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The impact of spinal cord injury on cardiorespiratory interactions: cardiovascular responses to sleep apnea and models of disordered breathing

In addition to motor and sensory deficits, individuals with spinal cord injury (SCI) often experience impaired autonomic function with dysregulation of breathing, heart rate, and blood pressure. Despite the alarmingly high prevalence (~77%) of sleep disordered breathing in populations with SCI, the cardiovascular consequences remain unclear. My thesis investigates cardiorespiratory interactions in individuals with SCI in laboratory and sleep contexts.

First, a community survey was conducted and authenticated to examine SCI-specific sleep disturbances, outcomes, and access to care. From these insights, the incidence of sleep disturbances emerged as a key determinant of global sleep health.

Then, cardiorespiratory interactions were assessed during wakefulness and sleeping. Voluntary changes in breathing rate during standard cardiovascular autonomic monitoring revealed the impact of autonomic severity of injury on baroreflex and cardiorespiratory interactions.

Further, using a novel biometric wearable system, an at-home sleep study captured episodes of sleep disordered breathing, characterised the cardiovascular responses to desaturations, and ultimately evaluated the cumulative impact of cardiorespiratory dysfunction over a night of sleep.

Finally, considering SDB as a source of hypoxic burden, an end-tidal forcing system elucidated the impact of autonomic injury on the cerebrovascular and ventilatory responses to hypoxia, finding insensitivity of both the hypoxic ventilatory response and cerebrovascular response to hypoxia to be related to the autonomic severity of injury.

Through complementary explorations of cardiorespiratory paradigms in people with SCI, this thesis contributes novel mechanistic and community insight into the complex relationships between autonomic regulation, sleep disordered breathing, adverse cardiovascular events, and impaired quality of life to inform clinical priorities for those living with SCI.