title: Transient hyperaemic response to assess vascular reactivity of skin; effect of locally iontophoresed sodium nitroprusside.
abstract: BACKGROUND
  We aimed to study if brief compression (20 s) of the brachial artery could provoke a hyperaemic response in forearm skin. In addition, we studied the effect of pre-dilating the skin vessels with locally iontophoresed sodium nitroprusside on the hyperaemic response.
  
  
  METHODS
  Ten healthy male volunteers were studied. A custom-made perspex iontophoresis chamber was attached to the anterior aspect of the distal forearm; this chamber allowed simultaneous administration of drugs by iontophoresis and measurement of skin blood flow flux by the laser Doppler probe. The flow flux signal, measured in volts, was continuously recorded onto a paper chart recorder. Three control transient hyperaemic response (THR) tests were performed by releasing the manual occlusion of the brachial artery maintained for 20 s. Thereafter, 2% sodium nitroprusside was iontophoresed using a current of 100 mAmp for 240 s. The THR tests were repeated three more times. From the recordings, baseline blood flow flux immediately before the onset of compression (or F1) and maximum blood flow flux immediately after the release of compression (or F2) were taken for analysis. The THR ratio (THRR) was calculated as: THRR = F2/F1. Average values of F1 and THRR were taken from the tests before and after iontophoresis and a paired t-test was used for analysing the changes.
  
  
  RESULTS
  Nine of the 10 subjects showed a hyperaemic response at the release of compression. Iontophoresis of sodium nitroprusside significantly increased the baseline flow flux from 0.77 (range 0.29-1.61) to 1.88 V (0.73-2.91). It also completely abolished the THR in all subjects; THRR decreased from 1.65 (1.00-2.78) to 1.00 (0.98-1.03).
  
  
  CONCLUSIONS
  A brief compression of the brachial artery results in a significant hyperaemic response in the forearm skin; this response is abolished by pre-dilatation of skin vessels. These findings support the hypothesis that the THR test assesses true vasodilatation occurring during arterial compression.
authors.affiliation: University Department of Anaesthesia and Intensive Care, University Hospital and City Hospital, Nottingham, UK.
authors.forename: V L
authors.initials: VL
authors.lastname: Webster
authors.forename: R P
authors.initials: RP
authors.lastname: Mahajan
mesh_terms: D000328:Adult; D001794:Blood Pressure; D001916:Brachial Artery / Q000502:physiology*; D005542:Forearm / Q000098:blood supply; D006801:Humans; D007478:Iontophoresis; D008297:Male; D009599:Nitroprusside / Q000494:pharmacology*; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D012867:Skin / Q000098:blood supply*; D014664:Vasodilation / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D014665:Vasodilator Agents; D009599:Nitroprusside