A new infrared laser Doppler blood flow instrument (Moor MBF3D) was evaluated using an in vitro model allowing measurements over a range of flow velocities and concentrations. The responses correlated well (r = 0.96, p less than 0.01) with those obtained simultaneously using a Perimed PF3 laser Doppler instrument. The different processing bandwidths of the instruments were investigated and the wideband mode of operation is recommended for flow measurements where there may be fast moving red blood cells (rbcs). The infrared instrument is capable of dual-channel operation, and the two channels are shown to respond almost identically for similar changes in blood flow through the in vitro model (r = 0.999, p less than 0.01). The main advantage of the dual-channel instrument is that continuous measurements may be made simultaneously at two different skin sites allowing dynamic flow responses to be compared.
This paper reports the results of a preliminary in vivo investigation in which laser Doppler blood-flow measurements were made in a variety of tissues in the anaesthetized rat using a twin wavelength laser Doppler system. The aim was to assess whether there was any detectable difference in the depth response of the laser Doppler system to blood-flow in skin, muscle and brain tissue using red light (633 nm) from a He-Ne laser source and near infrared (NIR) light (780 nm) from a semiconductor diode laser source. The results show that under normalized conditions, the flow signals obtained from the near infrared laser Doppler system is consistently larger than that recorded from the red He-Ne laser Doppler system. This suggests that laser Doppler flowmetry systems based on NIR laser sources sample larger volumes of tissue than those based on red He-Ne lasers.
A prototype instrument has been developed to combine the monitoring techniques of laser Doppler flowmetry and reflection pulse oximetry, both of which depend on laser light backscattered from the skin tissue. Simultaneous and continuous measurements of both microvascular blood flow and blood oxygen saturation were obtained from the same measurement site. Oximetry readings from the combined instrument were calibrated using a model system, and compared with those determined using a Nellcor N-100 transmission pulse oximeter in a limited clinical study: they showed a variability of +4% and read low by 5-10%.
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