Biophysical Agents & Pain Mechanisms

Nociceptive Pain

• Tissue is the issue

• Localized pain

• May be dull ache or throb at rest

• No night pain, dysesthesia, burning, shooting, or electric sensation

Peripheral Neuropathic Pain

• Nerve is the issue

• History of nerve injury, pathology, or mechanical compromise, cancer

• Pain referred in a dermatomal or cutaneous nerve distribution

• Provoked with mechanical testing (neurodynamic testing)

• Pins & needles or numbness

Nociplastic Pain

• Pain disproportionate to nature of injury 

• Central sensitization

• Unpredictable provocation & non-specific aggravating & easing factors

• Widespread pain 

• Maladaptive psychosocial factors 

• Pain catastrophization, anxiety, & depression 

How do you choose an intervention for your patient’s pain?

1. Subjective history, red flags, physical exam, outcome measures

2. Assess all biopsychosocial factors 

3. Identify primary driving pain mechanism

4. Consider sound evidence 

5. Choose best option for pt at that time

What are the main pain drivers of nociceptive pain?

• Immuno-inflammatory cascade (classic)

• Cytokines & chemokines

• Edema

• Post-op

What are potential biophysical agents to use for nociceptive pain?

• Cold therapy

• E-stim (NMES, TENS)

• Low-Light Laser Treatment (LLLT) or Photobiomodulation (PBM)

What are the main pain drivers of neuropathic pain?

• Immuno-inflammatory 

• Neurologic inflammation 

What are potential biophysical agents to use for neuropathic pain?

• E-Stim (TENS)

• Low Light Laser Treatment (LLLT)

Gamma-Aminobutyric Acid (GABA)

• Primary inhibitory NT of brain

• Major inhibitory NT in SC (modulates ion channels)

• E-Stim activates GABA → decrease pain

What are the main pain drivers of nociplastic pain?

• Immuno-inflammatory (acute)

• Neuro-inflammatory

• Centrally mediated

Gate Control Theory of Pain

• A-beta fibers = low threshold, fast, myelinated

  • Their activity activates inhibitory interneurons in dorsal horn → closes spinal gate → reduces/blocks pain transmission from C-fibers

• C-fibers = high threshold, slow, unmyelinated

  • Their activity inhibits the inhibitory interneurons → opens gate → increases pain transmission to brain

Updated Gate Control Theory of Pain

• Modulation is core concept 

• Primary afferents: 

  • low-threshold C-fibers = mechanoreceptors

  • high-threshold A-delta & A-beta fibers = nociceptors 

  • All primary afferents are excitatory 

• Dorsal horn complexity: 

  • Multiple inhibitory + excitatory interneurons

  • Several distinct projection neurons send signals to different brainstem & brain nuclei 

  • Non-neuronal cells actively contribute to pain processes 

• Descending modulation: brain exerts top-down control over spinal gating

• Endocrine involvement: hormones help inhibit pain 

• Immune involvement: T-cells & macrophages release opioid peptides that contribute to analgesia 

Cryotherapy

• Use of cold as therapeutic agent

• Locally → ice packs, ice massage, vapocoolant spray, gel packs

• Broadly → non-local application 

What are the general benefits of cryotherapy?

• Decrease vascular permeability

• Decrease pro-inflammatory cytokines

• Increases anti-inflammatory cytokines

• Decrease transmission velocity

• Induce analgesia

• Decrease oxidative stress

Nitrogen-Based Partial Body Cryotherapy

• Liquid nitrogen used to cool a cylindrical shaped chamber

• Gas enters from bottom at -150 - -200°

Whole Body Cryotherapy

• Electric

• Fresh, oxygenated air

• Temperature maintained at -150°

• Activates ANS → epi, norepi, & dopamine

• Higher cellular activation & mitochondrial biogenesis 

• Lowers oxidative stress 

Transcutaneous Neuromuscular Stimulation (TENS)

• Reduces hyperalgesia → activates large diameter afferent fibers → CNS → activates descending inhibitory systems

• High frequency → increase concentration of B-endorphins & methionine-enkephalin (CSF)

• Low frequency → activates opioid, GABA, & serotonin by reducing dorsal horn neuron activity

• Reduce central excitability

Low Level Laser Therapy (LLLT)

• Laser = light amplification by stimulated emission of radiation

• Molecular & cellular effects

• NOT for nociplastic pain