Daily acute intermittent hypoxia combined with walking practice enhances walking performance but not intralimb motor coordination in persons with chronic incomplete spinal cord injury

Brief exposure to systemic hypoxia enhances plasticity of the central nervous system in spinal cord injured animals and man

“…Similarly, in humans, daily AIH combined with conventional rehabilitation therapy, such as over ground walking or treadmill training augments locomotor function (e.g. walking speed and endurance) beyond that achieved with either intervention applied separately [17,18,19 ▪ ]. These results suggest that training is a crucial component for maximizing the benefits of daily AIH therapy.…”

“…Even though these studies report a wide range in response, including a significant proportion of nonresponders, the overall assessment was that intermittent hypoxia combined with some form of physical training produced a net effect that was usually greater than either hypoxia or exercise alone [17,18,19 ▪ ]. Over the years, this protocol has been replicated in various ways, with relatively consistent results indicating increased motor outflow, manifested either as changes in maximum voluntary strength or in gait speed or endurance when patients were exposed to AIH [18,19 ▪ ,20,21 ▪ ,22–24]. More recently, these observations in paraplegic individuals have been replicated in persons with incomplete cervical injury, that is, in patients with quadriplegia [25 ▪ ,26].…”

“…Hypoxia of this level and duration is almost indiscernible, and patients are unable to notice that they are breathing air with reduced oxygen levels. Clinical studies using a single AIH session or multiple sessions up to 14 sessions have been published [16–18,19 ▪ ,20,21 ▪ ,22,25 ▪ ,26,29]. There have been no reports of adverse events in either cardiovascular or cerebral vascular function.…”

“…There have been a number of publications reporting on the potential beneficial effects of AIH in persons with chronic, incomplete SCI [16–18,19 ▪ ,20,22,24,25 ▪ ,26,50]. These interventions have combined AIH with locomotor training, or with training of upper extremity function.…”

Effects of acute intermittent hypoxia on corticospinal excitability within the primary motor cortex

“…In animals, AIH can trigger endogenous mechanisms upregulating the expression of various neurotransmitters and neurotrophic factors (Prabhakar, 2001 ; Gangwar et al 2020 ). Several AIH studies investigating changes in the human CNS have focussed on patients with spinal cord injury and demonstrated chronic benefits for walking speed and endurance in individuals with incomplete lesions (Lovett-Barr et al 2012 ; Oudega and Perez 2012 ; Sandhu et al 2021 ; Sutor et al 2021 ; Tan et al 2021 ) with recent studies focusing on changes in corticospinal excitability following AIH (Christiansen et al 2018 , 2021 ; Welch et al 2021 ). However, the acute effects of AIH on the CNS, specifically regarding corticospinal function, remain largely unknown.…”