title: Local and remote thermoregulatory changes affect NIRS measurement in forearm muscles.
abstract: OBJECTIVE
  Near infrared spectroscopy (NIRS) assessment in skeletal muscle is potentially affected by circulatory changes occurring in superficial tissues. The aim of this study was to separately assess the interference from skin microcirculation and large vein blood flow by investigating the effect of selective local and remote warming-induced vasodilation, respectively.
  
  
  METHODS
  Blood volume and oxygenation changes were investigated in the forearm muscles of healthy subjects in two experimental series (ES) during selective forearm (ES1, n = 12) or hand warming (ES2, n = 10). In ES1, the response to muscle contraction (10 s, 70 % MVC) and occlusion before and after warming was also investigated, while in ES2 two NIRS probes were expressly positioned over a visible vein and over a vein-free area.
  
  
  RESULTS
  Local warming increased the modified Beer-Lambert (BL) blood volume indicator, tHb, by 5.3 ± 3.6 µmol/L cm to an extent comparable to post-contraction hyperemia (6.8 ± 2.9 µmol/L cm, p < 0.01). Remote warming increased skin blood flow at the hand and tHb at both forearm sites (on average: 5.4 ± 4.8 µmol/L cm, p < 0.01). Conversely, indicators of blood volume and oxygenation, based on spatially resolved spectroscopy (SRS), were not affected by any of the warming stimuli.
  
  
  CONCLUSIONS
  These results demonstrate for the first time that: (1) blood drained by superficial veins may affect BL measurement; (2) it is difficult to exclude veins from the measurement by simple visual inspection of the cutaneous surface; (3) SRS effectively rejects artifacts from superficial hemodynamic changes in both cutaneous microcirculation and large veins. These results bear implications to conditions in which thermoregulatory adjustments cannot be excluded.
authors.affiliation: Department of Neuroscience, University of Torino, c.so Raffaello 30, 10125, Turin, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Messere
authors.affiliation: Department of Neuroscience, University of Torino, c.so Raffaello 30, 10125, Turin, Italy. silvestro.roatta@unito.it.
authors.forename: Silvestro
authors.initials: S
authors.lastname: Roatta
mesh_terms: D000328:Adult; D005260:Female; D005542:Forearm / Q000098:blood supply*; D006358:Hot Temperature; D006801:Humans; D008297:Male; D008833:Microcirculation / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000098:blood supply / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology*; D019265:Spectroscopy, Near-Infrared
keywords: Muscle blood flow; Muscle oxygenation; Near infrared spectroscopy; Skin blood flow; Vein