Reduced Reflex Autonomic Responses Following Intradetrusor OnabotulinumtoxinA Injections: A Pre-/Post-study in Individuals With Cervical and Upper Thoracic Spinal Cord Injury

Frontiers in Physiology, 2021 · DOI: 10.3389/fphys.2021.796277 · Published: December 15, 2021

Simple Explanation

This study investigates how bladder injections of onabotulinumtoxinA affect heart rate responses during bladder function tests in people with spinal cord injuries. The aim was to see if these injections could improve the heart's regulation by the nervous system during these tests. Researchers measured heart rate variability (HRV), a marker of autonomic nervous system activity, before and after the injections. They found that the injections reduced the heart rate changes typically seen during bladder function tests, suggesting an improvement in autonomic cardiovascular function. These findings suggest that onabotulinumtoxinA injections may help improve the heart's response to bladder activity in individuals with spinal cord injuries, potentially reducing the risk of cardiovascular complications during routine procedures.

Study Duration

Between November 2014 and December 2019

Participants

19 participants with chronic SCI (5 women, mean age 42.5 ± 7.9 years)

Evidence Level

Level IV clinical trial, Pre-/Post-study

Key Findings

1
UDS pre-treatment resulted in increased RR-interval as well as time and frequency domain metrics of HRV, indicating a parasympathetic response to bladder filling.
2
Post-treatment with onabotulinumtoxinA, UDS had no significant effect on RR-interval and significantly reduced instances of bradycardia, suggesting a reduced vagal response.
3
Intradetrusor onabotulinumtoxinA injections significantly reduced time domain metrics of HRV and HF power responses to UDS across all participants, indicating improved autonomic cardiovascular function.

Research Summary

The study investigated the impact of intradetrusor onabotulinumtoxinA injections on heart rate variability (HRV) responses during urodynamic studies (UDS) in individuals with cervical and upper thoracic spinal cord injury (SCI). The findings demonstrated that bladder filling during UDS increased reflex parasympathetic activation, as assessed by HRV, and that intradetrusor onabotulinumtoxinA injections ameliorated this response. The study provides evidence that HRV is correlated with both autonomic dysreflexia (AD) and UDS metrics, suggesting it may be a useful monitoring tool for early prediction of AD during UDS.

Practical Implications

Improved Autonomic Control

Intradetrusor onabotulinumtoxinA injections can improve autonomic cardiovascular function by reducing reflex vagal responses to bladder filling during urodynamic studies.

Reduced Cardiovascular Risk

Minimizing reflex autonomic responses associated with UDS through onabotulinumtoxinA injections may reduce the risk of cardiovascular complications in individuals with SCI.

HRV as a Monitoring Tool

Heart rate variability monitoring during UDS may serve as a useful tool for early prediction of autonomic dysreflexia events.

Study Limitations

1
Respiratory rate was not controlled, which can have a significant effect on HRV.
2
The sample size may not be adequately powered to determine the sensitivity and specificity of HRV as a predictor of AD.
3
A larger sample size including a wider array of injury levels would improve the study's generalizability.

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