August 2019; Vol. 44; No. 15; pp. E914–E926
Brigitte Wirth, PT, PhD, Antonia Gassner, M Chiro Med, Eling D. de Bruin, PT, PhD, Iben Axen, DC, PhD, Jaap Swanenburg, PT, PhD, Barry Kim Humphreys, DC, PhD, Petra Schweinhardt, MD, PhD.
Spinal manipulative therapy (SMT) with a high velocity low amplitude thrust (HVLA-SMT) is a widely employed technique in manual therapy, particularly for managing back pain. Despite its effectiveness in alleviating pain, the underlying mechanisms of action have remained elusive. A recent systematic review, encompassing controlled studies of at least moderate quality, delves into the neurophysiological effects of HVLA-SMT in both asymptomatic and symptomatic individuals.
Key Points from the Study:
- Prevalence of HVLA-SMT:
- HVLA-SMT is a frequently utilized technique in manual therapy, commonly employed by healthcare professionals.
- Efficacy in Back Pain Management:
- While HVLA-SMT is effective in reducing back pain, the exact mode of its therapeutic action remains incompletely understood.
- Recommended for Specific Conditions:
- HVLA-SMT is recommended for the management of acute and chronic nonspecific low back pain (LBP) and disc herniation with radiculopathy, underscoring its clinical relevance.
- Dual Influences of HVLA-SMT:
- HVLA-SMT likely exerts both neurophysiological and biomechanical influences, contributing to its therapeutic effects.
- Insights from Animal Studies:
- Animal studies suggest that spinal manipulation-like forces increase the discharge frequency of proprioceptive afferents and inhibit sympathetic outflow, indicating broader effects beyond human subjects.
- Mechanical Force and Neurophysiological Responses:
- The mechanical force of HVLA-SMT primarily affects afferent neurons in paraspinal tissue, triggering neurophysiological responses in the peripheral and central nervous system, ultimately leading to pain inhibition.
- Biological Changes Induced by HVLA-SMT:
- HVLA-SMT induces changes in pressure pain thresholds and alters levels of Substance-P, neurotensin, oxytocin, interleukin, and cortisol, showcasing its multifaceted impact on biological processes.
- Focus on the Autonomic Nervous System:
- The majority of reviewed studies focused on the effects of HVLA-SMT on the autonomic nervous system, employing various proxy measures such as blood pressure, ECG parameters, oxygen saturation, heart rate, HRV, pupil diameter, and skin conductance.
- Sympathetic-Vagal Balance and HRV:
- Evidence suggests that HVLA-SMT influences sympathetic-vagal balance, with a consistent effect observed in changes to the sympathetic to parasympathetic ratio measured through HRV.
- Spinal Level Specificity:
- The effects of HVLA-SMT on the autonomic nervous system vary depending on the spinal level of application, particularly distinguishing between upper cervical and lower spinal applications.
- Differential Effects in Pain Patients:
- The study highlights potential differences in the effects of HVLA-SMT between healthy volunteers and pain patients, as well as variations between chronic and acute pain conditions.
- Systematic Review Insights:
- The systematic review underscores the impact of HVLA-SMT on the autonomic nervous system, with effects contingent on the spinal level of application and potential variations in different patient populations.
In conclusion, this comprehensive study sheds light on the intricate neurophysiological effects of HVLA-SMT, offering valuable insights that pave the way for a deeper understanding of its therapeutic mechanisms and tailored applications in clinical practice.