Heart rate variability after spinal cord injury

Abstract

In addition to motor and sensory dysfunction, a spinal cord injury (SCI) can lead to disruption of the autonomic nervous system (ANS). The ANS contributes to the regulation of multiple internal body functions, such as respiration, blood pressure, heart rate, and peristalsis. Disruption of such a system can lead to sometimes serious and often debilitating complications, including autonomic dysreflexia, orthostatic hypotension, bladder incontinence, cognitive impairment, pain, and fatigue. These complications can have a substantial impact on quality of life, affecting areas such as physical independence, relationships, work, and leisure.

To support improvements in autonomic function, advances in the assessment and treatment of autonomic dysfunction are needed. Among the available autonomic assessment measures, heart rate variability (HRV) is a cardiac autonomic biomarker that assesses the activity of the ANS

at the sino-atrial node of the heart. Its non-invasive and accessible nature, as well as its ability to assess vagal (parasympathetic) regulation of the heart has made HRV a very popular autonomic biomarker.

Despite this, the assessment of HRV is far from standardised, leading to highly heterogeneous results and difficulty implementing it into a clinical setting. Subsequently, the effect of interventions on HRV, namely non-invasive, non-pharmaceutical (NINP) interventions, after SCI is unclear. HRV biofeedback (HRV-F), in particular, is an under-researched NINP intervention in adults with SCI, despite demonstrating positive cardiovascular and psychosocial outcomes in other chronic disease populations.

In light of this, this thesis aimed to address some of these barriers associated with the use of HRV in adults with SCI. Key issues related to the assessment of HRV and the effect of NINP interventions on HRV, particularly HRV-F, are explored over seven chapters, including five manuscripts.