Single fibre laser Doppler flowmetry for skeletal muscle perfusion measurements : methodological developments and clinical applications

Sammanfattning: Measurements of microvascular blood flow in skeletal muscle by using the laser Doppler flowmetry (LDF) technique were first reported in 1979. The introduction of the single fibre technique in 1987 increased the possibilities of studying muscle perfusion under various physiological conditions without causing major tissue trauma.On-line processing of the LDF- and rms-EMG-signals made possible interpretation of the relationship between the perfusion and the activity of the muscle. Percutaneous single fibre LDF and bipolar surface electromyography (EMG) of the upper portion of trapezius muscle were performed continuously during a 10-minute long series of alternating periods of static contractions and rest, each of a one-minute duration. Regression analyses showed positive correlation between LDF and rms-EMG, as well as LDF and degree of arm elevation. Microcirculation in the trapezius muscle and the supraspinatus were measured simultaneously by continuous LDF during stepwise increased contractions related to the EMG too. Blood flow increased significantly in both muscles during increased shoulder torque. The blood flow in the trapezius muscle increased significantly at increased rms-EMG. But, no significant increase in muscle blood flow occurred in the supraspinatus muscle which thus seems to be more prone to develop ischemia during strenuous static work.A PC-based signal processor with a digital signal processing board was developed for evaluation of the different fibre tips' optic characters and laser Doppler algorithm, as well as for presentation of the laser Doppler measurement results. The Doppler signal power spectral density and corresponding flux values were visualized on the computer screen continuously in real-time. The single fibre technique has been further developed with the aim of improving the signal quality by modifying the geometry of the fibre tip and increasing the light wavelength, since the small monitored tissue volume in the muscle tissue by single fibre LDF is its drawback. The modified fibre tips, sphere and "pear" type, probes showed a higher flow sensitivity than did the flat end type. An infrared  laser diode with the wavelength of 750 nm was used in the new optical module. These improvements were interpreted as being related mostly to a larger, strongly irradiated tissue volume in front of the fibre. The results were evaluated theoretically with ray tracing simulations and experimentally with the mechanical and flow models. The modified fibre with the new signal processor for monitoring blood flow has been successfully used in intramuscular measurements.