title: Blood flow measurements at different depths using photoplethysmography and laser Doppler techniques.
abstract: OBJECTIVE
  This study has evaluated a multi-parametric system combining laser Doppler flowmetry and photoplethysmography in a single probe for the simultaneous measurement of blood flow at different depths in the tissue. This system will be used to facilitate the understanding of pressure ulcer formation and in the evaluation of pressure ulcer mattresses.
  
  
  METHODS
  The blood flow in the tissue over the sacrum was measured before, during and after loading with 37.5 mmHg, respectively, 50.0 mmHg. The evaluation of the system consisted of one clinical part, and the other part focusing on the technicalities of the probe prototype.
  
  
  RESULTS
  An increase in blood flow while loading was the most common response, but when the blood flow decreased during loading it was most affected at the skin surface and the blood flow responses may be different due to depths of measurement. Reactive hyperaemia may occur more frequently in the superficial layers of the tissue.
  
  
  CONCLUSIONS
  The study showed that the new system is satisfactory for measuring tissue blood flow at different depths. The laser Doppler complements the photoplethysmography, and further development of the system into a thin flexible probe with the ability to measure a larger area is required.
authors.affiliation: Department of Medical and Health Sciences, Linköping University, Linköping, Sweden. sara.bergstrand@imv.liu.se
authors.forename: Sara
authors.initials: S
authors.lastname: Bergstrand
authors.forename: Lars Göran
authors.initials: LG
authors.lastname: Lindberg
authors.forename: Anna-Christina
authors.initials: AC
authors.lastname: Ek
authors.forename: Maria
authors.initials: M
authors.lastname: Lindén
authors.forename: Margareta
authors.initials: M
authors.lastname: Lindgren
mesh_terms: D000368:Aged; D001783:Blood Flow Velocity / Q000502:physiology*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D017078:Laser-Doppler Flowmetry / Q000295:instrumentation* / Q000379:methods; D008297:Male; D017156:Photoplethysmography / Q000295:instrumentation* / Q000379:methods; D011312:Pressure; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012867:Skin / Q000098:blood supply*; D012879:Skin Physiological Phenomena; D018511:Systems Integration; D014159:Transducers