ABSTRACT
A new laser Doppler flowmeter, based on a personal computer with a digital signal processor for detecting the blood perfusion in skeletal muscle, was designed and evaluated. An infrared laser diode (750 nm) fed a single optical fibre, 400 microns in diameter, which was introduced into the muscle. A PC equipped with a digital processing unit was used for emulation of the laser Doppler algorithm and for presentation of the measurement results. The Doppler signal power spectral density and corresponding flow values were visualized on the computer screen continuously in real-time, and could also be saved on the hard disk for off-line analyses. The graphic-user interface supported by Labwindows software made the system easy to use. It is possible to alter in the software the signal processing and the ways in which the signals and results are presented. The new system was evaluated by using a flow model as well as a mechanical model. The model studies showed linear relationships between particle velocity and flow in the range of 0-5 mm s-1. The system was also tested in measurements of the blood flow in the brachioradial muscle, and was found to have advantages over our previously used systems.
Subject(s)
Laser-Doppler Flowmetry/instrumentation , Muscle, Skeletal/blood supply , Signal Processing, Computer-Assisted , Algorithms , Analog-Digital Conversion , Blood Flow Velocity , Computer Graphics , Equipment Design , Humans , Microcirculation , Models, Cardiovascular , Software , User-Computer InterfaceABSTRACT
The single-fibre percutaneous laser Doppler technique has been used in previous studies of intramuscular blood flow. This method facilitates studies of blood flow in deep tissue volumes and minimises the tissue trauma. The technique has been further developed with the aim of improving the signal quality. This has been accomplished by modifying the geometry of the fibre tip. By melting the fibre core material, lenses of different shapes are formed. Flat, spherical and 'pear'-type tips have been manufactured and are evaluated theoretically and experimentally. The paraxial theory cannot accurately predict the position of zones of highest irradiance. Therefore, a ray-tracing program has been developed in the C language, by means of which some of the optical properties of the modified fibre tips can be simulated. Iso-irradiance graphs and beam profiles are calculated for the three different fibre tips. Measured and calculated irradiance curves are used for evaluation of the properties of the ray-tracing model. The three types of fibre tips are also evaluated and compared in flow models. The sphere and pear-type probes show a higher flow sensitivity than the flat-end type. These improvements in flow sensitivity are interpreted as being related to the larger, strongly irradiated tissue volumes in front of the fibres. Intramuscular measurements with the pear-type probe show high sensitivities to induced blood flow changes.
Subject(s)
Laser-Doppler Flowmetry/methods , Evaluation Studies as Topic , Humans , Laser-Doppler Flowmetry/instrumentation , Muscles/blood supply , Regional Blood FlowABSTRACT
A miniaturized technique to administer vasoactive substances iontophoretically into the human finger skin and to continuously assess the resulting reaction of the vessels is described. Cutaneous blood flow is measured with a laser Doppler flow-meter. The technique has been used in 9 healthy volunteers with norepinephrine as test substance. The described method is a convenient way to evaluate the effects of transdermally applied vasoactive substances in a semiquantitative way without risking central effects of the substance to influence the registered blood flow.
