The effect of heart rate variability on blood pressure is augmented in spinal cord injury and is unaltered by exercise training

Clin Auton Res, 2021 · DOI: 10.1007/s10286-020-00677-2 · Published: April 1, 2021

Simple Explanation

Spinal cord injury (SCI) affects not only motor and sensory functions but also autonomic control, leading to issues like orthostatic hypotension and autonomic dysreflexia. Heart rate variability (HRV) and blood pressure variability (BPV) are linked; lower HRV is associated with cardiovascular disease, while higher BPV is linked to cardiac and vascular damage. This study investigates how SCI alters HRV, BPV, and their interaction, and whether exercise training can improve these variabilities in individuals with SCI.

Study Duration

6 Months

Participants

40 individuals with SCI and 22 uninjured controls

Evidence Level

Not specified

Key Findings

1
Individuals with SCI exhibited significantly lower LF and HF HRV, as well as LF BPV, compared to uninjured controls.
2
The HF phase relationship between pressure and heart rate differed significantly; SCI individuals showed a feedback mechanism, while controls showed a feedforward mechanism.
3
Six months of whole-body exercise increased mean VO2peak, but did not significantly alter HRV, BPV, or their cross-spectral relationships in individuals with SCI.

Research Summary

The study defines differences in heart rate and blood pressure variability (HRV/BPV) after spinal cord injury (SCI) compared with uninjured controls, and determines if variabilities are impacted by whole-body exercise after SCI. After SCI, marked frequency-specific differences exist in the relationship between heart rate and blood pressure variabilities. The high-frequency cross spectral relationship indicates a feedback mechanisms of blood pressure into heart rate may predominate in this range.

Practical Implications

Cardiovascular Risk Assessment

BPV and its interaction with HRV could potentially be considered an important component for cardiovascular risk assessment in SCI.

Autonomic Control Assessment

Assessing autonomic control in those with SCI may be an important clinical assessment in addition to standard motor and sensory testing.

Targeted Interventions

Further research is needed to determine effective interventions for improving HRV and BPV in individuals with SCI, considering the ineffectiveness of standard exercise training.

Study Limitations

1
The study acknowledges that neurological level of injury (based on bedside motor and sensory testing) may not reliably encompass autonomic deficits after SCI.
2
The study mentions that the lack of HRV and BPV improvement may have been due to insufficient intensity of the whole-body exercise.
3
Individuals with SCI may have varied degrees of spared autonomic regulation.

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