title: Tourniquet constriction exacerbates hyperalgesia-related pain induced by intradermal capsaicin injection.
abstract: BACKGROUND
  When capsaicin is injected intradermally, hyperalgesia develops around the injection site. The authors observed that volunteers report painful sensations in the skin remote from the injection site during tourniquet constriction of the affected extremity.
  
  
  METHODS
  Each volunteer received an intradermal injection of capsaicin on the volar forearm, followed by intermittent tourniquet constriction of the extremity. In some participants, the tourniquet position was rotated between different sites on the upper extremities. Laser Doppler measurements were made in the skin to measure capillary blood flow during pain magnification.
  
  
  RESULTS
  Hyperalgesia developed in the volunteers who were tested after the capsaicin injection. Blood flow increased three times in the dermal capillaries remote from the injection site after capsaicin injection. The tourniquet-induced pain reached peak intensity soon after tourniquet inflation. Tourniquet constriction of the arm on the affected side reliably induced painful exacerbation in each person tested. The quality of the sensation was described as burning and extended across the arm in most volunteers. Only when pinprick hyperalgesia was detectable did the volunteers experience the diffuse, immediate pain sensation. The pain initiated by the tourniquet constriction likely is related to changes in skin capillary blood flow.
  
  
  CONCLUSIONS
  Low cutaneous blood perfusion is related to the intensity of ongoing, spontaneous pain when secondary hyperalgesia is present. The specific trigger(s) have yet to be identified.
authors.affiliation: Pain and Neurosensory Mechanisms Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland, USA. Michael_Byas-smith@emory.org
authors.forename: M G
authors.initials: MG
authors.lastname: Byas-Smith
authors.forename: G J
authors.initials: GJ
authors.lastname: Bennett
authors.forename: R H
authors.initials: RH
authors.lastname: Gracely
authors.forename: M B
authors.initials: MB
authors.lastname: Max
authors.forename: E
authors.initials: E
authors.lastname: Robinovitz
authors.forename: R
authors.initials: R
authors.lastname: Dubner
mesh_terms: D000279:Administration, Cutaneous; D000328:Adult; D002196:Capillaries / Q000502:physiology; D002211:Capsaicin / Q000494:pharmacology*; D005260:Female; D006801:Humans; D006930:Hyperalgesia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000209:etiology*; D010147:Pain Measurement; D012039:Regional Blood Flow; D012867:Skin / Q000098:blood supply*; D014111:Tourniquets
chemical_list: D002211:Capsaicin