Microsurgery: Transplantation and Replantation by Harry J. Buncke, MD, et al.
  Table of Contents / Chapter 37:
  The laser Doppler measures capillary blood flow by calculating changes in the wave length of laser light reflected off moving red cells.5,21 In measuring tissue perfusion, the laser Doppler registers the presence or absence of red-cell motion in dermal capillaries and cannot distinguish between arterial and venous occlusion. Surface probes are fixed to the skin and provide continuous monitoring. Problems with probe applications include tissue compression caused by adhesive strips or loss of probe contact on moist or bloody surfaces. False-positive readings have been reported by several investigators.6,22


Pulse oximetry detects differences between wavelengths of light absorbed by reduced and oxygenated hemoglobin. The device also records the pulsations of the vascular bed. Pulse oximetry thus continuously monitors both oxygen saturation and pulse.23,24 This system, used widely in anaesthesia, is reliable, simple to apply, and does not require a sophisticated observer. If a pulse is absent as in an arterial occlusion, or oxygen saturation is decreased as in venous occlusion, an alarm sounds. The monitored tissue, however, must be of the correct shape to allow placement of the probe, which was designed to be placed on digits.


  Photophlethysmography detects changes in skin light reflection caused by pulsatile and quantitative changes in blood flow.5,6 By transilluminating the skin, the monitor detects, amplifies, and displays changes in the amount of reflected light that correspond to pulsatile changes and tissue blood volume. Inspection of variations in the monitored wave form configuration allows an experienced interpreter to make distinctions between normal flow, arterial occlusion, venous occlusion, arterial spasm, and venous spasm.5


Radioactive microspheres are used in experimental settings to study circulatory patterns in flaps.18,25,26 This technique is not applicable to clinical settings because it requires sacrifice of the subject and sectioning of the investigated tissue. The technique consists of intravascular injection of radioactive microspheres that become entrapped in tissues relative to the tissue's arterial blood supply. Subsequent measurement of radiation in the sectioned tissue gives quantitative approximation of arterial blood supply.


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