Laser Doppler velocimetry of tracheal blood flow in sheep

A laser-Doppler velocimetry (LDV) apparatus was adapted to assess sheep airway blood flow. The LDV signal obtained was compared to microsphere determinations of blood flow to tracheal tissues utilizing 15 μm radioactive microspheres injected before and after intubation and anesthesia, during hemorrhagic hypotension, and after reinfusion-resuscitation. During hemorrhagic hypotension, airway wall blood flow decreased to 16% of control by the microsphere method and to 30% by LDV. After reinfusion-resuscitation, airway wall blood flow increased over control values 40% and 33% by the two methods, respectively. Although at low flows LDV values were greater than microsphere determinations, the overall LDV recordings correlated with airway microsphere flow determinations of tracheal wall blood flow (R = 0.85) and tracheal mucosa flow (R = 0.81), but not with tracheal muscularis flow (R = 0.32). With certain but significant limitations, such as calibration in absolute units, stability of position placement, motion artifacts, and the effects of mechanical irritation-induced hyperemia, LDV represents a relatively noninvasive means for qualitatively evaluating changes in the microcirculatory blood flow of airway mucosa.