Proceedings
Petersen LG, Hargens A, Levine B. "Mobile Negative Pressure Suit as an Integrative Countermeasure." Poster, 2019 NASA Human Research Program Investigators’ Workshop, Galveston, TX, January 22-25, 2019.
Abstracts. 2019 NASA Human Research Program Investigators’ Workshop, Galveston, TX, January 22-25, 2019. , Jan-2019