The Variable Vector Countermeasure Suit (V2Suit) for space habitation and exploration

Neurosurgery and spinal adaptations in spaceflight: A literature review

BACKGROUND

Spaceflight places astronauts in multiple environments capable of inducing pathological changes. Alterations in the spine have a significant impact on astronauts' health during and after spaceflight. Low back pain is an established and common intra-flight complaint. Intervertebral disc herniation occurs at higher rates in this population and poses significant morbidity. Morphological changes within intervertebral discs, vertebral bodies, and spinal postural muscles affect overall spine function and astronaut performance. There remains a paucity of research related to spaceflight-induced pathologies, and currently available reviews concern the central nervous system broadly while lacking emphasis on spinal function.

OBJECTIVE

Our aim was to review and summarize available data regarding changes in spinal health with exposure to spaceflight, especially focusing on effects of microgravity. The authors also present promising diagnostic and treatment approaches wherein the neurosurgeon could positively impact astronauts' health and post-flight outcomes.

MATERIALS AND METHODS

Articles included in this review were identified via search engine using MEDLINE, PubMed, Cochrane Review, Google Scholar, and references within other relevant articles. Search criteria included "spine and spaceflight", "vertebral column and spaceflight", "vertebral disc and spaceflight", and "muscle atrophy and spaceflight", with results limited to articles written in English from 1961 to 2020. References of selected articles were included as appropriate.

RESULTS

Fifty-six articles were included in this review. Compositional changes at the intervertebral discs, vertebral bone, and paraspinal muscles contribute to undesirable effects on astronaut spinal function in space and contribute to post-flight pathologies. Risk of intervertebral disc herniation increases, especially during post-flight recovery. Vertebral bone degeneration in microgravity may increase risk for herniation and fracture. Paraspinal muscle atrophy contributes to low back pain, poorer spine health, and reduced stability.

CONCLUSION

Anatomical changes in microgravity contribute to the development of spinal pathologies. Microgravity impacts sensory neurovestibular function, neuromuscular output, genetic expression, among other systems. Future developments in imaging and therapeutic interventions may better analyze these changes and offer targeted therapeutic interventions to decrease the burden of pain and other diseases of the spine in this population.

Considerations for Wearable Sensors to Monitor Physical Performance During Spaceflight Intravehicular Activities

Wearable sensors provide the capability to noninvasively monitor physiological parameters during spaceflight, including those related to physical performance and daily activity. Regular monitoring of general health and exercise capabilities in astronauts can ensure adequate performance levels and record health changes caused by the space environment. Relevant measurables include vital signs, cardiovascular health, and activity monitoring. Wearable sensor devices can be comfortable for long-term use and easy to operate, which is particularly important during more autonomous future planetary missions. Many devices are currently being developed and tested, but few wearable devices or integrated "smart" garments have been assigned for regular use on the International Space Station. The unique needs of the space environment must be considered to facilitate the development and implementation of wearable devices, particularly "smart" sensor garments, for space applications.

Biarticular muscles are most responsive to upper-body pitch perturbations in human standing

Balancing the upper body is pivotal for upright and efficient gait. While models have identified potentially useful characteristics of biarticular thigh muscles for postural control of the upper body, experimental evidence for their specific role is lacking. Based on theoretical findings, we hypothesised that biarticular muscle activity would increase strongly in response to upper-body perturbations. To test this hypothesis, we used a novel Angular Momentum Perturbator (AMP) that, in contrast to existing methods, perturbs the upper-body posture with only minimal effect on Centre of Mass (CoM) excursions. The impulse-like AMP torques applied to the trunk of subjects resulted in upper-body pitch deflections of up to 17° with only small CoM excursions below 2 cm. Biarticular thigh muscles (biceps femoris long head and rectus femoris) showed the strongest increase in muscular activity (mid- and long-latency reflexes, starting 100 ms after perturbation onset) of all eight measured leg muscles which highlights the importance of biarticular muscles for restoring upper-body balance. These insights could be used for improving technological aids like rehabilitation or assistive devices, and the effectiveness of physical training for fall prevention e.g. for elderly people.

Assisting gait with free moments or joint moments on the swing leg

Wearable actuators in lower-extremity active orthoses or prostheses have the potential to address a variety of gait disorders. However, whenever conventional joint actuators exert moments on specific limbs, they must simultaneously impose opposing reaction moments on other limbs, which may reduce the desired effects and perturb posture. Momentum exchange actuators exert free moments on individual limbs, potentially overcoming or mitigating these issues.We simulate unperturbed gait to compare conventional joint actuators placed on the knee or hip of the swing leg, and equivalent angular momentum exchange actuators placed on the shank or thigh. Our results indicate that, while conventional joint actuators excel at increasing toe clearance when assisting knee flexion, free moments can yield greater increases in stride length when assisting knee extension or hip flexion.

The Variable Vector Countermeasure Suit (V2Suit) for space habitation and exploration

The “Variable Vector Countermeasure Suit (V2Suit) for Space Habitation and Exploration” is a novel system concept that provides a platform for integrating sensors and actuators with daily astronaut intravehicular activities to improve health and performance, while reducing the mass and volume of the physiologic adaptation countermeasure systems, as well as the required exercise time during long-duration space exploration missions. The V2Suit system leverages wearable kinematic monitoring technology and uses inertial measurement units (IMUs) and control moment gyroscopes (CMGs) within miniaturized modules placed on body segments to provide a “viscous resistance” during movements against a specified direction of “down”—initially as a countermeasure to the sensorimotor adaptation performance decrements that manifest themselves while living and working in microgravity and during gravitational transitions during long-duration spaceflight, including post-flight recovery and rehabilitation. Several aspects of the V2Suit system concept were explored and simulated prior to developing a brassboard prototype for technology demonstration. This included a system architecture for identifying the key components and their interconnects, initial identification of key human-system integration challenges, development of a simulation architecture for CMG selection and parameter sizing, and the detailed mechanical design and fabrication of a module. The brassboard prototype demonstrates closed-loop control from “down” initialization through CMG actuation, and provides a research platform for human performance evaluations to mitigate sensorimotor adaptation, as well as a tool for determining the performance requirements when used as a musculoskeletal deconditioning countermeasure. This type of countermeasure system also has Earth benefits, particularly in gait or movement stabilization and rehabilitation.