title: Near-infrared spectroscopy provides an index of blood flow and vasoconstriction in calf skeletal muscle during lower body negative pressure.
abstract: OBJECTIVE
  Near-infrared spectroscopy (NIRS) has been used previously for forearm blood flow estimation at rest and during exercise. In this study we applied NIRS to selectively monitor deep calf oxygenated haemoglobin (Hb) responses in order to estimate blood flow changes in the calf muscle during lower body negative pressure (LBNP). The purpose of this study was to test the hypothesis that changes in calf skeletal muscle oxygenated-Hb, after the removal of superficial tissue responses, were related to blood flow changes during orthostatic stress, and to determine the efficacy of using NIRS measurements as an index of vasoconstriction.
  
  
  METHODS
  Twenty-nine subjects participated in this study. All attempted a graded LBNP trial from baseline (0 mmHg) to -60 mmHg LBNP in 10 mmHg steps at 5-min intervals. Calf blood flow changes were estimated by oxygenated-Hb responses in relation to changes in mercury strain gauge plethysmography and muscle sympathetic nerve activity (MSNA).
  
  
  RESULTS
  Calf selective deep oxygenated-Hb decreased continuously from -10 mmHg LBNP. Regression analysis showed that oxygenated-Hb was significantly related to declines in plethysmography evaluations of blood flow [oxygenated-Hb = (-1.57 +/- 0.26) + (1.86 +/- 0.49) plethysmography, r(2) = 0.87 +/- 0.09]. Changes in MSNA (total activity) were also inversely related to oxygenated-Hb (slope < 0, P = 0.037; r(2) = 0.52 +/- 0.15).
  
  
  CONCLUSIONS
  These results suggest that changes in selective deep calf oxygenated-Hb can be utilized to estimate calf muscle blood flow changes that are most likely caused by vasoconstriction during graded LBNP.
authors.affiliation: Aerospace Physiology Laboratory, School of Kinesiology, Simon Fraser University, Burnaby, BC, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Hachiya
authors.forename: A P
authors.initials: AP
authors.lastname: Blaber
authors.forename: M
authors.initials: M
authors.lastname: Saito
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology; D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D005542:Forearm / Q000098:blood supply; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007866:Leg / Q000098:blood supply*; D008150:Lower Body Negative Pressure; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply*; D010101:Oxygen Consumption / Q000502:physiology; D010108:Oxyhemoglobins / Q000378:metabolism; D010991:Plethysmography / Q000379:methods; D012039:Regional Blood Flow / Q000502:physiology; D019265:Spectroscopy, Near-Infrared / Q000379:methods; D014661:Vasoconstriction / Q000502:physiology*
chemical_list: D010108:Oxyhemoglobins